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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
61

Estudo da aeroelasticidade em problema acoplado fluido-estrutura da semi-asa simplificada para veículo aéreo não tripulado – VANT.

PEÑA, Diego Paes de Andrade. 27 April 2018 (has links)
Submitted by Kilvya Braga (kilvyabraga@hotmail.com) on 2018-04-27T11:35:02Z No. of bitstreams: 1 DIEGO PAES DE ANDRADE PEÑA - DISSERTAÇÃO (PPGEM) 2016.pdf: 5093848 bytes, checksum: c6e79e54502ec5a0ff9ff5b410ffd362 (MD5) / Made available in DSpace on 2018-04-27T11:35:02Z (GMT). No. of bitstreams: 1 DIEGO PAES DE ANDRADE PEÑA - DISSERTAÇÃO (PPGEM) 2016.pdf: 5093848 bytes, checksum: c6e79e54502ec5a0ff9ff5b410ffd362 (MD5) Previous issue date: 2016-09-02 / CNPq / A aeroelasticidade é o campo da ciência que estuda a correlação entre as forças aerodinâmicas, elásticas e de inércia. Tal ciência é de grande importância no campo aeronáutico uma vez que as estruturas alares são flexíveis, devem suportar os esforços aerodinâmicos e serem rígidas o suficiente para garantir que esteja livre de todos os problemas aeroelásticos característicos (divergência, eficiência de controle, flutter e buffeting) dentro da faixa operacional de velocidades desenvolvida pela aeronave. Realizou-se uma análise modal da estrutura a fim de se conhecer os modos naturais de vibração e as respectivas frequências naturais. Para tal, utilizou-se o ANSYS Structural e o método dos elementos finitos, além de um estudo de malha para verificar a convergência dos resultados. Estudou-se também a influência da posição do lastro na ponta da placa plana, que causa a diminuição da segunda frequência natural. Além disso, realizou-se uma análise bidimensional de um volume de controle do tipo C-Grid, uma vez que o tamanho do volume de controle em uma análise aerodinâmica computacional é um fator extremamente importante. Com um volume de controle grande, tem se mais elementos na malha, caso o mesmo seja pequeno, as condições de contorno juntamente com os tamanhos dos elementos podem interferir nos resultados dos campos de velocidade e pressão em torno da estrutura. Nesse contexto, utilizou-se do software ANSYS Fluent para a simulação aerodinâmica da placa plana inclinada e obtenção dos coeficientes aerodinâmicos de sustentação e arrasto CL e CD. Os resultados foram comparados com resultados experimentais em túnel de vento de Goudeseune (SELIG; ROBERT; WILLIAMSON, 2011). Através do cálculo do Grid Convergence Index (GCI) e da comparação dos resultados numéricos com os dados experimentais constatou-se a convergência e conseguiu-se determinar um tamanho de volume de controle com erro baixo e aceitável. A análise fluido-estrutura acoplada de duas vias foi realizada com o ANSYS Structural para analisar a dinâmica estrutural através do método dos elementos finitos e o ANSYS CFX para resolver o campo do escoamento mediante método dos volumes finitos. Obtiveram-se o comportamento oscilatório da estrutura, além do coeficiente de amortecimento e tensões de von Mises. Analisando o comportamento transiente da dinâmica estrutural mediante um fluxo aerodinâmico constante (velocidade fixa). As simulações representaram bem o fenômeno, já que com o aumento da velocidade, o escoamento induz maior amortecimento à estrutura quando comparado com baixas velocidades. / The aeroelasticity is the field of science that studies the relationship between the aerodynamic elastic and inertia forces. Such knowledge is of great importance in the aviation field since the wing structures are flexible, must withstand the aerodynamic loads and be rigid enough to ensure that it is free from all aeroelastic problems like divergence, control efficiency, flutter and buffeting within the operating speed range. We carried out a modal analysis of the structure in order to know the natural vibration modes and natural frequencies. To this end, we used the ANSYS Structural with finite element method, a mesh study to verify the convergence of the results. It is also studied the influence of the slender body position of the tip of the flat plate, which causes the decrease of the second natural frequency. Furthermore, there was a twodimensional analysis of a volume control type C-Grid, since the control volume aerodynamic size in a computational analysis is an extremely important factor. A large volume of control has more elements in the mesh if it is small, the boundary conditions together with the sizes of elements may affect the results of the velocity field and pressure around the structure. In this context, we used the ANSYS FLUENT for the aerodynamic simulation of the inclined flat plate, and obtaining the aerodynamic support, and drag coefficients CL and CD. The results were compared with experimental results of Goudeseune wind tunnel (SELIG; ROBERT; WILLIAMSON, 2011). By calculating the Grid Convergence Index (GCI) and comparing the numerical results with experimental data found the convergence and managed to determine a control volume size with low and acceptable error. The fluid-structure coupled two-way analysis was performed using ANSYS Structural to analyze the structural dynamics through the finite element method and ANSYS CFX to resolve the flow field by the finite volume method. It was possible to obtain the oscillatory behavior of the structure, besides the damping coefficient and von Mises stresses. Analyzing the transient behavior of structural dynamics by a constant aerodynamic flow (fixed speed), the simulations represented the phenomenon as well, since with the increase in speed, the flow induces cushioning structure as compared to low speed
62

Reconstrução de espaços de estados aeroelásticos por decomposição em valores singulares / Aeroelastic state space reconstruction by singular value decomposition

Rui Marcos Grombone de Vasconcellos 13 September 2007 (has links)
Analisar fenômenos aeroelásticos não-lineares através de dados experimentais é uma poderosa ferramenta para a identificação e controle de comportamentos aeroelásticos adversos. A modelagem matemática de sistemas aeroelásticos não-lineares não é trivial, fato que muitas vezes leva a admissão de simplificações, afastando o modelo da realidade. Desta forma, a análise de sistemas dinâmicos sem a necessidade de um modelo, feita através da análise de séries temporais obtidas de experimentos, pode fornecer melhores resultados. Alguns métodos de análise de séries temporais, como o método da defasagem, para reconstrução do espaço de estados, são sensíveis ao ruído, inevitavelmente presente em qualquer série temporal experimental. Este trabalho apresenta a técnica da decomposição em valores singulares (SVD), que reconstrói o espaço de estados eliminando o ruído presente na série temporal em um único processo. O método SVD é aplicado em séries temporais aeroelásticas, obtidas experimentalmente de um modelo de asa ensaiado em túnel de vento. Com os espaços de estados reconstruídos, é feita uma análise qualitativa do sistema aeroelástico, a evolução dos atratores obtidos com a variação de alguns parâmetros é apresentada. Comparações com o método da defasagem são realizadas com a aplicação dos métodos a uma série temporal aeroelástica do experimento. Os resultados mostram que a técnica (SVD) é mais confiável que o método da defasagem, os atratores obtidos revelam a ocorrência de bifurcações e comportamentos complexos, possivelmente caóticos. / Nonlinear aeroelastic phenomena analysis by using experimental data is a powerful tool for identification and control of adverse aeroelastic behaviors. Mathematical models for nonlinear aeroelastic systems are not trivial, by this, simplifications are assumed, thereby deviating from reality. Then, the analysis of dynamic systems without the need of a mathematical model, done by the analysis of experimental time series, may provide better results. However, methods of time series analysis, like the method of delays, for state space reconstruction are sensitive to noise, unavoidably present in experimental data. This work presents the application of singular value decomposition (SVD) that reconstructs the state space, eliminating noise present in the time series. The SVD method is applied in experimental aeroelastic time series, obtained from a wind tunnel wing model. With the reconstructed state spaces, qualitative analyses are done and the evolutions of the obtained attractors with parametric variation are presented. Comparisons with the method of delays are realized by applying MOD and SVD in a same experimental aeroelastic time series. The results show that the SVD method is more reliable than MOD and the obtained attractors reveal the occurrence of bifurcations and complex behavior, possibly chaotic.
63

Projeto de dispositivo para realização de ensaios aeroelásticos em modelos seccionais de pontes em túnel de vento. / Design of an elastic suspension system for aeroelastic studies of bridge section models in wind tunnels.

Gabriel Borelli Martins 11 July 2016 (has links)
Uma base elástica para ensaios seccionais de pontes foi projetada a partir de mancais aerostáticos. Um sistema de dois graus de liberdade foi construído, de forma a possibilitar estudos de flutter, de galloping e de vibrações induzidas por vórtices em túneis de vento. A base mostrou-se bastante versátil, permitindo diversas configurações além da inicialmente prevista, o que possibilita a realização de estudos envolvendo diferentes fenômenos aeroelásticos nos mais variados modelos. Foram realizados ensaios para a caracterização de galloping em um prisma de seção quadrada e de flutter em um fólio NACA 0020. Os resultados de galloping obtidos, considerando o escoamento incidente perpendicular a uma das faces do prisma, foram condizentes com os encontrados na literatura. Por outro lado, as derivadas de flutter obtidas nos ensaios com o fólio não foram aquelas esperadas. Ensaios complementares deverão ser realizados no futuro com o objetivo de determinar as fontes das discrepâncias observadas. / A new elastic suspension system using air bearings for heaving and pitching motions was designed to test section models of suspended bridges in wind tunnels. The two-degrees-of-freedom system and its versatility makes possible the study of many aeroelastic phenomena, such as galloping, vortex-induced vibrations, buffeting and flutter. Moreover, as a modular system is proposed, degrees of freedom can be easily removed or added as desired. Therefore, it can be used to study not only bridge aeroelasticity, but also fluid-structure interaction of other geometries. In order to verify the suspension system, galloping tests, using a square cylinder, and flutter tests, using a foil NACA 0020, were done at IPT\'s wind tunnel facility. The galloping response obtained for the square cylinder was consistent with the literature. On the other hand, the flutter derivatives obtained for the foil differ from those expected. Therefore, other investigations must be done in the future in order to identify the sources of the discrepancies observed.
64

Large-Scale Testing to Study the Effects of Critical Parameters on the Aerodynamic Behavior of Long Span Bridges

Kargarmoakhar, Ramtin 25 March 2015 (has links)
Long-span bridges are flexible and therefore are sensitive to wind induced effects. One way to improve the stability of long span bridges against flutter is to use cross-sections that involve twin side-by-side decks. However, this can amplify responses due to vortex induced oscillations. Wind tunnel testing is a well-established practice to evaluate the stability of bridges against wind loads. In order to study the response of the prototype in laboratory, dynamic similarity requirements should be satisfied. One of the parameters that is normally violated in wind tunnel testing is Reynolds number. In this dissertation, the effects of Reynolds number on the aerodynamics of a double deck bridge were evaluated by measuring fluctuating forces on a motionless sectional model of a bridge at different wind speeds representing different Reynolds regimes. Also, the efficacy of vortex mitigation devices was evaluated at different Reynolds number regimes. One other parameter that is frequently ignored in wind tunnel studies is the correct simulation of turbulence characteristics. Due to the difficulties in simulating flow with large turbulence length scale on a sectional model, wind tunnel tests are often performed in smooth flow as a conservative approach. The validity of simplifying assumptions in calculation of buffeting loads, as the direct impact of turbulence, needs to be verified for twin deck bridges. The effects of turbulence characteristics were investigated by testing sectional models of a twin deck bridge under two different turbulent flow conditions. Not only the flow properties play an important role on the aerodynamic response of the bridge, but also the geometry of the cross section shape is expected to have significant effects. In this dissertation, the effects of deck details, such as width of the gap between the twin decks, and traffic barriers on the aerodynamic characteristics of a twin deck bridge were investigated, particularly on the vortex shedding forces with the aim of clarifying how these shape details can alter the wind induced responses. Finally, a summary of the issues that are involved in designing a dynamic test rig for high Reynolds number tests is given, using the studied cross section as an example.
65

Conception robuste en vibration et aéroélasticité des roues aubagées de turbomachines / Robust design in vibration and aeroelasticity of turbomachinery bladed disks

Mbaye, Moustapha 03 November 2009 (has links)
Les roues aubagées sont des composants dont le comportement dynamique est très sensible au désaccordage involontaire causé par les tolérances de fabrication qui rendent les aubes légèrement différentes les unes des autres. Cette sensibilité se traduit généralement par une amplification des vibrations. L’objectif de ce travail de recherche est de proposer de nouvelles méthodologies permettant d’optimiser la conception en vibration des roues aubagées vis à vis du désaccordage involontaire. L’optimisation est faite pour la réponse forcée et sous une contrainte de marge à la stabilité aéroélastique. Dans ce contexte, le désaccordage intentionnel par modification géométrique des aubes est utilisé. Pour réduire les temps de calcul, une nouvelle méthode de réduction de modèles de roues aubagées désaccordées intentionnellement par modification géométrique est développée et validée. La modélisation des incertitudes incluant le désaccordage involontaire, est faite avec une approche probabiliste non paramétrique. Une application à l’optimisation de la conception en vibration d’une roue réelle a finalement été effectuée en deux phases : (1) une optimisation de la répartition des différentes aubes désaccordées intentionnellement sur la roue aubagée et (2) une optimisation du niveau de modification géométrique de ces aubes. Les résultats montrent qu’une conception robuste par désaccordage intentionnel de la roue aubagée a été effectuée / Bladed disks are components which dynamic behaviour are very sensitive to mistuning induced by the manufacturing process which makes blades differ from one another. This sensitivity increases in general the vibrations. The objective of this research is to propose new methods for optimizing design in vibration of bladed disks with respect to mistuning. Optimization is done for the forced response while keeping a sufficient aeroelastic stability margin. In this context, detuning by modifying geometrically the blades’ shapes is used. To reduce numerical computational costs, a new reduction method for geometrically detuned bladed disks is developed and validate. Uncertainties modeling including mistuning is done with a non-parametric probabilistic approach. An application by optimizing the design in vibration of a realistic bladed disk is finally done in two steps : (1) An optimization of the different detuned blades arrangements around the disk and (2) an optimization of the geometric modification level of blades. The results show that a robust design of the bladed disks has been done using geometric detuning
66

Unsteady Aerodynamic and Aeroelastic Analysis of Flapping Flight

Gopalalkrishnan, Pradeep 22 January 2009 (has links)
The unsteady aerodynamic and aeroelastic analysis of flapping flight under various kinematics and flow parameters is presented in this dissertation. The main motivation for this study arises from the challenges facing the development of micro air vehicles. Micro air vehicles by requirement are compact with dimensions less than 15-20 cm and flight speeds of around 10-15 m/s. These vehicles operate in low Reynolds number range of 10,000 to 100,000. At these low Reynolds numbers, the aerodynamic efficiency of conventional fixed airfoils significantly deteriorates. On the other hand, flapping flight employed by birds and insects whose flight regime coincides with that of micro air vehicles offers a viable alternate solution. For the analysis of flapping flight, a boundary fitted moving grid algorithm is implemented in a flow solver, GenIDLEST. The dynamic movement of the grid is achieved using a combination of spring analogy and trans-finite interpolation on displacements. The additional conservation equation of space required for moving grid is satisfied. The solver is validated with well known flow problems such as forced oscillation of a cylinder, a heaving airfoil, a moving indentation channel, and a hovering fruitfly. The performance of flapping flight is analyzed using Large Eddy Simulation (LES) for a wide range of Reynolds numbers and under various kinematic parameters. A spiral Leading Edge Vortex (LEV) forms during the downstroke due to the high angle of attack, which results in high force production. A strong spanwise flow of the order of the flapping velocity is observed along the core of the LEV. In addition, the formation of a negative spanwise flow is observed due to the tip vortex, which slows down the removal of vorticity from the LEV. This leads to the instability of the LEV at around mid-downstroke. Analysis with different rotation kinematics shows that a continuous rotation results in better propulsive efficiency as it generates thrust during the entire flapping cycle. Analysis with different angles of attack shows that a moderate angle of attack which results in complete shedding of the LEV offers high propulsive efficiency. The analysis of flapping flight at Reynolds numbers ranging from 100 to 100,000 shows that higher lift and thrust values are obtained for Re?100. The critical reasons are that at higher Reynolds numbers, the LEV is closer to the surface and as it sheds and convects it covers most of the upper surface. However, the Reynolds number has no or little effect on the lift and thrust as identical values are obtained for Re=10,000 and 100,000. The analysis with different tip shapes shows that tip shapes do not have a significant effect on the performance. Introduction of stroke deviation to kinematics leads to drop in average lift as wing interacts with the LEV shed during the downstroke. A linear elastic membrane model with applied aerodynamic load is developed for aeroelastic analysis. Analysis with different wing stiffnesses shows that the membrane wing outperforms the rigid wing in terms of lift, thrust and propulsive efficiency. The main reason for the increase in force production is attributed to the gliding of the LEV along the camber, which results in a high pressure difference across the surface. In addition, a high stiffness along the spanwise direction and low stiffness along the chordwise direction results in a uniform camber and high lift and thrust production. / Ph. D.
67

Design and Development of Piezoelectric Stack Actuated Trailing Edge Flap for Helicopter Vibration Reduction

Mallick, Rajnish January 2014 (has links) (PDF)
This research investigates on-blade partial span active plain trailing edge flaps (TEFs)with an aim to alleviate the helicopter vibrations. Among all the available smart materials, piezoelectric stack actuator(PEA)has shown its strong candidature for full scale rotor systems. Although, PEAs are quite robust in operation, however, they exhibit rate dependent hysteresis phenomenon and can generate only very small displacements. Dynamic hysteresis is a complex phenomenon which, if not modeled, can lead to drift in the vibration predictions. In this research, a comprehensive experimental analysis is performed on a commercially available piezostack actuator, APA-500L, which is well suited for full scale applications. Rate dependent hysteresis loops are obtained for helicopter operational frequencies. Nonlinear rate-dependent hysteresis loops are modeled using conic section approach and the results are validated with experimental data. Dynamic hysteresis exhibited by the PEA is further cascaded with the helicopter aeroelastic analysis and its effect on helicopter vibration predictions is investigated. PEAs generate high force but are limited by small translational motions. A linear to rotary motion amplification mechanism is required to actuate the TEF for vibration alleviation. A smart flap is designed and developed using computer-aided-design models. A rotor blade test section is fabricated and a lever-fulcrum mechanism (AM-1) is developed for a feasibility study. Smart flap actuation is demonstrated on the rotor blade test section. The conventional motion amplification devices contain several linkages, which are potential sites for structural failure. A novel pinned-pinned post-buckled beam linear-to-rotary motion amplifier (AM-2) is designed and developed to actuate the flaps. A new design of linear-to-linear amplification mechanism (LX-4) is developed and is employed in conjunction with AM-2 to increase the flap angles by an order of magnitude. An analytical model is developed using Mathieu-Hill type differential equations. Static and dynamic tests are conducted on a scaled flap model. Helicopter aeroelastic simulations show substantial reduction in hub loads using AM-2 mechanism. To further enhance the flap angles, an optimization study is performed and optimal beam dimensions are obtained. A new technique is also proposed to actively bias the flaps for both upward and downward motion. Critical flap design parameters, such as flap span, flap chord and flap location influences the flap power requirement and vibration objective function significantly. A comprehensive parametric investigation is performed to obtain the best design of TEFs at various advance ratios. Although, parametric study equips the designer with vital information about various critical system parameters, however, it is a computationally expensive exercise especially when used with large comprehensive helicopter aero elastic codes. A formal optimization procedure is employed to obtain the optimal flap design and location. Surrogate models are developed using design of experiments based on response surface methodology. Two new orthogonal arrays are proposed to construct the second order polynomial response surfaces. Pareto analysis is employed in conjunction with a newly developed computationally efficient evolutionary multi-objective bat algorithm. Optimal flap design and flap locations for dual trailing edge flaps are obtained for mutually conflicting objectives of minimum vibration levels and minimum power requirement to actuate the flaps.
68

The aeroelastic tailoring of a high aspect-ratio composite structure / Taeke Nicolai van den Bosch

Van den Bosch, Taeke Nicolai January 2014 (has links)
The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014
69

The aeroelastic tailoring of a high aspect-ratio composite structure / Taeke Nicolai van den Bosch

Van den Bosch, Taeke Nicolai January 2014 (has links)
The aim of this investigation was to review literature for the most suitable aeroelastic tailoring analysis tools for long slender composite structures, and integrate them into an aeroelastic tailoring process. The JS1C Revelation is a high performance sailplane made from modern composites, mostly carbon fibre. This has the advantage of being more rigid than traditional engineering materials, thereby reducing the effects of the twisting deflections on these long slender structures due to aerodynamic loads. The implementing of aeroelastic tailoring can create bend-twist couples for performance improvements. Composites enable the use of aeroelastic tailoring to improve gliding performance. Flaperon 3 of the JS1C 21 m was used as the design problem for aeroelastic tailoring. Aeroelastic tailoring was done by analysing the flaperon structure at the different layup angles to determine the correct design point to tailor the structure to improve aerodynamic performance at thermalling and cruise, but mostly cruise since it accounts for 70% of the flight time. The composite structure analysis tool has the objective to get results during concept design. This directed the line of research of analysis tools to a solution method of two dimensional cross-section mesh properties projected onto a one dimensional beam. The literature of Hodges had good verification and published data on the analysis tools. The analysis tools comprised of three programs that were not very user friendly. Thus the author compiled a Matlab program as a user interface tool to run the three programs together. The aeroelastic tailoring process systematically works through the known design variables and objectives, which are given as inputs to the analysis tool. The analysis tool plots the coupling data versus layup angle. From this the best layup angles for a sought-after bend-twist couple is used to aeroelastically tailor the wing. The composite structure analysis tool’s accuracy was verified by analysing cantilever beam deflections and comparing the results with hand calculations and SolidWorks Simulation FEM results. The analysis tool’s accuracy was further verified by comparing the aerodynamic torsional load’s twist deflections with thin walled tube theory. The analysis tool was validated by applying a torsional load at the tip of a JS1C production Flaperon 3 in an experimental setup and then comparing this result with the Flaperon 3 modelled in the analysis tool. These comparisons also ensured that the model’s composite material properties and the meshing of the flaperon cross-sectional properties were correct. This aeroelastic tailoring was validated with the advantage of then being used to improve the aerodynamic performance of the JS1C Revelation 21 m tip’s flaperon. This improvement could be made by making use of a tailored bend-twist couple to reduce the effect of the aerodynamic load’s twist deflections. A test sample of the JS1C 21 m flaperon 3 was used to validate aeroelastic tailoring. The test sample was designed to be 1 m in length and have all the specified tailoring coupling characteristics that could improve the aerodynamic performance of the JS1C 21 m flaperon 3. The test sample was manufactured according to Jonker Sailplanes manufacturing standards and experimentally set up with the same applied deflections as in the analysis tool. The calculated bend-twist values and the experimental setup results were similar with a negligible difference, assuming small displacements and an aspect ratio greater than 13; this confirmed that the PreVABS/VABS/GEBT composite structure analysis tool could be used in aeroelastic tailoring to predict and design the bend-twist couple needed to improve the aerodynamic performance of the JS1C 21 m. While the twist behaviour of Flaperon 3 was improved by the tailored bend-twist couple, it was still necessary to add pre-twist as well, to fully address the effects of twisting by aerodynamic forces. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014
70

ANA-PSp: um sistema computacional para análise aeroelástica de pontes suspensas por modelos matemáticos reduzidos. / Ana-PSp: a computational system for aeroelastic analysis of suspended bridges for reduced mathematical models.

Kreis, Eri Sato 22 November 2007 (has links)
As características arquitetônicas e o desempenho estrutural de pontes suspensas, estaiadas ou pênseis, têm determinado a sua crescente utilização em obras de arte destinadas a vencer grandes vãos. Essa utilização crescente que ocorreu no mundo nas últimas décadas se repete agora nos últimos anos no país. Várias dessas obras estão em execução e em projeto. Um dos aspectos relevantes na análise estrutural das pontes suspensas é o de seu comportamento quando submetidas à ação do vento. Apresenta-se o sistema computacional ANA-PSp desenvolvido especialmente para o estudo do movimento de tabuleiros de pontes suspensas sujeitas a esforços aeroelásticos e aerodinâmicos. Esse sistema computacional formado por um conjunto de subsistemas, é elaborado para a análise aeroelástica de pontes suspensas sob a ação de vento e permite análises paramétricas extensas dos fenômenos de drapejamento (flutter) e de martelamento (buffeting). A discretização da estrutura é efetuada pelo método dos elementos finitos e a redução dos graus de liberdade é realizada por superposição modal com modos selecionados que melhor descrevem os movimentos do tabuleiro. Utiliza-se modelo matemático reduzido para a análise multimodal no domínio do tempo e da freqüência. A velocidade crítica ou velocidade de drapejamento é determinada por procedimento de autovalores complexos com a obtenção de freqüências e taxas de amortecimentos modais para várias velocidades do vento. Adicionalmente, o fenômeno do drapejamento é estudado por séries temporais de respostas de coordenadas generalizadas e de deslocamentos selecionados e por análise espectral dessas séries temporais, que permitem a verificação das características de vibração do tabuleiro da ponte no domínio da freqüência. O estudo do fenômeno de martelamento considera esforços aeroelásticos determinísticos e esforços aerodinâmicos estocásticos e apresentam-se resultados em espectros de potência de deslocamentos e em desvios padrão de deslocamentos ao longo do tabuleiro. Para validar o sistema ANA-PSp, apresentam-se estudos de caso para a ponte estaiada da Normandia, para a ponte pênsil colapsada de Tacoma Narrows e para a ponte estaiada projetada, mas não executada, sobre o Rio Tietê e localizada na extremidade do complexo viário Jacu-Pêssego. / The architectonic characteristics and the structural performance of suspension bridges and cable-stayed bridges have determined their growing use on large span bridges. This growing usage, which has occurred world-wide during the last decades, is now being repeated in Brazil during the last few years. Several such bridges are presently either undergoing construction or being designed. One of the outstanding aspects in the structural analysis of suspension bridges is their behavior under wind action. This paper presents the computer system ANA-PSp, specially developed for studying the movement of suspended bridge decks under aeroelastic and aerodynamic forces. This computer system is formed by a group of subsystems and is created for aeroelastic analysis of suspended bridges under wind action. It allows extended parametric analyses of the flutter and the buffeting phenomena. Structural discretization is done by the finite element method and the reduction of degrees of freedom is obtained by modal superposition of the selected modes which best describe the deck movements. A reduced mathematical model is used for the multimodal analysis in the time and frequency domains. Critical velocity or flutter velocity is determined by a procedure of complex eigenvalues which obtains frequencies and damping ratios for different wind speeds. Additionally, the flutter phenomenon is studied by temporal series of answers to generalized coordinate responses and of selected displacements by spectral analysis of such temporal series, which allow us to verify the characteristics of the vibrations of the bridge deck in the frequency domain. The study of the buffeting phenomenon considers deterministic aeroelastic and stochastic aerodynamic forces. The paper presents results in displacement power spectra and in the standard deviation of displacements along the deck. In order to validate system ANA-PSp, case studies are presented for the cable-stayed Ponte de Normandie in Le Havre (France), for the collapsed suspension bridge on Tacoma Narrows and for the cable-stayed bridge, already designed but not built, on Tietê River, located at one end of the highway complex Jacu-Pêssego (São Paulo, SP, Brazil).

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