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O'Connor, Joseph. "Fluid-structure interactions of wall-mounted flexible slender structures." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/fluidstructure-interactions-of-wallmounted-flexible-slender-structures(1dab2986-b78f-4ff9-9b2e-5d2181cfa009).html.
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The fluid-structure interactions of wall-mounted slender structures, such as cilia, filaments, flaps, and flags, play an important role in a broad range of physical processes: from the coherent waving motion of vegetation, to the passive flow control capability of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear response exhibits a wide variety of behaviours that is yet to be fully understood, especially when multiple structures are considered. The purpose of this work is to investigate, via numerical simulation, the fluid-structure interactions of arrays of slender structures over a range of input conditions. A direct modelling approach, whereby the individual structures and their dynamics are fully resolved, is realised via a lattice Boltzmann-immersed boundary model, which is coupled to two different structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results are presented for three selected test cases - which build in scale from a single flap in a periodic array, to a small finite array of flaps, and finally to a large finite array - and the key behaviour modes are characterised and quantified. Results show a broad range of behaviours, which depend on the flow conditions and structural properties. In particular, the emergence of coherent waving motions are shown to be closely related to the natural frequency of the array. Furthermore, this behaviour is associated with a lock-in between the natural frequency of the array and the predicted frequency of the fluid instabilities. The original contributions of this work are: the development and application of a numerical tool for direct modelling of large arrays of slender structures; the characterisation of the behaviour of slender structures over a range of input conditions; and the exposition of key behaviour modes of slender structures and their relation to input conditions.
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Fan, David. "Fluid-structure interactions in internal flows." Thesis, University of Dundee, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.744232.
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FOINY, DAMIEN. "COUPLED SYSTEMS IN MECHANICS: FLUID STRUCTURE INTERACTIONS." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2017. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=32283@1.
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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROCOORDENAÇÃO DE APERFEIÇOAMENTO DO PESSOAL DE ENSINO SUPERIOR
PROGRAMA DE EXCELENCIA ACADEMICA
As interações fluido-estrutura são muito comuns na engenharia mecânica e civil porque muitas estruturas, como pontes, plataformas de petróleo, linhas de transmissão ou turbinas eólicas, estão diretamente em contato com um fluido, que pode ser o ar, no caso de vento, ou água, que irá perturbar a estrutura através de ondas. Um papel importante do engenheiro é prevenir a falha da estrutura devido às instabilidades criadas pelas interações fluidoestrutura. Este trabalho apresentará em primeiro lugar todos os conceitos básicos necessários para o estudo de problemas de interação fluido-estrutura. Assim, é realizada uma análise dimensional visando classificar os problemas de fluido-estrutura. A classificação é baseada na velocidade reduzida, e algumas conclusões sobre as conseqüências das interações fluido-estrutura podem ser feitas em termos de estabilidade ou, o que é mais interessante, de instabilidade. De fato, usando modelos simplificados, pode-se mostrar instabilidades estáticas e dinâmicas, induzidas por fluxo, que podem ser críticas para a estrutura. As partes finais do trabalho apresentarão uma estrutura não-linear específica, uma ponte suspensa. Primeiro, a formulação de um modelo simplificado unidimensional é explicada e, em seguida, através de uma discretização por elementos finitos, é realizado um estudo dinâmico. Além disso, algumas conclusões são apresentadas sobre a dinâmica das pontes suspensas. A última parte deste trabalho apresenta um método que foi uma importante fonte de publicação para nós, o método de decomposição regular.
Fluid-structure interactions are very common in mechanical and civil engineering because many structures, as bridges, offshore risers, transmission lines or wind turbines are directly in contact with a fluid, which can be air, which will be source of wind, or water, which will perturb the structure through waves. An important role of the engineer is to prevent structure failure due to instabilities created by the fluid-structure interactions. This work will first present all the basic concepts needed for the study of fluid-structure interaction problems. Thus, a dimensional analysis of those problems is performed and also all the equations governing such cases are presented. Then, thanks to the dimensional analysis made, a classification of problems, namely based on the reduced velocity, can be done and some conclusions concerning the consequences of the fluid-structure interactions can be drawn in terms of stability or, which is more interesting, instability. Indeed, using simplified models one can show static and dynamic flow-induced instabilities that may be critical for the structure. The final parts of the work will present a specific non-linear structure, a suspension bridge. First the formulation of a simplified one-dimensional model is explained and then, through a finite element discretization, a dynamical study is performed. Also, some conclusions are made concerning the dynamic of suspension bridges. The last part of this work presents a method that was an important source of publication for us, the Smooth Decomposition method.
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Yuan, Y. "Blast response of structures : limits to deformation and fluid-structure interactions." Thesis, University College London (University of London), 2015. http://discovery.ucl.ac.uk/1472671/.
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This thesis investigates the blast response of simple structural components - fully clamped beams and plates - underwater and in air. Experimental work by others have shown that, with increasing loading intensity, these components deform in one of either three modes: mode I (large inelastic deformation), mode II (tensile tearing) or mode III (transverse shear failure). The aim of this thesis is to develop theoretical and numerical models that can accurately predict these damage modes, taking into account the effects of fluid-structure interactions, for both impulsive and non-impulsive blast loadings A fully-clamped ductile beam model is proposed that is capable of capturing large elasto-plastic deformation, progressive damage and failure through detachment from its supports. Predictions by the model were validated against experimental data in the literature and with finite element models developed in this thesis. Parametric studies were also performed to elucidate the effects of loading duration on the mode of deformation and the conditions governing their transition. Numerical evidence on elimination of pulse-shape effects using an effective rectangular pulse loading (Youngdahl's approach) has been provided. The effects of uid-structure interaction (FSI) are investigated for fully-clamped, elasto-plastic beams in deep underwater explosions and intense air blast loadings. The main objective is to understand how the introduction of fully-clamped clamped supports alter existing well known results grounded on rigid, free-standing counterpart; and, to quantify how different modes of deformation affects the impulse and energy transmitted to the structure by the blast wave. Sensitivity analyses were carried out to elucidate the dependence of the results on the beam's aspect ratio and inertial mass. The deformation and failure of fully clamped rectangular plates subjected to blast loading are modelled numerically using finite element method. The numerical results are validated against experimental data. Deformation maps delineating the different deformation regimes for different combinations of blast impulse and aspect ratio are constructed for plates of equal mass. The effects of imposing a finite period, as opposed to a zero-period, pressure pulse upon the deformation mode and maximum deflection are discussed.
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Daily, David J. "Fluid-Structure Interactions with Flexible and Rigid Bodies." BYU ScholarsArchive, 2013. https://scholarsarchive.byu.edu/etd/3791.
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Fluid structure interactions occur to some extent in nearly every type of fluid flow. Understanding how structures interact with fluids and visa-versa is of vital importance in many engineering applications. The purpose of this research is to explore how fluids interact with flexible and rigid structures. A computational model was used to model the fluid structure interactions of vibrating synthetic vocal folds. The model simulated the coupling of the fluid and solid domains using a fluid-structure interface boundary condition. The fluid domain used a slightly compressible flow solver to allow for the possibility of acoustic coupling with the subglottal geometry and vibration of the vocal fold model. As the subglottis lengthened, the frequency of vibration decreased until a new acoustic mode could form in the subglottis. Synthetic aperture particle image velocimetry (SAPIV) is a three-dimensional particle tracking technique. SAPIV was used to image the jet of air that emerges from vibrating human vocal folds (glottal jet) during phonation. The three-dimensional reconstruction of the glottal jet found faint evidence of flow characteristics seen in previous research, such as axis-switching, but did not have sufficient resolution to detect small features. SAPIV was further applied to reconstruct the smaller flow characteristics of the glottal jet of vibrating synthetic vocal folds. Two- and four-layer synthetic vocal fold models were used to determine how the glottal jet from the synthetic models compared to the glottal jet from excised human vocal folds. The two- and four-layer models clearly exhibited axis-switching which has been seen in other 3D analyses of the glottal jet. Cavitation in a quiescent fluid can break a rigid structure such as a glass bottle. A new cavitation number was derived to include acceleration and pressure head at cavitation onset. A cavitation stick was used to validate the cavitation number by filling it with different depths and hitting the stick to cause fluid cavitation. Acceleration was measured using an accelerometer and cavitation bubbles were detected using a high-speed camera. Cavitation in an accelerating fluid occurred at a cavitation number of 1.
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Mora, Araque Luis. "Port-Hamiltonian modeling of fluid-structure interactions in a longitudinal domain." Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD058.
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L'interaction fluide-structure (FSI) est un problème multi-physique (avec plusieurs domaines physiques) qui étudie l'action réciproque entre une structure et un écoulement de fluide à travers une surface ou une interface de couplage. Mathématiquement, l'interaction fluide-structure est décrite par un ensemble d'équations différentielles et de conditions aux limites, obtenues par une formulation d'Euler-Lagrange et les équations de Navier-Stokes, qui appartiennent respectivement à la structure et aux domaines fluides. Le comportement de FSI peut être étudié à l'aide de solutions numériques utilisant des méthodes d'éléments finis ou de différences finies. Une alternative à Euler-Lagrange dans la modélisation des systèmes physiques à économie d'énergie est le cadre port-hamiltonien, dans lequel la dynamique du système est décrite par une fonction non négative représentant l'énergie totale stockée dans le système, appelée Hamiltonian H. Le port -Le cadre Hamiltonien permet la modélisation du transfert d'énergie entre systèmes de différents domaines physiques. Un exemple intéressant de FSI est le mécanisme de production vocale des cordes vocales, où le flux d'air intraglottal génère un cycle de vibration qui produit la phonation. Dans ce contexte, les modèles numériques des cordes vocales sont pertinents pour explorer les effets de certaines procédures thérapeutiques ou chirurgicales. Ces dernières années, on s’intéresse de plus en plus à l’étude du flux d’énergie dans la glotte pour l’analyse de la physiopathologie des troubles de la voix. L'étude de ce type de système multi-physique peut être étendue à d'autres systèmes FSI dans lesquels un fluide en mouvement dans un domaine longitudinal interagit avec un système mécanique en mouvement transversal. Dans cette thèse, un modèle évolutif en dimension finie pour les systèmes FSI sera développé. La division du problème fluide-structure en n sous-systèmes interconnectés décrits par des modèles de dimension finie constitue une alternative à la formulation traditionnelle à dimension infinie. De plus, l'utilisation du cadre port-hamiltonien pour décrire la dynamique permet une caractérisation adéquate du flux d'énergie dans le système. Le but de cette étude est donc de développer un modèle dimensionnel dimensionnel et évolutif, axé sur le flux d’énergie pour les systèmes à structure fluide dans un domaine longitudinal et s’appliquant aux plis vocauxFluid-structure interaction (FSI) is a multi-physics problem (with multiple physic domains) that study the reciprocal action between a structure and a fluid flow through a coupling surface or interface. Mathematically, Fluid-structure interaction is described by a set of differential equations and boundary conditions, obtained by an Euler-Lagrange formulation and the Navier-Stokes equations, which belong to the structure an fluid domains respectively. The behavior of FSI can be studied through numerical solutions using finite elements or finite differences methods. An alternative to Euler-Lagrange in the modeling of the energy-conserving physical systems is the port-Hamiltonian framework where the system dynamics are described through a non-negative function that represents the total stored energy in the system, called Hamiltonian H. The port-Hamiltonian framework allows the modeling of the energy transfer between systems in different physical domains. An interesting example of a FSI is the voice production mechanism of the vocal folds, where the intraglottal airflow generates a vibration cycle that produces the phonation. In this context, numerical models of the vocal folds are relevant to explore the effects of certain therapeutic or surgical procedures. In recent years there has been a growing interest in the study of energy flux in the glottis for analysis of pathophysiology of vocal disorders. The study of this kind of multi-physics system can be extended to other FSI system where a fluid moving in a longitudinal domain interacts with a mechanical system that move in the transversal dimension. In this thesis, a scalable finite-dimensional model for FSI systems will be developed. The division of fluid-structure problem into n interconnected sub-systems described by finite-dimensional models, provide an alternative to the traditional infinite-dimensional formulation. In addition, the use of port-Hamiltonian framework to describe the dynamics allows an adequate characterization of the energy flux in the system. Thus, the aim of this study develop a scalable finite-dimensional model focused in the energy flux for fluid-structure systems in a longitudinal domain with application to vocal folds
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Nové-Josserand, Clotilde. "Converting wave energy from fluid-elasticity interactions." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC124/document.
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Le développement des systèmes houlomoteurs ainsi que la gestion du littoral reposent sur une bonne compréhension des mécanismes liés aux interactions houle-structure. Dans cette thèse, nous nous intéressons à l'étude d'un champ de structures flexibles soumises à des ondes de surface, en vue de développer un système qui puisse à la fois atténuer les vagues et absorber l'énergie qui leur est associée de manière efficace. Les résultats présentés se basent autour d'expériences réalisées dans des installations de petite échelle, dans lesquelles la disposition spatiale des objets flexibles est le principal paramètre étudié. Dans un premier temps, nous caractérisons notre champ modèle afin d'évaluer l'influence de divers paramètres (configuration, flexibilité, fréquences des vagues) sur la distribution de l'énergie dans le système. Sur la base de ces résultats, nous développons ensuite un modèle d'interférences permettant de décrire les observations globales du système à partir de paramètres locaux connus, associés à une portion unitaire du champ. Ce modèle nous sert ensuite d'outil pour l'exploration d'une multitude de configurations spatiales, afin de déterminer le choix optimal vis-à-vis de l'atténuation et de l'absorption des vagues incidentes. Enfin, une campagne de mesures supplémentaire est utilisée afin d'expliquer les résultats obtenus avec le modèle et d'identifier les principes sous-jacents à cette optimisationUnderstanding the mechanisms involved in wave-structure interactions is of high interest for the development of efficient wave energy harvesters as well as for coastal management. In this thesis, we study the interactions of surface waves with a model array of slender flexible structures, in view of developing an efficient system for both attenuating and harvesting wave energy. The presented results are based around experimental investigations, by means of small scale facilities, in which the spatial arrangement of the flexible objects is the key parameter of study. The model array is first characterised by evaluating the role played by various parameters (configuration, flexibility, wave frequency) on the energy distribution in our system. Following these first observations, an interference model is then developed in order to describe the observed global effects of the array on both the wave field and the blade dynamics, based on known local parameters of a unit item of the array. This model then serves as a tool for exploring many possible array configurations, in order to determine the optimal choice regarding both the attenuation and the absorption of the imposed waves. A final experimental study is presented, in which the key results from the interference model are evaluated and the underlying principles of array optimisation are identified
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Law, Adam Daniel. "Structure and interactions of colloidal particles at fluid interfaces." Thesis, University of Hull, 2011. http://hydra.hull.ac.uk/resources/hull:4716.
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The structure and stability of colloidal monolayers depends crucially on the effective pair interaction potential between colloidal particles. In the first part of the thesis, we present two novel methods for extracting the pair potential from the two-dimensional radial distribution function of dense colloidal monolayers. The first is a so-called Predictor-Corrector routine that replaces the conventionally unknown Bridge function, with an iteratively obtained hard-disk bridge function. The second method is based on the Ornstein-Zernike relation and the HMSA closure that contains a single fitting parameter which is determined by requiring thermodynamic consistency between the virial and compressibility equations of state. The accuracy of these schemes are tested against Monte Carlo simulation data from monolayers interacting via a wide range of commonly encountered pair potentials. We also test the stability of these methods with respect to noise levels and truncation of the source data to mimic experimentally obtained structural data. Finally we apply these inversion schemes to experimental pair correlation function data obtained for charged polystyrene particles adsorbed at an oil/water interface. We find that the pair interaction potential is purely repulsive at low densities, but an attractive component develops at higher densities. The origin of this attractive component at higher densities is at present unknown.In the second part of this thesis, we study how the colloid interactions studied above influence the structure of the colloidal monolayer. Specifically inspired by recent experimental results on mixed monolayers of large and small very hydrophobic silica particles at an octane/water interface, we study theoretically the structure of two-dimensional binary mixtures of colloidal particles interacting via a dipole-dipole potential. We find that at zero temperature, a rich variety of binary crystal structures are obtained whose structure depends on the dipole moment ratio and the number fraction of small particles. At experimentally relevant finite temperatures, we find that the AB2 and AB6 binary super-lattice structures are thermodynamically stable while other binary structures e.g. AB5, which are stable at zero temperature, are thermodynamically unstable at finite temperature. Specifically, the melting temperature of the AB5 system is found to be three orders of magnitude lower than that of the AB2 and AB6 systems and at experimentally relevant temperatures, melts into a semi-disordered phase with local AB6 order.
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Wang, Xiaodong. "On mixed finite element formulations for fluid-structure interactions." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38061.
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Nielson, Joseph R. "Three Dimensional Characterization of Vocal Fold Fluid Structure Interactions." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3662.
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Voice quality is strongly linked to quality of life; those who suffer from voice disorders are adversely affected in their social, family, and professional relationships. An effort has been made to more fully understand the physics behind how the voice is created, specifically the fluid structure interactions that occur during vocal fold vibration. Many techniques have been developed and implemented to study both the motion of the vocal folds and the airflow that creates the motion. Until recently these techniques have sought to understand a highly three-dimensional phenomenon with 1D or 2D perspectives.This research focuses on the development and implementation of an experimental technique to obtain three-dimensional characterizations of vocal fold motion and fluid flow. Experiments were performed on excised human vocal fold models at the University Hospital Erlangen Medical School in Erlangen, Germany. A novel technique for tracking the motion of the vocal folds using multiple camera viewpoints and limited user interaction was developed. Four high-speed cameras (2000 fps) recorded an excised vocal fold model vibrating at 250 Hz. Based on the images from these four cameras a fully 3D reconstruction of the superior surface of the vocal folds was achieved. The 3D reconstruction of 70 consecutive time steps was assembled to characterize the motion of the vocal folds over eight cycles. The 3D reconstruction accurately modeled the observed behavior of vocal fold vibration with a clearly visible mucosal wave. The average reprojection error for this technique was on par with other contemporary techniques (~20 micrometers). A whole field, time resolved, three-dimensional reconstruction of the vocal fold fluid flow was obtained using synthetic aperture particle image velocimetry. Simultaneous 3D flow fields, subglottal pressure waves, and superior surface motion were presented for 2 consecutive cycles of oscillation. The vocal fold fluid flow and motion measurements correlated with behavior observed in previous three-dimensional studies. A higher resolution view of one full cycle of oscillation was compiled from 16 time resolved data sets via pressure data. The result was a full three-dimensional characterization of the evolution and disintegration of the glottal jet.
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Hermange, Corentin. "Simulation des interactions fluide-structure dans le problème de l’aquaplaning." Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0014/document.
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Le problème de l’hydroplannage a fait l’objet de peu de travaux de simulation jusqu’à présent du fait de sa complexité : couplage fluide-structure, complexité de la structure du pneu du fait des matériaux en présence, contact avec l’asphalte, complexité de l’écoulement fluide résultant (interface extrêmement complexe,assèchement de la route, ventilation, développement éventuel de la turbulence et de cavitation). Dans ce contexte, Michelin, Centrale Nantes et NextFlowSoftware ont cherché récemment à évaluer la capacité du solveur SPH développé par ces deux derniers pour classifier des pneumatiques en fonction de la géométrie de leurs structures surfaciques, sans prendre en compte la phase gazeuse. Cela a permis de démontrer la faisabilité de telles simulations par méthode SPH, et même d’obtenir de bons résultats avec pour avantages de s’absoudre des difficultés liées au maillage. L’autre avantage conséquent d’utiliser la méthode SPH pour modéliser le fluide dans ce contexte est apparu dans sa capacité à se coupler relativement aisément à des solveurs classiques de type Eléments Finis pour le problème structurel. L’objectif du doctorat est triple, poursuivre la qualification du couplage SPH–Eléments Finis, en particulier en termes énergétiques, développer des schémas permettant d’assurer un bon compromis stabilité / précision / temps de calcul. Deuxièmement quantifier l’influence des différents phénomènes physiques en jeu pour déterminer lesquels doivent être modélisés. Enfin adapter des modélisations SPH permettant de prendre en compte simultanément les différents phénomènes influant pour réaliser des simulations du problème completThe aquaplaning problem has been the topic of simulation works emphasizing its complexity: fluid structure interactions, structures modelling, materials involved, contact with asphalt and the complexity of the resulting fluid flow (extremely complex interface, drying up the road, ventilation, possible development of turbulence and cavitation). As additional difficulty, the tire is a highly deformable body and fluid-structure interaction effects should be considered, leading to a challenging problem for the numerical modelling. Then Michelin, Ecole Centrale Nantes and NextFlow Software have recently tested the ability of the SPH solver developed by the two latter to classify tires based on their surface structure geometries, without considering the gas phase. In this context, the interest of SPH for modelling efficiently the aquaplaning flow has been underlined. The meshless and Lagrangian feature of SPH naturally avoid the problem of fluid/solid grid compatibility. The other significant advantage of the SPH method, in this context, appears in its ability to be relatively easily coupled to with conventional Finite Element solvers. The aim of this workis three fold. First, qualify the SPH-FE coupling strategy, especially in terms of energy and then develop schemes to ensure a good compromise among stability, accuracy and computation time. Second, quantify the influence of different involved physical phenomena to determine which should be modelled. Finally, adapt SPH models to simultaneously consider different phenomena and to performe simulations of the complete problem
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Allegret-Bourdon, Davy. "Experimental study of fluid-structure interactions oon a generic model." Licentiate thesis, KTH, Energy Technology, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1785.
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A new type of test facility is presented which allows theinvestigation of fluid-structure interactions using a genericflexible model. Rather than modelling the complex geometry of aturbomachine blade passage or blade row, this test facilityuses a two dimensional generic bump located in a straightchannel in order to reach a better understanding of the bendingflutter phenomenon. Thus, experimental campaigns are performedto observe and measure surface pressure fluctuations linked tothe interactions of a shock wave with the boundary layer formedover the oscillating structure. The new test facility modifiesan existing wind tunnel featuring a straight rectangular crosssection. The oscillating model used in the study is oftwo-dimensional prismatic shape and has been investigated inprevious studies, from which base case data are available. Inorder to introduce capabilities for the planned fluid-structureexperimental campaigns, a flexible version of the model hasbeen built. It is moulded of polyurethane at defined elasticityand hardness, and actuated by a novel type of fully integratedmechanical oscillating mechanism. A frequency controlled ACservomotor drives this oscillating mechanism. The whole drivetrain is able to produce an oscillation of the model atvariable amplitude and frequency up to 200Hz. At the same time,a one dimensional laser sensor measures precisely the wholemodel displacement through a top optical window. The flow inthe test section can be set at different operating conditions.Time-resolved pressure measurements are performed on theoscillating surfaceusing Kulite fast response transducerscoupled to an adapted long line probe technique. While theinstantaneous models shape is scanned using laser triangulationtechnique through the top window, unsteady Schlierenvisualization measurement are performed using the accessthrough two side windows. Similar coupling is also performedbetween unsteady flexible geometry measurements and unsteadypressure measurements. The mode shapes of this flexible bumpstrongly depend on the excitation frequency. It is consideredthat a first bending mode shape is obtained for reducedfrequencies up to 0.037. However, for reduced frequencieshigher than 0.037, the mode shapes are interpreted as higherharmonic stripe mode shapes. Thus a second order mode shape isreached for reduced frequencies between 0.037 and 0.074, and athird order mode shape is reached for reduced frequenciesbetween 0.074 and 0.294. In this experimental study, the modeloscillates at reduced frequencies from 0.015 to 0.294 attransonic flow condition characterized by an inlet Mach numberMiso1=0.69 and an outlet Mach number Miso2=0.80. Schlieren pictures as well as unsteadypressure repartitions are obtained for this operating flowcondition. The presented unsteady results demonstrate that thephase of shock wave movement towards bump local motion shows adecreasing trend for third bending mode shapes fluctuating withreduced frequencies higher than 0.074. At the pressure tapslocated after the shock wave formation, the phase of pressurefluctuations towards bump local motion present the samedecreasing trend for the same kind of mode shapes. However noconclusion can be drawn for this range of perturbationfrequencies at a non-fluctuating bending mode shape (a modeshape that remains the same in the whole perturbation frequencyrange). In conclusion, a new version of this generic bump willhave to be manufactured in order to perform similar experimentsat a non-rigid first bending mode shape.
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Wang, Yongxing. "A one-field fictitious domain method for fluid-structure interactions." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/21218/.
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We present a one-field fictitious domain method (FDM) for simulation of general fluid-structure interactions (FSI). "One-field" means only one velocity field is solved in the whole (fluid and solid) domain based upon the finite element interpolation. The proposed method has the same generality and robustness as the FDM with a distributed Lagrange multiplier (DLM): both of them solve the fluid equations and solid equations as one system. However the one-field FDM only needs to solve for one velocity field while the FDM/DLM usually solves for fluid velocity, solid displacement and Lagrange multiplier. The proposed one-field FDM also has similar features with immersed finite element methods (IFEM): the explicit or implicit IFEM places all the solid information in a FSI force term which is arranged on the right-hand side of the fluid equations. The one-field FDM assembles the solid equations and implicitly includes them with the fluid equations. What we achieve is theoretically equivalent to an implicit IFEM but avoiding convergence problems, and a wide range of solid parameters can be considered in this scheme. In short, the one-field FDM combines the FDM/DLM advantage of robustness and the IFEM advantage of efficiency. In this thesis, we present a thorough review, summary and categorization of the existing finite element methods for FSI problems. The finite element weak formulation of the one-field FDM and discretization in time and space are introduced, followed by a stability analysis by energy estimate. The proposed scheme is first implemented in implicit form, followed by numerical validation for the property of non-increasing energy under the conditions of $\rho^f\le\rho^s$ (densities of the fluid and solid respectively) and $\nu^f\le\nu^s$ (viscosities of the fluid and solid respectively), and numerical tests for stability under the conditions of $\rho^f>\rho^s$ and/or $\nu^f>\nu^s$. The proposed scheme is then implemented based upon three explicit splitting schemes: 2-step splitting, 3-step splitting and 4-step splitting scheme. The fully coupled implicit FSI system is decoupled into subproblems step by step, which can be effectively solved. The pros and cons of these splitting schemes are analysed followed by a selection of numerical tests in order to illustrate the capabilities and range of applicability of the proposed one-field FDM scheme. The thesis concludes with a presentation of some topics and open problems that may be worthy of further investigation.
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Ozsun, Ozgur. "Fundamentals and applications of fluid- structure interactions in compliant microchannels." Thesis, Boston University, 2014. https://hdl.handle.net/2144/19692.
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Thesis (Ph.D.)--Boston UniversityThe development of soft lithography techniques for fabricating microfluidic channels has enabled the study of microscale flows. These studies have become an essential component of experimental research in biology, fluid dynamics, engineering and related fields. A systematic understanding of microscale flows requires that the characteristics of the flow fields be determined accurately. However, as microchannels are scaled down, the size of most experimental probes becomes comparable to or even bigger than the micro-flows themselves, making the measurement of the distribution of flow fields problematic. In this work, we take advantage of the fact that most microfluidic channels are made up of soft materials and can deform during flow. We develop a non-invasive optical measurement technique to correlate the channel deformation with the pressure field inside the microchannel; we then apply this technique to studies of biological flows and flows on superhydrophobic surfaces. [TRUNCATED]
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Yan, Zhimiao. "Modeling of Nonlinear Unsteady Aerodynamics, Dynamics and Fluid Structure Interactions." Diss., Virginia Tech, 2015. http://hdl.handle.net/10919/71824.
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We model different nonlinear systems, analyze their nonlinear aspects and discuss their applications.
First, we present a semi-analytical, geometrically-exact, unsteady potential flow model is developed for airfoils undergoing large amplitude maneuvers. Towards this objective, the
classical unsteady theory of Theodorsen is revisited by relaxing some of the major assumptions such as (1) flat wake, (2) small angle of attack, (3) small disturbances to the mean flow components, and (4) time-invariant free-stream. The kinematics of the wake vortices is simulated numerically while the wake and bound circulation distribution and, consequently, the associated pressure distribution are determined analytically. The steady and unsteady behaviors of the developed model are validated against experimental and computational results.
The model is then used to determine the lift frequency response at different mean angles of attack.
Second, we investigate the nonlinear characteristics of an autoparametric vibration system. This system consists of a base structure and a cantilever beam with a tip mass. The dynamic equations for the system are derived using the extended Hamilton's principle. The method of multiple scales is then used to analytically determine the stability and bifurcation of the system. The effects of the amplitude and frequency of the external force, the damping coefficient and frequency of the attached cantilever beam and the tip mass on the nonlinear responses of the system are determined. As an application, the concept of energy harvesting based on the autoparametric vibration system consisting of a base structure subjected to the external force and a cantilever beam with a tip mass is evaluated. Piezoelectric sheets are attached to the cantilever beam to convert the vibrations of the base structure into electrical energy. The coupled nonlinear distributed-parameter model is developed and analyzed. The effects of the electrical load resistance on the global frequency and damping ratio of the cantilever beam are analyzed by linearizion of the governing equations and perturbation method. Nonlinear analysis is performed to investigate the impacts of external force and load resistance on the response of the harvester.
Finally, the concept of harvesting energy from ambient and galloping vibrations of a bluff body is investigated. A piezoelectric transducer is attached to the transverse degree of freedom of the body in order to convert the vibration energy to electrical power. A coupled nonlinear distributed-parameter model is developed that takes into consideration the galloping force and moment nonlinearities and the base excitation effects. The aerodynamic loads are modeled using the quasi-steady approximation. Linear analysis is performed to determine the effects of the electrical load resistance and wind speed on the global damping and frequency of the harvester as well as on the onset of instability. Then, nonlinear analysis is performed to investigate the impact of the base acceleration, wind speed, and electrical load resistance on the performance of the harvester and the associated nonlinear phenomena. Short- and open-circuit configurations for different wind speeds and base accelerations are assessedPh. D.
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Bogaers, Alfred Edward Jules. "Efficient and robust partitioned solution schemes for fluid-structure interactions." Doctoral thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/16486.
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Includes bibliographical referencesIn this thesis, the development of a strongly coupled, partitioned fluid-structure interactions (FSI) solver is outlined. Well established methods are analysed and new methods are proposed to provide robust, accurate and efficient FSI solutions. All the methods introduced and analysed are primarily geared towards the solution of incompressible, transient FSI problems, which facilitate the use of black-box sub-domain field solvers. In the first part of the thesis, radial basis function (RBF) interpolation is introduced for interface information transfer. RBF interpolation requires no grid connectivity information, and therefore presents an elegant means by which to transfer information across a non-matching and non-conforming interface to couple finite element to finite volume based discretisation schemes. The transfer scheme is analysed, with particular emphasis on a comparison between consistent and conservative formulations. The primary aim is to demonstrate that the widely used conservative formulation is a zero order method. Furthermore, while the consistent formulation is not provably conservative, it yields errors well within acceptable levels and converges within the limit of mesh refinement. A newly developed multi-vector update quasi-Newton (MVQN) method for implicit coupling of black-box partitioned solvers is proposed. The new coupling scheme, under certain conditions, can be demonstrated to provide near Newton-like convergence behaviour. The superior convergence properties and robust nature of the MVQN method are shown in comparison to other well-known quasi-Newton coupling schemes, including the least squares reduced order modelling (IBQN-LS) scheme, the classical rank-1 update Broyden's method, and fixed point iterations with dynamic relaxation. Partitioned, incompressible FSI, based on Dirichlet-Neumann domain decomposition solution schemes, cannot be applied to problems where the fluid domain is fully enclosed. A simple example often provided in the literature is that of balloon inflation with a prescribed inflow velocity. In this context, artificial compressibility (AC) will be shown to be a useful method to relax the incompressibility constraint, by including a source term within the fluid continuity equation. The attractiveness of AC stems from the fact that this source term can readily be added to almost any fluid field solver, including most commercial solvers. AC/FSI is however limited in the range of problems it can effectively be applied to. To this end, the combination of the newly developed MVQN method with AC/FSI is proposed. In so doing, the AC modified fluid field solver can continue to be treated as a black-box solver, while the overall robustness and performance are significantly improved. The study concludes with a demonstration of the modularity offered by partitioned FSI solvers. The analysis of the coupled environment is extended to include steady state FSI, FSI with free surfaces and an FSI problem with solid-body contact.
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Ma, Jieyan. "Development of numerical tools for hemodynamics and fluid structure interactions." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/development-of-numerical-tools-for-hemodynamics-and-fluid-structure-interactions(f7e72de2-c1f8-4d7a-aa2c-f2a4d239187f).html.
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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.
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Gatzhammer, Bernhard [Verfasser]. "Efficient and Flexible Partitioned Simulation of Fluid-Structure Interactions / Bernhard Gatzhammer." München : Verlag Dr. Hut, 2015. http://d-nb.info/1067708928/34.
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Yu, Zhanle. "Fluid-structure interactions : from the flapping flag to the swimming fish." Thesis, Ecole centrale de Marseille, 2016. http://www.theses.fr/2016ECDM0001/document.
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L'instabilité du drapeau et la nage des poissons sont deux des problèmes d'interaction entièrement couplés fluide-structure. Ils peuvent être considérés comme l’ interaction entre la structure déformable (plaque) et un écoulement de grand nombre de Reynolds. Si la plaque est allongée (petit rapport d’aspect), la théorie du corps élancé (Lighthill 1960) applique pour calculer la force de pression exercée sur la plaque par le fluide. Alors que pour une plaque avec une très grande envergure (grand rapport d’aspect), la théorie bidimensionnelle de l’aile instationnaire (Wu 1961) est utilisée pour modéliser la dynamique de l'écoulement. Cependant, aucun de ces deux modèles donne la force de pression précise agissant sur une plaque avec un rapport d'aspect intermédiaire. Généralement, l'écoulement entourant peut être modélisé par l'équation de Laplace (en termes de potentiel de vitesse) avec une condition aux limites de Neumann. Par la méthode de Green, le problème se réduit à une équation intégrale de surface portante (mathématiquement appelée l’équation intégrale de Fredholm de première espèce avec un noyau singulier). Le saut de potentiel peut être trouvé en inversant l'équation de surface portante, et la distribution de saut de pression peut être par conséquent obtenue en appliquant l'équation de Bernoulli instationnaire.Dans cette thèse, l'équation de surface portante est résolue numériquement par la méthode de surface portante à fréquence fixée. La méthode numérique proposée est validée par les modèles théoriques (théorie du corps élancé et 2D théorie de l’aile instationnaire). L'équation de surface portante est également résolue analytiquement dans la limite du petit rapport d’aspect, par la méthode de raccordement de développement asymptotique (Matched Asymptotic Expansion) ou encore la technique asymptotique proposée. La méthode analytique proposée donne la force de pression plus précise sur une surface avec un rapport d’aspect intermédiaire (de 0 à 0.5), par rapport à la théorie du corps élancé. Cela en fait est un bon candidat pour l'optimisation et le contrôle. Le modèle de fluide analytique proposée est ensuite couplé avec l'équation d’Euler-Bernoulli de poutre pour étudier l’ instabilité du drapeau. Nous étudions l'influence du rapport d'aspect et le ratio de masse sur la vitesse d'écoulement critique. Les résultats montrent de très bons accords à ceux de Eloy et al. 2007. Le modèle de fluide d'analyse proposée est également appliqué au problème de la nage des poissons. Une nouvelle formule de la moyenne de poussée est proposée, et une analyse qualitative sur la morphologie du poisson est effectuée. De ces études, nous pouvons conclure que le modèle proposé fluide peut être considéré comme la théorie du corps élancé corrigée pour l'effet de rapport d'aspect. Ainsi, l'écoulement autour d'une surface de rapport d’aspect intermédiaire peut être inclus par ce modèleThe flapping flag instability and fish swimming are two fully-coupled fluid-structure interaction problems. They can be considered as the interaction between a deformable structure (plate) and a high Reynolds number flow. If the plate is elongated (small aspect ratio), Slender-body theory (Lighthill 1960) applies to calculate the pressure force exerted on the plate by the surrounding flow. While for a plate with very large span (large aspect ratio), 2D unsteady airfoil theory (Wu 1961) is used to model the dynamics of the surrounding flow. However, none of these two models gives accurate pressure force acting on a plate with intermediate aspect ratio. Generally, the surrounding flow can be modeled by the Laplace equation (in terms of velocity potential) with a Neumann boundary condition. By means of Green representation theorem, the problem reduces to a lifting-surface integral equation (mathematically called Fredholm integral equation of first kind with a singular kernel). The potential jump can be found by inverting this lifting-surface equation, and the pressure jump distribution can be therefore obtained by applying unsteady Bernoulli equation. In this thesis, the lifting-surface equation is solved numerically through the fixed-frequency lifting-surface method. The proposed numerical method is validated by the theoretical models (Slender-body theory and 2D unsteady airfoil theory). The lifting-surface equation is also solved analytically in the limit of small aspect ratio, by the Matched Asymptotic Expansion method or alternatively the proposed asymptotic technique. The proposed analytical method gives more accurate pressure force on a surface with intermediate aspect ratio (ranging from 0 to 0.5), comparing to Slender-body theory. This makes it a good candidate for the optimization and control. The proposed analytical fluid model is then coupled with Euler-Bernoulli beam equation to study the flapping flag instability. We investigate the influence of plate aspect ratio and mass ratio on the critical flow velocity. The results show very good agreements to those of Eloy et al. 2007. The proposed analytical fluid model is also applied to the fish swimming problem. A new formula of mean thrust is proposed, and a qualitative analysis on the fish morphology is performed. From these studies, we can conclude that the proposed fluid model can viewed as Slender-body theory corrected for the aspect ratio effect. Thus, the flow surrounding a lifting-surface with intermediate aspect ratio can be included by this model
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Shaik, Eleyas. "Numerical simulations of blood flow in arteries using fluid-structure interactions." Diss., Wichita State University, 2007. http://hdl.handle.net/10057/1480.
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Cardiovascular disease (CVD) is the number one cause of death in the United States and worldwide. Among the various CVDs, coronary artery disease (CAD) is the leading cause of death among both men and women. Of the various forms of CADs, atherosclerosis is the primary cause. To investigate these arterial diseases, numerical simulations of blood flow in the arteries using fluid-structure interactions (FSI) with the finite element method were performed. First, simulations were performed assuming the arterial walls are rigid, and then they were extended to deformable arteries where contraction and expansion of the arteries are considered. Moreover, this study also investigated the outcome of bypass surgeries involving end-to-side and end-to-end bypass anastomosis. To help understand the effect of various flow/material characteristics on these surgeries and related issues, numerical investigations on artery-graft bypass models were conducted. The primary objectives of this research were as follows: (1) to validate the numerical simulations with existing experimental data, (2) to differentiate the effect of Newtonian and non-Newtonian fluid flow considering three-dimensional rigid models of the artery, (3) to investigate the effect of arterial geometry using both steady and pulsatile flow cases, (4) to provide some indication of the occurrence of atherosclerosis while describing the hemodynamic parameters, (5) to determine the extent of interaction between blood flow and the elastic walls while performing numerical simulations on various arterial geometries with steady and pulsatile flow, (6) to investigate the outcome of bypass surgery (various cases) with natural and synthetic grafts, and (7) to determine the occurrence of intimal hyperplasia following bypass surgery. In the computations, the non-Newtonian behavior of blood was described using the Carreau-Yasuda model. Generally, good agreement between the numerical and experimental results was observed in the velocity profiles, whereas some discrepancies were found in wall shear stress (WSS) distributions. The regions of the artery models for both steady and pulsatile flow cases, with low wall shear stresses correspond to regions of the body that are more susceptible to atherosclerosis; or intimal hyperplasia for the case of bypass surgery were identified. It was also found that the geometry of the artery plays an important role in the development of atherosclerosis. The comparison between the simulations considering rigid arteries and deformable arteries showed a substantial increase in wall shear stresses for the rigid artery. In addition, it was observed that the calculated difference in shear stress between the simulations performed using rigid wall assumptions with that of deformable walls was in the range of 30 to 40 percent at the maximum shear stress location. Therefore, it was concluded that the deformation of the arterial wall cannot be neglected while performing blood flow simulations.Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
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Shaik, Eleyas Hoffmann Klaus A. "Numerical simulations of blood flow in arteries using fluid-structure interactions /." Diss., A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1480.
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Thesis (Ph.D.)--Wichita State University, College of Engineering, Dept. of Aerospace EngineeringCardiovascular disease (CVD) is the number one cause of death in the United States and worldwide. Among the various CVDs, coronary artery disease (CAD) is the leading cause of death among both men and women. Of the various forms of CADs, atherosclerosis is the primary cause. To investigate these arterial diseases, numerical simulations of blood flow in the arteries using fluid-structure interactions (FSI) with the finite element method were performed. First, simulations were performed assuming the arterial walls are rigid, and then they were extended to deformable arteries where contraction and expansion of the arteries are considered. Moreover, this study also investigated the outcome of bypass surgeries involving end-to-side and end-to-end bypass anastomosis. To help understand the effect of various flow/material characteristics on these surgeries and related issues, numerical investigations on artery-graft bypass models were conducted. The primary objectives of this research were as follows: (1) to validate the numerical simulations with existing experimental data, (2) to differentiate the effect of Newtonian and non-Newtonian fluid flow considering three-dimensional rigid models of the artery, (3) to investigate the effect of arterial geometry using both steady and pulsatile flow cases, (4) to provide some indication of the occurrence of atherosclerosis while describing the hemodynamic parameters, (5) to determine the extent of interaction between blood flow and the elastic walls while performing numerical simulations on various arterial geometries with steady and pulsatile flow, (6) to investigate the outcome of bypass surgery (various cases) with natural and synthetic grafts, and (7) to determine the occurrence of intimal hyperplasia following bypass surgery. In the computations, the non-Newtonian behavior of blood was described using the Carreau-Yasuda model. Generally, good agreement between the numerical and experimental results was observed in the velocity profiles, whereas some discrepancies were found in wall shear stress (WSS) distributions. The regions of the artery models for both steady and pulsatile flow cases, with low wall shear stresses correspond to regions of the body that are more susceptible to atherosclerosis; or intimal hyperplasia for the case of bypass surgery were identified. It was also found that the geometry of the artery plays an important role in the development of atherosclerosis. The comparison between the simulations considering rigid arteries and deformable arteries showed a substantial increase in wall shear stresses for the rigid artery. In addition, it was observed that the calculated difference in shear stress between the simulations performed using rigid wall assumptions with that of deformable walls was in the range of 30 to 40 percent at the maximum shear stress location. Therefore, it was concluded that the deformation of the arterial wall cannot be neglected while performing blood flow simulations.
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Atalianis, Christos Andreas. "Hydrodynamic analysis of structures by a hybrid method." Thesis, University of Newcastle Upon Tyne, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283649.
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Capanna, Roberto. "Modelling of fluid structure interaction by potential flow theory in a pwr under seismic excitation." Thesis, Ecole centrale de Marseille, 2018. http://www.theses.fr/2018ECDM0013/document.
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Une modélisation efficace et une connaissance précise du comportement mécanique du cœur du réacteur sont nécessaires pour estimer les effets de l'excitation sismique sur une centrale nucléaire. La présence d'un écoulement d'eau (dans les REP) engendre des phénomènes d'interaction fluide structure. La modélisation des interactions fluide structure sur les assemblages combustible revêt donc une importance fondamentale pour la sécurité des réacteurs nucléaires. L’objectif principal du projet de thèse présenté dans ce document est d’étudier les interactions fluide structure afin de mieux comprendre les phénomènes impliqués. La modélisation et l'approche expérimentale sont considérées. Un nouveau modèle linéaire simplifié pour les interactions fluide structure est développé en utilisant la théorie de l'écoulement potentiel pour la modélisation des forces fluide, tandis que le modèle de poutre d'Euler-Bernoulli est utilisé pour la partie structurelle. Le modèle est d'abord développé pour un seul cylindre et il est validé avec des ouvrages de référence dans la littérature. Les effets de la taille de confinement et du nombre d'onde sont examinés. Le modèle d'écoulement potentiel développé pour un seul cylindre est ainsi étendu à une géométrie multicylindre. La démarche expérimentale est donc nécessaire pour valider le modèle développé. Une nouvelle installation expérimentale, ICARE, a été conçue pour étudier les phénomènes d’interaction fluide structure sur des assemblages combustible à demi-échelle. Dans ce document, les résultats fournis par les mesures de déplacement et de LDV sont largement analysés. Le comportement dynamique de l'assemblage combustible et les effets de couplage sont étudiés. Les calculs sont comparés aux résultats expérimentaux afin de valider le modèle et d’en analyser ses limites. Le modèle est en accord avec les résultats expérimentaux concernant l'effet de masse ajouté. De plus, le modèle prédit qualitativement les effets des couplages dans différentes directions. Par contre, le modèle d'écoulement potentiel ne permet pas de prédire des effets d'amortissement ajouté, principalement dus aux forces visqueuses. Enfin, dans ce document, une autre application du modèle développé est décrite. Le modèle est utilisé afin de simuler des expériences réalisées sur une maquette d'assemblage combustible dans l'installation expérimentale installée à l'Université George Washington (GWU). Le modèle est capable de prédire et de fournir une interprétation valide de la perturbation du débit d'eau due au mouvement de l'ensemble excité. La thèse se termine par des perspectives d'amélioration du modèle, en intégrant des termes visqueux dans les équations. L'analyse des données de vélocimétrie par image de particules (PIV) recueillies au cours des campagnes expérimentales ICARE doit être poursuivieEfficient modelling and accurate knowledge of the mechanical behaviour of the reactorcore are needed to estimate the effects of seismic excitation on a nuclear power plant. Thepresence of cooling water flow (in PWRs) gives rise to fluid structure interaction phenomena.Modelling of fluid structure interactions on fuel assemblies is thus of fundamentalimportance in order to assure the safety of nuclear reactors. The main objective of thePhD project which is presented in this document is to investigate fluid structure interactionsin order to have a better understanding of the involved phenomena. Both modellingand experimental approach are considered. A new simplified linear model for fluid structureinteractions is developed by using the potential flow theory for fluid force modellingwhile the Euler-Bernoulli beam model is used for the structural part. The model, is firstdeveloped for a single cylinder and it is validated with reference works in literature. Theeffects of the confinement size and of the wavenumber are investigated. The potential flowmodel developed for a single cylinder, is thus extended to a multi cylinders geometry. Theexperimental approach is thus needed in order to validate the developed model. A newexperimental facility, ICARE, is designed in order to investigate fluid structure interactionphenomena on half scale fuel assemblies. In this document, the results provided bydisplacement and LDV measurements are widely analysed. The dynamical behaviour ofthe fuel assembly and coupling effects are investigated. Calculations are compared to theexperimental results in order to validate the model and to analyse its limits. The model isin agreement with experimental results regarding the added mass effect. In addition, themodel qualitatively predicts couplings effects on different directions. As a drawback, thepotential flow model cannot predict added damping effects, which are mainly due to viscousforces. Finally in this document another application of the developed model is described.The model is used in order to simulate experiments performed on a surrogate fuel assemblyin the experimental facility installed at George Washington University (GWU). The modelis able to predict and to provide a valid interpretation for the water flow perturbation dueto the motion of the excited assembly. The thesis concludes with perspectives for furtherimprovements of the model, by integrating viscous terms in the equations. Work needs tobe carried out on the analysis of Particle Image Velocimetry (PIV) data collected duringICARE experimental campaigns
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Lelong, Alexandra. "Etude expérimentale du comportement hydroélastique d'une structure flexible pour différents régimes d'écoulement." Thesis, Brest, 2016. http://www.theses.fr/2016BRES0048/document.
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Cette thèse vise à analyser expérimentalement une structure flexible et légère dans différents régimes d’écoulement, dont le régime cavitant. Un protocole expérimental a donc été mis en place afin de caractériser le comportement hydroélastique d’un profil NACA 0015 en polyoxyméthylène (POM) et de le comparer à un profil en acier inoxydable considéré comme « rigide ». Des mesures en écoulement subcavitant ont été réalisées : chargement hydrodynamique, contraintes, déformées statiques, réponse vibratoire et champ de vitesse ont été mesurés pour les deux matériaux. Enfin, une analyse vibratoire a été menée en écoulement cavitant. Ces mesures nous ont permis de constater que les déformées statiques du profil flexible sont similaires aux déformations observées sur une poutre encastrée : la flexion est la déformation principale et la torsion est faible. Toutefois les performances du profil flexible sont moins bonnes que pour un profil rigide : la portance diminue tandis que la traînée augmente. D’autre part, il apparaît que la dynamique du profil est contrôlée par l’écoulement. En effet, lorsque l’incidence du profil est proche de l’angle de décrochage, une fréquence liée au détachement tourbillonnaire apparaît sur les spectres de vibration des profils. Elle conduit à une réduction des fréquences propres liées à la flexion : si l’influence de cette fréquence sur le profil rigide reste faible à basse vitesse, sa proximité avec la fréquence propre du profil flexible conduit à un lock-in. Celui-ci se produit également en écoulement cavitant : lorsque la poche de cavitation devient instable, sa fréquence d’oscillation devient très énergétique et prend le contrôle de la dynamique du profil flexible. Le lock-in prend fin quand une supercavitation se développe autour du profil. Il conduit à une augmentation de la masse ajoutée au profil alors qu’elle devrait diminuer en présence de vapeur d’eauThis work deals with an experimental analysis of a flexible and light lifting profile for various flow conditions, including cavitation. An experimental protocol was set up to study a flexible NACA 0015 made of polyoxymethylene (POM) and compare its behaviour with a foil made of steel, which is considered as rigid. The forces, strains, stresses and vibrations of the foils were measured, as well as the velocity field. Moreover, a vibratory analysis was performed in cavitating flow. The flexible foil behaves like a built-in beam : the deformations corresponds to predictions from the beam theory, with high bending and low twisting. These deformations imply lower lift and higher drag compared to the rigid foil. The vortex shedding frequency appears on the vibration spectra near stall. It increases with flow velocity and leads to a decrease of the natural bending frequency. But flexibility involves lower natural frequencies : the first bending frequency of the flexible foil is 3.5 times lower than the rigid one. This allows lock-in between the first bending frequency of the flexible foil and the vortex shedding frequency. Lock-in occurs in cavitating flows too : when cavitation becomes unstable, it oscillates with a frequency close to the bending natural frequency of the flexible foil. This lock-in ends when the cavitation number is low enough, what leads to a decrease of the cavitation oscillation frequency. In those conditions, the added mass of the flexible foil does not decrease with the cavitation number as the added mass of the rigid foil
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Bélanger, François. "A numerical method for confined unsteady flows related to fluid-structure interactions /." Thesis, McGill University, 1991. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=70306.
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This thesis elaborates three aspects in the field of flow-induced vibrations associated with annular geometries.A method to find the unsteady fluid forces on a cylinder oscillating in annular turbulent flow is developed by considering the superposition of the turbulent fluctuating quantities on potential flow. The theory is compared with experiments.
Then, the unsteady fluid forces acting on the vibrating cylinder walls of non-uniform annular configurations are computed by a method which performs the accurate time integration of the Navier-Stokes equations. It is the extension for unsteady flows of the method of artificial compressibility used for steady flows. A time-discretization of the momentum equation using a three-point-backward implicit scheme is introduced, and the addition of pseudo-time derivative terms to the semi-discretized equations, including artificial compressibility in the continuity equation, allows to use time-marching solution techniques thereafter.
Finally, the integration method used for the Navier-Stokes equations is combined with the equation governing the dynamical behavior of a structure in order to perform the fluid-structure stability analysis of this system in the time domain.
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Hussein, Ahmed Abd Elmonem Ahmed. "Dynamical System Representation and Analysis of Unsteady Flow and Fluid-Structure Interactions." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/85626.
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A dynamical system approach is utilized to reduce the representation order of unsteady fluid flows and fluid-structure interaction systems. This approach allows for significant reduction in the computational cost of their numerical simulations, implementation of optimization and control methodologies and assessment of their dynamic stability. In the first chapter, I present a new Lagrangian function to derive the equations of motion of unsteady point vortices. This representation is a reconciliation between Newtonian and Lagrangian mechanics yielding a new approach to model the dynamics of these vortices. In the second chapter, I investigate the flutter of a helicopter rotor blade using finite-state time approximation of the unsteady aerodynamics. The analysis showed a new stability region that could not be determined under the assumption of a quasi-steady flow. In the third chapter, I implement the unsteady vortex lattice method to quantify the effects of tail flexibility on the propulsive efficiency of a fish. I determine that flexibility enhances the propulsion. In the fourth chapter, I consider the stability of a flapping micro air vehicle and use different approaches to design the transition from hovering to forward flight. I determine that first order averaging is not suitable and that time periodic dynamics are required for the controller to achieve this transition. In the fifth chapter, I derive a mathematical model for the free motion of a two-body planar system representing a fish under the action of coupled dynamics and hydrodynamics loads. I conclude that the psicform fish family are inherently stable under certain conditions that depend on the location of the center of mass.Ph. D.
We present modeling approaches of the interaction between flying or swimming bodies and the surrounding fluids. We consider their stability as they perform special maneuvers. The approaches are applied to rotating blades of helicopters, fish-like robots, and micro-air vehicles. We develop and validate a new mathematical representation for the flow generated by moving or deforming elements. We also assess the effects of fast variations in the flow on the stability of a rotating helicopter blade. The results point to a new stable regime for their operation. In other words, the fast flow variations could stabilize the rotating blades. These results can also be applied to the analysis of stability of rotating blades of wind turbines. We consider the effects of flexing a tail on the propulsive force of fish-like robots. The results show that adding flexibility enhances the efficiency of the fish propulsion. Inspired by the ability of some birds and insects to transition from hovering to forward motion, we thoroughly investigate different approaches to model and realize this transition. We determine that no simplification should be applied to the rigorous model representing the flapping flight in order to model transition phenomena correctly. Finally, we model the forward-swim dynamics of psciform and determine the condition on the center of mass for which a robotic fish can maintain its stability. This condition could help in designing fish-like robots that perform stable underwater maneuvers.
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Haßler, Marc [Verfasser], and K. [Akademischer Betreuer] Schweizerhof. "Quasi-Static Fluid-Structure Interactions Based on a Geometric Description of Fluids / Marc Haßler. Betreuer: K. Schweizerhof." Karlsruhe : KIT-Bibliothek, 2009. http://d-nb.info/1014221803/34.
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Landajuela, Larma Mikel. "Coupling schemes and unfitted mesh methods for fluid-structure interaction." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066053/document.
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Cette thèse est dédiée à la simulation numérique des systèmes mécaniques impliquant l'interaction entre une structure mince déformable et un fluide incompressible interne ou qui l'entoure.Dans la première partie, nous introduisons deux nouvelles classes de schémas de couplage explicites en utilisant des maillages compatibles. Les méthodes proposées combinent une certaine consistance Robin dans le système avec (i) un schéma à pas fractionnaire pour le fluide ou (ii) une discrétisation temporelle d'ordre deux pour le fluide et le solide. Les propriétés de stabilité des méthodes sont analysées dans un cadre linéaire représentatif. Cette partie inclut aussi une étude numérique exhaustive dans laquelle plusieurs schémas de couplage (dont certains proposés ici) sont comparés et validés avec des résultats expérimentaux. Dans la seconde partie, nous considérons des maillages non compatibles. La discrétisation spatiale est basée, dans ce cas là, sur des variantes de la méthode de Nitsche avec éléments coupés. Nous présentons deux nouveaux types de schémas de découplage qui exploitent la susmentionée condition de Robin en utilisant des maillages incompatibles. Le caractère semi-implicite ou explicite du couplage en temps dépend de l'ordre dans lequel les discrétisations spatiales et temporelles sont effectuées. Dans le cas d'un couplage avec des structures immergées, la vitesse et la pression discrètes permettent des discontinuités faibles et fortes à travers l'interface, respectivement. Des estimations de stabilité et d'erreur sont fournies dans un cadre linéaire. Une série de tests numériques illustre la performance des différentes méthodes proposéesThis thesis is devoted to the numerical approximation of mechanical systems involving the interaction of a deformable thin-walled structure with an internal or surrounding incompressible fluid flow. In the first part, we introduce two new classes of explicit coupling schemes using fitted meshes. The methods proposed combine a certain Robin-consistency in the system with (i) a projection-based time-marching in the fluid or (ii) second-order time-stepping in both the fluid and the solid. The stability properties of the methods are analyzed within representative linear settings. This part includes also a comprehensive numerical study in which state-of-the-art coupling schemes (including some of the methods proposed herein) are compared and validated against the results of an experimental benchmark. In the second part, we consider unfitted mesh formulations. The spatial discretization in this case is based on variants of Nitsche’s method with cut elements. We present two new classes of splitting schemes which exploit the aforementioned interface Robin-consistency in the unfitted framework. The semi-implicit or explicit nature of the splitting in time is dictated by the order in which the spatial and time discretizations are performed. In the case of the coupling with immersed structures, weak and strong discontinuities across the interface are allowed for the velocity and pressure, respectively. Stability and error estimates are provided within a linear setting. A series of numerical tests illustrates the performance of the different methods proposed
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Bleischwitz, Robert. "Fluid-structure interactions of membrane wings in free-flight and in ground-effect." Thesis, University of Southampton, 2016. https://eprints.soton.ac.uk/397261/.
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Currently, there is a growing demand to improve the aerodynamic performance of Micro-Air-Vehicles for extended mission time, higher payload capacity and improved agility. Their wings have to operate within a challenging Reynolds number regime of Re =10(4)-10(5) which is known for its low energy content in the boundary layer, causing early flow separation and loss in lift production. Flexible wings, inspired from bats, could potentially exploit given flow separations by forming lift carrying shedding structures close to the upper wing surface. The aspect-ratio is one key parameter which modifies these vortex formations and their ability to couple with the membrane. However, vortex related lift production comes at a price of increased drag and limitation in aerodynamic efficiency. Membrane wings in ground-effect could combine ground-effect related efficiency enhancement with flexibility related stall improvements. Therefore, two separate wind tunnel experiments are conducted to understand the impact of aspect-ratio and ground-effect on the fluid-structure interaction of membrane wings. Multiple high-speed recordings involve lift, drag and pitch moment measurements with a load-cell, membrane deformation measurements with photogrammetry and digital image correlation (DIC)and flow measurements with planar/stereo particle image velocimetry (PIV). Next to time-averaged quantities, reduced order models are used to group predominant flow and membrane dynamics. Synchronised fluid-membrane coupling of flexible membrane wings allows to exploit separated flow conditions to provide further lift enhancement from vortical flow formations. An exemplary membrane wing at [alpha] = 25(o) shows similar vortex-shedding to a rigid at-plate at [alpha] = 15(o), but comes with 50 % more lift production. Higher aspect-ratios are found to exploit the benefits of wing flexibility to a larger extend, showing a gain in peak-lift of up to 60% for an aspect-ratio of 2 and 31% for an aspect-ratio of 1 (in reference to rigid at-plates). Membrane wings extend their performance window in ground-effect conditions by delaying ground-effect induced premature flow separation by [DELTA alpha] = 5(o). In addition, membrane wings in ground-effect are found to be up to 30% more efficiency than rigid at-plates.
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Tschisgale, Silvio. "A numerical method for fluid-structure interactions of slender rods in turbulent flow." TUDpress - Thelem Universitätsverlag, 2018. https://tud.qucosa.de/id/qucosa%3A38706.
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This thesis presents a numerical method for the simulation of fluid-structure interaction (FSI) problems on high-performance computers. The proposed method is specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic structures, the latter being modeled as Cosserat rods. From a numerical point of view, such kind of FSI requires special techniques to reach numerical stability. When using a partitioned fluid-structure coupling approach
this is usually achieved by an iterative procedure, which drastically increases the computational effort. In the present work, an alternative coupling approach is developed based on an immersed boundary method (IBM). It is unconditionally
stable and exempt from any global iteration between the fluid part and the structure part.
The proposed FSI solver is employed to simulate the flow over a dense layer of vegetation elements, usually designated as canopy flow. The abstracted canopy model used in the simulation consists of 800 strip-shaped blades, which is the
largest canopy-resolving simulation of this type done so far. To gain a deeper understanding of the physics of aquatic canopy flows the simulation data obtained are analyzed, e.g., concerning the existence and shape of coherent structures.
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Shin, James Jang-Sik. "A spectral element formulation for fluid-structure interactions : applications to flow through collapsible channels." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/41003.
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Pitman, Mark William. "An investigation of flow structure interactions on a finite compliant surface using computational methods." Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/625.
Full textAbstract:
A study of the interaction of one-sided flow over a compliant surface is presented. When fluid passes over a flexible surface the simultaneous interaction between the flow and structure gives rise to vibrations and instabilities on the surface as well as in the fluid. The fluid-structure interaction (FSI) has potential to be used in the control of boundary layer dynamics to achieve drag reduction through transition delay. The modelling and control of FSI systems apply to many fields of engineering beyond drag reduction, for example: the modelling and analysis of biomechanical systems; natural environmental systems; aero-elastics; and other areas where flow interacts moving or compliant boundaries. The investigation is performed through numerical simulation. This returns more detail than could be resolved through experiments, while also permitting the study of finite compliant surfaces that are prohibitively difficult, or impossible, to study with analytical techniques. In the present work, novel numerical modelling methods are developed from linear system analysis through to nonlinear disturbances and viscous effects.Two numerical modelling techniques are adopted to approach the analysis of the FSI system. A potential-flow method is used for the modelling of flows in the limit of infinite Reynolds numbers, while a grid-free Discrete Vortex Method (DVM) is used for the modelling of the rotational boundary-layer flow at moderate Reynolds numbers. In both inviscid and viscous studies, significant contributions are made to the numerical modelling techniques. The application of these methods to the study of flow over compliant panels gives new insight to the nature of the FSI system. In the linear inviscid model, a novel hybrid computational/theoretical method is developed that evaluates the eigenvalues and eigenmodes from a discretised FSI system. The results from the non-linear inviscid model revealed that the steady-state of the non-linear wall motion is independent of initial excitation. For the viscous case, the first application of a DVM to model the interaction of a viscous, rotational flow with a compliant surface is developed. This DVM is successfully applied to model boundary-layer flow over a finite compliant surface.
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Belakroum, Rassim. "Contribution à la modélisation des interactions fluides-structures." Thesis, Reims, 2011. http://www.theses.fr/2011REIMS009/document.
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Les buts principaux recherchés de la présente thèse visent au développement et à l’expertise d’une méthodologie de simulation numérique des problèmes d’interactions fluides-structures. Afin de cerner progressivement le problème étudié, nous nous sommes intéressés en premier lieu à la simulation numérique des écoulements autour d’obstacles solides, plus particulièrement au phénomène d’éclatements tourbillonnaires dans la zone de sillage d’obstacles de différentes formes. Nous avons utilisé la méthode des éléments finis en adoptant la technique de stabilisation GLS (Galerkin Least-Square). Pour le traitement de la turbulence, nous avons opté pour la méthode LES (Large-Eddy Simulation) en utilisant le filtre de Smagorinsky. En deuxième phase, nous nous sommes intéressés aux écoulements en milieux déformables. Nous avons entrepris la formulation ALE (Arbitrairement Lagrangienne Eulérienne) en considérant un maillage déformable. Pour la mise à jour de la grille du maillage dynamique, nous avons utilisé une approche pseudo-élastique. Afin d’expertiser la méthodologie mise en oeuvre, nous avons choisi d’aborder le problème des ballottements à la surface libre de réservoirs partiellement remplis de liquide. En dernière partie, nous nous sommes intéressés au comportement vibratoire d’un corps solide sous l’effet d’un écoulement de fluide. Par l’utilisation d’un algorithme de couplage totalement implicite basé sur la méthode de Gauss-Seidel par Bloc, nous avons abordé le phénomène des instabilités aéroélastiques des ponts à haubans. Pour la validation du modèle numérique traitant les interactions fluides-structures par les données expérimentales, nous nous sommes intéressés au comportement vibratoire d’une maquette sectionnelle d’un tablier de pont réel sous l’effet d’un vent soufflant uniformeThe main goals sought by this thesis target the development and expertise of a methodology for numerical simulation of fluid-structure interactions problems. In order to identify the studied problem progressively, we are interested primarily in numerical simulation of flows around bluff bodies, especially the phenomenon of vortex shedding in the wake zone of a bluff body of different shapes. We used the finite element method by adopting the stabilized GLS (Galerkin Least-Square) technique. For the treatment of turbulence, we opted the LES (Large-Eddy Simulation) method using the Smagorinsky filter. In the second phase, we were interested in flows in deformable media. We undertook the ALE (Arbitrary Lagrangian Eulerian) formulation by considering a deformable mesh. To update the grid of the dynamic mesh, we used a pseudo-elastic approach. To appraise the implemented methodology, we decided to approach the problem of sloshing at the free surface of a tank partially filled with liquid. In the final part, we were interested in vibration behavior of a solid body under the effect of fluid flow. By using a fully implicit coupling algorithm based on a relaxed Bloc Gauss-Seidel method, we studied the phenomenon of aeroelastic instability of cable-stayed bridges. To validate the numerical model treating fluid-structure interactions by experimental data, we investigated the vibration behavior of a real deck sectional model under the effect of a uniform wind
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Deborde, Julien. "Etude expérimentale et numérique d'un distributeur auto-régulant pour l'irrigation." Thesis, Aix-Marseille 1, 2011. http://www.theses.fr/2011AIX10130.
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Dans le cadre d’une collaboration avec la société PHYTOREM, nous avons élaboré un prototype de distribution autorégulé afin d’épandre des Eaux Usées après un simple dégrillage et via la Phytorémédiation (dépollution par les plantes).La première approche du projet de thèse a été de comprendre les comportements rhéologiques des effluents, mis à disposition par Phytorem, et mécaniques du matériau élastomère de type EPDM. Nous avons exposé les différentes façons de retrouver leurs propriétés rhéologiques et mécaniques par le biais de divers tests de rhéométrie, concernant les effluents, et de traction uni-, bi- et équibi-axiale, pour la partie matériau. Ceci nous a permis d’obtenir d’une part, la viscosité de nos effluents, et d’autre part, la loi de comportement la mieux adaptée à notre matériau.La deuxième et dernière approche porte sur les interactions entre un fluide et une membrane hyperélastique ayant pour fonction de réguler un écoulement. Le comportement de la membrane contrainte par la pression a été simulé sous Abaqus. Ces résultats ont permis de modéliser l’écoulement (code CFD commercial) lorsque la membrane est déformée et de déterminer numériquement la loi débit/pression du dispositif. Ces développements numériques s’appuient sur la méthode des éléments finis et un couplage partitionné simple en une étape pour une première approche entre le fluide, la membrane et la structure. Les modèles numériques sont validés expérimentalement. Ces travaux participent à l’élaboration d’un prototype de distributeur auto-réguléIn collaboration with PHYTOREM, we have developed a prototype of self-regulated drip emitter to spread the Wastewater after a simple screening using phytoremediation (remediation by plants).The first approach of the thesis project was to understand the rheological behaviour of waste provided by PHYTOREM, and mechanical properties behaviour of EPDM elastomer type. We have explained the different ways to find their rheological and mechanical properties through various rheometry tests on waste, and tension uni-, biand equibi-axiale, for the material part. This allowed us to obtain first, the viscosity of our waste, and secondly, the behaviour law of best suited to our material.The second and final approach focuses on the interactions between a fluid and a hyperelastic membrane whose function is to regulate flow. The membrane behaviour under pressure stress was simulated using Abaqus. These results were used to model the flow (commercial CFD) when the membrane is distorted and to determine numerically its flow versus pressure law. These developments are relying on numerical finite element method and partitionned into a single coupling step for a first approach between fluid, membrane and structure. The numerical models are validated experimentally. This work contributes to the development of a prototype of self-regulated drip emitter
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Potapov, Sergueï. "Un algorithme ALE de dynamique rapide basé sur une approche mixte éléments finis - volumes finis : Implémentation en langage orienté objet C++." Châtenay-Malabry, Ecole centrale de Paris, 1997. http://www.theses.fr/1997ECAP0534.
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Cette thèse propose un algorithme numérique permettant la résolution efficace d'une large gamme de problèmes de la dynamique rapide impliquant de grandes déformations plastiques des matériaux solides, des écoulements des fluides et des problèmes d'interaction forte fluide-structure. Pour uniformiser le traitement numérique des solides et des fluides, l'algorithme s'appuie sur la formulation ALE (Lagrange Euler arbitraire) du mouvement. Le problème ALE a été décomposé en deux phases : une phase lagrangienne (symétrique) et une phase de convection (non symétrique). Une telle décomposition a permis d'écrire les formulations intégrales appropriées à chaque phase : la formulation éléments finis centrée pour la phase lagrangienne et la formulation volumes finis décentrée pour la phase de convection. Pour convecter correctement des variables nodales et élémentaires, deux types de cellule de contrôle ont été utilisés : les cellules Inria pour convecter la quantité de mouvement et les cellules barycentriques pour convecter les variables élémentaires. Cela permet de résoudre proprement le problème de convection et de garantir des résultats corrects quelle que soit la vitesse de convection. Les solutions numériques présentées touchent à d'autres aspects de résolution du problème de dynamique rapide en formulation ALE : l'intégration temporelle avec un pas de temps adaptatif, la prise en compte des conditions initiales et aux limites, la gestion du maillage mobile, le traitement des ondes de choc. L’algorithme proposé a été mis en œuvre informatique en utilisant le langage oriente objet C++ et implémenté dans le prototype 3D du code de calcul de dynamique rapide DYRAC++. L’algorithme a été testé sur des cas-tests ayant les solutions analytiques ou des résultats de référence. L’analyse des résultats montre que l'algorithme permet de traiter avec la même aisance des problèmes hydrodynamiques avec un fluide compressible et des problèmes de la dynamique des solides avec des matériaux non-linéaires.
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Ivanizki, Dmitry [Verfasser]. "Numerical analysis of the relation between interactions and structure in a molecular fluid / Dmitry Ivanizki." Mainz : Universitätsbibliothek Mainz, 2015. http://d-nb.info/108050673X/34.
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Barnes, Caleb J. "Unsteady Physics and Aeroelastic Response of Streamwise Vortex-Surface Interactions." Wright State University / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=wright1431937866.
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Frei, Stefan [Verfasser], and Thomas [Akademischer Betreuer] Richter. "Eulerian finite element methods for interface problems and fluid-structure interactions / Stefan Frei ; Betreuer: Thomas Richter." Heidelberg : Universitätsbibliothek Heidelberg, 2016. http://d-nb.info/1180616197/34.
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Sheer, Francis Joseph. "Multi-Scale Computational Modeling of Fluid-Structure Interactions and Adhesion Dynamics in the Upper Respiratory System." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316287639.
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Pitman, Mark William. "An investigation of flow structure interactions on a finite compliant surface using computational methods." Curtin University of Technology, Department of Mechanical Engineering, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17209.
Full textAbstract:
A study of the interaction of one-sided flow over a compliant surface is presented. When fluid passes over a flexible surface the simultaneous interaction between the flow and structure gives rise to vibrations and instabilities on the surface as well as in the fluid. The fluid-structure interaction (FSI) has potential to be used in the control of boundary layer dynamics to achieve drag reduction through transition delay. The modelling and control of FSI systems apply to many fields of engineering beyond drag reduction, for example: the modelling and analysis of biomechanical systems; natural environmental systems; aero-elastics; and other areas where flow interacts moving or compliant boundaries. The investigation is performed through numerical simulation. This returns more detail than could be resolved through experiments, while also permitting the study of finite compliant surfaces that are prohibitively difficult, or impossible, to study with analytical techniques. In the present work, novel numerical modelling methods are developed from linear system analysis through to nonlinear disturbances and viscous effects.Two numerical modelling techniques are adopted to approach the analysis of the FSI system. A potential-flow method is used for the modelling of flows in the limit of infinite Reynolds numbers, while a grid-free Discrete Vortex Method (DVM) is used for the modelling of the rotational boundary-layer flow at moderate Reynolds numbers. In both inviscid and viscous studies, significant contributions are made to the numerical modelling techniques. The application of these methods to the study of flow over compliant panels gives new insight to the nature of the FSI system. In the linear inviscid model, a novel hybrid computational/theoretical method is developed that evaluates the eigenvalues and eigenmodes from a discretised FSI system. The results from the non-linear inviscid model revealed that the steady-state of the non-linear wall motion is independent of initial excitation. For the viscous case, the first application of a DVM to model the interaction of a viscous, rotational flow with a compliant surface is developed. This DVM is successfully applied to model boundary-layer flow over a finite compliant surface.
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Jallas, Damien. "Stabilité d’écoulements de sillages périodiques générés par des ailes battantes." Thesis, Toulouse 3, 2018. http://www.theses.fr/2018TOU30322.
Full textAbstract:
La thèse porte sur l'étude numérique de la stabilité d'écoulements de sillages périodiques en temps générés par des ailes battantes. Elle vise à expliquer trois phénomènes observés expérimentalement et simulés numériquement : (i) la déviation du sillage propulsif d'une aile battante en incidence nulle, (ii) les écoulements quasi-périodiques autour d'ailes battantes en incidence non nulle, et (iii) l'auto-propulsion d'ailes battantes symétriques dans des fluides au repos. Tous ces phénomènes sont reliés à l'existence d'instabilités de l'écoulement fluide autour de l'aile. Plusieurs méthodes originales ont été développées pour calculer les champs de base périodiques instables qui satisfont les symétries spatio-temporelles imposées par la cinématique des ailes. La stabilité de ces écoulements de sillages périodiques a ensuite été étudiée au moyen d'une analyse de Floquet. En plus de ces analyses linéaires, la connaissance des champs de base périodiques permet l'étude de la saturation non linéaire des instabilités rencontrées. Dans chaque cas, ces résultats permettent de discuter les effets observés sur les performances aérodynamiques des ailes battantesThe thesis investigates numerically the stability of time-periodic wake flows generated by flapping wings and aims at explaining three phenomena that have been observed experimentally or simulated numerically : (i) the deviation of propulsive wakes behind a flapping wing with zero mean angle, (ii) the quasi-periodic flows around flapping wings with non zero mean angle, and (iii) the self-propulsion of heaving symmetric wings in a quiescent fluid. All these phenomena are related to the existence of instabilities of timeperiodic base flows. Original methods are developed to compute unstable time-periodic flows that satisfy the spatio-temporal symmetries imposed by the wings kinematics. The stability analysis of these time-periodic base flows are then determined by computing the Floquet multiplier and corresponding modes. In addition to the linear stability analysis, the knowledge of time-periodic base flows allows to investigate the non-linear saturation of these perturbations. In each case, the influence of the instabilities developing in the wake-flows on the flapping wing performances are discussed
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Makanga, Ursy. "Transport and deformation of flexible fibers in structured environments." Electronic Thesis or Diss., Institut polytechnique de Paris, 2023. http://www.theses.fr/2023IPPAX080.
Full textAbstract:
Les fibres flexibles se rencontrent dans diverses situations dans la nature et les applications industrielles. Parmi lesquelles on trouve des fibres de microplastiques, des fibres de cellulose et des structures filamenteuses résultant de colonies bactériennes dites “biofilms". Dans la plupart des cas, les fibres flexibles sont généralement immergées dans des environnements fluidiques qui sont munis d'obstacles. A titre d'exemple, les lave-linge rejettent un grand nombre de fibres de microplastiques (environ 1900 fibres par lavage) dans des eaux usées contenant plusieurs débris. Dans de tels environnements complexes, les fibres peuvent adopter différentes formes non triviales et se déplacer suivant différents modes à travers les obstacles environnants. Ces différents comportements résultent du couplage complexe entre la réponse élastique des fibres, les collisions et les interactions hydrodynamiques. Leur compréhension est par conséquent essentielle pour l'étude des systèmes biologiques, environnementaux et industriels, où des phénomènes similaires sont observés, de même que pour éviter des problèmes majeurs comme la pollution ou le colmatage. Au cours des dernières décennies, la modélisation des particules élancées immergées dans un fluide visqueux a été un domaine majeur de recherche en mécanique des fluides. Cependant, le développement des modèles numériques permettant de prendre en compte des environnements munis d'obstacles a été peu abordé. Le problème raide à résoudre sous contraintes qui en résulte en est une des raisons. Modéliser des fibres dans de tels environnements est un défi majeur pour les approches numériques actuelles.Ainsi, dans cette thèse, nous proposerons une méthodologie pour simuler des fibres flexibles dans des environnements fluidiques munis d'obstacles. Notre implémentation permet de simuler des systèmes contenant un nombre considérable de fibres et d'obstacles en des temps raisonnables sur une seule carte graphique (GPU). Forts de cet outil, et d'expériences simples, nous étudierons ensuite le problème de sédimentation des fibres flexibles dans des environnements complexes. Nos résultats jettent les bases pour de futures expériences et fournissent des ingrédients physiques essentiels pour la conception des dispositifs de tri de particules sous l'action de la gravitéFlexible fibers are encountered in various situations in nature and industrial applications. Examples include microplastics fibers, cellulose fibers, and biofilm streamers. In a wide range of such situations, flexible fibers are often immersed in a fluidic environment with obstacles embedded. For instance, laundry washing machines discharge a large number of microplastics fibers (around 1900 fibers per wash) into wastewaters which contain a significant amount of debris. In such complex media, flexible fibers can exhibit nontrivial conformations and different modes of transport through the surrounding obstacles. These dynamics result from the complex interplay between their elastic response, collisions and hydrodynamic interactions. Understanding of these phenomena is therefore essential to study the physics of biological, environmental and industrial systems, but also to prevent issues such as pollution or clogging. While modeling slender particles in viscous fluids has been a major area of research over the past few decades, methodologies involving surrounding environments are scarce. The resulting complex coupling leads to a constrained formulation of the problem in addition of being stiff. Therefore, modeling fibers in complex media is challenging and can be computationally costly.In this thesis, we will propose a methodology to model flexible fibers in different environments that are made of rigid stationary obstacles. Our implementation enables dynamic simulations of large systems in a reasonable wall times on a single modern Graphics Processing Unit (GPU). Using the capabilities afforded by our method, together with simple experiments, we will investigate the sedimentation of flexible fibers in structured environments. The resulting findings provide physical insight into future experiments and the design of gravity-based sorting devices
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Gineau, Audrey Nathalie. "Modélisation multi-échelle de l'interaction fluide-structure dans les systèmes tubulaires." Thesis, Paris 6, 2015. http://www.theses.fr/2015PA066651/document.
Full textAbstract:
Cette thèse a pour objectif de modéliser le couplage fluide-structure pouvant survenir dans les faisceaux tubulaires des réacteurs nucléaires. Leurs simulations numériques directes étant hors de portée, on met en œuvre une approche multi-échelle: il s'agit de tirer profit du coût modeste d'une description macroscopique, et à la fois, de la précision des informations microscopiques. Vis-à-vis des modèles existants, le travail de développement se focalise sur la prise en compte de la convection dans le calcul des champs hydrodynamiques, mais surtout, sur la possibilité de restituer des réponses vibratoires variées au sein d'un même faisceau. L'homogénéisation aboutit à un système d'équations gouvernant les Interactions Fluide-Solide à une échelle macroscopique. Ces équations sont couplées par une source en quantité de mouvement, traduisant les charges hydrodynamiques exercées sur une structure donnée. Cette force à modéliser représente une loi de fermeture du problème homogénéisé, mettant en jeu des coefficients a priori inconnus. Une méthode d'estimation est proposée à partir des champs microscopiques obtenus par simulation directe sur un domaine réduit et représentatif du large système de référence. Les capacités prédictives du modèle homogénéisé sont évaluées en comparaison avec des données de référence, issues de calculs numériques directs microscopiques. Chaque système considéré présente une variété de réponses en déplacement que le modèle homogénéisé restitue avec un accord satisfaisant. Cette approche multi-échelle semble être un bon compromis entre le coût des réalisations numériques et la précision attendue des données vibratoires et hydrodynamiquesVibration of tubes arrays is a matter of safety assessments of nuclear reactor cores or steam generators. Such systems count up thousands of slender-bodies immersed in viscous flow, involving multi-physics mechanisms caused by nonlinear dynamic interactions between the fluid and the solid materials. Direct numerical simulations for predicting these phenomena could derive from continuum mechanics, but require expensive computing resources. Therefore, one alternative to the costly micro-scale simulations consists in describing the interstitial fluid dynamics at the same scale as the structures one. Such approach rely on homogenization techniques intended to model mechanics of multi-phase systems. Homogenization results in coupled governing equations for the fluid and solid dynamics, whose solution provides individual tubes displacements and average fluid fields for each periodic unit cell. An hydrodynamic force term arises from the formulation within this set of homogenized equations: it depends on the micro-scale flow in the vicinity of a given tube-wall, but needs to be estimated as a function of the macro-scale fields in order to close the homogenized problem. The fluid force estimation relies on numerical micro-scale solutions of fluid-solid interactions over a tube array of small size. The multi-scale model is assessed for arrays made up of hundreds tubes, and is compared with solutions coming from the numerical micro-scale simulations. The macro-scale solution reproduces with good agreement the averaged solution of the micro-scale simulation, indicating that the homogenization method and the hydrodynamic force closure are suitable for such tube array configurations
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Mistry, Zubin, Venkata Harish Babu Manne, Andrea Vacca, Etienne Dautry, and Martin Petzold. "A numerical model for the evaluation of gerotor torque considering multiple contact points and fluid-structure interactions." Technische Universität Dresden, 2020. https://tud.qucosa.de/id/qucosa%3A71111.
Full textAbstract:
This paper presents a numerical model for the evaluation of the actual torque in Gerotor units. The model consists of two major modules: the pre-processor module and the HYGESim module. The preprocessor module consists of the geometric and the mechanical module. The geometric pre-processor module considers the CAD geometry of Gerotor with tolerances as input and it provides as output the geometric features needed to evaluate the rotor loading and the flow features. The mechanical preprocessor module evaluates the forces of interaction at the contact points between the rotors. The flow displaced by the unit is evaluated using a lumped parameter model whereas the lubricating gaps are evaluated by solving the Reynolds Equation. The main novel aspects consist of the evaluation of the frictional losses at various interfaces. An Elasto-Hydrodynamic Lubrication (EHL) approach is used to evaluate the frictional losses at the contact points between the rotors. Tests on a prototype Gerotor unit are performed for the model validation, particularly as pertains to the features of the shaft torque. Additionally, the paper comments on the distribution of the different torque loss contributions associated with the operation of the unit taken as reference.
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Huang, Zhaoyuan. "Ship-waves modelling and their interactions with inland waterways." Electronic Thesis or Diss., Compiègne, 2022. http://www.theses.fr/2022COMP2686.
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Le sujet de thèse concerne la Modélisation de l’impact de la navigation fluviale sur la voie navigable par les méthodes CFD, en utilisant OpenFoam. Dans la première partie de la thèse, l’hydrodynamique des navires en milieux confinées a été étudiée. Elle consiste en la caractérisation de l’écoulement autour du navire et la génération des vagues de batillage en fonction des caractéristiques géométriques et cinématiques du bateau et également des caractéristiques géométriques du chenal de navigation. Pour cela, une étape de modélisation numérique adaptée à la navigation en milieux confinés, qui concerne le choix du type de maillage, de schéma numérique, etc.., a été élaborée. La deuxième partie est consacrée (i) tout d’abord à la validation et la comparaison des résultats numériques avec les mesures expérimentales en laboratoire du CNR (Compagnie Nationale du Rhône) (ii) ensuite à l’examen de la résistance à l’avancement du bateau suivant différentes configurations géométriques du canal de navigation (largeur, profondeur d’eau, etc.…) (iii) enfin, à la modélisation des processus du Sinkage et du Trim du bateau et à leur influence sur la résistance à l’avancement du bateau. Outre les dimensions géométriques du canal de navigation, l’enfoncement, le tirant d’eau, et la vitesse du bateau ont été également pris en compte pour étudier leur influence sur la résistance à l’avancement. La troisième partie de la thèse est consacrée à l’étude de l’influence des vagues d’étrave et des ondes de batillage générées par le déplacement des bateaux sur les berges des voies navigables et notamment sur la stabilité des blocs de protection des berges. Les blocs forment ici un milieu discret et sont considérés comme des corps rigides susceptibles d’entrer en collision les uns avec les autres et avec les berges. Ainsi, dans cette partie, un modèle de corps rigides à 6 Degrés de Liberté (6DoF), qui tient compte de la forme des blocs, a été utilisé pour (i) tenir compte des processus de contact et de collision solide-solide et solide-bords rigides et pour (ii) étudier la stabilité de la berge, en se basant sur la moyenne des mouvements des blocsThe subject of this thesis concerns the investigation of ship hydrodynamics, shipinduced wave modeling, and wave-bank interactions in restricted waterways by CFD approaches based on OpenFOAM. The first part of this thesis is focused on the study of the hydrodynamics of ships in a restricted environment. This consists of the characterization of the flow around the ship and the generation of waves according to the geometric and kinematic characteristics of the ship and also the geometric characteristics of the waterway channel. To this end, the steps of numerical modeling adapted to navigation in a confined environment, which concern the preference of meshgeneration, numerical schemes, etc., was developed. The second part is devoted (1) first to the validation and comparison of the numerical results with the experimental measurements from the laboratory of the CNR (Compagnie Nationale du Rhône) are carried out; (2) next to the examination of the ship’s forward resistance according to different geometric configurations of the waterway channel (width, water depth, slope, etc.) (3) finally, to the implementation of a six-degree-of-freedom model (6DoF) to assist in the modeling of the sinkage and trim processes of ships in restricted waterways. Meanwhile, the critical effects of ships under different speed conditions in restricted environments were also researched and analyzed. The third part of the thesis deals with the study of the influence of waves induced by ships on the banks of inland waterways and in particular on the stability of the bank protection blocks. The erosion effect caused by the impact and shear of ship-induced waves on the exposed river bank was studied. The armor protection layer on the river bank is composed of discrete blocks and these blocks are regarded as rigid bodies that can collide with each other and with the banks. Thus, in this part, a CFD-DEM solver, SediFoam, was applied to (1) take into account the solid-solid and solid-boundary of domain rigid contact and collision processes and (2) investigate the stability of the rocky layer of banks, based on the average of the movements of the blocks
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El, Alaoui-Faris Yacine. "Modélisation et contrôle optimal de micro-nageurs magnétiques." Thesis, Université Côte d'Azur, 2020. http://www.theses.fr/2020COAZ4094.
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Les micro-nageurs robotiques permettent d'effectuer des opérations à petite échelle telles que l'administration ciblée de médicaments et la chirurgie peu invasive. En raison de la difficulté de miniaturiser des sources d'énergie internes, les méthodes d'actionnement externes sont préférables aux sources intégrées, une stratégie populaire étant l'aimantation du nageur ou d'une de ses parties et son actionnement avec des champs magnétiques externes. L'étude qui suit se concentre sur les micro-nageurs magnétiques flexibles qui imitent les cellules flagellées commeles spermatozoïdes dans leur conception et leur mode de locomotion. Le but decette thèse est d'appliquer des outils numériques de modélisation et de contrôle optimal aux nageurs expérimentaux de l'Institut des Systèmes Intelligents et de Robotique (ISIR) afin d’améliorer leur contrôle et de fournir une méthode numérique pour la conception de commandes pour les micro-nageurs flexibles. La première étape de cette thèse a été le développement d'un modèle dynamique simplifié d'un nageur magnétique flexible en trois dimensions, basé sur une approximation des forces hydrodynamiques et sur la discrétisation de la courbure et de l'élasticité du flagelle. Une identification des paramètres hydrodynamiques et élastiques du modèle permet d'avoir un nageur simulé qui présente les mêmes caractéristiques de propulsion (notamment la réponse fréquentielle du nageur) que celles mesurées expérimentalement. La seconde étape a été d'utiliser le modèle développé pour la résolution numérique du problème de contrôle optimal consistant à de trouver le champ magnétique qui maximise la vitesse de propulsion du nageur sous des contraintes sur la commande reflétant les contraintes physiquement imposées au champ magnétique. La dernière étape a été l'implémentation des champ magnétiques calculés dans le dispositif expérimental de l'ISIR et l'étude de leur performances expérimentales ainsi que de la capacité du modèle à prédire la trajectoire du nageurRobotic micro-swimmers are able to perform small-scale operations such astargeted drug delivery, and minimally invasive medical diagnosis and surgery.However, efficient actuation of these robots becomes more challenging as their size decreases. Hence, wireless actuation is preferable over built-in actuation sources, one of the most popular strategies is the magnetization of parts of the swimmer and its actuation with an external magnetic field. In this thesis, we focus on flexible magnetic micro-swimmers that are similar to spermatozoa in their design and flagellar propulsion. Our goal is to use numerical modeling and optimal control tools to improve the performance of existing swimmers made at the ISIR laboratory (Institut des Systèmes Intelligents et de Robotique) and to propose a numerical control design method for experimental flexible micro-swimmers.Firstly, a simplified 3D dynamic model of a flexible swimmer has been developed, based on the approximation of hydrodynamic forces and the discretization of the curvature and elasticity of the tail of the swimmer. By fitting the hydrodynamic and elastic parameters of our model accordingly, we are able to obtain propulsion characteristics (mainly the frequency response of the swimmer) close to those experimentally measured. Secondly, we numerically solve the optimal control problem of finding the actuating magnetic fields that maximize the propulsion speed of the experimental swimmer under constraints on the control that reflect the constraints physically imposed on the magnetic field. The optimal magnetic fields found via numerical optimization are then implemented in the ISIR experimental setup in order to benchmark the experimental performance of the computed controls and the ability of the model to predict the trajectories of the experimental swimmer
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Chiambaretto, Pierre-Louis. "Modèle vibratoire de réservoir cryotechnique de lanceur : définition d’un méta-matériau équivalent." Thesis, Toulouse, ISAE, 2017. http://www.theses.fr/2017ESAE0022/document.
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L’hydrogène liquide est un ergol utilisé en complément de l’oxygène liquide pour la propulsion de nombreux lanceurs en particulier ceux de la famille Ariane. Cependant, sa dangerosité interdit la réalisation d’essais, en particulier vibratoires, sur des réservoirs remplis. Cette thèse explore une piste d’étude permettant de réaliser ces essais vibratoires sur le réservoir rempli d’un matériau de substitution : un ensemble de billes pré-contraintes. L’objectif est d’obtenir un comportement modal similaire en termes de modes et de fréquences propres à celui du réservoir rempli d’hydrogène liquide pour l’étude des premiers modes. Pour répondre à cet objectif, cette étude est développée en deux parties. Dans la première partie, une approche analytique basée sur une méthode par équivalences fréquentielles est détaillée. Après avoir présenté les grandes lignes de la méthodologie utilisée et l’ensemble des modèles développés, la méthodologie est appliquée au cas étudié expérimentalement de manière à mettre en évidence l’influence des différents paramètres et de proposer une première méthode pour choisir un jeu de billes adapté. La seconde partie, traite principalement des aspects expérimentaux et numériques. Après avoir détaillé la caractérisation des billes utilisées, le montage expérimental conçu et réalisé pour effectuer des essais vibratoires sur un réservoir rempli de billes pré-contraintes est présenté. Les différents résultats obtenus avec ce montage sont étudiés au regard de l’approche analytique, mais aussi de modèles numériques utilisant des éléments-discrets et des éléments-finisLiquid hydrogen is a propellant alternatively used with liquid oxygen for the propulsion of many launchers, especially those of the Ariane family. However, its dangerousness prohibits vibration tests on filled tank. The aim of this PHD is to explore the possibility to carry out such vibration tests by filling these tanks with a substitute material : a set of pre-stressed balls. As further argued and developed in the report, the objective is to obtain a modal behavior similar in term of mode shapes and natural frequencies to those of the tank filled with liquid hydrogen for the first modes. In the first part, an analytical approach based on a method using frequency equivalences is detailed. After presenting the outlines of the methodology used and all the models developed, the methodology is applied to the experimentally studied case in order to highlight the influence of the different parameters as well as then to propose a first method to choose a set of well adapted balls. The second part deals mainly with experimental and numerical aspects. Firstly, the balls used in the thesis are characterized. Then, the experimental set-up designed and realized to carry out vibration tests on a tank filled with pre-stressed balls is presented. The different results obtained are compared with both analytical results and numerical based on discrete-elements and finite-elements results
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Scherrer, Roch. "Analyse du comportement vibro-acoustique de structures immergées excitées par des sources transitoires." Thesis, Lyon, INSA, 2015. http://www.theses.fr/2015ISAL0037/document.
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Dans le cadre de la lutte en mer, la détection acoustique des structures immergées s’effectue généralement sur des signaux stationnaires. Une nouvelle génération de sonars permet de détecter sur des signaux transitoires. Ceci implique de compléter le processus de conception des projets industriels qui ne tient compte d’exigences qu'en matière de bruits rayonnés en régime stationnaire. Il est donc nécessaire de comprendre les mécanismes de transfert des sources de bruit transitoires sur les structures immergées. Cette thèse s’inscrit dans ce cadre et consiste à étudier les mécanismes de transfert vibratoire et de rayonnement acoustique qui peuvent intervenir sur ces structures lorsque l’excitation est transitoire. L’analyse porte sur différents éléments de la chaine de transfert : le rayonnement dans l’eau du bordé, la diffraction des ondes par les raidisseurs, et le comportement résonnant des structures internes supportant les matériels. Le premier chapitre présente une analyse bibliographique autour de l’étude des phénomènes vibroacoustiques transitoires des structures immergées, de l’influence d’un fluide lourd sur le comportement vibroacoustique des plaques, et des méthodes de calcul vibroacoustiques en régime transitoire. Dans le second chapitre nous étudions la réponse transitoire d’une plaque infinie immergée soumise à une force impulsionnelle ponctuelle. La méthode de calcul s’appuie sur les calculs spectraux fréquences-nombre d’onde. Les réponses temporelles sont obtenues par transformées de Fourier inverses. L’analyse des spectres et des réponses temporelles de l’accélération vibratoire de la plaque et de la pression rayonnée, met en évidence l’influence de la présence du fluide. La prise en compte de l’inertie rotationnelle et du cisaillement à travers le modèle de plaque de Mindlin-Timoshenko est également étudiée. Ces résultats sont confrontés à une expérimentation présentée dans le troisième chapitre. La structure étudiée est une plaque rectangulaire posée horizontalement à la surface d’une cuve remplie d’eau. Deux types de sources transitoires sont utilisés : marteau de choc, lâché d’une bille. La comparaison des résultats numériques et expérimentaux montre que l’on retrouve certains phénomènes évoqués précédemment. L’effet des raidisseurs sur le rayonnement acoustique fait l’objet du quatrième chapitre. Une plaque raidie périodiquement dans une direction est considéré. L’influence des ondes de Bloch-Floquet sur la réponse temporelle est étudiée. Les résultats sont comparés à des mesures effectuées sur une barge d’essais. Dans le cinquième chapitre, l’effet des structures internes est étudié à partir d’un modèle de plaque couplé à un système résonnant constitué d’un assemblage poutre-plaque. La méthode des inertances est utilisée pour obtenir les forces de couplage entre les différents éléments. Les signaux temporels sont étudiés en fonction de l’importance de la rupture d’inertance entre la plaque et l’assemblageIn the sea, the acoustic detection of other battle engines is done by detecting mostly stationary signals. However, new types of detection systems are being developed, and are able to detect and to analyze transient signals. Therefore, the industrial conception process needs to be improved, so that the underwater vehicles transient noises can be taken in account. In order to do so, the mechanism of vibroacoustic transfer of transient sources of submerged structures has to be understood. The object of this thesis is then the study of the mechanism of vibration transfer and acoustic radiation of those structures when they are excited by transient sources. The shell radiation in the water, the wave diffraction by circumferential stiffeners and the resonant behavior of internal substructures are analyzed. The first chapter presents the bibliographical study of three themes: the study of transient phenomenon of submerged structures, the influence of heavy fluid coupling on vibroacoustic behavior of plates, and the different calculation methods in transient vibroacoustics. In the second chapter, we study the transient response of a submerged infinite plate excited by an impulsively point force. First, the calculations are done in the wavenumber-frequency domain. Then the spatio-temporal responses are obtained using inverse Fourier transforms. The discretization of wavenumber and frequency domains and the damping model are studied. The analysis of frequency and time responses of the plate vibration and the radiated pressure enable us to observe the influence of heavy fluid coupling. Besides the Mindlin-Timoshenko plate model is also used and the effect of rotation inertia and shear stress are studied. In the third chapter, these numerical results are confronted to experimental data, obtained experimentally. The studied structure is a rectangular plate lying on the surface of a water tank. Two different excitations are used: an impact hammer and the free fall of a steel ball. The study of the correlation between numerical and experimental results showed that some phenomena are observed in both cases. The influence of stiffeners on the acoustic radiation is the theme of the fourth chapter. An infinite plate which is periodically stiffened through one direction is considered. The effect of Bloch-Floquet waves on time response is studied. Numerical results are compared to measurements data obtained on an industrial submerged structure. In the fifth chapter, the effect of internal structures is analyzed by modelling an infinite plate coupled to a resonant system made of a beam and a rectangular finite plate. The inertance coupling method is used to obtain the coupling forces between the different substructures. Influence of inertance difference between the substructures is illustrated by the time signals
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Fontenier, Benoît. "Contribution à la modélisation biofidèle de l’être humain par la prise en compte des interactions fluide-structure." Thesis, Valenciennes, 2016. http://www.theses.fr/2016VALE0020/document.
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Ces travaux visent à améliorer la biofidélité des modèles virtuels de l’être Humain. Les statistiques montrent que la tête humaine est fréquemment sujette à des traumatismes cérébraux, des lésions et autres blessures. Une attention particulière sera donc donnée à la modélisation de la tête. Afin de mieux prédire les mécanismes lésionnels de la tête, la biofidélite des modèles doit être améliorée, pour cela les effets du fluide situé à l’intérieur de la tête doivent être pris en compte. Cependant, la modélisation des interactions entre un fluide corporel visqueux et un matériau mou comme le cerveau reste un verrou scientifique. Il est proposé d’étudier en détail la modélisation des interactions fluide-structure entre un fluide et un corps mou. Premièrement, une étude bibliographique détaillée sur les méthodes numériques de modélisation des interactions fluides-structure a permis d’évaluer chacune d’elles et de juger de celle qui est la mieux adaptée pour la résolution de la problématique. Deuxièmement, lors de travaux de thèse précédents, une expérience a été réalisée montrant l’influence du liquide cérébrospinal sur la cinématique du cerveau lors d’un chargement dynamique. Cette expérience est utilisée dans un premier temps pour caractériser numériquement le gel silicone Sylgard 527 utilisé comme substitut de cerveau. Dans un second temps des méthodes de couplage partitionné disponible dans le code commercial LS-Dyna ICFD sont utilisées pour modéliser l’expérience. Bien que les modèles de gel précédemment caractérisés ont été utilisés, la version avec fluide n’a pas pu être modélisée avec succès. Troisièmement, un code de couplage partitionné est donc développé. Il consiste en un middleware écrit en C++ couplant deux codes éprouvés, OpenFOAM et LS-Dyna pour la modélisation du fluide et du solide respectivement. De plus, parce que très peu d’essais expérimentaux utilisables pour la validation de code d’interaction fluide-structure sont disponibles dans la littérature, une expérience permettant cela a été réalisée dans une soufflerie. La comparaison des prédictions numériques avec les résultats expérimentaux est prometteuse et donne des résultats globaux satisfaisants. Les points qui ne peuvent pas être validés nécessitent de plus amples investigations et permettront d’améliorer les techniques de modélisations et le développement du codeThe purpose of this work is to improve the biofidelity of the human body models. The work is focused on the human head as it is one of the most injured part. In order to improve the traumatic brain injury onset and mechanism, the biofidelity of the head models has to be increased, thus, the fluids embedded inside the head has to be taken into account. Nevertheless, the modelling of the interactions occurring between the viscous corporal fluids and the soft matter as the brain remains a challenge. This study intends to investigate the fluid-structure interactions between a soft structure and a fluid. Firstly, in order to found the most relevant methods to solve the problem, a deep literature survey has pointed-out all the numerical methods available nowadays. Secondly, in a previous PhD work an experimental test has been carried-out to demonstrate the influence of the cerebrospinal fluid on the brain kinematics under dynamical load case. On one hand, the Silicon Sylgard 527 gel used as brain substitut has been characterized . Subsequently the partitioned coupling methods available in LS-Dyna ICFD have been assessed to model the experiment. Although, the previous characterized gel model has been used, the experiment has been unsuccessfully completed. Accordingly, it has been decided to develop an in-house coupling code. Thirdly, a partitioned coupling code has been developed. It is a middleware in C++ between two well establishing solvers OpenFOAM and LS-Dyna respectively for the fluid and the solid. Because there is very few experimental tests for the coupling code validation, it has been carried-out in this work a fluid-structure interaction experiment involving a soft plate in a wind channel. This appealing experiment allows the scientific community to validate easily their coupling algorithms. Subsequently, the developed coupling code is used to model the wind channel. The results depict a good overall agreement between the experiment and the simulation. Nonetheless, in order to get validated results further investigation are required mainly about the flow modelling
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Tibba, Getachew Shunki Verfasser], Holm [Akademischer Betreuer] [Altenbach, and Eckehard [Akademischer Betreuer] Specht. "Modeling the inelastic behavior of heat exchangers accounting for fluid-structure interactions / Getachew Shunki Tibba. Betreuer: Holm Altenbach ; Eckehard Specht." Magdeburg : Universitätsbibliothek, 2013. http://d-nb.info/1054637709/34.
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