© 2017 Alexandre de Castro Alves et al.Renewable energy sources for vehicles have been the motivation of many researches around the world. The reduction of fossil fuels deposits and increase of the pollution in cities bring the need of more efficient and cleaner energy sources. In this way, this work will present the application of a compressed air engine applied to a bicycle. The engine is composed of two pneumatic cylinders connected to the bicycle wheel through a crank-connecting-rod mechanism. In order to control the velocity of the bicycle, a strategy of control composed of two controls was implemented: a feedback and a feedforward control. For feedback control, the State-Dependent Riccati Equation (SDRE) control and also a proportional-derivative (PD) control are considered, considering three cases for velocity bicycle variation: 10 km/h, 20 km/h, and 30 km/h. The equations of motion of the system were obtained through the Lagrangian energy method. Numerical simulations were performed in order to analyze the dynamics of the system and the efficiency of the controllers.

© 2017, Brazilian Association of Computational Mechanics. All rights reserved.A new C1 element is proposed to model Euler-Bernoulli beams in one and two-dimensional problems. The proposed formulation assures C1 continuity requirement without the use of rotational degrees of freedom, used in traditional elements, through the use of an Overhauser interpolation scheme for bending displacements. The principle of virtual displacements is used to determine the equilibrium equations and boundary conditions for one and two-dimensional Euler-Bernoulli beams. The Overhauser interpolation is introduced and the new bending interpolation functions are defined. Finally, beam and frame problems are solved with the new formulation and the results are compared to the traditional Euler-Bernoulli element and exact solutions.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The Flight Simulator (FS) is a key aspect of the traditional aeronautical industry and the general aviation. In the general aviation, the flight simulator contributes to decrease pilot training costs and keep safety the aviation. In the case of traditional industries such as Embraer, Boeing and Airbus, and beyond that, the FS avoid delays and decrease the costs in development of new aircraft. Thus, the aeronautical industry has invested hardly on modeling and simulation (M&S). The objective of this paper is to describe the process of updating the latero-directional aerodynamic coefficients from aerodynamic model of the FS using flight test data in order to establish a model in according with aviation rules. This process is called as aerodynamic matching, and has presented very satisfactory results in aeronautical industry. The methodology used and proposed here is one more tool to model with precision the flight dynamics of airplanes.

© 2017 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This work presents a proposed framework intended to be used for the optimization of highlift devices, namely Flaps and Slats for the present study. From the conceptual design up to flight test, as fidelity and design maturity increases, a robust and yet fast tool is needed to assist engineers to optimize and make better decisions regarding Flap and Slat deflection definitions in order to satisfy the multitude of design challenges such as take-off performance, climb performance, landing performance, deployment times, kinematics, icing effects, failures, only to name a few. Without such a tool or framework, one can be easily overwhelmed and the best solution or trade-offs cans be lost or obliterated by the huge amounts of possibilities, constraints and design goals. The proposed framework can used with multiple fidelity data such as physics based models, CFD models and semi-empirical ones, in order to accomadate the learning curve that exists under any product development timeline. For an initial approach, the takeoff performance calculation is conducted using statistical models constructed from wind tunnel test data and then optimized, having as main design goal the maximization of the MTOW for a certain runway and having 2nd segment gradient as main constraint. Other constraints can and will be added as needed, in order to assist in a robust decision. Once the framework is set, a multitude of design studies can be done, including design robustness, sensitiveness, design changes and many others. Not only a direct result in airplane performance is expected, but also an expressive reduction in development cycle times from conceptual design to flight test, since the framework will hugely speed up the design process.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A distinct wavy leading edge performance for finite wings can be expected in comparison to the infinite wing, due to the differences in geometry and flow conditions. An infinite span wing, unlike a partial span model, has a unique local Reynolds number, sweep angle, thickness and camber. In addition, it is not subjected to the wing tip phenomenon which changes the pressure coefficient along span, and, as consequence, the adverse pressure gradients. These differences on the flow over finite and infinite span geometries cause differences in tubercle performance, which have motivated some works, in order to investigate the influence of flow three-dimensionality on wavy leading edge performance. However, there are lack of works that evaluate the effects of the wing’s three-dimensional on flow topology of the wavy leading edge and their consequences in performance. The aim of this study is to investigate the effects of the wing’s three-dimensional flow on wavy leading edge phenomena at low Reynolds number. Experimental investigations were carried-out modifying geometric parameters of the wing planform (taper ratio and sweep) in order to understand the effects of these parameters on wavy leading edge phenomena. The tests are conducted for pairs of models with and without tubercles. A pair of two-dimensional models (NACA 0020) and four pairs of finite-wing models with taper ratios of 0.5 and 1, and sweep angles of 0º and 30º were tested. The experimental investigation was based on evaluation of force measurements (lift and drag) and flow visualizations (oil and mini-tufts). Additionally, the Reynolds number effects were also investigated by evaluating the wavy leading edge characteristics at Reynolds number 80,000 and 200,000.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.After a previous work showing the aerodynamic longitudinal coefficients modeling, the authors continue to present the techniques to obtain the aircraft coefficients and how to structure them in an aerodynamic model but now with focus on the lateral-directional coefficients. Thus, the aim of this work is to present appropriated methodologies available used to calculate and model aerodynamic lateral-directional coefficients in the distinct phases of the aircraft design, mainly in the Conceptual and Preliminary Phases. In addition, the main recommended practices and general structure of the aerodynamic model are described in order to satisfy the requirements of different technologies during design cycles, such as Loads and Flight Dynamics. The procedures to obtain lateral-directional aerodynamic coefficients and derivatives from wind tunnel tests, theoretical and empirical methods are also presented here. The methodologies and techniques described in this work are available in public domain. The methodologies approaches described achieve a specific model complexity level and accuracy that depends on the aircraft design phase, staff expertise, company experience and design budgets. Apart from the methodology approach the understanding of the best practices and methodologies regarding aerodynamic modeling is essential to achieve success in the aircraft design. Thus, this work brings a contribution in the sense to present appropriated procedures to develop aerodynamic models under design constraints.

© 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The interest in studying the aerodynamic performance of airfoils at low Reynolds number has been increasing recently. There are many applications for airfoil design at low Reynolds number as design point. These applications include sailplanes, propellers, unmanned aerial vehicles (UAVs) and micro air vehicles (MAVs). However, there are few works evaluating the thickness effect as a design parameter for airfoil performance at low Reynolds number regime as well as data from flow visualizations in order to clarify the aerodynamic phenomena regarding thickness variation. In this sense, the aim of this work is to investigate the thickness effect on flow characteristics and performance of symmetrical airfoils at low Reynolds number regime by experimental investigation correlating force measurements with mini-tuft and oil flow visualization data. In an overall view, this work intends to contribute for investigations of desirable flow and geometric conditions of airfoils applied in UAV and MAV designs. Experimental tests were carried out at subsonic blower-type wind tunnel of open loop with closed section at ITA (Technological Institute of Aeronautics). A set of three symmetrical airfoils with different thickness (NACA 0012, NACA 0020 and NACA 0030) were tested at Reynolds number regime between 50,000 and 290,000. The results show distinct thickness effect for Reynolds number condition borders where at Re = 50,000 the thickest airfoil causes full flow separation with a great aerodynamic deterioration. In contrast, at Re = 290,000 the thickest airfoil achieves the highest maximum lift value.

© 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The aim of this work is to investigate the wavy leading edge phenomena for the very thick airfoil NACA 0030 by experimental investigation correlating force measurements with mini-tuft and oil flow visualization data at low Reynolds number regime. Experimental tests were carried out at subsonic blower-type wind tunnel of open loop with closed section at ITA (Technological Institute of Aeronautics). A set of four very thick airfoils were tested composed by one smooth configuration and three wavy leading-edge configurations (A= 0.03c, λ = 0.40c; A= 0.03c, λ = 0.11c; A= 0.11c, λ = 0.40c). The wavy leading edge geometry variation and Reynolds number effects were evaluated at range of Reynolds number between 50,000 and 290,000. For the highest Reynolds number condition, the results show worse aerodynamic performance for wavy leading edge when compared to previous studies of thinner airfoils. However, at Reynolds number 120.000, the configuration with A= 0.03c and λ = 0.11c presents a unprecedented result on literature overcoming the baseline maximum lift coefficient in 19,4% and the stall angle in 44%. In addition, the flow visualization results indicate that the leading edge stall characteristics at airfoils lead the tubercle configurations for better aerodynamic performance.

© 2017 by the American Institute of Aeronautics and Astronautics, Inc.The aircraft design cycle is a complex process that involves various design phases with different levels of maturity always driven by market requirements and certification. These requirements involve disciplines such as performance, flight mechanics, environmental comfort, emissions and maintenance. However, for most aircraft designs, the requirements that define initially the aircraft lofting and are mandatory during the design cycle are related to aircraft performance since what sells the aircraft is its performance. Thus, an accurate drag polar prediction during the aircraft design phases guarantees the success of the design by a decrease in risks of do not accomplish performance requirements. In the past, certain aircraft designs achieved drag prediction errors of 10 to 20% showing outwith the range needed for success. Therefore, the aeronautical companies have been pursuing accurate drag polar prediction methodologies putting many efforts in semi-empirical formulation implementations, CFD simulations and wind tunnel campaigns in order to achieve minimum errors in predicting the drag polars before the first flight keeping errors at least below 10%. The aim of this work is to present in detail the distinct drag polar prediction methodologies applied during the design aircraft phases in the aeronautical industry as well as establish requirements that guarantee a minimum drag polar prediction errors pursuing at least values below 10% where an accurate prediction methodology could be considered achieving errors around 5%. Semi-empirical methods, numerical simulations (CFD) and wind tunnel test procedures applied during conceptual design and preliminary phase are described. In addition, processes proposed for updating the drag polar formulation before the first flight are suggested what could represent an improve in accuracy for drag polar prediction methodology in the future design cycles. This work also intend to reinforce the methodologies available and open opportunity to start discussions for new approaches regarding the drag polar prediction during design cycle such as increase in numerical simulation (CFD) and in using simulation model even in early phases in order to obtain accurate drag polars.

© 2017, Pleiades Publishing, Ltd.In this work, the reduction and oxidation of hydrogen peroxide on Au single crystals is studied in weakly adsorbing electrolytes. Results are discussed in terms of the potential of zero charge and the adsorption strength of different anions, which in turn depend on the crystallographic orientation of the electrode. Close to the reaction onset, both reactions follow the same activity trend with Au(100) and Au(111) being the most and the least active surface planes, respectively. At high potentials, gold oxides inhibit the oxidation of H2O2, which seems to be controlled by a surface process.

© 2017 Elsevier B.V.In this work, the effect of transition metals (TMs), such as Fe, Co, Ni and Cu, on the activity toward the hydrogen evolution reaction (HER) of modified molybdenum carbide (TM-Mo2C) catalysts has been evaluated. Catalysts were prepared by a temperature programmed reduction method in both an inert and a reductive atmosphere, and characterized by different physicochemical techniques. A high activity toward the HER is measured for all TM-Mo2C catalysts, with onset potentials lower than −0.06 V, as detected by on-line differential electrochemical mass spectrometry, and mass activities between 29 and 50 mA mg−1, which suggest them as promising non-precious electrocatalysts for this reaction. However, a decrease in the HER activity upon metal doping is measured, following an activity trend of α-Mo2C > Fe-Mo2C > Co-Mo2C > Ni-Mo2C > Cu-Mo2C. In situ near-edge X-ray adsorption analysis reveals a positive charge of the TM in the materials in the electrochemical environment, at the origin of the deleterious effect of Fe, Co, Ni and Cu, in terms of an electronic effect that modifies the d-electron configuration of α-Mo2C particles. Additionally, results also suggest that TM-Mo2C is more stable (lower catalyst dissolution) in acid media than α-Mo2C. Finally, because there is a catalyst deactivation toward the HER after the α-Mo2C component of the catalysts is oxidized at E > 0.7 V, the oxidation process of α-Mo2C is employed for estimating, as a first approximation, the number of surface active sites for the HER.

© Emerald Publishing Limited.Purpose - Flame-retardant plastics are used in critical applications, such as aircraft interior parts, when the occurrence of fire can lead to serious injury to people. However, there is a lack of related publications. The purpose of this study is to present experimental data regarding geometrical analysis, such as dimensional accuracy and surface roughness, tensile strength and elongation of parts manufactured with flame-retardant materials by additive manufacturing. Design/methodology/approach - Two additive manufacturing processes, selective laser sintering (SLS) and fused deposition modeling (FDM), were selected to manufacture the parts to be evaluated. Each process used its respective polymer, that is polyamide with flame-retardant additive (PA) for SLS and polyphenylsulfone (PPSF) for FDM. The samples consist of tensile specimens and representative parts of different products. Tensile tests were performed using standard tensile test machines, and geometrical analyses were performed using coordinate measuring machine as well as surface roughness tester. Findings - As each material can be, in commercial machines, produced by only one process, the material selection for final products has to consider the manufacturing process as well. In general, although the FDM/PPSF process provided specimens with the highest ultimate strength, because of its strong influence by the building direction, FDM/PPSF also provided the lowest strength. SLS/PA was able to provide average strength with less dependency on the build-up direction. The geometrical analysis showed that SLS/PA presents a much smoother surface, but FDM/PPSF presented slightly better dimensional accuracy. Originality/value - There is still lack of publications on polymers with flame resistance or flame-retardant polymers. Thus, this paper brings new technical information about processing such materials.

© 2016, The Brazilian Society of Mechanical Sciences and Engineering.In the aerospace industry, decision-making between conventional and innovative processes, such as selective laser melting (SLM), is somewhat challenging, not only because of the different technology readiness level [7] between them, but also because of the thorough comparison between the attributes of each alternative against evaluation criteria. In this scenario, the simulation among different decision methods under relevant criteria for aerospace industry can clarify the weight of the attributes of each technology and their influence in a trade study of metal parts. The main purpose of this paper is to compare additive manufacturing with machining process of a typical titanium part used in the aerospace industry by different decision-making approaches but bringing the focus onto the input data (characteristics) of alternative processes against requirements. Three decision approaches (AHP, SPA and VDI) are applied to compare three alternatives, that is, SLM, topology optimization and selective laser melting (TO and SLM), and machining process regarding three attributes (saving, weight and time). It was found that TO and SLM is a strong candidate for making titanium parts for aerospace application, mainly because of criteria, such as weight reduction and raw material saving. In addition, most methods got the same ranking of alternatives for a given scenario, even for different sub-criteria. This shows a good robustness level of those methods and a strong influence of the characteristics of each alternative.

© 2016, Springer-Verlag London.A considerable amount of research has focused on machining dynamics due to the impact it lays upon productivity and quality. Models have been developed with an ever-increasing accuracy in order to predict the dynamic behavior of cutting tools under different circumstances. However, workpiece behavior during machining is also a current limiting factor which is dealt with by means of restricting product designers of using features with thin characteristics. For this reason, designed products will be often oversized due to machining technology restrictions related to dimensions of thin walls. The main objective of this work is to investigate the behavior of thin walls during milling in order to identify the challenges imposed by the process. Different strategies are tested and evaluated through force signals, finite element analysis (FEA), analytical models, and analysis of the machined parts. The effect of cutting speed on cutting force is investigated from a force and excitation frequency standpoint. A method for prediction of resonance based on a frequency chart is proposed, for which variable speed tests are conducted. This variable speed approach is based on prediction of stable paths as machining progresses by means of the proposed chart. Validation of the frequency chart construction method is presented along with its applicability and restrictions considering a more complex geometry. Results indicate that the frequency chart method can be used to predict and explain the occurrence of instability but limiting factors still lie in implementing and improving the proposed method.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Experimental measurements of the flow structure evolving in the separated flow over an NACA 0009 wing at 12° angle of attack were obtained with particle image velocimetry, surface pressures, and force transducer measurements of the lift coefficient and pitching moment coefficient. Phase-averaged two-dimensional velocity field measurements provide details of the separated shear layer evolution following a four-pulse burst sequence from a synthetic jet actuator. The flow field development is quite similar to the observations made by Brzozowski, et al. (2010), who used a pulsed-combustion actuator that is orders of magnitude stronger than the synthetic jet. Proper orthogonal decomposition of the PIV data sets showed that the combination of the time-varying coefficients modes 1 and 2 correlate with the negative of the lift coefficient response. The surface pressure signals were correlated with the roll up and convection of the large-scale vortex structure that follows the actuator burst input. A spatially localized region of high pressure occurs below and slightly behind a “kink” that forms in the shear layer. A localized region of high surface pressure that follows the kinked region correlates with the lift reversal that occurs within 2.0t+ after the burst signal was triggered.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Regardless of plant model, robust flow estimation based on limited measurements remains a major obstacle to successful flow control applications. Aiming to combine the robustness of a high-dimensional representation of the dynamics with the cost efficiency of a low-order approximation of the state covariance matrix, a flow state estimator based on the Ensemble Kalman Filter (EnKF) is applied to two-dimensional flow past a cylinder and an airfoil at high angle of attack and low Reynolds number. For the development purposes, we use the numerical algorithm as both the estimator and as a surrogate for the measurements. Estimation is successful using a reduced number of either pressure sensors on the surface of the body or sparsely placed velocity probes in the wake. Because the most relevant features of these flows is restricted to a low-dimensional subspace/manifold of the state space, asymptotic behavior of the estimator is shown to be achieved with a small ensemble size. The relative importance of each sensor location is evaluated by analyzing how they in fluence the estimated flow field. Covariance in flation is used to enhance the estimator performance in the presence of unmodeled free stream perturbations. A combination of parametric modeling and augmented state methodology is used to successfully estimate the forces on immersed bodies.

© 2017 American Physical Society.This paper details the statistical and time-resolved analysis of the relationship between the near-field pressure fluctuations of unforced, subsonic free jets (0.4≤M≤0.6) and their far-field sound emissions. Near-field and far-field microphone measurements were taken on a conical array close to the jets and an azimuthal ring at 20 to the jet axis, respectively. Recent velocity and pressure measurements indicate the presence of linear wave packets in the near field by closely matching predictions from the linear homogenous parabolized stability equations, but the agreement breaks down both beyond the end of the potential core and when considering higher order statistical moments, such as the two-point coherence. Proper orthogonal decomposition (POD), interpreted in terms of inhomogeneous linear models using the resolvent framework allows us to understand these discrepancies. A new technique is developed for projecting time-domain pressure measurements onto a statistically obtained POD basis, yielding the time-resolved activity of each POD mode and its correlation with the far field. A single POD mode, interpreted as an optimal high-gain structure that arises due to turbulent forcing, captures the salient near-field-far-field correlation signature; further, the signatures of the next two modes, understood as suboptimally forced structures, suggest that these POD modes represent higher order, acoustically important near-field behavior. An existing Green's-function-based technique is used to make far-field predictions, and results are interpreted in terms of POD/resolvent modes, indicating the acoustic importance of this higher order behavior. The technique is extended to provide time-domain far-field predictions.

© 2017 Cambridge University Press.Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement, in terms of amplitude and phase, with those educed from turbulent jets. Compelling agreement has been demonstrated, for the axisymmetric and first helical mode, up to Strouhal numbers close to unity. We here extend the range of validity of wavepacket models to Strouhal number and azimuthal wavenumber by comparing solutions of the parabolised stability equations with a well-validated large-eddy simulation of a Mach 0.9 turbulent jet. The results show that the near-nozzle dynamics can be correctly described by the homogeneous linear model, the initial growth rates being accurately predicted for the entire range of frequencies and azimuthal wavenumbers considered. Similarly to the lower-frequency wavepackets reported prior to this work, the high-frequency linear waves deviate from the data downstream of their stabilisation locations, which move progressively upstream as the frequency increases.

© 2017 American Physical Society.Instability waves traveling within subsonic turbulent jets have a modal linear growth until approximatively the end of the potential core. At these stations it is believed that nonlinear and/or nonmodal effects become important and a mismatch appears between experimental measurements and linear models. In this paper the response of the linearized operator to nonlinearities treated here as an external forcing is found to be consistent with a simplified model of the Orr mechanism, supporting the idea that a nonmodal growth of disturbances occurs in the downstream region of the jet in response to the modeled nonlinear forcing.

© 2017 Cambridge University PressÂ.Coherent features of a turbulent Mach 0.9, Reynolds number jet are educed from a high-fidelity large eddy simulation. Besides the well-known Kelvin-Helmholtz instabilities of the shear layer, a new class of trapped acoustic waves is identified in the potential core. A global linear stability analysis based on the turbulent mean flow is conducted. The trapped acoustic waves form branches of discrete eigenvalues in the global spectrum, and the corresponding global modes accurately match the educed structures. Discrete trapped acoustic modes occur in a hierarchy determined by their radial and axial order. A local dispersion relation is constructed from the global modes and found to agree favourably with an empirical dispersion relation educed from the simulation data. The product between direct and adjoint modes is then used to isolate the trapped waves. Under certain conditions, resonance in the form of a beating occurs between trapped acoustic waves of positive and negative group velocities. This resonance explains why the trapped modes are prominently observed in the simulation and as tones in previous experimental studies. In the past, these tones were attributed to external factors. Here, we show that they are an intrinsic feature of high-subsonic jets that can be unambiguously identified by a global linear stability analysis.

© 2017 Cambridge University PressÂ.The purpose of this paper is to characterize and model waves that are observed within the potential core of subsonic jets and relate them to previously observed tones in the near-nozzle region. The waves are detected in data from a large-eddy simulation of a Mach 0.9 isothermal jet and modelled using parallel and weakly non-parallel linear modal analysis of the Euler equations linearized about the turbulent mean flow, as well as simplified models based on a cylindrical vortex sheet and the acoustic modes of a cylindrical soft duct. In addition to the Kelvin-Helmholtz instability waves, three types of waves with negative phase velocities are identified in the potential core: Upstream-A nd downstream-propagating duct-like acoustic modes that experience the shear layer as a pressure-release surface and are therefore radially confined to the potential core, and upstream-propagating acoustic modes that represent a weak coupling between the jet core and the free stream. The slow streamwise contraction of the potential core imposes a frequency-dependent end condition on the waves that is modelled as the turning points of a weakly non-parallel approximation of the waves. These turning points provide a mechanism by which the upstream-A nd downstream-travelling waves can interact and exchange energy through reflection and transmission processes. Paired with a second end condition provided by the nozzle, this leads to the possibility of resonance in limited frequency bands that are bound by two saddle points in the complex wavenumber plane. The predicted frequencies closely match the observed tones detected outside of the jet. The vortex-sheet model is then used to systematically explore the Mach number and temperature ratio dependence of the phenomenon. For isothermal jets, the model suggests that resonance is likely to occur in a narrow range of Mach number, <![CDATA[$0.82<M.

© 2017 Cambridge University Press.Three methods are considered for estimating the downstream evolution of wavepackets in turbulent jets based on upstream measurements. The parabolised stability equations are used to compute a transfer function between axially and radially separated points in the flow, and the performance of this theoretical model is compared with that of two empirical approaches, direct transfer function calculation and autoregressive moving-average exogenous system identification, both of which require unsteady experimental data. The three approaches, which perform equally well, prove suitable for estimation of the downstream evolution of wavepackets using pressure data measured in the near-nozzle region. Over distances of the order of a couple of jet diameters, correlations of up to 80 % are observed between estimation and measurement. The performance deteriorates as axial separation between input and output is increased. While the two empirical approaches are limited in terms of both the number of input-output pairs and the number of flow variables that can be reasonably considered, the parabolised stability equations-based approach has no such limitation and can be used to perform full-field estimates comprising all of the dependent variables; in this it constitutes a potentially formidable means by which to perform single-input-multiple-output estimation. It has the further advantage of not requiring unsteady data for its construction, the only necessary ingredients being the mean flow and the linearised equations of motion.

© 2017 American Physical Society.Sound radiation from a subsonic turbulent jet is examined after a hypothetical removal of the near-field coherent structures in the axisymmetric component of the velocity fluctuations. With the help of a well-validated database of large-eddy simulation, the near-field coherent structures are extracted using a discrete wavelet transform (DWT), and their spatial structures are examined using a proper orthogonal decomposition (POD). The acoustic far field is calculated using Lighthill's acoustic analogy. It is shown that the coherent part extracted by DWT accounts for most of the fluctuation energy in the axisymmetric component of axial velocity, whereas the incoherent part, assumed to have a Gaussian probability distribution, has little energy. After the coherent part is removed, the axisymmetric component of the sound is found to be significantly reduced, around 7 dB in the overall sound pressure level at 30 deg with respect to the jet axis. The reduction is mostly at low Strouhal numbers (St<0.4, based on the speed of sound and the nozzle exit diameter). The first few POD modes of the near-field coherent part, which capture most of the fluctuation energy, are found to be characterized by large-scale wavy structures. After these POD modes are removed, the axisymmetric component of the sound pressure level is also reduced considerably, by around 5 dB/St at St=0.2. The results suggest that there is a causal link between the axisymmetric components of the near-field hydrodynamic fluctuations and far-field low-angle jet noise, although the axisymmetric mode constitutes only a small proportion of total fluctuation energy. It is also suggested that not only the large-scale wavy structures in low POD modes but also the smaller scale structures in higher POD modes need to be included for jet noise modeling, because they are both shown to be efficient at sound radiation.

© 2016 Elsevier LtdA model for sound generation by a jet in the vicinity of a flat plate, mimicking an exhaust jet installed near an aircraft wing, is presented. An earlier model (Cavalieri et al. J. Sound Vib. 333 (2014) 6516—6531) is further simplified by considering that the sound source is an axially-extended, cylindrical wavepacket concentrated on the jet lipline, and that this source is scattered by the trailing edge of a semi-infinite flat plate; the model is shown to match earlier results and considerably simplifies the analysis. It is used to evaluate how the parameters of the problem influence sound radiation by subsonic jets. We show that the axisymmetric mode of the source is the most acoustically efficient, similarly to what is seen for free jets; but unlike the latter problem, the sound scattered by the trailing edge is only weakly dependent on the details of the wavepacket envelope and on the two-point coherence of the source, the wavepacket phase speed being the salient feature for installed jet noise. We then use the model to evaluate how geometrical parameters of jet-plate configurations modify the radiated sound. The acoustic radiation is particularly sensitive to the jet-plate distance due to the exponential radial decay of near-field disturbances; the relative axial position of jet and trailing edge is shown to play a comparably minor role. Finally, changes in the angle of attack of the plate and in the sweep angle of the trailing edge considerably modify the radiated sound, leading to significant reductions of the acoustic intensity in some directions. The various properties of installed jet noise are further explored by appealing to the wavenumber transform of the tailored Green's function used to compute the scattered field; insight is thus provided on how jet-wing configurations might be designed so as to reduce installation noise.

© 2017 American Physical Society.An experiment has been performed in order to provide support for wave-packet jet-noise modeling efforts. Recent work has shown that the nonlinear effects responsible for the two-point coherence of wave packets must be correctly accounted for if accurate sound prediction is to be achieved for subsonic turbulent jets. We therefore consider the same Mach 0.4 turbulent jet studied by Cavalieri et al. [Cavalieri, J. Fluid Mech. 730, 559 (2013)JFLSA70022-112010.1017/jfm.2013.346], but this time using two independent but synchronized, time-resolved stereo particle-image velocimetry systems. Each system can be moved independently, allowing simultaneous measurement of velocity in two, axially separated, crossflow planes, enabling eduction of the two-point coherence of wave packets. This and the associated length scales and phase speeds are studied and compared with those of the energy-containing turbulent eddies. The study illustrates how the two-point behavior of wave packets is fundamentally different from that of the more usually studied bulk two-point behavior, suggesting that sound-source modeling efforts should be reconsidered in the framework of wave packets. The study furthermore identifies two families of two-point-coherence behavior, respectively upstream and downstream of the end of the potential core, regions where linear theory is, respectively, successful and unsuccessful in predicting the axial evolution of wave-packets fluctuation energy.

© 2016 Cambridge University Press.Linear instability waves, or wavepackets, are key building blocks for the jet-noise problem. It has been shown in previous work that linear models correctly predict the evolution of axisymmetric wavepackets up to the end of the potential core of subsonic turbulent jets. Beyond this station, linear models fail, and nonlinearity is the likely missing piece. The essential underlying nonlinear mechanisms are unknown, and it remains unclear how these should be incorporated in a reduced-order model. The nonlinear interactions are considered in this work as an 'external' harmonic forcing added to the standard linear model. This modelling framework is explored using a locally parallel resolvent analysis to determine optimal forcing and associated responses, and a global approach based on 4D-Var data assimilation aimed at finding the optimal forcing of the parabolised stability equations that would minimise errors in the predictions of wavepackets. In all of the problems considered, the critical layer is found to be relevant: it is the position where sensitivity of wavepackets to nonlinearity is greatest. It is seen that disturbances are forced around the critical layer, and tilted by shear as they are advected, in a manner suggestive of an Orr-like mechanism. The ensemble of results suggests that critical-layer effects play a central role in the dynamics of wavepackets in subsonic turbulent jets, and that inclusion of such effects may remedy the shortcomings of linear reduced-order models.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.It has been previously demonstrated in several works that the dynamics of jets important for sound radiation are dominated by low-energy and coherent azimuthal structures, wavepackets. However, the link between these and the nozzle dynamics has received less attention. It is not clear, for instance, if wavepacket amplitudes are determined by mechanisms upstream or downstream of the nozzle exit plane. In this work, a statistical analysis of a Mach 0.9 isothermal turbulent round jet is carried out with a focus on the nozzle dynamics. High-fidelity large eddy simulation data are used in the analysis. First, the azimuthal, axial and radial structures of fluctuations in the nozzle are presented. Distinct hydrodynamic and acoustic components are identified within the nozzle, and a model for the latter, based on duct acoustics, is explored. Two-point statistics of pressure and velocity fields are computed between the upstream and the downstream of the jet exit, with an aim to identify casual relation and coupling in these domains. It is seen that acoustic modes within the nozzle are linked with similar, acoustic disturbances downstream of the jet exit. Moreover, boundary-layer velocity fluctuations are shown to present significant cross-spectral densities with the downstream hydrodynamic wavepackets, suggesting that these boundary-layer disturbances excite the Kelvin-Helmholtz instability in the jet mixing layer.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A formulation to evaluate the mean flow field of an assumed jet embedded by an outer coaxial stream is used to extrapolate measured mean-flow velocity profiles from static to flight conditions. This velocity field was then input in a parabolized stability equations (PSE) model, based on the same code of Sasaki et al.18 (2015), in order to retrieve the wavepacket signatures of axial velocity fluctuations. Overall results are in good agreement with experimental measurements. There is an observed increase in wavepacket wavelengths and phase velocities. Also, axial amplification rates are determined and show stabilization in the near-nozzle region, which is confirmed by experimental power spectral densities on the jet centreline. This tendency holds as the free-stream velocity increases.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Parabolized Stability Equations (PSE) have been shown to model wavepackets and, consequently, the near field of turbulent jets with reasonable accuracy. Because of these capabilities, PSE is a promising reduced-order model to derive control laws that could be employed to reduce the sound generation of a jet. The purpose of this work is to apply PSE to obtain time-domain transfer functions that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet. The results of this model were compared to results obtained from a database of a well-validated large-eddy simulation of a supersonic jet. Based on the unsteady pressure data at a input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and an empirical method based on the LES data. The prediction scheme employed is a single-input-single-output (SISO), linear model. The unsteady pressure predicted by PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer. For this region, the prediction capabilities of PSE are comparable to those of empirical transfer functions. The agreement is good even for output points taken in the acoustic field, showing that it is possible to estimate the time-domain behaviour of Mach-wave radiation using transfer functions. This indicates that PSE could not only be used to predict the sound generation, but also to open up new potentialities to attenuate noise by means of closed-loop control of the flow. The exploration of the regions where the method displayed good agreement, presented in this work, can guide the positioning of sensors and actuators for experimental implementation of closed-loop control in a jet.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper is focused on the investigation of the effect of coherence decay on the acoustic field generated by a wavepacket source. Coherence decay, which is the statistical signature of jitter in the time domain, has been identified by several studies as a key parameter for the acoustic effciency of jet-noise sources.1-3, 27 Here we study its effect using the model source proposed by Cavalieri and Agarwal1 which is based on two-point statistics. This source comprises a linear wavepacket with modulated growth and coherence. The wavepacket parameters necessary to estimate the sound pressure levels radiated by the source were educed from a dual-plane-time-resolved PIV experiment. The jet Mach number was Ma = 0.4. The sound pressure levels computed were compared with the acoustic m = 0 mode obtained experimentally and the results show that when coherence decay is correctly accounted, the sound-pressure levels generated are in reasonable agreement with experimentally measured values, especially for low Strouhal numbers. A Proper Orthogonal Decomposition of the model source was also performed motivated by the relationship between POD modes and turbulent forcing and coherence decay established by other studies.29, 35, 36 It is shown that only a few POD modes are necessary to recover acoustically important wavepacket traits.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We develop a reduced-order-model framework using the parabolized stability equations and identification techniques for the closed-loop control of unsteady fluctuations along fluidic systems. These models had been successfully applied to a turbulent jet as estimation techniques and to an incompressible shear-layer for the development of closed-loop control laws. Through this paper, we propose a further investigation of the PSE-based transfer functions, exploring its flexibility to educe different control schemes and to determine the most effective sensor/actuator positions. Emphasis is be given to the feedforward and feedback configurations for flow control, and differences are understood in terms of causality. A study of the robustness to uncertainties in Reynolds and mean flow velocity, along with external perturbations is also presented. These topics allow deeper insight into the active closed-loop flow control problem and therefore may lead to more effective schemes, particularly on what concerns the experimental implementation of closed-loop control.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We perform acoustic scattering calculations by 3D poroelastic plates with swept trailing edges. A boundary element method (BEM) is applied to solve the Helmholtz equation subjected to boundary conditions related to the vibration of trapezoidal plates. This analysis is performed by rewriting the BEM boundary conditions in terms of the structural modes of the plate, which allows a direct solution of the coupled fluid-structure interaction problem. In order to accelerate the solution of the large dense linear systems from the BEM formulation, a wideband adaptive fast multipole method (FMM) is employed. The structural modes of the plate are computed either by a pseudo-spectral method or a finite element method. A parametric study is carried out for the 3D acoustic scattering problem where a model source is placed close to a swept trailing edge. Firstly, the noise scattering by a compact quadrupole source is analyzed for low and high frequencies. Results are shown for different plate configurations including rigid, porous-rigid, impermeable-elastic and poroelastic plates. Then, acoustic scattering by a jet-installation problem is presented where a turbulent jet wavepacket is placed under a poroelastic plate with a swept trailing edge.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The flow patterns over a finite square cylinder of aspect ratio H/d = 3 were analyzed experimentally. The measurements were carried out in a subsonic wind tunnel using the technique of Time Resolved Particle Image Velocimetry (TR-PIV). The near wake flow structures and vortex shedding characteristics were investigated using instant velocity maps and proper orthogonal decomposition (POD). Tests were performed at a speed of 20m/s, resulting in Re = 65300, with the cylinder facing the flow at 90°. For the wind tunnel tests, the cylinders were fixed on flat plate, creating a boundary layer which interacted with the cylinder wake. The 2D PIV measurements were conducted at three horizontal planes (z/H = 0.3, z/H = 0.5, z/H = 1) and the symmetry x-z plane. Due to the complexity of the phenomena, the flow was characterized both in terms of average behavior and time-resolved velocity fields. Both symmetrical and anti-symmetrical vortices structures occur in the cylinder wake, which can be identified based on the coefficients of the first four POD modes. The results indicated that the alternating Karman vortex structures are dominant, described by the two first POD modes. However, this structure is sometimes suppressed, leading to periods of symmetrical vortex shedding.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We perform data-driven analyses in order to explore some well-documented discrepancies between linear models and observed wavepacket dynamics in turbulent jets. The paper asks if these discrepancies may be due to non-modal effects that are not usually incorporated in linear models. A locally parallel, spatial transient-growth analysis is first performed, the objective being to address differences between linear model and data in the region downstream of the potential core. The results show how in this region, following stabilisation of the KelviHelmholtz mode, non-modal effects become important in terms of both the streamwise and radial wavepacket organisation. LES data is then used in conjunction with the linearised Euler equations, where linearisation is about the global, non-parallel, mean flow. The objective is to explore two further questions. (i) Are the mechanisms identified in the optimal, locally parallel, transient-growth study present in the real flow, which is non-parallel and does not necessarily contain optimally excited structures? (ii) Are non-modal mechanisms important for two-point coherence decay? The answers to both questions are affirmative: non-modal phenomena are shown to be a key feature of turbulent-jet wavepacket dynamics. The study further-more suggests that these mechanisms are activated by non-linear interactions distributed throughout the flow and that might be modelled as a volume forcing of the linear operator.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We study a modified backwards-facing step flow, with the addition of two different splitter plates; one is a baseline, impermeable plate and the second a perforated one. An experimental investigation is carried out for a turbulent reattaching shear layer downstream of the two plates. The proposed setup is a model configuration to study how the plate characteristics affect the separated shear layer, and also how turbulent kinetic energies and large-scale coherent structures are modified. Hot-wire measurements show that the perforated plate changes the mean profile, mostly by reducing the intensity of backflow close to the bottom wall. Disturbance amplitudes are significantly reduced up to 5 step-heights downstream the trailing edge of the plate, more specifically in the recirculation region. A loudspeaker is then used to introduce phase-locked, low-amplitude perturbations up- stream of the splitter plates, and phase averaged measurements allow a quantitative study of large-scale structures in the reattaching shear-layer. The evolution of such coherent structures are evaluated in light of linear stability theory, comparing the eigenfunction of the Kelvin-Helmholtz mode to the experimental results. We observe a close match of linear- stability eigenfunctions with phase-averaged amplitudes for all tested Strouhal numbers. The perforated plate is found to reduce the amplitude of the Kelvin-Helmholtz coherent structures in comparison to the baseline, impermeable plate, a behavior consistent with the predicted amplification trends from linear stability.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A numerical method to compute the acoustic field scattered by finite perforated elastic plates is extended to include structural damping typical of viscoelastic materials. We employ a boundary element method to solve the Helmholtz equation subject to boundary conditions related to the vibration of the plate. In order to enable our investigation of the effect of damping, we rewrite the equations considering the terms responsible for the structural damping. Results show that by adding damping to the problem formulation, the flexural waves in the plate are attenuated and thus can modify the far-field sound scattered by turbulence near an edge of the plate. Parametric studies also show that structural damping tends to reduce scattered sound at structural ressonances. The combined effects of elasticity, porosity and damping may be more appropriate to represent the behavior of realistic materials.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The turbulent flow over a NACA 0012 airfoil at zero angle of attack was analysed numerically using a compressible-flow large-eddy simulation for Mach number M∞ = 0:115. Snapshots of the flow field were analysed using Proper Orthogonal Decomposition (POD) in frequency domain, in order to extract the dominant coherent structures of the flow. Homogeneity in the spanwise direction allows application of a Fourier decomposition in span prior to POD, and focus is given to two-dimensional disturbances since these are expected to dominate acoustic scattering. The POD results show, in general, coherent hydrodynamics waves propagating from the region of boundary-layer tripping towards the trailing-edge, characterising a non-compact source akin to wavepackets seen in turbulent jets. The results also show the high contribution of the first POD mode in the acoustic field for each analysed frequency. To understand how coherent structures in the turbulent field can be modelled, the optimal harmonic forcing and the associated linear response of the flow using the singular value decomposition of the linear resolvent operator was performed in a locally parallel analysis. Such resolvent analysis shows that the leading POD modes can be associated to optimal, linearised flow responses.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Futuristic aircraft designs and novel aircraft such as High Altitude Long Endurance (HALE) involve a higher level of structural flexibility than in conventional aircraft. Even at present, the trends in the aviation industry are to increase wing length (to reduce induced drag) and maximize use of composites, which lead to increased structural flexibility. This necessitates a rethink of conventional (linear) aeroelastic analysis, since the increased flexibility results in coupling between the flight dynamic and aeroelastic dynamics, and consequently, limit-cycle oscillations of the structure. In this paper, a new three-dimensional low-order model for unsteady aerodynamics that accounts for large oscillation amplitudes and nonplanar wakes is developed. An experiment with a cantilevered flat plate at low Reynolds number is set up and used to validate the low-order model, as well as to study post-flutter limit-cycle oscillations. Results from the low-order model are promising, but show that aerodynamic nonlinearities such as flow separation and leading-edge vortex shedding must also be modeled in order to predict all possible limit-cycle oscillations of the aeroelastic system.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.A simple and self-contained methodology to assess the validity of the assumption of small deformations in linear structural-dynamic models was recently proposed. The advantages of the methodology lie in the fact that it does not depend on the availability of higher-fidelity, nonlinear models: it is rather based on the selection of two different structural nodes where the structural motion is to be one at a time completely constrained, typically, a node near the center of mass and another in the region of maximum structural displacements with respect to mean axes. If the two displacement vectors calculated in each case can be transformed between themselves with linear rigid-body modes of the structure, then it is still in the regime of small deformations. In the present paper, in order to demonstrate the value of this methodology, it is applied to the X-HALE aircraft in its four-, six- and eight-meter-span configurations, and the results obtained with the assumption of small deformations are compared with a higher-fidelity model that comprises large structural deformations.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.Highly-flexible aircrafts present high-aspect-ratio wings that introduce nonlinearities into the flight dynamics and make more complex models and control methods necessary. In this paper, a loop separation concept is applied to the X-HALE aircraft, giving rise to a control system comprising an inner-loop capable of controlling the shape of the aircraft while keeping the plant stable, and an outer-loop capable of controlling velocity, altitude, bank angle and sideslip angle. The outer-loop has a decoupled structure for longitudinal and for the lateral-directional axes. The matrices of the compensators were obtained using non-smooth optimization. Gain-scheduling techniques are implemented to bypass stability problems arising from changes in the plant with flight speed. Nonlinear simulations show promising results for implementation on the real aircraft.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Real–time simulation is a valuable tool for aircraft development. However, flexible aircraft models are computationally expensive and can be prohibitive for fast simulations. This paper investigates the applicability of a nonlinear model order reduction technique to a moderate flexible aircraft for real–time simulation purposes. Details of the implementation and test cases are presented. Results show that the reduced–order model can be simulated in real–time and produces better results than linearized model and rigid–body model with aeroelastic correction and we conclude that the technique is promising for real–time simulations.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Formulations for the flight dynamics of flexible aircraft have been commonly applied to aircraft free to fly in the three-dimensional space, having all six rigid-body degrees of freedom. For risk reduction in the future flight operations of the X-HALE testbed at ITA, however, wind-tunnel tests of the remotely-piloted, four-meter-span configuration of the aircraft were performed. In the wind tunnel, the rigid-body translations were completely constrained, but the same was not valid for the rigid-body rotations, which could be conveniently left free or not with a proper selection of the connection between the aircraft and the wind-tunnel mount. In the present paper, in order to computationally assess the response and stability characteristics of the aircraft in the wind tunnel, we derive equations of motion for a constrained flexible aircraft with up to three rigid-body rotational degrees of freedom, mounted on an also flexible wind-tunnel strut. The numerical model has its value confirmed by the wind-tunnel tests in the predicted and observed roll-control reversal for anti-symmetrical deflections of the all-moving tails, and absence of reversal for aileron deflections.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.In this paper, the application of adaptive control is demonstrated for highly flexible aircraft in a dynamic gain scheduling approach. For that, an adaptive control law is designed for the stability augmentation system, taking as reference model the closed-loop dynamics provided by a baseline controller. Global stability is demonstrated by the Lyapunov direct method. Closed-loop nonlinear simulations are performed. The performance of the control system is evaluated considering the aircraft in high loading operations, specifically in accelerated turning maneuvers. Overall, this control strategy proved to overcome instabilities arising when linear control is applied, while conferring the aircraft adequate time response.

Copyright © 2016 by Flavio Silvestre. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.In this paper, the control law design for flexible aircraft is discussed. First, the traditional procedure of decoupling rigid-body and aeroelastic dynamics with low-pass and notch filters is addressed, with focus on controller performance as well as the resulting stability margin issues. A procedure based on a unified formulation of the flexible aircraft dynamics for flight control law design is proposed. In this procedure, the aeroservoelastic dynamics is assessed in the loop, and the offline filtering process is avoided. The formulation is applied to the virtual aircraft generic narrow-body airliner, with improvements in closed-loop performance and stability margins.

© 2017 IEEE.Zinc oxide thin films have high resistivity, plus thermal and chemical stability. Such properties make this material suitable for fabrication of piezo-electric sensors and surface acoustic wave devices that are used in Microelectromechanical systems (MEMS). The addition of metallic nanoparticles into the film matrix can reduce the value of resistivity, and, thus, qualify the material to be used in piezoresistive devices. In this work, a dc magnetron co-sputtering was used to grow Al doped ZnO (AZO) films with different applied voltages in the Al target, deposited on Si (100) p-type substrates with a layer of 1 micron of SiO2 by thermal oxidation. The microstructure and chemical composition of the films were characterized by X-ray diffraction and Rutterford-Backscattering techniques, respectively. The RBS results indicate the presence of aluminum, zinc, and oxygen in the films, which was confirmed by the XRD peaks of ZnO (002) at 2θ=34.4° Four probe technique confirmed a gradual reduction of resistivity up to 8.10-3 Ω.cm as the applied power on the Al-target increased.

© 2017, Springer Science+Business Media New York.Abstract: A promising strategy to reduce nosocomial infections related to prosthetic meshes is the prevention of microbial colonization. To this aim, prosthetic meshes coated with antimicrobial thin films are proposed. Commercial polypropylene meshes were coated with metal-containing diamond-like carbon (Me-DLC) thin films by the magnetron sputtering technique. Several dissimilar metals (silver, cobalt, indium, tungsten, tin, aluminum, chromium, zinc, manganese, tantalum, and titanium) were tested and compositional analyses of each Me-DLC were performed by Rutherford backscattering spectrometry. Antimicrobial activities of the films against five microbial species (Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis) were also investigated by a modified Kirby-Bauer test. Results showed that films containing silver and cobalt have inhibited the growth of all microbial species. Tungsten-DLC, tin-DLC, aluminum-DLC, zinc-DLC, manganese-DLC, and tantalum-DLC inhibited the growth of some strains, while chromium- and titanium-DLC weakly inhibited the growth of only one tested strain. In-DLC film showed no antimicrobial activity. The effects of tungsten-DLC and cobalt-DLC on Pseudomonas aeruginosa biofilm formation were also assessed. Tungsten-DLC was able to significantly reduce biofilm formation. Overall, the experimental results in the present study have shown new approaches to coating polymeric biomaterials aiming antimicrobial effect. Graphical Abstract: [InlineMediaObject not available: see fulltext.].

© 2016 Elsevier B.V.This paper presents a study about creep behavior of SiC thin films with Cr interlayer deposited by High Power Impulse Magnetron Sputtering (HiPIMS) on Ti-6Al-4V alloys with Widmanstätten microstructure. After SiC/Cr film depositions, a microstructural characterization was performed using Scratching Test, Scanning Electron Microscopy (SEM), Scanning and Transmission Electron Microscopy (STEM), and Energy Dispersive Spectroscopy (EDS) techniques. Scratching tests showed that the film was well adhered to the substrate, which proves that the Cr interlayer is closely related to the strength of adhesion between SiC film and the substrate. The SiC film surface morphology has columnar shape according to STEM images. Creep test results were compared with earlier Ti-6Al-4V Widmanstätten microstructure studies, and they showed an increased lifetime for the Ti-6Al-4V Widmanstätten microstructure with SiC/Cr film, which indicates a higher creep resistance than the specimen without the SiC/Cr film. The SiC/Cr film deposited by HiPIMS improved the creep behavior of the Ti-6Al-4V Widmanstätten microstructure.

© 2017 Elsevier B.V.The development of more efficient photoelectrochemical solar cells has been, over the years, the subject of many scientific researches. In this paper a methodology was established to carry out the sintering process of nanoporous TiO2 layer by using plasma, which was compared with sintered layers made by the conventional sintering process in a furnace. The TiO2 commercial paste was spread by doctor-blading technique and subjected to different sintering processes. Porous layer samples were subjected to structural and morphological analyses. Then photoelectrodes dye-loading was measured by optical spectrophotometry. The quality of the layers under plasma sintering process in terms of weight loss and removal of organic compounds was evaluated by thermogravimetric analysis, mass spectrometry and FT-IR. The results showed that the plasma sintering process favors the adsorption of dye on the layer surface due to the creation of active states caused by O2 reactive plasma. Furthermore the O2 plasma process provides enough energy for removing organic compounds arising from the TiO2 paste and for providing nanoparticle sintering. Solar cells assembled with the plasma-sintered layers had a power conversion efficiency 20.1% higher than the obtained in solar cells sintered in a conventional furnace, proving the efficiency of the plasma sintering process.

© 2017 Elsevier Masson SASLarge launch vehicles use their propulsion systems based on Liquid Rocket Engines (LRE) equipped with turbopumps. Turbopumps are complex rotary machines that supply high power, mass flow, and pressures in the engine system to reach the thrust requirements as determined in the rocket engine thermodynamic cycle. Strong engines need a secondary turbopump system called a booster. These boosters have pumps and turbines smaller than those of the main engine turbopumps, and their important function is to increase the fluid pressure at the inlet of the main turbopumps, mainly to avoid cavitation. In the present work, the influence of the tip clearance issues in an axial turbine installed to operate as oxidizer booster in the Space Shuttle Main Engine (SSME) were evaluated numerically. The results are compared with experimental data from National Aeronautics and Space Administration (NASA). The flow characteristics and the variation in the turbine efficiency for different jet velocities were determined for three different tip clearance values associated with the percentage of turbine blade height: 3.0%, 5.5%, and 8.0%. The turbine design, numerical issues, mesh generation and results are described and discussed. The methodology and numerical simulations used in the present work was consistent with the experimental data and can be extended for other correlated numerical simulations related to axial hydraulic turbines.

© 2016 Elsevier Masson SASThe choice of the most appropriate rotor tip configuration is important, because it helps to avoid high blade tip losses due to the leakage flow that are responsible for efficiency and pressure ratio drops, mainly in High Pressure Turbine (HPT). This subject has been investigated to improve the axial turbines performance. The HPT used in this work is the turbine designed during the Energy Efficient Engine Program (E3 Program). This HPT was evaluated with different rotor tip geometry configurations: without tip clearance (hypothetical condition), with standard tip clearance geometry (flat-tip), with squealer, with winglet and squealer with winglet. Results were obtained based on the three-dimensional turbulent flow calculations making the use of a commercial CFD RANS equation-based solver with the addition of a two-equation turbulence model, in which the numerical solutions were compared with data available in the open literature for a HPT design-point operation. It was determined that for the HPT studied in this work, the machine efficiency can be improved using the rotor tip geometry equipped with winglet tip configuration. However, the rotor tip geometry equipped with squealer–winglet tip configuration presented a better pressure ratio compromise.

Copyright © 2017 ASME.Due to the critical importance of the turbopump applied in Liquid-Propellant Rocket Engines (LPRE) and the importance in the use of specific engineering software to design and analyze turbomachines, a Project-Based Learning (PBL) methodology was implemented in the undergraduate Turbopumps (TP) discipline at the Aeronautics Institute of Technology (ITA), taught for aerospace engineering students. This methodology was applied, using as a class example, the Liquid Oxygen (LOX) booster turbine of the Space Shuttle Main Engine (SSME), aiming at an enhancement in the discipline's syllabus, to become the theory and practice closer to the real engineering, and to increase the discipline's attractiveness. The results obtained with this methodology showed that the students have more interest and attention in the classes in which an engineering problem is evaluated and discussed with details using appropriate examples and engineering software that are used by the academia and industry. Several turbomachines issues as velocity triangles, power, blade geometrical aspects, flow quality, losses and in this case, the importance of tip clearance, could be better understood by the students. About the numerical results, the aim is that the students, after the preliminary project ends, evaluate the results and compare them with experimental data from National Aeronautics and Space Administration (NASA). One of the most important experience in this project is the results evaluation by the students and the discussion around it, as lessons learned, given suggestions to improve the project, if the results are not in the right way what can be done to correct them and understanding all physical phenomena involved. The learning experience was fascinating and effective, as noticed by students and noted by Professors.

Copyright © 2017 ASME.The increasing fuel prices and stringent environmental legislation compel industries worldwide to pursue means to increase their processes efficiency. A higher efficiency relates to a reduction in fuel consumption, which results in a lower operational cost and emissions. When considering a steel mill, processes encountered in the blast furnace and in the coke oven, for example, generate gases that can be availed as low-grade fuels to return some sort of energy back to the process. This practice reduces the amount of high-grade fuel required and increases the global efficiency of the industrial site; however, demands higher investments and increase the management complexity. A thorough evaluation of such power cycles is important to assess their application. This paper is based on a currently operational combinedcycle power plant composed by two gas turbines that are adapted to use blast furnace gas as main fuel and one steam turbine with a total power rating of 490 MWe. This power plant configuration is compared to another one in which the topping cycle - composed by two gas turbines - is eliminated, and the same amount of blast furnace gas is burnt in a conventional steam generator, operating as a Rankine-cycle. The software Gate Cycle™ was used to model and simulate both cycles and provide the main parameters to analyze their performance. Parameters such as power rating, efficiency, emissions, and expected capital expenditure provided means to assess both options and evaluate their application. The combined-cycle provided higher efficiency and power rating when compared with the Rankine-cycle. However, the expected values for capital expenditure showed to be also higher. A major difference between both cycles is the higher flexibility of the combined-cycle power plant, which is essential to guarantee an electric energy source within the industrial site. As a counterpart, the operational complexity is significantly higher when compared with the Rankine-cycle. Overall, the present work provides valuable information to assess both solutions.

Copyright © 2017 ASME.Turbodrill is a type of hydraulic axial turbomachine that rotates a bit by the action of the drilling fluid on turbine blades, which converts the hydraulic power provided by the high pressure from drilling fluid into mechanical power through turbine stages. The evaluation of hydraulic turbine performance characteristics are important to define feasible rotational speed and mass flow to attend the bit torque requirements during drilling through the post-salt and salt layers. As a result, optimum operational parameters are proposed for gaining the required rotational speed and torque for post-salt environments. The turbine motor presented in this study was established by design methods based on classical aeronautical turbomachinery blade profile to supply 30k Newton-meters (Nm) of torque requested by a polycrystalline diamond compact (PDC) bit to power the complex heterogeneous layer of rock. The performance evaluation of this innovative hydraulic turbine with 200 stages was carried out using computational fluid dynamics (CFD). The simulation considers two different drilling fluid types, sea water and brine. Besides, different flow rates were considered to investigate how velocity vectors, pressure profile, output power and other performance parameters are affected. Due the large amount of data, the first and second stages of the turbine have been used to predict the performance characteristics. This assumption gives interesting results and avoids too heavy computational costs. A commercial CFD solver (ANSYS CFX 15.0®) was used to calculate the governing equations based on Reynolds-Averaged Navier-Stokes (RANS equations) with the addition of turbulence model. The two-equation Shear-Stress Transport (SST) turbulence model was used to account the effects of flow eddy viscosity.

© 2017, Journal of Aerospace Technology and Management. All rights reserved.Industry and universities around the world invest time and money to develop digital computer programs to predict gas turbine performance. This study aims to demonstrate a brand new digital model developed with the ability to simulate gas turbine real time high fidelity performance. The model herein described run faster than 30ms per point, which is compatible with a high-definition video refresh rate: 30 frames per second. This user-friendly model, built in Visual Basic in modular structure, can be easily configured to simulate almost all the existing gas turbine architectures (single, 2 or 3 shaft engines mixed or unmixed flows). In addition, its real time capability enables simulations with the pilot in the loop at earlier design phases when their feedback may lead to design changes for improvements or corrections. In this paper, besides the model description, it is presented the model run time capability as well as a comparison of the simulated performance with a commercial gas turbine tool for single, 2 and 3 shaft engine architecture.

© 2017 The Authors. Published by Elsevier Ltd.Experimental studies on the laminar burning velocity (LBV) and the flame propagation speed close to the wall of premixed methane-air flames at a pressure of 1 bar and ambient temperature, for poor and rich mixtures, have been conducted and analyzed. The methane-air mixture LBV and flame propagation speed are studied in a constant volume combustion chamber with acrylic windows using the shadowgraph technique and a high-speed camera. The recorded images are analyzed using a Matlab script and both the system and the Matlab code have been validated against literature data. The results are in quite good agreement with available literature for LBV that shows its decreasing with pressure increase. For the flame propagation speed little literature has been found for validation but using a different set-up. The results show that the flame propagation speed decreases almost linearly except close to the wall where some oscillations are present, due to a combination of multiple phenomena such as compression and heating of the unburned mixture, a combination of radiative heat loss to the wall, flame curvature and flame stretch.

© 2017, Brazilian Society for Automatics--SBA.This paper treats the problem of position formation flight control of a group of three multirotor aerial vehicles under obstacle and collision avoidance constraints. In order to solve the problem, a distributed architecture with model predictive controllers for each vehicle includes a set of convex constraints on the vehicles’s position to prevent collisions with other vehicles and obstacles. The resulting distributed scheme controls the formation based on a virtual structure approach where the computers of the architecture exchange position data through diagrams in Simulink. The performance of the method is assessed through simulations considering that the vehicles are subject to disturbance forces and the results show the effectiveness and the ability of the control architecture to handle the obstacle and collision avoidance constraints.

© 2016, Springer Science+Business Media Dordrecht.The employment of embedded cameras in navigation and guidance of Unmanned Aerial Vehicles (UAV) has attracted the focus of many academic researches. In particular, for the multirotor UAV, the camera is widely employed for applications performed in indoor environments, where the GNSS signal is often unreliable and electromagnetic interference can be a concern. In the literature, images are mostly adopted for position and velocity estimation, rather than attitude estimation. This paper proposes an attitude determination method for multirotor aerial vehicles using pairs of vector measurements taken from a downward-facing strapdown camera. The method is composed of three modules. The first one detects and identifies the visible landmarks by processing the images. The second module computes the vector measurements related to the direction from the camera to the landmarks. The third module estimates attitude from the vector measurements. In the last module, a version of the Multiplicative Extended Kalman Filter (MEKF) with sequential update is proposed as estimation method. The overall method is evaluated via Monte Carlo simulations, showing that it is effective in determining the vehicle’s attitude and revealing its properties.

© 2016, Brazilian Society for Automatics--SBA.This paper is concerned with state estimation of discrete-time linear systems subject to additive faults represented as inputs to both the state and measurement equations. Particularly, the sequence of fault inputs is assumed to be parameterizable by three fault parameters: fault magnitude, fault instant, and fault mode index. Moreover, these parameters are treated as unknown realizations of random variables defined so as to account for prior knowledge about possible faults. For tackling this problem, a two-stage filter structure is invoked.

© 2016, Springer Science+Business Media Dordrecht.This paper presents a polynomial chaos-based framework for designing optimal linear feedback control laws for nonlinear systems with stochastic parametric uncertainty. The spectral decomposition of the original stochastic dynamical model in an orthogonal polynomial basis, prescribed by the Wiener–Askey scheme, provides a deterministic model from which the optimal linear control law is designed. Optimality of the proposed control law is proved by solving the Hamilton–Jacobi–Bellman equation, and asymptotic stability of the controlled nonlinear systems is guaranteed in the Lyapunov sense. We are especially interested in synchronization of chaotic systems. For this reason, the control strategy is applied in the trajectory tracking of periodic orbits for the Duffing oscillator and the Rössler system with uncertain stochastic parameters and initial conditions. The results are verified with Monte Carlo simulations.

© 2017, Journal of Aerospace Technology and Management. All rights reserved.The present study faces the problem of safely controlling the position trajectory of a multirotor aerial vehicle subjected to a conic constraint on the total thrust vector and a linear convex constraint on the position vector. The problem is solved using a linear state-space model predictive control strategy, whose optimization is made handy by replacing the original conic constraint set on the thrust vector by an inscribed pyramidal space, which renders a linear set of inequalities. The proposed method is evaluated on the basis of Monte Carlo simulations taking into account a random disturbance force. The simulation results show the effectiveness of the method in tracking the commanded trajectory while respecting the constraints. They also predict the effect of both the speed command and the maximum allowed inclination angle on the system performance.

© 2017 IAAThe primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions different from zero for both attitude and elastic vibrations. Additionally, the control efforts for the three cases are compared. Results indicate that the attitude control is able to excite the solar panels' vibration modes and vice-versa. The piezoelectric vibration control shows significant performance improvement when compared to contributions of the attitude control to the vibration damping.

© 2016 Elsevier LtdViscoelastic materials have been widely used for the purpose of passive vibration mitigation in various types of mechanical systems, including, industrial machinery, civil structures and vehicles. In this paper, the use of those materials in aeroelastic systems is investigated, with emphasis placed on the influence of the viscoelastic behavior on the flutter speeds of two-degree-of-freedom typical section models, in which viscoelastic elements are introduced in addition to elastic elements associated to heave and pitch motions. The equations of motion of the aeroelastic system are modified to account for the dependence of the viscoelastic behavior on frequency and temperature, by using the concepts of complex modulus and shift factor. The aerodynamic forces and moments in subsonic regime are modeled according to Theodorsen's method. Numerical simulations are conducted to evaluate the influence of the addition of viscoelastic elements on the flutter speed and elucidate the separated influences of stiffness and damping additions. An experimental wind tunnel setup consisting of a rigid wing supported by flexible elements in pitch and plunge motions has been modified to enable the introduction of viscoelastic elements in parallel to those flexible elements. For various configurations of viscoelastic additions, the flutter instability is characterized from vibration measurements performed for increasing flow speeds in the vicinity of the stability boundary. The experimental results are used to validate the numerical model derived for the aeroviscoelastic system and confirm both qualitatively and quantitatively the predictions of the simulations, especially the possibility of increasing the flutter speed by the inclusion of viscoelastic materials.

Copyright © (2017) by International Astronautical Federation. All rights reserved.The main purpose of this paper is to implement a technique of passive elastic vibration control for a low Earth orbit satellite comprising two symmetric flexible solar arrays. While the solar arrays flexible vibration is passively controlled by using piezoelectric materials, the spacecraft attitude control is implemented by using the proportional integral derivative control technique. The idea is to compare the control effort when implementing the passive control with the control effort when using the piezoelectric for the same spacecraft. The solar panels are assumed to be in a sun synchronous rotation mode so its solar cells can continuously be illuminated by the Sun. The panels contain surface-bonded piezoelectric patches to implement the passive control of the solar panel elastic vibration. The gravitygradient torque as well as the torque due to the interaction of the Earth magnetic field with the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control. Computer simulations are performed using the MATLAB® software package. For analysis, one considers a station-keeping correction maneuver performed by a thruster actuator. Resulting elastic vibrations are investigated while considering the cases in which i) only the attitude control subsystem is considered; and ii) passive vibration control is adopted through piezoelectric shunt damping. As expected, the use of the considered passive control strategy is able to mitigate elastic vibrations effectively, and also help in reducing control efforts performed by the attitude reaction wheel controllers.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The utter behavior of tow steered composite panels, in which the fiber placement follow curvilinear trajectory, is evaluated. A simple structural model based on Ritz method combined with supersonic aerodynamic piston theory is used to analyze the aeroelastic behavior. Classical lamination plate theory and symmetric stacking sequence are used and the fiber trajectories are defined by Lagrange interpolation functions. The utter stability boundaries for optimal conventional (constant stiffness laminates) layups and non- conventional (variable stiffness laminates) steered panels are numerically compared. The effect of in-plane loads is also accounted for in the aeroelastic analyses.

© 2017, Brazilian Association of Computational Mechanics. All rights reserved.A broad class of engineering systems can be satisfactory modeled under the assumptions of small deformations and linear material properties. However, many mechanical systems used in modern applications, like structural elements typical of aerospace and petroleum industries, have been characterized by increased slenderness and high static and dynamic loads. In such situations, it becomes indispensable to consider the nonlinear geometric effects and/or material nonlinear behavior. At the same time, in many cases involving dynamic loads, there comes the need for attenuation of vibration levels. In this context, this paper describes the development and validation of numerical models of viscoelastic slender beam-like structures undergoing large displacements. The numerical approach is based on the combination of the nonlinear Cosserat beam theory and a viscoelastic model based on Fractional Derivatives. Such combination enables to derive nonlinear equations of motion that, upon finite element discretization, can be used for predicting the dynamic behavior of the structure in the time domain, accounting for geometric nonlinearity and viscoelastic damping. The modeling methodology is illustrated and validated by numerical simulations, the results of which are compared to others available in the literature.

© 2017 Elsevier B.V.The effect of an external magnetic field on electrical impedance was measured on tris-(8-hydroxyquinoline) aluminum (Alq3) based OLEDs at different temperatures. Magnetic field effects (MFEs) were responsible for significant changes on the real and imaginary components of the impedance, and for the intensification of the negative capacitance (NC) effect. The observed MFEs do not present a strong temperature dependence. Simulations via equivalent circuits and numerical solutions of Boltzmann transport equations in a drift-diffusion approximation and employing small sinusoidal signal analysis indicate that such effects are consistent with an enhancement of the carrier mobilities and a quenching of the recombination rates. Such changes lead to reduced resistance and more intense NC effects on the device. The results were interpreted in terms of the currently accepted OMAR models: electron-hole pair model, triplet-polaron reaction mechanism and bipolaron model.

© Emerald Publishing Limited.Purpose - The purpose of this article is the determination of the temperature fields in a weld region has always been an obstacle to the improvement of welding processes. As an alternative, the use of inverse problems to determine the heat flux during the welding process allows an analysis of these processes. Design/methodology/approach - This paper studies an alternative for the thermal analysis of the tungsten inert gas welding process on a 6,060 T5 aluminum alloy. For this purpose, a C++ code was developed, based on a transient three-dimensional heat transfer model. To estimate the amount of heat delivered to the plate, the specification function technique was used. Lab experiments were carried out to validate the methodology. A different experimental methodology is proposed to estimate the emissivity (radiation coefficient). Findings - The maximum difference between experimental and numerical temperatures is lower than 5 per cent. The determined emissivity value for the aluminum 6,060 T5 presented a good agreement with literature values. The thermal fields were analyzed as function of the positive polarity. The specification function method proved to be an adequate tool for heat input estimation in welding analysis. Originality/value - The proposed methodology proves to be a cheaper way to estimate the heat flux on the sample. The estimated power curves for the welding process are presented. The methodology to calculate the emissivity (radiation coefficient) was validated.

© 2017 by the authors.This work presents an analysis of the thermal influence of the heat transfer by convection and radiation during GTA (gas tungsten arc) welding process. The authors' in-house C++ previously-developed code was modified to calculate the amount of heat transfer by convection and radiation. In this software, an iterative Broydon-Fletcher-Goldfarb-Shanno (BFGS) inverse method was applied to estimate the amount of heat delivered to the plate when the appropriate sensitivity criteria were defined. The methodology was validated by accomplishing lab-controlled experiments on stainless steel AISI 304L and aluminum 6065 T5 plates. Due to some experimental singularities, the forced thermal convection induced by the electromagnetic field and thermal-capillary force were disregarded. Significant examples of these singularities are the relatively small weld bead when compared to the sample size and the reduced time of the welding process. In order to evaluate the local Nusselt number, empirical correlations for flat plates were used. The thermal emission was a dominant cooling effect on the aluminum cooling. However, it did not present the same behavior as the stainless steel samples. The study found that the heat losses by convection and radiation of the weld pool do not affect the cooling process significantly.

Copyright © 2017 John Wiley & Sons, Ltd.This paper discusses the applicability of agile methods to aircraft embedded software development. It presents the main results of an experiment that combines agile practices from Scrum with model-based development and distributed development. The experiment consists of the development of an aircraft cockpit display system divided in five distributed teams. Three features are analysed and quantified, using the output artefacts of each team: the artefacts' quality, the adherence to agile methods, and the adherence to standard DO-178C. The main conclusion of the experiment is that there is a high correlation between the adherence to agile methods and the artefacts' quality, motivating the use of agile methods in aircraft industry. Also, the experiment evinced that agile methods does not specifically address the integration of distributed teams and the hardware/software integration. This lacuna affects the artefacts' quality. The results of the experiment emphasize the importance of concentrating future work in the proposal of specific agile practices for these activities. Copyright © 2017 John Wiley & Sons, Ltd.

© 2017, Springer-Verlag London.Since the introduction of robots in the automotive industry for pick and place tasks, new technologies have been developed in order to adapt robots to different manufacturing processes. Among them, the use of robots as machine tools is a technological trend that demands further investigation. Industrial robots with 6 DOF (degrees of freedom) in a serial kinematic chain have larger workspace and more flexibility, when compared with CNC machines. However, robots’ stiffness is lower than that of CNC machines. Consequently, vibration problems are expected, which can have a direct impact on the quality of the machined workpieces. This work proposes a method to evaluate and customize the use of a COTS (commercial off-the-shelf) robot equipped with a spindle for machining processes. It aims at improving the machining processes based on the measurement of the workpiece waviness and explores the fact that the accuracy and rigidity of industrial robots with serial kinematic chains behave in an anisotropic way, according to the robot pose and the cutting force direction. The method is composed of a set of five experiments and is applied to the evaluation of a robot machining aluminium workpieces. The results allow the identification of the relevant factors that affect the surface quality of the workpiece and recommend the best robot configuration for meeting the waviness requirements of the workpiece. Even though the application case describes the machining of aluminium workpiece, the proposed method is generic enough to be applied to different workpiece geometries and materials.

© 2017 IEEE.Industry 4.0 brings a new productive period, in which companies that do not have its machinery updated and compatible with the precepts of the advanced manufacture will have difficulties to survive in this new competitive environment. This work proposes retrofit techniques alternatives to allow old automation and mechatronic components such as robotic arms and CNC machines to be reused in the new industrial revolution with low implementation cost, adapting them to advanced manufacturing. For the development of the techniques, the machines existent in an academic plant were used. A virtual commissioning was performed for previous validation of the plant operational layout. Then embedded computational platforms, off-the-shelf microcontrollers and programming techniques were used to modify the machinery communication interfaces, allowing the development of intelligence and remote communication. The alternatives were efficient and cost-effective.

© 2017 IEEE.New advanced traffic management solutions with fully or semi-autonomous vehicles that communicate over a wireless interface to coordinate their driving decisions create new challenges in distributed computing. In this paper we address the problem of dynamic group membership in three stages. First, we propose three criteria to specify correctness and performance of the group views created by such algorithms in terms of soundness, completeness and freshness. Second, we develop a group membership protocol tailored for vehicular coordination. Finally, we show through simulation and model-based verification that the protocol does indeed meet the criteria and provide at least 95% perfect group membership views under as adverse conditions as 70% packet loss or very high churn rate.

© 2016 Elsevier LtdThis work is motivated by an aeronautical issue: the fuel sloshing in the tank coupled with very flexible wings. Vibrations due to these coupled phenomena can lead to problems like reduced passenger comfort and maneuverability, and even unstable behavior. Port-Hamiltonian systems (pHs) provide a unified framework for the description of multi-domain, complex physical systems and a modular approach for the interconnection of subsystems. In this work, pHs models are proposed for the equations of liquid sloshing in moving containers and for the structural equations of beams with piezoelectric actuators. The interconnection ports are used to couple the sloshing dynamics in the moving tank to the motion the beam. This coupling leads to an infinite-dimensional model of the system in the pHs form. A finite-dimensional approximation is obtained by using a geometric pseudo-spectral method that preserves the pHs structure at the discrete level. Experimental tests on a structure made of a beam and a tank were carried out to validate the finite-dimensional model of liquid sloshing in moving containers. Finally, the pHs model proves useful to design an active control law for the reduction of sloshing phenomena.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.A simple and self-contained methodology to assess the validity of the assumption of small deformations in linear structural-dynamic models was recently proposed. The advantages of the methodology lie in the fact that it does not depend on the availability of higher-fidelity, nonlinear models: it is rather based on the selection of two different structural nodes where the structural motion is to be one at a time completely constrained, typically, a node near the center of mass and another in the region of maximum structural displacements with respect to mean axes. If the two displacement vectors calculated in each case can be transformed between themselves with linear rigid-body modes of the structure, then it is still in the regime of small deformations. In the present paper, in order to demonstrate the value of this methodology, it is applied to the X-HALE aircraft in its four-, six- and eight-meter-span configurations, and the results obtained with the assumption of small deformations are compared with a higher-fidelity model that comprises large structural deformations.

© Emerald Publishing Limited.Purpose: The purpose of this paper is to present a mathematical model of one very flexible transport category airplane whose structural dynamics was modeled with the strain-based formulation. This model can be used for the analysis of couplings between the flight dynamics and structural dynamics. Design/methodology/approach: The model was developed with the use of Hamiltonian mechanics and strain-based formulation. Nonlinear flight dynamics, nonlinear structural dynamics and inertial couplings are considered. Findings: The mathematical model allows the analysis of effects of high structural deformations on airplane flight dynamics. Research limitations/implications: The mathematical model has more than 60 degrees of freedom. The computational burden is too high, if compared to the traditional rigid body flight dynamics simulations. Practical implications: The mathematical model presented in this work allows a detailed analysis of the couplings between flight dynamics and structural dynamics in very flexible airplanes. The better comprehension of these couplings will contribute to the development of flexible airplanes. Originality/value: This work presents the application of nonlinear flight dynamics-nonlinear structural dynamics-strain-based formulation (NFNS-s) methodology to model the flight dynamics of one very flexible transport category airplane. This paper addresses also the way as the analysis of results obtained in nonlinear simulations can be made. Comparisons of the NFNS-s and nonlinear flight dynamics-linear structural dynamics methodologies are presented in this work.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.A simple and self-contained methodology to assess the validity of the assumption of small deformations in linear structural-dynamic models was recently proposed. The advantages of the methodology lie in the fact that it does not depend on the availability of higher-fidelity, nonlinear models: it is rather based on the selection of two different structural nodes where the structural motion is to be one at a time completely constrained, typically, a node near the center of mass and another in the region of maximum structural displacements with respect to mean axes. If the two displacement vectors calculated in each case can be transformed between themselves with linear rigid-body modes of the structure, then it is still in the regime of small deformations. In the present paper, in order to demonstrate the value of this methodology, it is applied to the X-HALE aircraft in its four-, six- and eight-meter-span configurations, and the results obtained with the assumption of small deformations are compared with a higher-fidelity model that comprises large structural deformations.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Formulations for the flight dynamics of flexible aircraft have been commonly applied to aircraft free to fly in the three-dimensional space, having all six rigid-body degrees of freedom. For risk reduction in the future flight operations of the X-HALE testbed at ITA, however, wind-tunnel tests of the remotely-piloted, four-meter-span configuration of the aircraft were performed. In the wind tunnel, the rigid-body translations were completely constrained, but the same was not valid for the rigid-body rotations, which could be conveniently left free or not with a proper selection of the connection between the aircraft and the wind-tunnel mount. In the present paper, in order to computationally assess the response and stability characteristics of the aircraft in the wind tunnel, we derive equations of motion for a constrained flexible aircraft with up to three rigid-body rotational degrees of freedom, mounted on an also flexible wind-tunnel strut. The numerical model has its value confirmed by the wind-tunnel tests in the predicted and observed roll-control reversal for anti-symmetrical deflections of the all-moving tails, and absence of reversal for aileron deflections.

© 2017, Brazilian Association of Computational Mechanics. All rights reserved.Aerospace vehicles are mostly exposed to random vibration loads during its operational lifetime. These harsh conditions excites vibration responses in the vehicles printed circuit boards, what can cause failure on mission functionality due to fatigue damage of electronic components. A novel analytical model to evaluate the useful life of embedded electronic components (capacitors, chips, oscillators etc.) mounted on Printed Circuit Boards (PCB) is presented. The fatigue damage predictions are calculated by the relative displacement between the PCB and the component, the lead stiffness, as well the natural vibration modes of the PCB and the component itself. Statistical methods are used for fatigue cycle counting. The model is applied to experimental fatigue tests of PCBs available on literature. The analytical results are of the same magnitude order of the experimental findings.

© 2017 Elsevier Ltd and Techna Group S.r.l.Carbon/carbon (C/C) composites are widely used in structural components, particularly in the aerospace and aeronautics sectors. However, the application of C/C composites is limited by low oxidation resistance at high temperatures. In order to overcome this problem, graded SiO2/SiC coatings were deposited on C/C composites by a high-velocity solution plasma spray (HVSPS) process. Graded coatings were formed by reactions between the Si(OH)4 sprayed liquid precursor and the C/C substrate; these reactions were promoted by the high temperature of the plasma torch. The morphologies, microstructures, and chemical compositions of the coatings were investigated by X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive X-ray spectroscopy. By altering the deposition time, the coating thickness was controlled, therefore demonstrating SiC formation and realizing graded SiO2/SiC coatings.

© 2017, Springer Science+Business Media B.V.The thermochemical decomposition of sunflower oil cake (SuOC) with ZnCl2 and AlCl3 additives was studied by thermogravimetric (TG) analysis at a heating rate of 5 °C/min under a controlled nitrogen atmosphere with flow value of (20 mL/min). The present study focused on the development of evaluation criteria of the thermal decomposition of SuOC with additives. Evaluation criteria were suggested based on a comparison of kinetic data of an actual mixture with that of a corresponding reference mechanical mixture (RMM). Assessment of the additives influences on the thermal behaviour of SuOC showed that AlCl3 provided up to a 70% enhancement of devolatilization in comparison with the RMM and a 7.5–10% decrease of activation energy at the low pyrolysis temperature of 242 °C by providing a biomass conversion degree of α = 60–70%. In contrast, the ZnCl2 provided the same value of biomass conversion degree, but only in the temperature range of 450–550 °C.

© 2017, ASM International.Plasma spray is a versatile technology used for production of environmental and thermal barrier coatings, mainly in the aerospace, gas turbine, and automotive industries, with potential application in the renewable energy industry. New plasma spray technologies have been developed recently to produce high-quality coatings as an alternative to the costly low-pressure plasma-spray process. In this work, we studied the properties of as-sprayed CoNiCrAlY coatings deposited on Ti-6Al-4V substrate with smooth surface (Ra = 0.8 μm) by means of a plasma torch operating in supersonic regime at atmospheric pressure. The CoNiCrAlY coatings were evaluated in terms of their surface roughness, microstructure, instrumented indentation, and phase content. Static and dynamic depositions were investigated to examine their effect on coating characteristics. Results show that the substrate surface velocity has a major influence on the coating properties. The sprayed CoNiCrAlY coatings exhibit low roughness (Ra of 5.7 μm), low porosity (0.8%), excellent mechanical properties (Hit = 6.1 GPa, Eit = 155 GPa), and elevated interface toughness (2.4 MPa m1/2).

© 2017 The Author(s).Results of experimental investigations of a new-type generator of an arc water plasma Having a high thermal efficiency close to 100% Are presented This generator represents a system comprising a vortex arc plasma generator In which an electric arc is stabilized by water vapor and a straight-through-flow tubular electric steam generator Such a high effi ciency of the plasma generator system was achieved due to the refi nement of the internal gas dynamics of the plasma generator and the heat and mass transfer in its discharge channel as a result of the improvement of the vortex stabilization and thermal insulation of an arc discharge in it by the specially organized ″instantly permeable″ channel wall cooled by only the working water used for generation of the plasma.

© 2017, Springer Science+Business Media New York.The motion of particles axially injected into the plasma spray process has been studied using a one-dimensional model. The effect of the initial particle velocity and particle diameter on the final particle velocity and temperature was evaluated. The aim of the work is to optimize the spraying process by defining the favorable particle injection velocity, considering a wide range of velocity and temperature of the plasma jet.

© 2017 Elsevier Ltd and Techna Group S.r.l.This work explores a new route for the synthesis of titanium dioxide using scraps and titanium chips, which are typically discarded as waste, as the precursor materials. The band-gap energy of the synthesised materials was determined using diffuse reflectance spectroscopy. The morphology, elemental analysis, crystallinity, and chemical structure of the synthesised materials were determined by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometry, and infrared and Raman spectroscopies, respectively. The X-ray and Raman analyses confirmed the formation of titanium dioxide in its tetragonal (anatase) crystalline form after heat treatment (400 °C, 2 h). Moreover, a mixture of (NH4)0,3TiO1,1F2,1 and anatase TiO2 was obtained as a by-product. After heat treatment, this by-product was converted into fluorine-doped titanium dioxide, also in anatase crystalline form. The apparent crystallite size (Lc) of anhydrous titanium dioxide was found to be smaller than that of the calcined by-product. The diffuse reflectance spectroscopy analysis revealed that the calcined by-product has a significantly higher absorption capacity at higher wavelengths, as well as a lower band-gap energy value. The scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) analyses showed large particulates on which smaller particles are deposited and good dispersion of the elemental components. The anhydrous titanium dioxide sample presents a smaller particle size than the calcined by-product.

© 2017 IOP Publishing Ltd.Carbon nanotube (CNT)-epoxy composites were prepared using carboxyl, amino and raw CNTs. The results of differential scanning calorimetry (DSC) showed that the effect of CNTs on the cure of epoxy resin is strongly dependent on the temperature and time. Raw and carboxyl CNTs accelerated the formation of branched chains (pre-cure at 80 °C), consuming the polymerization sites and leading to lower rates of crosslinking reaction (cure at 120 °C), resulting in lower storage modulus according to dynamic mechanical analysis (DMA). These results were explained by the catalysts of pre-cure (carboxylic groups and metallic residue of CNTs) and by CNT agglomerates, which could slow the crosslinking due to the consumption of epoxy sites. However, neat epoxy and amino-CNTs nanocomposites showed lower pre-cure rates and higher cure rates, resulting in higher storage modulus. Amino CNTs were the only nanotubes that increased the storage modulus of neat epoxy, due to the good homogeneity and adhesion of their composites.

© 2017 Taylor & Francis Group, LLC.Carbon nanotube (CNT) reinforced high-density polyethylene (HDPE) composites were prepared by a melt mixing procedure. The mechanical properties were analyzed using a central composite design where key factors were CNT concentration and sonication temperature during the sample preparation process. The results indicated that the optimum values were 0.8 wt% for the concentration of CNT and 55°C for the sonication temperature. The samples obtained at optimal conditions were systematically studied. Nanoindentation analysis showed an increase of 43% in Vickers hardness of the nanocomposite when compared to pure polymer. The improvement on the mechanical property is related to changes in the thermo-physical and viscoelastic properties of the nanocomposite.

© 2015 Society of Plastics EngineersCarbon nanotube-epoxy composites were prepared using amino-functionalized CNTs and sonication as a mixing process. Different times and sonication powers were used for preparing composites in order to study how the sonication process may influence the curing reaction of both systems: neat epoxy resin and amino-CNT/epoxy composite.The curing reaction was investigated with differential scanning calorimetry and the results were associated with analysis of gel permeation chromatography. The results showed that the effect of CNTs on the cure behavior of the epoxy resin depends on the sonication power. The sonication of neat resin with a 150 W powered device led to a molar mass reduction of the resin and an increase in the cure enthalpy. The CNT addition to this system reduced the cure enthalpy. However, when neat epoxy resin was sonicated with a 200 W powered device, the molar mass did not decrease (i.e., it was increased or was not changed) and the cure enthalpy did not increase (essentially it decreased or did not change). The CNT addition to such solutions did not reduce (i.e., it was increased or did not change) the cure enthalpy, which is a contrary result from that obtained with a 150 W powered device. POLYM. COMPOS., 38:1964–1973, 2017. © 2015 Society of Plastics Engineers.

© 2017 Elsevier B.V.This study presents the effect of dodecylamine (DDA) functionalization of carbon nanotubes (CNTs) on the thermo-physical and mechanical properties of high-density polyethylene (HDPE) based composites. Here, we showed that the functionalization with DDA improved the dispersion of the CNTs as well as the interfacial adhesion with the HDPE matrix via non-covalent interactions. The better dispersion and interaction of CNT in the HDPE matrix as a function of the surface chemistry was correlated with the improved thermo-physical and mechanical properties.

This paper investigates the application of the luminescence spectroscopy technique in steady-state to study the moisture influence in glass fiber/epoxy prepreg and their laminates. The studies were monitored by intrinsic luminescence comparing the results with gravimetric analysis and near infrared with Fourier transform. Samples are cured and submitted to humidity controlled at 60 and 80 °C until 90 days. It is verified that the decrease in the maximum emission of the samples is directly related to the material moisture content. However, for very short periods, there is an increase in the relative intensity and blue shift of the emission band for all samples treated at 60 °C, which is related to an increase of the rigidity of the polymeric matrix. The results in this paper have a great significance because it brings a wide discussion on the interaction of water in epoxy composites materials.

© 2017The heat transfer mechanism of natural convection has been extensively studied as a passive heat removal system of new nuclear power plants. Considering this aspect, the main objective of this study is to present an assessment of RELAP5 linear-equation solver under a transient two-fluid model for a two-phase natural circulation loop (NCL). For this assessment, three different approaches of linear-equation solvers for the hydrodynamic model are presented: the sparse matrix solver based on the Lower-Upper (LU) decomposition, the Border-Profile Lower Upper (BPLU) solver and the iterative method named Generalized Minimal Residual Method (GMRES). For comparison purposes, an experimental natural circulation loop made of glass tubes and using water as working fluid is analyzed. The onset of nucleate boiling observed during the experiment was predicted by all RELAP5 solvers as well as the representation of flow oscillations along the loop. Furthermore, it was noticed that the choice of the solver algorithm has a strong influence on the prediction of the two-phase natural circulation phenomena, since different wavelengths and amplitudes of flow instabilities were obtained for each approach.

© 2017 IMEKOThe present work evaluates the impact of carbon monoxide inhalation in the human lungs exergy behaviour for different levels of intoxications and altitude. It is significant because this substance is one of the most common air pollutants in cities and an increasing in the destroyed exergy can be associated with a reduction in lifespan. Moreover, an evaluation of the severity as a function of the city height may intensify the hazard associated with carbon monoxide. In order to evaluate these consequences, a carbon monoxide transportation model obtained in literature was used to calculate the concentrations of oxygen, carbon monoxide and carbon dioxide in the different respiratory system tissues. With the purpose to better evaluate the different levels of carbon monoxide intoxication and hemoglobin concentration (which is a function of acclimatization time) it was proposed an exergy efficiency for the lungs. From this model, it was possible to conclude that a higher level of intoxication is associated to lower exergy efficiency values. Higher hemoglobin levels when associated to carbon monoxide intoxication also results in lower efficiencies.

© 2017 IMEKOIn the past few years, different scientific papers have proposed the use of an exergy perspective to analyze some physiological systems of the human body under different physical and environmental conditions. Such perspective, focused on the exergy transformations and the efficiency of the biological processes, which may aid the medical field in its assessment of a patient’s physical health. Following this concept, this paper proposes a model of the human cardiovascular system in order to calculate the exergy transfers and its destruction from the intrasystemic and intersystemic interactions, taking into account all significant energy conversion processes that involve the heart and the blood vessels as blood circulates in both the systemic and the pulmonary circulations. With this model, a 7.86 W exergy destruction was obtained for a person under basal conditions. As a follow-up, a statistical model was developed to describe the evolution of the transvalvular pressure gradient in the aortic valve as a valve stenosis becomes more severe. This model was created using physiological data from 40 patients available in the literature, as well as 32 operating points from different Bileaflet aortic valve prosthesis. A final logarithmic regression resulted in a 14.6 kPa (109.7 mmHg) pressure gradient in the most severe case, evolving from 0.9 kPa (6.5 mmHg) from the healthy scenario. Finally, the pressure gradients were analysed using the base model, arriving at an extreme value of 1.04 W of destroyed exergy in the aortic valve and 9.64 W for the entire system, an increase of 22.6% when comparing with the result for the healthy condition.

© 2017 Elsevier LtdSome authors have been applying the exergy analysis to thermal comfort, where the environmental conditions for minimal exergy destruction are claimed to correspond to thermal comfort conditions. Herein, the exergy destroyed rate of the human body will be determined as a function of temperature and humidity for three levels of exercise. For the sake of comparison, thermal comfort will also be assessed by means of PMV (Predicted Mean Vote) index. Results indicate that, the higher the relative humidity, the lower the temperature of thermal comfort and, for the same humidity, the higher the exercise intensity, the smaller the temperature of thermal comfort. On the other hand, the values of PMV do not vary much with relative humidity, what indicates that the effect of this parameter is almost neglected by this method. Besides, the difference between the three levels of exercise was not as pronounced as in the exergy method. During activity, the values of the exergy flow rate due to evaporation for thermal comfort are smaller in the exergy method than in the conventional one. Thus, it can be said that, under physical activities, the exergy method for thermal comfort seems to be a reliable alternative to the conventional one.

© 2017 Elsevier Masson SASLarge launch vehicles use their propulsion systems based on Liquid Rocket Engines (LRE) equipped with turbopumps. Turbopumps are complex rotary machines that supply high power, mass flow, and pressures in the engine system to reach the thrust requirements as determined in the rocket engine thermodynamic cycle. Strong engines need a secondary turbopump system called a booster. These boosters have pumps and turbines smaller than those of the main engine turbopumps, and their important function is to increase the fluid pressure at the inlet of the main turbopumps, mainly to avoid cavitation. In the present work, the influence of the tip clearance issues in an axial turbine installed to operate as oxidizer booster in the Space Shuttle Main Engine (SSME) were evaluated numerically. The results are compared with experimental data from National Aeronautics and Space Administration (NASA). The flow characteristics and the variation in the turbine efficiency for different jet velocities were determined for three different tip clearance values associated with the percentage of turbine blade height: 3.0%, 5.5%, and 8.0%. The turbine design, numerical issues, mesh generation and results are described and discussed. The methodology and numerical simulations used in the present work was consistent with the experimental data and can be extended for other correlated numerical simulations related to axial hydraulic turbines.

© 2016 Elsevier Masson SASThe choice of the most appropriate rotor tip configuration is important, because it helps to avoid high blade tip losses due to the leakage flow that are responsible for efficiency and pressure ratio drops, mainly in High Pressure Turbine (HPT). This subject has been investigated to improve the axial turbines performance. The HPT used in this work is the turbine designed during the Energy Efficient Engine Program (E3 Program). This HPT was evaluated with different rotor tip geometry configurations: without tip clearance (hypothetical condition), with standard tip clearance geometry (flat-tip), with squealer, with winglet and squealer with winglet. Results were obtained based on the three-dimensional turbulent flow calculations making the use of a commercial CFD RANS equation-based solver with the addition of a two-equation turbulence model, in which the numerical solutions were compared with data available in the open literature for a HPT design-point operation. It was determined that for the HPT studied in this work, the machine efficiency can be improved using the rotor tip geometry equipped with winglet tip configuration. However, the rotor tip geometry equipped with squealer–winglet tip configuration presented a better pressure ratio compromise.

Copyright © 2017 ASME.Due to the critical importance of the turbopump applied in Liquid-Propellant Rocket Engines (LPRE) and the importance in the use of specific engineering software to design and analyze turbomachines, a Project-Based Learning (PBL) methodology was implemented in the undergraduate Turbopumps (TP) discipline at the Aeronautics Institute of Technology (ITA), taught for aerospace engineering students. This methodology was applied, using as a class example, the Liquid Oxygen (LOX) booster turbine of the Space Shuttle Main Engine (SSME), aiming at an enhancement in the discipline's syllabus, to become the theory and practice closer to the real engineering, and to increase the discipline's attractiveness. The results obtained with this methodology showed that the students have more interest and attention in the classes in which an engineering problem is evaluated and discussed with details using appropriate examples and engineering software that are used by the academia and industry. Several turbomachines issues as velocity triangles, power, blade geometrical aspects, flow quality, losses and in this case, the importance of tip clearance, could be better understood by the students. About the numerical results, the aim is that the students, after the preliminary project ends, evaluate the results and compare them with experimental data from National Aeronautics and Space Administration (NASA). One of the most important experience in this project is the results evaluation by the students and the discussion around it, as lessons learned, given suggestions to improve the project, if the results are not in the right way what can be done to correct them and understanding all physical phenomena involved. The learning experience was fascinating and effective, as noticed by students and noted by Professors.

Copyright © 2017 ASME.The increasing fuel prices and stringent environmental legislation compel industries worldwide to pursue means to increase their processes efficiency. A higher efficiency relates to a reduction in fuel consumption, which results in a lower operational cost and emissions. When considering a steel mill, processes encountered in the blast furnace and in the coke oven, for example, generate gases that can be availed as low-grade fuels to return some sort of energy back to the process. This practice reduces the amount of high-grade fuel required and increases the global efficiency of the industrial site; however, demands higher investments and increase the management complexity. A thorough evaluation of such power cycles is important to assess their application. This paper is based on a currently operational combinedcycle power plant composed by two gas turbines that are adapted to use blast furnace gas as main fuel and one steam turbine with a total power rating of 490 MWe. This power plant configuration is compared to another one in which the topping cycle - composed by two gas turbines - is eliminated, and the same amount of blast furnace gas is burnt in a conventional steam generator, operating as a Rankine-cycle. The software Gate Cycle™ was used to model and simulate both cycles and provide the main parameters to analyze their performance. Parameters such as power rating, efficiency, emissions, and expected capital expenditure provided means to assess both options and evaluate their application. The combined-cycle provided higher efficiency and power rating when compared with the Rankine-cycle. However, the expected values for capital expenditure showed to be also higher. A major difference between both cycles is the higher flexibility of the combined-cycle power plant, which is essential to guarantee an electric energy source within the industrial site. As a counterpart, the operational complexity is significantly higher when compared with the Rankine-cycle. Overall, the present work provides valuable information to assess both solutions.

Copyright © 2017 ASME.Turbodrill is a type of hydraulic axial turbomachine that rotates a bit by the action of the drilling fluid on turbine blades, which converts the hydraulic power provided by the high pressure from drilling fluid into mechanical power through turbine stages. The evaluation of hydraulic turbine performance characteristics are important to define feasible rotational speed and mass flow to attend the bit torque requirements during drilling through the post-salt and salt layers. As a result, optimum operational parameters are proposed for gaining the required rotational speed and torque for post-salt environments. The turbine motor presented in this study was established by design methods based on classical aeronautical turbomachinery blade profile to supply 30k Newton-meters (Nm) of torque requested by a polycrystalline diamond compact (PDC) bit to power the complex heterogeneous layer of rock. The performance evaluation of this innovative hydraulic turbine with 200 stages was carried out using computational fluid dynamics (CFD). The simulation considers two different drilling fluid types, sea water and brine. Besides, different flow rates were considered to investigate how velocity vectors, pressure profile, output power and other performance parameters are affected. Due the large amount of data, the first and second stages of the turbine have been used to predict the performance characteristics. This assumption gives interesting results and avoids too heavy computational costs. A commercial CFD solver (ANSYS CFX 15.0®) was used to calculate the governing equations based on Reynolds-Averaged Navier-Stokes (RANS equations) with the addition of turbulence model. The two-equation Shear-Stress Transport (SST) turbulence model was used to account the effects of flow eddy viscosity.

© 2017, Journal of Aerospace Technology and Management. All rights reserved.Industry and universities around the world invest time and money to develop digital computer programs to predict gas turbine performance. This study aims to demonstrate a brand new digital model developed with the ability to simulate gas turbine real time high fidelity performance. The model herein described run faster than 30ms per point, which is compatible with a high-definition video refresh rate: 30 frames per second. This user-friendly model, built in Visual Basic in modular structure, can be easily configured to simulate almost all the existing gas turbine architectures (single, 2 or 3 shaft engines mixed or unmixed flows). In addition, its real time capability enables simulations with the pilot in the loop at earlier design phases when their feedback may lead to design changes for improvements or corrections. In this paper, besides the model description, it is presented the model run time capability as well as a comparison of the simulated performance with a commercial gas turbine tool for single, 2 and 3 shaft engine architecture.

© 2017 Elsevier B.V.TiO2, glucose oxidase and carbon nanotube microparticles were ultrasonically formed to provide a large surface area for enzyme immobilisation and a favorable microenvironment for direct electron transfer. This simple architecture nanostructure was used to construct a glucose oxidase biosensor, which demonstrated good analytical performance with high reproducibility, and good detection for pathological glucose level.

© 2017 Elsevier LtdElectrochemical oxygen reduction and methanol oxidation are two important reactions in the development of clean energy technology. Substantial progresses in the design of cheap, robust, and efficient catalysts are still required and remain a significant challenge. Here, we report a double pulse electrodeposition process, capable of controlling the density and the size of silver nanoparticle supported on graphene. We found that this catalyst afforded a current density of 5.5 mA cm−2 at a low potential for ORR, comparing favourably with the state-of-the-art Pt/C catalyst. Additionally, we demonstrate that size and distribution effects are critical parameters for more efficient ORR and MOR catalysis. Our results suggest possibility for the development of effective and robust ORR and MOR electrocatalysts based on cheap silver metal and graphene and as replacements for the commercially available but expensive Pt/C catalysts.

© 2016In this work it is presented a facile and novel method for modification of bioglass surface based on (Camolten salt bath2 +| Naglass+) ion exchange by immersion in molten salt bath. This method allows changing selectively the chemical composition of a surface layer of glass, creating a new and more reactive bioglass in a shell that surrounds the unchanged bulk of the original BG45S5 bioglass (core-shell type system). The modified bioglass conserves the non-crystalline structure of BG45S5 bioglass and presents a significant increase of surface reactivity in comparison with BG45S5. Melt-derived bioactive glasses BG45S5 with the nominal composition of 46.1 mol% SiO2, 24.4 mol% Na2O, 26.9 mol% CaO, and 2.6 mol% P2O5 have been subjected to ion exchange at 480 °C in molten mixture of Ca(NO3)2 and NaNO3 with molar ratio of 70:30 for different time periods ranging from 0 to 60 min. The optimization studies by using XRF and XRD showed that ion exchange time of 30 min is enough to achieve higher changes on the glass surface without alters its non-crystalline structure. The chemical composition, morphology and structure of BG45S5 and bioglass with modified surface were studied by using several analytical techniques. FTIR and O1s XPS results showed that the modification of glass surface favors the formation of Si-ONBO groups at the expense of Si[sbnd]OBO[sbnd]Si bonds. 29Si MAS-NMR studies showed that the connectivity of SiQn species decreases from cross-linked SiQ3 units to chain-like SiQ2 units and finally to depolymerized SiQ1 and SiQ° units after ion exchange. This result is consistent with the chemical model based on the enrichment with calcium ions of the bioglass surface such that the excess of positive charges is balanced by depolymerization of silicate network. The pH changes in the early steps of reaction of bioactive glasses BG45S5 and BG45Ca30, in deionized water or solutions buffered with HEPES were investigated. BG45Ca30 bioactive glass exhibited a significant increase in the pH during the early steps of the reaction compared to BG45S5.

© The Royal Society of Chemistry.The immobilization of enzymes is an excellent alternative to overcome the drawbacks of using these biocatalysts in free form. This process plays a significant role in cost-effective recovery, increased catalyst productivity and in simplifying process operations. After the soybean peroxidase (SP) extraction, a residue at high carbon and low ash content is generated. This residue was used as carbonaceous precursor for production of carbon activated (AC) with high surface area (1603 m2 g−1). The AC produced was used as support for SP immobilization. The immobilization of SP was evaluated in different time conditions, enzyme load, pH and temperature. The samples, before and after immobilization, were characterized by thermogravimetric analysis, elemental analysis composition, specific surface area, X-ray powder diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy. In addition, repeated applications of immobilized biocatalyst were made in order to evaluate its operational stability and capacity to recover the reaction medium, in which was observed that after a decline in activity from the first to the second cycle, it remained constant until the tenth application. In the context, the process of material obtainment constitutes a clean route for the development of more sustainable biocatalysts capable of applications in various areas.

© 2017 Universidade Federal de Sao Carlos. All rights reserved.Plasma nitriding of a solution annealed and aged 300 grade maraging steel was studied aiming to increase the creep resistance. The surface microhardness reached 1,140 HV, producing 50 μm layer composed of ε-Fe3N and γ'-Fe4N nitrides at the uppermost sample layer. The inner core remained unaltered presenting typical plate-like martensite microstructure of maraging steels with average microhardness of 604 HV. Surface RMS roughness in the nanometric scale increase from 52 nm to 71 nm. The continuous layer of iron nitrides seems to behave as a barrier for oxidation and for inward oxygen diffusion improving the creep resistance by reducing the steady-state creep rate (εs) in 52-65% when compared with the literature results. Dominant creep mechanism is controlled by dislocations climb. Fracture surfaces of specimens presented ductile failure consisting of equiaxed and bi-modal dimples in the fibrous zone surrounded by 45ºshear lip. Nitrided sample presented a reduced ductility, associated to the hard surface layer.

© 2017 Trans Tech Publications, Switzerland.The influence of plasma nitriding of a maraging 300 steel on mechanical properties at high temperature has been studied. Samples were tensile tested at 600°C in four conditions: solution treated (MAR-S), solution treated and aged (MAR-SA), solution treated and plasma nitrited (MAR-SP) and solution treated, aged and plasma nitrited (MAR-SAP). In the same sequence, the yield strength and ultimate tensile strength increased slightly respectively from 1073 to 1189 MPa and 1174 to 1301 MPa, an increase of about 10% due to plasma nitriding. All the samples presented similar values of elongation, around 18%, but the cross section area reduction decreased significantly by plasma nitriding from ~70% for MAR-S and MAR-SA to ~45% for MAR-SP and MAR-SAP, that is an decrease of 36% in average. This decrease is attributed to brittle fracture nucleated at 50 µm thick iron nitride layer. The inner fracture surface of the tensile tested specimens was predominantly ductile presenting characteristic microcavities.

Magnesium/PTFE/FPM decoy flares, also named conventional flares, were designed in order to protect combat aircraft from the threat caused by infrared-guided missiles. Adverse storage or transport conditions may cause reactions that deteriorates chemical properties of the conventional flares, causing the aging and compromising its performance. The aim of this article was to characterize the influence of accelerated aging on conventional flares. The study was performed with the latest lot of conventional flares from Brazilian Air Force, subjected to 50 days exposure in a climatic chamber at 76 °C and 62% RH. Upon completion of the accelerated aging process, samples of aged conventional flares were compared with unaged material. Qualitative determination of chemical species present was carried out using the techniques FT-IR and SEM/EDS. Magnesium hydroxide, the main product of aging process and primary aging indicator on conventional flares performance, was determined using thermogravimetric analysis and the amount was correlated with results of the experimental techniques Density Determination, Calorimetry and Vacuum Stability Test. Formation of additional magnesium hydroxide mass, that increased 100% during the aging process, caused the passivation of magnesium, compromising the combustion process and making the composition less energy efficient, as verified in the results of the calorimetric tests.

Epoxy resins are an important class of thermostable polymers, widely used in structural applications or as adhesives. However, the low fracture resistance is their main weakness in many applications. Due to this fact, this study aims to modify a polymer matrix based on a novolac epoxy resin with an organo siloxane (AMS). The final properties of cured epoxys resins are affected by the curing process and the coatings modified in this study with AMS and cured with acid catalyst presented greater resistance to thermal decomposition compared to that cured with Aradur, demonstrating a higher content of crosslinking in the siloxane polyether and the novolak epoxy resin chains. This epoxy matrix modified was used to prepare coatings whose films applied to 1020 steel surfaces presented a resistance of 1010 Ohm-cm-2. This resistance value is one order of magnitude greater than that of epoxy resins films modified by siloxanes in published studies, which demonstrates a potential economy in terms of maintenance costs of metal structures and machines used in power plants (UTE). To obtain the developed inks in pilot plant scale, it was used an aromatic polyamine as curing agent, characterizing the product obtained as an epoxy bi-component paint for commercial use.

Solid rocket motors (SRM) are extensively employed in satellite launchers, missiles and gas generators. The design takes into account propulsive parameters with dimensional, manufacture, thermal and structural constraints. Gas generators and booster SRM frequently employ multiperforation in propellant grain geometries for rapid combustion. A computational tool for tracking the propagation of tridimensional interfaces and shapes is necessary for this task. In this sense, the objective of this paper is to present results using the developed computational tool (named RSIM) to simulate the burning surface regression during the combustion process of a solid propellant. This tool handles complex grain geometry for versatility, including multiple separate surfaces. The SRM internal ballistics simulation is based on 3D propagation, using the level set method approach. Geometrical and thermodynamic data are used as input for the computation, while simulation results of chamber pressure versus time are presented for multiperforated grains.

© 2017 by Begell House, Inc.Most of the coatings available on the market do not meet the protection requirements of high temperatures and oxidation of metallic surfaces exposed to chemically aggressive environments at high temperatures. Thus, the development of an inorganic base coating (potassium silicate) was proposed in the form of an aqueous solution for application in hybrid rocket motor metallic components. This coating distinguishes itself from others by supporting extreme operating conditions of operation without degrading or losing its original characteristics, thus forming a glassy film which anchors in/on the surface of the substrate in which it is applied, i.e., becoming a superficial layer. The investigation of the applicability of a high-temperature coating was studied in adverse conditions, as in the case of a hybrid rocket motor; different components of the engine have received the coating application. Once coated, the components were assembled as a hybrid engine and subjected to firing tests. The results were very promising, since the coating could reduce the erosion in the throat of the nozzle by 50%, improving the hybrid rocket motor operation time at temperatures around 2.000 Celsius.

In the solid propellant manufacturing process, one of the most important steps is the casting that consists in pouring the propellant in its more fluid state in a mold and then leaving it to cure or solidify. This step is very important because, if done wrong, could yield a propellant grain that contain lots of discontinuities such as voids and cracks and these could lead to a motor explosion. In a previous casting method, the propellant was subjected to stress of compression, but for candy propellants, that have a crystalline characteristics, this stress due to compression increase the chances of a crack in the grain. Thus, is necessary to change the casting process and the new process developed is described in this article.

© ASCE.Multiple blast tests were conducted on RC slabs at the Science and Technology Aerospace Department in Brazil. This paper presents the description of the experimental test set-up, instrumentation and results from a sub-set of the tests conducted on four 60 MPa concrete slabs with reinforcement ratios of 0.25% in two-way. In addition, one of the four slabs was retrofitted with 50 mm thick foam to determine if the foam has the capacity to reduce the blast response of the slab. The slabs were simply supported on two sides and the explosive was detonated at 2 m stand-off distance. The explosive charge was non-confined C4 plastic explosive cylinder. The equivalent TNT mass of the explosive ranges by 2.6-2.76 kg. Accelerometers, displacement and pressure gages were used to measure blast wave parameters and global response of the slabs. A high-speed digital camera in conjunction with a rugged notebook was used to capture images. Both qualitative and quantitative results are included. The foam on slab 3 varied the pattern of pressure recorded by the sensors and induced higher displacement, acceleration and linear momentum.

A [211]-oriented niobium single crystal was deformed by equal channel angular pressing (ECAP) at room temperature using the route Bc to a total strain of 9.2. A sharp cube texture develops after ECAP processing. The deformed samples were annealed in vacuum from 400ºC (673 K) to 900ºC (1173 K) for 1 h to evaluate their microstructural stability. Scanning electron microscopy (SEM) was used to image the microstructures of as-deformed and annealed specimens. Electron backscatter diffraction (EBSD) was employed to determine the respective microtextures before and after annealing. Coarsening of the microstructure occurs at a maximum rate at 550ºC (823 K) due to discontinuous recrystallization. Normal grain growth replaces discontinuous recrystallization as the main coarsening mechanism above 700ºC (973 K).

© 2017 Elsevier B.V.Strain partitioning and texture evolution of AISI 201 austenitic stainless steel were investigated upon cold rolling up to a true strain of ε = 0.92. ε-martensite formation is the main work hardening mechanism at low strains (ε = 0.11). With increasing strain, the volume fraction of α’-martensite increases with a sigmoidal-like behavior. Remaining untransformed austenite is intensely fragmented by mechanical microtwins. The in-grain misorientation increases for all phases up ε = 0.51 and then levels off for further strain. Strain partitions evenly between austenite and α’-martensite during cold rolling. X-ray texture measurements revealed that austenite develops Goss, Brass and S texture components up to the largest investigated strain. The presence of Brass component at the highest deformation seems to be assisted by mechanical twinning. The texture components of α’-martensite belong to the α- and γ- fibers. Texture evolution of ε-martensite was followed by electron backscatter diffraction data and results show that texture evolves up to ε = 0.51 and remains nearly unchanged at larger strains, similarly as observed for austenite and α’-martensite.

© 2017 Elsevier B.V.Oxide-dispersion strengthened materials are important candidates for several high-temperature structural applications in advanced nuclear power plants. Most of the desirable mechanical properties presented by these materials are due to the dispersion of stable nanoparticles in the matrix. Samples of ODS-Eurofer steel were annealed for 4320 h (6 months) at 800 °C. The material was characterized using atom probe tomography in both conditions (prior and after heat treatment). The particles number density, size distribution, and chemical compositions were determined. No significant changes were observed between the two conditions indicating a high thermal stability of the Y-rich nanoparticles at 800 °C.

© 2017, ASM International.Reduced-activation ferritic-martensitic (RAFM) steels are potential candidates for structural applications in future nuclear fusion power plants. A Ta-containing Fe-based commercial thermodynamic database was employed to calculate the phase volume fractions and their chemical compositions in Eurofer-97 RAFM steel. Results of the calculations were compared to those obtained from transmission electron microscopy, atom probe tomography and dilatometric experiments performed on short-term annealed samples. Despite minor discrepancies between experimental and calculation data, our findings suggest that the employed database is effective for calculating the phase equilibrium fields for Ta-containing steels.

© 2017 Elsevier Inc.Image features are widely used for object identification in many situations, including interpretation of data containing natural scenes captured by unmanned aerial vehicles. This paper presents a parallel framework to extract additive features (such as color features and histogram of oriented gradients) using the processing power of GPUs and multicore CPUs to accelerate the algorithms with the OpenCL language. The resulting features are available in device memory and then can be fed into classifiers such as SVM, logistic regression and boosting methods for object recognition. It is possible to extract multiple features with better performance. The GPU accelerated image integral algorithm speeds up computations up to 35x when compared to the single-thread CPU implementation in a test bed hardware. The proposed framework allows real-time extraction of a very large number of image features from full-HD images (better than 30 fps) and makes them available for access in coalesced order by GPU classification algorithms.

© 2017, Springer-Verlag London.Since the introduction of robots in the automotive industry for pick and place tasks, new technologies have been developed in order to adapt robots to different manufacturing processes. Among them, the use of robots as machine tools is a technological trend that demands further investigation. Industrial robots with 6 DOF (degrees of freedom) in a serial kinematic chain have larger workspace and more flexibility, when compared with CNC machines. However, robots’ stiffness is lower than that of CNC machines. Consequently, vibration problems are expected, which can have a direct impact on the quality of the machined workpieces. This work proposes a method to evaluate and customize the use of a COTS (commercial off-the-shelf) robot equipped with a spindle for machining processes. It aims at improving the machining processes based on the measurement of the workpiece waviness and explores the fact that the accuracy and rigidity of industrial robots with serial kinematic chains behave in an anisotropic way, according to the robot pose and the cutting force direction. The method is composed of a set of five experiments and is applied to the evaluation of a robot machining aluminium workpieces. The results allow the identification of the relevant factors that affect the surface quality of the workpiece and recommend the best robot configuration for meeting the waviness requirements of the workpiece. Even though the application case describes the machining of aluminium workpiece, the proposed method is generic enough to be applied to different workpiece geometries and materials.

© 2017, The Brazilian Society of Mechanical Sciences and Engineering.Outdoor optical mark recognition is an extremely useful tool for recognition of large industrial equipment and application of computer vision-based systems for tracking and positioning. However, current algorithms rely on thresholding and corner detection to identify checkerboard-like patterns, which is not appropriate for non-uniform lighting conditions. This paper presents a robust methodology to identify optical markers in outdoor environments. A GPU-based region filling algorithm automatically detects all contiguous color regions without computing seed points. Post-processing steps extract high-level information from these regions. Analysis of identified contiguous color region allows simultaneous identification of all checkerboard and targets (concentric regions) in the scene. Analysis of variance demonstrates that the proposed methodology is robust to lighting, environment, perspective, and occlusion. Tests indicate that precision and recall for checkerboard and target identification in outdoor conditions are expected to be above 97%. The parallel algorithm implementation using OpenCL yields better results and is two times faster than previous region filling algorithms, taking about 0.6 s to process a full-HD picture using modern hardware.

© 2017 IEEE.This work presents the development of a hybrid arm prosthesis controlled by EEG signals. A microcontroller in the prosthesis is responsible to process the signals sent by a headset that reads the electrical activity of the brain. Also presents the mechanical development of the prosthesis, respecting the ergonomic and anthropometric criteria. From this development, the work serves as a basis for improving the quality of life of the people and presents a low cost of production compared to the average price of hybrid prosthesis.

© World Scientific Publishing Co.This paper presents the integrated product development tool Design for Autonomy for reengineering of complex products. The objective is to assure that the product can be designed, produced and operated in Brazil for a defined period of time at a minimum risk of being dependent on export bans or unavailability of components. This tool is a new member of the Design for X family, which aims at integrating the requirements from the autonomy area into the conceptual phase of the product development process. Development guidelines derived from the procedures of the generic Design for X development framework are presented that lead to a balance between functionality and operability. The Design for Autonomy tool contains four steps: (1) Analysis of the product in order to identify critical elements; (2) Preparation of nationalization; (3) Reverse engineering of the original product in order to obtain technological know-how; and (4) Forward engineering for a national product, stimulating improvements and added value. The implementation can be evaluated by qualitative and quantitative performance criteria comparing the national product with the baseline configuration of the original product. The Design for Autonomy tool is being successfully applied and verified on a pilot project in the Brazilian space sector.

© 2017 Association for Computing Machinery.Air Hockey is a sport practiced in a table with low friction. Two players competing against each other holding paddles that are used to hit a puck with the objective of getting scores every time the puck enters the opponent's goal. This paper covers the development of low-cost vision based air hockey system capable of playing a match of Air Hockey against a human player. The system is composed by a robot, a camera and an Arduino MEGA board. The efficiency of the robot is presented in the final experiment, which justifies the possibility of using the system as a training environment for professional players.

© 2017, Journal of Aerospace Technology and Management. All rights reserved.This paper presents an analysis of the scenario of small satellites and its correspondent launch vehicles. The miniaturization of electronics, together with reliability and performance increase as well as reduction of cost, have allowed the use of commercials-off-the-shelf in the space industry, fostering the Smallsat use. An analysis of the launched Smallsats during the last 20 years is accomplished and the main factors for the Smallsat (r)evolution, outlined. Based on historic data, future scenarios for different mass categories of Smallsats are presented. An analysis of current and future launch vehicles reveals that we are currently in a phase of transition, where old launch vehicles get retired and new ones enter the market. However, the satellite launch vehicle business has been established to carry payloads of thousands of kilos into low Earth orbit and has not adjusted itself to the market of Smallsats. As a result, there is only 1 launch vehicle for dedicated Smallsat launches commercially available, but it carries a high price tag. Several small lowcost launch vehicles under development are identified and the challenges to overcome, discussed. Since these small launch vehicles have similar complexity as huge launch vehicles, high development costs are intrinsic, leading to a high specific price (USD/kg payload).

© 2017 IAAIn this work, a study about the influence of the Sun on optimal two-impulse Earth-to-Moon trajectories for interior transfers with moderate time of flight is presented considering the three-body and the four-body models. The optimization criterion is the total characteristic velocity which represents the fuel consumption of an infinite thrust propulsion system. The optimization problem has been formulated using the classic planar circular restricted three-body problem (PCR3BP) and the planar bi-circular restricted four-body problem (PBR4BP), and, it consists of transferring a spacecraft from a circular low Earth orbit (LEO) to a circular low Moon orbit (LMO) with minimum fuel consumption. The Sequential Gradient Restoration Algorithm (SGRA) is applied to determine the optimal solutions. Numerical results are presented for several final altitudes of a clockwise or a counterclockwise circular low Moon orbit considering a specified altitude of a counterclockwise circular low Earth orbit. Two types of analysis are performed: in the first one, the initial position of the Sun is taken as a parameter and the major parameters describing the optimal trajectories are obtained by solving an optimization problem of one degree of freedom. In the second analysis, an optimization problem with two degrees of freedom is considered and the initial position of the Sun is taken as an additional unknown.

© 2017 IEEE.Due to low-cost and simplicity, differential drive mobile robot are very popular in academic and hobby environments. However, in some applications, such as robot soccer, these robots need to move quickly and aggressively, thus requiring the use of techniques from control systems theory, where an accurate mathematical model is paramount. On the other hand, given budget limitations, the components used for academic robotics competitions are often acquired from hobby-grade manufacturers, which usually provide incomplete specifications. In this paper, we introduce a procedure to experimentally measure the parameters involved in the dynamical model of a differential drive robot. The procedure is intentionally based on a low-cost setup, which uses equipments found in academic laboratories. Moreover, we show experiments results that validate the mathematical model obtained through the experimental procedure.

© 2017 IAAThe primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions different from zero for both attitude and elastic vibrations. Additionally, the control efforts for the three cases are compared. Results indicate that the attitude control is able to excite the solar panels' vibration modes and vice-versa. The piezoelectric vibration control shows significant performance improvement when compared to contributions of the attitude control to the vibration damping.

© 2017, Brazilian Society for Automatics--SBA.This paper treats the problem of position formation flight control of a group of three multirotor aerial vehicles under obstacle and collision avoidance constraints. In order to solve the problem, a distributed architecture with model predictive controllers for each vehicle includes a set of convex constraints on the vehicles’s position to prevent collisions with other vehicles and obstacles. The resulting distributed scheme controls the formation based on a virtual structure approach where the computers of the architecture exchange position data through diagrams in Simulink. The performance of the method is assessed through simulations considering that the vehicles are subject to disturbance forces and the results show the effectiveness and the ability of the control architecture to handle the obstacle and collision avoidance constraints.

© 2017 IAAIn space the manipulators working space is characterized by the microgravity environment. In this environment the spacecraft floats and its rotational/translational motion may be excited by any internal and external disturbances. The complete system, i.e., the spacecraft and the associated robotic manipulator, floats and is sensitive to any reaction force and torque related to the manipulator's operation. In this sense the effort done by the robot may result in torque about the system center of mass and also in forces changing its translational motion. This paper analyzes the impact of the robot manipulator dynamics on the attitude motion and the associated control effort to keep the attitude stable during the manipulator's operation. The dynamics analysis is performed in the close proximity phase of rendezvous docking/berthing operation. In such scenario the linear system equations for the translation and attitude relative motions are appropriate. The computer simulations are implemented for the relative translational and rotational motion. The equations of motion have been simulated through computer by using the MatLab software. The LQR and the PID control laws are used for linear and nonlinear control, respectively, aiming to keep the attitude stable while the robot is in and out of service. The gravity-gradient and the residual magnetic torque are considered as external disturbances. The control efforts are analyzed for the manipulator in and out of service. The control laws allow the system stabilization and good performance when the manipulator is in service.

© 2017 Elsevier LtdThe objective of this paper is to describe a new method for modeling aeroelastic system in time domain based on a modification of the Laguerre Polynomials to represent complex quantities. These polynomials are used to approximate the unsteady aerodynamics forces which are defined in the frequency domain using the Doublet Lattice Method (DLM). In this approach, the size of the matrices representing the aeroelastic system remains the same as the matrices representing the structural dynamics behavior. It is an important point since classical state space aeroelastic models include lag states increasing the size of the matrices used to represent the system. The applicability of the method is demonstrated by numerical simulation performed on the benchmark wing structure. The approach offers promise mainly for complex systems such as real aircraft.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents the algorithms for autonomous modes for a tether airship. Switching between flight modes, the airship can perform different flight tasks as such as autonomous hovering, hovering aligned to the home point, take-of and waypoint navigation. The switch-ing scheme between flight modes and the designed control loop are also included in this paper. The control loop is divided into two loops, the inner and the outer control loop. The stability augmentation system has been included as inner control loop to stabilize longitudinal and lateral dynamics and for cancellation of external disturbance. The outer control loop generates control inputs depending of flight mode and given references. For each flight task it is performed outdoor flight experiment with a small size tethered airship, and on the results, the tethered airship performance is shown.

© 2017, American Institute of Aeronautics and Astronautics. All rights reserved.A preliminary investigation of applying system identification methodology for a tethered airship vehicle is presented. A series of flight test campaigns was carried out with the tethered airship providing flight data suitable for parameter estimation. A nonlinear model is selected and a set of state and observation equations is described; biases, and initial condition parameters are estimated by data compatibility check and the flight path reconstruction is presented. The Output Error Method is selected to estimate the aerodynamic parameters and the initial conditions taking into account the influence of tether disturbances. This paper also presents the experiment setup, flight conditions, and brings preliminary system identification results regarding the tethered airship dynamics. Finally, it brings a discussion regarding main considerations on approaching system identification methods for a tethered airship.

Copyright © (2017) by International Astronautical Federation. All rights reserved.This paper presents the mathematical modeling of a 5 degree-of-freedom robot manipulator-like spacecraft and the computer simulations of the attitude motion in a low earth orbit. The main goal of the study is the study the effects of the space vehicle center of mass changes in the rotational motion. The center of mass moves due to changes in the mass configuration of the robot arm during the robot manipulator orbital operations. In such analysis it is not reasonable to assume the inertia matrix diagonal since the motion of the robot links causes the appearing of products inertia. In the same way it is recommended to consider the non linear equations of motion. Another feature of the work is that the rotational motion control aims to suppress the reactions forces and torques in the manipulator joints. The reaction forces affect the translational and the attitude motion as well. The results show that the control of the translational and attitude motions keeps the dynamics as planned, showing and suppressing the center of mass motion when the manipulator is operating.

Copyright © 2017 by ASME.This work presents a study on double-diffusive free convection in a porous square cavity using the thermal equilibrium model. Transport equations are discretized using the control-volume method, and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effect of ks/kf on average Nusselt and Sherwood values was investigated. Results show that increasing ks/kf affects Nuw and Shw boosting mass transfer at the expense of reducing overall heat transport across the enclosure.

© 2017 Taylor & Francis.Composite cavities formed by a clear space, a layer of porous material, and a solid plate can be engineered for controlling the overall heat transfer across the enclosure. Using different layer dimensions, as well as distinct porous and solid materials, the value of the cavity Nusselt number can be modified with regard to traditional Nu∝Ran behavior, which is encountered either in completely empty cavities or in cavities fully fitted with porous materials. Motivated by such novel application, this work presents a study about turbulent natural convection in a composite concentric annulus. The annulus is assumed to be two-dimensional and positioned horizontally, being isothermally heated at the inner cylinder and cooled from the outer surface. Laminar flow is considered in addition to the turbulent regime, which is handled via the standard k–ε model. The wall treatment applied is the High Reynolds approach. The Two-Energy Equation Model (2EEM) is utilized in the porous section. The transport equations are discretized using the control-volume method. The system of algebraic equations is relaxed via the Semi Implicit Pressure-Linked Equations (SIMPLE) algorithm. A new numerical methodology is applied to resolve all three layers in a single computational domain by establishing two temperature sets, defined according to the location inside the composite structure. Nusselt number behavior shows that for Rayleigh number up to 104 there is no significant variation between the laminar and turbulence models, although the differences increase when the flow gets more intense and/or the porous material becomes more permeable. When comparing the effects of Rayleigh number, Darcy number, porosity, and thermal conductivity ratio between the solid and the fluid on Nu, the results indicate that the solid-phase properties have a greater influence in enhancing the overall heat transferred through the cavity.

© 2017 Elsevier LtdNumerical simulations for laminar double-diffusive free convection in a porous square cavity using the Thermal Non-Equilibrium Model were presented. Vertical surfaces were maintained at constant temperature and concentration whereas horizontal walls were kept insulated. The cavity was filled with a rigid and isotropic porous matrix, which was saturated with an incompressible fluid. Transport equations were discretized by means of the control volume method leading to a coupled algebraic equation set that was solved via the SIMPLE method. Results pointed that both Nuw and Shw are dependent on porosity ϕ and on the thermal conductivity ratio ks/kf. Nuw decreases as ϕ decreases or ks/kf increases due to enhancement of conduction transport across the cavity. On the other hand, Shw and wall mass flux increases as porosity decreases or ks/kf increases. Such dependence of Shw arises from the intensification of recirculating motion in the cavity as ϕ is reduced or ks/kf is of a higher value, which affects heat exchange between phases and, consequently, wall mass fluxes. Finally, this study shows that both average Nusselt and Sherwood numbers diverge from published correlation when ks/kf > 1 for same Da value.

© 2017 Taylor & Francis.This work presents numerical investigations for turbulent flow and heat transfer in a backward-facing step with and without porous inserts. Two classes of the model were employed, namely linear and nonlinear turbulence closures. The entire set of transport equations was discretized by means of the control volume method and the system of algebraic equations obtained was relaxed using the SIMPLE (Semi Implicit Pressure-Linked Equations) method. Results were first validated against the experimental data and the simulations follow experimental values and trends. Computations further indicated that when using the porous insert, the size, shape, and length of the recirculating region were drastically reduced in addition to being pushed toward the channel exit, leading eventually to a complete bubble suppression for thicker inserts. A more permeable medium gave better results in quickly suppressing the circulatory motions. By including porous inserts in the channel, turbulence generated due to the shear inside the recirculating region was damped, whereas high levels of k were concentrated within the permeable structure. Large variations for the skin friction factor along the bottom wall were also smoothed out by placing inserts, spanning from a typical distribution for an unobstructed back-step flow to a standard parallel channel flow distribution as the inserts got ticker. On the other hand, at the upper wall, flow pushed toward the top surface gave rise to a sudden increase of the skin friction factor, which was later stabilized downstream the flow. Heat transfer analysis followed showing damping for Nu at the bottom wall as the thickness of the porous substrate was increased. Overall, the thickness of the insert played a dominant role in changing the final flow and heat transfer characteristics rather than the porosity or permeability of the porous material. Finally, this work indicated that the sudden increase of Nu around the reattachment point, known to be undesirable in many practical situations for causing additional thermomechanical loads on the surface, may by avoided by the use of a porous obstacle past the back-step.

© 2017 Begell House Inc.. All rights reserved.Channels with contractions and obstructions are configurations that can model a number of flows in living bodies and in pipes, in general, and their investigation is of importance in medicine and engineering. Blood obstruction in arteries and clogged flows in ducts due to fouling are examples were such study might be useful. This article deals with flow in a channel having a sinusoidal contraction, which is covered from inside with a layer of porous material. Heat Transfer and turbulence flow are investigated by four distinct models, namely linear high Reynolds, linear low Reynolds, non-linear high Reynolds and non-linear low Reynolds. The equations of motion and mass continuity are discretized by means of the control volume method. The system of algebraic equations is relaxed via the SIMPLE method and the SIP Strong implicit procedure. Results for the size of the recirculating bubble past the contraction indicated that its value seems to be a function of the model used as well as the thickness and properties of the porous material covering the internal walls. The structure of the turbulent thermal field along the channel is also shown to be a function of the turbulence model used as well as the porosity, and permeability of the porous layer.

© 2017 Begell House Inc.. All rights reserved.This paper deals with simulation of turbulent forced convection heat transfer in a channel containing solid and porous baffles. Governing equations are written in their conservative form. Turbulence is simulated using four distinct models, namely linear high Reynolds, linear low Reynolds, non-linear high Reynolds and non-linear low Reynolds. Transport equations of motion and mass continuity are discretized by means of the control volume method. The system of algebraic equations is relaxed via the strong implicit procedure. Results for the recirculating flows past the baffles are shown to be a strong function of the models used as well as the characteristics of the porous material, namely the porosity, and permeability of the porous plates.

© 2017, Begell House Inc. All Rights Reserved.This work presents a study on double-diffusive free convection in a porous square cavity saturated with a Newtonian fluid under laminar flow simulated with the thermal equilibrium model. Transport equations are discretized using the control-volume method and the system of algebraic equations is relaxed via the SIMPLE algorithm. The effect of Ram and porosity on average Nusselt and Sherwood values were investigate. Results show that as Ram increases, both Nusselt and Sherwood numbers increase, indicating enhancement of heat and mass transfer across the cavity. Further, when the Lewis number is increased keeping the same thermal properties, reduction of mass diffusivity further enhances flow recirculation for aiding flows (N=1) within the cavity, which leads to further increase in Nuw and Shw. When varying the buoyancy ratio N from aiding (N>0) to opposing flow (N<0), simulations indicates that when both drives are of equal strength, minimum values for Nusselt and Sherwood occur for N =-1, regardless of Ram. For larger values of |N|, aiding drives will promote fluid rotation in the clockwise direction, for the gradients of T and C here applied, whereas for opposing flows, the fluid rotates in the counter-clockwise direction for opposed conditions at the lateral walls. Results show that porosity also affects Nuw and Shw.

© 2017 Elsevier LtdThis work presents numerical results for two-dimensional combustion of an air/methane mixture in inert porous media using a macroscopic turbulence model. Conservation equations for mass, momentum, energy and chemical species are obtained based on volume-and-time double averaging concept. Distinct energy balances are considered for the porous burner and the gas mixture. The numerical technique employed for discretizing the governing equations was the control volume method with a boundary-fitted non-orthogonal coordinate system. The SIMPLE algorithm was used to handle the pressure–velocity coupling. Effects of inlet mass flow rate, excess air, porosity and thermal conductivity ratio, on both the preheating section and combustion region, were investigated. Increasing the mass flow increases peak gas temperatures and pushes the flame front from the preheating zone towards the burner exit. Stoichiometric mixture provokes undesirable combustion in the preheating zone while lean mixtures lower temperatures and pushes flame front forward. Low porosity in the preheating zone promotes more conduction of heat in that region whereas low ϕ values in the combustion zone raises gas and solid temperatures everywhere in that zone.

© Springer Science+Business Media Singapore 2017.The search for alloys with improved high-temperature specific strength and creep-resistance properties for aerospace applications has led in the last decades to sustained research activities to develop new alloys and/or improve existing ones. Titanium and its alloys are excellent for applications in structural components submitted to high temperatures owing to their high strength to weight ratio, good corrosion resistance and metallurgical stability. However, the high affinity to oxygen is one of the main factors that limit their application as a structural material at high temperatures. Materials with adequate behavior at high temperatures and in aggressive environments have become a scientific requirement for technological and economic reasons. The goal of this work is the roughness and creep studies of the Ti–6Al–4V alloy after treatment by the nitrogen Plasma Immersion Ion Implantation (PIII-N) process. The aim of this process is the improvement of the superficial mechanical properties of the Ti–6Al–4V alloy. The selected alloy after ionic implantation process by plasma immersion was submitted to creep tests in 600 °C at 250 and 319 MPa. The techniques used in this work were Auger spectroscopy, Atomic Force microscopy (AFM), X ray, Raman spectroscopy and creep testing. The results show the significant increase of material resistance, it can be used as protection of oxidation in high temperatures applications.

Copyright © 2017 Eduards Skukis et al.Applicability of the vibration correlation technique (VCT) for nondestructive evaluation of the axial buckling load is considered. Thin-walled cylindrical shells with and without circular cutouts have been produced by adhesive overlap bonding from a sheet of aluminium alloy. Both mid-surface and bond-line imperfections of initial shell geometry have been characterized by a laser scanner. Vibration response of shells under axial compression has been monitored to experimentally determine the variation of the first eigenfrequency as a function of applied load. It is demonstrated that VCT provides reliable estimate of buckling load when structure has been loaded up to at least 60% of the critical load. This applies to uncut structures where global failure mode is governing collapse of the structure. By contrast, a local buckling in the vicinity of a cutout could not be predicted by VCT means. Nevertheless, it has been demonstrated that certain reinforcement around cutout may enable the global failure mode and corresponding reliability of VCT estimation.

© 2017 World Scientific Publishing Company.The present paper describes a numerical modeling approach to predict impact resistance and residual Shear Strength After Impact (SSAI) of fiber reinforced polymer composites subjected to bird strike loading. An improved damage mechanics based on material model, previously developed by the authors, is combined with an equation of state to simulate the progressive failure in composite aerostructures subjected to bird strike loading. A series of bird strike impacts on flat panels fabricated from low cost woven glass composite materials are used to validate the material model for practical composite component applications. A numerical study on the residual SSAI of a typical composite shear web is also presented. The panels are modelled with shell elements only. The proposed material model formulation accounts for the strain rate enhancement to strength and shear nonlinearities observed in composite materials. A hydrodynamic model for the bird, based on 90% water and 10% air, is derived to represent the behavior of the bird for all impact scenarios considered. The bird is heterogeneous in nature. However, a uniform material behavior is assumed with a geometry based on a 2:1 length to diameter ratio with a cylindrical body and spherical end caps using Lagrangian mesh. Appropriate contact definitions are used between the bird and the composite panel. The simulations results are compared to experimental results and conclusions drawn.

© 2017 Universidade Federal de Sao Carlos. All rights reserved.Aiming to reduce aircraft weight, aeronautic industry seeks alternative materials and processes used to join its different structural parts. An option to traditional methods are high performance adhesive joints, which reduce weight, number of parts and component final cost, also resulting in higher strength structures. Although, the lack of experimental data to provide a detailed structural characterization of these joining techniques had limited their commercial application. The proposal of this work is to investigate the Mode I interlaminar fracture toughness under quasi-static loading using DCB specimens of carbon composite joints made by co-bonding and secondary bonding techniques, the latter giving more reliable results. For a better understanding on the failure in the systems, DSC and microscopy techniques were applied, from which three stages of delamination process during testing were observed: 1st Stage) Cohesive failure represented by an unstable crack propagation from a high energy level; 2nd Stage) transition from cohesive to adhesive and final intralaminar failure mode with lower energy levels than Stage 1; and 3rd Stage) completely stable propagation at low energy levels (delamination migrates from intralaminar to interlaminar, entirely in the substrate).

© 2017 The Authors.Non-destructive methods to estimate the actual buckling load in particularly for imperfection sensitive thin-walled structures, are of severe interest among many fields. Particular techniques for validation of structural limit state and numerical model predictions for large scale structures are getting momentum. The vibration correlation technique (VCT) allows to correlate the ultimate load our instability point with rapid decrement of self-frequency response. Nevertheless this technique is still under development for thin-walled shells and plates. The current research discusses an experimental verification of extended approach, using vibration correlation technique, for the prediction of actual buckling loads on unstiffened cylindrical shells loaded in axial compression. Validation study include two laminated composite cylinders which were manufactured and repeatedly loaded up to instability point. In order to characterize a correlation with the applied load, several initial natural frequencies and mode shapes were measured during tests by 3D laser scanner. Results demonstrate that proposed vibration correlation technique allows one to predict the experimental buckling load with high reliability, without actually reaching the instability point. Additional experimental tests and numerical models are currently under development to further validate the proposed approach to extended composite and metallic structures.

© 2017 Elsevier LtdThis work investigates the effects of temperature in the shape memory alloy hybrid composites (SMAHC) cylindrical stiffened panels’ aeroelastic stability. The SMAHC is modelled using a micromechanical formulation embedding carbon fiber, SMA wire and resin to the same lamina and taking into account the martensite/austenite phases of transformation in the material response. Virtual work principle formulation is implemented with classical laminate plate theory (CLPT) panel formulation and one-dimensional Euler-Bernoulli beam theory formulation for the stiffener. Numerical results are obtained by using an energy based semi-analytical method applying hierarchical polynomials to approximate the membrane and out of plane displacement fields. Different geometric configurations, laminate stacking sequences, boundary conditions and radii of curvature are investigated. The study shows that the variation of temperature induce stiffening due to changes in the martensite/austenite fractions of the SMA, increasing the critical flutter dynamic pressure. Therefore, it can be achieved certain control in the flutter critical boundary by increasing the temperature of the shape memory alloy (SMA) wire. The effects due to the SMA wire stiffening with the temperature are more pronounced for cross-ply stiffened cylindrical panels with unitary aspect ratio and for angle-ply panels with aspect ratio higher than one.

© 2017 World Scientific Publishing Company.The present paper describes a numerical modeling approach to predict impact resistance and residual Shear Strength After Impact (SSAI) of fiber reinforced polymer composites subjected to bird strike loading. An improved damage mechanics based on material model, previously developed by the authors, is combined with an equation of state to simulate the progressive failure in composite aerostructures subjected to bird strike loading. A series of bird strike impacts on flat panels fabricated from low cost woven glass composite materials are used to validate the material model for practical composite component applications. A numerical study on the residual SSAI of a typical composite shear web is also presented. The panels are modelled with shell elements only. The proposed material model formulation accounts for the strain rate enhancement to strength and shear nonlinearities observed in composite materials. A hydrodynamic model for the bird, based on 90% water and 10% air, is derived to represent the behavior of the bird for all impact scenarios considered. The bird is heterogeneous in nature. However, a uniform material behavior is assumed with a geometry based on a 2:1 length to diameter ratio with a cylindrical body and spherical end caps using Lagrangian mesh. Appropriate contact definitions are used between the bird and the composite panel. The simulations results are compared to experimental results and conclusions drawn.

© 2017 Wiley Publishing Ltd.Composite structures usually undergo to temperature variations in aircraft during landing/taking off and when cruising at high altitude. Under these conditions and in combination with curved structures, they can generate severe thermal stresses that induce delaminations. Considering the importance of studying delamination in these conditions, this research imposed an anti-symmetrical laminate to cyclic temperature variations of 130 °C and −70 °C with the objective of inducing varied curvatures and, consequently, crack growth. Different from standardized test procedures, this test setup elastically deformed coupons without external forces and forward experimentally and numerically evaluated the strain energy release rate (SERR) during crack propagation. This procedure enabled the assessment of delamination rate (da/dN) as a function of maximum SERR. The experimental results were compared with numerical results obtained by ABAQUS Finite Element code. Despite large scatter in experimental results, a reasonable correlation between experimental and numerical results was obtained in terms of crack growth rate (da/dN) as a function of the maximum SERR.

© 2016, © The Author(s) 2016.The increasing use of composite in the aircraft industry has raised the interest for a better understanding of the failure process in these materials, which can be also influenced by the manufacturing process of the laminate. Some materials used in vacuum assisted resin transfer molding process have been studied in the open literature but very few data have been published for resin transfer molding-6 epoxy based laminates, in particular studies showing the influence of the temperature on the interlaminar fracture behavior of this type of laminates. The aim of this article is to investigate the interlaminar fracture behavior of resin transfer molding-6 based carbon composite laminates manufactured by vacuum assisted resin transfer molding subjected to Modes I and II at 25℃ and 80℃. The results show the influence of the temperature on the interlaminar fracture toughness of composites and provide a database to design composite aerostructures subjected to temperatures commonly experienced in civil aviation. The fracture aspects of the tested laminates were also investigated and directly related to the trend in results found for the fracture toughness values.

© 2017, ASM International.In a 3D preform, the out-of-plane reinforcement is effective for decelerating or suppressing the delamination process as the non-crimp fabric does not connect the neighboring laminae effectively. Hence, the interlaminar strength of the stitched laminae is supposed to behave in the same way as a regular unidirectional composite. In order to determine whether or not the stitched yarns contribute to the interlaminar fracture toughness, this study determinated the delamination resistance of a quasi-isotropic laminate. The analysis was based on interlaminar fracture toughness (GIc) and propagation energy curve in tests conducted in mode I opening with double cantilever beam specimen geometry. The results of fracture toughness as well as strain energy for propagation were compared to their fracture surface. A decrease in the propagation energy prevailed in the surface because the stitch yarn replaced the carbon fiber/epoxy interface, which has better chemical affinities, i.e., covalent bonds.

© 2016 Elsevier LtdThe substitution of conventional mechanical fasteners by adhesive joints has been advocated by the aircraft and aerospace industries due to the weight saving potential. Flaws such as debonding of the adhesive layer between the skin and the stiffener may greatly affect the structural behavior of composite panels. Within this context, this work presents a semi-analytical approach for the numerical investigation on the effects of skin-stiffener bonding flaw size on the vibration and linear buckling behavior of T-stiffened composite panels. Skin and stiffener have been modeled using an assembly of curved and flat panel components, with each domain approximated using a set of hierarchical polynomial functions. A penalty-based approach has been used to assemble the various domains and to model the debonded region between the stiffener flange base and the plate. This approach ensures full compatibility in terms of displacements and rotations between the stiffener's base top face and the panel bottom face allowing to model different skin/stiffener debonding lengths. The results obtained using the proposed semi-analytical models have been compared and verified against numerical predictions based on finite element analyses.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A numerical method to compute the acoustic field scattered by finite perforated elastic plates is extended to include structural damping typical of viscoelastic materials. We employ a boundary element method to solve the Helmholtz equation subject to boundary conditions related to the vibration of the plate. In order to enable our investigation of the effect of damping, we rewrite the equations considering the terms responsible for the structural damping. Results show that by adding damping to the problem formulation, the flexural waves in the plate are attenuated and thus can modify the far-field sound scattered by turbulence near an edge of the plate. Parametric studies also show that structural damping tends to reduce scattered sound at structural ressonances. The combined effects of elasticity, porosity and damping may be more appropriate to represent the behavior of realistic materials.

© 2017 Universidade Federal de Sao Carlos. All rights reserved.Aiming to reduce aircraft weight, aeronautic industry seeks alternative materials and processes used to join its different structural parts. An option to traditional methods are high performance adhesive joints, which reduce weight, number of parts and component final cost, also resulting in higher strength structures. Although, the lack of experimental data to provide a detailed structural characterization of these joining techniques had limited their commercial application. The proposal of this work is to investigate the Mode I interlaminar fracture toughness under quasi-static loading using DCB specimens of carbon composite joints made by co-bonding and secondary bonding techniques, the latter giving more reliable results. For a better understanding on the failure in the systems, DSC and microscopy techniques were applied, from which three stages of delamination process during testing were observed: 1st Stage) Cohesive failure represented by an unstable crack propagation from a high energy level; 2nd Stage) transition from cohesive to adhesive and final intralaminar failure mode with lower energy levels than Stage 1; and 3rd Stage) completely stable propagation at low energy levels (delamination migrates from intralaminar to interlaminar, entirely in the substrate).

© 2016 Elsevier LtdThis work focuses on the determination of failure envelopes of unidirectional fiber reinforced composites. A two scale analysis is considered and the mathematical theory of asymptotic homogenization is applied to model the problem. For a given stress applied to the macro level, it is possible to assess stresses at the micro level domain. Three regions of the micro level are considered: matrix, fiber and the interface between them, and each region is ruled by its own failure criterion. A methodology to determine failure of composites using the homogenization is proposed. In the methodology, the strengths of the composite are used to determine the strengths of the constituents: a curve fitting adjustment is applied to calculate the strengths of the matrix and an analytical procedure is used to obtain the strengths of the fiber and interface. Then, the strengths of the constituents are used to evaluate failure criteria at the micro level, and the numerical failure envelopes are built. The advantage of the proposed methodology is that it is capable of calculating numerical failure envelopes with good approximation to experimental envelopes and also to the Puck & Schürmann criterion, requiring only five unidirectional strengths of the composite as inputs.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Structured mesh computational fluid dynamic solvers are inherently faster than unstructured solvers, which is particularly advantageous for aerodynamic design optimization, where hundreds of flow solutions are required. However, generating body-fitted multiblock meshes for complex geometries is challenging and is a time consuming task. The overset mesh technique greatly reduces the manual effort required to generate meshes over complex geometries by overlapping a series of simpler meshes. However, generating the necessary connectivity information between meshes in a robust and computationally efficient manner remains a challenge. We address this challenge by developing an efficient parallel overset grid assembly technique based on implicit hole cutting that is fully automatic. The method is fully parallel and scales to hundreds of processors. Several optimizations of the Common Research Model wing-body-tail configuration are performed using the meshes generated by our technique. We compare the best drag reduction obtained from multiblock and overset meshes using two different artificial dissipation schemes. The smooth, highly orthogonal overset meshes produce better results than the multiblock meshes, by up to 3 drag counts. An application to rotorcraft design is also presented. The demonstrated meshing flexibility and accurate transonic solutions make the overset mesh technique ideally suited for aerodynamic shape optimization.

© 2017 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Mesh generation for high-fidelity CFD simulation and aerodynamic shape optimization is a timeconsuming task. We can model complex geometries accurately using overset meshes where multiple high-quality structured meshes corresponding to different aircraft components overlap to model the full aircraft configuration. Nevertheless, from the geometry manipulation standpoint, most methods operate on the entire geometry rather than on each component, which diminishes the advantages of overset meshes. To address this issue, we introduce a geometry module that operates on individual components and automatically computes their intersections to automate the overset mesh updates during optimization. This method is also differentiated to compute derivatives with respect to component-based design variables and is integrated within an optimization framework. Using these automatically updated meshes and the corresponding derivatives, we perform aerodynamic shape optimization including the wing-body intersection for the DLR-F6 geometry and achieve a reduction of 15 drag counts (5%) compared to the baseline design.

© 2017 Emerald Publishing Limited.Purpose - Multidisciplinary design frameworks elaborated for aeronautical applications require considerable computational power that grows enormously with the utilization of higher fidelity tools to model aeronautical disciplines like aerodynamics, loads, flight dynamics, performance, structural analysis and others. Surrogate models are a good alternative to address properly and elegantly this issue. With regard to this issue, the purpose of this paper is the design and application of an artificial neural network to predict aerodynamic coefficients of transport airplanes. The neural network must be fed with calculations from computational fluid dynamic codes. The artificial neural network system that was then developed can predict lift and drag coefficients for wing-fuselage configurations with high accuracy. The input parameters for the neural network are the wing planform, airfoil geometry and flight condition. An aerodynamic database consisting of approximately 100,000 cases calculated with a full-potential code with computation of viscous effects was used for the neural network training, which is carried out with the back-propagation algorithm, the scaled gradient algorithm and the Nguyen-Wridow weight initialization. Networks with different numbers of neurons were evaluated to minimize the regression error. The neural network featuring the lowest regression error is able to reduce the computation time of the aerodynamic coefficients 4,000 times when compared with the computing time required by the full potential code. Regarding the drag coefficient, the average error of the neural network is of five drag counts only. The computation of the gradients of the neural network outputs in a scalable manner is possible by an adaptation of back-propagation algorithm. This enabled its use in an adjoint method, elaborated by the authors and used for an airplane optimization task. The results from that optimization were compared with similar tasks performed by calling the full potential code in another optimization application. The resulting geometry obtained with the aerodynamic coefficient predicted by the neural network is practically the same of that designed directly by the call of the full potential code. Design/methodology/approach - The aerodynamic database required for the neural network training was generated with a full-potential multiblock-structured code. The training process used the back-propagation algorithm, the scaled-conjugate gradient algorithm and the Nguyen-Wridow weight initialization. Networks with different numbers of neurons were evaluated to minimize the regression error. Findings - A suitable and efficient methodology to model aerodynamic coefficients based on artificial neural networks was obtained. This work also suggests appropriate sizes of artificial neural networks for this specific application. We demonstrated that these metamodels for airplane optimization tasks can be used without loss of fidelity and with great accuracy, as their local minima might be relatively close to the minima of the original design space defined by the call of computational fluid dynamics codes. Research limitations/implications - The present work demonstrated the ability of a metamodel with artificial neural networks to capture the physics of transonic and subsonic flow over a wing-fuselage combination. The formulation that was used was the full potential equation. However, the present methodology can be extended to model more complex formulations such as the Euler and Navier-Stokes ones. Practical implications - Optimum networks reduced the computation time for aerodynamic coefficient calculations by 4,000 times when compared with the full-potential code. The average absolute errors obtained were of 0.004 and 0.0005 for lift and drag coefficient prediction, respectively. Airplane configurations can be evaluated more quickly. Social implications - If multidisciplinary optimization tasks for airplane design become more efficient, this means that more efficient airplanes (for instance less polluting airplanes) can be designed. This leads to a more sustainable aviation. Originality/value - This research started in 2005 with a master thesis. It was steadily improved with more efficient artificial neural networks able to handle more complex airplane geometries. There is a single work using similar techniques found in a conference paper published in 2007. However, that paper focused on the application, i.e. providing very few details of the methodology to model aerodynamic coefficients.

Copyright © 2017 SAE International.Pressures on vehicle manufacturers to reduce emissions have resulted in an increased interest to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO2 output per vehicle. The use of bio-gas fuels in internal combustion engines has become a real alternative to traditional liquid fuels derived from petroleum. To extract the maximum benefits from these emergent fuels through optimized engine design and calibration, a deep understanding of the behavior is necessary. The combustion process of a single cylinder research engine with optical access, four stroke PFI-SI, was experimentally investigated. High spatial resolution cycle resolved digital imaging, in the visible and UV spectral range was used to characterize the flame front propagation. A post-processing routine was developed to evaluate flame areas and various local and global morphology characteristics to have a detail understanding of the flame behavior in an engine combustion chamber. The engine was fueled with Methane as baseline fuel and compared with an equivalent syngas mixture (blend of hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen). It was operated at 900 rev/min, under partial load condition. For the equivalent syngas blend the results suggest an increase in the combustion duration. The flame speed propagation was higher to methane, with a difference of 1.9 m/s. Also both fuels present a preferential flame center movement in direction of the intake valves, and the average curvature was negative. The cyclic variations in the combustion process were around 1% for syngas and 0.5% for methane, indicating a stable combustion process.

Copyright © 2017 SAE International.In the last few decades a significant effort has been stablished in the automotive industry as well as in academic community towards increasing the renewable fuels applications in internal combustion engines, such as alcohol and gas derived sources. Meanwhile, turbo charging direct-injection spark-ignition engines have become fundamental features to achieve downsizing purposes, increasing power generation efficiency and attending high restrictive emissions regulations that have being taking place recently. For this study, experimental tests were carried out in a single cylinder research engine considering direct injection (DI) and port fuel injection (PFI) operations with anhydrous ethanol. The aim of this paper is to present a review and conduct further investigation about methodologies applied for imaging post processing considering chemiluminescence technique applied in an optical research engine. Crank angle resolved OH∗ and CH∗ flame chemiluminescence images were acquired in cycle based temporal evolution for consecutive engine cycles. Distinct intensification setups were adjusted based on an intensifier usage to evaluate its influence on radicals' evolution and on flame front determination. Forthwith image acquisition, a post processing routine was conducted in order to determine flame radius, and speed through distinct image segmentation and algorithms techniques. Finally, former researches are referenced and compared to current results in order to better correlate the study conducted. The contribution of current research work within the state-of-the-art in optical engines researches remains in the adoption of different cameras set up and post-processing methods for the characterization of flame behavior in an optical spark ignition (SI) engine fueled with anhydrous ethanol.

©2017 Sociedade Brasileira de Química.In this work the presence of soot in laminar diffusion of diesel and blends diesel/biodiese flames were investigated in the following proportions: 5, 10, 20 and 50% of biodiesel. The techniqu of laser-induced incandescence (LII) was used for the soot detection. Horizontal mapping wer performed at two heights (80 and 260 mm above the burner) to investigate the distribution of soo along the studied flames. The experiment was performed with a pulsed Nd:YAG laser with th wavelength of 1064 nm. The results have shown that the soot emission decreases as the amoun of biodiesel increases in the blends.

© 2017, The Brazilian Society of Mechanical Sciences and Engineering.There has been an ever increasing demand for research into alternative and environmentally friendly fuels since the oil crisis in the 1970s. Nowadays, with increasing energy demands and tightening environmental constraints, the need for research into these alternative fuels is mandatory. The use of microturbines for distributed power generation is already a reality and presents some environmental and operational advantages. However, this kind of thermal machine is designed for operation using hydrocarbons. The difference of the physical–chemical properties between hydrocarbons and alcohols impacts strongly the characteristics of the spray and hence the performance of combustion. In this context, an investigation about the behavior of the atomization process for an atomizer designed for ethanol operation and feasibility is mandatory. This study is divided into two parts: the characterization of the atomizer and spray in a laboratory environment and the assessment for pollutant emissions and combustion efficiency determination. The designed atomizer was machined and the main atomizer and spray characteristics data were acquired and then assembled on a gas generator operating with hydrous ethanol.

© 2017 IMEKOThe combustion process of a single cylinder research engine with optical access, four stroke with port fuel injection (PFI) and spark ignition (SI), was experimentally investigated. It was fueled with methane as baseline fuel and compared with a mixture of Syngas (blend of hydrogen, methane, carbon monoxide, carbon dioxide and nitrogen). The in-cylinder pressure and the related parameters were analyzed as indicators of the combustion behavior. Digital imaging measurements with OH filter were performed to evaluate the flame propagation. Therefore, UV chemiluminescence is applied to follow the OH radicals formation in the flame front from spark ignition to the cylinder walls through an optical access in the combustion chamber. The engine was operated at 900 rev/min, with the throttle being held in the partial-open position to get 7 mbar inlet pressure. The spark timing was set at 7° crank angle (CA) before top dead center (BTDC), and a stoichiometric air/fuel ratio was considered. For syngas blend the results suggest an increase in the combustion duration, with a difference in peak pressures and center of combustion location of 1.81ºCA and 1.99ºCA respectively, compared with methane. The cyclic variations in the combustion process were around 3% for both fuels, indicating a stable combustion process.

© 2017 by the authors. Licensee MDPI, Basel, Switzerland.Lean fueling of spark ignited (SI) engines is a valid method for increasing efficiency and reducing nitric oxide (NOx) emissions. Gasoline direct injection (GDI) allows better fuel economy with respect to the port-fuel injection configuration, through greater flexibility to load changes, reduced tendency to abnormal combustion, and reduction of pumping and heat losses. During homogenous charge operation with lean mixtures, flame development is prolonged and incomplete combustion can even occur, causing a decrease in stability and engine efficiency. On the other hand, charge stratification results in fuel impingement on the combustion chamber walls and high particle emissions. Therefore, lean operation requires a fundamentally new understanding of in-cylinder processes for developing the next generation of direct-injection (DI) SI engines. In this paper, combustion was investigated in an optically accessible DISI single cylinder research engine fueled with gasoline. Stoichiometric and lean operations were studied in detail through a combined thermodynamic and optical approach. The engine was operated at a fixed rotational speed (1000 rpm), with a wide open throttle, and at the start of the injection during the intake stroke. The excess air ratio was raised from 1 to values close to the flammability limit, and spark timing was adopted according to the maximum brake torque setting for each case. Cycle resolved digital imaging and spectroscopy were applied; the optical data were correlated to in-cylinder pressure traces and exhaust gas emission measurements. Flame front propagation speed, flame morphology parameters, and centroid motion were evaluated through image processing. Chemical kinetics were characterized based on spectroscopy data. Lean burn operation demonstrated increased flame distortion and center movement from the location of the spark plug compared to the stoichiometric case; engine stability decreased as the lean flammability limit was approached.

© 2017 Elsevier LtdThe objective of this work is the mechanical characterization of materials produced by 3D printing based on fused filament fabrication (FFF, analogous to FDM®). The materials chosen are a polylactic acid (PLA) and a PLA reinforced with short carbon fibers in a weight fraction of 15% (PLA+CF). In view of the FFF nature, which produces specimens layer by layer and following predefined orientations, the main assumption considered is that the materials behave like laminates formed by orthotropic layers. If the 3D printing is made in the 1−2 plane, where 1 is the deposition direction and 2 is a direction perpendicular to 1, the mechanical properties obtained are the tensile moduli E1 and E2, the Poisson ratios ν12 and ν21, the shear modulus G12 and related strength properties. For this purpose, only unidirectional or specially oriented specimens are used. After tests up to material failure, scanning electron microscopy (SEM) is employed to observe fracture surfaces. It was noticed that, in the microstructure of the PLA+CF, the short carbon fibers stay highly oriented with the material deposition direction in the FFF specimens. This fact, and the also observed length of the fibers, explains differences in material properties encountered among the performed experiments.

© 2016 Elsevier LtdThis work focuses on the determination of failure envelopes of unidirectional fiber reinforced composites. A two scale analysis is considered and the mathematical theory of asymptotic homogenization is applied to model the problem. For a given stress applied to the macro level, it is possible to assess stresses at the micro level domain. Three regions of the micro level are considered: matrix, fiber and the interface between them, and each region is ruled by its own failure criterion. A methodology to determine failure of composites using the homogenization is proposed. In the methodology, the strengths of the composite are used to determine the strengths of the constituents: a curve fitting adjustment is applied to calculate the strengths of the matrix and an analytical procedure is used to obtain the strengths of the fiber and interface. Then, the strengths of the constituents are used to evaluate failure criteria at the micro level, and the numerical failure envelopes are built. The advantage of the proposed methodology is that it is capable of calculating numerical failure envelopes with good approximation to experimental envelopes and also to the Puck & Schürmann criterion, requiring only five unidirectional strengths of the composite as inputs.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.To asses the state of art and best practices in computational aeroelasticity (CAe) for static and dynamic phenomena is the key objective of the AIAA Aeroelastic Prediction Workshop series (AePW). The workshop is an excellent opportunity for academia and in- dustrial exchange through transparent discussions and collaborative learning on relevant aeroelastic topics. During the second edition of the event (AePW-2), held in January 2016, the efforts were concentrate on unsteady aerodynamics and utter prediction for the Benchmark Supercritical Wing (BSCW). Three transonic cases were proposed: steady and unsteady forced aerodynamics under attached flow; utter on set prediction for weak shock attached flow condition; and a third more challenging case of transonic detached flow with steady, forced pitch oscillations and utter on set prediction. The workshop discussions pointed to some relevant issues in CAe while analyzing the participants results: turbulence modeling, temporal convergence, mesh convergence and fluid-structural coupling effects. Each analysis team explored some of those aspects, but not a consensus was established as best practices for numerical setup. As Computational Fluid Dynamics (CFD) become massive parallel processed, the number of grid points applied to relatively simple geometry as the BSCW becomes millions quickly. Parametric numerical studies of unsteady aero- dynamics and aeroelasticity including viscous effects in such meshes become too expensive for most researchers or industries and the physics of fluid flow and dynamics analysis can go to second plan faced the computational efforts to run and post-process such amount of generated data, risking to loose the engineering feeling of the analysis. This paper proposes the inclusion of a verification study case for the upcoming AePW editions in a lightweight 2D configuration, where some of the questions raised during the AePW-2 could be parametrically clarified regarding the CFD turbulence modeling, fluid-structure coupling and time and grid convergence. The aim is to explore the flow physics and see how the numerical setup behaves, identifying the limitations of the CFD methodologies applied, before jump into a fully 3D buffet aeroelastic configuration. The first results of this initiative are presented here as a CFD characterization of the BSCW airfoil section in steady, unsteady, unsteady forced and utter cases for the transonic regime of interest. All the data, models details and meshes are made available for the research community.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We study a modified backwards-facing step flow, with the addition of two different splitter plates; one is a baseline, impermeable plate and the second a perforated one. An experimental investigation is carried out for a turbulent reattaching shear layer downstream of the two plates. The proposed setup is a model configuration to study how the plate characteristics affect the separated shear layer, and also how turbulent kinetic energies and large-scale coherent structures are modified. Hot-wire measurements show that the perforated plate changes the mean profile, mostly by reducing the intensity of backflow close to the bottom wall. Disturbance amplitudes are significantly reduced up to 5 step-heights downstream the trailing edge of the plate, more specifically in the recirculation region. A loudspeaker is then used to introduce phase-locked, low-amplitude perturbations up- stream of the splitter plates, and phase averaged measurements allow a quantitative study of large-scale structures in the reattaching shear-layer. The evolution of such coherent structures are evaluated in light of linear stability theory, comparing the eigenfunction of the Kelvin-Helmholtz mode to the experimental results. We observe a close match of linear- stability eigenfunctions with phase-averaged amplitudes for all tested Strouhal numbers. The perforated plate is found to reduce the amplitude of the Kelvin-Helmholtz coherent structures in comparison to the baseline, impermeable plate, a behavior consistent with the predicted amplification trends from linear stability.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents a detailed overview of hybrid RANS/LES methods as implemented within the open-source SU2 software package. We focus on the extensions of the existing RANS framework based upon the Spalart-Allmaras turbulence model that are necessary to apply the Delayed Detached-Eddy Simulation (DDES) technique. Particular emphasis is placed upon the low dissipation and low Mach number convective schemes required to maintain accuracy within the context of performing DDES in a second-order, finite volume, unstructured flow solver. We conclude with a suite of test cases across different regimes to demonstrate our DDES capability on both academic and industrial-grade applications.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A new criterion, based on the chordwise movement of the aerodynamic center, is proposed to estimate the transonic buffeting onset of transport aircraft. Wind tunnel results obtained on four different aircraft are used to evaluate three existing traditional criteria that are based on CL x α and CM x α curves. The wind tunnel tests were performed at a chord Reynolds number of 3 million and the results were extrapolated to flight Reynolds number using cryogenic wind tunnel data for two similar aircraft. The proposed criterion presents the best predictions when compared to flight test data.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A passive self-adaptive camber airfoil proposes to reduce fatigue and increase durability of lifting surfaces lifetime. The airfoil stability is investigated in an incompressible flow using a two-dimensional four degree of freedom model on pitch, plunge, slat and flap angles, in which the kinematic of slat and flap are coupled by a linear relationship. Concentrated cubic structural restoring forces as effect of nonlinearities are considered. The aeroelastic governing equations are written and integrated numerically using a fourth order Runge-Kutta scheme for the time domain evaluations. The identification and stability analysis of limit cycle oscillations are evaluated in the time domain by the Duhamel formulation and compared to the quasi-steady approximation and a method in the frequency domain using describing functions combined with the Sherman-Morrison formula. Investigations revealed that system parameters and initial conditions are crucial for the system dynamic stability that could lead to basin of attractions of periodic motions, heteroclinic orbits, jump phenomena and chaos.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper reports the current status of a joint Swedish-Brazilian research project aiming at exploring sub scale flight testing. A 13% scale fighter aircraft is used as a test bench for developing methods and procedures for data acquisition. This paper will present an Aerodynamic database as a partial result of the collaborative project.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Futuristic aircraft designs and novel aircraft such as High Altitude Long Endurance (HALE) involve a higher level of structural flexibility than in conventional aircraft. Even at present, the trends in the aviation industry are to increase wing length (to reduce induced drag) and maximize use of composites, which lead to increased structural flexibility. This necessitates a rethink of conventional (linear) aeroelastic analysis, since the increased flexibility results in coupling between the flight dynamic and aeroelastic dynamics, and consequently, limit-cycle oscillations of the structure. In this paper, a new three-dimensional low-order model for unsteady aerodynamics that accounts for large oscillation amplitudes and nonplanar wakes is developed. An experiment with a cantilevered flat plate at low Reynolds number is set up and used to validate the low-order model, as well as to study post-flutter limit-cycle oscillations. Results from the low-order model are promising, but show that aerodynamic nonlinearities such as flow separation and leading-edge vortex shedding must also be modeled in order to predict all possible limit-cycle oscillations of the aeroelastic system.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All rights reserved.A simple and self-contained methodology to assess the validity of the assumption of small deformations in linear structural-dynamic models was recently proposed. The advantages of the methodology lie in the fact that it does not depend on the availability of higher-fidelity, nonlinear models: it is rather based on the selection of two different structural nodes where the structural motion is to be one at a time completely constrained, typically, a node near the center of mass and another in the region of maximum structural displacements with respect to mean axes. If the two displacement vectors calculated in each case can be transformed between themselves with linear rigid-body modes of the structure, then it is still in the regime of small deformations. In the present paper, in order to demonstrate the value of this methodology, it is applied to the X-HALE aircraft in its four-, six- and eight-meter-span configurations, and the results obtained with the assumption of small deformations are compared with a higher-fidelity model that comprises large structural deformations.

© 2017 International Forum on Aeroelasticity and Structural Dynamics (IFASD). All Rights Reserved.Formulations for the flight dynamics of flexible aircraft have been commonly applied to aircraft free to fly in the three-dimensional space, having all six rigid-body degrees of freedom. For risk reduction in the future flight operations of the X-HALE testbed at ITA, however, wind-tunnel tests of the remotely-piloted, four-meter-span configuration of the aircraft were performed. In the wind tunnel, the rigid-body translations were completely constrained, but the same was not valid for the rigid-body rotations, which could be conveniently left free or not with a proper selection of the connection between the aircraft and the wind-tunnel mount. In the present paper, in order to computationally assess the response and stability characteristics of the aircraft in the wind tunnel, we derive equations of motion for a constrained flexible aircraft with up to three rigid-body rotational degrees of freedom, mounted on an also flexible wind-tunnel strut. The numerical model has its value confirmed by the wind-tunnel tests in the predicted and observed roll-control reversal for anti-symmetrical deflections of the all-moving tails, and absence of reversal for aileron deflections.

Copyright 2018, IADC/SPE Drilling Conference and Exhibition.An extension of Delayed Detached-Eddy Simulation (DDES) capabilities developed in SU2 to unsteady transonic buffet flow is present. An assessment of Spalart-Allmaras turbulence model variants with the 2D OAT15 airfoil reveals that the mixing layer compressibility correction plus the quadratic constitutive relation (SA-Comp-QCR) was the combination able to capture shock buffet accurately. Refined Roe scheme was also implemented, including adaptive dissipation function with Ducros shock sensor and Travin’s blending. The SU2 DDES implementation is tested in the Benchmark Supercritical Wing, analyzing the case 3 of the Second AIAA Aeroelastic Prediction Workshop. The results obtained are encouraging, showing good agreement for mean pressure coefficient and coherent fluid flow structures behind the shock.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Aircraft icing is a matter that still demands considerable research efforts because of its great impact on aircraft performance and safety. In most applications, the power source of Ice Protection Systems (IPS) is the engine, and thus fuel burn, engine thrust, and aircraft performance are affected by the compressed bleed air or shaft horsepower extracted. IPS pre-activation, intercycle, and residual ice shape and position in the leading edge are also important and do affect aircraft performance. This paper presents a proof of concept of a novel ice protection system based on Carbon Nanotubes (CNT) used as electrical heaters, installed in the leading edge of a two-dimensional horizontal tail model, and tested in an icing wind tunnel. The main advantages of the CNT heaters are their light weight, easiness to conform (very thin layer), and uniform electrical and thermal properties. The CNT based IPS model was tested in de-icing mode, except for a narrow zone along the leading edge highlight referred to as ‘parting strip’ that was operated in anti-icing mode. Based on the residual and intercycle ice accretions footprint obtained in the icing wind tunnel tests, the de-icing configuration tested was deemed successful. The associated aircraft performance degradation will be further investigated in on-going and future work by means of numerical analysis, wind-tunnel tests, flight tests with artificial ice shapes, and flight tests in natural icing conditions. In addition, future research will investigate the optimization of the de-icing system heating zones distribution (size and position) and de-icing sequence to potentially reduce the required power input or the residual and intercycle ice accretions.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A detailed investigation of the shock wave formation patterns over a NACA0012 airfoil in a mostly laminar, transonic regime is presented. Information regarding the position of the boundary layer transition was obtained using Temperature Sensitive Paint (TSP) for similar conditions previously studied using Pressure Sensitive Paint (PSP). In this paper, previous results regarding shockwave formation patterns are revisited and further analyzed with the additional input of TSP data. Results indicate a strong correlation between the position of the boundary layer transition and the shockwave onset, confirming the hypothesis proposed in the previous investigation. Thus, the process of shockwave formation and the role of boundary layer interaction in it is further clarified. Besides Pressure and Temperature Sensitive Paints, the traditional method of pressure taps was used to confirm PSP measurements and account for possible deviations.

© Emerald Publishing Limited.Purpose: The purpose of this paper is to present a mathematical model of one very flexible transport category airplane whose structural dynamics was modeled with the strain-based formulation. This model can be used for the analysis of couplings between the flight dynamics and structural dynamics. Design/methodology/approach: The model was developed with the use of Hamiltonian mechanics and strain-based formulation. Nonlinear flight dynamics, nonlinear structural dynamics and inertial couplings are considered. Findings: The mathematical model allows the analysis of effects of high structural deformations on airplane flight dynamics. Research limitations/implications: The mathematical model has more than 60 degrees of freedom. The computational burden is too high, if compared to the traditional rigid body flight dynamics simulations. Practical implications: The mathematical model presented in this work allows a detailed analysis of the couplings between flight dynamics and structural dynamics in very flexible airplanes. The better comprehension of these couplings will contribute to the development of flexible airplanes. Originality/value: This work presents the application of nonlinear flight dynamics-nonlinear structural dynamics-strain-based formulation (NFNS-s) methodology to model the flight dynamics of one very flexible transport category airplane. This paper addresses also the way as the analysis of results obtained in nonlinear simulations can be made. Comparisons of the NFNS-s and nonlinear flight dynamics-linear structural dynamics methodologies are presented in this work.

© 2017.The stakeholder analysis is applied in numerous disciplines and may be called differently in each. In the discipline of Strategic Planning, the stakeholder analysis is performed when analyzing organizational environments. In the discipline of Project Management, a stakeholder analysis is performed for the feasibility of managing the Stakeholder Management Plan. In the discipline of Systems Engineering, the stakeholder analysis is performed during requirements analysis. In organizations that develop complex products, these three disciplines are relevant and activities of stakeholder analysis are repeated when each discipline is applied. This creates duplication and therefore waste. As a result, this article proposes to develop a unique method of stakeholder analysis that can achieve the goals of different stakeholders analyzes performed when applying the disciplines mentioned above. In general, it was concluded that the proposed method and its application show that a single stakeholder analysis can be performed to meet the objectives of Systems Engineering, Project Management and Strategic Planning, without the need for replication of analysis when applying each of these disciplines.

Copyright © 2016 by Flavio Silvestre. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.In this paper, the control law design for flexible aircraft is discussed. First, the traditional procedure of decoupling rigid-body and aeroelastic dynamics with low-pass and notch filters is addressed, with focus on controller performance as well as the resulting stability margin issues. A procedure based on a unified formulation of the flexible aircraft dynamics for flight control law design is proposed. In this procedure, the aeroservoelastic dynamics is assessed in the loop, and the offline filtering process is avoided. The formulation is applied to the virtual aircraft generic narrow-body airliner, with improvements in closed-loop performance and stability margins.

© 2016 The AuthorsWe present estimates of spectral resolution power for under-resolved turbulent Euler flows obtained with high-order discontinuous Galerkin (DG) methods. The ‘1% rule’ based on linear dispersion–diffusion analysis introduced by Moura et al. (2015) [10] is here adapted for 3D energy spectra and validated through the inviscid Taylor–Green vortex problem. The 1% rule estimates the wavenumber beyond which numerical diffusion induces an artificial dissipation range on measured energy spectra. As the original rule relies on standard upwinding, different Riemann solvers are tested. Very good agreement is found for solvers which treat the different physical waves in a consistent manner. Relatively good agreement is still found for simpler solvers. The latter however displayed spurious features attributed to the inconsistent treatment of different physical waves. It is argued that, in the limit of vanishing viscosity, such features might have a significant impact on robustness and solution quality. The estimates proposed are regarded as useful guidelines for no-model DG-based simulations of free turbulence at very high Reynolds numbers.

We present a study on the suitability of under-resolved DNS (uDNS)-also called implicit LES (iLES)-approaches based on spectral element methods (SEM), with emphasis on high-order continuous and discontinuous Galerkin (i.e. CG and DG) schemes. Broadly speaking, these are model-free eddy-resolving approaches to turbulence which solve the governing equations in unfiltered form and rely on numerical stabilization techniques for small-scale regularization. Model problems in 1D, 2D and 3D are used in the assessment of solution quality and numerical stability. A rationale for the excellent potential of these methods for transitional and turbulent flows is offered on the basis of linear dispersion-diffusion analysis.

© 2017, Springer International Publishing AG.We suggest a new interpretation of implicit large eddy simulation (iLES) approaches based on discontinuous Galerkin (DG) methods by analogy with the LES-PLB framework (Pope, Fluid mechanics and the environment: dynamical approaches. Springer, Berlin, 2001), where PLB stands for ‘projection onto local basis functions’. Within this framework, the DG discretization of the unfiltered compressible Navier-Stokes equations can be recognized as a Galerkin solution of a PLB-based (and hence filtered) version of the equations with extra terms originating from DG’s implicit subgrid-scale modelling. It is shown that for under-resolved simulations of isotropic turbulence at very high Reynolds numbers, energy dissipation is primarily determined by the property-jump term of the Riemann flux employed. Additionally, in order to assess how this dissipation is distributed in Fourier space, we compare energy spectra obtained from inviscid simulations of the Taylor-Green vortex with different Riemann solvers and polynomial orders. An explanation is proposed for the spectral ‘energy bump’ observed when the Lax-Friedrichs flux is employed.

© 2017 IAAIn this work, a study about the influence of the Sun on optimal two-impulse Earth-to-Moon trajectories for interior transfers with moderate time of flight is presented considering the three-body and the four-body models. The optimization criterion is the total characteristic velocity which represents the fuel consumption of an infinite thrust propulsion system. The optimization problem has been formulated using the classic planar circular restricted three-body problem (PCR3BP) and the planar bi-circular restricted four-body problem (PBR4BP), and, it consists of transferring a spacecraft from a circular low Earth orbit (LEO) to a circular low Moon orbit (LMO) with minimum fuel consumption. The Sequential Gradient Restoration Algorithm (SGRA) is applied to determine the optimal solutions. Numerical results are presented for several final altitudes of a clockwise or a counterclockwise circular low Moon orbit considering a specified altitude of a counterclockwise circular low Earth orbit. Two types of analysis are performed: in the first one, the initial position of the Sun is taken as a parameter and the major parameters describing the optimal trajectories are obtained by solving an optimization problem of one degree of freedom. In the second analysis, an optimization problem with two degrees of freedom is considered and the initial position of the Sun is taken as an additional unknown.

© 2017 IAAThe primary purpose of this paper is to provide insight into control-structure interaction for satellites comprising flexible appendages and internal moving components. The physical model considered herein aiming to attend such purpose is a rigid-flexible satellite consisting of a rigid platform containing two rotating flexible solar panels. The solar panels rotation is assumed to be in a sun-synchronous configuration mode. The panels contain surface-bonded piezoelectric patches that can be used either as sensors for the elastic displacements or as actuators to counteract the vibration motion. It is assumed that in the normal mode operation the satellite platform points towards the Earth while the solar arrays rotate so as to follow the Sun. The vehicle moves in a low Earth polar orbit. The technique used to obtain the mathematical model combines the Lagrangian formulation with the Finite Elements Method used to describe the dynamics of the solar panel. The gravity-gradient torque as well as the torque due to the interaction of the Earth magnetic field and the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control and piezoelectric actuators to control the flexible motion of the solar arrays. Computer simulations are performed using the MATLAB® software package. The following on-orbit satellite operating configurations are object of analysis: i) Satellite pointing towards the Earth (Earth acquisition maneuver) by considering the initial conditions in the elastic displacement equal to zero, aiming the assessment of the flexible modes excitation by the referred maneuver; ii) the satellite pointing towards the Earth with the assumption of an initial condition different from zero for the flexible motion such that the attitude alterations are checked against the elastic motion disturbance; and iii) attitude acquisition accomplished by taking into account initial conditions different from zero for both attitude and elastic vibrations. Additionally, the control efforts for the three cases are compared. Results indicate that the attitude control is able to excite the solar panels' vibration modes and vice-versa. The piezoelectric vibration control shows significant performance improvement when compared to contributions of the attitude control to the vibration damping.

Copyright © (2017) by International Astronautical Federation. All rights reserved.The main purpose of this paper is to implement a technique of passive elastic vibration control for a low Earth orbit satellite comprising two symmetric flexible solar arrays. While the solar arrays flexible vibration is passively controlled by using piezoelectric materials, the spacecraft attitude control is implemented by using the proportional integral derivative control technique. The idea is to compare the control effort when implementing the passive control with the control effort when using the piezoelectric for the same spacecraft. The solar panels are assumed to be in a sun synchronous rotation mode so its solar cells can continuously be illuminated by the Sun. The panels contain surface-bonded piezoelectric patches to implement the passive control of the solar panel elastic vibration. The gravitygradient torque as well as the torque due to the interaction of the Earth magnetic field with the satellite internal residual magnetic moment is included as environmental perturbations. The actuators are three reaction wheels for attitude control. Computer simulations are performed using the MATLAB® software package. For analysis, one considers a station-keeping correction maneuver performed by a thruster actuator. Resulting elastic vibrations are investigated while considering the cases in which i) only the attitude control subsystem is considered; and ii) passive vibration control is adopted through piezoelectric shunt damping. As expected, the use of the considered passive control strategy is able to mitigate elastic vibrations effectively, and also help in reducing control efforts performed by the attitude reaction wheel controllers.

© 2017, Brazilian Association of Computational Mechanics. All rights reserved.A broad class of engineering systems can be satisfactory modeled under the assumptions of small deformations and linear material properties. However, many mechanical systems used in modern applications, like structural elements typical of aerospace and petroleum industries, have been characterized by increased slenderness and high static and dynamic loads. In such situations, it becomes indispensable to consider the nonlinear geometric effects and/or material nonlinear behavior. At the same time, in many cases involving dynamic loads, there comes the need for attenuation of vibration levels. In this context, this paper describes the development and validation of numerical models of viscoelastic slender beam-like structures undergoing large displacements. The numerical approach is based on the combination of the nonlinear Cosserat beam theory and a viscoelastic model based on Fractional Derivatives. Such combination enables to derive nonlinear equations of motion that, upon finite element discretization, can be used for predicting the dynamic behavior of the structure in the time domain, accounting for geometric nonlinearity and viscoelastic damping. The modeling methodology is illustrated and validated by numerical simulations, the results of which are compared to others available in the literature.

In 2011, the German Aerospace Center and the Brazilian Space Agency started to cooperate in the field of liquid rocket engines. They agreed to jointly develop the L75 engine which is using Liquid Oxygen and Ethanol as propellants. Within the last year, the first hot-firing test campaign with pre-development models of the thrust chamber assembly successfully took place. Furthermore, important milestones in the development of the turbomachinery of the L75 engine, as run-in of test facilities and spin testing, have been achieved. This paper details the progress of the project, concentrating on the description of the joint activities of the consortium.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc.Paraffin stands out as a promising solid combustible grain for the classical hybrid propulsion rocket motor. However, its low mechanical properties increase the risk of grain cracking and rupturing. The purpose of this experimental study is to address the existing drawbacks by formulating paraffin particles within a hydroxylterminated polybutadiene binder. Paraffin particles are prepared by crystallization in emulsion, which allows the control of particle size distribution, based on the droplets breakup and coalescence equilibrium. The paraffin particles are suspended in hydroxyl-terminated polybutadiene, and the maximum paraffin loading (62% volume fraction) is attained with the use of bimodal systems. A combustible grain (paraffin particles/hydroxyl-terminated polybutadiene) is cast with the maximum loading and submitted to thermal and mechanical tests. The results are compared to hydroxyl-terminated polybutadiene and paraffin wax counterparts, and they meet the criteria of performance and safety required for this kind of combustible. The crystallization in paraffin-in-water emulsion proves to be an efficient method to prepare spherical paraffin particles with controllable sizes, which may be used to get bimodal systems that improve the packing of paraffin particles. The resulting combustible grain exhibits adequate thermal and mechanical properties (ultimate elongation of 206%) for a hybrid propulsion rocket motor.

© 2017 Emerald Publishing Limited.Purpose - The centrifugal instability mechanism of boundary layers over concave surfaces is responsible for the development of quasi-periodic, counter-rotating vortices aligned in a streamwise direction known as Görtler vortices. By distorting the boundary layer structure in both the spanwise and the wall-normal directions, Görtler vortices may modify heat transfer rates. The purpose of this study is to conduct spatial numerical simulation experiments based on a vorticity-velocity formulation of the incompressible Navier-Stokes system of equations to quantify the role of the transition in the heat transfer process. Design/methodology/approach - Experiments are conducted using an in-house, parallel, messagepassing code. Compact finite difference approximations and a spectral method are used to approximate spatial derivatives. A fourth-order Runge-Kutta method is adopted for time integration. The Poisson equation is solved using a geometric multigrid method. Findings - Results show that the numerical method can capture the physics of transitional flows over concave geometries. They also show that the heat transfer rates in the late stages of the transition may be greater than those for either laminar or turbulent ones. Originality/value - The numerical method can be considered as a robust alternative to investigate heat transfer properties in transitional boundary layer flows over concave surfaces.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Parabolized Stability Equations (PSE) have been shown to model wavepackets and, consequently, the near field of turbulent jets with reasonable accuracy. Because of these capabilities, PSE is a promising reduced-order model to derive control laws that could be employed to reduce the sound generation of a jet. The purpose of this work is to apply PSE to obtain time-domain transfer functions that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet. The results of this model were compared to results obtained from a database of a well-validated large-eddy simulation of a supersonic jet. Based on the unsteady pressure data at a input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and an empirical method based on the LES data. The prediction scheme employed is a single-input-single-output (SISO), linear model. The unsteady pressure predicted by PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer. For this region, the prediction capabilities of PSE are comparable to those of empirical transfer functions. The agreement is good even for output points taken in the acoustic field, showing that it is possible to estimate the time-domain behaviour of Mach-wave radiation using transfer functions. This indicates that PSE could not only be used to predict the sound generation, but also to open up new potentialities to attenuate noise by means of closed-loop control of the flow. The exploration of the regions where the method displayed good agreement, presented in this work, can guide the positioning of sensors and actuators for experimental implementation of closed-loop control in a jet.

© 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A distinct wavy leading edge performance for finite wings can be expected in comparison to the infinite wing, due to the differences in geometry and flow conditions. An infinite span wing, unlike a partial span model, has a unique local Reynolds number, sweep angle, thickness and camber. In addition, it is not subjected to the wing tip phenomenon which changes the pressure coefficient along span, and, as consequence, the adverse pressure gradients. These differences on the flow over finite and infinite span geometries cause differences in tubercle performance, which have motivated some works, in order to investigate the influence of flow three-dimensionality on wavy leading edge performance. However, there are lack of works that evaluate the effects of the wing’s three-dimensional on flow topology of the wavy leading edge and their consequences in performance. The aim of this study is to investigate the effects of the wing’s three-dimensional flow on wavy leading edge phenomena at low Reynolds number. Experimental investigations were carried-out modifying geometric parameters of the wing planform (taper ratio and sweep) in order to understand the effects of these parameters on wavy leading edge phenomena. The tests are conducted for pairs of models with and without tubercles. A pair of two-dimensional models (NACA 0020) and four pairs of finite-wing models with taper ratios of 0.5 and 1, and sweep angles of 0º and 30º were tested. The experimental investigation was based on evaluation of force measurements (lift and drag) and flow visualizations (oil and mini-tufts). Additionally, the Reynolds number effects were also investigated by evaluating the wavy leading edge characteristics at Reynolds number 80,000 and 200,000.

© 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The interest in studying the aerodynamic performance of airfoils at low Reynolds number has been increasing recently. There are many applications for airfoil design at low Reynolds number as design point. These applications include sailplanes, propellers, unmanned aerial vehicles (UAVs) and micro air vehicles (MAVs). However, there are few works evaluating the thickness effect as a design parameter for airfoil performance at low Reynolds number regime as well as data from flow visualizations in order to clarify the aerodynamic phenomena regarding thickness variation. In this sense, the aim of this work is to investigate the thickness effect on flow characteristics and performance of symmetrical airfoils at low Reynolds number regime by experimental investigation correlating force measurements with mini-tuft and oil flow visualization data. In an overall view, this work intends to contribute for investigations of desirable flow and geometric conditions of airfoils applied in UAV and MAV designs. Experimental tests were carried out at subsonic blower-type wind tunnel of open loop with closed section at ITA (Technological Institute of Aeronautics). A set of three symmetrical airfoils with different thickness (NACA 0012, NACA 0020 and NACA 0030) were tested at Reynolds number regime between 50,000 and 290,000. The results show distinct thickness effect for Reynolds number condition borders where at Re = 50,000 the thickest airfoil causes full flow separation with a great aerodynamic deterioration. In contrast, at Re = 290,000 the thickest airfoil achieves the highest maximum lift value.

© 2017 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The aim of this work is to investigate the wavy leading edge phenomena for the very thick airfoil NACA 0030 by experimental investigation correlating force measurements with mini-tuft and oil flow visualization data at low Reynolds number regime. Experimental tests were carried out at subsonic blower-type wind tunnel of open loop with closed section at ITA (Technological Institute of Aeronautics). A set of four very thick airfoils were tested composed by one smooth configuration and three wavy leading-edge configurations (A= 0.03c, λ = 0.40c; A= 0.03c, λ = 0.11c; A= 0.11c, λ = 0.40c). The wavy leading edge geometry variation and Reynolds number effects were evaluated at range of Reynolds number between 50,000 and 290,000. For the highest Reynolds number condition, the results show worse aerodynamic performance for wavy leading edge when compared to previous studies of thinner airfoils. However, at Reynolds number 120.000, the configuration with A= 0.03c and λ = 0.11c presents a unprecedented result on literature overcoming the baseline maximum lift coefficient in 19,4% and the stall angle in 44%. In addition, the flow visualization results indicate that the leading edge stall characteristics at airfoils lead the tubercle configurations for better aerodynamic performance.