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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.
191

Experimental analysis of fluid-structure interaction phenomena on a vertical flexible cylinder: modal coeficients and parametric resonance. / Análise experimental de fenômeno de interação fluido-estrutura em um cilindro vertical flexível: coeficientes modais e ressonância paramétrica.

Rafael Salles 18 April 2016 (has links)
Oil and gas exploitation in deep waters has become more than just a profit business to be a daily necessity, since the world energy matrix is based on fossil components. Risers are offshore structures that are intimately linked with oil and gas exploitation and those are subjected to a great variety of effects in field, e.g., marine currents, Vortex Induced Vibration (VIV), heave motion caused by gravitational waves, non-linear contact with the sea floor, and many others. Riser dynamics is essentially non-linear and experimental tests in real scale are almost impossible due to a great variety of control parameters acting concomitantly. Small-scale models are a better experimental approach. Nevertheless, there are many structural and hydrodynamical parameters to be evaluated. Considering only vertical risers in the present work, Galerkin\'s modal decomposition is used in order to reduce the dynamics of a vertical flexible cylinder to a few linear modes in which the majority of energy and information are contained. From the modal analysis, added mass and structural parameters damping of a vertical flexible cylinder using data obtained from free-decay tests performed both in water and in air are evaluated. Finally, a modal Mathieu-Hill oscillator with non-linear damping is constructed and, based on aStrutt diagram, modal stability under parametric resonance is discussed. / Exploração de óleo e gás em bacias de águas profundas tem-se tornado mais do que apenas uma economia lucrativa, para ser uma necessidade diária, já que a matriz energética mundial está baseada em componentes fósseis. Risers são estruturas offshore ligadas intimamente com a exploração de óleo e gás e essas estão sujeitas a uma grande variedade de efeitos na operação, e.g., correntes marítimas, Vibrações Induzidas por Vórtices (VIV), movimento de heave causado por ondas gravitacionais, contato não-linear com o solo marinho, entre outros. Dinâmica de risers é essencialmente não-linear e testes experimentais em escala real são praticamente impossíveis devido a uma enorme variedade de parâmetros de controle agindo concomitantemente. Modelos em escala reduzida são uma abordagem experimental mais conveniente. Não obstante, há muitos parâmetros estruturais e hidrodinâmicos a serem determinados. Considerando apenas risers verticais no trabalho presente, a decomposição modal de Galerkin é usada a fim de reduzir a dinâmica de um cilindro fléxivel vertical a alguns modos lineares em que a maior parte da energia e informação estão contidos. A partir da análise modal, parâmetros de massa adicional e amortecimento estrutural de um cilindro flexível vertical são obtidos usando testes de decaimento livre conduzidos na água e no ar. Finalmente, um oscilador modal de Mathieu-Hill com amortecimento não-linear é proposto e, baseado em um diagrama de Strutt, a estabilidade modal sob excitação de ressonânica paramétrica é discutida.
192

Desenvolvimento da modelagem de turbulência e interação fluido-estrutura para as vibrações induzidas por vórtices de cilindro rígido. / Improvements in the numerical modeling of turbulence and fluid-structure interaction for the vortex-induced vibrations of a rigid cylinder.

Guilherme Feitosa Rosetti 18 June 2015 (has links)
Esta tese apresenta o desenvolvimento e aplicação de modelos de turbulência, transição laminar-turbulenta e de interações fluido-estrutura ao escoamento externo em cilindro rígido estacionário e em vibrações induzidas por vórtices. Tais desenvolvimentos foram realizados no código ReFRESCO, baseado em técnicas de dinâmica de fluidos computacional (CFD). Realizou-se um estudo quanto ao desempenho do modelo k- SST em extensa faixa de números de Reynolds, segundo o qual se identificaram as deficiências de modelagem para este escoamento. A modelagem adaptativa das escalas (SAS) e o modelo de transição por correlações locais (LCTM), ambos combinados ao SST, melhoraram a aderência aos resultados experimentais para este escoamento, em uma contribuição original deste trabalho. A aplicação de técnicas de verificação e validação possibilitou a estimação de incertezas e erros para os modelos e números de Reynolds e também de identificada como outra contribuição deste trabalho. A combinação da modelagem em SST, SAS e LCTM com movimentos impostos de realizada para números de Reynolds moderados, diferentes frequências e amplitudes de vibração, algo que poucas publicações abordam em detalhes. Com relação aos movimentos livres, este trabalho traz contribuições com a aplicação dos modelos SST e SAS ao estudo de vibrações induzidas por vórtices em dois graus de liberdade, baixa razão de massa e números de Reynolds moderados, mais altos do que normalmente observados na literatura. Por fim, a investigação da importância relativa de efeitos da turbulência aos casos de movimentos livres e impostos, com relação ao caso de cilindro estacionário, comprovou a conjetura formulada na parte inicial deste trabalho, no que tange à escolha do modelo de turbulência em determinadas aplicações. Tal escolha mostrou-se menos decisiva no caso do cilindro em movimento imposto e ainda menos nos movimentos livres, em comparação ao caso estacionário, uma vez que a resposta em movimentos do corpo filtra grande parte dos efeitos turbulentos de ordem superior. Esta observação mostra-se relevante, uma vez que pode permitir simplificações na modelagem e aplicação de ferramentas de CFD em uma classe importante de projetos de engenharia. / This thesis presents the development, implementation and application of turbulence and laminar-turbulent transition models and fuid-structure capabilities to address the vortexshedding and vortex-induced vibrations of a rigid cylinder. These numerical developments have been carried out in the computational fuid dynamics (CFD) code ReFRESCO. In the current work, an investigation of the performance of the turbulence modeling with k- SST in a broad range of Reynolds numbers is carried out identifying its modeling deficiencies for this fow. The implementation and systematic application of the scale adaptive simulations (SAS) and the local correlation transition model (LCTM), both combined with the SST, have improved the agreement with experimental results for the cylinder ow, in a novel contribution of this work. The application of verification and validation technique has allowed the estimation of numerical errors and uncertainties for the diferent models. That is also identified as a contribution of this thesis. The combination of SST modeling with imposed motions is carried out as well as with the SAS and LCTM for moderate Reynolds numbers, diferent vibration frequencies and amplitudes, which is considered novel, as few publications address this issue in extent. Regarding the free-moving cylinder capabilities, the present work brings contributions with the application of SST and SASSST with free-moving cylinder for the study of VIV of two degrees of-freedom, low mass ratio and moderate Reynolds numbers, higher than commonly seen in the literature. Finally, the investigation of the relative importance of turbulence effects on the freemoving cylinder and the imposed-motions case, with respect to the fixed case is carried out. A natural conjecture that has been raised early on this work and proved correct is that, for engineering applications, the choice of turbulence modeling strategy is less decisive when the cylinder is moving with prescribed motion and even less stringent, for free motions as the body response filters most of the higher order turbulence effects. That is a relevant observation as it might allow modeling simplifications and the application of CFD tools to a range of engineering problems.
193

Análise do efeito da interação fluido-estrutura nas forças fluidodinâmicas em um elemento de pá flexível 3D

Bordin, Franciele Stail January 2014 (has links)
Elementos de materiais flexíveis são empregados em diversas aplicações na engenharia, como por exemplo, em pás de turbinas eólicas. O comportamento do escoamento é afetado pela alteração na forma da estrutura. Muitas vezes, seu movimento e deformação são induzidos pelas próprias forças fluidodinâmicas. O trabalho apresenta o estudo de escoamentos externos envolvendo a interação fluido-estrutura, com o interesse voltado ao comportamento de pás de turbinas eólicas. Simulações numéricas são realizadas com o intuito de avaliar o efeito que a deformação da estrutura, devido à resposta elástica às forças oriundas do escoamento, tem nas próprias forças fluidodinâmicas. A plataforma ANSYS Workbench é utilizada, combinando o software ANSYS CFX para a análise do fluido e o ANSYS Mechanical para a análise da estrutura. Como validação do método, o escoamento laminar sobre um cilindro apoiado elasticamente é estudado e comparado com dados da literatura. O caso escolhido para o presente trabalho é o de um escoamento turbulento sobre um elemento de pá, fixo em uma das suas extremidades e livre na outra. A geometria da pá é retangular com o perfil NACA 0012 e o modelo de turbulência utilizado é o k-ω SST. Os resultados demonstram a influência significativa que a deformação da estrutura tem nas forças fluidodinâmicas de sustentação e arrasto e concordam com a literatura existente. / Elements of flexible materials are employed in several engineering applications, for instance, in wind turbine blades. The flow behavior is affected by any change in the shape of the structure. Often, its displacement and deformation are induced by the fluid-dynamic forces themselves. This paper presents the study of an external flow using fluid-structure interaction (FSI), focused on the behavior of wind turbine blades. Numerical simulations are performed in order to evaluate the effect that the deformation of the structure, caused by the elastic response to the flow forces, has on the fluid-dynamic forces themselves. The ANSYS Workbench platform is used, combining the software ANSYS CFX for the fluid analysis and ANSYS Mechanical for the structural analysis. As a form of validation of this method, the laminar flow over an elastically mounted cylinder is studied and compared with literature data. The chosen case for this work is a turbulent flow over a 3D blade element, fixed at one end and free at the other. The blade geometry is rectangular with the NACA 0012 profile and the turbulence model used is the k-ω SST. The results demonstrate the significant influence that the deformation of the structure has on the fluid-dynamic lift and drag forces, leading to an agreement with the existing literature.
194

Analyse expérimentale et simulation numérique de l’interaction fluide-structure d’un hydrofoil élastique en écoulement subcavitant et cavitant / Numerical and experimental analisys of the fluid-structure interaction between an elastic hydrofoil and a subcavitating And cavitating flow

Gaugain, Fabien 11 December 2013 (has links)
Le développement de structures portantes flexibles dans le domaine naval, telles que les hélices ou les safrans, pose de nouveaux problèmes de dimensionnement. Cette thèse a pour but de développer une méthode de dimensionnement validée par des essais pour des structures portantes déformables soumises à des écoulements, éventuellement diphasiques de type cavitant. Les essais sont réalisés sur un hydrofoil de type NACA66-312(mod.), fabriqué en polyacetate, au sein du tunnel hydrodynamique de l'Institut de Recherche de l'Ecole Navale. Lors des essais, des mesures de déformations du profil portant ainsi que de niveaux vibratoires sont réalisées. Une méthode numérique couplant un code structure éléments finis (ANSYS Mechanical) avec un code fluide volumes finis (ANSYS CFX) par une méthode partitionnée, itérative, synchrone et séquentielle, laquelle est validée en terme de prédiction du déplacement et des contraintes pour des écoulements subcavitants dans un premier temps, puis pour des écoulements cavitants stables et instables. / The design of flexible lifting bodies in the naval industry, such as propelleror rudders, create some new design problems. This thesis proposes a numerical method validated by experimental comparison for solving the case of lifting bodies loaded by flow with or whitout cavitation. The tests are carried out in the hydrodynamic tunnel of the French Naval Academy Research Institute, on a polyacetate flexible hydrofoil NACA66-312 (mod.). During tests, strains and vibrations are measured for comparisons with numerical results. The numerical method uses a sequential synchrone iterative partitionned coupling betweena structural finite-element code (ANSYS Mechanical) and a finite-volume code (ANSYS CFX). Good agreement between numerical and experimental results for displacements, and stresses of the structure is highlighted. For the cavitating flow, a good agreement for the cavitation dynamic is observed and the stresses are evaluated with satisfying accuracy.
195

Simulation numérique d’écoulements diphasiques autour d’un solide mobile / Numerical simulation of two-phase flows around a moving body

Doradoux, Adrien 28 April 2017 (has links)
Les méthodes de domaines fictifs permettent de simuler numériquement des écoulements autour de structures complexes et/ou mobiles à l’aide de maillages simples. L’objet solide est alors « immergé » dans un domaine de calcul englobant le fluide et le solide. Dans un premier temps, on étudie une méthode de pénalisation, qui consiste à ajouter un terme dans l’équation de conservation de la quantité de mouvement du fluide afin d’imposer la vitesse du solide. Grâce à des développements asymptotiques, on obtient une estimation de l’erreur induite par cette approche lorsque le solide est en mouvement. Ce procédé est ensuite couplé avec un schéma de projection vectorielle permettant d’imposer la contrainte d’incompressibilité. La convergence du schéma ainsi obtenu, vers les équations de Navier-Stokes, est établie. Dans un second temps,une approche originale capable de traiter des écoulements multiphasiques est développée : la méthode de porosité variable. L’idée principale est de considérer le solide comme un milieu sans masse. La discrétisation des bilans massiques de chaque phase est alors modifiée, de sorte que le volume total occupé par l’ensemble des phases fluides soit égal au volume laissé libre parle solide. Cette méthode est validée numériquement sur un ensemble varié de cas test comprenantd es écoulements monophasiques incompressibles et compressibles ainsi que des écoulements diphasiques. / Fictitious domain methods allow to simulate flows around complex and/or moving bodies with simple meshes. The object is "immersed" in a domain that contains fluid and solid volumes. The penalization method, which consists in adding a term in the momentum balance equation, in order to impose the solid velocity, is studied in a first part. Thanks to asymptotic expansions, the order of the error induced by this method is computed for moving bodies. This approach is then coupled with a Vector Penalty Projection scheme that permits to impose the incompressibility constraint. The convergence of the penalized scheme towards the Navier-Stokes equations is established. In a second part, an original approach, able to treat multiphase flowsis presented: the Time and Space Dependent Porosity method. The key idea is to consider the solid as a medium without mass. The discretization of the mass balance equation is modified,so that the total volume occupied by all fluid phases and the solid is equal to the total volume.This method is numerically validated on a set of various test cases including incompressible or compressible single phase flows and two-phase flows.
196

Modélisation et caractérisation expérimentale des joints à brosse / Modelling and experimental characterization of brush seals

Deville, Lilas 16 December 2016 (has links)
Les joints à brosse sont des joints compliants utilisés dans les turbomachines. Ils sont constitués d'une brosse de fils très fins compactés entre deux plaques, de telle manière que l'ensemble comble l'écart séparant le stator du rotor. Les fils sont le plus souvent constitués d'un alliage à base de cobalt appelé Haynes 25 (d'autres matériaux peuvent être utilisés, tels que le Kevlar). Le comportement de ces joints présente un fort couplage entre l'écoulement du fluide et la déformation de la brosse. Ce type de joints peut être modélisé en considérant la brosse comme un milieu poreux. Cette méthode présente l'avantage de permettre un calcul relativement simple de l'écoulement, mais elle demande l'usage de données expérimentales afin de calibrer ses perméabilités (i.e. sa capacité à laisser un fluide s'écouler à travers lui). L'objectif de cette thèse est de proposer une modélisation par milieu poreux indépendante des données expérimentales. Une simulation itérative entre le calcul de la déformation des fils sous l'action des efforts de pression et la résolution de l'écoulement dans le milieu poreux formé par la brosse déformée a été mise au point. Elle repose sur le calcul numérique des perméabilités obtenues à partir de la perte de charge générée par un réseau de cylindres représentatifs de la brosse.Des joints de faible diamètre en Haynes 25 ont été testés avec de l'air afin de vérifier la validité des résultats donnés par la simulation. L'évolution du débit avec la différence de pression et avec l'interférence des joints avec le rotor a été étudiée. Les déplacements du rotor et la température des joints ont été suivis durant les essais. / Brush seals are compliant dynamic seals that are used in the turbomachines. They are made of a brush of fine bristles sandwiched between two plates, in such a way that the assembly fills the gap between the rotor and the stator. The bristles are usually made from a cobalt based alloy called Haynes 25 (other materials can be used, such as Kevlar). The behaviour of these seals shows a strong coupling between the fluid flow and the brush deformation.This kind of seal can be modelled by considering the brush as a porous medium. This method presents the benefit of a rather simple calculation of the flow, but it requires the use of experimental data in order to calibrate its permeabilities (i.e. its ability to let the fluid flow through it). The aim of this thesis is to propose a model using the porous medium approach but without the need of preliminary experimental data. An iterative simulation between the calculation of the bristles' deformation under the influence of the pressure forces and the solving of the flow in the porous medium formed by the deformed brush was developed. It relies on the numerical calculation of the permeabilities obtained from the pressure drop generated by an array of cylinders representative of the brush.Low diameter Haynes 25 seals were tested with air in order to verify the validity of the results given by the simulation. The evolution of the mass flow rate with the pressure difference and the interference between the seal and the rotor was studied. Displacements of the rotor and temperature of the seals were also monitored during the tests.
197

Capsule deformation in a microfluidic channel : experiments, characterization and Proper Orthogonal Decomposition / Déformation d'une capsule dans un canal microfluidique : expériences, caractérisation et décomposition orthogonale aux valeurs propres

Sévénié, Benjamin 20 June 2016 (has links)
Nous étudions la déformation d'une capsule dans un canal microftuidique expérimentalement et numériquement. L'écoulement des rnicrocapsules est d'abord étudié numériquement dans un canal droit à section carrée. L'objectif est de développer une méthode de caractérisation des propriétés mécaniques de la membrane des capsules, à partir de leur déformation dans le canal. Nous avons mis en place une méthode d’identification afin de comparer la déformation des capsules observée expérimentalement et celle prédite par un modèle numérique tridimensionnel correspondant. La précision et la robustesse de l'algorithme d'analyse inverse ont été étudiées en faisant varier légèrement la géométrie des canaux. Finalement, la méthode a été utilisée afin de déterminer les propriétés mécaniques de rnicrocapsules dont la membrane est faite d’albumine réticulée. Nous avons ensuite appliqué une méthode de décomposition orthogonale aux valeurs propres (POD) aux formes prises par les capsules lors de leur passage dans un canal droit ou bifurqué. Des données numériques ont d 'abord été utilisées afin de déterminer la dimension de la variété des formes prises par une capsule dans un canal droit. La base POD ainsi construite a été utilisée pour interpoler les formes et obtenir la déformation d'une capsule à tous les temps, et pour tout paramètre d’écoulement. Nous avons également étudié expérimentalement les microcapsules lors de leur déformation dans un canal bifurqué. Nous avons ainsi obtenu les premiers résultats qualitatifs pour cette configuration. Nous avons développé un programme de détection de contour semi-automatique afin de faciliter le traitement d’image. Enfin, nous avons appliqué la méthode POD sur ces contours 2D réalistes et ainsi démontré la faisabilité d'utiliser une base réduite POD pour décrire la déformation de capsules clans un canal bifurqué. / The motion and deformation of a liquid-filled classic microcapsule flowing in microchannels is investigated bath experimentally and numerically. The flow of capsules into a straight microfluidic channel with a square cross-section is firstly studied. The objective is to develop a method to determine the mechanical properties of the capsule membrane from its hydrodynamic deformation. A method of identification has been devised to compare the particle deformed shape measured experimentally in the microchannels to the ones predicted by a three-dimensional numerical model for the same configuration. The precision and robustness of the inverse analysis algorithm have been tested when the microfluidic channels slightly depart from pure squareness. We have finally applied the method on microcapsules with a membrane made of reticulated albumin and determined their rnechanical properties. A Proper Orthogonal Decomposition (POD) has then been applied to the shapes assumed by the capsules while flowing in either a straight or bi­ furcated channel. Using numerical data in a straight channel, we have determined the dimension of the capsule shape variety. We have then interpolated the coefficients resulting from the POD analysis to compute the capsule deformed shape at any time for any flow parameter. Capsules have finally been investigated flowing in a bifurcated microchannel. Qualitative results of the motion and deformation of capsules in such channel have been obtained. A semi-automatic contour detection program has been developed to improve the image analysis. The POD method has been applied to the experimental results, thus proving the feasibility of building a reduced-order model of the phenomenon by using a POD reduced basis.
198

Mise en oeuvre expérimentale et analyse vibratoire non-linéaire d'un dispositif à quatre maquettes d'assemblages combustibles sous écoulement axial / Design, installation and nonlinear vibratory analysis of an experimental facility containing four fuel assemblies under axial flow.

Clement, Simon 11 December 2014 (has links)
Cette thèse s'inscrit dans le cadre général de la tenue au séisme des coeurs de réacteurs nucléaires à eau pressurisée (REP). Plus précisément, l'objectif de cette thèse est l'étude expérimentale du couplage entre assemblages combustibles induit par un écoulement d'eau axial. Les phases de conception, réalisation et mise en service d'une nouvelle installation appelée ICARE EXPERIMENTAL sont présentées. ICARE EXPERIMENTAL a été conçue pour observer simultanément les vibrations de quatre maquettes d'assemblages combustibles (2x2) confinées sous écoulement ascendant. Une nouvelle méthode d'analyse de données combinant analyse temps-fréquence et décomposition sur modes propres orthogonaux (POD) est décrite. Cette méthode, appelée Sliding Window POD (SWPOD), permet l'analyse de signaux à plusieurs composantes dont la répartition spatiale de l'énergie et le contenu fréquentiel varient avec le temps. Dans le cas de systèmes mécaniques (linéaires et non-linéaires), le lien entre les modes propres orthogonaux obtenus par la SWPOD et les modes normaux (linéaires et non-linéaires) est étudié. Les mesures obtenues avec l'installation ICARE EXPERIMENTAL sont analysées avec la SWPOD. Les premiers résultats mettent en évidence des mouvements caractéristiques des assemblages non excités, au passage de leurs résonances. Ce couplage entre assemblages combustibles, induit par le fluide, est reproduit par les simulations réalisées à l'aide du code de calcul COEUR3D. Ce code est basé sur une approche milieu poreux pour simuler un réseau d'assemblages combustibles sous écoulement. / The present study is in the scope of pressurized water reactors (PWR) core response to earthquakes. The goal of this thesis is to measure the coupling between fuel assemblies caused an axial water flow. The design, production and installation a new test facility named ICARE EXPERIMENTAL are presented. ICARE EXPERIMENTAL was built in order to measure simultaneously the vibrations of four fuel assemblies (2x2) under an axial flow. A new data analysis method combining time-frequency analysis and orthogonal mode decomposition (POD) is described. This method, named Sliding Window POD (SWPOD), allows analysing multicomponent data, of which spatial repartition of energy and frequency content are time dependent. In the case of mechanical systems (linear and nonlinear), the link between the proper orthogonal modes obtained through SWPOD and the normal modes (linear and nonlinear) is studied. The measures acquired with the ICARE EXPERIMENTAL installation are analysed using the SWPOD. The first results show characteristic behavior of the free fuel assemblies at their resonances. The coupling between fuel assemblies, induced by the fluid, is reproduced by simulations performed using the COEUR3D code. This code is based on a porous media model in order to simulate a fuel assemblies network under axial flow.
199

Development of numerical tools for hemodynamics and fluid structure interactions

Ma, Jieyan January 2014 (has links)
The aim of this study is to create CFD tools and models capable of simulating pulsatile blood flow in abdominal aortic aneurysm (AAA) and stent graft. It helps to increase the current physiological understanding of rupture risk of AAA and stent graft fixation or migration. Firstly, in order to build a general solver for the AAA modeling with reasonable accuracy, a third/fourth order modified OCI scheme is originally developed for general numerical simulation. The modified OCI scheme has a wider cell Reynolds number limitation. This high order scheme performs well with general rectangular mesh for incompressible fluid. Second, a velocity based finite volume method is originally developed to calculate the stress field for solid in order to capture the transient changes of the blood vessel since the artery is a rubber like material. All one, two and three dimensional classical cases for solid are tested and good results are obtained. The velocity based finite volume method show good potential to calculate the stress field for solid and easy to blend with the finite volume fluid solver. It has been recognized that fluid structure interaction (FSI) is very crucial in biomechanics. In this regard, the velocity based finite volume method is then further developed for FSI application. A well known one dimensional piston problem is studied to understand the feasibility of the fluid structure coupling. The numerical prediction matches the analytical solution very well. The velocity based method introduces less numerical damping compared with a stagger method and a monolithic method. Finally, the work focuses on practical pulsatile boundary conditions, non-Newtonian blood viscous properties and bifurcating geometry, and provides an overview of the hemodynamic within the AAA model. A modified Womersley inlet and imbalance pressure outlet boundary conditions are originally used in this study. The Womersley inlet boundary represents better approximation for pulsatile flow compared with the parabolic inlet condition. Numerical results are presented providing comparison between different boundary conditions using different viscous models in both 2D and 3D aneurysms. Good agreement between the numerical predictions and the experimental data is achieved for 2D case. 3D stent models with different bifurcation angles are also tested. The Womersley inlet boundary condition improves the existing inlet conditions significantly and it can reduce the Aneurysm neck computation domain. The influence of the non-Newtonian model to the wall shear stress (WSS) and strain-rate is also studied. The non-Newtonian model tends to produce higher WSS at both proximal and distal end of the aneurysm as compared with the Newtonian model (both 2D and 3D cases). The computed strain-rate distribution at the centre of the aneurysm is different between these two models. The influence of imbalance outlet pressure at the iliac arteries to the blood flow is originally investigated. The imbalance outlet pressure boundary conditions affect the computed wall shear stress significantly near the bifurcation point. All the pulsatile Womersley inlet, non-Newtonian viscosity properties and the imbalance pressure outlet need to be considered in blood flow simulation of AAA.
200

Análise estrutural dinâmica de grade de proteção de turbina de uma usina hidroelétrica

Lucas Giovanetti 17 December 2015 (has links)
Grades da tomada dágua de usinas hidroelétricas são equipamentos de grande importância porque são responsáveis pela proteção das turbinas hidráulicas contra impacto de corpos flutuantes. Tais estruturas estão submetidas à ação de cargas dinâmicas oriundas do escoamento da água através das barras. O objetivo do presente trabalho é analisar grades submetidas à ação de fluxo de água. Ou seja, analisar as respostas da estrutura e o comportamento do escoamento da água utilizando os cálculos de dinâmica de estruturas acopladas às técnicas de dinâmica de fluidos computacional (CFD). Para a elaboração destas análises, foi utilizado o software comercial CFX versão 14. Tais análises foram elaboradas mediante o processo de interação fluido-estrutura. Primeiramente, um modelo estrutural simplificado das barras verticais das grades é elaborado a partir de dados de projetos conhecidos. A partir deste modelo define-se um volume de controle que representa o escoamento do fluido. Devido ao número de Reynolds calculado, utiliza-se o modelo de turbulência para obtenção dos resultados tais como tensões e deslocamentos nas barras verticais, e perfil de velocidades do escoamento. Considerando o modelo proposto, foram elaboradas análises com sete diferentes valores de velocidade de modo a comparar os dados calculados numericamente através do método de elementos finitos com valores obtidos experimentalmente. A partir do modelo verificado, é apresentada uma análise de uma grade inclinada submetida a um fluxo paralelo. / Trashracks are very important equipment because they are responsible for protecting turbines of hydroelectric plants against floating bodies. These structures are subjected to the action of dynamic loads due to the water flow through the vertical and horizontal bars. The objective of this study was to analyze trashracks submitted by action of water flow. In other words, to analyze the responses of the structure and the behavior of water flow using dynamic of structures calculations coupled with computational fluid dynamics techniques (CFD) for a turbulent regime, through the use of commercial software CFX version 14. This analysis is elaborated by the process of fluid structure interaction. First of all, a simplified structural model of vertical bars is defined from other similar projects. For this model is defined a volume of control that represents fluid flow. Due to the Reynolds number calculated, it is utilized a turbulence model in order to obtain the results. These results are: stresses and displacements of vertical bars; and profile of velocities of flow. The results are analyzed and discussed. After that, considering the simplified model, analyzes with seven different values of speed are executed in order to compare the results between the data calculated numerically by finite elements method, and the values obtained experimentally. Considering the model verified, an analysis, of an inclined trashrack subjected to a parallel flow, is presented.

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