© 2020, Springer Nature B.V.The driver coupled to a driven system through mechanical couplings is very common in rotating machinery. These couplings can present angular and parallel misalignments with more or less degree due to manufacturing tolerances or maintenance proceedings. Theoretical and experimental analyses have been published demonstrating the effects of rotor misalignment and the vibration stability of rotor systems. In this work the nonlinear formulation of a magnetorheological fluid journal bearing is included in the finite element model that evaluates the nonlinear responses of a complete rotor system subject to rigid coupling misalignment. The modified Reynolds equations for Bingham viscoplastic materials are implemented in the finite element procedures to evaluate the nonlinear hydrodynamic reaction forces acting on the bearing positions. The finite element formulation for the shaft-line and mechanical couplings is based on the Timoshenko beam theory. Misalignment forces are calculated and included in the equations of motion. The nonlinear dynamic responses are calculated by the modified Newmark method incorporating the Newton–Raphson iteration method to find the equilibrium position at each time step. Bifurcation analysis demonstrates the influence of misalignment to obtain periodic and period-doubling orbit for the center position of the rotor. Results are demonstrated through displacements versus time and frequency responses.

© 2021 International Institute of Acoustics and Vibrations. All rights reserved.Merging analytical and numerical models with experimental results improve the behaviour predictions of mechanical elements applied to rotor machinery, such as the bearings. This work aims to present the design of a hydrodynamic bearing prototype, a comparison and validation between the numerical and experimental results of critical speeds, and the differences of behaviour when the bush geometries and lubrication are changed. The bush geometries and the fluid film properties are analysed by measuring the dynamic behaviour of a rotor supported by these bearings. The experimental evaluation is based on measuring the Jeffcott test bench supported in a pair of bearings, showing the anisotropic behaviour caused by the stiffness difference in horizontal and vertical directions. It also presents an optimization of bushings for isotropic conditions when they were changed for different geometries (elliptical, offset halves) and different materials with boundary lubrication. This detailed study shows how the dynamic behaviour of rotating machinery can be predicted using numerical models and its validation by a test rig. Results also show how the vibration occurs if the bushes geometries are modified or its lubrication condition is changed.

© 2021 SPIEThis paper discusses the vulnerability across Brazilian borders considering illicit trade. Smuggling affronts the public administration by bringing prohibited goods into the country. The typical characteristic of smuggling is the lack of collected taxes on goods transported across the border. Since the intelligence analysis estimates the events that are taking place for the movement of illicit goods, it can provide subsidies for agencies to make decisions to fight crime. The policy of the Brazilian State seeks to foster technologies that safeguard Brazil's immense land border with ten of the South American countries. The collection of satellite images is used for analyzes involving the recognition of paths that can be taken in the country. A technological trend is the periodic updating of the images to identify changes in the terrain. The analysis of the images allows monitoring of traffic routes known by the authorities, as well as identifying new routes. Because of their characteristics, satellite images allow, with good precision, the calculation of the distances traveled on each road segment, official or otherwise, and the estimation of the maximum speed that vehicles can travel according to the characteristics observed for the roughness and sinuosity of the road. It is considered unfeasible to observe the Brazilian borders with almost 17 thousand kilometers in length using only the military force. The authorities recognize the need to use equipment such as radios, antennas, radars, film cameras, X-ray sensors, UAVs, etc. to improve surveillance of these borders. Even so, the improvement of the information system speeds the planning of traffic control actions. The illicit drugs reaching at consumer center puts a flag in the information system. The combinations of these flags are triggered, and a control plan is mitigated. The more intelligence is used in this system, the greater the success of actions to combat illicit products.

© The Author(s) 2021.This paper describes a classical laminate theory-based constitutive model for portraying thermoplastic composites’ mechanical properties and the development of residual stresses during consolidation. The extended Hillier model is applied to describe the material’s crystallisation and as such is able to provide final part quality as a function of the process cooling history while taking into account the first and second crystallisation mechanisms occurring concurrently. With the developed model, a parametric study was performed taking into account layups that are commonly used in the aerospace industry, where general design guidelines are suggested. Some of the advantages of using cross-ply and quasi-isotropic laminates became clear as no shear residual stresses were predicted for those laminates. However, highly anysotropic laminates may also offer structural advantages. Numerical simulations indicate that the crystallisation residual strains can be, although smaller than thermal residual strains, relevant to final part quality. The combination of both effects may result in high residual stresses at ply level which in turn can compromise the ultimate strength of the laminates and make it difficult to attain the desired part’s geometrical tolerances.

© 2021, Springer-Verlag London Ltd., part of Springer Nature.Different residual stress magnitude and profile are generated after every crankshaft manufacturing stage. The processes are often investigated separately, regardless of their possible influence. The acknowledgement of the stress evolution can be useful when investigating crankshaft fatigue behavior. This study contributes to the matter by evaluating the resultant residual stress generated at the fillet region after crankshaft’s machining and deep rolling processes. Prior to it, a procedure was developed to guarantee the position of the samples in the X-ray diffractometer after surface electropolishing and depth measurement. Repeatability and reproducibility analyses attest the measurements’ accuracy. An in-depth profile assessment was made at the crankpin radii top and bottom regions in two stress directions. The influence of the machining process over the residual stress left after deep rolling can be inferred. The results were also compared with the outcomes from a finite element model for the deep rolling process. They pointed out that new features should be included in its development in order to account for the influence of previous processes. Moreover, unexpected residual stress results, and consequently fatigue behavior, can be better understood with more data regarding the whole manufacturing chain.

© 2021 Universidade Federal de Sao Carlos. All rights reserved.The objective of the present paper is to propose a framework, utilizing the OpenCV library, for post-processing infrared images obtained using Long-Pulse Thermography (LPT), with the goal of segmenting the images into defective and sound areas. A series of thermograms of a carbon fiber/epoxy specimen, containing precision milled flat-bottom holes, was acquired using an LPT system comprised of an uncooled microbolometer imager and halogen optical sources. Flaw detectability and planar size estimation were used to evaluate the results obtained with the proposed post-processing framework, in comparison to raw images, and images subjected only to pre-processing algorithms.

© 2021 Elsevier B.V.. All rights reserved.Early product development phases are decisive to determine the environmental impacts of an aircraft during its life cycle. In order to reduce overall environmental impacts, the designers and engineers must be able to assess the consequences of their design choices. In this research, an aircraft eco-design tool was developed to support the decision-making process during the aircraft conceptual design phase. The tool uses a streamlined Life Cycle Assessment (LCA) approach to calculate cradle-to-grave environmental impacts of the aircraft's life cycle using its design parameters and the ecoinvent database as inputs. The tool performs Uncertainty Analysis via Monte Carlo Simulation (MCS), giving the practitioner insight on the distribution and uncertainty of the results. Input parameters are fitted to Beta-PERT distributions and randomly sampled for each iteration of the MCS. The tool was used to analyze different concepts for a freighter aircraft and a "what-if" scenario, the manufacturing of a composite airframe. The results are coherent with other LCA studies, showing predominance of the operation life cycle stage in all midpoint and endpoint indicators. Furthermore, visualizing the results as distributions rather than single values is of key importance in the decision-making process. The tool is demonstrated to be a versatile eco-design asset for evaluation and comparison of aircraft environmental impacts during the conceptual design phase and may contribute to designing aircraft with minimal environmental impacts.

© 2021 American Physical Society.A method is proposed in order to optimally decompose the trace of cross-covariances of flow fluctuations, such as Reynolds stresses. Such method, referred to as cross proper orthogonal decomposition (CPOD), leads to a basis of modes extracted from a flow database that are optimal in representing an inner product related to the cross-covariance of interest. A sample application is shown for the representation of Reynolds shear stress in a turbulent channel flow with friction Reynolds number equal to 179. Leading modes are shown to comprise streamwise vortices and streaks with phase opposition between streamwise (u′) and wall-normal (v′) velocities, representing ejections and sweeps, and higher-order modes show similar structures, but with u′ and v′ in phase. A combination of such structures leads to an accurate reconstruction of the Reynolds stress, and consequently of the mean flow, with a reasonable near-wall reconstruction with the leading CPOD mode pair (even and odd modes) for each considered wave number, and a close match of the profiles with the five leading CPOD mode pairs. The present method is thus a valuable modal decomposition technique targeting cross-covariances of flow quantities such as Reynolds stresses.

© 2021 Acoustical Society of America.Parabolized stability equations (PSE) have been shown to model wavepackets and, consequently, the near-field of turbulent jets with reasonable accuracy. In this work, PSE were employed to obtain a reduced-order model that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet in a computationally efficient approximation for resolvent-based estimation based on a single input. From the unsteady pressure data at an input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and a data-driven method based on a well-validated large-eddy simulation (LES). The prediction scheme employed is a single-input single-output, linear model. The unsteady pressure predicted by the PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer, where the prediction capabilities of the PSE are comparable to those of the data-driven transfer functions. The good agreement indicates that PSE could not only be used to predict the sound generation but also to open up different potentialities to attenuate the noise by flow control. The exploration of the regions where the method displayed good agreement, which are presented in this work, can guide the positioning of the sensors for experimental implementation of closed-loop control in a jet.

© 2021 American Physical Society.In this work we perform reactive control of stochastic disturbances in forced turbulent jets based on destructive interference. The study is motivated by the success of recent studies in applying this type of control on instability waves in transitional boundary layers and free-shear flows. Linear convective mechanisms in the initial region of turbulent jets are explored in order to perform reactive control, wherein the actuation signal is updated in real time based on sensor measurements performed upstream, resulting in an inverse feedforward approach. The control law is based on empirical transfer functions of the jet response to stochastic forcing and actuation, which are measured experimentally. Since turbulent jets have energy content spread in a number of azimuthal wave numbers, we apply axisymmetric forcing at the nozzle lip in order to be able to perform control using a reduced number of sensors and actuators. The external forcing produces axisymmetric wave packets which possess stochastic phases and amplitudes, akin to turbulent fluctuations found in unforced jets. We demonstrate the successful implementation of real-time reactive control of these disturbances, achieving order-of-magnitude attenuations of associated velocity fluctuations. Control is shown to reduce fluctuation levels over an extensive streamwise range.

© 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Optimization of antibiotic administration helps minimizing cases of bacterial resistance. Dosages are often selected by trial and error using a pharmacokinetic (PK) model. However, this is limited to the range of tested dosages, restraining possible treatment choices, especially for the loading doses. Colistin is a last-resort antibiotic with a narrow therapeutic window; therefore, its administration should avoid subtherapeutic or toxic concentrations. This study formulates an optimal control problem for dosage selection of colistin based on a PK model, minimizing deviations of colistin concentration to a target value and allowing a specific dosage optimization for a given individual. An adjoint model was used to provide the sensitivity of concentration deviations to dose changes. A three-compartment PK model was adopted. The standard deviation between colistin plasma concentrations and a target set at 2 mg/L was minimized for some chosen treatments and sample patients. Significantly lower deviations from the target concentration are obtained for shorter administration intervals (e.g. every 8 h) compared to longer ones (e.g. every 24 h). For patients with normal or altered renal function, the optimal loading dose regimen should be divided into two or more administrations to attain the target concentration quickly, with a high first loading dose followed by much lower ones. This regimen is not easily obtained by trial and error, highlighting advantages of the method. The present method is a refined optimization of antibiotic dosage for the treatment of infections. Results for colistin suggest significant improvement in treatment avoiding subtherapeutic or toxic concentrations.

© Authors 2021We employ a resolvent-based methodology to estimate velocity and pressure fluctuations within turbulent channel flows at friction Reynolds numbers of approximately 180, 550 and 1000 using measurements of shear stress and pressure at the walls, taken from direct numerical simulation (DNS) databases. Martini et al. (J. Fluid Mech., vol. 900, 2021, p. A2) showed that the resolvent-based estimator is optimal when the true space-Time forcing statistics are utilised, thus providing an upper bound for the accuracy of any linear estimator. We use this framework to determine the flow structures that can be linearly estimated from wall measurements, and we characterise these structures and the estimation errors in both physical and wavenumber space. We also compare these results to those obtained using approximate forcing models-an eddy-viscosity model and white-noise forcing-and demonstrate the significant benefit of using true forcing statistics. All models lead to accurate results up to the buffer layer, but only using the true forcing statistics allows accurate estimation of large-scale logarithmic-layer structures, with significant correlation between the estimates and DNS results throughout the channel. The eddy-viscosity model displays an intermediate behaviour, which may be related to its ability to partially capture the forcing colour. Our results show that structures that leave a footprint on the channel walls can be accurately estimated using the linear resolvent-based methodology, and the presence of large-scale wall-Attached structures enables accurate estimations through the logarithmic layer.

© We investigate spanwise-coherent structures in the turbulent flow around airfoils, motivated by their connection with trailing-edge noise. We analyse well-resolved large-eddy simulations (LES) of the flow around NACA 0012 and NACA 4412 airfoils, both at a Reynolds number of 400 000 based on the chord length. Spectral proper orthogonal decomposition performed on the data reveals that the most energetic coherent structures are hydrodynamic waves, extending over the turbulent boundary layers around the airfoils with significant amplitudes near the trailing edge. Resolvent analysis was used to model such structures, using the mean field as a base flow. We then focus on evaluating the dependence of such structures on the domain size, to ensure that they are not an artefact of periodic boundary conditions in small computational boxes. To this end, we performed incompressible LES of a zero-pressure-gradient turbulent boundary layer, for three different spanwise sizes, with the momentum-thickness Reynolds number matching those near the airfoils trailing edge. The same coherent hydrodynamic waves were observed for the three domains. Such waves are accurately modelled as the most amplified flow response from resolvent analysis. The signature of such wide structures is seen in non-premultiplied spanwise wavenumber spectra, which collapse for the three computational domains. These results suggest that the spanwise-elongated structures are not domain-size dependent for the studied simulations, indicating thus the presence of very wide structures in wall-bounded turbulent flows.

© 2021 American Physical Society.In shock wave/boundary layer interactions, two mechanisms have been recognized to drive the low-frequency unsteadiness of the reflected shock: upstream boundary layer forcing and downstream feedback. The current work presents a quantitative analysis of the causal mechanisms underlying such flow unsteadiness. The analysis is based on a large-eddy simulation database covering approximately 300 cycles of the low-frequency shock fluctuations in a Mach 2 turbulent boundary layer. This time span enables the accurate application of frequency-domain system identification methods targeting such low frequencies. The evaluation of the spectrum in the interaction zone indicates that the broadband low-frequency unsteadiness is predominantly two-dimensional and can be isolated via spanwise averaging. Empirically derived transfer functions are computed using the averaged flow field and indicate the occurrence of a feedback between the locations downstream of the flow separation and the shock fluctuations. The results indicate that this mechanism dominates over the upstream forcing of the interaction region. Accordingly, the computed transfer functions are also used as an estimation tool to predict the shock motion accurately; for the largest streamwise separation between input and output signals, correlations above 0.6 are observed between predictions and raw data. Computation of spectral proper orthogonal decomposition modes reveals the existence of upstream traveling waves in the leading spectral mode at the main shock frequency; higher frequencies do not exhibit this trend. Furthermore, the spectral modes obtained using selected flow regions downstream of the shock enable the reconstruction of a significant portion of the energy in the interaction zone. Finally, a linear stability analysis is conducted using the mean turbulent flow, showing the existence of upstream traveling waves. Evaluation of a vortex sheet model indicates that these upstream traveling modes are of acoustic nature. The predicted modes from this local analysis present a compelling match against the spectral modes, both in terms of the shape and phase speed of the fluctuations. The combined analysis of the techniques indicates that downstream disturbances are the dominant cause of shock oscillations in the present configuration, leading to shock motion by upstream traveling acoustic modes.

© 2021 American Physical Society. New reduced-order models (ROMs) are derived for sinusoidal shear flow (also known as Waleffe flow) and plane Couette flow in small periodic domains. A first derivation for Waleffe flow exploits Fourier modes that form a natural orthonormal basis for the problem. A ROM for such basis is obtained by a Galerkin projection of the Navier-Stokes equation. A large basis was reduced to 12 modes that contribute significantly in maintaining chaotic, turbulent dynamics. A key difference from earlier ROMs is the inclusion of two roll-streak structures, with spanwise wavelengths equal to Lz and Lz/2, where Lz is the spanwise length of the computational box. The resulting system was adapted to Couette flow by rewriting the Galerkin system for the same 12 modes, modified so as to satisfy no-slip conditions on the walls. The resulting dynamical systems lead to turbulence with finite lifetimes, in agreement with earlier ROMs and simulations in small domains. However, the present models display lifetimes that are much longer than in earlier ROMs, with differences of more than an order of magnitude. The Couette-flow model is compared to results of direct numerical simulation (DNS), with statistics displaying fair agreement. The inclusion of the Lz and Lz/2 length scales is seen to be a key feature for longer turbulence lifetimes: Neglecting any of the roll modes, or their nonlinear interaction, leads to drastic reductions of turbulence lifetimes. The present ROMs thus highlight some of the dominant nonlinear interactions that are relevant in maintaining turbulence for long lifetimes.

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.This manuscript presents a successful application of the inverse feed-forward control (IFFC) technique for control of the Tollmien–Schlichting (TS) waves over a wing profile placed in an open-circuit wind tunnel. Active cancellation of two-dimensional broadband TS disturbances is performed using a single dielectric barrier discharge (DBD) plasma actuator. The measurements required for the IFFC are performed with microphones, instead of hot wires often used for this purpose, in order to reduce the space occupied by the sensors and assess the suitability of simpler and cheaper devices. An attenuation of the TS-wave amplitude of one order of magnitude is achieved. Direct numerical simulations (DNS) are also performed and compared to the outcome of the experiments. The plasma-actuator model used in DNS is a mapping of the force field used by Fabbiane et al. (In: Proceedings of TSFP-9, Melbourne, 2015a) to the actual geometry, whereas the sensors (microphones) are modeled as pressure probes. Despite these modelling choices, a good agreement between the results of DNS and the experiments is achieved. However, the control performance is better in the DNS, with attenuation of three orders of magnitude of TS-wave amplitude. Further analysis of experiments and simulations shows that the limiting factor in the experiments is the ambient low-frequency acoustic waves in the wind tunnel. These waves are sensed by the microphones and act as noise in the analysis of TS-wave evolution and thus leading to lower coherence between sensors and actuators. This in turn leads to a suboptimal control kernel in the experiment.Please confirm if the inserted city and country are correct in Affiliations [Aff1, Aff2]. Amend if necessary.Confirmed. It is correct.Please confirm if the corresponding author is correctly identified. Amend if necessary.Confirmed. The corresponding author is Pedro P. C. Brito. Graphic abstract: [Figure not available: see fulltext.]

© 2021 American Physical Society.A method is proposed in order to optimally decompose the trace of cross-covariances of flow fluctuations, such as Reynolds stresses. Such method, referred to as cross proper orthogonal decomposition (CPOD), leads to a basis of modes extracted from a flow database that are optimal in representing an inner product related to the cross-covariance of interest. A sample application is shown for the representation of Reynolds shear stress in a turbulent channel flow with friction Reynolds number equal to 179. Leading modes are shown to comprise streamwise vortices and streaks with phase opposition between streamwise (u′) and wall-normal (v′) velocities, representing ejections and sweeps, and higher-order modes show similar structures, but with u′ and v′ in phase. A combination of such structures leads to an accurate reconstruction of the Reynolds stress, and consequently of the mean flow, with a reasonable near-wall reconstruction with the leading CPOD mode pair (even and odd modes) for each considered wave number, and a close match of the profiles with the five leading CPOD mode pairs. The present method is thus a valuable modal decomposition technique targeting cross-covariances of flow quantities such as Reynolds stresses.

© The Author(s), 2021.The presence of elongated streaks of high and low streamwise velocity in the shear layer of circular jets breaks the axisymmetry of their steady-state solution. If the streaks are considered to be part of the base flow, for the purpose of linear instability analysis, the instability eigenmodes are thus affected by their presence. The resulting changes of growth rate and spatial shapes of eigenmodes, related to the shear instability in jets, are investigated here for parallel base flows. Optimal streamwise vortices ('rolls') with prescribed azimuthal periodicity are computed, such that the transient temporal growth of the streaks that they produce is maximal. The presence of finite-amplitude streaks requires the formulation of eigenvalue problems in a two-dimensional cross-plane. Sinuous rolls and streaks are found to have a stabilising effect on the Kelvin-Helmholtz instability, whereas the varicose rolls and streaks have a destabilising effect. Absolute instability is not found to occur. This work shows that the effects of rolls and streaks need to be taken into account for more precise modelling of jet instability.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Experimental observations of laminar separation bubbles show that the dynamics of the separated shear layer are dominated by the amplification of external disturbances. For low-to-moderate levels of free-stream turbulence intensity, the laminar-to-turbulent transition process is initiated by the formation of spanwise-aligned vortices associated with inflectional instability. The spanwise coherence of such structures varies strongly depending on the intensity of the flow recirculation and the amplitude of the external disturbances. On the other hand, two-dimensional laminar separation bubbles are intrinsically unstable and tend to become distorted along the spanwise direction even in the absence of external disturbances. This three-dimensional distortion can affect qualitatively and quantitatively the flow receptivity to external disturbances and their subsequent amplification, and thus it needs to be accounted for in the modeling of separation bubbles. This work addresses the receptivity of two-dimensional and three-dimensional separation bubbles to three-dimensional disturbances by analyzing the optimal inputs and outputs via the resolvent operator. A novel matrix-free strategy is used, which provides optimal gains and modes for all frequencies using a single iterative scheme, resulting in total costs an order of magnitude lower than previous methods. Results show that three-dimensional distortion of bubbles may enhance amplification of external disturbances by more than an order of magnitude.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.We introduce a new algorithm for computing resolvent modes of large systems based on randomized singular value decomposition (RSVD) combined with a time-marching method. The most expensive steps of the RSVD algorithm in the context of resolvent analysis, which constitute a bottleneck in its application to large systems, are replaced by leveraging the time-domain equations that have given rise to the resolvent operator. Specifically, the actions of the resolvent operator and its adjoint on a vector are obtained by equivalent direct and adjoint marching operations in the time domain. Our algorithm exploits streaming calculations to alleviate memory issues emerging for large systems, and we develop strategies to minimize the time-stepping cost while maintaining a desired level of accuracy. We validated our proposed algorithm by comparing the resolvent modes and gains of a Ginzburg-Landau model problem to those obtained from RSVD. Then, we use an axisymmetric jet and a three-dimensional extension thereof to assess and demonstrate the accuracy, cost, and memory efficiency of our new algorithm when applied to a high-dimensional system. In the three-dimensional case, we achieve orders-of-magnitude reduction in both CPU and memory usage compared to a direct application of RSVD.

© We study a turbulent jet issuing from a cylindrical nozzle to characterise coherent structures evolving in the turbulent boundary layer. The analysis is performed using data from a large-eddy simulation of a Mach 0.4 jet. Azimuthal decomposition of the velocity field in the nozzle shows that turbulent kinetic energy predominantly resides in high azimuthal wavenumbers; the first three azimuthal wavenumbers, that are important for sound generation, contain much lower, but non-zero amplitudes. Using two-point statistics, low azimuthal modes in the nozzle boundary layer are shown to exhibit significant correlations with modes of the same order in the free-jet region. Spectral proper orthogonal decomposition is used to distill a low-rank approximation of the flow dynamics. This reveals the existence of tilted coherent structures within the nozzle boundary layer and shows that these are coupled with wavepackets in the jet. The educed nozzle boundary-layer structures are modelled using a global resolvent analysis of the mean flow inside the nozzle to determine the most amplified flow responses using the linearised Navier-Stokes system. It is shown that the most-energetic nozzle structures can be successfully described with optimal resolvent response modes, whose associated forcing modes are observed to tilt against the nozzle boundary layer, suggesting that the Orr mechanism underpins these organised, turbulent, boundary-layer structures.

© 2021 Cambridge University Press. All rights reserved.Resolvent analysis of the linearized Navier-Stokes equations provides useful insight into the dynamics of transitional and turbulent flows and can provide a model for the dominant coherent structures within the flow, particularly for flows where the linear operator selectively amplifies one particular force component, known as the optimal force mode. Force and response modes are typically obtained from a singular-value decomposition of the resolvent operator. Despite recent progress, the cost of resolvent analysis for complex flows remains considerable, and explicit construction of the resolvent operator is feasible only for simplified problems with a small number of degrees of freedom. In this paper we propose two new matrix-free methods for computing resolvent modes based on the integration of the linearized equations and the corresponding adjoint system in the time domain. Our approach achieves an order of magnitude speedup when compared with previous matrix-free time-stepping methods by enabling all frequencies of interest to be computed simultaneously. Two different methods are presented: one based on analysis of the transient response, providing leading modes with fine frequency discretization; and another based on the steady-state response to periodic forcing, providing optimal and suboptimal modes for a discrete set of frequencies. The methods are validated using a linearized Ginzburg-Landau equation and applied to the three-dimensional flow around a parabolic body.

© The Author(s), 2021. Published by Cambridge University Press.We present a two-point model to investigate the underlying source mechanisms for broadband shock-associated noise (BBSAN) in shock-containing supersonic jets. In the model presented, the generation of BBSAN is assumed to arise from the nonlinear interaction between downstream-propagating coherent structures with the quasi-periodic shock cells in the jet plume. The turbulent perturbations are represented as axially extended wavepackets and the shock cells are modelled as a set of stationary waveguide modes. Unlike previous BBSAN models, the physical parameters describing the hydrodynamic components are not scaled using the acoustic field. Instead, the source characteristics of both the turbulent and shock components are extracted from the hydrodynamic region of large-eddy simulation and particle image velocimetry datasets. Apart from using extracted data, a reduced-order description of the wavepacket structure is obtained using parabolised stability equations. The validity of the model is tested by comparing far-field sound pressure level predictions to azimuthally decomposed experimental acoustic data from a cold Mach 1.5 underexpanded jet. At polar angles and frequencies where BBSAN dominates, encouraging comparisons of the radiated noise spectra for the first three azimuthal modes, in both frequency and amplitude (at peak frequency), reinforce the suitability of using reduced-order wavepacket sources for predicting BBSAN peaks. On the other hand, wavepacket jitter is found to have a critical role in recovering sound amplitude at interpeak frequencies. The paper presents a quantitative demonstration that the wavepacket-shock interaction, carefully reconstructed by extracting components from data or linearised models, contains the correct essential flow physics that accounts for most features of the far-field BBSAN spectra.

© 2021 The Author(s). Published by Cambridge University Press.This study is focused on the prediction of coherent structures, propagating within a turbulent channel flow. We propose a derivation of the linearised problem based on a stochastic formulation of the Navier-Stokes equations. It consists in considering the transport of quantities by a resolved velocity (i.e. solution of the model) perturbed by a Brownian motion which models the unresolved turbulent fluctuations over the time-averaged field, here thought of as the underlying background turbulence. The associated linearised model, considering the mean velocity profile as given, predicts linear solutions evolving within a corrected mean velocity field and perturbed by modelled background turbulence. Two ways to define the statistics of the Brownian motion are proposed and compared: One based on full simulation data, and the second, data free, based on preliminary predictions from resolvent analysis. The technique is applied on turbulent channel flows at friction Reynolds numbers and, and predictions are compared with direct numerical simulation results. We show that the principal components of an ensemble of solutions of this stochastic linearised system are able to represent the leading spectral proper orthogonal decomposition modes with a similar accuracy to optimal responses coming from resolvent analysis with an eddy-viscosity model at scales where strong production occurs. For the other scales, receiving energy by nonlinear redistribution, the present strategy improves the prediction. Moreover, the second mode is systematically well predicted over all scales. This behaviour is understood by the ability of the stochastic modelling to model positive and negative inter-scale energy transfers through stochastic diffusion and random stochastic transport, while the eddy-viscosity term in resolvent analysis is purely diffusive.

© 2020 by The Authors. Published by the American Institute of Aeronautics and Astronautics, Inc.This paper studies the amplitude of large-scale coherent wave-packet structures in jets, modeled by the parabolized stability equations (PSEs). Linear PSEs can retrieve the shape of the wave packets, but linearity leads to solutions with a free amplitude, which has traditionally been obtained in an ad hoc manner using limited data. We systematically determine the free amplitude as a function of frequency and azimuthal wave number by comparing the fluctuation fields retrieved from PSEs with coherent structures educed from large-eddy simulation data using spectral proper orthogonal decomposition. The wave-packet amplitude is shown to decay exponentially with the Strouhal number for axisymmetric and helical modes at both Mach numbers considered in the study: 0.4 and 0.9. Analytical fit functions are proposed, and the scaled wave packets provide reasonable reconstructions of pressure and velocity spectra on the jet centerline and lip line over a range of streamwise positions.

© 2021 by Rafael M. Bertolin, Antônio B. Guimarães Neto, Guilherme C. Barbosa, Juliano A. Paulino, and Flávio J. Silvestre.There are many challenges related to the design and operation of flexible aircraft. Flight control law design for improving handling qualities is one of them because the major problem in the design of controllers then concerns aeroservoelastic stability. To deal with this difficulty, methodologies for flight control law design considering the aeroelastic dynamics of the aircraft are being pursued. In this paper, a static output-feedback-based stability augmentation system is proposed and designed to improve the handling qualities and the structural dynamics decoupling of a flexible aircraft. The design is based on the projective control technique, which allows preserving in the closed-loop system the eigenstructure of certain modes of interest whose dynamic characteristics stem from an optimal state feedback solution. An experimental prototype of a flexible aircraft that mimics a high-altitude long-endurance airplane, called X-HALE, is considered in the case studies. Robustness analysis based on classical and disk-based stability margins, and nonlinear simulations of gusts and turbulent flight conditions evaluated and confirmed the effectiveness of the proposed controller.

© 2021 Wiley-VCH GmbHThis study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma-activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans.

© 2021, Associação Brasileira de Engenharia Química.Mercury and its compounds are very dangerous to environmental and human health. Methods to contain and/or limit its emission through the filters, gas cleaning systems, and alternative processes for purification of industrial residues are necessary. This study focused on mercury removal from diatomite sorbent samples–used as a filter in chemical industries–using an oxygen low-pressure hollow cathode discharge (HCD). The effects of the exposure time and temperature were investigated. Thermal desorption (at 500 and 650 °C) and plasma oxidation were performed at low pressures (between 36 and 80 Pa). The results show a considerable acceleration of the diatomite decontamination to a temperature of 650 °C, bringing the concentration of mercury below 100 µg/kg after 10 min and 39 µg/kg after 110 min of HCD exposure time. A comparative analysis of the virgin diatomite characteristics used in the filter press and after treatment show the possibility of recycling this material. Additionally, the mercury extracted by condensation in the vacuum line (by using a dry ice trap) can be purified for reuse and returned to the industrial process.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.In this study, the potential antimicrobial activity of plasma-activated tap water (PAW) was evaluated against Staphylococcus aureus, Escherichia coli, and Candida albicans. For this, PAW was prepared in a gliding arc plasma system using two treatment conditions: stagnant water and water stirring by a magnetic stirrer, called moving water. Subsequently, their oxidation-reduction potential (ORP), pH, electrical conductivity (σ), and total dissolved solids (TDS) were monitored in different areas of the sample divided according to the depth of the beaker. It was observed that PAW obtained in dynamic conditions showed a more uniform acidity among the evaluated areas with pH 3.53 and ORP of 215 mV. Finally, standardized suspensions of Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 10799), and Candida albicans (SC 5314) were treated with PAW, and the reduction of viable cells determined the antimicrobial effect. Our results indicate that the tap water, activated by plasma treatment using gliding arc, is an excellent inactivation agent in the case of Staphylococcus aureus and Escherichia coli. On the other hand, no significant antimicrobial activity was achieved for Candida albicans.

© 2020The increase in the biointegration speed of titanium alloys is an important factor in the recovery and quality of life after an implant. The coating of these materials with thin films using plasma technologies is a viable alternative that can change the surface properties without changing the bulk properties. In this work, Diamond-like Carbon films doped with silver nanoparticles were deposited on the surface of Ti6Al4V alloys using a conjugate reactor, which uses Plasma Enhanced Chemical Vapor Deposition technique associated with a silver hollow cathode. The flow of argon was varied (from 20 to 80 sccm) to evaluate its influence on surface roughness and biointegration. Secondary Ion Mass Spectrometry depth profile showed the effectiveness of the hollow cathode to form a silver concentration gradient from the substrate up to the film surface, which is desirable in biomedical applications. Atomic Force Microscopy detected that increasing argon flow from 20 to 80 sccm produced a more acicular relief and promoted an increase in sp3 hybridization, which characterizes films with better adhesion and mechanical resistance, as well as biomedical applications in which the material is subjected to load-bearing and wear. These results indicated the possibility of tuning the film roughness according to its biomedical application. The results of in vivo tests suggested that silver doping in Diamond-like Carbon films promoted faster biointegration than non-doped Diamond-like Carbon films and indicated the potential for their applicability in medical prosthetic materials.

© 2021 Universidade Federal de Sao Carlos. All rights reserved.Every year, billions of dollars are invested in research and development for space applications, including new systems, new technologies, and new materials. DLC (Diamond-Like Carbon) is a promising material for use in these applications, but its use faces a technological barrier, since it is severely etched by atomic oxygen and ozone. In this study, SiOx-DLC thin films were deposited as a top layer of diamond-like carbon (DLC) films on Ti-6Al-4V substrates to increase resistance against corrosion by atomic oxygen and ozone as well as meet the requirements for use in Low Earth Orbit (LEO) satellites. The corrosion resistance of the films was evaluated using oxygen plasma, and the tribological and mechanical properties were investigated. The SiOx-DLC top layer reduced the corrosion rate two orders of magnitude and increased the critical load from 16.2 ± 1.5 N to 18.4 ± 0.4 N.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The chemical, structural, morphological, and optical properties of Al-doped TiO2 thin films, called TiO2/Al2O3 nanolaminates, grown by plasma-enhanced atomic layer deposition (PEALD) on p-type Si <100> and commercial SLG glass were discussed. High-quality PEALD TiO2/Al2O3 nanolam-inates were produced in the amorphous and crystalline phases. All crystalline nanolaminates have an overabundance of oxygen, while amorphous ones lack oxygen. The superabundance of oxygen on the crystalline film surface was illustrated by a schematic representation that described this phenomenon observed for PEALD TiO2/Al2O3 nanolaminates. The transition from crystalline to amorphous phase increased the surface hardness and the optical gap and decreased the refractive index. Therefore, the doping effect of TiO2 by the insertion of Al2O3 monolayers showed that it is possible to adjust different parameters of the thin-film material and to control, for example, the mobility of the hole-electron pair in the metal-insulator-devices semiconductors, corrosion protection, and optical properties, which are crucial for application in a wide range of technological areas, such as those used to manufacture fluorescence biosensors, photodetectors, and solar cells, among other devices.

© 2020 International Ozone Association.The purpose of the current study was to investigate the effect of ozone exposure on the process of water uptake and germination of lentil (Lens culinaris) seeds. For this, a commercial ozone generator that provides a concentration of 1 g/m3 generated from atmospheric air was used. In the experiments 10 lentil seeds were used per treatment carried out at different times of exposure to ozone: 2, 3, 5, 10 and 15 min. Imbibition curves were performed following the seed mass for 180 min. For germination tests, wet neutral pH germination paper was used where, every 24 h, the mass, root size and stem size of the plant were measured over 7 days. Furthermore, contact angle analysis and Fourier transform infrared spectroscopy (FT-IR) were performed on the seeds. The maximum water uptake in the seeds as a function of the imbibition time was optimum for the samples treated with 3 and 5 min. This fact was reflected in the growth rates of the stem, root and mass that were significantly higher than the control sample, after 7 days of germination. The FT-IR analysis indicated the formation of bands in 1345 cm−1 (NO3−) related to ethylene ozonolysis. Also, it was observed a reduction of the N-H band (amide II) at 1551–1550 cm−1 and increase of the C-H bond at 1543 cm−1, evidencing a possible action of ozone on lentil proteins. This fact is probably related to the enhancement of the seed germination process, allowing the germination rates to be 90% for samples treated with ozone for 3 and 10 min.

© 2021 by GE Research.The aim of this work is an evaluation of different turbulence models applied in Computational Fluid Dynamics (CFD) techniques in the turbomachinery area, in this case, in an axial turbine stage used in turbopump (TP) application. The tip clearance region was considered in this study because it has a high influence in turbomachinery performance. In this region, due to its geometry and the relative movement between the rotor row and casing, there are losses associated with vortices and secondary flow making the flowfield even more turbulent and complex. Moreover, the flow that leaks in the tip region does not participate in the energy transfer between the fluid and rotor blades, degradating the machine efficiency and performance. In this work, the usual flat tip rotor blade geometry was considered. The modeling of turbulent flow based on Reynolds Averaged Navier-Stokes (RANS) equations predicts the variation of turbine operational characteristics that is sufficient for the present turbomachine and flow analysis. Therefore, the appropriate choice of the turbulence model for the study of a given flow is essential to obtain adequate results using numerical approximations. This comparison become important due to the fact that there is no general turbulence model for all engineering applications that has fluid and flow. The turbomachine considered in the present work, is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME), considering the 3.0% tip clearance configuration relative to rotor blade height. The turbulence models evaluated in this work were the SST (Shear Stress Transport), the k-e Standard and the k-e RNG. The computational domain was discretized in several control volumes based on unstructured mesh. All the simulations were performed using the commercial software developed by ANSYS, CFX v15.0 (ANSYS). All numerical settings and how the boundary conditions were imposed at different surfaces are explained in the work. The boundary conditions settings follow the same rule used in the test facility and needs some attention during the simulations to vary the Blade-Jet-Speed ratio parameter adequately. The results from numerical simulations, were synthesized and compared with the experimental data published by National Aeronautics and Space Administration (NASA), in which the turbine efficiency and its jet velocity parameter are analyzed for each turbulence model result. The work fluid considered in this work was water, the same fluid used in the NASA test facility.

© 2020 Elsevier LtdThe present work experimentally investigates hydrous ethanol/air flame stability. The experimental data were obtained using spherically expanding flames in a constant volume bomb with optical access for high-speed schlieren photography. It explores the effect of flame parameters, such as thermal expansion rate, flame thickness, activation energy, and effective Lewis numbers, on flame dynamics at elevated pressures (2 to 6 bar) and temperatures (380 and 450 K), at various equivalence ratios (0.6 to 1.3) and water dilution contents (0, 5, 20 and 30% in volume). Adding water to the ethanol/air mixture and increasing its content leads to a significant decrease in flame instability, reducing the thermal expansion ratio while increasing the flame thickness and therefore reducing the propensity of hydrodynamic instability appearance on the flame front. The equivalence ratio has a significant effect on flame stability as well. Slightly rich mixtures present the maximum thermal expansion ratio and minimum flame thickness, therefore, presenting the highest propensity for hydrodynamic instability of the flame front. Besides, the effective Lewis number significantly decreases with equivalence ratio, showing a higher propensity of diffusional-thermal instability for rich mixtures. The flame front instability significantly increases with the mixture initial pressure, which results from the enhancement of the hydrodynamic instability due to the significant decrease in the flame thickness for all equivalence ratios. The initial temperature has a weaker effect on flame stability compared to the other thermo-chemical properties investigated. However, the flame front instability slightly increases with temperature.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Propellers are one of the most efficient ways to generate propulsion for low-speed flights. About 84% of the energy generated by the engines is utilized, being therefore widely used in several different aircraft. However, studies show that propellers with a diameter less than 16 inches have efficiency reduced by up to 15% when compared to larger ones. This deficiency is not always captured by the mathematical models, since they are not as accurate for that scale. The present study aims to increase the accuracy of simulations performed by a blade element/vortex software to predict the performance of different motor-propeller assemblies. For this purpose, neural networks are trained to correct thrust and torque values given by the software in relation to wind tunnel tests. For this, 28 propellers from different manufacturers and geometries are tested in wind tunnel and simulated in the software under the same conditions to generate the training database. Geometric data of propellers and operational conditions were used as inputs for the neural networks. The outputs are the difference between the results of the test in a wind tunnel and the software simulation. The use of neural networks to correct the simulation results reduced the mean squared error of the estimates at least in 80% in the case of thrust and 70% in the case of torque.

© 1965-2011 IEEE.Due to a production error, in the original article [1], Figs. 1, 2 and 3 were incorrectly published. We apologize for this error. The correct figures, with their corresponding captions, are shown below (Figure Presented).

© 2020 Elsevier LtdThe emergence of automated manufacturing techniques has allowed the realization of the so-called tow-steered composite laminates, in which the fibers are deposited following continuous curvilinear paths. This enables to broaden the design space to satisfy a variety of design objectives. Previous studies have shown that conventional composites can be designed to maximize the modal frequencies and modal damping factors. However, similar investigations have not been devoted to tow-steered composites so far. In this context, the objective of this paper is to investigate the use of multi-objective optimization aiming at simultaneously maximizing the fundamental modal frequency and corresponding specific damping capacity of tow-steered composite laminates. The fiber trajectories are parameterized using two different schemes, and the parameters are taken as design variables. The equations of motion are derived from the combination of the Classical Lamination Theory with the Rayleigh–Ritz method. Damping is modeled by using the Strain Energy Method. Numerical optimization is performed using the evolutionary Direct Multisearch method, which provides optimal solutions forming Pareto fronts. Results obtained from various scenarios, including fully and partially steered laminates, and different boundary conditions, show that fiber steering can indeed improve substantially the dynamic characteristics, including damping, of composite laminates.

© 2020 Elsevier LtdMany studies previously reported in the literature have demonstrated, both theoretically and experimentally, the influence of thermally-induced stresses on the static and dynamic behavior of structures, due to the so-called stress-stiffening effect. In most cases of practical interest, temperature variations associated to environmental and operational conditions are governed by rather complex combinations of conduction, convection and radiation mechanisms. As a result, the temperature values at different points of a structure are very difficult to control and can rationally be considered as random quantities. In this context, the present paper addresses the stochastic modeling and characterization of the influence of thermal stresses on the natural frequencies of thin rectangular plates, assuming space-dependent temperature fluctuations modeled as stationary two-dimensional Gaussian random fields. For this purpose, based on the hypotheses of the classical Kirchhoff plate theory, a Rayleigh-Ritz-based dynamic model is first derived for the bending vibrations of plates, accounting for the presence of thermal stresses. This model is combined with the Karhunen-Loève expansion (KL), which is used to discretize the temperature random field, after which the statistics of the random natural frequencies are estimated by Monte Carlo sampling. Numerical simulations are performed for plates under free boundary conditions. Simulation results, which encompass sampling-based statistics for the thermal stresses and the first six natural frequencies of the plate, are presented and discussed. In addition, since thermal stresses can induce buckling, reliability has also been estimated considering this type of failure. Results enable to conclude that space-dependent temperature uncertainty can be significant upon the vibration and buckling behavior of plates, which justifies its consideration.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Transonic flows at high Reynolds numbers can lead to high dynamic pressures and, consequently, aerostructural deflections of the aircraft structures, mainly in the wings. In this work, the in-house Computational Fluid Dynamics (CFD) code, BRU3D, and previously developed fluid-structure interaction (FSI) tools are tested for different loading conditions using the High Reynolds Number Aero-Structural Dynamics (HIRENASD) model. The work also investigates the effects of grid refinement on the improvement of the correlation obtained with the results of the present simulations and the experimental and computational data available from the AIAA Aeroelastic Prediction Workshop (AePW). Comparisons are made in terms of aerodynamic coefficients and wing structural deflections.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.The present work has the objective of presenting recent developments of a static aeroelastic computational process for the analysis of typical aircraft configurations in transonic flows. The analysis procedure is assessed through the study of static aeroelastic characteristics of the HIRENASD model, which is a test cases with extensive experimental database for validation of computational results. The in-house BRU3D computational fluid dynamics (CFD) solver, which uses the fully turbulent compressible Reynolds-averaged Navier-Stokes (RANS) equations, is combined with a finite element method (FEM) modal basis code through the uses of radial basis functions (RBF) for smooth volume grid movements. Results in terms of structural displacements have shown good agreement with experimental data, although indicating that further grid refinement for the fluid domain is still necessary in order to improve the correlation of the aerodynamic coefficients.

© "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. All rights reserved.Over the last decades, the development of novel permanent magnets, especially those having rare earth metals in their composition, has led to a great improvement in their performance, as compared to conventional ferrite permanent magnets. Therefore, there has been an increasing demand for these magnets in many (including new) application fields. In particular, the strong magnetic forces exerted between magnets can be explored as a means of promoting contactless mechanical coupling between separate parts and structural components. In this context, this paper investigates the dynamic behavior of a multiphysics system composed of two parallel cantilever beams at the extremity of which cubic permanent magnets are attached. Given the nonlinear nature of the magnetic forces, the main interest is to characterize the dynamic phenomena induced by the magnetic coupling. The study also encompasses analyses of the influence of the gaps between the two magnets and the relative orientation of their polarization axes. For this purpose, an elasto-magnetic structural model is developed, accounting for the flexibility and mass distributions of the beams and also the magnetic interactions. Upon resolution of the equations of motion, this model is used to perform a number of numerical simulations, the results of which are presented and discussed.

© Springer Nature Switzerland AG 2021.Previous studies have demonstrated the influence of thermal stresses on the static and dynamic behavior of structures. In most cases of practical interest, temperature variations are governed by complex combinations of heat transfer mechanisms. As a result, the temperature values at different points of a structure can be considered as random variables. The present paper addresses the stochastic modeling of the influence of space-dependent temperature variations on the natural frequencies of beams. For this purpose, based on the hypotheses of the classical Euler-Bernoulli beam theory, a finite element model is constructed for the bending vibrations of beams, accounting for thermal influences. A particular scenario is considered in which the beam is subjected to random linearly-varying temperature fields, parameterized by two random variables. A probabilistic model is derived, which provides the PDF of the thermally-induced axial force from the PDFs of the random variables. Numerical simulations are performed for a clamped aluminum beam. Sampling-based statistics for the thermal axial load and the first six natural frequencies of the beam are presented. In addition, since thermal stresses can induce buckling, the probability of failure by this mechanism is also computed. Results enable to conclude that temperature uncertainty can be significant upon the vibration and buckling behavior of beams, which justifies its consideration in structural analyses.

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.Electroactive Co3O4 films were deposited by reactive magnetron sputtering (RMS) onto an assembly composed of a thin TiO2 layer over a commercial indium-doped tin oxide (ITO) conductor electrode, forming an ITO/TiO2/Co3O4 electrocatalytic platform. The platform was tested as a non-enzymatic device for glucose electrooxidation. The characterization of the electroactive TiO2/Co3O4 heterojunction was carried out by x-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscope (FE-SEM), and energy dispersive spectroscopy (EDS) techniques. It was shown that the Co3O4 top layer is homogeneous and free from undesirable secondary phases. The electrochemical measurements, characterization and performance, were carried out by cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). The cyclic voltammogram shows the linear dependence between the anodic and cathodic current peak of the redox process at the electrode surface, showing the electrochemical activity of the Co3+/Co4+ redox pair, as well as good reversibility and efficiency of charge transfer. From the chronoamperometric curves, two electrochemical parameters were estimated, the diffusion coefficient (D) and catalytic rate constant (kobs) of glucose with the values of 1.2 × 10−6 cm2 s−1 and 2.8 × 106 cm3 mol−1 s−1, respectively. The ITO/TiO2/Co3O4 heterojunction electrode showed an acceptable linear range from 10 to 1000 μM glucose concentration with a molar sensitivity (S) of 30.0 μA cm−2 mM−1 and a detection limit (LOD) of 1.42 μM (S/N = 3). These electrochemical results show the higher electroactivity of TiO2/Co3O4 heterojunction electrode than that of bare Co3O4 electrode and other literature results.

© 2020The increase in the biointegration speed of titanium alloys is an important factor in the recovery and quality of life after an implant. The coating of these materials with thin films using plasma technologies is a viable alternative that can change the surface properties without changing the bulk properties. In this work, Diamond-like Carbon films doped with silver nanoparticles were deposited on the surface of Ti6Al4V alloys using a conjugate reactor, which uses Plasma Enhanced Chemical Vapor Deposition technique associated with a silver hollow cathode. The flow of argon was varied (from 20 to 80 sccm) to evaluate its influence on surface roughness and biointegration. Secondary Ion Mass Spectrometry depth profile showed the effectiveness of the hollow cathode to form a silver concentration gradient from the substrate up to the film surface, which is desirable in biomedical applications. Atomic Force Microscopy detected that increasing argon flow from 20 to 80 sccm produced a more acicular relief and promoted an increase in sp3 hybridization, which characterizes films with better adhesion and mechanical resistance, as well as biomedical applications in which the material is subjected to load-bearing and wear. These results indicated the possibility of tuning the film roughness according to its biomedical application. The results of in vivo tests suggested that silver doping in Diamond-like Carbon films promoted faster biointegration than non-doped Diamond-like Carbon films and indicated the potential for their applicability in medical prosthetic materials.

© 2021 Universidade Federal de Sao Carlos. All rights reserved.Every year, billions of dollars are invested in research and development for space applications, including new systems, new technologies, and new materials. DLC (Diamond-Like Carbon) is a promising material for use in these applications, but its use faces a technological barrier, since it is severely etched by atomic oxygen and ozone. In this study, SiOx-DLC thin films were deposited as a top layer of diamond-like carbon (DLC) films on Ti-6Al-4V substrates to increase resistance against corrosion by atomic oxygen and ozone as well as meet the requirements for use in Low Earth Orbit (LEO) satellites. The corrosion resistance of the films was evaluated using oxygen plasma, and the tribological and mechanical properties were investigated. The SiOx-DLC top layer reduced the corrosion rate two orders of magnitude and increased the critical load from 16.2 ± 1.5 N to 18.4 ± 0.4 N.

© 2021 Elsevier LtdThe actual experimental methods applied to determine the materials' thermal properties at high temperatures usually do not provide good quality values for matching simulations to experimental data. To solve this problem, this work proposes an alternative inverse methodology to estimate the thermal properties of a material at high temperatures. The developed technique is called Quadrilateral Optimization Method (QOM). The QOM is a multivariable estimation technique developed to determine the function's parameters. To regularize the results, the Time Traveling Regularization (TTR) was applied in the objective function. To prove the methodology efficiency, the specific heat is estimated through this inverse approach for a LASER welding problem. In this case, the specific heat was treated as an exponential function. Then, the QOM estimates the parameters of this function. A sensitivity analysis is performed to determine the estimation range. To minimize the computational time, in the direct model the non-linear heat diffusion equation was solved through the Finite Volume Method in an in-house CUDA-C code. A numerical welding experiment was performed to eliminate the real experimental errors. The results demonstrated that the proposed approach had an average error of less than 0.075% in the parameters' estimation in the best-case-scenario. The new methodology was validated, and it proved to be an easier and cheaper way to determine the thermal properties at high temperatures without the need to use advanced experimental apparatus.

© 2021 Elsevier B.V.The use of remelting as heat treatment for metallic components has grown on an industrial scale, particularly in sectors where surface hardness is a requirement. Using a conventional Tungsten Inert Gas (TIG) welding torch, it is possible to induce desirable microstructures, promote grain refinement, and as a result, increase hardness. However, one of the main challenges concerns understanding the effects of remelting strategies based on the torch/tool path planning. It is possible to draw different conclusions under the same processing parameters depending on the tool's trajectory. Therefore, the present study aims to assess the influence of remelting path strategies on the AISI 1045 steel hardness, correlating its microstructure with thermal variables obtained from an in-house Finite Volume numerical model. Two different approaches are analyzed, namely Strategy 1 and Strategy 2.The former was characterized as a single direction movement with 77 s average time between beads, while Strategy 2 was chosen as double direction movement (zigzag) without interbead time. In both cases, TIG remelting was applied autogenously with 120A Direct Current Electrode Negative (DC-), at 15 cm/min, with a 30% overlap ratio for five parallel beads, and with Argon as shielding gas. The results pointed out that both strategies promoted a hardness increase relative to the base metal, 23% for Strategy 1 and 9% for Strategy 2. This factor was attributed to grain refining. The simulation revealed that Strategy 1 is more suitable than Strategy 2 to boost the hardness is related to the higher solidification cooling rate (166 °C/s versus 137 °C/s, respectively) and lower time above 900 °C (7 s versus 12 s, respectively).

© 2021Anisotropic characteristics of certain materials can be used as a design asset in several fields of research and industry. Anisotropic thermal conductivity data available in the literature are limited. This work proposes an alternative experimental methodology to determine the thermal conductivity of anisotropic materials. In the suggested apparatus, samples are settled in a vacuum chamber to assure convective insulation; aluminum films, fixed on the surrounding walls, achieved radiative insulation. To validate the methodology, the research determined the thermal conductivities of known isotropic materials, such as stainless steel, copper, and aluminum. The investigation compared the measured experimental data to the literature ones, which exhibits good coincidence, thus validating the technique. In addition, the study experimentally investigated a phenol-formaldehyde resin reinforced by the presence of cotton fibers called Celeron-C1001. The analysis describes the Celeron-C1001 anisotropic thermal conductivity coefficients by the use of experimentally assessed temperature fields and heat fluxes.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Temperature measurement in welding constitutes relevant information for process understanding and simulation, as it can be used to validate and predict microstructure. Monitoring can be performed at specific points through transducers. The typical one is the thermocouple. In laser welding processes, due to the high energy concentration of the beam, the acquisition with thermocouples should be performed closer to the bead when compared to electric arc welding processes. This measurement is critical because of overheating by spatters, which can result in damage. The present work covers developing a Capacitive Discharge Welding device for thermocouple fixing and assessing possible temperature acquisition positions in keyhole laser welding. The study performed all tests with a fiber laser of 9 kW power and 3 m/min scanning speed. When placed at 2 mm from the weld centerline, the results showed a high probability of spattering due to the 71° range of incidence angle. Therefore, the thermocouple should be placed far from the weld centerline to minimize the spattering. However, it must be close enough to acquire temperatures above 727 °C. This temperature corresponds to the envisaged austenitization microstructure correlation. The study found the maximum distance at 3.5 mm based on an interpolation map, where the incidence spatters angle reduced to 59°. At a 2 mm distance from the weld centerline, the weld cross section temperatures reached more than 727 °C. However, the microstructural changes did not occur due to insufficient austenitization time. The Heat Affected Zone boundary was at 1.64 mm from the weld centerline. Therefore, to correlate microstructure with thermal cycles, it is necessary to place thermocouples at a distance below this value. However, spatter can be a problem since the range of incidence angle is about 75°. Therefore, this work recommends using more than one thermocouple for each position (redundancy) to increase valuable data. Graphic abstract: [Figure not available: see fulltext.].

© 2020The estimation of the imposed heat rate in welding processes has always been an obstacle to improve the thermal efficiency of these processes. Thus, the use of inverse problem techniques is an alternative procedure to estimate the heat rate. In this study, the problem is highly nonlinear; therefore, the heat flux provided by the welding process is estimated by the iterative Function Specification method. This method was modified to estimate the heat supply based on the heat rate sensitivity coefficient, which represents the influence of the welding power in the temperatures of 304 stainless steel plates. In order to avoid the problem of low thermal sensitivity due to the movement of the welding source on the upper face of the plate, this methodology is based on the concept of temperature moving sensor. The software COMSOL was used to solve the three-dimensional heat diffusion equation with enthalpy function to model the phase change problem. 10 type K thermocouples, equally spaced, were attached by capacitive discharge on the opposite heated surface to measure the temperature. The efficiency of the process was calculated with the estimated net heat rate which ranged from 63% to 87%. The average efficiency obtained was 75% for this welding process. A relation between the energy rate given by the power supply and the estimated efficiency was also observed. The thermal efficiency of the arc decreases as the power increases. Thus, an analysis using the Taguchi method was performed in order to better understand the influence of the welding parameters on the efficiency of the process. It was concluded that with a significance level of 10%, the welding current and arc length have a strong correlation with thermal efficiency. These results are discussed and compared with results obtained experimentally by other researchers. Besides, an uncertainty analysis in the estimated heat rate is also presented.

© 2021 IEEERobotic flight simulators have emerged as a low-cost alternative to conventional flight simulators. Despite the enormous potential, few research works have been conducted regarding the representativeness of the movement of these simulators. Thus, the present work seeks to propose an optimization of the washout filter using the genetic algorithm to obtain the parameters capable of maximizing pilot's acceleration perception during the plane's takeoff. 3 configurations were proposed: solution 1 that does not impose displacement limits for channel B of the simulator, solution 2 with a limited displacement of 15° for the channel B and solution 3 that considers the limit of 15° and a different configuration of the cost function. It was found that the solution that maximizes pilot perception is the solution 1. Solutions 2 and 3 were similar, which indicates that it is the best configuration to be obtained with the current workspace limitation. The comparison of the 3 solutions also indicates that the trail could be further explored to increase the sensation of acceleration during takeoff.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.Aircraft conceptual design has mostly been characterized by sizing by the use of rather simple analytical models. Such models serve a purpose since they can be easily be manipulated for e.g. trade studies to see the effect of requirements on the design parameters and general performance of the aircraft. However, there is a trend to involve more advanced calculations, e.g. more advanced aerodynamics calculations and flight dynamics analysis, already at the conceptual design, in order to further reduce uncertainty. In the same way, it could be argued that more detailed analysis of behaviour of the aircraft in a mission should be useful. We propose the simulation of hybrid systems in the framework of transmission line modelling, TLM. We extend an existing continuous time methodology, and adopt UML Activity Diagram and Petri nets for the discrete event dynamics, to describe complex behaviour. This allows for full system simulation of a mission where a more accurate evaluation of mission performance can be obtained. In this paper the methodology is outlined and demonstrated on a UAV mission application.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.Cockpit flight control interfaces have remained largely unchanged since the beginnings of Aviation (sticks, yokes, pedals and thrust levers). New technologies have emerged that have successfully been employed in other fields of technology regarding Human-Machine interaction, one such technologies is eye tracking. The pilot is a fundamental element even in modern aircraft with high levels of computerized assistance. Emergency situations or environmental factors can lead to a situation were a pilot is overwhelmed by simultaneous tasks and this can lead to the conditions for an accident. With these points into consideration, a modernized flight control interface is proposed were Eye tracking is used as a complementary input for yokes, side sticks and pedals. Review of literature and previous research suggests that this application has considerable merit for its potential benefits, this paper is in regard of early experimentation using the system in a highly realistic flight simulator. The development uses equipment available at the Instituto Tecnologico de Aeronautica (ITA) to create a prototype that enables the characterization of the proposed a system. Results from this set of experiments contributed to the further refinement of the system, error correction, obtaining of operational experience and collection of data and feedback from participants that suggest that the proposed system could have a positive impact in the controlability of an aircraft by an inexperienced pilot during a high-workload situation.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.During the development of a flight control system that uses gaze as an alternative input method from the pilot, the human factors analysis is one of the most important processes. This gaze tracking system's architecture integrates three hardware elements that were not originally designed to operate with each other; the Tobii Pro Glasses 2, the HTC Vive Trackers, and the Aeronautics Institute of Technology' SIVOR flight simulator. This paper deals with an experiment that involves the visual search and acquisition of a target on a spherical screen, and the application of fitts's law to the eye tracking signal.

© 2021, Springer Nature Switzerland AG.This study evaluated the mental workload of military pilots during day and night conditions using night vision goggles (NVG) in a Flight Training Device, in order to rectify or ratify the fatigue correction factor used for flights using NVG. The experiment used basic military operational tasks measuring physiological data, specifically data on electrocardiography activity and galvanic skin response. Subjective data were gathered using NASA TLX and Psychomotor Vigilance Test methods. After collection, the data were subjected to treatment to correct possible errors during data acquisition and later analyzed in the domains of time and frequency. The analysis did not show a great change in mental workload between the day and night periods, which could be explained by the small sample, the small period between flights and the learning effect between day and night flight.

© 2021 by the authors.This work proposes a set of complementary practices to agile methodologies, aiming at adapting them to the development of critical aerospace embedded systems by distributed teams. To identify the main gaps in this context, two approaches are used. The first one confronts the main activities required by aerospace standards for the development of critical embedded systems with a set of compiled agile practices derived from a review of the most common agile methodologies. The second one confronts the same set of compiled agile practices with the main problems of distributed development. The two approaches resulted in the identification of four gaps related to software integration, software traceability, communication management, and organizational differences. One complementary practice is then proposed for each gap. Two case studies were performed to assess the gaps and evaluate the proposed practices. Both emulate the development of critical embedded systems by distributed teams using agile methodologies. The case studies were performed with and without the use of the complementary practices. The results confirmed three of the four identified gaps and pointed to a clear contribution of the complementary practices.

© 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.How do people with visual impairment see the world? In this literature review based on cognitive sciences findings, we have analyzed the main concepts used in the human brain’s cognitive processes to represent our perception of the surrounding environment. One of these concepts is mental imagery, which resembles perceptual experience without external sensory stimulation. This concept plays a central role in multisensory design cognition. It can help us understand the designer’s cognition process, design better systems for people with disabilities, and open opportunities for multisensory design teams.

© The Author(s) 2020.This paper presents a structure-preserving spatial discretization method for distributed parameter port- Hamiltonian systems. The class of considered systems are hyperbolic systems of two conservation laws in arbitrary spatial dimension and geometries. For these systems, a partitioned finite element method (PFEM) is derived, based on the integration by parts of one of the two conservation laws written in weak form. The non-linear one-dimensional shallow-water equation (SWE) is first considered as a motivation example. Then, the method is investigated on the example of the non-linear two-dimensional SWE. Complete derivation of the reduced finite-dimensional port-Hamiltonian system (pHs) is provided and numerical experiments are performed. Extensions to curvilinear (polar) coordinate systems, spacevarying coefficients and higher-order pHs (Euler-Bernoulli beam equation) are provided.

© The Authors. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0/)The dissipative Shallow Water Equations (DSWEs) are investigated as port-Hamiltonian systems. Dissipation models of different types are considered: either as nonlinear bounded operators, or as linear unbounded operators involving a classical diffusion term in 1D, or the vectorial Laplacian in 2D. In order to recast the dissipative SWE into the framework of pHs with dissipation, a physically meaningful factorization of the vectorial Laplacian is being used, which nicely separates the divergent and the rotational components of the velocity field. Finally, the structure-preserving numerical scheme provided by the Partitioned Finite Element Method (PFEM) is applied to the nonlinear bounded dissipative fluid models. For the linear unbounded cases, a change of variables is highlighted, to transform the DSWEs into a new pHs with a polynomial structure, which proves more suitable for numerics.

© The Author(s) 2020. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved.The free surface motion in moving containers is an important physical phenomenon for many engineering applications. One way to model the free surface motion is by employing shallow water equations (SWEs). The port-Hamiltonian systems formulation is a powerful tool that can be used for modeling complex systems in a modular way. In this work, we extend previous work on SWEs using the port-Hamiltonian formulation, by considering the two-dimensional equations under rigid body motions. The resulting equations consist of a mixed-port-Hamiltonian system, with finite and infinite-dimensional energy variables and ports.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.This paper presents a hybrid methodology for loads measurement on aircraft structures. It is based on both experimental data from the actual structure and numerical prediction from finite element models. The model is firstly adjusted based on a reduced amount of experimental data, so it can predict the structure load response in terms of simulated strain-gage bridge responses. Once adjusted, the model is loaded at several points while gathering the corresponding simulated strains responses. Based on regression analysis, the calibration coefficients are established to be used for in-flight load measurements. Comparing with the conventional calibration method, purely based on experimental tests, the new calibration methodology requires less calibration load cases, which makes the test setup also simpler. The new calibration method is applied to a horizontal empennage from a commercial aircraft, for which the conventional calibration was previously conducted, providing therefore the reference for both flight and ground test comparisons. A good correlation was found between the loads estimated by the conventional calibration and present method. Nowadays, virtual tests are getting importance for validation and demonstration purposes, and this work is adherent with this tendency.

© AIAA International. All rights reserved.An experimental remotely piloted aircraft named X-HALE was designed and built at the University of Michigan to collect experimental data for the flight dynamics of vehicles with very flexible wings. Similar aircraft with a wing span of 4 and 6 m were later developed and built at the Aeronautics Institute of Technology, Brazil, to study the flight dynamics and control of highly flexible aircraft. In the present Paper, the steady structural response of the wing of the X-HALE is investigated by the finite element method assuming 1) linear behavior (small displacement, small strain analysis) and 2) nonlinear behavior (large displacement, small strain analysis). This Paper aims to investigate the influence of geometric nonlinearities in the numerical prediction of load distribution and displacements along the wing span when compared with linear analyses results. For this purpose, four versions of the X-HALE with different structural layouts are presented. Two aircraft have a 4 m wing span constructed with fiberglass and aluminum, respectively. The other two have a wing span of 6 m and were also constructed with fiberglass and aluminum. Internal force redistributions were observed in the nonlinear structural analyses. The redistribution of these forces caused the twist angle to increase and the bending angle to decrease compared to the linear analyses when under the same loading conditions.

© 2021 Wiley-VCH GmbHThis study applies a proof of concept for future applications in controlling the microbiota in tubes and tracheal appliances used in the respiratory tract. Therefore, the physical–chemical parameters of the plasma-activated and nebulized water (NPAW) are measured in a nebulizer tube with different lengths between 0.1 and 3.0 m. The pH values and oxidation–reduction potential (ORP) do not change during nebulization of PAW over a 1.0 m tube. However, for longer lengths, there is an increase in pH and a decrease in ORP. At 3.0 m, the pH increases approximately 16% compared with the 1.0 m position with a 20% decrease in the ORP values. Hydrogen peroxide (H2O2) measured quantitatively using test strips presents values between 0.5 and 2.0 mg/L for condensed NPAW in different tube lengths between 0.1 and 3.0 m, and maintains the approximate value of 2.0 mg/L in tubes up to 1.0 m, with a reduction proportional to the increase in the length of the tube. The antimicrobial efficacy of NPAW applied for 15 min shows the inactivation of Staphylococcus aureus and Escherichia coli but without significant inactivation of Candida albicans.

© 2021 Elsevier LtdThermal plasma technology is a process that demonstrates high performance for the processing of different types of waste. This technology can also be applied in the treatment of radioactive wastes, which requires special care. Beyond that, volumetric reduction, inertization, as well as a cheap and efficient process are necessary. In this context, the purpose of this paper is to demonstrate the application of thermal plasma technology for the treatment of solid radioactive waste. For this, stable Co and Cs were used to simulate compactable and non-compactable radioactive waste; about 0.8 g Co and 0.6 g Cs were added in each experimental test. The experimental tests were conducted using plasma of transferred arc electric discharge generated by the graphite electrode inside the process reactor. The behavior and distribution of the radionuclides present in the waste were assessed during the plasma process. The results show that the significant amounts of Co and Cs leave the melt by volatilization and are transferred to the gas phase with a small portion retained in the molten slag. The retention rate of Co in the slag phase is about 0.03% and 0.30% for compactable and non-compactable waste, respectively. On the other hand, Cs is completely transferred to the gas phase when added to the compactable waste. Conversely, when in the non-compactable waste, only 1.4% Cs is retained.

© 2021, Associação Brasileira de Engenharia Química.Mercury and its compounds are very dangerous to environmental and human health. Methods to contain and/or limit its emission through the filters, gas cleaning systems, and alternative processes for purification of industrial residues are necessary. This study focused on mercury removal from diatomite sorbent samples–used as a filter in chemical industries–using an oxygen low-pressure hollow cathode discharge (HCD). The effects of the exposure time and temperature were investigated. Thermal desorption (at 500 and 650 °C) and plasma oxidation were performed at low pressures (between 36 and 80 Pa). The results show a considerable acceleration of the diatomite decontamination to a temperature of 650 °C, bringing the concentration of mercury below 100 µg/kg after 10 min and 39 µg/kg after 110 min of HCD exposure time. A comparative analysis of the virgin diatomite characteristics used in the filter press and after treatment show the possibility of recycling this material. Additionally, the mercury extracted by condensation in the vacuum line (by using a dry ice trap) can be purified for reuse and returned to the industrial process.

© 2021 Elsevier LtdNb2O5 polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb2O5 is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb2O5 coatings, and its effect on their morphology and properties. Phase evolution from H-Nb2O5 in the feedstock, to T-Nb2O5, TT-Nb2O5, N-Nb2O5, H-Nb2O5, Nb12O29 and NbO2 in the coatings depends on the plasma Ar/H2 ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb2O5 or TT-Nb2O5. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb2O5 incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The garment industry demands stamping processes that are increasingly more agile and less damaging to the environment. In this scenario, digital printing, with the sublimation transfer printing technique, presents itself as a viable option for synthetic textile substrates. Among the synthetic fibres, polyamide (P.A.) fibres stand out, as they are light, soft, durable, and boast moderate sweat absorption; however, before sublimation, superficial treatment is necessary in order to present good results such as withstanding washing and maintaining colour intensity. This study addresses the surface modification of the PA6.6 textile substrate by activating non-thermal plasma at atmospheric pressure to receive dye through the sublimation method with dispersed dye. The knitted PA6.6 fabric surface treatment was performed with plasma application at atmospheric pressure using air in the Plasmatreater AS400 equipment. The sublimation transfer effects were evaluated by wash fastness and colourimetric tests. To assess the wettability effect of the control and treated samples, a contact angle test was carried out on PA6.6 samples. Fourier transform infrared spectroscopy (FTIR) proved the changes in chemical functional groups in the fibres. The results showed a decrease in the contact angle of the textile surface, 4–5 grayscale results for colour change and transfer for washing, and an increase in colour strength. In the FTIR tests, there is an increase in the transmittance value of aromatic, carboxylic groups (C=O, 580 cm−1), amides (N=H, 1630 cm−1), and methyl groups (CH 1369 to 1463 cm−1) as well as the presence of new functional groups in the 3064 cm−1 and 2860 cm−1 bands. These conditions allowed sublimation in the knitted PA6.6 fabric and showed increased colour strength and good wash fastness.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.In this study, the potential antimicrobial activity of plasma-activated tap water (PAW) was evaluated against Staphylococcus aureus, Escherichia coli, and Candida albicans. For this, PAW was prepared in a gliding arc plasma system using two treatment conditions: stagnant water and water stirring by a magnetic stirrer, called moving water. Subsequently, their oxidation-reduction potential (ORP), pH, electrical conductivity (σ), and total dissolved solids (TDS) were monitored in different areas of the sample divided according to the depth of the beaker. It was observed that PAW obtained in dynamic conditions showed a more uniform acidity among the evaluated areas with pH 3.53 and ORP of 215 mV. Finally, standardized suspensions of Staphylococcus aureus (ATCC 6538), Escherichia coli (ATCC 10799), and Candida albicans (SC 5314) were treated with PAW, and the reduction of viable cells determined the antimicrobial effect. Our results indicate that the tap water, activated by plasma treatment using gliding arc, is an excellent inactivation agent in the case of Staphylococcus aureus and Escherichia coli. On the other hand, no significant antimicrobial activity was achieved for Candida albicans.

© 2021 by the authors. Licensee MDPI, Basel, Switzerland.The chemical, structural, morphological, and optical properties of Al-doped TiO2 thin films, called TiO2/Al2O3 nanolaminates, grown by plasma-enhanced atomic layer deposition (PEALD) on p-type Si <100> and commercial SLG glass were discussed. High-quality PEALD TiO2/Al2O3 nanolam-inates were produced in the amorphous and crystalline phases. All crystalline nanolaminates have an overabundance of oxygen, while amorphous ones lack oxygen. The superabundance of oxygen on the crystalline film surface was illustrated by a schematic representation that described this phenomenon observed for PEALD TiO2/Al2O3 nanolaminates. The transition from crystalline to amorphous phase increased the surface hardness and the optical gap and decreased the refractive index. Therefore, the doping effect of TiO2 by the insertion of Al2O3 monolayers showed that it is possible to adjust different parameters of the thin-film material and to control, for example, the mobility of the hole-electron pair in the metal-insulator-devices semiconductors, corrosion protection, and optical properties, which are crucial for application in a wide range of technological areas, such as those used to manufacture fluorescence biosensors, photodetectors, and solar cells, among other devices.

© 2020 International Ozone Association.The purpose of the current study was to investigate the effect of ozone exposure on the process of water uptake and germination of lentil (Lens culinaris) seeds. For this, a commercial ozone generator that provides a concentration of 1 g/m3 generated from atmospheric air was used. In the experiments 10 lentil seeds were used per treatment carried out at different times of exposure to ozone: 2, 3, 5, 10 and 15 min. Imbibition curves were performed following the seed mass for 180 min. For germination tests, wet neutral pH germination paper was used where, every 24 h, the mass, root size and stem size of the plant were measured over 7 days. Furthermore, contact angle analysis and Fourier transform infrared spectroscopy (FT-IR) were performed on the seeds. The maximum water uptake in the seeds as a function of the imbibition time was optimum for the samples treated with 3 and 5 min. This fact was reflected in the growth rates of the stem, root and mass that were significantly higher than the control sample, after 7 days of germination. The FT-IR analysis indicated the formation of bands in 1345 cm−1 (NO3−) related to ethylene ozonolysis. Also, it was observed a reduction of the N-H band (amide II) at 1551–1550 cm−1 and increase of the C-H bond at 1543 cm−1, evidencing a possible action of ozone on lentil proteins. This fact is probably related to the enhancement of the seed germination process, allowing the germination rates to be 90% for samples treated with ozone for 3 and 10 min.

© 2021 Elsevier LtdThe increasing demand for high performance gears requires in-depth investigations of alternative materials to those commonly used. In this respect, microalloyed steels may appear as an alternative with technical and economic potential. Microalloyed steels may exhibit a more refined grain structure than conventional steels, which is commonly induced by the precipitation of highly stable and dispersed second-phase particles. This investigation aimed at understanding how the steel grain structure obtained by the addition of niobium (Nb) and titanium (Ti) as microalloying elements correlates to the material surface integrity promoted by a conventional gear manufacturing chain. The results indicated that the addition of microalloying elements leads to a refined and homogeneous grain structure. The residual stress state also proved to be both more compressive and homogeneous and the roughness exhibited greater stability. Such characteristics place the microalloyed steels in a prominent position regarding their application in the gear manufacturing, indicating the possibility of fatigue lifetime improvement.

© 2021 Elsevier B.V.In this work, β-TCP (β-tricalcium phosphate) bioresorbable scaffolds were prepared by the gel casting method. Then, they were impregnated with a 45S5 bioglass sol gel solution to improve biocompatibility and promote bioactivity and antimicrobial activity. The β-TCP scaffolds had an apparent porosity of 72%, and after the incorporation of the bioglass, this porosity was maintained. The elements of the bioglass were incorporated into β-TCP matrix and there was a partial transformation from the β-TCP phase to the α-TCP (α-tricalcium phosphate) phase, besides the formation of bioactive calcium and sodium‑calcium silicates. The scaffolds β-TCP with 45S5 bioglass incorporated (β-TCP/45S5) did not show a reduction in their values of mechanical strength and Weibull modulus, despite the partial transformation to the α-TCP phase. Bioactivity, cell viability, and antimicrobial activity improved significantly for the β-TCP/45S5 scaffold comparing to the scaffold without the bioglass. The mineralization of carbonated hydroxyapatite was verified in Simulated Body Fluid (SBF). The cell viability, evaluated by the reduction of 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide – MTT in MG63 cells, increased by 178%, and β-TCP/45S5 scaffold also enhanced cell activity and osteoblast differentiation observed by means of total protein contend and alkaline phosphatase activity, respectively. The formation of growth inhibition zones was also observed in the disk diffusion assay for three tested microorganisms: Staphylococcus aureus, Escherichia coli and Candida albicans. To conclude, the vacuum impregnation method in 45S5 bioglass sol gel solution was effective in penetrating all the interconnected macroporosity of the scaffolds and covering the surface of the struts, which improved their biological properties in vitro, bioactivity and antibacterial activity, without reducing mechanical strength and porosity values. Thus, the β-TCP/45S5 scaffolds are shown as potential candidates for use in tissue engineering, mainly in bone tissue regeneration and recovery.

© 2020 Elsevier B.V.The authors regret Thus, our results from FTIR and Raman spectroscopies are in accordance with the possible structural model for the NbO6 groups in the silicate network for silicate glasses containing Nb2O proposed by Samuneva et al. [7] (Fig. 5). Fig. 5. Possible structural model for the NbO6 groups into the silicate network. R+ and R+2: alkaline ions used as compensator of the excess negative charge at Nb5+ cations [7]. The authors would like to apologise for any inconvenience caused.

© 2020 Wiley Periodicals LLC.To characterize the physicomechanical properties of an alumina-toughened zirconia (ATZ). ATZ synthesis consisted of the addition of alumina particles in an yttria-stabilized tetragonal zirconia polycrystals (3Y-TZP) matrix. Specimens were obtained by uniaxial and isostatic pressing ATZ and 3Y-TZP powders and sintering at 1600°C/1 h and 1550°C/1 h, respectively. Crystalline content and residual stress were evaluated using X-ray diffraction (XRD). Microstructure was characterized by scanning electron microscopy (SEM). Optical properties were determined by reflectance test. Mechanical properties were assessed by biaxial flexural strength test. All analyses were performed before and after aging (134°C, 20 h, 2 bar). XRD and SEM revealed a typical ATZ and 3Y-TZP crystalline content, chiefly tetragonal phase, with a dense polycrystalline matrix, though a smaller grain size for ATZ. Aging triggered a similar monoclinic transformation for both systems; however, ATZ exhibited higher residual compressive stresses than 3Y-TZP. While as-processed 3Y-TZP demonstrated significantly higher characteristic strength relative to ATZ, no significant difference was observed after aging (~215 MPa increase in the ATZ strength). ATZ presented significantly higher opacity relative to 3Y-TZP, although aging significantly increased the translucency of both systems (increase difference significantly higher in the 3Y-TZP compared to ATZ). ATZ physicomechanical properties support its applicability in the dental field, with a lower detrimental effect of aging relative to 3Y-TZP.

© 2020 Wiley Periodicals LLC.The adhesion of microorganisms on biomaterials can impair its effective application. The addition of antimicrobial agents is a promising alternative to overcome this limitation. In this work, films of polycaprolactone (PCL) and nanostructured β-AgVO3 (SV) were produced by solvent casting with 0.1, 0.5, and 1.0 wt% of SV. The effect of SV on the structure of PCL was investigate using Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Raman spectroscopy, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The antimicrobial activity of the films against Staphylococcus aureus and Escherichia coli was evaluated by the agar diffusion method and by direct contact test. FTIR confirmed the presence of SV into the PCL films, with chemical interaction between them. SEM showed that SV nanorods were well dispersed and with good interfacial adhesion with PCL. XRD diffraction and Raman spectroscopy showed that the presence of SV increased the number of nucleation sites, reducing the size of crystallites and increasing the amorphous domains in the PCL matrix, consequently reducing crystallinity. This behavior was confirmed by DSC, which showed a reduction in the crystallinity with increasing SV content. Films with 1 wt% of SV showed antimicrobial activity against Staphylococcus aureus in direct contact test.

© 2020This work studied the crystallization process of two bioglass series derived from 45S5® containing niobium (BGNb5 and BGNb10). In vitro biological analyzes of cell viability corroborate with the qualitative interpretation of the NC values, of a open and fragmented structure, which is interesting from a biological point of view and with the FTIR and Raman results which demonstrated that the breakdown of Si-O-Si bonds and the formation of Si-O-NBO bonds play an important role in the interface of the biological responses of the bioactive materials. X-ray diffraction (XRD) and Differential scanning calorimetry analysis (DSC) also generated insight into the structure of the glasses. To the best of our knowledge, this seems to be the first time that structural changes in bioactive glasses derived from 45S5 resulting from the addition of niobium are studied during its crystallization process.

© The Royal Society of Chemistry 2021.Cases of respiratory diseases have been increasing around the world, affecting the health and quality of life of millions of people every year. Chronic respiratory diseases (CRDs) and acute respiratory infections (ARIs) are responsible for many hospital admissions and deaths, requiring sophisticated treatments that facilitate the delivery of therapeutics to specific target sites with controlled release. In this context, different nanoparticles (NPs) have been explored to match this demand, such as lipid, liposome, protein, carbon-based, polymeric, metallic, oxide, and magnetic NPs. The use of NPs as drug delivery systems can improve the efficacy of commercial drugs due to their advantages related to sustained drug release, targeting effects, and patient compliance. The current review presents an updated summary of recent advances regarding the use of NPs as drug delivery systems to treat diseases related to the respiratory tract, such as CRDs and ARIs. The latest applications presented in the literature were considered, and the opportunities and challenges of NPs in the drug delivery field are discussed.

© 2020 Elsevier Ltd and Techna Group S.r.l.Studies related to biomaterials that stimulate the repair of living tissue have increased considerably, improving the quality of many people's lives that require surgery due to traumatic accidents, bone diseases, bone defects, and reconstructions. Among these biomaterials, bioceramics and bioactive glasses (BGs) have proved to be suitable for coating materials, cement, scaffolds, and nanoparticles, once they present good biocompatibility and degradability, able to generate osteoconduction on the surrounding tissue. However, the role of biomaterials in hard tissue engineering is not restricted to a structural replacement or for guiding tissue regeneration. Nowadays, it is expected that biomaterials develop a multifunctional role when implanted, orchestrating the process of tissue regeneration and providing to the body the capacity to heal itself. In this way, the incorporation of specific metal ions in bioceramics and BGs structure, including magnesium, silver, strontium, lithium, copper, iron, zinc, cobalt, and manganese are currently receiving enhanced interest as biomaterials for biomedical applications. When an ion is incorporated into the bioceramic structure, a new category of material is created, which has several unique properties that overcome the disadvantages of primitive material and favors its use in different biomedical applications. The doping can enhance handling properties, angiogenic and osteogenic performance, and antimicrobial activity. Therefore, this review aims to summarize the effect of selected metal ion dopants into bioceramics and silicate-based BGs in bone tissue engineering. Furthermore, new applications for doped bioceramics and BGs are highlighted, including cancer treatment and drug delivery.

© 2020The need for improved mechanical properties in regions of higher masticatory loads led to the introduction of zirconia in dentistry. However, zirconia needs a characterization and glaze to have a more natural, tooth-like appearance. An experimental glass was produced based on the sol-gel method to exhibit a thermal expansion coefficient similar to that presented by zirconia. The experimental glass was used as glazing material on the previously sintered zirconia (vita YZ) surface. There was a significant reduction in the roughness and hardness of the material, caused by the formation of smooth, void-free and highly uniform glass coating. The glass infiltrated among superficial zirconia grains and caused the formation of monoclinic zirconia at the zirconia/glass interface. A consequent decrease in surface roughness and an increase in flexural strength and reliability was then observed in the experimental glass group. On the other hand, a significant decrease in the reliability of conventionally glazed group was observed. Therefore, the use of experimental glass instead of conventional glaze can improve the mechanical properties, smoothness, and mechanical reliability of fully sintered zirconia.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.The present study proposes the assessment of closure relations related to bubble parameters found in the wall heat flux partitioning model, as well as the assessment of interfacial heat transfer correlations, via CFD (computational fluid dynamics) simulation. The selection of these closure relations, most of the time, does not consider its applicability and scope, neglecting the effects that might affect the results obtained in two-phase flow simulations. In order to assess which relations can properly predict the boiling two-phase flow characteristics found in PWRs, an upward subcooled flow boiling in an annulus, with R-134a as the working fluid, was simulated based on the Eulerian two-fluid model. The void fraction radial profile of two-phase flow was attained, analyzed and compared to a benchmark study at different elevations. It can be concluded that the increase in pressure has a distinguishable impact on the predicting performance of the correlations. A trend of void fraction overprediction was observed at the inlet channel, whereas an underpredicting performance was found at the outlet channel. A crossed effect between bubble departure diameter, nucleate site density, and interfacial heat transfer coefficient on the void fraction profile was evidenced. Insightful considerations regarding the best models to be chosen for the simulation of subcooled boiling flows can be extracted from this investigation.

© 2021 Elsevier LtdCompact and efficient energy conversion systems for space applications enable the appearance of new mission opportunities and technological discoveries resulted from space exploration. Besides energy availability, another crucial factor of any energy conversion system for space purposes is its total mass and size. Focusing on a recuperated closed Brayton cycle (CBC), thermodynamic modeling of a CBC is proposed. Moreover, a thermal model is carried out to predict the overall properties of the cold side of the system (i.e., heat pipes and radiator) for different CBC conditions. Both models are coupled and their conjunct solution provides operational data for the design of the heat rejection system, such as the number of heat pipes (HP), total assembly mass, length, and second-law efficiency. Furthermore, by means of this coupling, the heat source temperature and the cold heat exchanger (CHE) inlet temperature are defined, using an optimization procedure where the specific mass (i.e., radiator mass to cycle power ratio) is minimized. Based on this objective variable, the optimized heat source temperature of 1200 K is achieved, while the CHE inlet temperature of 513.2 K is obtained. Such temperature conditions ensure the future design of a space energy conversion system that aligns good efficiency and compactness.

© ECOS 2021 - 34th International Conference on Efficency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems.This work intends to assess the characteristics, penalties, gains, and challenges through the Electrification and Hybridization process for long-range aircraft. A system, engines and mission level analysis was created focusing on a Thermodynamics and financial approach. A conventional reference aircraft was compared with enhanced more electric and hybrid-electric versions of itself. These new models may carry batteries, which supply the aircraft systems and/or engines, or not. State-of-the-art propulsion and systems’ architecture were also implemented within the cutting-edge airplanes. A full factorial analysis was conducted to vary the batteries’ energy density and the hybridization ratio for the hybrid configurations. A typical mission profile was developed to match the boundary conditions in all cases. Hybrid powertrains confirmed superior behavior than any other cases. The least efficient hybrid configuration, with intermediate battery choices, reduced 10.7% the fuel consumption upon the conventional aircraft and 1.0% facing the battery powered more electric option. Moreover, both baseline models were also surpassed by the worst midway-battery hybrid airplane by 3.6% and 1.0% in overall mission exergy efficiency. Notwithstanding the markets’ actual low battery density, long-range hybrid-electric aircraft will take substantial time to become viable. Nevertheless, only after a significant period, the use of hybrid-electric aircraft will be economically feasible. In the end, preliminary well-to-wake CO2 emissions analysis was developed in all cases for different electricity mix scenarios to observe the environmental impact and viability of the conventional and state-of-the-art configurations.

© 2021 by GE Research.The aim of this work is an evaluation of different turbulence models applied in Computational Fluid Dynamics (CFD) techniques in the turbomachinery area, in this case, in an axial turbine stage used in turbopump (TP) application. The tip clearance region was considered in this study because it has a high influence in turbomachinery performance. In this region, due to its geometry and the relative movement between the rotor row and casing, there are losses associated with vortices and secondary flow making the flowfield even more turbulent and complex. Moreover, the flow that leaks in the tip region does not participate in the energy transfer between the fluid and rotor blades, degradating the machine efficiency and performance. In this work, the usual flat tip rotor blade geometry was considered. The modeling of turbulent flow based on Reynolds Averaged Navier-Stokes (RANS) equations predicts the variation of turbine operational characteristics that is sufficient for the present turbomachine and flow analysis. Therefore, the appropriate choice of the turbulence model for the study of a given flow is essential to obtain adequate results using numerical approximations. This comparison become important due to the fact that there is no general turbulence model for all engineering applications that has fluid and flow. The turbomachine considered in the present work, is the first stage of the hydraulic axial turbine used in the Low Pressure Oxidizer Turbopump (LPOTP) of the Space Shuttle Main Engine (SSME), considering the 3.0% tip clearance configuration relative to rotor blade height. The turbulence models evaluated in this work were the SST (Shear Stress Transport), the k-e Standard and the k-e RNG. The computational domain was discretized in several control volumes based on unstructured mesh. All the simulations were performed using the commercial software developed by ANSYS, CFX v15.0 (ANSYS). All numerical settings and how the boundary conditions were imposed at different surfaces are explained in the work. The boundary conditions settings follow the same rule used in the test facility and needs some attention during the simulations to vary the Blade-Jet-Speed ratio parameter adequately. The results from numerical simulations, were synthesized and compared with the experimental data published by National Aeronautics and Space Administration (NASA), in which the turbine efficiency and its jet velocity parameter are analyzed for each turbulence model result. The work fluid considered in this work was water, the same fluid used in the NASA test facility.

© 2021 Elsevier B.V.Electrospun ultrathin polymer fibers hybridized with bioactive ceramics find use in many biomedical applications due to their unique and versatile abilities to modulate structure–performance relationships at the nano–bio interface. These organic–inorganic hybrid fibers present synergies that are otherwise rare, even when the precursors are used individually, such as bioactivity in polymers and stiffness–toughness balance in bioactive ceramics. Despite these unique advantages, a comprehensive and timely review on this important topic is still missing. Herein we describe the most recent and relevant developments on electrospun ultrathin polymer fibers hybridized with bioactive ceramics, with emphasis on bone tissue regeneration. This review addresses the preparation of bioactive ceramics, particularly (nano) hydroxyapatite (HA; nHA) and bioactive glass (BG), which stand out as the ceramics of interest for bone regeneration. The anatomy and mechanical properties of bone as well as fundamental tissue–scaffold interaction mechanisms are covered. The process–structure–property relationships of electrospun ultrathin fibers are discussed in detail from a technical standpoint, as well as fabrication strategies, process variables, characterization methods, and biological requirements (in vitro and in vivo performances). Finally, we highlight the major challenges and outline perspectives to pave the route for the next-generation hybrid materials for bone tissue engineering.

© 2020 Elsevier B.V.The sol-gel method is versatile and one of the well-established synthetic approaches for preparing bioactive glass with improved microstructure. In a successful approach, alkoxide precursors undergo rapid hydrolysis, followed by immediate condensation leading to the formation of three-dimensional gels. On the other hand, a slow kinetics rate for hydrolysis of one or more alkoxide precursors generates a mismatch in the progression of the consecutive reactions of the sol-gel process, which makes it difficult to form homogeneous multicomponent glass products. The amorphous phase separation (APS) into the gel is thermodynamically unstable and tends to transform into a crystalline form during the calcination step of xerogel. In the present study, we report a combined experimental and theoretical method to investigate the stability towards hydrolysis of triethyl phosphate (TEP) and its effects on the mechanism leading to phase separation in 58S bioactive glass obtained via sol-gel route. A multitechnical approach for the experimental characterization combined with calculations of functional density theory (DFT) suggest that TEP should not undergo hydrolysis by water under acidic conditions during the formation of the sol or even in the gel phase. The activation energy barrier (ΔG‡) showed a height of about 20 kcal·mol−1 for the three stages of hydrolysis and the reaction rates calculated for each stage of TEP hydrolysis were kFHR = 7.0 × 10−3s−1, kSHR = 6.8 × 10−3s−1 and kTHR = 3.5 × 10−3s−1. These results show that TEP remains in the non-hydrolyzed form segregated within the xerogel matrix until its thermal decomposition in the calcination step, when P species preferentially associate with calcium ions (labile species) and other phosphate groups present nearby, forming crystalline domains of calcium pyrophosphates permeated by the silica-rich glass matrix. Together, our data expand the knowledge about the synthesis by the sol-gel method of bioactive glass and establishes a mechanism that explains the role played by the precursor source of phosphorus (TEP) in the phase separation, an event commonly observed for these biomaterials.

© 2021 Wiley-VCH GmbHThe present study evaluated the influence of the level of load in the mixer on the processability and mechanical properties of the solid composite propellant. The mixtures were processed with the same composition and process conditions but using different percentages of levels of the maximum mixing capacity of the mixer. Both vertical and horizontal types of mixers were used to verify the existence of an optimal level of operation and whether it would depend on the type of mixer adopted. Levels of 50 %, 60 %, 70 %, 80 %, and 90 % were adopted in each macerator. In terms of processability, the 70 % level for the horizontal macerator and the 60 % level for the vertical macerator was the most suitable ones. Regarding the mechanical properties, the optimal operating level to obtain propellants with better properties would be 60–70 % in the horizontal macerator and 70 % in the vertical macerator. The results were interesting as they demonstrated the influence of the level adopted on the final grain. In addition, it is necessary to avoid using the mixers close to their maximum capacity. Therefore, the mixer level should be considered in any rocket motor casting project, both in single-batch and multi-batch processes.

© 2021 Wiley-VCH GmbHIn the Brazilian Aerospace Program, even though all developed rocket motors are manufactured in the same plant of the Department of Aerospace Science and Technology, differences are observed in the magnitude of the masses applied in each motor. Thus, depending on the volume of the combustion chamber, it is common for the casting to carry out multi-batch processes when a required mass of solid propellant is greater than the maximum capacity of the reactor. In this context, the studies that systematically evaluate multi-batch processes on an industrial scale of composite propellants based on polyurethanes obtained from HTPB are incipient. Furthermore, each batch preparation of the casting process for large motors is carried out on different days, so that each of these has a different storage time until the day of the effective casting. As a result, this wait can generate changes in the properties of the propellant grain as a whole, which can modify the motor's performance. Thusly, through the analysis of data of multi-batch processes, the present study evaluated the influence of the storage time in the preparation of the propellant and on the final properties of the grain. It was concluded that the grain becomes softer with a reduction in its hardness, greater elongation at break, and less modulus for batches with longer storage times before casting.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Energetic materials have been used over time in civil and military applications. Concomitantly, studies were conducted focusing on the combustion mechanisms of these materials, including their kinetic and thermodynamic behavior during firing. The objective of this work was to systematically study the mechanisms of thermal decomposition of ammonium dinitramide (ADN), and ADN formulated as a solid composite propellant with glycidyl azide polymer (GAP), through reactive molecular dynamics simulations. The main reactions of the mechanisms were elucidated and analyzed, and the Arrhenius parameters were determined for the global processes. Calculated activation energies for the systems were 127.84 and 354.72 kJ/mol for ADN and ADN/GAP, respectively. Comparison to literature data shows up to 14% of deviation, which proves the methodology useful for predictions and kinetic analyzes of combustion/pyrolysis reactions of energetic materials.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In propulsion systems, to ensure a suitable thrust, the selection of the pair fuel/oxidizer is of utmost importance. Combination of propellant influences the characteristics of the chemical reaction process, the fuel vaporization speed, the ignition temperature, the volatility of hot gases. After the propellant, a suitable injector design is important, which allows better use of the propellant mixture, and thus achieve better engine performance and less combustion instability. This study evaluated the radial injector data, compared with those for other types of injectors, orifice-plate and swirl. Combustion behaviour was analysed by reactive molecular dynamics simulations. It was analysed how each contributes to the engine’s performance, by using solid fuel-based paraffin and oxygen gas in the gas phase (GOx), constituting a hybrid propellant. For orifice plate and swirl injectors, the specific impulse values were higher at higher test pressures. However, for the radial injector, the Isp was increased to the test pressure up to 25 bar. All injectors yielded good operation and met the goal of injecting oxidizer flow efficiently. The RMD simulation was able to show the behaviour of paraffin during decomposition and combustion, as well as explain the pressure effects on the system by the gaseous molecules generation.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In this work are presented pyrolysis and combustion simulations of alternative jet fuels using reactive molecular dynamics methods. Three fuels obtained from renewable resources are compared: farnesane, α-farnesene and β-farnesene. The pyrolysis and combustion simulations were done in different temperatures. Significant differences have been observed among the compound reactions during the decompositions. The Arrhenius parameters of the global process were obtained for all species, considering a first-order approach. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene and β-farnesene were 132.55, 117.28 and 112.88 kJ mol-1, respectively.

© 2021, Universidade Federal do Rio de Janeiro. All rights reserved.The present study evaluated different formulations of solid propellants based on HTPB / AP / Al modified by the short chain diols, 1,4-butanediol and 1,2-propanediol at different mass concentrations. In this context, this was done in order to obtain differentiated mechanical properties without neglecting the other imposed requirements, such as processability and ballistic properties. In this sense, a methodology for calculating the formulations was developed and their processing was carried out in a small reactor. Moreover, with a view to evaluating the influence of the mass content of plasticizer used, the formulation containing a higher content of 1,4-butanediol was also processed employing a greater amount of plasticizer. The post-processing dynamic viscosity profile and the evolution of the hardness during curing were evaluated, and a mechanical characterization was performed. In addition, a specific mass determination test, X-rays of samples and a calorimetric bomb test were carried out. Hence, it became evident that the formulations modified with 1,4-butanediol are promising. Nevertheless, it was not possible to achieve, in this study, all the requirements expected in a final product for immediate use.

© 2021, Academia Brasileira de Ciencias. All rights reserved.Hydroxyl-terminated polybutadiene (HTPB) is widely used in the formulations of solid propellants used in rocket motors. Furthermore, in general, chain extenders and short chain diols, such as 1,4-butanediol and 1,2-propanediol, can also be used in propellant formulations to improve mechanical properties, especially tensile strength. However, the incorporation of these diols can result in a considerable increase in the viscosity of the mixture during the processing of propellants. Thus, the present study evaluated the compatibility of these diols with the HTPB prepolymer, through a viscometric study, with the aim to determine the order of addition that results in greater homogeneity for the mixture. It was concluded that 1,4-butanediol, due to its larger chain size, has better compatibility with HTPB resin than 1,2-propanediol. On top of that, it was found that when the resin is added first, it results in mixtures with greater compatibility.

© 2021 Sociedade Brasileira de Quimica. All rights reserved.In recent years, research on the development of protective materials has expanded significantly in order to find efficient and economically viable solutions for application in various industrial segments. Among these materials, those aimed at protecting metallic substrates against high temperatures that end up causing corrosive processes, stand out due to the huge market demand. Advantages such as reproducibility in the process, cost reduction and reduction in environmental impact also directly contribute to the search for protective coatings as an efficient protective alternative. This article presents the characterization of a ceramic coating developed in a previous study that used silicon carbide as a filler, using potassium silicate (water glass) as a matrix (binder), and whose anti-corrosion and thermal protection properties stood out, mainly in applications in the aerospace industry. In this stage of the work, tests of thermal analysis (thermogravimetry) were carried out for the physical and chemical characterization of the material. The results corroborate those previously achieved when applying the coating on components of a hybrid rocket engine tested on a fixed-point bench.

© 2021, Academia Brasileira de Ciencias. All rights reserved.Dynamic loads continue to draw the interest of structural engineers. The sources of these loads can be earthquakes, blast effects or transportation loads from railroads or highways. Especially for blast loads, terrorist attacks or military actions have caused many loses of lives and damages in several buildings. The verification of structural behavior is necessary to help designers to plan structures that support these loads and reduce damages. Although computer simulation with, specific software, have helped these designers, full-scale tests can provide valuable information about the real response of the structure. This paper presents damage diagram from ten full-scale field tests using approximately 2.70 kg of non-confined plastic bonded explosive against reinforced concrete slabs with different scaled distance, reinforcement ratio and concrete strength. The damage diagram is expected to be a help tool for designers to understand the effects of blast loads on slabs.

© 2021Parts produced by laser powder-bed fusion (LPBF) show unique microstructures consisting of dislocation structures and an oxide nanoparticle dispersion usually embedded in epitaxially-grown grains. Thermomechanical processing is an alternative to enhance the microstructure of such materials. However, the deformation mechanisms and the resulting microstructures following annealing are not yet well understood, hindering further microstructure control. We apply cold rolling and subsequent annealing in AISI 316L stainless steel processed by LPBF and perform an in-depth microstructural characterization to understand the origin of abnormal growth and how to avoid it. Upon deformation, mechanical twinning occurs. Early plastic instabilities arise due to the fine substructure with high defect density, resulting in profuse shear banding. Such shear bands carry most of the subsequent deformation, reducing the volume fraction of oxide particles along these regions due to enhanced particle dissolution via cracking/fragmentation. Upon annealing, the cold-rolled specimens show abnormal <110> || ND grains nucleating at shear bands. The earlier recrystallization onset and fragmented particle dissolution in shear bands result in a local lower Zener pinning and generate a size advantage for <110> || ND grains. Based on this investigation, abnormal growth may be triggered by shear bands in cold-rolled and annealed LPBF alloys for grain boundary engineering. Our results suggest that avoiding shear banding (and the consequent particle fragmentation) inhibits abnormal grain growth, thus yielding a more uniform and fine-grained microstructure.

© 2021Alloys manufactured by laser powder-bed fusion have intrinsic and hierarchical microstructural features inherited from the fast solidification (up to 104 K/s) and subsequent thermal cycles. This creates epitaxed grains, dislocation cell structures, and second-phase oxide nanoparticles. Epitaxed grains follow a pattern where finer grains are found in the melt pool centerline along the laser track. Upon further annealing, this characteristic microstructure has pronounced consequences on the recrystallization mechanisms and thus on grain topology. By changing the scanning strategy, we control the emerging grain patterns in a representative alloy (AISI 316L austenitic stainless steel) by creating linear strings for unidirectional scans, while a chessboard grain pattern arises by applying a 90°-rotation between layers. Upon post-processing annealing (at 1150 °C from 15 min to 8 h), we study the relationship between the as-built and recrystallized microstructures. Recrystallization starts with fine nuclei in regions with high dislocation density along the melt pool centerlines, resulting in early-stage linear impingement (linearly clustered nucleation), as revealed by microstructural path analysis. Recrystallization is sluggish, due to dynamic Zener-Smith pinning. This effect leads to jerky boundary motion due to periodic pinning and depinning from oxide particles, caused by their gradual coarsening. Lower nuclei number density slows kinetics for the case of unidirectional scanning, while twinning aids in the nucleation of grains with mobile grain boundaries. Our findings show that changes in the laser scanning strategy are a suitable design tool for tailoring recrystallization and thus microstructure.

© 2021 Elsevier B.V.The annealing behavior of cold-rolled 317L austenitic stainless steel was investigated. The material was rolled to a true strain (ε) of 2.04 and subjected to both stepwise and continuous annealing up to 1000 °C, the latter conducted in the presence of an external magnetic field. Electron backscatter diffraction, dilatometry, thermodynamic calculations, Vickers microhardness testing, and electron channeling contrast imaging were used to follow the microstructure evolution upon annealing. The microstructure of the cold-rolled steel has about 2.3% of strain-induced α′-martensite, 4% of delta ferrite, and austenite as the predominant phase. Eye-shaped deformation heterogeneities are also noticeable and contrast with the predominant lamellar structure typical of cold-rolled materials. Microstructure changes were followed by means of magnetic measurements, with emphasis on both Ms (saturation magnetization) and Hc (coercive field) parameters. Our findings confirm the occurrence of austenite reversion, decrease of delta ferrite, and massive sigma phase precipitation for the annealing temperature and time intervals herein investigated. At 800 °C the steel is almost fully recrystallized, except for the eye-shaped structures, in whose interior precipitation is much less intense. Precipitation of sigma phase occurs preferentially at the delta ferrite lamellae. Magnetization was able to capture the fragmentation of the ferromagnetic delta ferrite lamellae due to sigma phase precipitation and the changes associated with the decrease of delta ferrite and austenite reversion upon annealing.

© 2021 Elsevier Inc.The 15-5PH (UNS S 15500) stainless steel combines high mechanical strength, ductility, and good corrosion resistance for aircraft and aerospace applications. This set of properties and its high added-value applications make it an excellent choice for additive manufacturing processes such as laser powder-bed fusion (LPBF). However, there is a need to understand the complex microstructure developed in LPBF-processed parts, which may show particularities such as columnar solidification, preferential orientation, different kinds of porosities, chemical segregation along the melt pools, metastable phases, and oxide nanoinclusions. We report the microstructural characterization of LPBF-processed 15-5PH stainless steel in the as-built condition and after aging. Low porosity (<1%), high hardness (420 HV0.1), and a large amount of retained austenite (15%) were found in the as-built samples. The microstructure shows the usual “fish scale”-like morphology. Grain size and hardness vary depending on the location within the melt pools. Reconstruction of the parent grains from EBSD maps indicates a microstructural refinement due to in situ reaustenitization of parts of the previous consolidated layers, where these heat-affected zones are harder and present larger amounts of retained austenite. After aging, as-built samples were harder and more resistant to overaging than annealed or wrought counterparts. Transmission electron microscopy reveals a large amount of nanometric crystalline silicon-oxide inclusions, indexed as cristobalite. The combination of fine-grained martensite, coherent Cu-rich clusters, nanometric oxide particles, and retained austenite makes LPBF-processed 15-5PH stainless steel a very promising material for high-end structural applications.

© 2020 Elsevier B.V.Strain-induced α′-martensite and austenite reversion in a cold rolled UNS S32304 lean duplex steel were tracked by means of magnetic measurements, with emphasis on both Ms (saturation magnetization) and Hc (coercive field) parameters. Grain-averaged quality metrics derived from EBSD (electron backscatter diffraction) analysis were also used to distinguish the phases during austenite reversion. The material was cold rolled to a true strain (ε) of 1.61 and subjected to isothermal and continuous annealing, the latter conducted in the presence of an external magnetic field. The evolution of the α′-martensite fraction upon straining and after isothermal annealing was monitored by coupling the Ms values and thermodynamic simulations, as well as from EBSD analysis. For the isothermally annealed material (ε = 1.61), the overall behavior of Ms and hardness displayed similar trends with a strong decrease for temperatures higher than 500 °C, suggesting austenite reversion. Results confirmed the occurrence of austenite reversion for the temperature interval investigated here. At 800 °C, austenite reversion is complete, and the steel is fully recrystallized. Besides, from the EBSD analysis, evidence of ferrite transformation into austenite was rather noticeable, in accordance with thermodynamic simulations and magnetic probing. Complementary electron channeling contrast imaging (ECCI) revealed that precipitation reactions mainly occur in the recrystallized austenite at 700 and 800 °C. The Hc behavior of both, the strained and annealed conditions was inferred to be mostly driven by microstructural changes in ferrite.

© 2021, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.In this paper, a preliminary study of optimal round-trip trajectories for Earth–Moon–Earth missions is presented. The outgoing mission consists in transferring a space vehicle from a circular low Earth orbit (LEO) to a circular low Moon orbit (LMO) with minimum fuel consumption. The class of two-impulse trajectories is considered: A first accelerating velocity impulse is applied to insert the space vehicle into an Earth–Moon transfer trajectory, and a second braking velocity impulse is applied to insert the space vehicle into the terminal LMO. It is assumed that the velocity increments are applied tangentially to the terminal orbits. The fuel consumption is defined by the arithmetic sum of the velocity increments. The return trip is similarly described with the initial orbit corresponding to LMO and the final orbit corresponding to LEO. Two dynamical models are considered: an extended version of the patched-conic approximation which includes the eccentricity of the Moon’s orbit and the planar elliptic restricted three-body problem. The optimization problem is solved by means of two gradient techniques: Newton–Raphson–gradient algorithm and sequential gradient–restoration algorithm. Clockwise and counterclockwise arrivals at LMO are considered for outgoing trips, and clockwise and counterclockwise departures from Moon are considered for return trips. The time of flight varies from 4.5 to 5.3 days for outgoing trips or for return trips. Numerical results show that the fuel can be saved if the initial position of the Moon is appropriately determined.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.With an always increasing demand for more efficient aircraft due to both economic and environmental purposes, academy and industry are studying hybrid-electric and full-electric concepts to explore new aircraft design opportunities. This paper expands on the results of previous publications, using a Cessna 208B Grand Caravan as a platform for the implementation of distributed electric propulsion to enable the use of high-lift propellers. The design space is swept to evaluate the impacts of the technology in wing weight, propulsive system sizing and weight as well as in payload, range and fuel consumption on different simulated missions. The models are integrated using SUAVE, a conceptual level design environment, which is used to integrate the aircraft model and run the simulations. Results show that generating enough extra lift with the propellers require large amounts of power, resulting in a heavy propulsive system that hinders the payload and range capabilities of the aircraft and are unfortunately not compensated by the small aerodynamic gains generated by this configuration.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.In the development of automatic piloting systems nowadays, flight tests are required to validate operations and tuning of the control loops, making the process costly. For an optimal point of stability within a region of operation, this work aims to use the modern control technique of Linear Quadratic Regulator (LQR), with minimization through the Riccati equation for the optimization of Proportional, Integral, and Derivative (PID) control loops in longitudinal piloting. The aircraft considered for the flight tests was the C2 fixed-wing Unmanned Aerial Vehicles (UAV) used for agricultural purposes. The nonlinear model coefficients of the aircraft were acquired using well-known computational methods. The inertia properties were acquired through drawings made in Computer-Aided Design (CAD) with the Catia® software and the aerodynamic properties' estimation with the Omni3d® software. The aircraft's applied system was the Micropilot® LRC2 autopilot that has cascade PID control loops for altitude and trajectory control; however, the control loops tuning responsible for longitudinal movement are this work's main contribution. In parallel, a flight test campaign was carried out to collect data and tune the autopilot gains in flight by an empirical method based on Ziegler-Nichols' method. The gain data collected during the flights are used to compare the data obtained by the theoretical computer model of the aircraft. Different performances related to the gains obtained by the flight test and the PID control loops' optimization method through the LQR method are demonstrated with the non-linear model's application under the effects of disturbances. The main achieved results are about the minimum energy cost. This minimization in energy cost is due to the PID in-flight tuning that takes more energy in the actuators than the PID optimized with the LQR method, which proves to be a promising system for faster development of agricultural UAVs.

© 2021, Journal of Aerospace Technology and Management. All rights reserved.Combustion instability can severely impair the operation of many kinds of combustion engines. Acoustic resonators are widely used to suppress the pressure oscillations caused by the coupling between the combustion process and the combustion chamber acoustic modes. Combustion chambers with subsonic flow in its inlets and outlets, like gas turbine combustors, exhibit some acoustical damping due to the presence of openings. In such chambers, the acoustic modes are complex. In a complex mode, the antinode regions can be shifted from its position in the corresponding real mode. In this work an experimental acoustic modal analysis of a cavity with an opening was performed. Acoustic frequency response functions were obtained by using a volume acceleration source, a microphone and a data acquisition system. The PolyMAX algorithm was used to estimate longitudinal modes in its real and complex versions. A comparison was performed and the results show that, for some modes, the antinode region placement could change reasonably. This suggests that the use of complex modes for location of antinode regions provides more accurate results and consequently could be a better way to identify positions, where resonators provide maximum damping in order to minimize combustion instability in subsonic combustion chambers.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Operational Modal Analysis (OMA) is a methodology to obtain the modal properties of a structure using the dynamical responses of the system only. That methodology is very useful in aeroelastic in-fligh testing where there are difficulties in measuring directly the aerodynamic loads on aircraft. For risk reduction in the future flight operations of the EOLO at ITA, wind-tunnel tests were performed. EOLO is an Unmanned Aerial Vehicle (UAV) with high aspect ratio and structural flexibility, designed to study aeroelastic phenomena and to evaluate the interaction of flexible effects with the aircraft flight dynamics. In this work The Frequency Domain OMA techniques: Decomposition (FDD), Enhanced Frequency Domain Decomposition (EFDD), Spatial and Frequency Domain Decomposition (SFDD) are applied to the vibrational data from wing tunnel test campaign in different operation conditions, using acceleration and strain measurements. The results between the OMA techniques are compared with previous modal characterization from Ground Vibration Test (GVT) and numerical aeroelastic analysis. The different generations of the frequency domain decomposition methods proved their suitability for use in aircraft aeroelastic characterization using accelerations and strain measurements.

© 2021, Publishing House of the Romanian Academy. All rights reserved.We aim at providing a preliminary approach on the dynamics of a spacecraft in orbit about the asteroid (99942) Apophis during its Earth close approach. The physical properties from the polyhedral shape of the target are derived by assigning each tetrahedron to a point mass in its center. That considerably reduces the computation processing time compared to previous methods to evaluate the gravitational potential. The surfaces of section close to Apophis are build considering or not the gravitational perturbations of the Sun, the planets, and the SRP. The Earth is the one that most affects the investigated region making the vast majority of the orbits collide or escape from the system. Moreover, from numerical analysis of orbits started on March 1, 2029, the less perturbed region is characterized by the variation of the semimajor axis of 40-day orbits, which do not exceed 2 km very close to the central body (a < 4 km, e < 0.4). However, no regions investigated could be a possible option for inserting a spacecraft into natural orbits around Apophis during the close approach with our planet. Finally, to solve the stabilization problem in the system, we apply a robust path following control law to control the orbital geometry of a spacecraft. At last, we present an example of a successful operation of our orbit control with a total △v of 0.495 m/s for 60 days. All our results are gathered in the CPM-ASTEROID database, which will be regularly updated by considering other asteroids.

© 2021 Elsevier Masson SASThe continuous exploration of oil wells has increased the demand for plug and abandonment procedures. Current techniques used for well plugging involve the cementing process, which is extremely expensive and difficult to perform. Aiming to overcome these challenges, a new approach in this area has been investigated. This novel technology, named here as Thermal Plug and Abandonment (TP&A), proposes a chemical mixture that would be introduced through the production tube or the steel casing. Then, this mixture is ignited and the exothermic reaction generates enough heat to melt the wellbore components. After the cooling stage, the solidified mass composed by these components and the products of the reaction will serve as a seal to plug the well. Under such circumstances, this work aims to investigate this new technology assuming a thermite mixture that is introduced through the steel casing. For that, a numerical analysis is employed to investigate the heat conduction and the phase change through the oil well structure, which is modelled as a two-dimensional axisymmetric domain. The heat generated by the reaction is approached as a spatial and time-dependent heat flux profile that was estimated based on experiments found in literature. The thermal behavior is assessed to discover if the heat generated by the reaction is enough to form a plug composed by all components found in an oil well environment. It was found that temperatures are high enough to melt most part of the steel and a significant amount of the cement layer. The investigation also found that temperatures heavily drop through the cement layer, which avoids any notable melting of the cap rock. Finally, the heat fluxes’ profiles were increased, and it was found that a TP&A procedure that accounts for a seal composed by only the thermite products and the melted steel layer might be a more practical approach.

© 2021 Elsevier Masson SASThis work presents a hybrid analytical/numerical approach for transient heat conduction through composite hollow cylinder structures applied for Plug and Abandonment (P&A). The Distribution Transfer Function Method (DTFM) is a mathematical framework able to solve both nonhomogeneous boundary conditions and a nonlinear partial differential equation with spatial-temporal source term, presenting good agreement with Finite Element Method (FEM) and other analytical approaches. A new technology of Thermal Plug and Abandonment (TP&A) devoted for P&A operation is studied in this work, where a heat generator is used to melt the first layer of the well structure. The heat source will be modeled using thermite within the oil well manifold structure, which must be descended to desirable depths along the borehole through a cylindrical container. After an exothermic reaction the temperature fields will be determined by means of DTFM method. A novel adaptative step-wise procedure applied for DTFM allows one to solve non-differentiable heat flux, thermal and volumetric heat source profiles which exact quadrature regression are not able to solve. This method provides simple replicability, which can be reproduced for many emerging fields where transient heat conduction is an important parameter to be accounted for. Using experimental data as input in DTFM provides insight that the temperature response overcame the design melting point of the production tube, being capable of melting down the production tubing wall, which is a valuable achievement for oil industries since not removing the production tubing can save a great amount of time, and hence save costs for oil industries.

© 2021 Elsevier Masson SASIn this study, a thermal energy storage system is modeled as an axisymmetric ventilated cavity partially filled with a porous medium that is subject to turbulent flow. Local thermal non-equilibrium is considered to analyze the heat transport and the turbulent k−ε model is used to account for the high inlet flow velocities. Finite volume method is employed for discretization of the equations that are relaxed with the SIMPLE method. The investigation is concerned with the turbulence field, heat fluxes and pressure drop in the system relative to variations in Reynolds number (from 8.3 × 103 to 5 × 104), porosity (ϕ from 0.6 to 0.8) and Da number (from 4x10−5 to 4x10−7). Results indicate that porosity effects slight changes in the turbulence field while the temperatures increase significantly faster for higher porosity cases. Turbulence in higher porosity cases was lower, accompanying the increase in thermal efficiencies. Variations in Da number with fixed porosity showed that, for lower Da number, recirculation in the clear region increased while for higher Da number porous region turbulence increased. Also, higher Da decreased heat exchange between fluid and solid phases. Finally, an increase in thermal efficiency for lower Da number flows was followed by increased average turbulent kinetic energy and relative pressure drop.

© 2021 Wiley-VCH GmbHA thermite reaction is a self-propagating exothermic reaction with many practical applications in welding processes, material synthesis, pyrotechnic and initiator technologies. Motivated by the above-mentioned, the present study involves modeling and simulation of common hematite-aluminum thermite reaction with the aim of predicting temperature levels and radial burning speeds in a thin disk ignited at the center. Balance equations of species and energy conservation were solved in one dimension space by applying a finite difference method, considering no species transport and a one-step mechanism. The Arrhenius equation was adopted to model the kinetics rate. Phase change and temperature dependence of the thermochemical properties were also considered. Analyses of spatial and temporal meshes revealed that numerical results were independent of the grid used. Predictions show that the ignition procedure affects the formation of the reaction-front, higher temperatures, and longer ignition zones can start the self-sustained reaction earlier. However, once the reaction wave is established, its velocity and peak temperature are the same, independent of the initial temperature profile. Simulations herein also show that an increase of the activation energy and decrease of the pre-exponential factor slows down the reaction speed considerably, impacting on accurate prediction of reaction-wave velocity. Further, the activation energy influences the burning velocity much more drastically than the pre-exponential factor. The maximum temperature observed in the model is around the melting temperature of alumina (2327 K), which is in agreement with the experimental results reported in the literature.

© 2021 by Begell House, Inc.A laminar natural convection local thermal nonequilibrium model of porous media is used to simulate the standby cycle of a thermal energy storage system that uses hot air as a heat transfer fluid. For this, an axisymmetric cavity, partially filled with a porous medium, is considered. The initial temperature field of the system is taken as being the final one for a charging cycle with the same properties. Results for the two-dimensional temperature fields, axis line temperatures, and energy loss after the standby cycle are compared for different properties, namely, porosity (0.6 < φ < 0.8), Da number (4 × 10-7 < Da < 4 < 10-5), thermal conductivity ratio (3.5 < ks / kf < 1062), and thermal capacity ratio (1483 < ρscps / ρf cpf < 7415). It was found that higher porosities result in higher rates of energy loss. Also, an increase in the Da number affects a significant thermal destratification of the system although the rate of energy loss does not vary. Increasing the thermal conductivity ratio meant increasing losses through the tank wall. Finally, the higher the thermal capacity ratio the slower the energy loss of the system.

© 2021 by Begell House, Inc.This work investigates the use of variable fluid properties when simulating the behavior of solar volumetric receivers (SVR) via the thermal nonequilibrium approach. Energy balances for both air and porous ceramic materials are numerically solved using the SIMPLE method. The system of algebraic equations is relaxed by the SIP procedure. Thermal efficiency increases for lower inlet velocities and higher solid-to-fluid thermal conductivity ratios. For variable properties cases, a further increase in thermal efficiency is higher for lower solid-to-fluid thermal conductivity ratios and less noticeable for higher solid-to-fluid thermal conductivity values and lower velocities. Thermal efficiency is reduced for more permeable structures and higher porosities and for variable properties cases higher values are calculated due to increase in equilibrium temperatures. No appreciable dependence on Darcy number was detected when efficiencies were calculated with either constant or variable properties.

© 2021 Begell House Inc.. All rights reserved.Ducts with walls having a sinusoidal shape can be used to enhance heat and mass transfer in a number of industrial flows. Modern solar energy systems can benefit by the use of such wavy surfaces resulting in improvements on their overall thermal efficiencies. If a layer of porous material is attached to the walls, further increase in transfer rates of mass and energy can be achieved due to the increase of surface contact area between the fluid and the walls. This article investigates the pressure drop in wavy ducts having different aspect ratios and distinct porous layer thicknesses, porosities, and permeabilities. A mathematical model for flow in a unique computational domain, encompassing both the porous region and the centered clear passage, was applied and numerically resolved. Results indicate that pressure losses were mostly affected by the thickness of the layers rather than the properties of the porous substrate.

© 2021 Universidade Federal de Sao Carlos. All rights reserved.Maraging steels are ferrous alloys with Ni, Co, Mo, and Ti additions. These materials are a special class of ultra high mechanical strength steels with wide and special applications in strategic areas, which makes their knowledge very valuable. Computational advances allowed to analyze the behavior of these materials numerically, using the finite element method and developing mathematical models that can represent numerically its mechanical behavior. The present work has the objective of surveying the mechanical properties of maraging steels 300 and 350 by slow strain rate tensile (SSRT) tests, after the solution treatment at 1183K for 1h. Additionally, it was evaluated the hydrogen embrittlement in samples tested by SSRT under cathodic protection with a potential -1.2 VSCE in 3.5% NaCl solution. The study was complemented with detailed fractographic analysis. This work also presents the analysis of representative models by use of Hollomon, Swift, Voce and coupled Swift-Voce equations to describe the strain-hardening behavior. Compared to the others, the Voce's model was the one which best fitted the experimental results, with values of R2 higher than 0.992. Through the variation of the chemical composition found in the different grades of maraging steels, this work contemplates the creation of a generalized Voce model based on the variation of the Ti content. The work concludes presenting the generalized Voce model proposed and a numerical analysis of the SSRT results with a good accuracy of the strain-hardening response.

© 2021 Elsevier LtdMode I delamination fatigue crack growth behavior was investigated in a carbon-epoxy prepreg fabric laminate by evaluating the mean load effects. The fatigue crack growth rate was determined as a function of the maximum Mode I strain energy release rate considering an exponential fitting function according to the Compliance Based Beam Method (CBBM). Classical data reduction techniques were combined with the proposed method, indicating less scatter on results and satisfying basic assumptions of smoothness and continuity for the fatigue crack growth process. The delamination growth rate curve proved to be strongly affected by the applied mean load as the fatigue onset delamination. The number of cycles to onset is higher for lower load levels and, considering the stable propagation region, a higher delamination growth rate was reported for higher load levels. The fractographic analysis has confirmed the effects of cyclic loading and the mean load levels on fracture surfaces. For a higher mean load, failure mechanisms expose static aspects and substantial presence of microcracks at fiber imprints, while, under lower mean load were noticed significant wear and plasticity and featureless fiber tracks.

© 2021, AIAA International. All rights reserved.Recent works have addressed piezoelectrically induced stresses as a potential technique for aeroelastic stability augmentation of biclamped structures. Because active-control-based techniques are conventionally used for aeroelastic stabilization, this paper presents a comparative study on the effectiveness of piezoelectrically induced stresses and active control for aeroelastic stability augmentation. A finite-element-method-based piezoaeroelastic model is proposed employing two-node, eight-degree-of-freedom smart beam elements and an unsteady, strip-theory-based aerodynamic approach involving vertical gust components. A stability augmentation system was designed for stiffness control and used for comparison in a particular wing configuration. Analyses involving the stability margins, input signal energy, and the response to vertical gust were performed and discussed. The results showed that piezoelectrically induced stresses and active control can provide equivalent flutter speed increase for the two cases of gain margin considered. However, the system can become unstable due to control signal saturation when submitted to high-amplitude gusts, which was not observed when piezoelectrically induced stresses is used. On the other hand, it was observed that the active control required a much smaller amount of energy for stabilization. In general, it was noticed that the piezoelectrically induced stresses technique was not as effective as active control to increase the flight envelope of biclamped structures, because active control can provide equivalent aeroelastic stability improvement with smaller amount of energy. However, it is found to be a promising strategy to be used on emergency devices, where the aeroelastic stability of biclamped structures needs to be guaranteed in critical aerodynamic disturbance conditions.

© The Author(s) 2021.Carbon fiber fabrics have been largely used in composite structures as they provide high mechanical strength and potential weigh reduction, allowing more efficiency in product design. However, the production of the parts generates scraps that is discarded as a waste, becoming a challenge to recycle the carbon fiber with predictable mechanical strength. Within this context, this research analyzed strategies of laying up carbon woven fabrics based scraps, in order to reach a desirable mechanical properties in bending loading. Three types of laminates were manufactured using varied fabric size and number of discontinuities in the layup combined with polyethylene terephthalate (PET) film as a matrix. The obtained composites were tested under four-point-bending test and an energy-strength based analysis was conducted. This analysis explained a strategic position of fabric scrap to maximize the bending strength: providing a value of 106.33 MPa for a composite with high number of discontinuities against 83.11 MPa for another with less discontinuity.

© 2021 John Wiley & Sons Ltd.In this article, a nonlinear structural formulation that uses a new dimensionless set of generalized displacements is proposed for solving geometrically nonlinear beam problems, being validated by several applications given in literature where a cantilever beam is likely to undergo large displacements. By this approach, useful simplifications and insights are achievable in the analysis process, as the system matrices becoming linear and the reduction of required interpolation continuity degree. The formulation is firstly developed—in a Lagrangian perspective—and the equilibrium equations are then derived using Hamilton's principle. In the sequence, using finite element method, it is substantiated by comparison to examples given in literature in static, dynamic, and finally in an application where piezoelectric effects intervene, in order to assess its multiframework capabilities and deliver a convenient approach whereby beams constituted of smart or conventional materials can be efficiently studied.

© 2021 Elsevier LtdMode I delamination fatigue crack growth behavior was investigated in a carbon-epoxy prepreg fabric laminate by evaluating the mean load effects. The fatigue crack growth rate was determined as a function of the maximum Mode I strain energy release rate considering an exponential fitting function according to the Compliance Based Beam Method (CBBM). Classical data reduction techniques were combined with the proposed method, indicating less scatter on results and satisfying basic assumptions of smoothness and continuity for the fatigue crack growth process. The delamination growth rate curve proved to be strongly affected by the applied mean load as the fatigue onset delamination. The number of cycles to onset is higher for lower load levels and, considering the stable propagation region, a higher delamination growth rate was reported for higher load levels. The fractographic analysis has confirmed the effects of cyclic loading and the mean load levels on fracture surfaces. For a higher mean load, failure mechanisms expose static aspects and substantial presence of microcracks at fiber imprints, while, under lower mean load were noticed significant wear and plasticity and featureless fiber tracks.

© The Author(s) 2021.This paper describes a classical laminate theory-based constitutive model for portraying thermoplastic composites’ mechanical properties and the development of residual stresses during consolidation. The extended Hillier model is applied to describe the material’s crystallisation and as such is able to provide final part quality as a function of the process cooling history while taking into account the first and second crystallisation mechanisms occurring concurrently. With the developed model, a parametric study was performed taking into account layups that are commonly used in the aerospace industry, where general design guidelines are suggested. Some of the advantages of using cross-ply and quasi-isotropic laminates became clear as no shear residual stresses were predicted for those laminates. However, highly anysotropic laminates may also offer structural advantages. Numerical simulations indicate that the crystallisation residual strains can be, although smaller than thermal residual strains, relevant to final part quality. The combination of both effects may result in high residual stresses at ply level which in turn can compromise the ultimate strength of the laminates and make it difficult to attain the desired part’s geometrical tolerances.

© 2021 Elsevier LtdThis work presents an efficient explicit finite element model for predicting the nonlinear aeroelastic behavior of composite panels in the supersonic regime. The first-order shear deformation plate theory in conjunction with the von Kármán nonlinear strains is used for structural modeling and the linear piston theory is used to model the aerodynamic loads. In order to reduce the computational cost of the simulations, a lumping procedure is employed in the mass and aerodynamic damping matrices of the finite element model. No modal reduction is performed and the central difference method is used for the numerical direct integration in time of the nonlinear equations. The model is verified using results from the literature and it is demonstrated that the lumping procedure drastically reduces the computational cost of the simulations.

© 2021 Elsevier LtdThis study performs an experimental and numerical investigation on the nonlinear aeroelastic response of cantilever high-aspect-ratio beam-like wings with a ballast at their free tips, emulating the effects of a store. As an extent, the effects of different chord-wise ballast positions are experimentally examined for two highly flexible rectangular wings. Furthermore, the numerical model proposed brings forward a nonlinear finite element beam model accounting for aerodynamic nonlinearities, via stall and follower forces models, along with geometrical nonlinearities due to large displacements and rotations. A great variety of analyses were performed: First, the flutter boundaries of the wings were analyzed; second, the limit cycle oscillation amplitudes and frequencies in the oscillating wings were evaluated; third, the coupling behavior and the nonlinear responses obtained were discussed under several attributes. The geometrical nonlinearities were taken into account by a total Lagrangian formulation based on a straightforward and consistent interpolation field in order to describe the exact kinematics of a Timoshenko's beam. Nonlinear aerodynamic loads were computed via an unsteady strip theory in the time-domain with the Jones approximation for the Wagner's function along with a follower aerodynamic loads assumption. Additionally, a non-usual stall model based on an experimental quasi-static stall curve for flat plates was used to interpolate the lift-curve slope. The experimental and numerical results indicated a minimum flutter speed for ballast positions about of −5 mm toward the leading edge. Next, different nonlinear post-flutter LCO behaviors were obtained for the different ballast positions tested. To conclude, the good correlation between model and experiments indicated that the nonlinear modeling approach proposed herein was capable to predict the aeroelastic behavior of the tested high aspect-ratio wings.

© 2020 Elsevier LtdDespite composite materials presenting a viable design solution for structural weight savings, their low resistance to impact damage portraits a potential drawback. This work presents a study on the compressive pre-loading effects on Low Velocity Impact, LVI, for composite laminated plates. Despite the absence of a standard testing procedure accounting for pre-load effects, a test rig was designed specifically for LVI on pre-loaded plates while preserving ASTM D7136M-15 guidelines for the stress-free specimens. Woven fabric composite laminated plates were manufactured using the Resin Transfer Moulding (RTM) process and subjected to impact on pre-loaded conditions. Three pre-load levels were prescribed, representing conditions ranging from low strain levels until post buckling regime. FE numerical models were implemented in ABAQUS FE code, comparing different Continuum Damage Mechanics (CDM) constitutive model formulations with experimental results. Analytical and numerical predictions showed good correlation with experimental results, allowing for further application of the test apparatus and methodology.

© 2020 Elsevier LtdThis work presents an experimental study on the mechanical behaviour of thermoplastic polyarlyetherketone (PAEK) based composite laminates reinforced with woven carbon fibres, subjected to high strain rates under compression loading. The specimens were tested using a Split Hopkinson Pressure Bar (SHPB). The tests covered the working temperatures and stress envelopes of −54 °C, RT (25 °C), and 80 °C, each tested at six different off-axis angles. The high-speed imaging system was used to monitor the failure process. The strain on the loading direction was determined using Digital Image Correlation (DIC). Fractography analysis was performed to understand the influence of temperature on the damage aspects, using Scanning Electron Microscopy (SEM). The −54 °C and RT SHPB tests showed more intralaminar damage aspects than the ones tested at 80 °C, which presented a preference for the interlaminar damage aspect and exhibited the lowest strength. A new failure criterion dependent on temperature and strain rate was proposed, based on a phenomenological approach and experimental results. The fabric architecture at the ply level was idealised as a two-part mosaic model. The crystallinity of the PAEK thermoplastic matrix was analysed using Differential Scanning Calorimetry (DSC). Results showed no evidence of crystallinity degree variation induced by the high strain rate tests.

© 2021, The Minerals, Metals & Materials Society.The plastic anisotropic response of stainless steel materials is investigated in this paper by using Barlat’s Yld 2000-2d yield criterion. A new set of anisotropy coefficients is proposed and calibrated based on material experimental data. The new set of coefficients for the Lankford anisotropy coefficient, normalized yield stress, and equal biaxial stress were numerically obtained using the Newton–Raphson method. Study cases for AISI 409L and AISI 430 materials are presented and discussed. Correlations between predictions and experimental results indicate that Barlat’s yield stress criterion and plastic stress potential for stainless materials are not coincident. Hence, the Barlat’s non-associate flow rule gives better fitting with the experimental Lankford’s coefficient of anisotropy results.

© 2020 Elsevier LtdIn the open literature, many authors have used the fractional calculus in conjunction with the finite element method to model certain viscoelastic systems. The so-named fractional derivative model may be a better option for transient analyses of systems containing viscoelastic materials due to its causal behavior and its capability to fit accurately the viscoelastic damping properties and to represent properly their fading memory. However, depending on the situation, it leads to costly computations due to the integration of the non-local viscoelastic displacement and stress fields, especially for long time intervals. In this contribution, it is proposed a new and efficient general three-dimensional fractional constitutive formulation based on the use of a recurrence term to give a simplest and low-cost constitutive law to describe the frequency- and temperature-dependent behavior of viscoelastic materials, especially for complex systems. To demonstrate the efficiency and accuracy of the proposed formulation compared with those available in the literature, an academic example formed by a thin three-layer sandwich plate is performed and the main features and capabilities of the proposed methodology are highlighted.

© 2021 Cambridge University Press. All rights reserved.This paper presents a framework to support decision-making in aircraft conceptual design optimisation under uncertainty. Emphasis is given to graphical visualisation methods capable of providing holistic yet intuitive relationships between design, objectives, feasibility and uncertainty spaces. Two concepts are introduced to allow interactive exploration of the effects of (1) target probability of constraint satisfaction (price of feasibility robustness) and (2) uncertainty reduction through increased state-of-knowledge (cost of uncertainty) on design and objective spaces. These processes are tailored to handle multi-objective optimisation problems and leverage visualisation techniques for dynamic inter-space mapping. An information reuse strategy is presented to enable obtaining multiple robust Pareto sets at an affordable computational cost. A case study demonstrates how the presented framework addresses some of the challenges and opportunities regarding the adoption of Uncertainty-based Multidisciplinary Design Optimisation (UMDO) in the aerospace industry, such as design margins policy, systematic and conscious definition of target robustness and uncertainty reduction experiments selection and prioritisation. &copy; 2020 The Author(s). Published by Cambridge University Press on behalf of Royal Aeronautical Society.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.This paper examines aerodynamic shape optimization considering the two-dimensional Euler equations and adaptive unstructured meshes. In this work, the adaptive process uses primal and adjoint solutions to estimate the error in functional outputs and to formulate adaptive indicators to locally refine the mesh to improve the accuracy of the solution. We investigate four design strategies, two of which include adaptive grids, to check if using adaptive grids in aerodynamic shape optimization is beneficial in terms of the final design and total time. Two test cases considering the NACA0012 airfoil at transonic flows are used, one of which is the AIAA Aerodynamic Design Optimization Discussion Group Case 1 problem and the second is a similar case but considering lift constraint. The results show that adaptive grids can be beneficial in the design process both in terms of the final design and also the total time spent to optimize.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Propellers are one of the most efficient ways to generate propulsion for low-speed flights. About 84% of the energy generated by the engines is utilized, being therefore widely used in several different aircraft. However, studies show that propellers with a diameter less than 16 inches have efficiency reduced by up to 15% when compared to larger ones. This deficiency is not always captured by the mathematical models, since they are not as accurate for that scale. The present study aims to increase the accuracy of simulations performed by a blade element/vortex software to predict the performance of different motor-propeller assemblies. For this purpose, neural networks are trained to correct thrust and torque values given by the software in relation to wind tunnel tests. For this, 28 propellers from different manufacturers and geometries are tested in wind tunnel and simulated in the software under the same conditions to generate the training database. Geometric data of propellers and operational conditions were used as inputs for the neural networks. The outputs are the difference between the results of the test in a wind tunnel and the software simulation. The use of neural networks to correct the simulation results reduced the mean squared error of the estimates at least in 80% in the case of thrust and 70% in the case of torque.

© 2021, Emerald Publishing Limited.Purpose: This paper aims to investigate the possibility of lowering the time taken during the aircraft design for unmanned aerial vehicles by using machine learning (ML) for the configuration selection phase. In this work, a database of unmanned aircraft is compiled and is proposed that decision tree classifiers (DTC) can understand the relations between mission and operational requirements and the resulting aircraft configuration. Design/methodology/approach: This paper presents a ML-based approach to configuration selection of unmanned aircraft. Multiple DTC are built to predict the overall configuration. The classifiers are trained with a database of 118 unmanned aircraft with 57 characteristics, 47 of which are inputs for the classification problem, and 10 are the desired outputs, such as wing configuration or engine type. Findings: This paper shows that DTC can be used for the configuration selection of unmanned aircraft with reasonable accuracy, understanding the connections between the different mission requirements and the culminating configuration. The framework is also capable of dealing with incomplete databases, maximizing the available knowledge. Originality/value: This paper increases the computational usage for the aircraft design while retaining requirements’ traceability and increasing decision awareness.

© AIAA International. All rights reserved.Mesh generation and deformation are critical elements in gradient-based aerodynamic shape optimization (ASO). Improperly generated or deformed meshes may contain bad-quality cells that degrade the accuracy of computational fluid dynamics (CFD) solvers. Moreover, an inefficient mesh deformation method can become the bottleneck for the entire ASO process. To perform practical ASO, mesh generation and deformation methods need to be automated, scalable, robust, and computationally efficient. This paper tackles these challenges by developing an efficient approach for generating high-quality structured meshes in a semi-automatic manner. An automatic mesh generation approach is also proposed to handle intersections of multiple structured meshes with the overset mesh approach. In addition to mesh generation, a flexible mesh deformation method is developed, along with an efficient approach for computing mesh deformation derivatives using automatic differentiation. Finally, the performance of the proposed approaches is evaluated in terms of speed, scalability, and robustness. The mesh generation approach scales up to 100 million cells and 256 CPU cores. In addition, the robust mesh deformation approach enables a large range of valid mesh deformations, which gives more freedom to explore the design space in ASO. Moreover, the mesh deformation and the computation of its derivatives require only 0.1% of the CFD runtime. The mesh generation and deformation approaches have been implemented in the pyHyp and IDWarp software packages, which are publicly available under open-source licenses. The proposed approaches are useful tools to handle general ASO problems for aircraft, turbomachinery, and ground vehicles.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.One critical step of conceptual design of future aircraft is the selection of technologies to be integrated in the system. This paper presents a framework under development to support the selection and prioritization of technologies in the presence of uncertainty for future Aerospace & Defense programs. The work is a product of a collaboration between Saab Aeronautics, Embraer, and Instituto Tecnológico de Aeronáutica. This article expands the capabilities from previous publications by introducing Uncertainty Quantification to a problem involving a larger number of technologies and multiple Measures of Performance. Strategies to handle the upsized problem are investigated and visual analytics is explored to communicate results in an intuitive and understandable fashion. A de-coupled strategy is proposed to enable pursuing Effectiveness-Based Design by translating Measures of Effectiveness into Measures of Performance to guide the selection and prioritization of technology clusters.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Uncertainty-based Design Optimization techniques present a powerful toolkit to achieve robust and reliable optimal designs in the presence of uncertainty, having probability theory as its backbone. The central limit theorem is a key concept in probability theory due to its notorious usefulness in a wide number of statistical problems. However, it seems that the theorem applicability to problems involving non-normal probability distributions has led to a mistaken belief that stochastic responses resulting from the propagation of input uncertainties naturally tend to be normally distributed. The purpose of this paper is to briefly discuss why this is not necessarily true and why this misconception can be detrimental. Three reasons are identified and illustrated through simple test cases using Monte Carlo simulations and Anderson-Darling test.

© 2020 by the authors. Licensee MDPI, Basel, Switzerland.Sugarcane bagasse has a great potential to be used as biofuel; however, its use as feedstock in fluidized bed reactors is hampered due to its fibrous nature, low apparent density, high moisture content, and difficulties with its fluidization. The present study evaluated the torrefaction of sugarcane bagasse to propose suitable process conditions that balance the properties of the fuel obtained in the torrefaction and the process’s energy requirements. Based on the thermogravimetric analysis and previous reports, two final process temperatures (230 °C and 280 °C) and residence times (35 and 45 min) for the same heating rate (5 °C/min) and nitrogen flow (1 L/min) were evaluated. Within the experimental conditions evaluated, it can be concluded that for 30 min of residence time, the average target temperature of 230 °C should be high enough to produce a stable torrefacted bagasse with a 3.41% reduction in the volatile content and obtain 98.85% of energy yield. Higher temperatures increase the feedstock’s carbon content and energy density, but the reduction in energy yield and the fraction of volatiles do not justify higher temperatures or longer residence times for pretreating the sugarcane bagasse.

© 2021 SAE International.Compression ignition engines are widely used in the cargo and passenger transport sectors, this is due to their high energy efficiency and can operate with renewable fuels. The search for increased efficiency in internal combustion engines and reduced emissions are increasingly stringent, so to meet regulatory emission standards, new technologies are being studied and developed to reduce emissions generated by engines, in the case of diesel engines compression ignition, studies of techniques to reduce NOx and soot have been carried out. One of the techniques studied is the application of the DFI - Ducted Fuel Injection concept, which makes the fuel spray pass through a small cylindrical duct installed upstream of the injection orifice of the injector nozzle, thus improving the air/fuel, making it more homogeneous and allowing a more complete combustion. This work addresses a study of this application of DFI with different compression ratios. To carry out the tests, a thermodynamic single-cylinder engine was used where its compression ratio is 16.0:1 in its normal condition, when the ducts are installed in the combustion chamber the engine starts to operate with a compression ratio of 16.5:1, thus, this study is necessary so that it is possible to visualize the behavior of the engine when the compression ratio changes, aiming at the thermodynamic behavior and emissions. CO, HC and NOx emissions were measured with FTIR spectroscopy equipment, and soot was measured by Laser Induced Incandescence - LII. The difference in compression ratio between DFI and free spray causes soot levels to increase considerably with increasing load in free spray mode, while for DFI the indices are almost unchanged.

© 2021 SAE International.Hybrid vehicles have been developed for improving efficiency and the consequent reduction of fossil fuels consumption in the transportation sector. The complexity of such vehicles allows for countless architectures, being one of them the range extender concept, which corresponds to an electrically powered vehicle equipped with a small combustion engine to improve the vehicle range. In the literature there is no current consensus whether range extenders should adopt simple engine technology aiming at cost reduction, or should they incorporate complex systems in order to achieve a remarkable thermal efficiency and low emissions. In the context of exploring the advanced options for range extenders, the combustion characterization is a fundamental step, which provides information on combustion behavior for several fuel types under a wide range of combustion modes. That information can both yield useful insights for engine development and provide combustion datasets for engine simulation. This study proposes the characterization of the flame morphology of hydrous ethanol combustion under port fuel injection mode and mixture dilution with synthetic exhaust gas recirculation (EGR) on a spark ignition, optically accessible engine. Flame natural luminosity was recorded by a high speed camera and their post-processing provided the flame morphology, which was correlated to the in-cylinder pressure data and indicated parameters. The gaseous emissions were measured using FTIR technique, for three engine speed conditions (1500, 2250 and 2500 rpm) and three conditions of EGR dilution (5%, 10% and 15%) besides the baselines conditions with no dilution, under a constant load of 5 bar IMEP. Thermodynamic results indicate that there was no power de-rating with EGR dilution. However, the optical analysis revealed that dilutions rate beyond 10% of EGR led to a slower combustion and lower combustion stability. Specific emissions of NOx, aldehydes and CO were reduced with increasing EGR rates, while the unburned ethanol increased.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Aircraft electrification is subject of several studies in the aeronautical field, due to the increasing need to enhance efficiency and to reduce the contribution of the aviation sector to climate change. In this scenario, the use of hydrogen fuel cells (FCs) is one means to explore new designs for propulsion electrification. Thus, this study aims to assess the feasibility of using gaseous hydrogen with proton-exchange membrane FCs (PEMFC) to provide electric power for the propulsion of a small aircraft. Firstly, current commercially available FC and hydrogen storage systems were analyzed to obtain data of these systems. Secondly, FC powered hybrid-electric propulsion system (PEMFC and batteries) was proposed, considering versions with 700 bar and 350 bar hydrogen tanks, and then compared with versions having an internal combustion engine (ICE) and another having just batteries. For a fair comparison, the propulsion system for each version was size-fitted for the defined mission profile. The aircraft aerodynamics, weight, propulsive efficiency, sizing parameters and other aspects were modeled and simulated in a virtual environment (SUAVE). The result evidenced that the ICE version has the lowest aircraft mass throughout the cruise duration range (60 min to 120 min), also having the best performance, in terms of Energy Specific Air Range (ESAR), for cruise longer than 65 min. For the airplanes with electric propulsion, the hybrid versions are more suitable in longer missions, being able to double the cruise duration of the battery version, while the battery version has the best ESAR for cruise shorter than 65 min. Therefore, the propulsion hybridization with PEMFC, gaseous hydrogen and batteries is feasible for small airplanes in flights longer than 65 min, when compared to an electric propulsion with only batteries. However, although having a range extender potential, hybrid versions need great improvements in order to outperform the ICE version.

© 2021, American Institute of Aeronautics and Astronautics Inc.. All rights reserved.Aircraft propulsion electrification is currently considered by industry and academia as one of the most promising strategies to reduce air transport emissions and to increase overall efficiency levels. In the past decade, a multitude of papers was published in this subject, most of them indicating encouraging fuel burn benefits versus conventional, fossil-fuel based propulsion systems, when incorporating future technologies and especially when novel aircraft configurations and synergistic propulsive-airframe integration are used. However, a much smaller effort has been applied to the economical aspects of hybrid and full electric propulsion, which is crucial for a successful product introduction. The present paper describes the modelling of a baseline general aviation type aircraft and its electrified propulsion derivatives, exploring different electrification strategies. Analyses are performed at aircraft level, comparing recurring and cash operating costs of the considered concepts for several cost and durability scenarios. It is shown that while considerable CO2 reductions may be achieved in some electrification strategies, important improvements on economical figures of merit are needed in order to make electrified propulsion competitive on a cost perspective. This is because electric architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increase direct maintenance costs, especially at higher degrees of energy hybridization.

© 2021 AIAA.Aircraft propulsion electrification is currently considered by industry and academia as one of the most promising strategies to reduce air transport emissions and to increase overall efficiency levels. In the past decade, a multitude of papers was published in this subject, most of them indicating encouraging fuel burn benefits versus conventional, fossil-fuel based propulsion systems, when incorporating future technologies and especially when novel aircraft configurations and synergistic propulsive-airframe integration are used. However, a much smaller effort has been applied to the economical aspects of hybrid and full electric propulsion, which is crucial for a successful product introduction. The present paper describes the modelling of a baseline general aviation type aircraft and its electrified propulsion derivatives, exploring different electrification strategies. Analyses are performed at aircraft level, comparing recurring and cash operating costs of the considered concepts for several cost and durability scenarios. It is shown that while considerable CO2 reductions may be achieved in some electrification strategies, important improvements on economical figures of merit are needed in order to make electrified propulsion competitive on a cost perspective. This is because electric architectures tend to increase costs: turboelectric increases recurring equipment costs, while hybrid-electric increase direct maintenance costs, especially at higher degrees of energy hybridization.

© 2021 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.This paper presents a conceptual study of a regional aircraft with a turboelectric propulsion system and boundarylayer ingestion. The aircraft has an additional electric propulsor installed at the aircraft tail cone, which is driven by generators installed on both underwing engines, aiming to ingest the fuselage boundary layer and improve the aircraft overall performance. The proposed configuration is an aircraft reengining of the reference aircraft platform, the Embraer 175-E1, targeting minimizing airframe modifications. Parametric variations of the thrust split ratio as well as the electric fan pressure ratio were performed in order to create a design space of possible solutions for the proposed concept and also to provide insights of the aircraft key variables trends. From that, a feasible and optimized configuration in terms of efficiency was selected and compared to the reference aircraft. As the main conclusion, it was determined that the studied propulsion system has the potential to provide specific air range benefits in the order of 4 to 7%, which may not be enough to justify a new development.

© 2021 The Author(s)The present work describes a computational mechanism based failure analysis conducted for 3D-printed continuous carbon fiber reinforced thermoplastic composites (CFRTPCs), which could not be seen in the available literature. The material failure is investigated based on intraply failure evaluation and adopts different failure criteria for the material constituents. The micromechanical modeling employs the Asymptotic Homogenization technique and comprises the selection of a representative volume element statistically equivalent to the microstructure of the material, which is identified from cross-section micrographs. In contrast to recent work, it is demonstrated that an additional relation is required for the macroscopic deviatoric stresses acting over the matrix. This avoids an overestimation of the matrix failure when the reinforced lamina is subjected to longitudinal and shear loads. The resulting failure envelopes are presented and compared to those provided by analytical failure theories available in the literature. The results obtained by the micromechanical approach showed its ability to predict failure of 3D-printed CFRTPCs, in addition to bring different elements for the discussion that could not be captured with analytical models. In this context, it is believed that the characteristics inherent to the microstructure reproduced in the RVE, particularly contributed to obtaining more realistic failure envelopes.

© 2021Parts produced by additive manufacturing have final characteristics (such as mechanical properties and dimensional accuracy) strongly dependent on how material is deposited during production. This study presents a modelling concept called VOLCO-X (VOLume COnserving model - eXtended version), which extends a recently developed simulation technique to be able to accurately simulate deposited structures that were not possible with the previous model. A major advantage of the proposed modelling approach is that it does not require any experimental calibration or fitting. The modelling approach is based on a principle of conservation of volume in a voxelized space, in conjunction with a new deposition modelling concept that re-distributes the deposited material when neighboring filaments are in contact. In addition, an acceleration-dependent extrusion rate correction was implemented in the software to predict changes in the material distribution as function of the printing speed, as well as a mechanism to effectively consider possible asymmetry of deposited filaments. The model is shown to accurately predict the geometry and porosity of specimens manufactured by Fused Filament Fabrication (FFF) with varied printing speeds, distance between filaments and extrusion widths. The numerical results correlated well with validation experiments, being able to capture the transition from triangle to diamond void shapes and to predict defects observed in printed parts. VOLCO-X could simulate printing conditions from fully dense structures to under-extruded structures with gaps. It has potential to aid in the design of functional printed parts by predicting the final dimensions, void shapes and void volume fraction of 3D printed parts, and represents an important step towards enabling the predictive simulation of full-sized parts.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Energetic materials have been used over time in civil and military applications. Concomitantly, studies were conducted focusing on the combustion mechanisms of these materials, including their kinetic and thermodynamic behavior during firing. The objective of this work was to systematically study the mechanisms of thermal decomposition of ammonium dinitramide (ADN), and ADN formulated as a solid composite propellant with glycidyl azide polymer (GAP), through reactive molecular dynamics simulations. The main reactions of the mechanisms were elucidated and analyzed, and the Arrhenius parameters were determined for the global processes. Calculated activation energies for the systems were 127.84 and 354.72 kJ/mol for ADN and ADN/GAP, respectively. Comparison to literature data shows up to 14% of deviation, which proves the methodology useful for predictions and kinetic analyzes of combustion/pyrolysis reactions of energetic materials.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In propulsion systems, to ensure a suitable thrust, the selection of the pair fuel/oxidizer is of utmost importance. Combination of propellant influences the characteristics of the chemical reaction process, the fuel vaporization speed, the ignition temperature, the volatility of hot gases. After the propellant, a suitable injector design is important, which allows better use of the propellant mixture, and thus achieve better engine performance and less combustion instability. This study evaluated the radial injector data, compared with those for other types of injectors, orifice-plate and swirl. Combustion behaviour was analysed by reactive molecular dynamics simulations. It was analysed how each contributes to the engine’s performance, by using solid fuel-based paraffin and oxygen gas in the gas phase (GOx), constituting a hybrid propellant. For orifice plate and swirl injectors, the specific impulse values were higher at higher test pressures. However, for the radial injector, the Isp was increased to the test pressure up to 25 bar. All injectors yielded good operation and met the goal of injecting oxidizer flow efficiently. The RMD simulation was able to show the behaviour of paraffin during decomposition and combustion, as well as explain the pressure effects on the system by the gaseous molecules generation.

Copyright © 2021 by the International Astronautical Federation (IAF). All rights reserved.In this work are presented pyrolysis and combustion simulations of alternative jet fuels using reactive molecular dynamics methods. Three fuels obtained from renewable resources are compared: farnesane, α-farnesene and β-farnesene. The pyrolysis and combustion simulations were done in different temperatures. Significant differences have been observed among the compound reactions during the decompositions. The Arrhenius parameters of the global process were obtained for all species, considering a first-order approach. For the pyrolysis, the obtained activation energies for farnesane, α-farnesene and β-farnesene were 132.55, 117.28 and 112.88 kJ mol-1, respectively.

© 2021 The Authors. Human Brain Mapping published by Wiley Periodicals LLC.Understanding decision-making in complex and dynamic environments is relevant for designing strategies targeting safety improvements and error rate reductions. However, studies evaluating brain dynamics in realistic situations are scarce in the literature. Given the evidence that specific microstates may be associated with perception and attention, in this work we explored for the first time the application of the microstate model in an ecological, dynamic and complex scenario. More specifically, we evaluated elite helicopter pilots during engine-failure missions in the vicinity of the so called “dead man's curve,” which establishes the operational limits for a safe landing after the execution of a recovery maneuver (autorotation). Pilots from the Brazilian Air Force flew a AS-350 helicopter in a certified aerodrome and physiological sensor data were synchronized with the aircraft's flight test instrumentation. We assessed these neural correlates during maneuver execution, by comparing their modulations and source reconstructed activity with baseline epochs before and after flights. We show that the topographies of our microstate templates with 4, 5, and 6 classes resemble the literature, and that a distinct modulation characterizes decision-making intervals. Moreover, the source reconstruction result points to a differential activity in the medial prefrontal cortex, which is associated to emotional regulation circuits in the brain. Our results suggest that microstates are promising neural correlates to evaluate realistic situations, even in a challenging and intrinsically noisy environment. Furthermore, it strengthens their usage and expands their application for studying cognition under more realistic conditions.

© 2021 IEEE.This paper presents a method to synchronize data acquisition devices that are mechanically coupled, having attached an accelerometer to each device. A common time base for the accelerometer signals are obtained through the identification of pairing salient peaks and applying line-fitting through the potential matches. Aligning data recorded from different sources is important to precisely provide an observation of the state of a system in time (sensor fusion), to estimate the correlation between its variables and to correlate variables to time-based events. A data link between devices is not always possible or convenient. If the acquisition devices are mechanically coupled, such as being in the same body or vehicle, we propose to synchronize the data recorded from both by using the accelerometers signals to bridge. The provided solution is an automated process to find the temporal reference between accelerometer signals. Several signal processing steps are taken after data collection and storage: inconsistency removal and filtering, detection of maxima and minima, selection of saliencies, description through a characteristic pair of numbers: the interval lengths between it and its successor and its predecessor, listing possible matches between salient points, selection of the topmost relevant matches and line fitting with consensus. We discuss qualitative similarities of related work. Quantitative results are also presented by using the multidisciplinary study that motivated this work, with simultaneous data from the instrumentation of a helicopter and pilot physiological data. To conclude, we discuss the limitations of the presented approach and future work.

© 2020 IOP Publishing Ltd Printed in the UKTemperature-sensitive paint (TSP) is a type of luminescent temperature sensor that can provide surface temperature measurements on the surface of a test article. These surface temperature measurements can be used to determine heat flux and visualize boundary layer transition on an aerodynamic body. This paper presents the static response characteristics of a TSP based on rhodamine B (RhB) applied on a polymer-ceramic supporting matrix. Six solvents with varying polarity indices were used to apply the RhB to the sensors, which were then evaluated in terms of luminescent signal level and temperature sensitivity. The results are presented and also compared to previous results for RhB on an anodized aluminum matrix. The temperature range was between 150 K and 365 K. The study confirms that the influence of the solvent on the sensor's final characteristics is significant, and shows temperature sensitivities as high as −4.8% K−1 at 150 K when dichloromethane is used as the application solvent.

© 2020, The Society for Experimental Mechanics, Inc.The new aeronautical structures have become more flexible and light weight to reduce energy consumption, emissions, and noise, and to operate at high altitudes for long periods in the air, such as those required in the NASA Helios project. The increased structural flexibility of these aircraft has reignited concerns related to aeroelastic instabilities, such as flutter. Improving the techniques and methods used in aircraft certification flights is an important concern of the aeronautical community, because current standards and procedures do not provide recommendations and guidelines for aircraft with a high degree of flexibility. The techniques traditionally used in commercial airplanes cannot be used in this new aircraft concept, because they have a high degree of non-linearity in their flight dynamics. Current research indicates an increasing awareness about the importance of vision in the monitoring of UAV structural health. This work presents a new methodology to measure natural frequencies of aeronautical structures using a computer vision system. We also discusses new approaches to sense and acquire vibration data on aeroelastic certification flights test. These new approaches aim to reduce both the time required to identify the aeroelastic phenomenon and the size of the hardware that must be boarded on the aircraft, thus minimizing the risks and costs of the vibration tests. The advance of computer vision systems enables the use of cameras as a motion tracker sensor with millimeter precision and accuracy. Non-contact sensors are suitable for flutter analysis because they do not interfere with the dynamics of the aircraft. Therefore, this new methodology is able to process the obtained images and provide the user with the data about movements in a ready to use vector, at a reasonable cost. Using the data provided by this methodology the natural frequencies of the first bending modes were identified. This new methodology can be a user-friendly tool to support the Brazilian National Civil Aviation Agency - ANAC program called iBR 2020, which aims to certify small aircraft.

© 2020, Krishtel eMaging Solutions Private Limited.purpose: This paper aims to investigate the post-flutter nonlinearities due to the wing high aspect ratio. Flutter is an aerodynamic auto-excited phenomenon which occurs due to the coupling of two or more different vibration modes. This coupling results from the interaction between aerodynamic, elastic, and inertial forces. The present investigation scope is the comparison between experimental aeroelastic analysis of high-aspect-ratio wings using subsonic wind tunnels with computational experiments for three different center of gravity conditions. Methods: The computational nonlinear aeroelastic analysis is performed using a formulation based on the variation of the energy functional and considering Peters’ unsteady aerodynamic model. The post-flutter analysis consists in the comparison between the attractor reconstructed using the Takens’ theory with the result of the 0–1 test for chaos for both computational and wind tunnel experiments. Results: First, the 0–1 test is performed for both computational nonlinear analysis and wind tunnel experiment and they are in good agreement for each condition. After that, the procedure to obtain the reconstructed attractor is followed for both cases and they are again in good agreement. The difference between computational experiment reconstructed attractors and wind tunnel experiment reconstructed attractors is mainly because of wind turbulence in wind tunnel section. Conclusion: This research shows that all three experimented conditions presented periodic dynamic behavior. The 0–1 test predicted well the dynamic behavior; therefore, it is recommended to apply this test for all nonlinear experiments so that a first qualitative evaluation is possible. All Lyapunov exponents calculated are negative, confirming the periodicity of the three center of gravity conditions for both computational and wind tunnel experiments.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.Aiming to build a 6DOF flight simulation model for NASA-CRM and, in the lack of experimental lateral-directional data, three different methodologies were assessed and compared: usual semi-empirical method based on historical wind tunnel experiments and first principals physics, vortex lattice method (using XFLR5 software), and panel method (using OpenVSP software). The comparison presented is exhaustive in the aspect of isolating each component aerodynamic contribution and presents a clear view of the agreement between the studied methodologies. This work serves as basis for a first assessment of the uncertainty of the stability derivatives, associated with each methodology, usually used during preliminary design of aircraft.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.A method for calculation of dynamic response to gust and control surface excitations, which allows the inclusion of nonlinear terms such as nonlinear control laws, without the need to use rational function approximation, is presented. This method is based on characteristic responses obtained with frequency domain equations, which associated with Fourier transforms, can be used to calculate time domain dynamic responses via Duhamel Integrals. The Duhamel Integral method is demonstrated for a typical airfoil section with three degrees of freedom, making use of frequency domain equations and direct and inverse Fourier Transforms for the characteristic response computation. In addition, applications where this method presents advantages, such as in the application of non-linear control laws and analysis of Oscillatory Malfunction (OMF), are demonstrated.

© 2021 32nd Congress of the International Council of the Aeronautical Sciences, ICAS 2021. All rights reserved.In the development of automatic piloting systems nowadays, flight tests are required to validate operations and tuning of the control loops, making the process costly. For an optimal point of stability within a region of operation, this work aims to use the modern control technique of Linear Quadratic Regulator (LQR), with minimization through the Riccati equation for the optimization of Proportional, Integral, and Derivative (PID) control loops in longitudinal piloting. The aircraft considered for the flight tests was the C2 fixed-wing Unmanned Aerial Vehicles (UAV) used for agricultural purposes. The nonlinear model coefficients of the aircraft were acquired using well-known computational methods. The inertia properties were acquired through drawings made in Computer-Aided Design (CAD) with the Catia® software and the aerodynamic properties' estimation with the Omni3d® software. The aircraft's applied system was the Micropilot® LRC2 autopilot that has cascade PID control loops for altitude and trajectory control; however, the control loops tuning responsible for longitudinal movement are this work's main contribution. In parallel, a flight test campaign was carried out to collect data and tune the autopilot gains in flight by an empirical method based on Ziegler-Nichols' method. The gain data collected during the flights are used to compare the data obtained by the theoretical computer model of the aircraft. Different performances related to the gains obtained by the flight test and the PID control loops' optimization method through the LQR method are demonstrated with the non-linear model's application under the effects of disturbances. The main achieved results are about the minimum energy cost. This minimization in energy cost is due to the PID in-flight tuning that takes more energy in the actuators than the PID optimized with the LQR method, which proves to be a promising system for faster development of agricultural UAVs.

© 2021, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Operational Modal Analysis (OMA) is a methodology to obtain the modal properties of a structure using the dynamical responses of the system only. That methodology is very useful in aeroelastic in-fligh testing where there are difficulties in measuring directly the aerodynamic loads on aircraft. For risk reduction in the future flight operations of the EOLO at ITA, wind-tunnel tests were performed. EOLO is an Unmanned Aerial Vehicle (UAV) with high aspect ratio and structural flexibility, designed to study aeroelastic phenomena and to evaluate the interaction of flexible effects with the aircraft flight dynamics. In this work The Frequency Domain OMA techniques: Decomposition (FDD), Enhanced Frequency Domain Decomposition (EFDD), Spatial and Frequency Domain Decomposition (SFDD) are applied to the vibrational data from wing tunnel test campaign in different operation conditions, using acceleration and strain measurements. The results between the OMA techniques are compared with previous modal characterization from Ground Vibration Test (GVT) and numerical aeroelastic analysis. The different generations of the frequency domain decomposition methods proved their suitability for use in aircraft aeroelastic characterization using accelerations and strain measurements.

\bigcirc c 2021 Society for Industrial and Applied MathematicsWe present a successful deployment of high-fidelity large-eddy simulation (LES) technologies based on spectral/hp element methods to industrial flow problems, which are characterized by high Reynolds numbers and complex geometries. In particular, we describe the numerical methods, software development, and steps that were required to perform the implicit LES of a real automotive car, namely, the Elemental Rp1 model. To the best of the authors' knowledge, this simulation represents the first high-order accurate transient LES of an entire real car geometry. Moreover, it constitutes a key milestone toward considerably expanding the computational design envelope currently allowed in industry, where steady-state modeling remains the standard. A number of novel developments had to be made in order to overcome obstacles in mesh generation and solver technology to achieve this simulation, which we detail in this paper. The main objective is to present to the industrial and applied mathematics community a viable pathway to translating academic developments into industrial tools that can substantially advance the analysis and design capabilities of high-end engineering stakeholders. The novel developments and results were achieved using the academic-driven open-source framework Nektar++.

© 2021 Elsevier LtdThe increasing demand for high performance gears requires in-depth investigations of alternative materials to those commonly used. In this respect, microalloyed steels may appear as an alternative with technical and economic potential. Microalloyed steels may exhibit a more refined grain structure than conventional steels, which is commonly induced by the precipitation of highly stable and dispersed second-phase particles. This investigation aimed at understanding how the steel grain structure obtained by the addition of niobium (Nb) and titanium (Ti) as microalloying elements correlates to the material surface integrity promoted by a conventional gear manufacturing chain. The results indicated that the addition of microalloying elements leads to a refined and homogeneous grain structure. The residual stress state also proved to be both more compressive and homogeneous and the roughness exhibited greater stability. Such characteristics place the microalloyed steels in a prominent position regarding their application in the gear manufacturing, indicating the possibility of fatigue lifetime improvement.

© 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0)Triply periodic minimal surfaces such as Gyroid structures have been widely used in additive manufacturing as a strategy to reduce material usage, printing time, and part weight, which are of high interest by the automotive industry. Most Software dedicated to additive manufacturing have lattice tools for infill available, but they usually do not consider the influence of the infill strategy on the part`s mechanical properties. Therefore, this study analyzed numerically and experimentally the influence of lattices on the compressive behavior of samples manufactured by selective laser melting and developed a procedure to use the finite element method as a tool for mechanical properties evaluation. The procedure employed the software nTopology to generate gyroid structures and Ansys for the structural analyses. Different gyroid densities were numerically analyzed and samples with the best weight/stress ratio were selected for experimental validation with compression tests according to the ASTM E9 standard. The material considered was a carburizing steel DIN 5120 suitable for industrial applications. The results showed that the infill percentage is not associated with a linear relationship between weight and stress. It was observed that besides the infill ratio, the material distribution has a significant effect on the sample performance, which was affected by the stress concentration phenomena. A good representativity was found between the numerical model and experiments, enabling it as a reliable method to evaluate how the infill affects mechanical behavior

© 2021, Springer Nature Switzerland AG.A gap between basic research and production characterizes a technology colony. An open innovation alliance gives low-wage countries the chance to stand for technological leadership using the improved efficiency of resources. This chapter explores the “Engrena ITA” case study, an open innovation alliance created in Brazil for the gear technology sector. By sharing benefits and responsibilities, the initiative aims to enhance research prospections and knowledge dissemination. Along 2 years, the metrics of project prospection have become twice higher than the ones summed in the 6 years before its creation. Collective contribution in intellectual and financial aspects, as well as a systematic exchange between university and industry, shows to be the conversion motor from ideas to innovation. Organization proved to overcome the importance of resources available for innovation, indicating a feasible roadmap to unlink low-wage countries to technology colonies.

© Springer Nature Switzerland AG 2021.Over a hundred million gears are annually produced in Brazil. They are applied to automobiles, wind turbines, aircraft and sugar and alcohol energy systems, among others. Despite the variety of applications, these segments share similar demands for technological solutions within the same economic challenges to investing in innovation. This context engendered the launch of “Engrena ITA”, in 2017, as an alliance among organizations with the aim of enhancing research prospections about gears and power transmission systems. Sharing benefits and responsibilities among its members, Engrena ITA assumes the integrative role established by the Open Innovation concept. The operational essence is the systematic interaction among members, who receive the right of defining guidelines of the gear-dedicated research group of ITA. The fundamental interaction occurs in workshops twice a year. Deep technical discussions precede the definition of a priority list of research topics to be prospected. The top priority is taken to further discussions on the scope content, and its generated project proposal is submitted either to government calls or to a pool of companies. The first year of operation, executed as a pilot plan, joined 24 companies of the segment, from tooling developers to OEM’s. In one year, 15 projects were prospected, involving 29 organizations worldwide. Projects were prospected on a partnership basis, involving Brazilian and foreign research institutes. The systematic integration which drove new ideas creation is now the basis for the initiative’s continuity and for multiplying the model to further technologies.

© 2021, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.In this paper, a preliminary study of optimal round-trip trajectories for Earth–Moon–Earth missions is presented. The outgoing mission consists in transferring a space vehicle from a circular low Earth orbit (LEO) to a circular low Moon orbit (LMO) with minimum fuel consumption. The class of two-impulse trajectories is considered: A first accelerating velocity impulse is applied to insert the space vehicle into an Earth–Moon transfer trajectory, and a second braking velocity impulse is applied to insert the space vehicle into the terminal LMO. It is assumed that the velocity increments are applied tangentially to the terminal orbits. The fuel consumption is defined by the arithmetic sum of the velocity increments. The return trip is similarly described with the initial orbit corresponding to LMO and the final orbit corresponding to LEO. Two dynamical models are considered: an extended version of the patched-conic approximation which includes the eccentricity of the Moon’s orbit and the planar elliptic restricted three-body problem. The optimization problem is solved by means of two gradient techniques: Newton–Raphson–gradient algorithm and sequential gradient–restoration algorithm. Clockwise and counterclockwise arrivals at LMO are considered for outgoing trips, and clockwise and counterclockwise departures from Moon are considered for return trips. The time of flight varies from 4.5 to 5.3 days for outgoing trips or for return trips. Numerical results show that the fuel can be saved if the initial position of the Moon is appropriately determined.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.This work considers the development of a numerical-analytical procedure for computing optimal time-fixed low-thrust limited-power transfers between arbitrary orbits. It is assumed that Earth’s gravitational field is described by the main three zonal harmonics J2, J3 and J4. The optimization problem is formulated as a Mayer problem of optimal control with the state variables defined by the Cartesian elements—components of the position vector and the velocity vector—and a consumption variable that describes the fuel spent during the maneuver. Pontryagin Maximum Principle is applied to determine the optimal thrust acceleration. A set of classical orbital elements is introduced as a new set of state variables by means of an intrinsic canonical transformation defined by the general solution of the canonical system described by the undisturbed part of the maximum Hamiltonian. The proposed procedure involves the development of a two-stage algorithm to solve the two-point boundary value problem that defines the transfer problem. In the first stage of the algorithm, a neighboring extremals method is applied to solve the “mean” two-point boundary value problem of going from an initial orbit to a final orbit at a prescribed final time. This boundary value problem is described by the mean canonical system that governs the secular behavior of the optimal trajectories. The maximum Hamiltonian function that governs the mean canonical system is computed by applying the classic concept of “mean Hamiltonian”. In the second stage, the well-known Newton–Raphson method is applied to adjust the initial values of adjoint variables when periodic terms of the first order are included. These periodic terms are recovered by computing the Poisson brackets in the transformation equations, which are defined between the original set of canonical variables and the new set of average canonical variables, as described in Hori method. Numerical results show the main effects on the optimal trajectories due to the zonal harmonics considered in this study.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.This paper considers the dynamics of the circular restricted three-body problem (CRTBP) for the Earth–Moon system designing stationkeeping controllers at periodic orbits. Taking into account the L1 and L2 equilibrium points in this dynamics, it is constructed a family of periodic orbits in the vicinity of these libration points, called halo orbits. The orbits are constructed using an analytical approach as a first guess with a numerical method in addition, in order to correct the linear approximation procedure. Withal the stability of these libration points, trajectories are analyzed and proved to be unstable; a spacecraft moving near these points must use some correction maneuver to remain close to the nominal orbit. Two types of controllers are proposed for stationkeeping maneuvers performed by low-thrust power-limited propulsion system. The first controller is based on the linear quadratic regulator (LQR) and the second one is based on the nonlinear feedback control which uses the state-dependent Riccati equation control (SDRE). Finally, a parameters comparison analysis is performed taking into account different values of the weight matrices for both controllers at both halo orbits.

© 2020 Elsevier LtdThe emergence of automated manufacturing techniques has allowed the realization of the so-called tow-steered composite laminates, in which the fibers are deposited following continuous curvilinear paths. This enables to broaden the design space to satisfy a variety of design objectives. Previous studies have shown that conventional composites can be designed to maximize the modal frequencies and modal damping factors. However, similar investigations have not been devoted to tow-steered composites so far. In this context, the objective of this paper is to investigate the use of multi-objective optimization aiming at simultaneously maximizing the fundamental modal frequency and corresponding specific damping capacity of tow-steered composite laminates. The fiber trajectories are parameterized using two different schemes, and the parameters are taken as design variables. The equations of motion are derived from the combination of the Classical Lamination Theory with the Rayleigh–Ritz method. Damping is modeled by using the Strain Energy Method. Numerical optimization is performed using the evolutionary Direct Multisearch method, which provides optimal solutions forming Pareto fronts. Results obtained from various scenarios, including fully and partially steered laminates, and different boundary conditions, show that fiber steering can indeed improve substantially the dynamic characteristics, including damping, of composite laminates.

© 2020 Elsevier LtdMany studies previously reported in the literature have demonstrated, both theoretically and experimentally, the influence of thermally-induced stresses on the static and dynamic behavior of structures, due to the so-called stress-stiffening effect. In most cases of practical interest, temperature variations associated to environmental and operational conditions are governed by rather complex combinations of conduction, convection and radiation mechanisms. As a result, the temperature values at different points of a structure are very difficult to control and can rationally be considered as random quantities. In this context, the present paper addresses the stochastic modeling and characterization of the influence of thermal stresses on the natural frequencies of thin rectangular plates, assuming space-dependent temperature fluctuations modeled as stationary two-dimensional Gaussian random fields. For this purpose, based on the hypotheses of the classical Kirchhoff plate theory, a Rayleigh-Ritz-based dynamic model is first derived for the bending vibrations of plates, accounting for the presence of thermal stresses. This model is combined with the Karhunen-Loève expansion (KL), which is used to discretize the temperature random field, after which the statistics of the random natural frequencies are estimated by Monte Carlo sampling. Numerical simulations are performed for plates under free boundary conditions. Simulation results, which encompass sampling-based statistics for the thermal stresses and the first six natural frequencies of the plate, are presented and discussed. In addition, since thermal stresses can induce buckling, reliability has also been estimated considering this type of failure. Results enable to conclude that space-dependent temperature uncertainty can be significant upon the vibration and buckling behavior of plates, which justifies its consideration.

© "Advances in Acoustics, Noise and Vibration - 2021" Proceedings of the 27th International Congress on Sound and Vibration, ICSV 2021. All rights reserved.Over the last decades, the development of novel permanent magnets, especially those having rare earth metals in their composition, has led to a great improvement in their performance, as compared to conventional ferrite permanent magnets. Therefore, there has been an increasing demand for these magnets in many (including new) application fields. In particular, the strong magnetic forces exerted between magnets can be explored as a means of promoting contactless mechanical coupling between separate parts and structural components. In this context, this paper investigates the dynamic behavior of a multiphysics system composed of two parallel cantilever beams at the extremity of which cubic permanent magnets are attached. Given the nonlinear nature of the magnetic forces, the main interest is to characterize the dynamic phenomena induced by the magnetic coupling. The study also encompasses analyses of the influence of the gaps between the two magnets and the relative orientation of their polarization axes. For this purpose, an elasto-magnetic structural model is developed, accounting for the flexibility and mass distributions of the beams and also the magnetic interactions. Upon resolution of the equations of motion, this model is used to perform a number of numerical simulations, the results of which are presented and discussed.

© 2021, The Brazilian Society of Mechanical Sciences and Engineering.Since 2008, Institute of Aeronautics and Space (IAE) has made efforts into L75 Liquid Rocket Engine and a cooperation agreement was signed in 2011 with the Deutsches Zentrum für Luft—und Raumfahrt, the German Aerospace Center (DLR), aiming the L75 engine development. The achievement of adequate combustion stability was a major task, since the beginning. A novel methodology in stability studies regarding combustion stability of Lox/Ethanol propellant combination is proposed in this work. Basic studies and design investigations were performed, adopting a stability assessment strategy in two phases: First phase: L75 combustion chamber acoustics (frequencies and mode shapes) were obtained at room and hot temperatures by theoretical/experimental approaches. Second phase: two hot test campaigns were conducted at P8 test facility-DLR, with 21 hot tests. In 7 run-in tests, a Stainless Steel Capacitive cooled Thrust Chamber (SCTC) was used allowing burning up to 2 s. Instability phenomena were observed during pressure build up. Afterward, 14 tests were performed using Copper Cooled Thrust Chamber (CCTC) and no instability phenomena were observed, even at lower mass-flow then expected in test envelop (load point E6*) combined with low O/F ratios. CCTC allowed longer burning, increased up to 6 s. It is important to highlight that the burning times were calculated by using heat flux estimations at the SCTC/CCTC chamber throats to avoid damages in this critical region by steel/cooper melting. As the CCTC has better heat conductivity, longer burning times were established for this chamber. The measured data showed good agreement regarding the natural frequencies (and respective mode shapes), estimated in the first phase, indicating that the acoustic dynamics of the chamber was appropriately characterized.

© 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.This manuscript presents a successful application of the inverse feed-forward control (IFFC) technique for control of the Tollmien–Schlichting (TS) waves over a wing profile placed in an open-circuit wind tunnel. Active cancellation of two-dimensional broadband TS disturbances is performed using a single dielectric barrier discharge (DBD) plasma actuator. The measurements required for the IFFC are performed with microphones, instead of hot wires often used for this purpose, in order to reduce the space occupied by the sensors and assess the suitability of simpler and cheaper devices. An attenuation of the TS-wave amplitude of one order of magnitude is achieved. Direct numerical simulations (DNS) are also performed and compared to the outcome of the experiments. The plasma-actuator model used in DNS is a mapping of the force field used by Fabbiane et al. (In: Proceedings of TSFP-9, Melbourne, 2015a) to the actual geometry, whereas the sensors (microphones) are modeled as pressure probes. Despite these modelling choices, a good agreement between the results of DNS and the experiments is achieved. However, the control performance is better in the DNS, with attenuation of three orders of magnitude of TS-wave amplitude. Further analysis of experiments and simulations shows that the limiting factor in the experiments is the ambient low-frequency acoustic waves in the wind tunnel. These waves are sensed by the microphones and act as noise in the analysis of TS-wave evolution and thus leading to lower coherence between sensors and actuators. This in turn leads to a suboptimal control kernel in the experiment.Please confirm if the inserted city and country are correct in Affiliations [Aff1, Aff2]. Amend if necessary.Confirmed. It is correct.Please confirm if the corresponding author is correctly identified. Amend if necessary.Confirmed. The corresponding author is Pedro P. C. Brito. Graphic abstract: [Figure not available: see fulltext.]

© 2021 Acoustical Society of America.Parabolized stability equations (PSE) have been shown to model wavepackets and, consequently, the near-field of turbulent jets with reasonable accuracy. In this work, PSE were employed to obtain a reduced-order model that could estimate both the fluid-dynamic and the acoustic fields of a supersonic jet in a computationally efficient approximation for resolvent-based estimation based on a single input. From the unsteady pressure data at an input position, the time-domain pressure field was estimated using transfer functions obtained using PSE and a data-driven method based on a well-validated large-eddy simulation (LES). The prediction scheme employed is a single-input single-output, linear model. The unsteady pressure predicted by the PSE showed good agreement with the LES results, especially if the input position is outside the mixing layer, where the prediction capabilities of the PSE are comparable to those of the data-driven transfer functions. The good agreement indicates that PSE could not only be used to predict the sound generation but also to open up different potentialities to attenuate the noise by flow control. The exploration of the regions where the method displayed good agreement, which are presented in this work, can guide the positioning of the sensors for experimental implementation of closed-loop control in a jet.

© Published under licence by IOP Publishing Ltd.Floating offshore wind turbines (FOWTs) are the next frontier in offshore wind energy, allowing exploration of deep-water regions previously unavailable to fixed-foundation turbines. Since offshore turbines operate in lower turbulence levels, the intrinsic hydrodynamic unstable modes of the tip vortices can have even more relevance than in onshore turbines. For floating turbines, platform motion induced by wind and wave loads can trigger vortex instabilities, modifying the wake structure, possibly influencing the flow reaching downstream wind turbines. In the present paper, we study those effects by the means of numerical simulations and their comparison with analytical studies. In our simulations, the wind turbine blades are modeled as actuator lines in the incompressible Navier-Stokes equations. Heave motion with different amplitudes and frequencies are studied. The effect of increasing amplitude is to advance the onset of vortex interaction. For the lower frequency of heave motion, several vortices coalesce to form a large flow structure. High amplitude of oscillations in the streamwise velocity were observed due to these flow structures, which may increase fatigue or induce high amplitude motion on downstream turbines. The number of vortices that interact, as other qualitative phenomena of the numerical simulation, were well predicted by a simple stability model of two-dimensional row of vortices. The disturbances imposed by the heave motion were also compared to the eigenvectors resulting from linear stability theory for helical vortices and the predicted growth rates for the wavenumbers resulting from this comparison were consistent with the model of a row of vortices. These results motivate further studies to understand the impact of the larger flow structures on downstream turbines.

© 2021 IEEERobotic flight simulators have emerged as a low-cost alternative to conventional flight simulators. Despite the enormous potential, few research works have been conducted regarding the representativeness of the movement of these simulators. Thus, the present work seeks to propose an optimization of the washout filter using the genetic algorithm to obtain the parameters capable of maximizing pilot's acceleration perception during the plane's takeoff. 3 configurations were proposed: solution 1 that does not impose displacement limits for channel B of the simulator, solution 2 with a limited displacement of 15° for the channel B and solution 3 that considers the limit of 15° and a different configuration of the cost function. It was found that the solution that maximizes pilot perception is the solution 1. Solutions 2 and 3 were similar, which indicates that it is the best configuration to be obtained with the current workspace limitation. The comparison of the 3 solutions also indicates that the trail could be further explored to increase the sensation of acceleration during takeoff.

© 2021 IEEE.Silicon nanophotonics is contributing to develop devices with small dimensions and low energy consumption. In space systems, whether in large or small satellites, such as CubeSat the demand for photonic devices has been growing, especially in the communication subsystem. For CubeSat the need to develop optical communication devices with reduced dimensions, low energy consumption and a precision aiming system, with no movable parts, is a challenge. In order to meet these requirements, this article presents a theoretical study on the use of a silicon nanophotonic device, in the form of Archimedean spiral waveguide, for phase modulation in Optical Phased Array antennas.