© The Authors, published by EDP Sciences, 2016.Fractional damping is appearing in different contexts in any systems with memory and hysteresis. Such damping is defined by a fractional derivative term, in contrary to classical viscous damping which takes into account the first order derivative. In this work, we characterize the nonlinear dynamics of a non-ideal Duffing system, with fractional damping using nonlinear dynamical tools. The non-ideal excitation originates from a DC electric motor with limited power supply driving an unbalanced rotating mass. The response of the system is investigated with the voltage as a control parameter. Numerical simulations show the occurrence of regular and non-regular motions, which are investigated via bifurcation diagramoccurrence diagrams and phase plane portraits.

© The Authors, published by EDP Sciences, 2016.Piezoelectric energy harvesting from a vertical geometrically nonlinear cantilever beam with a tip mass subject to transverse harmonic base excitations is analyzed. One piezoelectric patch is placed on the slender beam to convert the tension and compression into electrical voltage. Applying the homotopy analysis method to the coupled electromechanical governing equations, we derive analytical solutions for the horizontal displacement of the tip mass and consequently the output voltage from the piezoelectric patch. Analytical approximation for the frequency response and phase of the geometrically forced nonlinear vibration system are also obtained. The research aims at a rigorous analytical perspective on a nonlinear problem which has previously been solely investigated by numerical and experimental methods.

This paper overviews recent developments on some problems related to elastic structures, such as portal frames, taking into account the full interactions of the vibrating systems, with an energy source of limited power supply (small motors, electro-mechanical shakers). We include a discussion on fractional (rational) damping and stiffness effects on the adopted modelling. This was a plenary lecture, delivered in the event titled: Mechanics of Slender Structures, organized in Northampton, England from 21-22, September 2015.

Copyright © 2016 by ASME.In this paper we consider the flight dynamics of fighter aircraft at high angles of attack with uncertain aerodynamic coefficients. Stochastic parametric uncertainty is dealt with by employing spectral decomposition of the random variables by means of the generalized polynomial chaos expansion. We propose an optimal linear feedback strategy for the automatic pilot system to recover the aircraft from stall and provide acceptable dynamic response. Optimality of the proposed control law is proved by solving the Hamilton-Jacobi-Bellman equation and asymptotically stability of the controlled nonlinear aircraft model is guaranteed in the Lyapunov sense. Numerical results are verified with Monte-Carlo simulations.

Copyright © 2016 by ASME.In literature, the classic parametrically excited pendulum is vastly studied. It consists of a pendulum vertically displaced with a harmonic motion in the support while it oscillates. The chaos in this mechanism may appear depending on the frequency and amplitude of excitation in superharmonic and subharmonic resonance. The double pendulum is also well analyzed in literature, but not under parametric excitation. Therefore, this is the novelty in the present paper. The present analysis considers a double pendulum under a harmonic excitation following the same idea performed previously for a single pendulum. The results are obtained based on methods, such as, phase portraits, Poincaré sections and bifurcation diagrams. The 0-1 tests analyze the presence of chaos while the parameters are varied. The dimensionless parameters take into account the excitation frequency and amplitude as mentioned for the classic parametric pendulum. In this case, we have the particular characteristic that the two pendulums have the same length, the same mass and the same friction coefficient in the joints. The types of motion observed include fixed points, oscillations, rotations and chaos. Results also demonstrated that there was a self-synchronization between these pendulums in ideal excitation.

This study investigates forced nonlinear vibrations of a simply supported Euler-Bernoulli beam on a nonlinear elastic foundation with quadratic and cubic nonlinearities. Applying the homotopy analysis method (HAM) to the spatially discretized governing equation, we derive novel analytical solutions and discuss their convergence to present nonlinear frequency responses with varying contributions of the nonlinearity coefficients. A comparison with numerical solutions is conducted and nonlinear time responses and phase planes are compared to the results from linear beam theory. The study demonstrates that apart from nonlinear problems of free vibrations, HAM is equally capable of solving strongly nonlinear problems of forced vibrations.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Nonlinear aeroelastic phenomena is continuously investigate in aeronautical researches. The nonlinearity nature, for these cases, could be aerodynamic, such as dynamic stall or shock waves or structural, for example, free play or large displacements due to high aspect ratio and high flexibility. This work will investigate a very flexible wing with high aspect ratio subjected to unsteady flow. A flutter analysis is proceeded in order to evaluate the error between the computational result and the experiment. Since the linear flutter theory consider small displacements, it is expected a nonlinear phenomena. In this case, the experiment time series is analyzed in order to understand this nonlinearity and a 0-1 test is performed to evaluate if the system has chaotic behavior.

© 2016, Brazilian Association of Computational Mechanics. All rights reserved.This study analyzes the fourth-order nonlinear free vibration of a Timoshenko beam. We discretize the governing differential equation by Galerkin’s procedure and then apply the homotopy analysis method (HAM) to the obtained ordinary differential equation of the generalized coordinate. We derive novel analytical solutions for the nonlinear natural frequency and displacement to investigate the effects of rotary inertia, shear deformation, pre-tensile loads and slenderness ratios on the beam. In comparison to results achieved by perturbation techniques, this study demonstrates that a first-order approximation of HAM leads to highly accurate solutions, valid for a wide range of amplitude vibrations, of a highorder strongly nonlinear problem.

© The Author(s) 2015.The metallic airplane structure fuselage design is characterized by skin, frames, stiffeners, and attachments. In most airplanes, the attachments between these components are made by rivets. The influence of the attachments in the panel behavior under diagonal tension can be verified in the metallic Wagner beam. For stiffened composite panels, like metallic Wagner beams, there is insufficient data about attachment design. In order to design and build lightweight composite structures, the analyst must consider different ways in which the skin is connected to the stiffeners and frames. Therefore, the objective of this paper is to investigate different conceptions of a real-reinforced composite panel used in the aeronautical industry. Experimental and numerical results for strains showed good agreement. The finite element model and the criteria used in the failure analysis are also presented. Comparisons between different panel configurations are made, and conclusions are drawn about attachment efficiency.

© 2016 Elsevier Masson SAS. All rights reserved.This work investigates the aeroelastic stability boundary of flutter in Shape Memory Alloy Hybrid Composite laminates (SMAHC). The SMAHC consists of SMAs wires and continuous carbon fibers embedded into a polymeric matrix resulting in a three constituent composite material. The derivation of the effective mechanical properties of the SMAHC is based on micromechanical model which accounts for temperature and fraction of martensite/austenite transformation phases of the shape memory alloy. Hamilton's principle is used for the formulation of the energy functional and to obtain the equilibrium equations and boundary conditions of the aeroelastic problem. The finite element method is employed to numerically solve the equations. Different geometric configuration, laminate stacking sequence, boundary conditions and curvatures are investigated. The study shows that the stiffening effect induced by the changes in the fraction of martensite/austenite transformation phases of the shape memory alloy increases the rate of occurrence of flutter, stabilizing the plate. Thus, one can control the occurrence of flutter speed by controlling the temperature of the SMA wires and the proper design of the geometric properties of the panel and tailoring of the composite laminate.

© 2016, European Conference on Composite Materials, ECCM. All rights reserved.Shape Memory Alloy Hybrid Composite (SMAHC) laminates are built with continuous carbon fibers and Shape Memory Alloy (SMA) wires, both embedded in a polymeric matrix thereby forming a three constituent composite material. The SMA actuation is triggered by temperature changes, resulting in modifications in the structural responses of SMAHC laminates. A particularly important structural characteristic of SMAHC laminates which is investigated in this paper is the aeroelastic stability boundary of flutter. The derivation of the effective mechanical properties of the SMAHC is based on micromechanical model which accounts for temperature and fraction of martensite/austenite transformation phases of the shape memory alloy. The mathematical problem is formulated using Hamilton's principle, allowing for derivation of the equilibrium equations and boundary conditions of the aeroelastic response. The governing equations are then discretized and solved by the finite element method. A parametric study is conducted where different geometric configurations, laminate stacking sequence, boundary conditions and curvatures are investigated. It is observed that the SMAHC structure is stabilized against flutter by proper tailoring of stiffening effects induced by the changes in the fraction of martensite/austenite transformation phases of the SMA. Therefore, it is possible to increase critical flutter speed by controlling the temperature of the SMA wires.

© 2016 American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents a new approach on aircraft design education based on LPD principles in order to expand knowledge generation and communication during early aircraft design phase, and as a consequence support the emergence of innovative, efficient design solutions as well as provide wide knowledge on aircraft design problematization. The benefits of working with set-based and visible knowledge in a new process framework are evidenced in a case study of early aircraft design at PEE (Embraer Engineering Specialization Program), an environment of aeronautical industry simulation focused on the capacitation of young engineers.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA . All rights reserved.Considering the lack of studies in airfoil geometry effect on tubercle performance and in order to contribute to research in this topic by expanding the investigation of the flow characteristics and aerodynamic performance for distinct airfoils, the aim of this paper is to investigate the effect of the airfoil thickness variation in the wavy leading edge phenomenon by experimental investigation correlating force measurements with mini-tuft and oil flow visualization at low Reynolds number regime. Besides, the Reynolds number effect will be evaluated in the sensitive range between 50.000 and 290.000. Experimental tests were carried out at subsonic blower-type wind tunnel of open loop with closed section at ITA (Technological Institute of Aeronautics). Two different sets of airfoils with distinct thickness (NACA 0012 and NACA 0020) were tested where each set contents a smooth leading-edge configuration and three wavy leading-edge configurations. The results show that the increase in airfoil thickness causes aerodynamic deterioration at pre-stall regime for wavy leading edge airfoil. In addition, the data show that the Reynolds number effect is sensitive on wavy airfoil performance where in some cases at lowest Reynolds number the wavy leading edge configuration achieves maximum lift higher than smooth configuration.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.The objectives of this work is to show appropriated available methodologies used to calculate and modeling aerodynamic coefficients in the distinct aircraft design phases, mainly the Conceptual and Preliminary Phases, as well as present the main recommended practices and general structure of the aerodynamic model to attend the requirements of different technologies during design cycles, such as Loads and Flight Dynamics. This work shows how to get longitudinal aerodynamic coefficients and derivatives from wind tunnel tests, theoretical and empirical methods. The whole approach of this paper will focus on methodologies and techniques that are in public domain. Another important concern of this paper is to make clear that the use of each methodology regards complexity and accuracy is dependent on the aircraft design phase, staff expertise, company experience and design budget. However, understanding the best practices of the aerodynamic modeling is essential to achieve success in the aircraft design. Thus, this work brings a contribution in the sense to show appropriated methodology options under design constraints, starting with the general arrangement concept of an Aerodynamic Model as a part of the Aircraft Simulation Model.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc. 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 longitudinal 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.

© 2016 Elsevier LtdIn the last years, transition metal carbides have appeared as novel materials with promising catalytic properties toward important practical reactions. In this work, the use of the thin porous electrodes for evaluating the hydrogen evolution reaction (HER) of hexagonal molybdenum carbides (α-Mo2C)-based materials is analyzed and the effect of catalyst's load, Lcat, and catalyst's dispersion are discussed in terms of kinetic parameters calculated by employing the electrode geometric area. Catalysts were characterized by X-ray diffraction, energy dispersive X-ray analysis, X-ray photoelectron spectroscopy, cyclic voltammetry and differential electrochemical mass spectrometry. Results have shown that, even for the same catalyst, mass activities and specific activities depend on Lcat. and catalyst's dispersion. In contrast, intrinsic kinetic parameters, calculated from double layer capacitance normalizations, can be considered rather constant. XPS analysis of samples under different electrochemical treatments reveals a surface enrichment of carbon terminated planes after the HER, suggesting a higher HER activity on these planes. An investigation of the electrochemical oxidation of α-Mo2Cand the catalyst's HER activity show a direct correlation between active sites for HER and active sites for catalyst oxidation. Therefore, this oxidation is also used to estimate HER intrinsic parameters. Finally, the activity of a composite sample, in which α-Mo2C is the only active component, is also evaluated.

© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, WeinheimIn the last few years, transition metal carbides have emerged as novel materials with promising catalytic properties toward important practical reactions. In this work, cubic and hexagonal molybdenum carbides are synthesized and evaluated as carbon-supported catalysts and as support materials for Pt nanoparticles for the electrochemical oxygen reduction reaction (ORR). The catalysts are characterized by XRD, energy-dispersive X-ray spectroscopy, TEM, XPS, and cyclic voltammetry on stationary and rotating ring-disk electrodes. The results suggest different reactivity of the molybdenum carbide phases as both catalysts and supports for the ORR. Enhanced mass and specific ORR activities at 0.9 V are calculated for Pt–molybdenum carbide-derived composites compared to commercial Pt and Pt/C catalysts prepared by depositing Pt by the same method. The origin of the improved ORR activity is discussed in terms of the synergistic effect between Pt and the carbide-derived support and a decrease in the adsorption strength of oxygen-containing species on the Pt surface, similar to that proposed for Pt–metal alloys. Additionally, the possible formation of a Pt–Mo alloy on the catalyst surface is proposed.

© 2015 Elsevier B.V. All rights reserved.In this work, the effect of temperature on the adsorption states of Pt(111) vicinal surface electrodes in perchloric acid is studied through a thermodynamic analysis. The method allows calculating thermodynamic properties of the interface. In this framework, the concept of the generalized isotherm and the statistical thermodynamics description are applied to calculate formal entropies, enthalpies and Gibbs energies, ΔG¯i0, of the adsorption processes at two-dimensional terraces and one-dimensional steps. These values are compared with data from literature. Additionally, the effect of the step density on ΔG¯i0 and on the lateral interactions between adsorbed species, ωij, at terraces and steps is also determined. Calculated ΔG¯i0, entropies and enthalpies are almost temperature-independent, especially at steps, but they depend on the step orientation. In contrast, ΔG¯i0 and ωij at terraces depend on the step density, following a linear tendency for terrace lengths larger than 5 atoms. However, while ΔG¯i0 increases with the step density, ωij decreases. Results were explained by considering the modification in the energetic surface balance by hydrogen, Hads, and water, H2Oads, co-adsorption on the electrode, which in turn determines the whole adsorption processes on terraces and steps.

© 2015 Elsevier B.V.Most of electrocatalytic reactions occur in an aqueous environment. Understanding the influence of water structure on reaction dynamics is fundamental in electrocatalysis. In this work, the role of liquid water structure on the oxygen reduction at Pt(1 1 1) electrode is analyzed in methanesulfonic (MTSA) and perchloric acids. This is because these different anions can exert a different influence on liquid water structure. Results reveal a lower ORR electrode activity in MTSA than in HClO4 solutions and they are discussed in light of anion's influence on water structural ordering. From them, the existence of an outer-sphere, rate determining, step in the ORR mechanism is suggested.

© 2014, The Brazilian Society of Mechanical Sciences and Engineering.Vibration analysis of cutting processes has been shown to be an effective method of increasing productivity. Significant improvements can be achieved in terms of quality of machined surfaces, cutting tool wear, and cutting parameters. Literature is widely based on end-milling processes, where stable cutting may be obtained under resonance, as long as the cutting tool is restricted to vibrate only along the feed direction. Thus, the occurrence of instability depends not only on the frequencies involved, but also on the contact conditions between the tool and the workpiece. This paper concerns the analysis of an industrial gear hobbing machining process in regards to its vibrational behavior. The supposition that the cutting tool (hob) presents some similarities to the full immersion end-milling case due to the contact conditions was investigated. Two similar machines which showed high discrepancy regarding productivity were analyzed. It was discovered that minor differences between the two machines changed their modal behavior considerably, implicating in lower productivity. Additionally, besides the tooth passing frequency, a second excitation frequency was found due to the cutting tool geometry. Modal analysis was used to determine new possible parameters and tests were conducted to determine stability limits. New parameters allowed for a reduction of over 18 % in process time under stable conditions. Also, it was concluded that one should avoid resonance conditions when machining gear’s teeth through hobbing.

© 2016 Elsevier Inc.This paper proposes two important improvements to shock-capturing strategies using a discontinuous Galerkin scheme, namely, accurate shock identification via finite-time Lyapunov exponent (FTLE) operators and efficient shock treatment through a point-implicit discretization of a PDE-based artificial viscosity technique. The advocated approach is based on the FTLE operator, originally developed in the context of dynamical systems theory to identify certain types of coherent structures in a flow. We propose the application of FTLEs in the detection of shock waves and demonstrate the operator's ability to identify strong and weak shocks equally well. The detection algorithm is coupled with a mesh refinement procedure and applied to transonic and supersonic flows. While the proposed strategy can be used potentially with any numerical method, a high-order discontinuous Galerkin solver is used in this study. In this context, two artificial viscosity approaches are employed to regularize the solution near shocks: an element-wise constant viscosity technique and a PDE-based smooth viscosity model. As the latter approach is more sophisticated and preferable for complex problems, a point-implicit discretization in time is proposed to reduce the extra stiffness introduced by the PDE-based technique, making it more competitive in terms of computational cost.

© 2016 Acoustical Society of America.Installed jet noise is studied by means of a simplified configuration comprising a flat plate in the vicinity of a round jet. The effects of Mach number, jet-plate radial distance, and trailing-edge sweep angle are explored. Acoustic measurements are performed using a traversable 18-microphone azimuthal array, providing pressure data at 360 points on a cylindrical surface surrounding the jet-plate system. Key observations include a decrease, with increasing Mach number, of the relative level of the scattered field in comparison to the uninstalled jet; an exponential dependence of the scattered sound pressure level on the radial jet-plate separation; and considerable sideline noise reductions with increasing sweep angle, with which there is an overall reduction in acoustic efficiency. The measurements are compared with results obtained using a kinematic wavepacket source model, whose radiation is computed in two ways. A TGF for a semi-infinite flat plate is used to provide a low-order approximation of the scattering effect. Use of a more computationally intensive boundary element method provides additional precision. Good agreement between model predictions and experiment, encouraging from the perspective of low-cost prediction strategies, demonstrates that the models comprise the essential sound generation mechanisms.

© 2015, Springer-Verlag Berlin Heidelberg.A large eddy simulation of flow over a forward-facing plate is performed and the resulting database analyzed with respect to sound radiation. Aeroacoustic analysis motivates an initial data compression comprising eduction of the zeroth-order spanwise Fourier mode. The space–time structure of this component of the flow is then analyzed using POD and DMD in order to probe both the energetics and dynamics of the sound-producing flow skeleton. Both data processing techniques educe flapping and shedding modes and identify a nonlinear interaction between the two. POD shows the flapping mode to be energetically unimportant, while DMD highlights its dynamic importance. The difference mode—vortex shedding modulated by flapping of the separation bubble—is found to be the most acoustically important feature of the flow.

© 2016 The Author(s) Published by the Royal Society. All rights reserved.We present a numerical method to compute the acoustic field scattered by finite perforated elastic plates. A boundary element method is developed to solve the Helmholtz equation subjected to boundary conditions related to the plate vibration. These boundary conditions are recast in terms of the vibration modes of the plate and its porosity, which enables a direct solution procedure. A parametric study is performed for a two-dimensional problem whereby a cantilevered perforated elastic plate scatters sound from a point quadrupole near the free edge. Both elasticity and porosity tend to diminish the scattered sound, in agreement with previous work considering semi-infinite plates. Finite elastic plates are shown to reduce acoustic scattering when excited at high Helmholtz numbers k0 based on the plate length. However, at low k0, finite elastic plates produce only modest reductions or, in cases related to structural resonance, an increase to the scattered sound level relative to the rigid case. Porosity, on the other hand, is shown to be more effective in reducing the radiated sound for low k0. The combined beneficial effects of elasticity and porosity are shown to be effective in reducing the scattered sound for a broader range of k0 for perforated elastic plates.

© 2016 Cambridge University Press.We present a study of the turbulent and acoustic fields of subsonic jets, controlled by means of a novel actuator that introduces perturbations via steady-fluidic actuation from a rotating centrebody. The actuation can produce louder or quieter jets, and these are analysed using time-resolved stereoscopic particle image velocimetry and a hot-wire anemometer. We place the analysis in the framework of wavepackets and linear stability theory, whence we show, using solutions of the linear parabolised stability equations, that the quieter flows can be understood to result from a mean-flow deformation that modifies wavepacket dynamics, and in particular their phase velocities, which are significantly reduced. The mean-flow deformation is shown, by a triple decomposition, to be due to the generation of Reynolds stresses associated with incoherent turbulence (rather than coherent structures) which arises when the actuation energises the flow with a frequency-azimuthal wavenumber (-) combination to which the mean flow is stable. When the actuation excites the flow with an-combination to which the mean flow is unstable, the response is dominated by coherent structures, whose rapid growth takes them beyond the linear limit, where they undergo quadratic wave interactions and lead, consequently, to a louder flow.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Linear instability waves, 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. Beyond this station linear models fail to predict single-point statistics; they fail more broadly in the prediction of two-point properties such as coherence; and their underprediction of the radiated noise is believed to be associated with these errors. Non-linearity is the likely missing piece. But how might it be incorporated? What are the essential underlying mechanisms? Might it be amenable to a reduced-order modelling methodology? The work described in this paper is concerned with these questions. The non-linear interactions are considered as an “external” harmonic forcing of the standard linear model; the forcing can be viewed as comprising those Fourier components of the non-linear term of the Navier-Stokes equations which are most amplified by the linear wavepackets. This modelling framework is explored using three complementary problems in which we try to understand the relationship between “external” forcing, linear system and flow response. The response of an incompressible, two-dimensional, locally parallel, shear-flow to direct, spatially localised, harmonic forcing is first considered. A resolvant analysis is then performed, again in a locally parallel context, both for the incompressible, 2D problem and for a compressible axisymmetric shear-flow where the mean flow is taken from experiments. Finally, in order to incorporate the slow axial variation of the real jet, a novel approach is considered where 4D-Var data assimilation is applied using experimental data and the Parabolised Stability Equations (PSE-4D-Var). The objective of this third, data-driven, approach is to search for an optimal forcing that might improve the match between wavepaket solutions and measurements. In all of the problems considered the critical layer, where the phase speed of the wave is equal to the local mean velocity, is found to be relevant. It is at this point that the sensitivity of the linear waves to non-linearity is greatest. In the 2D, incompressible, problem the largest response is produced when the flow is forced in the vicinity of the critical layer. The resolvant analyses show optimal forcing modes that peak on the critical layer and the optimal response modes have a critical-layer structure. The PSE-4D-Var approach shows highest sensitivity near the critical layer. Furthermore, the structure of the forced perturbations are tilted in a manner that suggests an Orr-like mechanism. The ensemble of results suggest that the critical layer may play a central role in the modelling of wavepackets in subsonic turbulent jets, and indeed may be the key to remedying the deficiencies evoked above.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.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 Auto-Regressive Moving-Average eXogneous (ARMAX) 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 PSE-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 (SIMO) 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.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A formulation to evaluate the sound generated by a jet in the vicinity of a semi-infinite flat plate based on a PSE (Parabolised Stability Equations) code is proposed. Complexity is added to the model used in Cavalieri et al.,1 where the flat plate is considered semiinfinite, focusing on the trailing edge scattering of the acoustic source, by exchanging the sound source, previously considered as a semi-empirical wavepacket, for linear PSE solutions, which are based on a linearisation of the Navier-Stokes equations and avoid thus the empiricism of the previous approach. The calculation reproduces the main trends expected for this case, such as the superdirectivity at low polar angles for the free jet and the cardioid shape of the acoustic field for the installed jet, although the amplitudes reached are yet to be validated. We first study the influence of the radial distance between jet and plate, considering that this analysis is only weakly dependent on the two-point coherence of the source. We expect that, although the hydrodynamic field from the PSE has differences in comparison to the semi-empirical wavepacket, the main features observed using the previous model should be identified. This work will lead to a more reliable tool, based on first principles, to study the characteristics of the sound generated by a jet near a trailing edge.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We explore the stability characteristics of non-circular jets, by means of the direct numerical solution of a compressible Rayleigh equation considering a parallel base flow which is a function of radius and azimuth. The formulation is based on the Floquet theory of differential equations with periodic coefficients. In this sense, solutions of eigenfunctions, growth rates and phase speeds are possible for arbitrarily shaped base-flows, with azimuthal periodicity. For validation purposes, previous results for chevrons and elliptical jets were reproduced. Base flows representative of jets with chevrons and micro-jets were then fitted using an extended version of Michalke’s1 hyperbolic tangent profile, allowing here azimuthal inhomogeneities in the base flow. Sample velocity profiles in the near-nozzle region can be described by an azimuthal variation of the mixing layer position R and momentum thickness Θ. The effect of these parameters is studied so as to discern their instability properties, and it is seen that the combined azimuthal variations of R and Θ produces significant reductions of growth rates for a profile representative of chevrons; micro-jets induce mainly changes in R, with consequent reductions of spatial amplifications, but less significant than the chevron case. The influence of the number of lobes in the base-flow is also investigated, and growth rates for different numbers of chevrons collapse once the afore mentioned base-flow parameters (with the same values obtained for the chevron case) are preserved in the representative piece of the base-flow.

© American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. Acoustic waves trapped in the potential core of subsonic turbulent jets have recently been observed and explained by Towne et al. 11, 13, 14 We show that these waves also radiate outside the jet, primarily into the upstream arc. We provide an experimental identification of the Mach-number dependence of the phenomenon, which indicates that the modes are active even when evanescent, probably due to turbulent forcing. Finally, we show that for Mach numbers lower than about 0.8, the strong tonal dynamics and sound radiation (up to 170dB) that occur when a sharp edge is placed close to the jet are related to a resonance mechanism involving convective hydrodynamic wavepackets and a ‘slow’, upstream-propagating, trapped acoustic mode. A Helmholtz scaling of the resonance at higher Mach number suggests involvement of the ‘fast’ trapped modes in the range 0.8 ≤ M ≤ 1.

© American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Wavepackets obtained as solutions of the flow equations linearised around the mean flow have been shown in recent work to yield good agreement with the amplitudes and phases of turbulent fluctuations in jets. Compelling agreement has been demonstrated up to Strouhal numbers, St ≈ 1. We extend the range of validity of wavepacket models to higher values, 1.0 < St < 4.0, by comparing Parabolised Stability Equation solutions with well resolved large-eddy simulation data. The initial growth rates of the high-frequency fluctuations continue to be well predicted, but saturation occurs earlier and agreement with simulation begins to deteriorate upstream of the end of the potential core of the jet. Results show that near-nozzle dynamics for a broad range of frequencies can be modelled using linearised models, which capture well the spatial growth of Kelvin-Helmholtz wavepackets for all the studied Strouhal numbers.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.An investigation of a semi-empirical wavepacket model for free-jet and jet-surface in- teraction noise was conducted. The source term for the axisymmetric mode was extracted from a Mach 0:9 jet Large Eddy Simulation (LES) and employed to adjust the parameters of a simple line source wavepacket model. Streamwise coherence decay, in particular, was considered. The source model was propagated with both the free-field and tailored Green’s function for a semi-infinite at plate positioned at a distance of r=D = 1 from the jet axis. For the free jet, the original unit-coherence source produced a sound field with 40dB errors in comparison with experimental data. When the coherence decay extracted from the LES was used in the line source, noise levels presented very good agreement with experimental data at all polar angles. With the tailored function, at the polar angles most affected by the trailing-edge scattering, the unit-coherence source presented noise levels about 10dB lower than the experiments. Inclusion of the coherence decay extracted from the LES improved the results in the whole directivity range. These results not only confirms the importance of matching source coherence in addition to amplitude and phases of the real source, but also that the installed case is somehow less sensitive to source coherence than is the free jet.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This study aims at the attenuation of the unsteady fluctuations along a two-dimensional mixing layer which may be considered as a prototypical problem for the evaluation of estimation and control techniques, and also a canonical problem, when compressibility is considered, for sound radiation by low-Reynolds-number free shear flows. Two strategies are proposed for the estimation of the time evolution of wavepackets based on upstream data of the simulation: a Parabolised-stability-equation (PSE) based transfer function between two positions and an empirical-transfer-function identification technique, which relies on the theoretical background established by the PSE. Both techniques present a similar performance for prediction of the fluctuations between streamwise-separated input and output positions. Furthermore, the identification method is used to determine the response of the flow to a body force actuation which allows for the elaboration of a Feedforward control framework for the fluctuations via a phase-opposition actuation. This strategy, which is evaluated with three di erent control laws, presents encouraging results both for the linearized system (i.e. described in terms of transfer functions) and for the non-linear, direct numerical simulation of the mixing layer, in which significant delays of vortex pairing are observed. The established framework is thus seen as a promising technique for real-time flow control aiming at the attenuation of wavepackets, and the corresponding reduction of the radiated sound.

© 2016 by The Authors.Coherent fluctuations in a turbulent jet at Ma = 0.4 and Re = 4.6 × 105 are analysed by combining experiments and linear stability analysis. Following the work by Dergham et al,1 we explore the connection between singular modes of the resolvent operator and the measured covariance, within the framework introduced by Farrell and Ioannou.2 Instantaneous velocity fields are measured by means of time-resolved, stereoscopic PIV, in the radial-azimuthal plane at different locations along the streamwise direction. Proper orthogonal decomposition of the cross-spectral density covariance is applied for extracting coherent wavepackets, at a given frequency. The mean flow field is used for the linear stability analysis. We compute the singular value decomposition of the linear resolvent operator, derived from the fully compressible Navier-Stokes equations, in order to identify the optimal harmonic forcing and the associated linear flow response. The analysis shows a remarkable agreement between the modal structures computed by linear analysis and the wavepackets extracted by statistical analysis of experimental measurements. These results suggest that the stochastic framework may help in shedding light on the structure of the non-linear forcing responsible for the wavepackets as observed in experiments.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The mean flow stability of a Mach 0.9 turbulent jet is investigated by means of global linear theory with a focus on acoustic effects. A novel class of resonant acoustic modes that are trapped within the potential core, and whose eigenvalues appear as discrete branches in the global stability spectrum, is studied in detail. A dispersion relation is reconstructed from the global modes, and shown to accurately predict energy bands observed in the PSD of a high-fidelity LES. Similarly, the acoustic far-field radiation patterns of the trapped modes are compared to the LES. A favorable agreement between the global mode waveforms and coherent structures educed from the LES is found for both the trapped acoustic wave component inside the core and the far-field radiation.

© 2016 by The Authors.An experiment has been designed in order to address the questions that remain open following the experiments, analysis and modelling reported in Cavalieri et al (2013). The same Mach 0.4 turbulent jet is considered, but this time using two independent-but-synchronised, time-resolved, stereo PIV systems. Each system can be moved independently, allowing simultaneous measurement of velocity in two, axially separated, cross-flow planes, enabling eduction of the two-point coherence of wavepackets. This and the associated lengthscales are studied and compared with those of the energy containing turbulent eddies. Different scaling behaviours are observed which have important implications for jet-noise modelling.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Sound radiation from a subsonic turbulent jet is examined after a hypothetical removal of near-field coherent structures in the low azimuthal components of the velocity fluctuations. With the help of a well-validated database of large-eddy simulation, the near-field coherent structures are extracted using discrete wavelet transform (DWT), and their spatial structures are examined using 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 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 by around 7 dB in the overall sound pressure level at 30 degrees 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 characterised 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. When velocity components in the first and second helical azimuthal modes are removed, the overall sound pressure levels are reduced for a wide range of polar angles. The results also show that axial velocity fluctuations in the second helical mode are closely associated with sound radiation at high polar angles. Far-field azimuthal decomposition indicates that the sound reduction takes place in multiple azimuthal modes. The results suggest that there is a causal link between the axisymmetric components of the near-field coherent fluctuations and far-field low-angle jet noise. On the other hand, velocity components in near-field helical azimuthal modes are coupled for sound radiation in helical azimuthal modes. It is also suggested that not only the large-scale wavy structures in low POD modes, but also the smaller-scale coherent structures in higher POD modes need to be included for jet noise modelling, because they are both shown to be efficient at sound radiation.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Installed jet noise is studied by means of a simplified configuration comprising flat rectangular plates situated in the nearfield of a round jet. Acoustic measurements are performed using a traversable 18-microphone azimuthal array, providing pressure data at 360 points on a cylindrical surface surrounding the jet-plate system. A rigid aluminium plate and a flexible, composite plate were tested to assess the influence of the plate stiffness on the scattered sound. The numerical predictions are confirmed by experiments and suggest that a reduction in the scattered sound level can be achieved as the flexibility of the plate is increased.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.It is well known that large-scale coherent structures play a crucial role in sound radiation from jets. Their acoustic efficiency is believed to be associated with their interaction with smaller-scale structures. This study conducts numerical experiments on a low Reynolds number jet where smaller-scale structures are artificially suppressed by increasing the eddy viscosity in a subgrid model. It is found that when the smaller-scale structures are sup- pressed, the fluctuation energy of the large-scale structures around the most unstable Strouhal numbers (0.25 < St < 0.4, based on jet exit velocity and nozzle diameter) remains at almost the same level as the original. The coherence length scales of the large-scale structures (at 0.3 < St < 0.6) generally increase after the flow transitions into turbulence. A proper orthogonal decomposition (POD) shows that the first POD mode at low Strouhal numbers have wavelike patterns, and that the peak energy and convection speed of these wavepackets are not influenced much by the increasing eddy viscosity. The radiated sound is shown to decrease significantly at high Strouhal numbers at various polar angles, but to remain approximately the same at low Strouhal numbers (St < 0.4). It is suggested that the instability waves at the most unstable Strouhal numbers (St ≈ 0.35) are not significantly affected by the structures at high Strouhal numbers (St > 0.6), and that the sound radiation at low Strouhal numbers (0.25 < St < 0.35) at various polar angles possibly comes from the large-scale structures in the similar Strouhal number range.

© American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.To improve understanding and modeling of jet-noise source mechanisms, extensive experimental and numerical databases are generated for an isothermal Mach 0.9 turbulent jet at Reynolds number Re = 106. The large eddy simulations (LES) feature localized adaptive mesh refinement, synthetic turbulence and wall modeling inside the nozzle to match the fully turbulent nozzle-exit boundary layers in the experiments. Long LES databases are collected for two grids with different mesh resolutions in the jet plume. Comparisons with the experimental measurements show good agreement for the flow and sound predictions, with the far-field noise spectra matching microphone data to within 0.5 dB for most relevant angles and frequencies. Preliminary results on the radiated noise azimuthal decomposition and temporal intermittency are also discussed. The azimuthal analysis shows that the axisymmetric mode is dominant at the peak radiation angles and that the first 3 Fourier azimuthal modes of the LES data recover more than 97% of the total acoustic energy at these angles. The temporal analysis highlights the presence of recurring intermittency in the radiated sound for the low-frequency range and main downstream angles. At these frequencies and angles, temporally-localized bursts of noise can reach levels up to 3 or 4 dB higher (or lower) than the long-time average.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The purpose of this paper is to characterize and model waves that are observed within the potential core of subsonic jets and that have been previously detected as tones in the near-nozzle region. Using three models (the linearized Euler equations, a cylindrical vortex sheet, and a cylindrical duct with pressure release boundary conditions), we show that these waves can be described by linear modes of the jet and correspond to acoustic waves that are trapped within the potential core. At certain frequencies, these trapped waves resonate due to repeated reflection between end conditions provided by the nozzle and the streamwise contraction of the potential core. Our models accurately capture numerous aspects the potential core waves that are extracted from large-eddy-simulation data of a Mach 0.9 isothermal jet. Furthermore, the vortex sheet model indicates that this behavior is possible for only a limited range of Mach numbers that is consistent with previous experimental observations.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.A 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 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 sweep angle of the trailing edge considerably modify the radiated sound, leading to significant reductions of the acoustic intensity in some directions. The sweep-angle dependency of installed jet noise is 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.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.We study mechanisms of noise generation by an airfoil at zero angle of attack using flow-acoustic correlations. We use a large-eddy simulation (LES) of the compressible flow around a NACA0012 airfoil for M∞ = 0.115 and Rec = 408000. With this simulation we analyse flow fluctuations around the airfoil, such as pressure and velocity, and relate them to the far-field sound using standard correlation techniques. Similar to the results of Cava- lieri et al.,3 who have obtained more significant flow-acoustic correlation for turbulent jets when the axisymmetric mode was isolated, we have noticed much higher correlations in the present problem when the two-dimensional mode, i.e. spanwise-averaged uctuations, was isolated from the turbulent flow and subsequently correlated to the acoustic pressure. This result is justified theoretically by an analysis of the tailored Green's function for a half plane, where we find that a necessary condition for trailing edge scattering is ǀkzǀ < k, where kz is the spanwise wavenumber of turbulent disturbances and k is the acoustic wave number. Two-dimensional perturbations, associated to kz = 0, are always radiating. Isolation of spanwise-coherent disturbances is thus a means of filtering non-radiating structures. Another feature that tends to increase correlation coefficients is the use of the difference between uctuations in the upper and lower surfaces of the airfoil, which again is in line with theory: when disturbances are in phase opposition between the two sides of the airfoil acoustic scattering is maximal.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Recent studies have shown that while linear wavepacket models accurately reproduce experimentally observed, low azimuthal-wavenumber pressure fluctuations in the near field of turbulent jets, they significantly under-predict the intensity of the acoustic radiation produced in the subsonic case. In a linear context, “jittering” of the wavepackets, which can arise due to both stochastic and nonlinear interactions that force the wavepackets, has been hypothesized as a mechanism by which the radiation efficiency of wavepackets is greatly increased. We use data from a carefully validated large-eddy-simulation of a Mach 0.9 turbulent jet to explore this hypothesis. We analyze the LES data in frequency space using windowed segments of a set of snapshots spanning two thousand acoustic time units. We apply the linearized Navier-Stokes operator to this data in order to compute the non- linear forcing field that occurred in the LES simulations, and propose several techniques for educing the relation between the forcing and the observed flow fields. In particular, we employ empirical techniques to identify high energy modes (via proper orthogonal decomposition) in both the flow and acoustic fields, as well as a set of empirical resolvent modes that maximize either the gain between the forcing and flow fields, or the gain between the forcing and acoustic fields. The high gain modes are similar to the high energy modes in both cases, suggesting that the forcing fields are nearly uncorrelated in each realization. Both flow and acoustic fields appear to be driven by largely incoherent forcing corresponding to turbulence in the region of strong shear and, in particular, close to the critical layer. With the caveat that we have thus far only analyzed the axisymmetric mode of the disturbance fields, the results suggest that accurate linear wavepacket models that capture both the coherent flow and acoustic fields can be constructed if appropriate parameterizations of the stochastic forcing can be found, i.e. such forcings will excite the high gain modes to produce the observed coherent structures in both the near and far field.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The mechanism of sound generation in the downstream direction of jets is often associated with large-scale structures, or wavepackets. These are often modelled using frequency-domain models based on the linearisation of the Navier-Stokes system. A closed-loop control formulation requires a time-domain model in order to calculate appropriate gains between sensors and actuators so as to minimise a given objective. In the present work, we address how such a control scheme can be developed using time-domain transfer functions, derived from corresponding frequency-domain models. We first exemplify the application of the present technique for a simplified 1D problem based on the nonlinear Burgers’ equation. The proposed method is then applied for time-domain transfer functions obtained using wave-packet models for jets, as an attempt to control large-scale structures in such flows and consequently reduce their sound radiation.

Copyright © 2016 by Daniel Drewiacki, Flavio Jose Silvestre, Antonio Bernardo Guimaraes Neto. Published by the American Institute of Aeronautics and Astronautics, Inc.Frequency domain handling qualities criteria were developed in order to predict and prevent Pilot Induced Oscillation (PIO) occurrences. However, these criteria have been developed neglecting the influence of airframe flexibility. Since aircraft are becoming more flexible, this influence has to be considered during the development of y-by-wire systems. In this paper, we address the effects of aeroelastic dynamics in aircraft handling qualities.

© Copyright 2016 by the American Institute of Aeronautics and Astronautics, Inc.An inertially-coupled formulation for the flight dynamics of flexible aircraft undergoing small deformations is developed. The availability of a structural-dynamic finite element model of the aircraft is presupposed. With all the coupled dynamics taken into account, an arbitrary choice of the body reference frame can be made. This frame is also allowed to be noncoincident with the frame of reference used to calculate the aerodynamic loads. In the equations of motion, the inertial coupling terms are linearized in the elastic displacements around a calculated equilibrium condition. Appropriate modes of vibration are then used in the calculation of the dynamic deformation of the structure. A simple quasi-steady incremental aerodynamic model based on the vortex-lattice method is used. The formulation is tested in the flight simulation of an idealized forward-swept-wing aircraft model. Numerical results show that, under small deformations, different body axes lead to the same overall motion of the aircraft with respect to an inertial frame. The stiffness level at which geometrically nonlinear formulations would become necessary is also determined.

© 2016 American Chemical Society.In this study, the authors have presented a numeric model (NM) for application to naphthalene (C10H8) conversion via ionization reaction in a microwave air plasma torch. The NM has included a pressure-independent enhanced electron energy distribution function (EEDF) and cross-section calculation, enhanced by a new formula of phase shift determination. Based on the validated NM, electron density ne and O2+, O-, C10H8, N2, and O2 particles densities were calculated, as well as the conversion rate of C10H8 molecules was predicted. The predicted results showed that the ionization impact on C10H8 molecules conversion has not exceeded 0.81 × 10-10%. Based on the calculated collision cross-section of each species (O2, N2, and C10H8) of carrier gas, the authors suggested using cubic polynomial approximations of the cross-section curves with R-Square (COD) parameter R2 = 99%. MW power increasing in the range 1.75-20 kW has raised the electron density in the range (0.5-4.5) × 1012 m-3. The maximal effect of electron density decreasing with pressure increasing was simulated at values of MW power greater than 7.5 kW. Herewith, pressure increasing and MW power increasing have not had any significant effect on the average electron energy.

© 2016 Elsevier Ltd. All rights reserved.In the last few years, the concentrating solar power (CSP) systems have been studied and growing surprisingly in several countries. The science and technology involved to manufacture the special materials for these devices has been a determining factor for the system performance. Among these special materials, ceramic-metal composite (cermet) is an important class largely used as a main absorber in the selective surfaces of evacuated tube collectors. This work aims to manufacture Mo-AlNxOy thin films by magnetron sputtering technique. The parameter studied was the effect of annealing temperature (600C-1100 °C) on the optical properties and surface morphology of the films. The results showed that the annealing (800-1100 °C) increase the absorptance, produces an oxidation in the bulk of the films and a breakage in the AlN surface bonds, reducing the initial quantity of nitrogen. It is noteworthy that the annealing at 600 °C did not alter the optical and morphology properties of the films, suggesting that the films of Mo-AlNxOy produced can be applied in selective surfaces in the future.

© 2016 Elsevier B.V. All rights reserved.The limitations of stainless steel as prosthesis material should be overcome in order to better satisfy the required specifications in bone replacements. One strategy to improve the corrosion and wear resistance and diminish the ion release is the surface modification of the implants by protective coatings. In this work, thin films of FeAlCr alloy were grown on ASTM F138 stainless steel by using DC magnetron sputtering technique. The films were produced by varying the sputtering power (from 50 to 200 W) and the substrate temperature (room temperature, 150 °C and 300 °C). The films obtained in all processing conditions were crystalline and presented the same chemical composition of the target material. It was found that the deposition rate of the films and their adhesion to the substrate increased with both the sputtering power and the substrate temperature. The best result was obtained for depositions carried out at 100 W and substrate heated at 300 °C.

© 2016 Published by Elsevier Ltd.Two kinds of reactively sputtered titanium dioxide films with columnar and fine-grained structures were investigated as diffusion barriers, preventing the silicon diffusion. The only differences in the deposition conditions were the oxygen percentage concentration (OC) in the discharge, kept for 10% and 30% of the total working pressure. The resulting films were found to have different thicknesses being 800 and 240 nm for 10% and 30% OC, respectively. The films were studied by X-Ray diffraction spectrometry (XRD) and their composition by Rutherford Backscattering Spectrometry (RBS). In order to describe the diffusion processes, the two batches were annealed up to temperature of 800°C. The diffusivity from 300°to 800°C is D(m2/s)=2.43.10-18exp[-(15kJ/mol)/(RT)] and D(m2/s)=2.36.10-18exp[-(18.4kJ/mol)/(RT)] for (10% OC) and TiO2 (30% OC), respectively. The physical meaning of the derived diffusion parameters are discussed in view of the crystalline peculiarities of the obtained films. Arrhenius plots show clearly that higher activation energy is characteristics for films with better-packed crystallites. These results are compared with known diffusion barrier layer such as TiN.

© 2016 Elsevier B.V. All rights reserved.Since Grätzel and O'Regan started in 1991, dye-sensitized solar cells (DSSC) have been extensively studied around the world. In addition to increasing efficiency, their characteristics such as low cost materials and inexpensive manufacturing processes are attractive for organic solar cells. Several parts of DSSC devices are being researched such as semiconductor engineering, low cost counter electrodes, electrolytes, and dyes. In this work, platinum (Pt) thin films were deposited by sputtering technique to produce counter electrodes for DSSC. The films were characterized by profilometry, elipsometry, four-point probe sheet resistance, spectrophotometry, and electrochemical impedance spectroscopy. The electrode response was also compared to that built from a commercial platinum solution. The results allow us to determine the minimum Pt film thickness necessary to achieve a relevant reduction of the sheet resistance and charge transfer resistance, which preserve a significant electrode transparency. The 22 nm and 24.8 nm thick films combined low charge transfer resistance and good transparency. The 122 nm Pt film presented the lowest charge transfer resistance.

© 2016 American Chemical Society.In this paper, a naphthalene (C10H8) thermal cracking model is presented. The model is based on a simple model that takes into account the microwave (MW) plasma thermal influence on naphthalene cracking, accompanying its steam reforming reactions. The temperature level of 1573 K was established for complete C10H8 cracking at 1.75 kW plasma power. High conversion efficiency of C10H8 is achieved varying the air flow rate in the range of 0.6-1.2 m3/h. The model approximates the characteristics of the considered MW plasma to thermal plasma in local thermodynamic equilibrium (LTE). Experimental data have good agreement with calculated data at the cited region of the air flow rate and power. Conversion efficiency up to 99.36% was obtained.

Background: The influence of diamond-like carbon (DLC) films on bacterial leakage through the interface between abutments and dental implants of external hexagon (EH) and internal hexagon (IH) designs was evaluated. Methods: Film deposition was performed by plasmaenhanced chemical vapor deposition. Sets of implants and abutments (n = 30 per group, sets of 180 implants) were divided according to connection design and treatment of the abutment base: 1) no treatment (control); 2) DLC film deposition; and 3) Ag-DLC film deposition. Under sterile conditions, 1 mL Enterococcus faecalis was inoculated inside the implants, and abutments were tightened. The sets were tested for immediate external contamination, suspended in test tubes containing sterile culture broth, and followed for 5 days. Turbidity of the broth indicated bacterial leakage. At the end of the period, the abutments were removed and the internal content of the implants was collected with paper points and plated in Petri dishes. After 24-hour incubation, they were assessed for bacterial viability and colony-forming unit counting. Bacterial leakage was analyzed by X2and Fisher exact tests (a = 5%). Results: The percentage of bacterial leakage was 16.09% for EH implants and 80.71% for IH implants (P <0.0001). The bacterial load was higher inside IH implants (P = 0.000). The type of implant significantly influenced the results (P = 0.000), whereas the films did not (P = 0.487). Conclusion: IH implants show a higher frequency of bacterial leakage; and DLC and Ag-DLC films do not significantly reduce the frequency of bacterial leakage and bacteria load inside the implants.

© 2016, Journal of Aerospace Technology and Management. All rights reserved.Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.

© 2016 Elsevier Ltd. All rights reserved.The increase in electricity demand in Brazil and the frequent interruptions in its supply forced the industry and commerce use stationary generator sets, mainly in large urban centers like São Paulo. This city established a decree in order that these devices use cleaner fuels than diesel oil, or adopt post-gas treatment systems, since there are no national regulations for generator sets emissions. To meet this decree, ethanol appears as a good option because it is an environmentally friendly fuel, does not affect the ozone layer, since it is obtained from sugarcane, which helps to reduce the carbon dioxide emissions to the atmosphere through photosynthesis in sugarcane field. Within recommended specifications ethanol can be blended with diesel and gasoline, but can also be used without additives, without damaging the engine. The ethanol availability in Brazil and its consolidation in the automotive market make it an alternative for use in generator sets. The aim of this work was to characterize the performance of a heavy duty Otto cycle engine, developed based on 12 l diesel longblock, prepared to run on ethanol without additives, as a prototype generator set. The performance tests of the generator set were conducted at three different altitudes. A load bank was used to simulate the real electrical load in five different power settings. The performance characteristics obtained experimentally were compared with results obtained with a one-dimensional model using the commercial software GT-Power®. The results obtained during the development phase showed that the engine achieve up to 39.6% of the brake efficiency and a peak power of the 326 kW. The maximum electrical power achieved by the generator set was 302 kW at sea level and 278 kW at 1640 m, according to the employed methodology. The results showed that is feasible to use ethanol without additives for the energy generation, replacing diesel oil in heavy-duty engines, operating in the evaluated steady state condition.

© 2016 Elsevier LtdDeveloping exact models of combustion instabilities is not an easy task to carry out and requires a great deal of time prior to obtaining success. The present study proposes a low-order model for pressure oscillations that does not require any knowledge of the systems, any new physical findings nor intricate details regarding its operating condition. This new approach is obtained using a Modified Van der Pol's equation (MVDP) which is tuned by use of a Dual Extended Kalman Filter (DKEF) as a recursive estimator with perspectives in control by computer. This phenomenological model is used to predict the pressure signal from a variety of different combustors. Input data were taken from experimental cases such as a Rijke tube, a gas turbine and a liquid-fuel aero-engine combustor. Furthermore, a simulation considering high frequency oscillations to show the capability of the new approach is presented. In all cases, the results demonstrated the feasibility of applying the tractable model MVDP and DKEF running together to investigate pressure oscillations in practical cases.

© 2016The recently increasing interest in plasma assisted combustion is mainly motivated by new possibilities for ignition and flame stabilization, in addition to pollutant emission reduction and control. In a chemically active environment, the plasma generates radicals, excited chemical species and ions, thus increasing the combustion process reaction rate. In this paper, the effect of plasma assisted combustion on pollutant emissions of a premixed flame of natural gas and air is investigated by using two gas analyzer systems to acquire a diversity of pollutant gases. The plasma is created by using a gliding arc discharge at the equivalence ratios of ϕ = 1.2 and 1.4, with applied electrical power ranging between 220 W and 370 W. The use of a gliding arc discharge leads to a reduction in the emissions of hydrocarbons and carbon monoxide. Meanwhile, the carbon dioxide emissions increase due to a faster oxidation of carbon monoxide and the water concentration in the exhaust gases is reduced with the use of plasma at the expense of higher hydrogen generation.

© 2016 Elsevier LtdA detailed literature review of laminar burning velocity and flammability limits of biogas mixtures combustion is presented. Biogas alone and in mixtures with other fuels is particularly significant because of its capability of application as fuels for internal combustion engines (ICEs). Therefore, a strict determination of the fundamental combustion characteristics required for their application in ICEs is crucial. Producing energy from biogas has the additional advantage of preventing its release into the atmosphere, where it results into significant air pollution. CH4 and CO2 are the main compounds of biogas, such as landfill, agricultural and sewage gas, after the removal of the trace amounts of organic compounds. For the same equivalence ratio, the presence of CO2 in the fuel feed results in substantial reduction of the laminar flame speed and flammability limits. Several research projects have shown that the decrease in the laminar flame speed of a fuel mixture containing dilution components is caused by the increase in specific heat capacity and the decrease in heat release, flame temperature and thermal diffusivity. The most promising strategies to increase the laminar burning velocity and the flammability limits of biogas are revised and discussed. The thermodynamic conditions under which these properties are determined are analyzed and the work still required for a comprehensive laminar burning velocity and flammability limits determination, at typical ICEs thermodynamic conditions, is addressed. The article provides a brief review of pollutant emissions of ICEs running on biogas and the current and future technological solutions to meet the increasing strict regulation.

© The Authors, published by EDP Sciences, 2016.This work presents the modeling and control of a multirotor aerial vehicle with tethered configuration. It is considered an octocopter with a saturated proportional-plus-derivative position control. A viscoelastic model is considered for the tether, which has a tension control. Numerical simulations are carried out to compare the performance of the tethred configuration with the vehicle in free flight.

© The Authors, published by EDP Sciences, 2016.The interest for multirotor aerial vehicles (MAVs) is currently growing due to their low cost, high manoeuvrability, simplified mechanics, capability to perform vertical take-off and landing as well as hovering flight. These characteristics make them a promising technology suitable for applications such as surveillance of indoor and urban environments. The present work faces the problem of controlling the attitude of a MAV by means of a linear feedback control which guarantees asymptotic stability when controlling nonlinear dynamics. The simulations show the effectiveness of the method.

© The Authors, published by EDP Sciences, 2016.This paper proposes a method for in-flight parameter estimation for Multirotor Aerial Vehicles (MAV). This task is important because it provides parameters with better accuracy for the actual vehicle operation. In order to simulate a flight it is adopted a simulation environment Software-In-the-Loop (SIL).

© 2016, Journal of Aerospace Technology and Management. All rights reserved.The cooperative control of small unmanned aerial vehicles such as the multicopters has been extensively investigated worldwide for functionality augmentation and cost reduction with respect to a single larger vehicle. The present paper proposes a software-in-the-loop simulation scheme for performance evaluation and demonstration of formation flight control systems of multicopters. The simulation scheme consists of a computer network where each computer simulates one of the vehicles using the MATLAB/Simulink for implementing the local control system and the X-Plane for simulating the flight dynamics and environment. For cooperation, the local control systems exchange position data by means of the network. In order to illustrate the proposed scheme, a group of 3 octocopters is taken into consideration and a leader-follower strategy is chosen for triangular position formation, with the leader moving in a straight line with constant speed.

© 2016 Elsevier Ltd.Flutter in aeronautical panels is a type of self-excited oscillation which can occur during supersonic flights. At the flutter point the vibrations of the panel become unstable and increase significantly in time. This manuscript presents a semi-analytical model taking into account the stiffener's base effects, in order to predict the aeroelastic response of laminated composite stiffened panels under supersonic flow. Krumhaar's modified supersonic piston theory, which considers the radius effect, is adopted to model the aerodynamic loading. The proposed model has been validated against results available in the literature for various configurations. A parametric study considering different panels and stiffener configurations is also presented. The numerical results indicate that the stiffener base significantly affects the panel aeroelastic behavior. Preliminary studies also indicate that redistributing the laminate plies from the stiffener's flange to its base significantly increases the torsion stiffness of the panel locally, opening new design possibilities that may lead to higher critical flutter speeds and therefore to better designs. The results also indicate that designs with plies distributed on the base may lead to a better flutter performance when the airflow is transverse to the longitudinal stiffener direction.

© 2016 Elsevier LtdThis paper describes the development and experimental evaluation of a particular type of piezoelectric energy harvester, composed of four aluminum cantilever blades to which piezoelectric patches are bonded, in such way that electric energy is generated when the blades undergo bending vibrations. Concentrated masses, whose values can be varied, are attached to the tips of the blades. Due to the geometric shape of the harvester, in which the four blades are oriented forming right angles, the harvester is named cruciform. As opposed to the large majority of previous works on the subject, in which harvesters are excited at their bases by prescribed acceleration, herein the harvester is connected to a vibrating structure excited by an imbalance force. Hence, the amount of harvested energy depends upon the dynamic interaction between the harvester and the host structure. Laboratory experiments were carried-out on a prototype connected to a tridimensional truss. The experimental setup includes a force generator consisting of an imbalanced disc driven by an electrical motor whose rotation is controlled electronically, a voltage rectifier circuit, and a battery charged with the harvested energy. After characterization of the dynamic behavior of the harvester and the host structure, both numerically and experimentally, the results of experiments are presented and discussed in terms of the voltage output of the piezoelectric transducers as function of the excitation frequency and the values of the tip masses. Also, the capacity of the harvester to charge a Lithium battery is evaluated.

© Springer International Publishing Switzerland 2016. All rights are reserved.Structural Health Monitoring-SHM-is known as the nondestructive process of online, in service, allowing the systems and structures to monitor their own integrity all along their useful lives. The most important goals in this context are to prevent failures, to increase security, and to reduce maintenance costs. One of the most important available techniques is the so-called impedance-based structural health monitoring, which is the focus of the present chapter. Practical implementations of the technique are described for illustration purposes.

© Springer International Publishing Switzerland 2016. All rights are reserved.This chapter first introduces the basic definitions and concepts related to smart materials and structures. Then, the underlying physical principles and main operational features of some of the smart materials most widely used in engineering applications are described. The potential of the technology of smart materials and structures for innovative solutions of practical problems is put in evidence by the description of some relevant research studies and engineering applications, with the support of relevant bibliographic references. The concepts introduced in this chapter are further developed in the other chapters of the book.

Smart and periodic structures have received the attention of researchers by virtue of their great potential. These structures have powerful properties like adaptiveness and the ability to operate as mechanical filters. Although, the presence of uncertainties must be taken into account to guarantee robustness. Thus, a finite element model is proposed to elucidate the importance of stochastic aspects and to present the concept of robust frequency bandgap. The smart part consists of piezoelectric actuators connected to resonant circuits in a tridimensional truss unit cell. The periodic part is the replication of this cell to assemble the final structure. Floquet/Bloch conditions are used to model the infinite representation. Then, a Monte Carlo Simulation is carried out and the bandgaps' bounds are analyzed considering frequency responses and dispersion diagrams. The goal being to evaluate the influence of uncertainties affecting the prediction of the attenuation zones. Likewise, the consequences of increasing the uncertainty level are evaluated.

This paper deals with attitude and vibration control of a satellite containing flexible solar arrays. The vibration motion is controlled by using piezoelectric transducers as sensors and as actuators. A lab test is conducted with a piezoelectric element bonded on a thin plate for two specific applications, the piezoelectric acting as a sensor and as an actuator. The attitude motion is controlled by using reaction wheels and thruster. For this purpose a mathematical model is developed for a rigid-flexible satellite comprising reactions wheels, thrusters, and piezoelectric transducers to act as sensors and actuators aiming the solar panels vibration control. The Finite Elements method is used to model the piezoelectric elements and the solar arrays. The method is combined with the Lagrangian formulation to obtain the complete mathematical model of the spacecraft taking into account the attitude and the vibration coupled motions. The sensor mathematical model involves the electric potential in addition to the conservative potential energy associated with the elastic properties of the piezoelectric element. The Linear Quadratic Regulator controller is designed for the attitude and vibration control. The MatLab software is used to simulate the dynamics of the system. The interaction between the attitude and the vibration motion is analyzed as well as the performance of the piezoelectric actuator to damp the vibration motion of the solar arrays.

© 2016 Elsevier B.V. All rights reserved.Since Grätzel and O'Regan started in 1991, dye-sensitized solar cells (DSSC) have been extensively studied around the world. In addition to increasing efficiency, their characteristics such as low cost materials and inexpensive manufacturing processes are attractive for organic solar cells. Several parts of DSSC devices are being researched such as semiconductor engineering, low cost counter electrodes, electrolytes, and dyes. In this work, platinum (Pt) thin films were deposited by sputtering technique to produce counter electrodes for DSSC. The films were characterized by profilometry, elipsometry, four-point probe sheet resistance, spectrophotometry, and electrochemical impedance spectroscopy. The electrode response was also compared to that built from a commercial platinum solution. The results allow us to determine the minimum Pt film thickness necessary to achieve a relevant reduction of the sheet resistance and charge transfer resistance, which preserve a significant electrode transparency. The 22 nm and 24.8 nm thick films combined low charge transfer resistance and good transparency. The 122 nm Pt film presented the lowest charge transfer resistance.

© 2016 Elsevier Ltd. All rights reserved.Numerical software based on the tridimensional diffusion equation with a moving source, a phase change and heat flux estimation by the non-linear interactive Broydon-Fletcher-Goldfarb-Shanno (BFGS) inverse technique was used to study the heat affected zone (HAZ) in GTA aluminum 6065 T5 alloy welding. GTA welding experiments were performed using thin aluminum plates in four t+ experimental conditions. In previous studies, the authors determined that the peak temperature tends to increase as the positive polarity becomes higher. To confirm this behavior, the samples were cut on the welded region and later characterized using an optical microscope (OM) and a scanning electronic microscope (SEM). The heating and cooling rates, determined from an in-house code, were compared with the microstructures and the grain size of the HAZ found in the samples. The results revealed a linear correlation between the grain size on the HAZ and the positive polarity. The study also showed that a significant change in the microstructure occurs during the process while the GTAW torch is still turned on. After the welding, when the GTAW torch was turned off, the cooling rate was the same for all welded zones, which indicates that the microstructural changes had already occurred.

© 2016 IEEE.Satellite simulators are developed in the context of a space mission lifecycle to represent the real behavior of a satellite during operation and may be used for different purposes. To attend a particular purpose new functions are added or modified according to the mission phase needs, requiring models re-adaptation in a system evolving concept. The process of verification of satellite simulator software requires high-efficiency in accomplishing realistic functional and behavioral requirements. Based on the complex set of requirements the satellite behavior is represented in the simulator through software models specified by tables of cause-effect rules. Considering that the Satellite Simulator is an evolving systems and it needs to assure that the logic implemented in the simulator conforms to the requirements, the manual verification process becomes impracticable, therefore demanding a compatible verification approach. The approach suggested here unifies two techniques Conformance and Fault Inject (CoFI), constructed on Model-Based Testing and Model Checking added to a method so that it can translate the tables of cause-effect rules into finite state machines. This paper presents the verification approach illustrating it with the Data Collection Subsystem (DCS) model of the CBERS satellite simulator being developed at National Institute for Space Research (INPE).

© Emerald Group Publishing Limited.Purpose-This paper aims to propose an evaluation method to compare two different Human-Robot Interaction (HRI) solutions that can be used for on-line programming in an industrial context: a force guidance system and the traditional teach pendant operation. Design/methodology/approach-The method defines three evaluation criteria (agility, accuracy and learning) and describes an experimental approach based on the analysis of variance to verify the performance of guidance systems according to these criteria. This method is used in this paper to compare the traditional teach pendant interface with an implementation of a force guidance system based on the use of an external force/torque sensor. Findings-The application of the proposed method to an off-the-shelf industrial robot shows that the force guidance system has a better performance according to the agility criterion. Both solutions have a similar performance for the accuracy criterion, with a limit of about 2 mm in the achieved position accuracy. Regarding the learning criterion, the authors cannot affirm that any of the methods has an improved agility when the operator repeats the tasks. Practical implications-This work supports the selection of guidance systems to be used in on-line programming of industrial applications. It shows that the force guidance system is an option potentially faster than the teach pendant when the required positioning accuracy is greater than 2 mm. Originality/value-The new method proposed in this paper can be applied to a large range of robots, not being limited to commercial available collaborative robots. Furthermore, the method is appropriate to accomplish further investigations in HRI not only to compare programming methods but also to evaluate guidance systems approaches or robot control systems.

This work addresses the modeling and control of fluid-structure systems. In the first part, the port-Hamiltonian systems (PHS) formulation is used for modeling fluid-structure interactions. This formulation allows describing fluid dynamics and structural dynamics separately and coupling the subsystems easily through physically relevant interconnection ports, which naturally arise in the PHS models. The modeling method is validated on the experimental set-up available at ISAE. The second part is devoted to the control of sloshing using damping injection, that is a classical passivity-based control method, in order to reduce vibrations in flexible structures. One difficulty of this approach is that collocated (and power conjugated) actuators and sensors are needed. This paper presents a method for dealing with damping injection in mechanical systems with non-collocated inputs/outputs making use of a state observer. Finally, control by damping injection is performed, and the overall method is successfully tested on the experimental device.

© 2016A model reduction method for infinite-dimensional port-Hamiltonian systems with distributed ports is presented. The method is applied to the Euler-Bernoulli equation with piezoelectric patches. The voltage is considered as an external input of the system. This gives rise to an unbounded input operator. A weak formulation is used to overcome this difficulty. It also allows defining a discretization method which leads to a finite-dimensional port-Hamiltonian system; the energy flow of the original system is preserved. Numerical results are compared to experimental ones to validate the method. Further work should use this model to couple the approximated equations with a more complex system, and to design active control laws.

© 2015 by Danilo C. Branco and Flávio Luiz S. Bussamra.The damage tolerance analysis, which uses the force structural management plan, is usually employed in airplane fatigue life prediction. This plan, based on a mission "mix" defined at the airplane structure design phase, induces the squadrons to follow this mix and interferes in the fleet's usage efficiency. Deviations in the mission mix have impacts on inspection intervals and maintenance costs. In this paper, a fatigue life monitoring system is proposed. It is able to incorporate each mission, individually, in a specific aircraft's fatigue life analysis, adjusting the maintenance plan into a more realistic usage profile, based on the individual aircraft tracking methodology. This monitoring system is implemented in a computer software and it is applied to F-5E fighter aircraft of the Brazilian Air Force. In addition, experimental fatigue tests that simulate critical locations of this aircraft are compared with the proposedmonitoring system, which shows ability to predict, in conservative and approximate ways, the crack length after each flight, disregarding the predefined mission mix. This makes the flexibilization of the operations possible without jeopardizing the inspection and maintenance planning.

© 2016, Brazilian Association of Computational Mechanics. All rights reserved.Hybrid quasi-Trefftz finite elements have been applied with success to the analysis of laminated plates. Two independent fields are approximated by linearly independent, hierarchical polynomials: the stress basis in the domain, adapted from Papkovitch- Neuber solution of Navier equations, and the displacement basis, defined on element surface. The stress field that satisfies the Trefftz constraint a priori for isotropic material is adapted for orthotropic materials, which leads to the term “quasi”. In this work, the hexahedral hybrid quasi-Trefftz stress element is applied to the modeling of nonsymmetric laminates and laminated composite plates with geometric discontinuities. The hierarchical prefinement is exploited.

© 2016 Elsevier B.V.This work presents a plasma torch able to operate at supersonic regime with axial injection of feedstock. In contrast to commonly used linear scheme, the principal axis of the plasma torch is perpendicular to feedstock injection direction, which is aligned with coming out plasma jet. The plasma torch has slightly ascending current voltage characteristics and fixed arc length. Electrical, thermal and kinetic characteristics outlined from comparison with conventional linear plasma spray torches are intermediate between APS, HVOF and VPS. The plasma torch developed in this work has an elevated arc voltage (370 V) and low arc current (100 A), which contribute to increase the electrode life and decrease the arc voltage relative fluctuation (10%). According to in-flight particle monitoring the CoNiCrAlY particles were sprayed at 500 m/s and temperature of 2400 °C, whereas the 7%YSZ at 491–683 m/s and 2535–2636 °C.

© 2016 American Chemical Society.In this study, the authors have presented a numeric model (NM) for application to naphthalene (C10H8) conversion via ionization reaction in a microwave air plasma torch. The NM has included a pressure-independent enhanced electron energy distribution function (EEDF) and cross-section calculation, enhanced by a new formula of phase shift determination. Based on the validated NM, electron density ne and O2+, O-, C10H8, N2, and O2 particles densities were calculated, as well as the conversion rate of C10H8 molecules was predicted. The predicted results showed that the ionization impact on C10H8 molecules conversion has not exceeded 0.81 × 10-10%. Based on the calculated collision cross-section of each species (O2, N2, and C10H8) of carrier gas, the authors suggested using cubic polynomial approximations of the cross-section curves with R-Square (COD) parameter R2 = 99%. MW power increasing in the range 1.75-20 kW has raised the electron density in the range (0.5-4.5) × 1012 m-3. The maximal effect of electron density decreasing with pressure increasing was simulated at values of MW power greater than 7.5 kW. Herewith, pressure increasing and MW power increasing have not had any significant effect on the average electron energy.

© 2016 American Chemical Society.In this paper, a naphthalene (C10H8) thermal cracking model is presented. The model is based on a simple model that takes into account the microwave (MW) plasma thermal influence on naphthalene cracking, accompanying its steam reforming reactions. The temperature level of 1573 K was established for complete C10H8 cracking at 1.75 kW plasma power. High conversion efficiency of C10H8 is achieved varying the air flow rate in the range of 0.6-1.2 m3/h. The model approximates the characteristics of the considered MW plasma to thermal plasma in local thermodynamic equilibrium (LTE). Experimental data have good agreement with calculated data at the cited region of the air flow rate and power. Conversion efficiency up to 99.36% was obtained.

© 2016 Elsevier B.V. The effect of carbon nanotube treatment on the mechanical property of polyethylene/carbon nanotube composite (HDPE/CNT) was investigated. CNTs were initially treated with HCl and then with H 2 SO 4 /HNO 3 . Nanocomposites reinforced with untreated and treated CNTs were prepared by a mechanical mixture of the molten polymer. The results demonstrated a correlation among the surface treatment, dispersion and mechanical properties of HDPE/CNT composites. Raman spectroscopy and TGA analysis showed that both acid treatments removed efficiently amorphous carbon and residual metal catalysts of CNTs. However, these treatments not only removed impurities, they also decreased the crystallinity degree of CNTs due to the addition of oxygenated functional groups to the CNTs walls, as observed by XPS analysis. SEM micrographs revealed that the functional groups improved the CNTs dispersion in the polymeric matrix, resulting in an improvement of the mechanical properties of nanocomposites.

© 2016 Elsevier B.V. All rights reserved.Due to its high efficiency, low cost and a simple operation, the adsorption process is an important and widely used technique for industrial wastewater treatment. Recent studies on the removal of artificial dyes by adsorption include a large number of adsorbents, such as: activated carbon, silicates, carbon nanotube, graphene, fibers, titanates and doped titanates. The carbon insertion in the TiO2 structure promotes a synergistic effect on the adsorbent composite, improving the adsorption and the charge-transfer efficiency rates. However, there are few studies regarding the adsorption capacity of TiO2/Carbon composites with the carbon concentration. This study evaluates the effect of carbon (resorcinol/formaldehyde) insertion on TiO2 structure through the adsorption process. Adsorbents were prepared by varying the carbon weight percentages using the sol-gel method. The physicochemical properties of the catalysts prepared, such as crystallinity, particle size, surface morphology, specific surface area and pore volume were investigated. The kinetic study, adsorption isotherm, pH effect and thermodynamic study were examined in batch experiments using methylene blue as organic molecule. In addition, the effect of carbon phase on the adsorption capacity of TiO2-carbon composite was deeply investigated. SEM micrographs showed that TiO2 phase grows along the carbon phase and FT-IR results showed the presence of Ti-O-C chemical bonding. The experiments indicate that the carbon phase acted as a nucleation agent for the growth of TiO2 during the sol-gel step, with a TiO2 structure suitable for blue methylene adsorption, resulting in a material with large surface area and slit-like or wedge-shaped pores. Further experiments will show the best carbon concentration for methylene blue adsorption using a TiO2 based material.

Nanostructures based on ZnO have been widely studied due to their electronic and piezoelectric properties. Experimental studies have shown that thin films based on ZnO can be used as chemical and optoelectronic sensors. The great goal of this work is to study of the role of the number of graphene-like layers in the physical properties of the ZnO. Therefore, the geometrical and electronic properties of graphene-like structures will be compared with the wurtzite one. In this work, the pn-type semiconducting behavior of the graphene-like structures and its relationship with the number of layers will be also analyzed.

© 2015 Elsevier B.V. All rights reserved. The adsorption of H 2 O molecules on metal surfaces is important to understand the early process of water corrosion. This process can be described by computational simulation using molecular dynamics and Monte Carlo. However, this simulation demands an efficient description of the surface interactions between the water molecule and the metallic surface. In this study, an effective force field to describe the iron-water surface interactions was developed and it was used in a molecular dynamics simulation. The results showed a very good agreement between the simulated vibrational-DOS spectrum and the experimental vibrational spectrum of the iron-water interface. The water density profile revealed the presence of a water double layer in the metal interface. Furthermore, the horizontal mapping combined with the angular distribution of the molecular plane allowed the analysis of the water structure above the surface, which in turn agrees with the model of the double layer on metal surfaces.

© The Author(s) 2016.Graphene is a new member of the nanocarbon family that has revolutionized the field of materials science and has attracted much attention due to its exceptional properties. Recent progress has shown that graphene-based nanocomposites can be used in nanoelectronics, touch screens, optics, catalysis, supercapacitors, fuel cell transistors, flexible electronics, H2 storage, and polymer nanocomposites. The functionalization is a surface modification much used to reduce the cohesive force between the graphene sheets and also to manipulate the physical and chemical properties. The aim of this book was to provide a comprehensive scientific progress of graphene, containing topics such as synthesis, characterization, and application of functionalized graphene. The characterization of the functionalized graphene is extremely important for determining the physicochemical properties of the material obtained after the functionalization treatments. However, this characterization is rarely addressed in books or in review articles. Generally, the functionalization reviews are too wide-ranging, discussing the functionalization of various materials (e.g., nanomaterials) or too specific, analyzing only one functionalization agent (with some specific chemical group, for example). This book, however, proposes to discuss the functionalization of one of the most widely used nanomaterials in recent years: graphene. Thus, the reader will find information on graphene functionalization, using several functionalization agents, in the same book.

© The Author(s) 2016.Carbon nanotubes (CNTs) have unique structures, comprising diameters of few nanometers and length of several hundred nanometers, which provides outstanding mechanical, electrical, and thermal properties. Since their discovery in 1991, CNTs have received much attention and are a worldwide research subject due to their wide range of applications as biosensors, drug delivery, electrochemistry, nanoelectronics, superconductors, nanowires, graphene nanoribbons, nanocomposite materials, and so on. The functionalization treatments can enhance the usual CNT poor dispersion in solvents and improve their interactions with other materials, improving their technological application. Then, carbon nanotube is an extremely hot topic, and every day new research papers are published on this subject. This book contains complete and current reviews on CNT topics, such as synthesis, characterization, and application of functionalized CNTs. The characterization of functionalized CNTs is extremely important for determining the real physicochemical properties of the material obtained after functionalization treatments. However, this characterization is rarely addressed in books or review articles. Generally, the functionalization reviews are too wide-ranging, discussing the functionalization of various materials (e.g., nanomaterials), or too specific, analyzing only one functionalization agent (with some specific chemical group, e.g.). This book, however, proposes to discuss the functionalization of one of the most widely used nanomaterials in recent years: carbon nanotube. Thus, the reader will find information on CNT functionalization, using several functionalization agents, in the same book.

© 2016 Elsevier B.V.The present study concerns a detailed analysis of flow boiling phenomena under high pressure systems using a two-fluid Eulerian approach provided by a Computational Fluid Dynamics (CFD) solver. For this purpose, a vertical heated pipe made of stainless steel with an internal diameter of 15.4 mm was considered as the modeled domain. Two different uniform heat fluxes and three saturation pressures were applied to the channel wall, whereas water mass flux of 900 kg/m2 s was considered for all simulation cases. The model was validated against a set of experimental data and results have indicated a promising use of the CFD technique for estimation of the wall temperature, the liquid bulk temperature and the location of the departure of nucleate boiling. Changes in factors applied in the modeling of the interfacial heat transfer coefficient and bubble departure frequency were suggested, allowing a better prediction of the void fraction along the heated channel. The commercial CFD solver FLUENT 14.5 was used for the model implementation.

© 2016 Elsevier Ltd and IIRRefrigeration equipment as the compressor has had its size reduced and cooling capacity increased in the last years, which leads to a continuous rise of the level of heat flux dissipated through the compressor shell and may cause reliability issues related to the compressor's moving parts. Furthermore, extreme conditions as high ambient temperatures augment the importance of keeping the compressor shell temperature under safe limits. To overcome such difficulties, a novel vapor-compression refrigerating loop was created especially for the compressor thermal management. A cooling unit was assembled using the proposed loop and later compared experimentally with two thermoelectric coolers under ambient temperatures of 25, 35 and 55 °C. The results have shown that the novel refrigerating loop enables the vapor-compression unit to work at a high ambient temperature (55 °C) and nearly a two times higher coefficient of performance (COP) was achieved, when compared to thermoelectric solutions.

© 2016 Elsevier LtdAir-conditioning applications using propane (R-290) have several environmental and thermodynamic advantages over more commonly used refrigerants, such as R-410A and R-22. This paper presents the development of a mathematical model for variable capacity air conditioning systems that use R-290/POE ISO 22 as refrigerant/lubricant. The thermodynamic performance of the refrigeration system is evaluated in terms of the SEER (Seasonal Energy Efficiency Ratio). The thermodynamic properties of the refrigerant/lubricant mixture were obtained from a departure-function approach using the Peng-Robinson equation of state. The effect of the oil on the condenser and evaporator heat transfer coefficients and pressure drops was also taken into account. Sub-models were developed for each component of the air conditioning system, including the connecting lines and the scroll compressor. Furthermore, an air conditioner experimental calorimeter was constructed and tested in order to validate the proposed model.

© 2016 The Author.The analysis based on the second law of thermodynamics of a lightweight vapor compression refrigeration system is presented. A small-scale linear compressor was applied in a DC-powered portable cooler for vehicles and for the medical field, using finned-tube heat exchangers and R600-a (Isobutane) as the working fluid. The cooler was tested in an environmental chamber (with controlled temperature and humidity) under three different ambient temperatures (21, 25 and 32 °C) in order to measure key parameters of the system, such as cooling capacity, power consumption and internal air temperature. For the comparison of thermodynamic irreversibilities, a conventional vapor compression refrigerating system was also tested under the same ambient conditions. Results indicated that the system with the proposed lightweight system kept the lowest internal air temperature with higher coefficients of performance, showing how a lightweight cooling unit can enlarge the use of refrigerating systems due to its attributes.

© 2016 Elsevier LtdA precedent study about the effects of obesity on exergy behavior concluded that higher body fat per se does not lead to higher mortality among obese people; the focus must be turned to obesity-related diseases. Therefore, the next step towards the understanding of the effects of pathologies on the exergy behavior of human body is to analyze human heart. In the present work, an exergy model of human heart is developed. The heart is divided into two control volumes: the left heart, which pumps arterial blood from the lungs to the organs, and the right heart, which pumps venous blood from the organs to the lungs. Exergy of metabolism, exergy transfer associated to heat of metabolism, difference of exergy of blood flows and performed work are taken into account in the exergy balance for normotensive and hypertensive people under different levels of exercise. The left part of the heart is always responsible for more than 80% of the total exergy destruction. Moreover, a hypertensive heart destroys more exergy; this surplus value, when integrated along life cycle, represents 170 MJ/kg of destroyed exergy, which, according to the rate of living theory, would lead to a loss of 4.4 years in life expectancy.

© 2016 University of Ljubljana.Arteries can be compared to industrial pipes, being also susceptible to local pressure drops that may occur due to narrowing of the artery at some point, which is called stenosis. This phenomenon is taken as a singularity in the blood flow that leads to a localized head loss and, consequently, irreversibilities. In the present work, the exergy destruction in a given artery due to a stenosis is determined as a function of the diameter reduction taking into account the exergy variation of the flow between the inlet and the outlet, caused by distributed and localized head losses. The contribution of the stenosis is determined based on experimental results available in the literature. Arteries located in four different segments of the body are evaluated: trunk, leg, arm and neck. From the results, it can be noted that the effect of the severity of the stenosis is more pronounced for reductions higher than 55%. From this point on, the exergy destruction increases exponentially. It is also observed that, despite showing different behaviors for individual parcels, the total destroyed exergy rate of stenotic arteries of the leg and the trunk are very similar for high severities. Meanwhile, the arm presents the lowest values. About the contribution of the stenosis to the total destroyed exergy, the segment less susceptible was the trunk. When the specific destroyed exergy due to the stenosis is analyzed, it becomes clearer the impact of the mass flow rate. In this case, the highest values are obtained in the leg, followed by the neck, the trunk and the arm.

© 2016, Journal of Aerospace Technology and Management. All rights reserved.Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.

© 2016 Elsevier Ltd. All rights reserved.The increase in electricity demand in Brazil and the frequent interruptions in its supply forced the industry and commerce use stationary generator sets, mainly in large urban centers like São Paulo. This city established a decree in order that these devices use cleaner fuels than diesel oil, or adopt post-gas treatment systems, since there are no national regulations for generator sets emissions. To meet this decree, ethanol appears as a good option because it is an environmentally friendly fuel, does not affect the ozone layer, since it is obtained from sugarcane, which helps to reduce the carbon dioxide emissions to the atmosphere through photosynthesis in sugarcane field. Within recommended specifications ethanol can be blended with diesel and gasoline, but can also be used without additives, without damaging the engine. The ethanol availability in Brazil and its consolidation in the automotive market make it an alternative for use in generator sets. The aim of this work was to characterize the performance of a heavy duty Otto cycle engine, developed based on 12 l diesel longblock, prepared to run on ethanol without additives, as a prototype generator set. The performance tests of the generator set were conducted at three different altitudes. A load bank was used to simulate the real electrical load in five different power settings. The performance characteristics obtained experimentally were compared with results obtained with a one-dimensional model using the commercial software GT-Power®. The results obtained during the development phase showed that the engine achieve up to 39.6% of the brake efficiency and a peak power of the 326 kW. The maximum electrical power achieved by the generator set was 302 kW at sea level and 278 kW at 1640 m, according to the employed methodology. The results showed that is feasible to use ethanol without additives for the energy generation, replacing diesel oil in heavy-duty engines, operating in the evaluated steady state condition.

© 2016 Elsevier Ltd.This paper investigates the microstructure and the mechanical properties of β-tricalcium phosphate (β-TCP) three-dimensional (3D) porous materials reinforced with 45S5 bioactive glass (BG). β-TCP and β-TCP/x%-BG scaffolds with interconnected pores networks, suitable for bone regeneration, were fabricated by gel-casting method. Mechanical properties, porosity, and morphological characteristics were evaluated by compressive strength test, scanning electron microscopy (SEM) and X-ray microtomography analysis, whereas the structures were fully explored by XRD, and Raman spectroscopy. To the best of our knowledge, this is the first time where the mechanism for understanding the effect of bioglass on the mechanical properties and microstruture of β-TCP/45S5-BG scaffolds has been systematically studied. The findings showed that ionic product lixiviated from 45S5 bioactive glass, rich in silicon species and sodium ion, catalyzes a phase transition from β-TCP to Si-TCP by replacement of phosphorus for silicon and contributes to the improvement of scaffolds mechanical properties. The compressive strength of β-TCP/5%-BG and β-TCP/7.5%-BG was improved around 200% in comparison to pure β-TCP. Osteoblast-like cells (MG 63) were exposed to the materials for 24 h through the use of medium conditioned by β-tricalcium phosphate/bioactive glass. Cell viability was measured by MTT assay in the cells and the data obtained were submitted to ANOVA, Tukey[U+05F3]s multiple comparison (p<0.05). The β-TCP/7.5-BG promoted an increase of cell proliferation. The results suggest that compositions and processing method studied may provide appropriate materials for tissue engineering.

© The Author(s) 2016.Platinum (Pt) based electrocatalysts have electrochemical performance that outperforms many other noble metal and metal oxide based materials. Increasing performance allows a reduction in the platinum load, and thus reduce the cost of various devices such as fuel cells. A double pulse electrochemical approach was developed to nucleate and grow Pt nanoparticles into flower shaped assemblies on graphene sheets. The unique morphology and structure of the Pt were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM). The electrocatalytical activities of the Pt nanoflowers were evaluated using methanol and ethanol oxidation as model reactions. This proposed method has led to the synthesis of Pt nanoflowers with the ability to control, both their density and their size on defect free graphene.

© 2016, Springer Science+Business Media New York.The possibility of a reverse strain-induced martensitic transformation (RSIMT) of ferrite into austenite was evaluated in two duplex stainless steels (DSS) solution treated at 1000, 1100, and 1200 °C. For each temperature, we evaluated the effect of stress–strain state (tensile tests—triaxial; compression tests—uniaxial, and plate rolling—biaxial) on the reverse martensitic transformation behavior. For each strain level, the ferrite volume fraction was measured with a ferritscope, and finite element analyses allowed the correlation of the stress–strain states to the total transformed ferrite. X-ray diffraction and metallographic analyses showed that microstructures of all samples are composed only by ferrite and austenite, and the general trend of lower ferrite contents associated to higher strains corroborates the hypothesis of RSIMT of the ferrite in austenite. The amount of martensitic transformation is proportional to equivalent strain or to the respective strain energy, but different stress–strain states lead to different transformation behaviors. In the triaxial stress state during necking, the amount of transformed ferrite by RSIMT in a specific strain energy level is higher than that obtained in the biaxial stress state of the plate rolling, which in turn is higher than that observed for uniaxial stress state generated by compression tests. It can be then concluded that different strain states, and not only the amount of plastic deformation, affect the behavior of the RSIMT of ferrite in austenite of DSS.

Ti-50.13Ni and Ti-49.62Ni (at.%) shape memory alloy ribbons were fabricated by melt-spinning method at different circumferential wheel velocities. The effects of wheel velocity, chemical composition and heat treatments on microstructure and Transformation temperature were investigated. Differences in wheel velocity led to differences in cooling rate and sample dimension, as well as in phase transformation temperatures. Two heat treatment conditions were studied, 350°C for 1h and 350°C for 5h. In the samples produced at high wheel velocity and heat-Treated at 350°C for 5h, nanosized Ti-rich precipitates were observed in both chemical compositions. Cross-sectional microstructure was studied by optical microscopy; SEM was used to study the nanometric grains and nano precipitation. The transformation temperatures were analyzed by DSC.

This work deals with structural, electrical and mechanical characterization of Ti-50.13Ni and Ti-49.62Ni (at.%) shape memory alloys (SMAs) fabricated at different circumferential wheel velocities. The effect of wheel velocity, chemical composition and heat treatments are investigated. The characterization of crystallographic phases of the Ti-Ni ribbons was carried out using X-ray diffraction. Electrical resistance variations as function of temperature (δR/R %) were analyzed using a non-commercial technique, which consists in a thermal-adjustable bath apparatus revealing the temperatures of B2→R→B19′ two stage transformation, whereby the presence of R-phase can be definitively confirmed. The Stress-Assisted Two-Way Memory Effect was measured by an own designed apparatus with an Linear Variable Differential Transformer captor and a current controlled heating, and results indicate that the as-spun condition, promotes the Stress-Assisted Two-Way Memory Effect. On the other hand, increments in Ni content tend to decrease transformation temperatures and high wheel velocities help to the R-phase formation.

Copyright © 2016 The Authors.NiTi SMA wire with Ni-free surface is desirable as construction materials for a range of biomaterials to actuators associated to shape memory and superelastic properties. In biomaterials a potential problem with NiTi implant devices is the release of Ni in the human body. This work analyzes the effects of nitrogen plasma based ion implantation (PBII) technique in a wire of NiTi with shape memory effect associated to a Ni-free surface. The samples were treated for 60 min at 741 °C, with 16 kV high voltage pulses. Results of the thermo-mechanical properties of the PBII treated samples showed that there is no effect of the PBII treatment on the shape memory effect when compared to NiTi samples with no PBII treatment, which is desirable for applications addressing Ni-free surface and shape memory effect. Although it was noted that the stress-strain test causes cracks perpendicular to the stress direction on the treated surface.

© 2016 Trans Tech Publications, Switzerland.An in situ high-temperature X-ray diffraction (HTXRD) study in maraging 300 steel was carried out to study the martensite to austenite transformation and effect of time of exposure in the austenite reversion below austenite start temperature. Solution annealed materials were subjected to controlled heating-holding cycles. The first sample was heated at a rate of 10°C/min from room temperature to 800°C, showing that the microstructure is completely martensitic (α110) until 600°C. From 650°C until 800°C, the microstructure is gradually changing from martensitic to austenitic, showed by the increasing peaks of λ111 and reducing peaks of α110. At 800°C the microstructure is completely austenitic (λ111). Another sample was heated at 10°C/min from room temperature to 600°C and held for 4 hours. At 600°C, at 0 h time of exposure, only a martensitic peak was observed. An austenite peak can be observed after some time of exposure at this temperature. The volume fraction of austenite increased with increasing time of exposure at 600°C, reaching 50/50 volume fraction after 4 hours of exposure. XRD diffraction patterns for the same sample that was held for 4 hours at 600°C and then cooled down in air to room temperature showed the same intensity of austenite and martensitic peaks found in situ at 600°C for 4 hours (retained austenite), with the volume fraction of 50/50 of austenite and martensite phases. The HTXRD technique can be used to identify and quantify martensite to austenite transformation and austenite retention.

© 2015 Material Reserch Society.Shape memory alloys (SMA) are metallic attractive engineering materials due to their capacity to store pre-defined shapes through a thermally induced phase transition from a solid state. This paper aims to evaluate the influence of solubilization thermal treatments on a NiTi shape memory alloy originally fabricated by vacuum induction melting and then reprocessed by plasma melting followed by injection molding (Plasma Skull Push Pull process) into different metal molds (steel, aluminum, brass and copper) in order to compare the thermal properties regarding to its raw state. The thermal treatments of solubilization were carried out at 850°C in different times (2n function, n = 0, 1,2 and 3, in hours). The influence of solubilizing treatments in the NiTi shape memory alloy was analyzed using the following characterization techniques: Differential Scanning Calorimetry (DSC) and Electrical Resistance as a function of Temperature (ERT). The results demonstrate that the solubilization heat treatments applied on the reprocessed NiTi shape memory alloy through the plasma skull push pull process, provides important changes in the phase transformation of the material. Therefore, it was demonstrated that it is necessary to solubilize the material after melting or remelting the NiTi shape memory alloy via this process to obtain mini-Actuators products with homogeneous properties.

© 2016 Trans Tech Publications, Switzerland.A study was conducted on the corrosion behavior and characteristics of the passive oxide film of Fe-Mn-Si-Cr-Ni-(Co) shape memory stainless steels (SMSS) in a concentrated nitric acid (HNO3) solution, based on potentiodynamic polarization, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses. The results indicated that Fe-Mn-Si-Cr-Ni-(Co) SMSSs exhibit a passive behavior similar to that of 304L austenitic stainless steel (304L SS). However, unlike 304L SS, their high silicon (Si) content renders them insensitive to intergranular attack in highly oxidizing environments. The XPS analysis also indicated that Si appears to be the main element responsible for the high protectiveness afforded by the passive film formed on Fe– Mn–Si–Cr–Ni–Co SMSS.

© 2016, Journal of Aerospace Technology and Management. All Rights Reserved.In order to quantify ferrite content, three techniques, XRD, ferritoscope and optical metallography, were applied to a duplex stainless steel UNS S31803 solution-treated for 30 min at 1,000, 1,100 and 1,200 °C, and then compared to equilibrium of phases predicted by ThermoCalc® simulation. As expected, the microstructure is composed only by austenite and ferrite phases, and ferrite content increases as the solution treatment temperature increases. The microstructure presents preferred grains orientation along the rolling directions even for a sample solution treated for 30 min at 1,200 °C. For all solution treatment temperatures, the ferrite volume fractions obtained by XRD measurements were higher than those achieved by the other two techniques and ThermoCalc® simulation, probably due to texturing effect of previous rolling process. Values obtained by quantitative metallography look more assertive as it is a direct measurement method but the ferritoscope technique should be considered mainly for in loco measurement.

This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 °C for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 °C. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.

© 2016, Springer-Verlag Berlin Heidelberg.This work presents a comprehensive DFT study on the interaction between hydrazine derivatives with a platinum catalyst surface, which is represented by a tetrahedral Pt4 cluster model. Three separate reaction pathways were investigated; two of which are related to possible pathways of NH3 formation. The first pathway describes the intramolecular transfer of one hydrogen atom in the hydrazine molecule forming the NHNH3 intermediate, then dissociating into NH and NH3. The second describes the addition of one external hydrogen atom to hydrazine forming N2H5, followed by its dissociation to NH2 and NH3. The third reaction pathway involves the formation of N2H3 by means of hydrogen abstraction by an external hydrogen. The reactions were studied in both the absence and the presence of a Pt4 cluster. We find that the assistance of the Pt4 cluster lacks a systematic effect on the reactions barrier heights. It is also shown that the ammonia formation can possibly proceed through the formation of the N2H5 intermediate, leading to more exothermic intermediate steps in the presence of the Pt4 cluster.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.The ITA Candy Rocket Program is a student program of undergraduate students to develop and fly a sounding rocket motor and compete at the Intercollegiate Rocket Engineering Competition. The program was kicked off in August 2011 and every year the design is altered for improvements. This paper shows the solid propellant preparation from easily available raw ingredients. The propellants are potassium nitrate and sorbitol. The potassium nitrate was purified, sieved, and recrystallized. A ground test program with small and real scale tests was conducted to evaluate the motor design and development.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.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. Experiments using real scale rocket models are expensive, therefore simulations are required to decrease the overall project time and cost. Solid propellant geometry and computation of its burning rate are essential for the calculation of pressure versus time and thrust versus time curves. The propellant grain geometry changes during SRM burning are also important for structural integrity and analysis. 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 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 NAWC SRM number 6.

© 2016. Journal of Aerospace Technology and Management. all right reserved.This paper describes the polycarbonate acrylic laminated development that can be applied in aeronautics and aerospace transparencies. The case studied is a laminated double-curved transparency (bubble form) used in an observation side window of a military aircraft. Side windows need strength and specific characteristics, similar to windshields, allowing the perfect visualization and image capture. Laminated transparencies composed by different materials have better qualities than the monolithic ones. This kind of transparency can offer high mechanical and chemical resistance, high transparency, no fragmentation and easy maintenance or recovery. A significant amount of information about materials and processes was jointed in order to build the reinforced transparency and validate this study. The final results were analyzed based on two points of view: mechanic resistance and, especially, optical quality.

© 2016, Springer-Verlag London.This paper demonstrates the advantages reached on project management of automated solutions when a customized QFD method is applied to this specific objective. The main contribution of this paper is a new matrix to support the project manager to plan requirement verifications over project phases, using the team skills based on customer needs. The application of the proposed method can identify a set of requirements for each project phase, which are critical to project success.

© Emerald Group Publishing Limited.Purpose-This paper aims to propose an evaluation method to compare two different Human-Robot Interaction (HRI) solutions that can be used for on-line programming in an industrial context: a force guidance system and the traditional teach pendant operation. Design/methodology/approach-The method defines three evaluation criteria (agility, accuracy and learning) and describes an experimental approach based on the analysis of variance to verify the performance of guidance systems according to these criteria. This method is used in this paper to compare the traditional teach pendant interface with an implementation of a force guidance system based on the use of an external force/torque sensor. Findings-The application of the proposed method to an off-the-shelf industrial robot shows that the force guidance system has a better performance according to the agility criterion. Both solutions have a similar performance for the accuracy criterion, with a limit of about 2 mm in the achieved position accuracy. Regarding the learning criterion, the authors cannot affirm that any of the methods has an improved agility when the operator repeats the tasks. Practical implications-This work supports the selection of guidance systems to be used in on-line programming of industrial applications. It shows that the force guidance system is an option potentially faster than the teach pendant when the required positioning accuracy is greater than 2 mm. Originality/value-The new method proposed in this paper can be applied to a large range of robots, not being limited to commercial available collaborative robots. Furthermore, the method is appropriate to accomplish further investigations in HRI not only to compare programming methods but also to evaluate guidance systems approaches or robot control systems.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents the current status of the development of a new Brazilian Thrust Vector Control (TVC) system, designed for thrust vectoring of the first stages of the Brazil-ian small satellite launch vehicle VLM-1. The TVC system design is brie y described and compared to other systems available in literature. The model philosophy and development strategy is summarized and a verification approach of the vehicle control system, Hardware- in-the-Loop, presented. Experimental data of step responses are analyzed and compared to tests of an actuator flight model of the Brazilian satellite launch vehicle VLS-1.

© 2016 The Authors.In kaizen improvement projects, the stages of analysis, and application of the proposed improvements are often a trial-and-error cycle carried out by direct experimentation. This feature is a major source of uncertainty in resource dimensioning. This paper presents the design and development of a sequence of activities that emphasizes the application of simulation capabilities as a tool to aid the continuous improvement process at discrete manufacturing, in the context of the Lean Manufacturing approach.

© 2016 The authors and IOS Press.This paper presents the integrated product development tool Design for Autonomy for reengineering of foreign complex products. Design for Autonomy is a new member of the Design for X family, which aims at integrating the requirements from the X area, in this case autonomy, into the conceptual phase of the product development process. This tool regards to decision making activities and their outcomes: decisions about the interrelations with the design of products. The objective of Design for Autonomy 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 can be accomplished by the Design for Autonomy model comprising four steps: (1) An analysis to identify critical elements and means for achieving their technological domain; (2) Preparation of nationalization; (3) Reverse engineering of the original product in order to obtain the technological know-how; and (4) Forward engineering including the adaptation for the new environment in Brazil, stimulating improvements and added value. In a pilot project, the Design for Autonomy tool is being successfully applied to the development of a Brazilian thrust vector control system, a subsystem used for attitude control of satellite launch vehicles. The technology originates from the German Aerospace Center (DLR) and is transferred to the Brazilian Institute of Aeronautics and Space (DCTA/IAE).

© 2016This paper presents the current status of the development of a Thrust Vector Control system for new Brazilian launch vehicles, looking for the highest performance by closed-loop servo hydraulic actuator identification. Therefore, a test environment with a mass-spring test bench is introduced. Engineering models of two different types of actuators, three-way and four-way valve controlled pistons with direct drive control valves are developed. The dynamic responses are experimentally determined and subsequently mathematically modeled.

© 2016, Journal of Aerospace Technology and Management. All Rights Reserved.This paper investigates how Knowledge Management patterns in a Brazilian Air Force flight test environment can be simulated using a System Dynamics approach. The research has been conducted initially by a literature review on the main Knowledge Management and System Dynamics theories. Data for this research has been collected in a previous study consisted of documental research regarding the flight test environment Knowledge Management and a questionnaire-based survey which identified both a low Knowledge Management maturity level and the flight test core competence as the capability of performing flight test campaigns. The issued problem was the tradeoff between actions focused on performing flight test campaigns versus Knowledge Management to transfer the core competence inside organization in order to keep it in a high level. A system dynamics quantitative model has been developed as a result of this research. Fluxes and stokes were identified within the model and the relation between them emerged by identifying systemic feedback loops that may compromise the Knowledge Management and the core competence transferring. These features enable a holistic visualization and better understanding of the problem as well as the possibilities of identifying ways of improvement.

© 2015, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional.A study of optimal bi-impulsive trajectories of round trip lunar missions is presented in this paper. The optimization criterion is the total velocity increment. The dynamical model utilized to describe the motion of the space vehicle is a full lunar patched-conic approximation, which embraces the lunar patched-conic of the outgoing trip and the lunar patched-conic of the return mission. Each one of these parts is considered separately to solve an optimization problem of two degrees of freedom. The parameters to be optimized are two: the phase angle of the point at which the space vehicle reaches the edge of the Moon’s sphere of influence and the initial velocity at departure. The Sequential Gradient Restoration Algorithm is employed to achieve the optimal solutions. Analytical and numerical derivatives of expressions describing the lunar patched-conic approximations are utilized to ensure the results. The results based on the patched-conic approximation show a good agreement with the ones provided by literature, and the solution trajectories proved to be consistent with the image trajectories theorem.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This work deals with a preliminary mission analysis to find the best geometrical parameters of the terminal orbits – Low Earth Orbit (LEO) and Low Moon Orbit (LMO) – of an Earth-Moon mission by means of a spatial lunar patched-conic approximation formulated in the present paper. The Earth-Moon transfer problem considers that the terminal orbits are circular, and that all the Keplerian elements of the LEO and of the LMO are prescribed, but the true latitude of the point of the application of the impulses. The transfer problem based on the spatial patched-conic approximation involves the solution of a two-point boundary value problem obtained by means of Newton-Raphson algorithm. After that, a one degree of freedom optimization problem is formulated which minimizes the fuel consumption represented by the total velocity increment. The transfer problem is also formulated considering the dynamics of the Spatial Circular Restricted Three-Body Problem (SCR3BP). A two-point boundary value problem and a one degree of freedom optimization problem are also enunciated for this model. The optimization problems based on the two dynamical models are solved by means of the Sequential Gradient Restoration Algorithm (SGRA). In the present study, only direct ascent maneuvers with a time of flight of 2. 5 to 4. 0 days are considered. The altitude of the LEO and the altitude of the LMO are set equal to 167 km and 100 km, respectively. Numerical results show that the trajectories provided by the patched-conic approximation and the SCR3BP are too close to each one, which enhances the possibility to utilize this patched-conic approximation in a preliminary mission analysis. According to the results, a great amount of fuel consumption can be saved if the longitude of the ascending node of the LMO is chosen properly. By taking advantage of the numerical performance associated to the processing speed of the spatial patched-conic approximation, this model is applied to determine several optimal trajectories by parameterization of the terminal orbital elements to find the best combination of them that minimizes the fuel consumption.

© 2016 The Authors.This work presents experimental results of two damage detection techniques based on modal properties, with the application on a full-size composite helicopter main rotor blade. The damage detection methods used in this study are the coordinate modal assurance criterion (COMAC) and the modal strain energy method, which are respectively based on the comparison of vibration modes and on the comparison of the modal strain energy of a beam. Modal parameters were obtained with experimental modal analysis and damage was introduced artificially on the blade by attaching a small mass to it, changing its global properties in this way. Finally, experimental results for the damage detection technique are shown for both methodologies, and remarks concerning sensitivity and robustness of the methods are discussed.

© 2016, Journal of Aerospace Technology and Management. All rights reserved.The Operational Modal Analysis technique is a methodology very often applied for the identification of dynamic systems when the input signal is unknown. The applied methodology is based on a technique to estimate the Frequency Response Functions and extract the modal parameters using only the structural dynamic response data, without assuming the knowledge of the excitation forces. Such approach is an adequate way for measuring the aircraft aeroelastic response due to random input, like atmospheric turbulence. The in-flight structural response has been measured by accelerometers distributed along the aircraft wings, fuselage and empennages. The Enhanced Frequency Domain Decomposition technique was chosen to identify the airframe dynamic parameters. This technique is based on the hypothesis that the system is randomly excited with a broadband spectrum with almost constant power spectral density. The system identification procedure is based on the Single Value Decomposition of the power spectral densities of system output signals, estimated by the usual Fast Fourier Transform method. This procedure has been applied to different flight conditions to evaluate the modal parameters and the aeroelastic stability trends of the airframe under investigation. The experimental results obtained by this methodology were compared with the predicted results supplied by aeroelastic numerical models in order to check the consistency of the proposed output-only methodology. The objective of this paper is to compare in-flight measured aeroelastic damping against the corresponding parameters computed from numerical aeroelastic models. Different aerodynamic modeling approaches should be investigated such as the use of source panel body models, cruciform and flat plate projection. As a result of this investigation it is expected the choice of the better aeroelastic modeling and Operational Modal Analysis techniques to be included in a standard aeroelastic certification process.

© 2015, The Brazilian Society of Mechanical Sciences and Engineering.The acoustic design of cavities is an important task in a variety of engineering applications, from automotive or aerospace industries to equipment coating designs. In this work, the acoustic impedance functions (a frequency domain model) were calculated using analytical, numerical, and experimental methods. Those different approaches were presented in a unified manner in order to allow comparisons among them. The relationship of the impedance function and a classical frequency response function (FRF) was also established. A circular duct of rigid walls was assumed with different boundary conditions as closed end, as well as opened and absorbed extremities. Three duct configurations were implemented in order to compare analytical, numerical, and experimental results. Finally, it could be possible to evaluate some aspects that are characteristic of a large range of acoustic systems applications as the existence of complex modes and frequency-dependent behavior of absorption material. This study aims the usage of the impedance functions to analyze the acoustic behavior of cavities, as well as to compose the background in order to develop, in the future, an acoustic modeling process using impedance functions.

Complex modes are commonly observed in systems where damping acts locally, i.e., in cases the damping distribution is not uniform. The present work aims to compare the natural modes resultant from different boundary conditions of a cavity, considering a circular duct of rigid walls as the cavity under test. In one end, a volume velocity source was installed. At the other end, were considered four cases: closed end, open end, and two absorbing ends with different thickness. An Acoustic Experimental Modal Analysis was performed, in order to evaluate the mode shapes, using as basis a set of Acoustic Impedance Functions. Quantitative (phase scatter) and qualitative (variation of the node location) analysis were performed to estimate the "complexity" of the mode shapes. The comparison among the resultant complex mode shapes for each boundary condition showed the relation between the level of resistance and its effect in the complex modes.

The most common and established way of performing experimental modal analysis is to use acceleration based transducers that lead to the calculation of the displacement mode shapes. However, the use of strain measurements for experimental modal analysis has recently gained a lot of popularity. Not only there are applications where the use of strain measurements makes for a more attractive and interesting option, such as structural health monitoring methods, but there are also applications where sensor size and placement might be critical and therefore strain sensors are the most eligible candidate. This work has as the main focus of research the use of strain sensors for experimental modal analysis. In this sense, experimental methodologies and improvements on the current ways of carrying out strain modal analysis are presented, paying particular attention to the relationship between strain and displacement modes. This study of the strain displacement relationship led to the development of a scaling methodology for strain modes and is used to demonstrate the presence of reciprocity under certain conditions. To validate the proposed methodologies, beam and plate structures will be analyzed and experimental results will be shown.

Copyright © 2016 by ASME.Increasingly, the product development industry coexists with highly complex and integrated systems, parallel to the search for engineering tools that are not difficult to use, reduce the complexity and effort to successfully model the systems and, at the same time, provide reliable results. In this context, to demonstrate the differences between the signal-port and the multi-port modeling approaches, and to analyze the modeling effort demanded by each, this work aims at building, in MATLAB/Simulink® and LMS Imagine. Lab AMESim, a model of flight control's electro-hydrostatic actuator (EHA). Further, this same EHA system is built in a model that integrates both environments. Simulations then provided data for performance comparisons and conclusions about the possible gains of this integration, for industrial research & development purpose. Lastly, the physical nonlinear EHA AMESim model is linearized, rendering a transfer function model, available to be used in linear control studies in MATLAB-Simulink.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.This paper presents the dynamic analysis of an unmanned tethered airship in hovering flight using a stability augmentation system. A comparison between tethered aerostats and airships is made, and the benefits and issues related to a tethered airship are highlighted. Since airships are not designed to be stable as tethered aerostats, a stability augmentation system is implemented in the flight control system. The dynamic equations of motion and the controller for the tethered airship are described. A linearized model is obtained by finite difference approach and the gains are obtained using LQR technique. The details of the flight control system and experimental set up are provided. Outdoor flight testing of the tethered airship was conducted and the stability of natural dynamics and active control response was analyzed in the time domain using flight test data. The results obtained validated the closed-loop system for the range of wind condition tested once the stability augmentation is achieved.

© The Society for Experimental Mechanics, Inc. 2016.Experimental modal analysis is commonly associated with the use of simulation models for validation, correlation and model updating. However, this interaction between simulation and test is constantly evolving, not in the least because it can be applied to model-based design engineering in the broad sense. Over time, new simulation methods have emerged and consequently, new approaches combining experimental and numerical methodologies are needed and possible. Model Based System Testing (MBST) is an innovative paradigm that allows to structure this process and, in particular, to investigate how the well-established modal testing and analysis procedures and ways of working can be adopted to the multiphysical nature of mechatronic systems. As a result, many possibilities arise: test data can be used to validate multiphysical models, models help gaining insights into test conditions, hybrid approaches allow combining testing and simulation on hardware-in-the-loop and system-in-the-loop test benches, where physical systems can be combined with simulation models to apply loads and more realistic test conditions, as well as the use of data coming from feedback control system information for testing purposes. In this paper, the context and concepts of MBST will be introduced, and application examples will be shown, highlighting the advantages of such a methodology.

© The Society for Experimental Mechanics, Inc. 2016.Strain modal analysis has been used for a long time as an alternative way of identifying the vibration modes of a structure, whenever the use of accelerometers is not suited (such as in aerospace applications) or when information about the dynamic strain levels in the structure is required (e.g. structural health monitoring or durability applications). However, some practical aspects of strain-based modal analysis are not always studied in such applications. For instance, how to visualize and interpret multi-directional modal strain is still an open topic. Similarly, the optimal way to correlate and distinguish these strain modes is also not usually discussed. This work will focus on clarifying some concepts related to multi-directional strain, and will show some examples on how modal strain in multiple directions can be better interpreted. For this purpose, the use of strain gauges (and strain rosettes) for modal analysis in two-dimensional structures will be introduced and some insights will be given on how to properly measure and interpret normal and shear strain modes and how to carry out modal correlation. Finally. these concepts will be applied to numerical and experimental examples.

© 2016 IAA.This paper deals with Earth-to-Moon transfers in the patched three-body approach, in which the Sun-Earth-Moon-Spacecraft four-body system is approximated by two coupled Circular Restricted Three-Body Problems (CR3BP). This approach provides preliminary solutions that can be numerically refined into full four-body solutions. The standard transfers in this approach are low-energy manifold guided solutions with long transfer time which connect transit and non-transit orbits of each three-body system. Besides the standard transit-non-transit connections, there are alternative solutions involving a bi-parametric family of quasi-periodic orbits around the Earth. These solutions connect quasi-periodic orbits on two-dimensional tori of the Sun-Earth-Spacecraft system with L1 or L2 transit solutions of the Earth-Moon-Spacecraft system to provide transfers with lunar ballistic capture and short flight time. We review the dynamical elements employed to obtain the different classes of transfers and give examples of solutions obtained from sets of initial conditions around the Earth that are consistent with current infrastructure for space exploration.

Copyright © 2016 by Priscilla Sousa-Silva, Maisa O. Terra, Collin R. McInnes, and Matteo Ceriotti.The problem of finding optimal trajectories is essential for modern space mission design. In order to obtain low-cost solutions, the models employed in mission analysis have become more realistic, considering multi-body gravitational dynamics, enabling orbits that do not exist in two-body dynamics. Besides that, the missions have increased in complexity, exploiting both low-thrust and high-thrust, including alternative forms of propulsion such as solar sailing. In this context, sets of good initial guesses are fundamental for the convergence to local or global optimal solutions, using both direct or indirect methods available to solve the optimal control problem. Thus, this paper deals with producing trajectories in the patched three-body approach that are designed to be good initial guesses as input to search optimal low-energy short-time Earth-Moon transfers with ballistic capture. We introduce a more realistic modelling in which the restricted four-body system Sun-Earth-Moon-Spacecraft is decoupled in two patched Planar Circular Restricted Three-Body Problems (PCRTBP). Contrary to previous works that consider these two systems as coplanar, we take into account the inclination of the orbital plane of the Moon with respect to the ecliptic by considering that the PCRTBPs are tilted with respect to each other, with the line of the nodes of the orbit of the Moon being the intersection of the orbital planes of the pairs of primaries. First, we present a heuristic strategy to obtain ensembles of ballistic capture orbits around the Moon relying on the hyperbolic invariant structures associated to the Lagrangian points of the Earth-Moon system that fulfill specific mission requirements. Then, we propose a patching procedure between the two three-body systems that takes into account that the motion of the primaries is not coplanar, but allows to exploit the fundamental solutions of the planar dynamics as a starting point for the search of optimal fully refined three-dimensional transfer orbits. Finally, we exploit quasi-periodic orbits of the Sun-Earth system to produce good initial guesses for the departing stage aiming optimized solutions, with low, high, and hybrid thrust. Given that setup, we exploit the proposed algorithm in order to obtain a diverse set of good low-cost and short-time initial guesses for different strategies of thrust. An assessment of these solutions will be performed as a function of chosen relevant parameters.

Copyright © 2016 by Sullo, de Sousa-Silva, O. Terra and Ceriotti.The need to drive the Δv down has led, in recent times, to improve the trajectory models, and take into account the forces that were considered just unwanted perturbations in the past. One of the examples is the exploration and exploitation of multi-body dynamics, to replace the Keplerian two-body problem, from the very initial phases of the trajectory design. Multi-body dynamics allows to exploit families of trajectories that simply do not exist in the two-body problem, at the additional cost of considerably increased the complexity of the design problem. One example is in the Earth-Moon transfer trajectories, where high-energy Apollo-like transfers are possible but highly expensive, as opposed to solutions that make use of the gravitational attraction of the sun, such as weak stability boundary transfers, to reduce the Δv. This paper presents an optimization procedure to generate fast and low-Δv Earth-Moon transfer trajectories. Ideal (first-guess) trajectories are generated at first, using two coupled planar circular restricted three-body problems, one representing the Earth-Moon system, and one representing the Sun-Earth. The two systems are rotating with respect to each other and tilted around a common line of the nodes, to account for the obliquity of the Moon over the ecliptic. The trajectories consist of a first ballistic arc in the Sun-Earth system, and a second ballistic arc in the Earth-Moon system. The two are connected at a patching point on the line of the nodes at one end (with an instantaneous Δv), and they are bounded at Earth and Moon respectively at the other end. Families of these trajectories are found by means of an evolutionary optimization method, with patching Δv of the order of a hundred m/s and transfer time of about 10 days. Subsequently, they are used as first-guess for solving an optimal control problem. At this stage, the full-three dimensional problem is introduced and the patching point is set free, and realistic analytical ephemerides are used. The objective of the optimisation, carried out with pseudospectral methods and sequential quadratic programming, is to reduce the total Δv, and the time of flight, together with introducing the constraints of the considered propulsion technology. In this work, we will present a trade-off of different options, including conventional solar-electric low-thrust, chemical high-thrust, and also a hybridisation of the two, envisaging future spacecraft that can carry both systems. A trade-off of the different optimal trajectories and propulsion options will be shown.

© 2015 Elsevier Masson SAS.This paper presents a mathematical model and corresponding numerical results for a power-law fluid flowing in a channel partially filled with a homogeneous and isotropic porous medium. At the interface between the clear fluid and the porous material, a model for the stress jump condition takes into consideration the behavior of a power-law fluid. This study shows that the use of a modified permeability, K∗, satisfactorily describes the friction factor of the flow for Reη∗ ≤ 1 (Darcy regime). The mathematical modeling presented, supported by comparisons with analytical and numerical results, also shows that the form drag must be taken into account in the momentum equation, even for a power-law fluid. The mathematical modeling presented has been used to simulate Newtonian as well as power-law fluids flowing in both porous and unobstructed media. For a channel partially filled with porous material and under a fixed mass flow rate, results indicated that the pressure drop is a function of porosity, Darcy number, shear jump coefficient, β, and flow behavior index, n.

© 2016, The Author(s).This book presents, in a self-contained fashion, a series of studies on flow and heat transfer in porous media, in which distinct energy balances are considered for the porous matrix and for the permeating fluid.

© 2016, The Author(s).There is an increasing interest in the use of moving bed technology for chemical compound separation, recuperation of petrochemical processes, drying of grains and seeds and removal of organic matter in affluents, to mention a few applications. The advantages of using a moving bed configuration are low investment, low energy consumption, low maintenance and improvement process performance.

© 2016, The Author(s).Modeling of flows in inert porous media has attracted the attention of scientists and engineers worldwide and in the last decade a number of outstanding books, handbooks and edited books have been written on the subject [Pop I, Ingham DB, Convective heat transfer: mathematical and computational modeling of viscous fluids and porous media (2001)–Nield DA, Bejan A, Convection in porous media, 4th edn (2013)].

© 2016, The Author(s).Convection heat transfer in porous media has been extensively investigated due to its many important engineering applications. The wide applications available have led to numerous investigations in this area. Such applications can be found in solar receiver devices, building thermal insulation, heat exchangers, energy storage units, etc. From the point of view of the energy equation there are two different models, local thermal equilibrium model and two energy approach.

© 2016, The Author(s).Analyses of double-diffusive phenomena in free convection in permeable media has many environmental and industrial applications, such as in oil and gas extraction, movement of gas concentration into the ground, contaminant dispersion in soils, grain storage and drying, petrochemical processes, electrochemical processes, to mention a few [Nithiarasu P, Sundararajan T, Seetharamu KN, Int Commun Heat Mass Transf 24(8):1121 (1997)–Khadiri A, Amahmid A, Hasnaoui M, Rtibi A, Numer Heat Transf Part A, 57(1 I):848–868 (2010)].

© 2016, The Author(s).This book presented, in a self-contained fashion, a series of studies on flow and heat transfer in porous media, in which distinct energy balances are considered for the porous matrix and for the permeating fluid.

Copyright © 2016 by ASME.This work investigates the influence of thermal conductivity ratio on energy and mass transport across a porous square cavity. Modeling of heat transfer from side to side of the enclosure assumed the hypothesis of thermal nonequilibrium between the solid matrix and the fluid phase. Transport equations were discretized using the control-volume method and the system of algebraic equations obtained was relaxed via the SIMPLE algorithm. Results showed that Shw, mass flux of chemical species and heat flux in the solid phase are strongly dependent of ks/kf, significantly increasing their values as such ratio increases.

Copyright © 2016 by ASME.Turbulent natural convection in a two-dimensional horizontal composite square cavity is numerically analyzed using the finite volume method and the thermal non-equilibrium approach. Distinct energy equations for the working fluid and for the porous matrix are proposed reflecting different energy balances for each phase. The composite square cavity is formed by three distinct regions, namely, clear, porous and solid region. It was found that the fluid begins to permeate the porous medium for values of Ra greater than 106. Nusselt number values show that for the range of Ra analyzed there are no significant variation between the laminar and turbulent model solution. When comparing the effects of Ra and Da on Nu, results indicate that the solid phase properties have a greater influence in enhancing the overall heat transferred trough the cavity.

Copyright © 2016 by ASME.We present numerical results for turbulent heat transfer past a backward-facing-step channel with a porous insert. A non-linear eddy viscosity model was applied to handle turbulence. For a constant Darcy number, the thickness of the porous insert was varied in order to analyze its effects on the flow pattern, particularly the damping of the recirculating bubble past the insert. Further, the reduction of the Nusselt number along the bottom heated surface, when using porous materials inside the channel, was investigated. The numerical technique employed for discretizing the governing equations was the control-volume method. The SIMPLE algorithm was used to correct the pressure field and the classical wall function approach was utilized in order to handle flow calculations near the wall. Comparisons of results simulated with different porous materials were presented.

Copyright © 2016 The Authors.NiTi SMA wire with Ni-free surface is desirable as construction materials for a range of biomaterials to actuators associated to shape memory and superelastic properties. In biomaterials a potential problem with NiTi implant devices is the release of Ni in the human body. This work analyzes the effects of nitrogen plasma based ion implantation (PBII) technique in a wire of NiTi with shape memory effect associated to a Ni-free surface. The samples were treated for 60 min at 741 °C, with 16 kV high voltage pulses. Results of the thermo-mechanical properties of the PBII treated samples showed that there is no effect of the PBII treatment on the shape memory effect when compared to NiTi samples with no PBII treatment, which is desirable for applications addressing Ni-free surface and shape memory effect. Although it was noted that the stress-strain test causes cracks perpendicular to the stress direction on the treated surface.

© 2016, Springer Science+Business Media Dordrecht.Buckling is a critical failure phenomenon for structures, and represents a threat for thin shells subjected to compressive forces. The global buckling load, for a conical structure, depends on the geometry and material properties of the shell, on the stacking sequence, on the type of applied load and on the initial geometric imperfections. Geometric imperfections, occurring inevitably during manufacturing and assembly of thin-walled composite structures, produce a reduction in the carrying load capability with respect to the design value. This is the reason why investigating these defects is of major concern in order to avoid over-conservative design structures. In this paper, the buckling behavior a conical structure with 45° semi-vertical angle is numerically investigated. The initial imperfections are taken into account by using different strategies. At first, the Single Perturbation Load Approach (SPLA), which accounts for defects in the form of a lateral load, normal to the surface, has been adopted. Then, the actual measured defects have been applied to the structure by using the Real Measured Mid-Surface Imperfections (MSI) approach. Investigations on cylindrical shells using the first strategy have already shown the occurrence of a particular phenomenon called “local snap-through”, which represents a preliminary loss of stiffness. In order to better understand this phenomenon for conical shells, both the aforementioned techniques have been used to provide an exhaustive overview of the imperfections sensitiveness in conical composite shells. This study is related to part of the work performed in the frame of the European Union (EU) project DESICOS.

© 2016 Elsevier LtdA better understanding and improvements on the dynamic and aeroelastic behaviors of composite structures by using active and passive control strategies are nowadays key issues in designing advanced lightweight aerospace structures with smaller levels of vibrations in order to perform their tasks with success, reliability and safety. However, since light structures tend to be more flexible, it is necessary that the structure itself shows the ability of dissipating energy and stabilizing itself when subjected to external dynamic loadings imposed by the airflow. In this sense, smart materials can be used as an excellent alternative, being able to stabilize these structures. The interest here is to investigate the possibility of increasing the supersonic flutter boundary of a composite flat panel by applying a multimode shunted piezoceramic in series topology, in which active control strategies cannot be easily performed. Despite the fact that much research on passive aeroelastic control strategies have been conducted in the open literature, few works have been suggested the use of multimode shunt circuits to deal with the flutter problem of aeroelectromechanical systems, which motivate the study reported herein.

© 2016 Elsevier Masson SAS. All rights reserved.This work investigates the aeroelastic stability boundary of flutter in Shape Memory Alloy Hybrid Composite laminates (SMAHC). The SMAHC consists of SMAs wires and continuous carbon fibers embedded into a polymeric matrix resulting in a three constituent composite material. The derivation of the effective mechanical properties of the SMAHC is based on micromechanical model which accounts for temperature and fraction of martensite/austenite transformation phases of the shape memory alloy. Hamilton's principle is used for the formulation of the energy functional and to obtain the equilibrium equations and boundary conditions of the aeroelastic problem. The finite element method is employed to numerically solve the equations. Different geometric configuration, laminate stacking sequence, boundary conditions and curvatures are investigated. The study shows that the stiffening effect induced by the changes in the fraction of martensite/austenite transformation phases of the shape memory alloy increases the rate of occurrence of flutter, stabilizing the plate. Thus, one can control the occurrence of flutter speed by controlling the temperature of the SMA wires and the proper design of the geometric properties of the panel and tailoring of the composite laminate.

© 2016 Elsevier Masson SAS. All rights reserved.The present study involves the application of surface viscoelastic damping treatments to remedy panel flutter problems in existing aircraft components in which active control strategies cannot be easily performed. The rationale for such study is the fact that as the viscoelastic materials are often used to solve a variety of resonant noise and vibration problems in aerospace industry, it becomes important to quantify the increase of aeroelastic stability that can be obtained by the inclusion of viscoelastic treatments. The flutter boundaries of the aeroviscoelastic system accounting for the frequency- and temperature-dependent behavior of the viscoelastic material are computed by adopting the so-named Golla-Hughes-McTavish model. Since the inclusion of internal variables in the viscoelastic model leads to an augmented coupled system of equations of motion, a numerical pre-processing is found to be necessary prior to the resolution of the complex eigenvalue problem for the purposes of flutter analysis. After the theoretical foundations, the stability analysis of a three-layer sandwich plate under supersonic flow is addressed. The results show that it is possible to increase the critical flutter speeds of flat panels using surface viscoelastic damping treatments. However, the temperature and the thicknesses of the layers have significant effect on the flutter boundary.

© 2016 Elsevier Ltd.Flutter in aeronautical panels is a type of self-excited oscillation which can occur during supersonic flights. At the flutter point the vibrations of the panel become unstable and increase significantly in time. This manuscript presents a semi-analytical model taking into account the stiffener's base effects, in order to predict the aeroelastic response of laminated composite stiffened panels under supersonic flow. Krumhaar's modified supersonic piston theory, which considers the radius effect, is adopted to model the aerodynamic loading. The proposed model has been validated against results available in the literature for various configurations. A parametric study considering different panels and stiffener configurations is also presented. The numerical results indicate that the stiffener base significantly affects the panel aeroelastic behavior. Preliminary studies also indicate that redistributing the laminate plies from the stiffener's flange to its base significantly increases the torsion stiffness of the panel locally, opening new design possibilities that may lead to higher critical flutter speeds and therefore to better designs. The results also indicate that designs with plies distributed on the base may lead to a better flutter performance when the airflow is transverse to the longitudinal stiffener direction.

© SAGE Publications.This work presents an experimental characterization of the curvature effects on the compression-after-impact strength of laminated composite shells. Curved panels impacted on the outer (convex) face and with normal pressure on the inner (concave) face with three different curvatures at three different impact energy levels were tested. A compression-after-impact testing setup was designed and implemented to evaluate the impact-induced damage tolerance of the composite shells. An analytical modeling methodology for compression-after-impact strength predictions based on the Mar-Lin and Whitney-Nuismer failure criteria is also proposed. The approach proposed herein consists of replacing the damaged area of the impacted coupon by an equivalent hole. The analytical compression-after-impact predictions obtained using the Mar-Lin and Whitney-Nuismer failure criteria were compared with experimental results. A good agreement between analytical predictions and experimental results was found. The experimental results also indicate that the compressive residual strength of the composite shells is significantly affected by the shell curvature and internal pressure effects.

© 2015 Elsevier Ltd. All rights reserved.A major concern in laminated composites for structural applications has been crack nucleation between plies and its propagation through the interface. A better comprehension of stable crack propagation may lead to more reliable predictions of the rate with which cracks grow in weave fabric laminated composites. To this aim, a number of empirical relationships proposed in the literature were studied for their applicability to satin weave fabric (5HS) composite with spread tows. In order to understand the fatigue delamination process, Double Cantilever Beam specimens were submitted to cyclic loading, and their respective da/dN vs strain energy release rate (SERR) data collected and correlated to these empirical relationships. Despite that the empirical or semi-empirical relations fit equally well to the data, the well-known Hartman-Schijve equation was adopted. This equation was properly modified according to the fracture surface investigation which had its fracture patterns qualitatively correlated with SERR parameters.

© 2016 Elsevier LtdFlutter in aeronautical panels is a self-excited aeroelastic phenomenon which occurs during supersonic flights due to dynamic instability of inertia, elastic and aerodynamic forces of the system. In the flutter condition, when the critical aerodynamic pressure is reached, the vibration amplitudes of the panel become dynamically unstable and increase exponentially with time, significantly affecting the fatigue life of the existing aeronautical components. Thus, in this paper, the interest is to investigate the possibility reducing the effects of the supersonic aeroelastic instability of rectangular plates by applying passive constrained viscoelastic layers. The rationale for such study is the fact that as the addition of viscoelastic materials provides decreased vibration amplitudes it becomes important to quantify the suppression of plate flutter coalescence modes that can be obtained. Moreover, despite the fact that much research on the suppression of panel flutter has been carried out by using passive, semi-active and active control techniques, few works have been proposed to deal with the problem of predicting the flutter boundary of aeroviscoelastic systems, since they must conveniently account for the frequency- and temperature-dependent behavior of the viscoelastic material. After the presentation of the theoretical foundations of the methodology, the description of a numerical study on the flutter analysis of a three-layer sandwich plate is addressed.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Installed jet noise is studied by means of a simplified configuration comprising flat rectangular plates situated in the nearfield of a round jet. Acoustic measurements are performed using a traversable 18-microphone azimuthal array, providing pressure data at 360 points on a cylindrical surface surrounding the jet-plate system. A rigid aluminium plate and a flexible, composite plate were tested to assess the influence of the plate stiffness on the scattered sound. The numerical predictions are confirmed by experiments and suggest that a reduction in the scattered sound level can be achieved as the flexibility of the plate is increased.

© 2016, European Conference on Composite Materials, ECCM. All rights reserved.Shape Memory Alloy Hybrid Composite (SMAHC) laminates are built with continuous carbon fibers and Shape Memory Alloy (SMA) wires, both embedded in a polymeric matrix thereby forming a three constituent composite material. The SMA actuation is triggered by temperature changes, resulting in modifications in the structural responses of SMAHC laminates. A particularly important structural characteristic of SMAHC laminates which is investigated in this paper is the aeroelastic stability boundary of flutter. The derivation of the effective mechanical properties of the SMAHC is based on micromechanical model which accounts for temperature and fraction of martensite/austenite transformation phases of the shape memory alloy. The mathematical problem is formulated using Hamilton's principle, allowing for derivation of the equilibrium equations and boundary conditions of the aeroelastic response. The governing equations are then discretized and solved by the finite element method. A parametric study is conducted where different geometric configurations, laminate stacking sequence, boundary conditions and curvatures are investigated. It is observed that the SMAHC structure is stabilized against flutter by proper tailoring of stiffening effects induced by the changes in the fraction of martensite/austenite transformation phases of the SMA. Therefore, it is possible to increase critical flutter speed by controlling the temperature of the SMA wires.

This work presents a successful methodology for obtaining failure envelopes of unidirectional fiber reinforced composites based on micromechanical analysis by the asymptotic homogenization [1] method. Given a structure (in this case a composite material lamina) and external loads, plus having its material heterogeneity geometrically represented by a periodic unit cell of microstructure, the asymptotic homogenization method is able to predict its micromechanical stresses. Such stresses may be evaluated by failure criteria of the composite's constituents for several loading conditions, and this way it is possible to assess the composite's failure envelope. In the methodology developed, a periodic unit cell of the composite microstructure is isolated, consisting of a parallelepiped of polymeric matrix reinforced by cilindrical fibers oriented in one direction, and its behaviour is evaluated by an appropriate finite elements model. At first, the unit cell is tested in several directions to find strengths for the matrix and fiber and also matrix/fiber interface, thus evaluating failure characteristics of the composite constituents. The tests are carried out considering several possible orientations for the unit cell inside the related macroscopic media, which take into account the possible relative positions of the chosen unit cell inside the material heterogeneity of the composite. Then, the strengths of the constituents are used to predict the failure envelope for the fiber reinforced material, according to failure criteria devoted to the constituents. In this prediction, it is possible to say which is the constituent that fails first for each of the test loads. The results obtained are in good agreement with experimental data for carbon/epoxi and glass/epoxi composites. Moreover, the envelopes obtained are similar to the Puck & Schürmann [2] criterion, widely used to predict failure of such composites. This way, the present methodology renders good failure envelopes for fiber reinforced composites and gives information on the strengths of the constituents and material phase of failure, benefits from an incorporated micromechanical analysis.

Copyright © 2016 SAE International.Since 70′, ethanol has risen as an alternative and ecological fuel, it has also been pointed as a potential candidate for replacing partial, or even totally, oil derived fuel application on internal combustion engines, supporting automotive industry. Ethanol is obtained from renewable sources and contributes to pollutants emission reduction in the atmosphere. In Brazil, it is obtained from sugarcane, but it can be obtained from others vegetable growing, such as beet or corn, common in other countries. For Brazilian automotive applications two types of ethanol are commonly applied: anhydrous, that contains at most 0.4% water in volume and has been used in gasoline blends up to 27%; and hydrous, with a maximum water content of 4.9% in volume, used as a substitute to gasoline on flex fuels engines. Although the widely application of ethanol, there is still lack of data available in literature regarding the fuel properties. The purpose of this research work is to gather the information published until now regarding anhydrous and hydrous ethanol as well as its blends. Furthermore, the investigation is enhanced with new data obtained at laboratory for respective fuel properties.

© 2016 Elsevier Ltd. All rights reserved.The effects of a non-steady state plasma discharge on flammability limits and flame structure of air-natural gas mixtures are investigated. As plasma power increases, flame structure is changed and flammable range is extended. In the absence of a visible flame, a higher hydrogen production is observed, revealing that the discharge is a source of molecular hydrogen. The reduction on hydrogen production inside the flammable range suggests a burning of hydrogen in the flame.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Three standard rocket motor tests (Lg/Dg ≈ 3.2 and 10 kg of propellant mass) casted with same HTPB/AP/Al solid propellant were conditioned at three different temperatures (20°C, 50°C and 72°C) in order to be fired at an horizontal bench test and investigate the influence of a thermal gradient appearance on the propellant grain by reducing its time of conditioning. The motors were instrumented with thermocouples placed over the case, nozzle and over the propellant spoke. The temperature levels were acquired prior and during the firing. Additionally, pressure and thrust profiles measured from the firings were plotted emphasizing the instant of membrane rupture and other important ballistic aspects. It was observed an important increasing on the Isp of the Motor Test #03 (72°C) and a thermal gradient induction of 2.9 °C, which led to slight variations on its pressure and thrust profiles with augmentation of progressive shape of the curves. Due to it, higher gradients must be investigated in new tests.

© 2016 Elsevier LtdA detailed literature review of laminar burning velocity and flammability limits of biogas mixtures combustion is presented. Biogas alone and in mixtures with other fuels is particularly significant because of its capability of application as fuels for internal combustion engines (ICEs). Therefore, a strict determination of the fundamental combustion characteristics required for their application in ICEs is crucial. Producing energy from biogas has the additional advantage of preventing its release into the atmosphere, where it results into significant air pollution. CH4 and CO2 are the main compounds of biogas, such as landfill, agricultural and sewage gas, after the removal of the trace amounts of organic compounds. For the same equivalence ratio, the presence of CO2 in the fuel feed results in substantial reduction of the laminar flame speed and flammability limits. Several research projects have shown that the decrease in the laminar flame speed of a fuel mixture containing dilution components is caused by the increase in specific heat capacity and the decrease in heat release, flame temperature and thermal diffusivity. The most promising strategies to increase the laminar burning velocity and the flammability limits of biogas are revised and discussed. The thermodynamic conditions under which these properties are determined are analyzed and the work still required for a comprehensive laminar burning velocity and flammability limits determination, at typical ICEs thermodynamic conditions, is addressed. The article provides a brief review of pollutant emissions of ICEs running on biogas and the current and future technological solutions to meet the increasing strict regulation.

This work presents a successful methodology for obtaining failure envelopes of unidirectional fiber reinforced composites based on micromechanical analysis by the asymptotic homogenization [1] method. Given a structure (in this case a composite material lamina) and external loads, plus having its material heterogeneity geometrically represented by a periodic unit cell of microstructure, the asymptotic homogenization method is able to predict its micromechanical stresses. Such stresses may be evaluated by failure criteria of the composite's constituents for several loading conditions, and this way it is possible to assess the composite's failure envelope. In the methodology developed, a periodic unit cell of the composite microstructure is isolated, consisting of a parallelepiped of polymeric matrix reinforced by cilindrical fibers oriented in one direction, and its behaviour is evaluated by an appropriate finite elements model. At first, the unit cell is tested in several directions to find strengths for the matrix and fiber and also matrix/fiber interface, thus evaluating failure characteristics of the composite constituents. The tests are carried out considering several possible orientations for the unit cell inside the related macroscopic media, which take into account the possible relative positions of the chosen unit cell inside the material heterogeneity of the composite. Then, the strengths of the constituents are used to predict the failure envelope for the fiber reinforced material, according to failure criteria devoted to the constituents. In this prediction, it is possible to say which is the constituent that fails first for each of the test loads. The results obtained are in good agreement with experimental data for carbon/epoxi and glass/epoxi composites. Moreover, the envelopes obtained are similar to the Puck & Schürmann [2] criterion, widely used to predict failure of such composites. This way, the present methodology renders good failure envelopes for fiber reinforced composites and gives information on the strengths of the constituents and material phase of failure, benefits from an incorporated micromechanical analysis.

This article aims to estimate the shelf life of the PBX by thermal analysis estimated by the Arrhenius equation, equivalent to the time of storage at accelerated aging. The PBX was subjected to accelerated aging in an oven at controlled temperature 60 °C for periods of 5, 10, 15 and 25 weeks, which are equivalent to 5, 10, 15 and 25 of natural aging, respectively, at a temperature of 25 °C. The curves of thermal decomposition of the samples were obtained by the DSC (Differential Scanning Calorimetry) technique. The kinetic parameters, such as the activation energy and pre-exponential factor, were determined by the Ozawa method and the Kissinger method. Initial results of this study indicated that, for a period of 25 years of storage in the cargo hold, the material did not change this aging significantly. To study the life of PBX analyzes, vacuum chemical stability were also conducted to verify the safety of explosive handling.

© 2016, Journal of Aerospace Technology and Management. All rights reserved.The Operational Modal Analysis technique is a methodology very often applied for the identification of dynamic systems when the input signal is unknown. The applied methodology is based on a technique to estimate the Frequency Response Functions and extract the modal parameters using only the structural dynamic response data, without assuming the knowledge of the excitation forces. Such approach is an adequate way for measuring the aircraft aeroelastic response due to random input, like atmospheric turbulence. The in-flight structural response has been measured by accelerometers distributed along the aircraft wings, fuselage and empennages. The Enhanced Frequency Domain Decomposition technique was chosen to identify the airframe dynamic parameters. This technique is based on the hypothesis that the system is randomly excited with a broadband spectrum with almost constant power spectral density. The system identification procedure is based on the Single Value Decomposition of the power spectral densities of system output signals, estimated by the usual Fast Fourier Transform method. This procedure has been applied to different flight conditions to evaluate the modal parameters and the aeroelastic stability trends of the airframe under investigation. The experimental results obtained by this methodology were compared with the predicted results supplied by aeroelastic numerical models in order to check the consistency of the proposed output-only methodology. The objective of this paper is to compare in-flight measured aeroelastic damping against the corresponding parameters computed from numerical aeroelastic models. Different aerodynamic modeling approaches should be investigated such as the use of source panel body models, cruciform and flat plate projection. As a result of this investigation it is expected the choice of the better aeroelastic modeling and Operational Modal Analysis techniques to be included in a standard aeroelastic certification process.

© 2016 Elsevier LtdThis paper aims to estimate the modal parameters of composite flat plate models through Experimental Modal Analysis (EMA) using piezoelectric transducers. The flat plates are composed of three ply carbon-epoxy fibers oriented in the same direction. Five specimens with different unidirectional fiber nominal orientations θk (0o, 30o, 45o, 60o and 90o) were tested. These models were instrumented with one PZT (Lead Zirconate Titanate) actuator and one PVDF (Polyvinylidene Fluoride) sensor and an EMA was performed. The natural frequencies and damping factors estimated using only a single PVDF response were compared with the estimated results using twelve measurement points acquired by laser doppler vibrometry. For comparison purposes, the percentage error of each natural frequency estimation and the percentage error of the damping factor estimations were computed, as well as their averages. Even though the comparison was made between a SISO (Single-Input, Single-Output) and a SIMO (Single-Input, Multiple-Output) techniques, both results are very close. The vibration modes were estimated by means of laser measurements and were used in the modal validation. In order to verify the accuracy of the modal parameters, the Modal Assurance Criterion (MAC) was employed and a high correlation among mode shapes was observed.

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.In spite of occurring during a short period of time, the transonic regime plays an important role in the flight envelope of an aerospace vehicle, given that complex flow phenomena take place at this speed range, as for example shock wave occurrences and associated shock waveboundary layer interactions (SBLIs). The present study is aimed at investigating the shock wave formation patterns over a NACA 0012 airfoil in the transonic regime as the Mach number and the angle of attack is varied. The angles of attack, α, of 0°, 2°, 4° and 5° were considered, and the Mach number, M, was varied between 0.2 and 0.8. In all tested conditions, measurements were conducted for very small variations of Mach number in the range close to shock wave occurrence, in order to study the shock wave patterns in this region and also to get insights on shockwave-boundary layer interactions (SBLIs) taking place. Significant differences both between laminar and turbulent shockwave formation patterns and fullydeveloped shock structures were detected, as well as Cpvariations due to laminar-turbulent transition.

Copyright © 2016 by ASME.In this paper we consider the flight dynamics of fighter aircraft at high angles of attack with uncertain aerodynamic coefficients. Stochastic parametric uncertainty is dealt with by employing spectral decomposition of the random variables by means of the generalized polynomial chaos expansion. We propose an optimal linear feedback strategy for the automatic pilot system to recover the aircraft from stall and provide acceptable dynamic response. Optimality of the proposed control law is proved by solving the Hamilton-Jacobi-Bellman equation and asymptotically stability of the controlled nonlinear aircraft model is guaranteed in the Lyapunov sense. Numerical results are verified with Monte-Carlo simulations.

Recent technological advances in mechatronics enhance the possibilities of utilizing subscale flight testing as a tool in the development of aircraft. This paper reports the current status of a joint Swedish-Brazilian research project aiming at exploring these possibilities. A 13% scale fighter aircraft is used as a test bench for developing methods and procedures for data acquisition. The aircraft is equipped with an instrumentation system assembled from off the shelf components as well as open source hardware and software.

© Copyright 2016 by the American Institute of Aeronautics and Astronautics, Inc.An inertially-coupled formulation for the flight dynamics of flexible aircraft undergoing small deformations is developed. The availability of a structural-dynamic finite element model of the aircraft is presupposed. With all the coupled dynamics taken into account, an arbitrary choice of the body reference frame can be made. This frame is also allowed to be noncoincident with the frame of reference used to calculate the aerodynamic loads. In the equations of motion, the inertial coupling terms are linearized in the elastic displacements around a calculated equilibrium condition. Appropriate modes of vibration are then used in the calculation of the dynamic deformation of the structure. A simple quasi-steady incremental aerodynamic model based on the vortex-lattice method is used. The formulation is tested in the flight simulation of an idealized forward-swept-wing aircraft model. Numerical results show that, under small deformations, different body axes lead to the same overall motion of the aircraft with respect to an inertial frame. The stiffness level at which geometrically nonlinear formulations would become necessary is also determined.

© 2016 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.Nonlinear aeroelastic phenomena is continuously investigate in aeronautical researches. The nonlinearity nature, for these cases, could be aerodynamic, such as dynamic stall or shock waves or structural, for example, free play or large displacements due to high aspect ratio and high flexibility. This work will investigate a very flexible wing with high aspect ratio subjected to unsteady flow. A flutter analysis is proceeded in order to evaluate the error between the computational result and the experiment. Since the linear flutter theory consider small displacements, it is expected a nonlinear phenomena. In this case, the experiment time series is analyzed in order to understand this nonlinearity and a 0-1 test is performed to evaluate if the system has chaotic behavior.

© 2016 Elsevier Inc.This paper proposes two important improvements to shock-capturing strategies using a discontinuous Galerkin scheme, namely, accurate shock identification via finite-time Lyapunov exponent (FTLE) operators and efficient shock treatment through a point-implicit discretization of a PDE-based artificial viscosity technique. The advocated approach is based on the FTLE operator, originally developed in the context of dynamical systems theory to identify certain types of coherent structures in a flow. We propose the application of FTLEs in the detection of shock waves and demonstrate the operator's ability to identify strong and weak shocks equally well. The detection algorithm is coupled with a mesh refinement procedure and applied to transonic and supersonic flows. While the proposed strategy can be used potentially with any numerical method, a high-order discontinuous Galerkin solver is used in this study. In this context, two artificial viscosity approaches are employed to regularize the solution near shocks: an element-wise constant viscosity technique and a PDE-based smooth viscosity model. As the latter approach is more sophisticated and preferable for complex problems, a point-implicit discretization in time is proposed to reduce the extra stiffness introduced by the PDE-based technique, making it more competitive in terms of computational cost.

© 2015 The Authors.This study addresses linear dispersion-diffusion analysis for the spectral/hp continuous Galerkin (CG) formulation in one dimension. First, numerical dispersion and diffusion curves are obtained for the advection-diffusion problem and the role of multiple eigencurves peculiar to spectral/hp methods is discussed. From the eigencurves' behaviour, we observe that CG might feature potentially undesirable non-smooth dispersion/diffusion characteristics for under-resolved simulations of problems strongly dominated by either convection or diffusion. Subsequently, the linear advection equation augmented with spectral vanishing viscosity (SVV) is analysed. Dispersion and diffusion characteristics of CG with SVV-based stabilization are verified to display similar non-smooth features in flow regions where convection is much stronger than dissipation or vice-versa, owing to a dependency of the standard SVV operator on a local Péclet number. First a modification is proposed to the traditional SVV scaling that enforces a globally constant Péclet number so as to avoid the previous issues. In addition, a new SVV kernel function is suggested and shown to provide a more regular behaviour for the eigencurves along with a consistent increase in resolution power for higher-order discretizations, as measured by the extent of the wavenumber range where numerical errors are negligible. The dissipation characteristics of CG with the SVV modifications suggested are then verified to be broadly equivalent to those obtained through upwinding in the discontinuous Galerkin (DG) scheme. Nevertheless, for the kernel function proposed, the full upwind DG scheme is found to have a slightly higher resolution power for the same dissipation levels. These results show that improved CG-SVV characteristics can be pursued via different kernel functions with the aid of optimization algorithms.

© Institution of Mechanical Engineers.The residual stress analysis is a well-established method for predicting fatigue failures of mechanical components. Within industrial constraints, the X-ray diffraction is a technique usually applied to measuring a small spot of the workpiece surface. This punctual and averaged outcome does not allow the proper representation of the residual stress. The objective of this study is to define a feasible method for assessing the heterogeneity of the surface residual stress state. The proposal is based on the theoretical relationship between the deviation of the residual macrostress and the intensity of the microstress. Steel shot peened gears were produced and their microstresses were assessed by means of the diffraction profiles broadening. The reference database was composed of topography measurements, metallographic analyses and residual macrostress maps. The stress heterogeneity was reasonably correlated to the intensity of the Gauss integral breadth. Applied to ground parts, the correlation's parameter filled a comprehension gap between the measured residual stress intensity and observed contact fatigue failures. Using the same data from the macro residual stress measurement, the method proved to be feasibly applied. Moreover, by providing a deviation perspective to the residual stress state, the heterogeneity assessment enhances the analysis of a fatigue failure.

© 2016, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional.A numerical study of optimal time-fixed low-thrust limited power transfers (no rendezvous), in an inverse-square force field, between coplanar orbits with small eccentricities is performed by means of two different approaches. The first approach uses a numerical method based on the second variation theory, usually known as neighboring extremals method, to solve the two-point boundary value problem obtained from the application of the Pontryagin Maximum Principle to the optimization problem formulated as a Mayer problem with the radial distance and the components of the velocity vector as state variables. The second approach is based on the solution of the two-point boundary value problem defined by a first-order analytical solution expressed in terms of non-singular orbital elements, which include short periodic terms, and derived through canonical transformations theory in a previous work. For transfers between close orbits, a simplified solution expressed by a linear system of algebraic equations is straightforwardly derived from this analytical first-order solution. In this case, the two-point boundary value problem can be solved by simple techniques. Numerical results are presented for transfers between circular orbits, considering several radius ratios and transfer durations. Some maneuvers involving orbits with arbitrary small eccentricities are also considered. The fuel consumption is taken as the performance criterion in comparison of the results.

© 2015, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional.In this paper, a first-order analytical solution, which includes the short periodic terms, for the problem of optimal time-fixed low-thrust limited-power transfers (no rendezvous), in an inverse-square force field, between coplanar orbits with small eccentricities is obtained through canonical transformation theory. Short periodic terms are eliminated from the maximum Hamiltonian, expressed in non-singular orbital elements, through an infinitesimal canonical transformation built through the Hori method. Closed-form analytical solutions are obtained for the average canonical system by solving the Hamilton–Jacobi equation through the separation of variables technique. For long duration maneuvers, the existence of conjugate points is investigated through the Jacobi condition.

© 2015, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional.A study of optimal bi-impulsive trajectories of round trip lunar missions is presented in this paper. The optimization criterion is the total velocity increment. The dynamical model utilized to describe the motion of the space vehicle is a full lunar patched-conic approximation, which embraces the lunar patched-conic of the outgoing trip and the lunar patched-conic of the return mission. Each one of these parts is considered separately to solve an optimization problem of two degrees of freedom. The parameters to be optimized are two: the phase angle of the point at which the space vehicle reaches the edge of the Moon’s sphere of influence and the initial velocity at departure. The Sequential Gradient Restoration Algorithm is employed to achieve the optimal solutions. Analytical and numerical derivatives of expressions describing the lunar patched-conic approximations are utilized to ensure the results. The results based on the patched-conic approximation show a good agreement with the ones provided by literature, and the solution trajectories proved to be consistent with the image trajectories theorem.

© Emerald Group Publishing Limited.Purpose-This paper aims to propose an evaluation method to compare two different Human-Robot Interaction (HRI) solutions that can be used for on-line programming in an industrial context: a force guidance system and the traditional teach pendant operation. Design/methodology/approach-The method defines three evaluation criteria (agility, accuracy and learning) and describes an experimental approach based on the analysis of variance to verify the performance of guidance systems according to these criteria. This method is used in this paper to compare the traditional teach pendant interface with an implementation of a force guidance system based on the use of an external force/torque sensor. Findings-The application of the proposed method to an off-the-shelf industrial robot shows that the force guidance system has a better performance according to the agility criterion. Both solutions have a similar performance for the accuracy criterion, with a limit of about 2 mm in the achieved position accuracy. Regarding the learning criterion, the authors cannot affirm that any of the methods has an improved agility when the operator repeats the tasks. Practical implications-This work supports the selection of guidance systems to be used in on-line programming of industrial applications. It shows that the force guidance system is an option potentially faster than the teach pendant when the required positioning accuracy is greater than 2 mm. Originality/value-The new method proposed in this paper can be applied to a large range of robots, not being limited to commercial available collaborative robots. Furthermore, the method is appropriate to accomplish further investigations in HRI not only to compare programming methods but also to evaluate guidance systems approaches or robot control systems.

© 2016, American Astronautical Society.Integration, test and validation results, in a real-time environment, of a novel concept for spacecraft control are presented in this paper. The proposed method commands simultaneously a group of actuators optimizing a given set of objective functions based on a multiobjective optimization technique. Since close proximity maneuvers play an important role in orbital servicing missions, the entire GNC system has been integrated and tested at a hardware-in-the-loop (HIL) rendezvous and docking simulator known as European Proximity Operations Simulator (EPOS). During the test campaign at EPOS facility, a visual camera has been used to provide the necessary measurements for calculating the relative position with respect to the target satellite during closed-loop simulations. In addition, two different configurations of spacecraft control have been considered in this paper: a thruster reaction control system and a mixed actuators mode which includes thrusters, reaction wheels, and magnetic torqrods. At EPOS, results of HIL closed-loop tests have demonstrated that a safe and stable rendezvous approach can be achieved with the proposed GNC loop.

© 2015, SBMAC - Sociedade Brasileira de Matemática Aplicada e Computacional.This paper explores the optimal design problem of a linear time-invariant control system composed of three different types of linear parallel actuators. The actuators’ time constants have been defined to achieve a conflicting behavior among the transient response provided by them. Thus, a novel solution has been proposed to find the best selection of actuators’ gains to improve the performance parameters. Such methodology is based on a discrete multiobjective optimization technique. The transfer functions, as well as the transient response, have been derived and evaluated throughout this work. In addition, the stability conditions have been analyzed for a range of closed-loop poles and zeros. The discrete multiobjective optimization problem is formulated with a couple of objective functions: overshoot and settling time of the closed-loop response. A decision-making method has been used to find the best compromise solution from a group of candidate solutions. The results have indicated that a better performance can be achieved with a systematic multiobjective optimization methodology.