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1
Mawson, Mark. "Interactive fluid-structure interaction with many-core accelerators." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/interactive-fluidstructure-interaction-with-manycore-accelerators(a4fc2068-bac7-4511-960d-41d2560a0ea1).html.
Testo completoAbstract (sommario):
The use of accelerator technology, particularly Graphics Processing Units (GPUs), for scientific computing has increased greatly over the last decade. While this technology allows larger and more complicated problems to be solved faster than before it also presents another opportunity: the real-time and interactive solution of problems. This work aims to investigate the progress that GPU technology has made towards allowing fluid-structure interaction (FSI) problems to be solved in real-time, and to facilitate user interaction with such a solver. A mesoscopic scale fluid flow solver is implemented on third generation nVidia ‘Kepler’ GPUs in two and three dimensions, and its performance studied and compared with existing literature. Following careful optimisation the solvers are found to be at least as efficient as existing work, reaching peak efficiencies of 93% compared with theoretical values. These solvers are then coupled with a novel immersed boundary method, allowing boundaries defined at arbitrary coordinates to interact with the structured fluid domain through a set of singular forces. The limiting factor of the performance of this method is found to be the integration of forces and velocities over the fluid and boundaries; the arbitrary location of boundary markers makes the memory accesses during these integrations largely random, leading to poor utilisation of the available memory bandwidth. In sample cases, the efficiency of the method is found to be as low as 2.7%, although in most scenarios this inefficiency is masked by the fact that the time taken to evolve the fluid flow dominates the overall execution time of the solver. Finally, techniques to visualise the fluid flow in-situ are implemented, and used to allow user interaction with the solvers. Initially this is achieved via keyboard and mouse to control the fluid properties and create boundaries within the fluid, and later by using an image based depth sensor to import real world geometry into the fluid. The work concludes that, for 2D problems, real-time interactive FSI solvers can be implemented on a single laptop-based GPU. In 3D the memory (both size and bandwidth) of the GPU limits the solver to relatively simple cases. Recommendations for future work to allow larger and more complicated test cases to be solved in real-time are then made to complete the work.
2
Altstadt, Eberhard, Helmar Carl, and Rainer Weiß. "Fluid-Structure Interaction Investigations for Pipelines." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28993.
Testo completoAbstract (sommario):
The influence of the fluid-structure interaction on the magnitude fo the loads on pipe walls and support structures is not yet completely understood. In case of a dynamic load caused by a pressure wave, the stresses in pipe walls, especially in bends, are different from the static case.
3
Plessas, Spyridon D. "Fluid-structure interaction in composite structures." Thesis, Monterey, California: Naval Postgraduate School, 2014. http://hdl.handle.net/10945/41432.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimited.<br>In this research, dynamic characteristics of polymer composite beam and plate structures were studied when the structures were in contact with water. The effect of fluid-structure interaction (FSI) on natural frequencies, mode shapes, and dynamic responses was examined for polymer composite structures using multiphysics-based computational techniques. Composite structures were modeled using the finite element method. The fluid was modeled as an acoustic medium using the cellular automata technique. Both techniques were coupled so that both fluid and structure could interact bi-directionally. In order to make the coupling easier, the beam and plate finite elements have only displacement degrees of freedom but no rotational degrees of freedom. The fast Fourier transform (FFT) technique was applied to the transient responses of the composite structures with and without FSI, respectively, so that the effect of FSI can be examined by comparing the two results. The study showed that the effect of FSI is significant on dynamic properties of polymer composite structures. Some previous experimental observations were confirmed using the results from the computer simulations, which also enhanced understanding the effect of FSI on dynamic responses of composite structures.
4
Randall, Richard John. "Fluid-structure interaction of submerged shells." Thesis, Brunel University, 1990. http://bura.brunel.ac.uk/handle/2438/5446.
Testo completoAbstract (sommario):
A general three-dimensional hydroelasticity theory for the evaluation of responses has been adapted to formulate hydrodynamic coefficients for submerged shell-type structures. The derivation of the theory has been presented and is placed in context with other methods of analysis. The ability of this form of analysis to offer an insight into the physical behaviour of practical systems is demonstrated. The influence of external boundaries and fluid viscosity was considered separately using a flexible cylinder as the model. When the surrounding fluid is water, viscosity was assessed to be significant for slender structural members and flexible pipes and in situations where the clearance to an outer casing was slight. To validate the three-dimensional hydroelasticity theory, predictions of resonance frequencies and mode shapes were compared, with measured data from trials undertaken in enclosed tanks. These data exhibited differences due to the position of the test structures in relation to free and fixed boundaries. The rationale of the testing programme and practical considerations of instrumentation, capture and storage of data are described in detail. At first sight a relatively unsophisticated analytical method appeared to offer better correlation with the measured data than the hydroelastic solution. This impression was mistaken, the agreement was merely fortuitous as only the hydroelastic approach is capable of reproducing-the trends recorded in the experiments. The significance of an accurate dynamic analysis using finite elements and the influence of physical factors such as buoyancy on the predicted results are also examined.
5
Giannopapa, Christina-Grigoria. "Fluid structure interaction in flexible vessels." Thesis, King's College London (University of London), 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413425.
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6
Wright, Stewart Andrew. "Aspects of unsteady fluid-structure interaction." Thesis, University of Cambridge, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.621939.
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7
Altstadt, Eberhard, Helmar Carl, and Rainer Weiß. "Fluid-Structure Interaction Investigations for Pipelines." Forschungszentrum Rossendorf, 2003. https://hzdr.qucosa.de/id/qucosa%3A21726.
Testo completoAbstract (sommario):
The influence of the fluid-structure interaction on the magnitude fo the loads on pipe walls and support structures is not yet completely understood. In case of a dynamic load caused by a pressure wave, the stresses in pipe walls, especially in bends, are different from the static case.
8
Holder, Justin. "Fluid Structure Interaction in Compressible Flows." University of Cincinnati / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=ucin159584692691518.
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9
Paton, Jonathan. "Computational fluid dynamics and fluid structure interaction of yacht sails." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/14036/.
Testo completoAbstract (sommario):
This thesis focuses on the numerical simulation of yacht sails using both computational fluid dynamics (CFD) and fluid structure interaction (FSI) modelling. The modelling of yacht sails using RANS based CFD and the SST turbulence model is justified with validation against wind tunnel studies (Collie, 2005; Wilkinson, 1983). The CFD method is found to perform well, with the ability to predict flow separation, velocity and pressure profiles satisfactorily. This work is extended to look into multiple sail interaction and the impact of the mast upon performance. A FSI solution is proposed next, coupling viscous RANS based CFD and a structural code capable of modelling anistropic laminate sails (RELAX, 2009). The aim of this FSI solution is to offer the ability to investigate sails' performance and flying shapes more accurately than with current methods. The FSI solution is validated with the comparison to flying shapes of offwind sails from a bespoke wind tunnel experiment carried out at the University of Nottingham. The method predicted offwind flying shapes to a greater level of accuracy than previous methods. Finally the CFD and FSI solution described here above is showcased and used to model a full scale Volvo Open 70 racing yacht, including multiple offwind laminate sails, mast, hull, deck and twisted wind profile. The model is used to demonstrate the potential of viscous CFD and FSI to predict performance and aid in the design of high performance sails and yachts. The method predicted flying shapes and performance through a range of realistic sail trims providing valuable data for crews, naval architects and sail designers.
10
Gregson, James. "Fluid-structure interaction simulations in liquid-lead." Thesis, University of British Columbia, 2009. http://hdl.handle.net/2429/12340.
Testo completoAbstract (sommario):
An Eulerian compressible flow solver suitable for simulating liquid-lead flows involving fluid-structure interaction, cavitation and free surfaces was developed and applied to investigation of a magnetized target fusion reactor concept. The numerical methods used and results of common test cases are presented. Simulations were then performed to assess the smoothing properties of interacting mechanically generated shocks in liquid lead, as well as the early-time collapse behavior of cavities due to free surface reflection of such shocks. An empirical formula to estimate shock smoothness based on the shock smoothing results is presented, and issues related to shock driven cavity collapse in liquid liner magnetized target fusion reactors are presented and discussed.
11
Blair, Stuart R. "Lattice Boltzmann Methods for Fluid Structure Interaction." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/17325.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimited<br>The use of lattice Boltzmann methods (LBM) for fluid flow and its coupling with finite element method (FEM) structural models for fluid-structure interaction (FSI) is investigated. A body of high performance LBM software that exploits graphic processing unit (GPU) and multiprocessor programming models is developed and validated against a set of two- and three-dimensional benchmark problems. Computational performance is shown to exceed recently reported results for single-workstation implementations over a range of problem sizes. A mixed-precision LBM collision algorithm is presented that retains the accuracy of double-precision calculations with less computational cost than a full double-precision implementation. FSI modelling methodology and example applications are presented along with a novel heterogeneous parallel implementation that exploits task-level parallelism and workload sharing between the central processing unit (CPU) and GPU that allows significant speedup over other methods. Multi-component LBM fluid models are explicated and simple immiscible multi-component fluid flows in two-dimensions are presented. These multi-component fluid LBM models are also paired with structural dynamics solvers for two-dimensional FSI simulations. To enhance modeling capability for domains with complex surfaces, a novel coupling method is introduced that allows use of both classical LBM (CLBM) and a finite element LBM (FELBM) to be combined into a hybrid LBM that exploits the flexibility of FELBM while retaining the efficiency of CLBM.
12
Nitikitpaiboon, Chanwut. "Finite element formulations for fluid-structure interaction." Thesis, Massachusetts Institute of Technology, 1993. http://hdl.handle.net/1721.1/37500.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1993.<br>Includes bibliographical references (leaves 123-128).<br>by Chanwut Nitikitpaiboon.<br>Ph.D.
13
Mullaert, Jimmy. "Numerical methods for incompressible fluid-structure interaction." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066683/document.
Testo completoAbstract (sommario):
Cette thèse présente une famille de schémas explicites pour la résolution d'un problème couplé d'interaction entre un fluide visqueux incompressible et une structure élastique (avec possiblement un comportement visco-élastique et/ou non linéaire). La principale propriété de ces schémas est une condition de Robin consistante à l'interface, qui représente une caractéristique fondamentale du problème continu dans le cas où la structure est mince. Si le couplage s'effectue avec une structure épaisse, une condition de Robin généralisée peut être formulée pour le problème semi-discret en espace, à l'aide d'une condensation de la matrice de masse de la structure. Une deuxième caractéristique majeure de ces schémas est la capacité d'obtenir une condition de Robin qui intègre à la fois des extrapolations de la vitesse et des efforts du solide (donnant lieu à un schéma de couplage explicite), mais également un traitement implicite de l'inertie de la structure, qui rend le schéma stable quelle que soit l'intensité de l'effet de masse ajoutée. Un résultat général de stabilité et de convergence est présenté pour tous les ordres d'extrapolations dans un cadre linéaire représentatif. On montre, en particulier, que les propriétés de stabilité se conservent lorsque le couplage s'effectue avec une structure mince ou épaisse. En revanche, la précision optimale obtenue dans le cas d'une structure mince n'est pas retrouvée avec une structure épaisse. L'erreur introduite par le schéma de couplage comporte en effet une non-uniformité en espace, qui provient de la non-uniformité des reconstructions discrètes des opérateurs viscoélastiques. L'approximation induite par la condensation de la matrice de masse solide n'est pas responsable de cette non-uniformité. À partir de ce schéma,on propose également des méthodes itératives pour la résolution du schéma fortement couplé.La convergence de cette méthode est démontrée dans un cadre linéaire et ne montre pas de sensibilité à l'effet de masse ajoutée. Finalement, les résultats théoriques obtenus sont illustrés par des exemples numériques variés, dans les cas linéaire et non linéaire<br>This thesis introduces a class of explicit coupling schemes for the numerical solution of fluid-structure interaction problems involving a viscous incompressible fluid and a general elastic structure (thin-walled or thick-walled, viscoelastic and non-linear).The first fundamental ingredient of these methods is the notion of interface Robin consist encyon the interface. This is an intrinsic (parameter free) feature of the continuous problem, in the case of the coupling with thin-walled solids. For thick-walled structures, we show that an intrinsic interface Robin consistency can also be recovered at the space semi-discrete level, using a lumped-mass approximation in the structure.The second key ingredient of the methods proposed consists in deriving an explicit Robin interface condition for the fluid, which combines extrapolations of the solid velocity and stresses with an implicit treatment of the solid inertia. The former enables explicit coupling,while the latter guarantees added-mass free stability. Stability and error estimates are provided for all the variants (depending on the extrapolations), using energy arguments within a representative linear setting. We show, in particular, that the stability properties do not depend on the thin- or thick-walled nature of the structure. The optimal first-order accuracy obtained in the case of the coupling with thin-walled structuresis, however, not preserved when the structure is thick-walled, due to the spatial non uniformityof the splitting error. The genesis of this problem is the non-uniformity of the discrete viscoelastic operators, related to the thick-walled character of the structure,and not to the mass-lumping approximation. Based on these splitting schemes, new, parameter-free, Robin-Neumann iterative procedures for the partitioned solution of strong coupling are also proposed and analyzed. A comprehensive numerical study, involving linear and non linear models, confims the theoretical findings reported in this thesis
14
Andersson, Christoffer, and Daniel Ahl. "Fluid Structure Interaction: Evaluation of two coupling techniques." Thesis, Högskolan i Halmstad, Sektionen för Informationsvetenskap, Data– och Elektroteknik (IDE), 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:hh:diva-16050.
Testo completoAbstract (sommario):
This thesis concerns one of the upcoming and well discussed subjects withincalculations these days, namely how to perform an analysis of the interactionbetween fluid and structure, called FSI (Fluid Structure Interaction). In the report,evaluations of two different methods of simulating FSI are done. These are knownas Practical FSI (P-FSI) and Direct Coupled FSI (DC-FSI). The methods aredeveloped by Acusim in cooperation with Simulia and the softwares used areAbaqus and AcuSolve.The first part of the thesis is dedicated to explain the general theory and thegoverning equations for FSI. After the general explanation a more delimitatedexplanation regarding P-FSI and DC-FSI are given. After this we show how tosetup and perform the couplings regarding which parameters that need to bedefined and how to perform the analyses using Abaqus and AcuSolve.The last section of the thesis covers the evaluation process. We started withevaluating the methods against a benchmark problem where we compared thecalculation time and accuracy regarding displacements and frequencies. The nextthing we evaluated was how different numbers of modes used in the P-FSIcoupling affects the result. The last thing we evaluated was the robustness of themethods using different mass densities of the structure and different time-stepsizes.The result of the evaluation regarding the criteria: accuracy, calculation time androbustness showed that the P-FSI method is the most efficient method comparedto DC-FSI regarding FSI problems when the structural response is linear.
15
Hamdan, Fadi. "Finite element solutions for transient fluid-structure interaction." Thesis, Imperial College London, 1993. http://hdl.handle.net/10044/1/8119.
Testo completoAbstract (sommario):
The objective of this thesis is to develop numerical tools capable of modelling the nonlinear behaviour of bounded and unbounded transient fluid-structure interaction systems. Towards this end, a numerical approach based on the finite element method was developed and implemented into a general purpose computer program ASAS-NL. Four main developments are reported: (i) The Mixed-Eulerian-Lagrangian description of the continuum has been developed to account for the nonlinear effects of fluid-structure interaction systems and a mesh rezoning scheme derived to be used with it. In addition a predictor-multi-corrector time marching scheme has been used for nonlinear dynamic analysis and implicit temporal integration schemes based on Newmark and a-Bossak methods have been reviewed and implemented. Nonlinear iterative schemes based on the Modified Newton Raphson and full Newton Raphson methods have also been included. (ii) Two-dimensional and axi-symmetric fluid finite elements were developed. The elements are compatible with the Mixed-Eulerian-Lagrangian description of the continuum. In addition the free surface gravity wave (sloshing effect) has been addressed. The purpose of these elements is to model the bounded fluid medium in fluid-structure interaction problems. (iii) Two-dimensional and axi-symmetric Mixed-Eulerian-Lagrangian four-noded sliding interface elements have been developed. The purpose of these elements is to prevent artificial penetration of the fluid into the structure during analysis of fluid-structure interaction problems. (iv) A non-radiating boundary has been developed. This is to be used for modelling the unbounded fluid medium in fluid-structure interaction problems. Furthermore, numerical techniques for modelling shock waves were reviewed and included in the analysis. This new analytical formulation has been applied to several problems for which solutions are available to prove its versatility, accuracy and efficiency and has been shown to give satisfactory results for the cases examined.
16
Jeans, Richard. "Innovative methods for three dimensional fluid-structure interaction." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/8189.
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Lea, Patrick D. "Fluid Structure Interaction with Applications in Structural Failure." Thesis, Northwestern University, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3605735.
Testo completoAbstract (sommario):
<p> Methods for modeling structural failure with applications for fluid structure interaction (FSI) are developed in this work. Fracture as structural failure is modeled in this work by both the extended finite element method (XFEM) and element deletion. Both of these methods are used in simulations coupled with fluids modeled by computational fluid dynamics (CFD). The methods presented here allow the fluid to pass through the fractured areas of the structure without any prior knowledge of where fracture will occur. Fracture modeled by XFEM is compared to an experimental result as well as a test problem for two phase coupling. The element deletion results are compared with an XFEM test problem, showing the differences and similarities between the two methods. </p><p> A new method for modeling fracture is also proposed in this work. The new method combines XFEM and element deletion to provide a robust implementation of fracture modeling. This method integrates well into legacy codes that currently have element deletion functionality. The implementation allows for application by a wide variety of users that are familiar with element deletion in current analysis tools. The combined method can also be used in conjunction with the work done on fracture coupled with fluids, discussed in this work. </p><p> Structural failure via buckling is also examined in an FSI framework. A new algorithm is produced to allow for structural subcycling during the collapse of a pipe subjected to a hydrostatic load. The responses of both the structure and the fluid are compared to a non-subcycling case to determine the accuracy of the new algorithm. </p><p> Overall this work looks at multiple forms of structural failure induced by fluids modeled by CFD. The work extends what is currently possible in FSI simulations.</p>
18
Violette, Michael A. "Fluid structure interaction effect on sandwich composite structures." Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5533.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimited.<br>The objective of this research is to examine the fluid structure interaction (FSI) effect on composite sandwich structures under a low velocity impact. The primary sandwich composite used in this study was a 6.35-mm balsa core and a multi-ply symmetrical plain weave 6 oz E-glass skin. The specific geometry of the composite was a 305 by 305 mm square with clamped boundary conditions. Using a uniquely designed vertical drop-weight testing machine, there were three fluid conditions in which these experiments focused. The first of these conditions was completely dry (or air) surrounded testing. The second condition was completely water submerged. The final condition was a wet top/air-backed surrounded test. The tests were conducted progressively from a low to high drop height to best conclude the onset and spread of damage to the sandwich composite when impacted with the test machine. The measured output of these tests was force levels and multi-axis strain performance. The collection and analysis of this data will help to increase the understanding of the study of sandwich composites, particularly in a marine environment.
19
Skelton, E. A. "Some mixed boundary problems of fluid-structure interaction." Thesis, Imperial College London, 1989. http://hdl.handle.net/10044/1/47663.
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Boyd, Alistair Richard. "Fluid-structure interaction under fast transient dynamic events." Thesis, University of Edinburgh, 1999. http://hdl.handle.net/1842/10835.
Testo completoAbstract (sommario):
Underwater explosive loading resulting from rapid phase transitions (RPT's) is one example of a fast transient dynamic event. The leakage of substances such as LPG or LNG when stored underwater can cause an RPT. These substances are often stored in a combination of very low temperatures and high pressures with respect to the surrounding fluid (seawater) and their leakage can cause the equivalent of an underwater explosion. Such containers are usually found to be part of a much larger 'storage field' of containers. An RPT occurring in one container will cause underwater explosive loading on neighbouring containers. By simulating an RPT using explosive charges experiments were initially designed using theoretical and empirical techniques. The fluid and structural response of a prototype container subject to symmetric and axisymmetric underwater explosive (UNDEX) loading was then examined experimentally. Theoretical predictions using the finite element hydrocode LS-DYNA and boundary element code USA-DYNA3D were undertaken and compared with experimental observations. Several non-destructive techniques were employed to estimate dynamic collapse buckling criteria from both experimental and theoretical results. The experimental work concluded that the critical regions of the prototype container were the apex and the base under both forms of loading. The quality of the numerical predictions varied dependent on the form of the loading. In some cases the fluid and structural responses were overpredicted, and in others underpredicted. Within the limitations of these numerical procedures it was possible to predict a conservative estimate of a critical charge size under axisymmetric UNDEX loading using LS-DYNA. The critical stand off distance was also estimated from experimental results under symmetric UNDEX loading. The use of numerical approaches to predict fluid-structure interaction as successful for the shock phase of an underwater loading and both LS-DYNA and USA-DYnA3D have been validated for shock loading. Bubble loading simulations proved unsuccessful. Suggested improvements are proposed to increase the application of, and enhance the reliability of, the techniques used in this work.
21
Ridzon, Matthew C. "Quantifying Cerebellar Movement With Fluid-Structure Interaction Simulations." University of Akron / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=akron1590752448366714.
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Ramirez, Villalba Leidy catherine. "Towards an efficient modeling of Fluid-Structure Interaction." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0029.
Testo completoAbstract (sommario):
Les applications industrielles FSI se caractérisent par des géométries et des matériaux complexes. Afin de prédire avec précision leur comportement, des coûts de calcul élevés sont associés, à la fois en temps et en ressources informatiques. Pour améliorer la qualité de la prédiction sans pénaliser le temps de calcul, et pour réduire le temps de calcul sans impacter la précision disponible aujourd'hui, deux axes principaux sont explorés dans ce travail. Le premier est l'étude d'un algorithme asynchrone qui pourrait permettre l'utilisation de modèles structurels complexes. Le second consiste à étudier la méthode des tranches en combinant l'utilisation d'un modèle RANS et d'un modèle FEM non linéaire. D'une part, l'étude de l'asynchronicité dans le domaine FSI a révélé différents aspect d'intérêt qui doivent être approfondis avant que l'approche puisse être utilisée industriellement. Cependant, un premier traitement des points mentionnés ci-dessus a montré des signe d'amélioration qui pourraient conduire à un algorithme prometteur, qui se situe naturellement entre l'algorithme explicite et l'algorithme implicite. D'autre part, il a été montré que la méthode des tranches développée dans ce travail conduit à une réduction significative du temps de calcul sans dégradation de la précision<br>FSI industrial applications are often described by complex geometries and materials. In order to accurately predict their behavior, high computational costs are associated, both in time and in computational resources. To improve the quality of the prediction without penalizing the computational time, and to reduce the computational time without impacting the accuracy that is available today, two main axes are explored in this work. The first one is the study of an asynchronous algorithm that could allow the use of complex structural models. The second axis consists of the study of the strip method while combining the use of a RANS model and a non-linear FEM model. On the one hand, the study of asynchronicity in the FSI domain revealed different aspects of interest that must be addressed before the approach can be used industrially. However, a first treatment of the limitations found showed signs of an improvement that could lead to a promising algorithm, one that naturally lies between the implicit external algorithm and the implicit internal algorithm. On the other hand, it was shown that the strip method developed in this work achieves a significant reduction in calculation time while maintaining excellent accuracy
23
Avcu, Mehmet. "Fluid-structure interaction effects resulting from hull appendage coupling." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Sep%5FAvcu.pdf.
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Tello, Guerra Alexis. "Fluid structure interaction by means of reduced order models." Doctoral thesis, Universitat Politècnica de Catalunya, 2020. http://hdl.handle.net/10803/669328.
Testo completoAbstract (sommario):
The standard Fluid Structure Interaction coupling (velocity--pressure/displacement) is compared against two novel types of coupling, a Two Field coupling (velocity--pressure/displacement--pressure) and a Three Field coupling (velocity--pressure--stress/displacement--pressure--stress) in this way completing our set of, what we call, field to field equations, all stabilized by means of the VMS method using dynamic and orthogonal sub-scales. The solid Two field fluid structure interaction coupling formulation is benchmarked statically and dynamically. POD is applied to all three fluid structure interaction formulations to obtain reduced basis and asses their performance in a reduced space. Usual numerical benchmarks are shown comparing all three formulations. The three field fluid structure interaction coupling proves to provide very accurate results in both FOM and ROM spaces, making it a reliable formulation. Field to field pairing appears to be beneficial providing more accurate results in all cases shown.
A reduced order model designed by means of a variational multi-scale method stabilized formulation has been applied successfully to fluid structure interaction problems in a strongly coupled partitioned solution scheme. Details of the formulation and the implementation both for the interaction problem and for the reduced models, for both the off-line and on-line phases, are shown. Results are obtained for cases in which both domains are reduced at the same time. Numerical results are presented for a semi-stationary and a fully transient case.<br>El acople estandar para casos de Interacción Fluido Estructura (Velocidad-Presión/Desplazamiento) se compara contra dos nuevas formas de acople, el primero de Dos Campos (Velocidad-Presión/Desplazamiento-Presión) y el segundo de Tres Campos (Velocidad-Presión-Esfuerzo/Desplazamiento-Presión-Esfuerzo) de esta forma completando lo que se ha llamado acoplamiento de Campo a Campo, todo estabilizado por medio del método VMS usando sub-escalas dínamicas y ortogonales. Se hacen comprobaciones estáticas y dínamicas para las dos nuevas formulaciones de sólidos (Dos y Tres campos). Se utiliza POD para obtener una base reducida y verificar el comportamiento de dichas formulaciones en el espacio reducido. La formulacion de Tres Campos resulta ser la mas precisa produciendo los resultados mas exactos tanto para los espacios FOM y ROM. La formulacion de Campo a Campo resulta ser beneficiosa al producir los resultados mas exactos en todas las pruebas realizadas.
Un modelo estabilizado de orden reducido por medio del método de VMS ha sido aplicado satisfactoriamente a problemas de Interacción Fluido-Estructura en un modelos particionado de acople fuerte. Se muestran detalles de la formulación y su implementación tanto para casos de Interacción como para Problemas Reducidos para las fases de cálculo de base y ejecución del modelo. Se han obtenido resultados para problemas de Interacción en el cual se reducen ambos dominios al mismo tiempo. Se presentan resultados numéricos para ejemplos semi-transitorios y totalmente dinámicos.
25
Lee, Wee Siang. "Exterior domain decomposition method for fluid-structure interaction problems." Thesis, Imperial College London, 1999. http://hdl.handle.net/10044/1/8533.
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Franco, Flavio Jose Borges Fortes. "Finite element analysis of fluid-structure interaction in turbomachines." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/7913.
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Eeg, Thomas Bertheau. "Fluid Structure Interaction Simulation on an Idealized Aortic Arch." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for konstruksjonsteknikk, 2012. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-19319.
Testo completoAbstract (sommario):
The aortic arch is at risk of several cardiovascular diseases, such as aortic dissection. Many of these risk factors are due to the fluid-structure interaction that occurs in the aorta. Fluid-structure interation (FSI) simulations are a very useful tool in identifying these risks. The goal of this study is to obtain a simplified picture of healthy physiological flow and lay the foundation for further studies on cardiovascular diseases in the aortic arch. A 3-dimensional idealized FSI model of the aorta was constructed from measurements found in the literature. This model was simulated using the commerical codes Abaqus and Ansys Fluent, coupled with the in-house code Tango. Attempts at simulating the model geometry including the braciocephalic, left common and left subclavian carotid arteries were unsuccesful, so a simlified model of only the aortic arch was simulated. Emphasis was placed on the investigation of different boundary conditions. An imposed massflow condition, a pressure condition with resistance or a varying elastance model was set on the inlet and combined with zero pressure, reflection free or Windkessel outlet boundaries. The mass flow inlet with Windkessel outlet gave the most reliable results since the other inlets were mostly incomplete approximations. No conclusion could be drawn on the viability of Ansys Workbench as a meshing utility for studies using Tango, due to lack of information.
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Seddon, Caroline Michelle. "Modelling transient dynamic fluid-structure interaction in aerospace applications." Thesis, University of Salford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492434.
Testo completoAbstract (sommario):
Although significant progress has been made in the study of dynamic loading of aircraft structures, several areas have been identified that require further research. In particular, attention is drawn to problems involving transient, dynamic fluid-structure interaction, where fluids play an important role, heavily influencing the response of the structure to the applied dynamic load. In this work the use of existing numerical modelling techniques for the evaluation of such problems is investigated.
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He, Tao. "Hybrid interface conditions for partitioned fluid-structure interaction simulations." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8650/.
Testo completoAbstract (sommario):
This thesis proposes the combined interface boundary condition (CIBC) method for fluid-structure interaction (FSI) within the arbitrary Lagrangian-Eulerian finite element framework. The CIBC method employs a Gauss-Seidel-like procedure to transform the traditional interface conditions into the velocity and traction corrections in a mixed manner. A free parameter is adopted to control the effect of such a treatment on the interface. Nevertheless, the restricted use of the CIBC method is realized after recalling its recent development. Then the thorough derivation of the CIBC method are presented, providing the principle of two improved formulations of the method. The improvements are established as: (i) the method is reformulated by using the complete fluid stress tensor; (ii) the structural traction rate is eliminated via a simple revision; (iii) we analyze the instability source due to the CIBC compensation and propose an approach to recover the two-sided corrections for interface conditions; (iv) the method is extended to the generalized planar rigid-body motion. The improved CIBC methods are subsequently introduced into various partitioned solution algorithms. Different FSI examples are investigated and important flow-induced phenomena are successfully captured.
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Kambouchev, Nayden Dimitrov 1980. "Analysis of blast mitigation strategies exploiting fluid-structure interaction." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/42045.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Includes bibliographical references (p. 163-177).<br>Blast attacks have become the most pervasive threat in both civil and military contexts. However, there is currently a limited understanding of the mechanisms of loading, damage and failure of structures, and injury to humans produced by blast. This thesis seeks to advance our current understanding of the mechanisms of blast loading on structures. Towards this end, a comprehensive analytical and numerical study of basic problems in the interaction of blast waves with structures is conducted. The analysis is of interest in the conception of blast mitigation strategies and in the design and optimization of protection systems with improved performance against blast. The approach builds on a classic solution by G. I. Taylor on the interaction of acoustic blast waves with free-standing plates (In G. K. Batchelor, editor, The Scientific Papers of Sir Georey Ingram Taylor, vol. III, p.287-303, Cambridge University Press, 1963). Taylor's analysis demonstrates that the coupled fluid-structure interaction eect can be exploited for the purpose of reducing the impulse transmitted from the blast to the structure. This basic result is not applicable to the case of air blasts due to non-linear compressibility effects. In this thesis, a number of extensions of Taylor's theory is proposed. The case of air blast waves interacting with free-standing plates of variable mass is given special attention. The limiting cases of extremely heavy and extremely light plates are explored analytically for arbitrary blast intensities, from where it is concluded that a modified non-dimensional parameter representing the mass of compressed fluid relative to the mass of the plate governs the fluid-structure interaction.<br>(cont.) The intermediate asymptotic regimes are studied using a numerical method based on a Lagrangian formulation of the Euler equations of compressible ow and conventional shock-capturing techniques. Based on the analytical and numerical results, approximate formulae for the transmitted impulse describing the entire range of relevant conditions are proposed. The main conclusion of the theory is that non-linear fluid compressibility further enhances the beneficial effect selects of fluid-structure interaction in reducing the impulse transmitted to the structure. More specifically, it is found that impulse reductions due to fluid-structure interaction are more significant than in the acoustic limit when compared to those obtained ignoring fluid-structure interaction effect selects. In addition, a number of acoustic results for uniform shocks, viscoelastic supports, two fluid media, impulsively deployed and pressure actuated plates are proposed which provide the basis for evaluation of the benefits of the fluid-structure interaction in a wide variety of settings. The governing non-dimensional parameters in each specific context are determined and exact solutions to the fluid-structure interaction problem are provided. The results for the actively deployed plates reveal that significant cancellation of the blast impulse can be achieved thus suggesting a plausible blast mitigation strategy.<br>by Nayden Kambouchev.<br>Ph.D.
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Luu, Van Chi. "Boundary-integral formulations for three-dimensional fluid-structure interaction." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/42518.
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Taylor, Richard. "Finite element modelling of three dimensional fluid-structure interaction." Thesis, Swansea University, 2013. https://cronfa.swan.ac.uk/Record/cronfa42308.
Testo completoAbstract (sommario):
This work is focused on the numerical modelling of fluid-structure interaction in three dimensions. Both internal and external laminar flow around flexible bodies are considered. The fluid flow simulated is based on the incompressible Navier-Stokes equations and the general focus is on laminar Newtonian flow. The streamline upwind/ pressure stabilising Petrov-Galerkin (SUPG/PSPG) method is employed to achieve a stable low order finite element discretisation of the fluid, while the solid is discretised spatially by a standard Galerkin finite element approach. The behavior of the solid is governed by Neo-Hooke elasticity. For temporal discretisation the discrete implicit generalised-alpha method is employed for both the fluid and the solid domains. The motion of the fluid mesh is solved using an arbitrary Lagrangian-Eulerian (ALE) scheme employing a nonlinear pseudo-elastic mesh update method. The fluid-solid interface is modelled using a finite element interpolation method that allows for non-matching meshes and satisfies the required conservation laws. The resulting sets of fully implicit strongly coupled nonlinear equations are then decomposed into a general framework consisting of fluid, interface and solid domains. These equations are then solved using different solution techniques consisting of strongly coupled monolithic Newton and block Gauss-Seidel methods as well as a weakly coupled novel staggered scheme. These solvers are employed to solve a number of three dimensional numerical examples consisting of: External flow: o a soft elastic beam fixed at both ends o a thin cantilever plate.
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Yang, Liang. "An immersed computational framework for multiphase fluid-structure interaction." Thesis, Swansea University, 2015. https://cronfa.swan.ac.uk/Record/cronfa42413.
Testo completoAbstract (sommario):
The objective of this thesis is to further extend the application range of immersed computational approaches in the context of hydrodynamics and present a novel general framework for the simulation of fluid-structure interaction problems involving rigid bodies, flexible solids and multiphase flows. The proposed method aims to overcome shortcomings such as the restriction of having to deal with similar density ratios among different phases or the restriction to solve single-phase flows. The new framework will be capable of coping with large density ratios, multiphase flows and will be focussed on hydrodynamic problems. The two main challenges to be addressed are: - the representation, evolution and compatibility of the multiple fluid-solid interface - the proposition of unified framework containing multiphase flows, flexible structures and rigid bodies with possibly large density ratios First, a new variation of the original IBM is presented by rearranging the governing equations which define the behaviour of the multiple physics involved. The formulation is compatibile with the "one-fluid" equation for two phase flows and can deal with large density ratios with the help of an anisotropic Poisson solver. Second, deformable structures and fluid are modelled in a identical manner except for the deviatoric part of the Cauchy stress tensor. The challenging part is the calculation of the deviatoric part the Cauchy stress in the structure, which is expressed as a function of the deformation gradient tensor. The technique followed In this thesis is that original ISP, but re-expressed in terms of the Cauchy stress tensor. Any immersed rigid body is considered as an incompressible non-viscous continuum body with an equivalent internal force field which constrains the velocity field to satisfy the rigid body motion condition. The "rigid body" spatial velocity is evaluated by means of a linear least squares projection of the background fluid velocity, whilst the immersed force field emerges as a result of the linear momentum conversation equation. This formulation is convenient for arbitrary rigid shapes around a fixed point and the most general translation- rotation. A characteristic or indicator function, defined for each interacting continuum phase, evolves passively with the velocity field. Generally, there are two families of algorithms for the description of the interfaces, namely, Eulerian grid based methods (interface tracking). In this thesis, the interface capturing Level Set method is used to capture the fluid-fluid interface, due to its advantages to deal with possible topological changes. In addiction, an interface tracking Lagrangian based meshless technique is used for the fluid-structure interface due to its benefits at the ensuring mass preservation. From the fluid discretisation point of view, the discretisation is based on the standard Marker-and-Cell method in conjunction with a fractional step approach for the pressure/velocity decoupling. The thesis presents a wide range of applications for multiphase flows interacting with a variety of structures (i.e. rigid and deformable) Several numerical examples are presented in order to demonstrate the robustness and applicability of the new methodology.
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Guadarrama, Lara Rodrigo. "Modelling fluid-structure interaction problems with coupled DEM-LBM." Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/17444/.
Testo completoAbstract (sommario):
When studying the properties and behaviour of particulate systems, a multi-scale approach is an efficient way to describe interactions at different levels or dimensions; this means that phenomena taking place at one scale will inherently impact the properties and behaviour of the same system in a different scale. Numerical representation and simulation of fluid-structure interaction (FSI) systems is of particular interest in the present work. Conventional computational fluid dynamics (CFD) methods involve a top-down approach based on the discretisation of the macroscopic continuum Navier-Stokes equations; cells are typically much larger than individual particles and the hydrodynamic force is calculated for all the solid particles contained in singular a cell. Unlike traditional CFD solvers, the lattice Boltzmann method (LBM) is an alternative approach to simulate fluid flows in complex geometries in a mesoscale level. In LBM the fluid is deemed as a collection of cells, each one containing a particle that represents a density distribution function with a velocity field. The distinct element method (DEM) is in charge of handling the motion of particles and calculating the interparticle contact forces. The two methodologies LBM and DEM were selected among the available approaches to be combined in a single computational code to represent FSI systems. The key task to undertake was the implementation of a coupling code to exchange information between the two solvers LBM and DEM in a correct and efficient manner. The calculation of hydrodynamic forces exerted by the fluid on the particles is the major challenge in coupled FSI simulations. This was addressed by including the momentum exchange method, based on the link bounce-back technique, together with the immersed boundary method to deal with moving particles immersed in a fluid. In addition, in order to better understand the dynamics of FSI systems in a mesoscale level, the present work paid special attention to the accurate representation of individual particles displaying irregular geometries instead of the preferred spherical particles. This goal was achieved by means of X-ray microtomography digitisation of particles, allowing the capture of complex micro-structural features such as particle shape, texture and porosity. In this way a more realistic particle representation was achieved, extending its use to the implementation into computational simulations. The DEM-LBM coupling implementation carried out was tested quantitatively and qualitatively based on theoretical models and experimental data. Different cases were selected to simulate the dynamic process of packing particles, particle fluidisation and segregation, particles sedimentation, fluid permeability calculations and fluid flow through porous media. Results and predictions from simulations for a number of configurations showed good agreement when compared with analytical and experimental data. For instance, the relative error in terminal velocity of a non-spherical particle settling down in a column of water was 4.2%, showing an asymptotic convergence to the reference value. In different tests like the drag on two interacting particles and the flow past a circular cylinder at Re = 100, the corresponding deviations from the references published were 20% and 8.23% respectively. The extended Re range for the latter case followed closely the reference curve for the case of a rough cylinder, indicating the effects of the inherent staircase-like boundary in digital particles. Three dimensional simulations of applications such as fluidisation and sedimentation showed the expected behaviour, not only for spherical particles but also considering complex geometries such as sand grains. A symmetric array of spheres and randomly mixed particles were simulated successfully. Segregation was observed in a case configured with particles with different size and density. Hindered settling was also observed causing the slow settling of the small particles. Incipient fluidisation of spherical and irregular geometries was observed in relatively large computational domains. However, the minimum fluidisation velocity configured at the inlet was commonly 10 times larger than the calculated from the Ergun equation.
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Miller, Samuel C. "Fluid-Structure Interaction of a Variable Camber Compliant Wing." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1428575972.
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Liu, Xinyang. "A Monolithic Lagrangian Meshfree Method for Fluid-Structure Interaction." Case Western Reserve University School of Graduate Studies / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=case1459348741.
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Diniz, dos Santos Nuno Miguel. "Numerical methods for fluid-structure interaction problems with valves." Paris 6, 2007. http://www.theses.fr/2007PA066683.
Testo completoAbstract (sommario):
Cette thèse est motivée par la modélisation et la simulation numérique des phénomènes d’interaction fluide-structure autour de valves cardiaques. L’interaction avec la paroi des vaisseaux est traitée avec une formulation Arbitraire Lagrange Euler (ALE), tandis que l’interaction avec les valves est traitée à l’aide de multiplicateurs de Lagrange, dans une formulation de type Domaines Fictifs (FD). Après une présentation de synthèse des di- verses méthodes utilisées en interaction fluide-structure dans les écoulements sanguins, nous décrivons une méthode permettant de simuler la dynamique d’une valve immergée dans un écoulement visqueux incompressible. L’algori- thme de couplage est partionné, ce qui permet de conserver des solveurs fluides et structures indépendants. Le maillage du fluide est mobile pour suivre la paroi des vaisseaux, mais indépendant du maillage des valves. Ceci autorise des très grands déplacements sans nécessiter de remaillage. Nous proposons une stratégie pour gérer le contact entre plusieurs valves. L’algorithme est totalement indépendant des solveurs de structures et est bien adapté au couplage fluide-structure partionné. Enfin, nous proposons un schéma de couplage semi-implicite permettant de méler efficacement les formulations ALE et FD. Toutes les méthodes considérées sont accom- pagnées de nombreux tests numériques en 2D et 3D<br>This thesis is motivated by the modelling and the simulation of fluid-structure interaction phenomena in the vicinity of heart valves. On the one hand, the interaction of the vessel wall is dealt with an Arbitrary Lagrangian Eule- rian (ALE) formulation. On the other hand the interaction of the valves is treated with the help of Lagrange multipliers in a Fictitious Domains-like (FD) formulation. After a synthetic presentation of the several methods available for the fluid-structure interaction in blood flows, we describe a method that permits capture the dynamics of a valve immersed in an in- compressible fluid. The coupling algorithm is partitioned which allows the fluid and structure solvers to remain independent. In order to follow the ves- sel walls, the fluid mesh is mobile, but it remains none the less independent of the valve mesh. In this way we allow large displacements without the need to perform remeshing. We propose a strategy to manage contact between several immersed structures. The algorithm is completely independent of the structure solver and is well adapted to the partitioned fluid-structure coupling. Lastly we propose a semi-implicit coupling scheme allowing to mix, effectively, the ALE and FD formulations. The methods considered are followed with several numerical tests in 2D and 3D
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CARO, DIAZ FREDDY SANTIAGO. "ANALYSIS OF FLUID STRUCTURE-INTERACTION (FSI) PROBLEMS IN ANSYS." Thesis, Faculty of Engineering and Information Technologies. School of Aerospace, Mechanical & Mechatronic Engineering, 2015. https://hdl.handle.net/2123/30023.
Testo completoAbstract (sommario):
The Fluid-Structure Interaction problems occur in many natural phenomena and man-made engineering systems, this fact has promoted the research in this area. The research in this field of study is implementing two different methodologies. The first one is the use of commercial programs that have developed FSI capabilities such as Ansys or ADINA. The second methodology is the development of computational codes to solve specific problems of FSI analysis. This Project in particular focuses in the evaluation of Ansys-Fluent to perform FSI simulations. Two aeroelastic cases were simulated in Ansys, they were: the delta wing, and the Onera M6 wing. The delta wing simulation is subsonic and its structure is a simple flat plate made out of aluminum. The Onera M6 wing simulation is transonic and its structure has multiple components that are made out of an orthotropic material. The FSI simulations of the delta wing were validated through comparison with experimental data reported in literature. A turbulence analysis and a mesh independence analysis were carried out as well. The validation showed a limited capability to replicate the results that were obtained in the experiment. The FSI simulations of the Onera M6 wing were validated through comparison with a simulation that was carried out in Patran-Nastran. In addition, a computational fluid dynamics (CFD) simulation in steady state was performed in Ansys in order to establish the bases of the configuration that was implemented in the FSI simulations in Ansys. The validation showed that Ansys-Fluent is able to reproduce the results obtained in Patran-Nastran.
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Joosten, Martina Maria. "Aspects of interface modelling in fluid-structure interaction problems." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa42211.
Testo completoAbstract (sommario):
Different aspects of computational fluid-structure interaction are considered in this work. A brief introduction to fluid dynamics, structural mechanics and the finite element method is given, followed by an overview of interface modelling and the different solution strategies available for the coupling of the domains. A number of time integration schemes are explained in detail with a focus on their stability and accuracy properties. A model problem is introduced to investigate the situation where different domains of a coupled problem are solved with different time integration schemes. It is shown that appropriate interpolation of the solution variables at the interface is required to maintain the stability and accuracy properties of the individual time integration schemes. The Gauss-Seidel solution strategy is analysed in detail. Stability limitations are investigated and are shown to be related to the mass ratio between the different domains. Different relaxation strategies are introduced to improve the convergence behaviour. Finally, a number of 2D fluid-structure interaction examples are considered, in order to compare the different solution strategies.
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Zhang, Runze. "Modeling of coupled vibration systems with fluid-structure interaction." Electronic Thesis or Diss., université Paris-Saclay, 2024. http://www.theses.fr/2024UPAST136.
Testo completoAbstract (sommario):
Cette thèse porte sur deux aspects de la dynamique vibratoire des structures en interaction fluide-structure (IFS) : le contrôle des vibrations des structures immergées dans un fluide et la récupération des vibrations induites par un fluide pour leur conversion en énergie électrique. Ce mémoire présente nos contributions dans ces deux domaines.Premièrement, concernant le contrôle des vibrations, l'émergence récente des méta-structures a ouvert de nouvelles perspectives pour maîtriser les vibrations des structures en IFS. Ces structures, souvent constituées de microstructures périodiques, permettent de moduler la propagation des ondes vibratoires. Leur conception, prenant en compte les conditions spécifiques à l'IFS, constitue un sujet de grande importance. Nous avons développé un modèle par éléments finis basé sur l'analyse d'une cellule élémentaire, qui permet de prédire les bandes de fréquences interdites pour des plaques composites périodiques soumises aux conditions IFS. Une contribution clé de ce travail réside dans la formulation d'une nouvelle matrice de masse ajoutée, intégrant les conditions de Bloch dans les domaines solide et fluide de la cellule élémentaire. Cette approche permet un contrôle passif des vibrations et la conception de structures minces avec des bandes de fréquences spécifiques.Ensuite, nous avons exploré la modulation active de ces bandes de fréquences dans des scénarios similaires de structures minces avec IFS, en introduisant un système couplé comprenant des composants piézoélectriques. Le modèle de cellule élémentaire fluide-structure, tenant compte des conditions de Bloch, inclut également les effets de couplage piézoélectrique. Nos recherches montrent que les effets inertiels du fluide influencent fortement les bandes de fréquences des structures minces, en raison de leur faible inertie propre. Une optimisation de la microstructure, incluant la disposition et la forme des composants piézoélectriques, ainsi que la définition d'une loi de contrôle, permet d'obtenir une modulation optimale des bandes de fréquences, en fonction des applications spécifiques.Dans la seconde partie du travail, nous avons étudié les vibrations induites par un écoulement fluide comme source d'énergie, pouvant être convertie en électricité grâce à l'effet piézoélectrique direct. Un système couplé, composé d'une structure vibrante intégrant des composants piézoélectriques connectés à un circuit externe, a été modélisé pour être soumis à un écoulement fluide. Contrairement aux modèles simplifiés de type poutre souvent utilisés, nous avons proposé un modèle à échelle complète basé sur des éléments finis solides. Cela permet de prendre en compte des caractéristiques complexes, telles que l'utilisation de transducteurs microstructurés et de cantilevers non uniformes. À l'aide de ce modèle, diverses configurations de systèmes de récupération d'énergie avec générateurs de turbulence, permettant une efficacité améliorée, ont été étudiées.En résumé, la modélisation multiphysique du couplage pour différentes conditions d'IFS proposée dans cette étude, permet non seulement de prédire et de contrôler efficacement les vibrations structurelles en milieu fluide, mais elle offre également des outils numériques pour le développement de systèmes de récupération d'énergie piézoélectrique performants<br>This thesis addresses two key aspects of the vibrational dynamics of structures with fluid-structure interaction (FSI): the control of vibrations in structures immersed in a fluid and the conversion of fluid-induced vibrations into electrical energy. This dissertation presents our contributions to these two domains. To this end, the study first proposes an unit cell-based finite element model to predict vibration bandgaps in periodic composite plates under FSI conditions. By introducing a novel fluid-added mass matrix integrating Bloch boundary conditions, the fluid's inertial effects are incorporated into the bandgap analysis, enabling designing for vibration control in periodic plates submerged in liquids, achieving passive control.Based on this foundation, the research further explores the potential for actively tuning the vibration bandgaps of periodic composite plates submerged in liquids, which integrate connected piezoelectric sensors and actuators with feedback control. Therefore, an unit cell-based vibration bandgap tuning model with inertial fluid is developed, which integrates Bloch boundary conditions for both fluid and piezoelectric coupled solid domains. Then, the study reveals that in liquid environments, the fluid-added mass effect significantly impacts the bandgap characteristics of thin-walled structures, reducing the effectiveness of control strategy. Increasing the structure's self inertia or optimizing the arrangement of piezoelectric patches can mitigate this effect.On the other hand, the rivers and oceans are in constant motion, containing substantial kinetic energy. When fluid flows over a structural surface, the induced structural vibrations can be viewed as a potential source of clean and renewable energy. By utilizing the direct piezoelectric effect of piezoelectric materials, the kinetic energy of the fluid can be converted into usable electrical energy, enabling fluid energy harvesting. However, in such energy harvesting systems, significant FSI and electro-mechanical coupling effects are often accompanied by complex nonlinear dynamic behavior. The presence of these coupling effects complicates numerical simulations in this field, making it challenging, especially when considering practical applications where a deep understanding of these nonlinear behaviors and their impact on system performance is essential. Therefore, this thesis develops a full-scale finite element model to capture the strong local FSI behavior of complex thin-walled piezoelectric fluid energy harvesters (PFEH) involving microstructured transducers and non-uniform cantilevers, which are often ignored by simplified models. The research analyzes different energy harvester designs through numerical simulations, examining the influence of substrate cross-sectional shape, piezoelectric patch arrangement, and microstructure on the system's dynamic response and energy output efficiency.Finally, the study further enhance the power output of PFEHs using synergistic vortex generators composed of upstream double plates and downstream cylinder with a small spacing in dynamic water environments. With the synergistic effects of multi vortex generators, it is possible to achieve higher frequency and stable larger amplitude vibrations for the piezoelectric flag, thereby obtaining higher energy harvesting efficiency. Overall, the multi-physics coupling modeling for different FSI conditions proposed in this study not only effectively predict and control structural vibrations in fluid environments but also provide a theoretical foundation and technical support for the development of efficient piezoelectric energy harvesting systems
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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.
Testo completoAbstract (sommario):
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 proposées<br>This 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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Marella, Saikrishna V. Udaykumar H. S. "A Parallelized sharp-interface fixed grid method for moving boundary problems." Thesis supplements, 2006. http://ir.uiowa.edu/etd/88.
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Sieber, Galina. "Numerical simulation of fluid structure interaction using loose coupling methods." Phd thesis, [S.l. : s.n.], 2002. http://elib.tu-darmstadt.de/diss/000254.
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Baumgart, Johannes. "The Hair Bundle: Fluid-Structure Interaction in the Inner Ear." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-63810.
Testo completoAbstract (sommario):
A multitude of processes cooperate to produce the sensation of sound. The key initial step, the transformation from mechanical motion into an electrical signal, takes place in highly specialized mechanosensitive organelles that are called hair bundles due to their characteristic appearance. Each hair bundle comprises many apposed cylindrical stereocilia that are located in a liquid-filled compartment of the inner ear. The viscous liquid surrounding the hair bundle dissipates energy and dampens oscillations, which poses a fundamental physical challenge to the high sensitivity and sharp frequency selectivity of hearing. To understand the structure-function relationship in this complex system, a realistic physical model of the hair bundle with an appropriate representation of the fluid-structure interactions is needed to identify the relevant physical effects. In this work a novel approach is introduced to analyze the mechanics of the fluid-structure interaction problem in the inner ear. Because the motions during normal mechanotransduction are much smaller than the geometrical scales, a unified linear system of equations describes with sufficient accuracy the behavior of the liquid and solid in terms of a displacement variable. The finite-element method is employed to solve this system of partial differential equations. Based on data from the hair bundle of the bullfrog's sacculus, a detailed model is constructed that resolves simultaneously the interaction with the surrounding liquid as well as the coupling liquid in the narrow gaps between the individual stereocilia. The experimental data are from high-resolution interferometric measurements at physiologically relevant amplitudes in the range from a fraction of a nanometer to several tens of nanometers and over a broad range of frequencies from one millihertz to hundred kilohertz. Different modes of motion are analyzed and their induced viscous drag is calculated. The investigation reveals that grouping stereocilia in a bundle dramatically reduces the total drag as compared to the sum of the drags on individual stereocilia moving in isolation. The stereocilia in a hair bundle are interconnected by oblique tip links that transmit the energy in a sound to the mechanotransduction channels and by horizontal top connectors that provide elastic coupling between adjacent stereocilia. During hair-bundle deflections, the tip links induce additional drag by causing small but very dissipative relative motions between stereocilia; this effect is offset by the horizontal top connectors that restrain such relative movements, assuring that the hair bundle moves as a unit and keeping the total drag low. In the model the stiffness of the links, the stiffness of the stereocilia, and the geometry are carefully adjusted to match experimental observations. The references are stiffness and drag measurements, as well as the coherence measurements for the bundle's opposite edges, both with and without the tip links. The results are further validated by a comparison with the relative motions measured in a sinusoidally stimulated bundle for the distortion frequencies at which movements are induced by the nonlinearity imposed by channel gating. The model of the fluid-structure interactions described here provides insight into the key step in the perception of sound and the method presented provides an efficient and reliable approach to fluid-structure interaction problems at small amplitudes<br>Bei der Hörwahrnehmung eines Klangs spielen viele komplexe Prozesse zusammen. Der Schlüsselprozess, die Umwandlung mechanischer Schwingungsbewegung in elektrische Signale, findet in den Haarbündeln im Innenohr statt. Diese Haarbündel sind hoch entwickelte mechanosensitive Organellen, bestehend aus vielen nahe beieinander stehenden Stereozilien umgeben von Flüssigkeit. Die beträchtliche Viskosität dieser Flüssigkeit führt zur Energiedissipation und zur Schwingungsdämpfung, was im Gegensatz zur bekannten hohen Empfindlichkeit und der ausgezeichneten Frequenzselektivität der Hörwahrnehmung steht. Um die Komponenten des Haarbündelsystems in ihrem funktionalen Zusammenspiel besser zu verstehen, bedarf es eines wirklichkeitsgetreuen Modells unter Einbeziehung der Wechselwirkung zwischen Flüssigkeit und Struktur. Mit dieser Arbeit wird ein neuer Ansatz vorgestellt, um die Mechanik der Fluid-Struktur-Wechselwirkung im Innenohr zu analysieren. Da die Bewegungen bei der normalen Mechanotransduktion wesentlich kleiner als die geometrischen Abmessungen sind, ist es möglich, das Verhalten von Fluid und Struktur in Form der Verschiebungsvariable in einem linearen einheitlichen System von Gleichungen ausreichend genau zu beschreiben. Dieses System von partiellen Differentialgleichungen wird mit der Finite-Elemente-Methode gelöst. Basierend auf experimentell ermittelten Daten vom Haarbündel des Ochsenfrosches wird ein detailliertes Modell erstellt, welches sowohl die Interaktion mit der umgebenden Flüssigkeit als auch die koppelnde Flüssigkeit in den engen Spalten zwischen den einzelnen Stereozilien erfasst. Die experimentellen Daten sind Ergebnisse von hochauflösenden interferometrischen Messungen bei physiologisch relevanten Bewegungsamplituden im Bereich von unter einem Nanometer bis zu mehreren Dutzend Nanometern, sowie über einen breiten Frequenzbereich von einem Millihertz bis hundert Kilohertz. Das Modell erlaubt die Berechnung der auftretenden viskosen Widerstände aus der numerischen Analyse der verschiedenen beobachteten Bewegungsmoden. Es kann gezeigt werden, dass durch die Gruppierung zu einem Bündel der Gesamtwiderstand drastisch reduziert ist, im Vergleich zur Summe der Widerstände einzelner Stereozilien, die sich individuell und unabhängig voneinander bewegen. Die einzelnen Stereozilien in einem Haarbündel sind durch elastische Strukturen mechanisch miteinander verbunden: Die Energie des Schalls wird durch schräg angeordnete sogenannte Tiplinks auf die mechanotransduktiven Kanäle übertragen, wohingegen horizontale Querverbindungen die Stereozilien direkt koppeln. Während der Haarbündelauslenkung verursachen die Tiplinks zusätzlichen Widerstand durch stark dissipative Relativbewegungen zwischen den Stereozilien. Die horizontalen Querverbindungen unterdrücken diese Bewegungen und sind dafür verantwortlich, dass sich das Haarbündel als Einheit bewegt und der Gesamtwiderstand gering bleibt. Die Steifigkeit der Stereozilien und der Verbindungselemente sowie deren Geometrie sind in dem Modell sorgfältig angepasst, um eine Übereinstimmung mit den Beobachtungen aus verschiedenen Experimenten zu erzielen. Als Referenz dienen Steifigkeits- und Widerstandsmessungen, sowie Kohärenzmessungen für die gegenüberliegenden Außenkanten des Bündels, die jeweils mit und ohne Tiplinks durchgeführt wurden. Darüberhinaus sind die Ergebnisse durch den Vergleich mit experimentell beobachteten Relativbewegungen validiert, die das Haarbündel infolge von sinusförmiger Anregung bei Distorsionsfrequenzen zeigt. Diese haben ihren Ursprung in dem nichtlinearen Prozess des öffnens von Ionenkanälen. Das entwickelte Modell eines Haarbündels liefert neue Einblicke in den Schlüsselprozess der auditiven Wahrnehmung. Zur Behandlung von Problemen der Fluid-Struktur-Wechselwirkungen bei kleinen Amplituden hat sich der hier ausgearbeitete Ansatz als effizient und zuverlässig erwiesen
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Larsson, Martin. "Numerical Modeling of Fluid-Structure Interaction in the Human Larynx." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2010. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-11198.
Testo completoAbstract (sommario):
This thesis presents a method for fluid-structure interaction in a simplified 2D model of the human larynx using the arbitrary Lagrangian–Eulerian (ALE) approach and a strictly stable high order finite difference method. The ALE method is first tested for the fluid solver with a prescribed boundary movement, and then the method is extended to a two-way coupled explicit fluid-structure interaction where the vocal folds interact with the airflow in the larynx. In each case, the fluid is treated as a Newtonian fluid obeying the perfect gas law and laminar flow is always assumed. Since the interest is ultimately phonation, the compressible Navier–Stokes equations are solved in order to resolve both the flow field and the acoustic waves. Characteristic-based non-reflecting boundary conditions are used so that no unphysical reflections occur at the outflow boundary of the limited computational domain. The finite difference method relies on the summation by parts (SBP) technique which allows energy estimates to be made for the discretized equations in an analogous way as for the continuous problem. In the interior, the difference operator corresponds to the standard sixth order explicit difference method and is third order accurate near the boundaries. The classical explicit fourth order Runge–Kutta method is used for time integration. For the structure field, the linear elastic wave equation is formulated as a first order system. The spatial derivatives are discretized by the same high order difference operator as employed for the flow equations. To implement boundary conditions for displacement or traction, a simultaneous approximation term (SAT) method is derived. Verification proves that the method is nearly fourth order accurate. The linear model is then extended to a nonlinear hyperelastic model based on a neo-Hookean constitutive relation. The strict energy estimate is only valid for the linear equation, but the SAT approach provides a consistent way to implement the traction boundary condition also for the nonlinear equations. Fluid-structure interaction simulations are performed with model parameters corresponding to the real geometry of the human larynx and physical properties of the human vocal folds. Results for the vortex dynamics are investigated and preliminary acoustic results are obtained.
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Thiriat, Paul. "FLUID-STRUCTURE INTERACTION : EFFECTS OF SLOSHING IN LIQUID-CONTAINING STRUCTURES." Thesis, KTH, Bro- och stålbyggnad, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-125353.
Testo completoAbstract (sommario):
This report presents the work done within the framework of my master thesis in the program Infrastructure Engineering at KTH Royal Institute of Technology, Stockholm. This project has been proposed and sponsored by the French company Setec TPI, part of the Setec group, located in Paris. The overall goal of this study is to investigate fluid-structure interaction and particularly sloshing in liquid-containing structures subjected to seismic or other dynamic action. After a brief introduction, the report is composed of three main chapters. The first one presents and explains fluid-structure interaction equations. Fluid-structure interaction problems obey a general flow equation and several boundary conditions, given some basic assumptions. The purpose of the two following chapters is to solve the corresponding system of equations. The first approach proposes an analytical solution: the problem is solved for 2D rectangular tanks. Different models are considered and compared in order to analyze and describe sloshing phenomenon. Liquid can be decomposed in two parts: the lower part that moves in unison with the structure is modeled as an impulsive added mass; the upper part that sloshes is modeled as a convective added mass. Each of these two added mass creates hydrodynamic pressures and simple formulas are given in order to compute them. The second approach proposes a numerical solution: the goal is to be able to solve the problem for any kind of geometry. The differential problem is resolved using a singularity method and Gauss functions. It is stated as a boundary integral equation and solved by means of the Boundary Element Method. The linear system obtained is then implemented on Matlab. Scripts and results are presented. Matlab programs are run to solve fluid-structure interaction problems in the case of rectangular tanks: the results concur with the analytical solution which justifies the numerical solution. This report gives a good introduction to sloshing phenomenon and gathers several analytical solutions found in the literature. Besides, it provides a Matlab program able to model effects of sloshing in any liquid-containing structures.
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Nobari, Soroush. "Fluid structure interaction and hemodynamic analysis of the aortic valve." Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=114410.
Testo completoAbstract (sommario):
Cardiovascular pathologies specifically valvular heart diseases remain the biggest cause of deaths worldwide with a mortality rate of 4% in industrialized countries and up to 42% in developing countries. Aortic valve and coronary arteries have in particular been the focus of many studies during the recent years. This is due to the prevalence of pathologies in these regions and the subsequent critical consequences. In certain pathological conditions such as aortic sclerosis, the micro-structure of the aortic root and the aortic valve leaflets are altered in response to stress resulting in changes in tissue thickness, stiffness or both. Such pathologies are thought to affect coronary blood flow which could be life threatening. Numerical studies have greatly assisted in understanding the biomechanics of the aortic valve, its function as well as the impact of pathologies on cardiac tissue mechanics and local hemodynamic. The interaction between the blood and the cardiac tissue is critical in properly studying the response of the system to its physiological conditions. However, due to the inherent complexity of fluid-structure interaction modeling of aortic leaflets, there is a clear lack of a global representation of the aortic valve region which would aid in understanding the overall behaviour of this structure in pathological conditions. Recently, there have been clinical investigations that have observed simultaneous structural and hemodynamic variations in the aortic valve and coronary arteries due to regional pathologies. The main objective of this work is to elucidate this observed and yet unexplained phenomenon where, a regional pathology could lead to global variations in the structure and hemodynamic of the aortic valve region as well as in the coronary arteries. Therefore this thesis concentrates on three aspects: physiological heart valve modeling, investigating coronary hemodynamic variables in presence of valvular pathologies, and the possible impact of coronary stenosis on valvular dynamics. This model can aid in explaining the underlying behaviour that leads to the observed inter-relation between the aortic valve and coronary flow. Moreover, within the clinical practice our model has the potential to serve as a possible diagnostic tool; as the cardiac surgeons and interventional cardiologists can benefit from the additional input provided by this model for choosing the time of surgical intervention in the diseased aortic valve region.<br>Les pathologies cardiovasculaires, en particulier les maladies des valves cardiaques, restent toujours les causes prédominantes de mortalité, à un taux de 4% dans les pays développés et à 42% dans les pays en développement. La valve aortique et les artères coronariennes sont l'emphase de nombreux articles récents. Cela est surtout attribuable à l'occurrence élevée de ses maladies dans ces régions et les conséquences critiques qui suivent. Avec certaines pathologies cardiovasculaires, comme la sclérose aortique, les microstructures de la racine et des feuillets aortiques peuvent être modifié avec des contraintes résultantes des changements de l'épaisseur ou de l'élasticité du tissu, ou des deux. Ces pathologies sont reliées à l'altération du débit sanguin, ce qui peut être mortel.Des études numériques ont assisté considérablement à la compréhension des biomécaniques de la fonctionnalité et des pathologies des feuillets, leur effet sur les tissus cardiaques et l'hémodynamie locale. Par contre, ces investigations ont plutôt analysé la structure des valves que les interactions entre le sang et le tissu cardiaque. Ce facteur simple mais sophistiqué est critique pour suffisamment étudier la réponse du système face aux conditions physiologiques. Par ailleurs, à cause de la complexité inhérente de l'analyse d'interaction fluide-structure des feuillets aortiques, il y a un manque évident d'une représentation globale de la région des valves aortiques, ce qui pourrait avancer la connaissance du comportement global de cette structure sous les conditions physiologiques. L'objectif primaire de cette thèse est d'expliquer ce phénomène inconnu dans lequel une pathologie régionale conduit à des variations globales structurelles et hémodynamiques au niveau de la région aortique ainsi que sur les artères coronaires. Ces dernières ont été ajoutées dans le modèle global pour explorer la possibilité d'une interrelation entre ces structures et la valve aortique. Par conséquent, cette thèse est concernée par trois aspects en particulier : la modélisation physiologique de la valve cardiaque, l'investigation des variables hémodynamiques des coronaires par rapport aux pathologies valvulaire, et l'impact possible d'une sténose coronarienne sur la dynamique valvulaire. Ce modèle peut aider à explorer et confirmer le comportement de base de l'interaction entre la valve aortique et le débit coronarien. En plus, au point de vue de la pratique clinique, notre modèle a le potentiel d'être un outil diagnostique ; considérant que les chirurgiens cardiaques et les cardiologues interventionnels pourraient profiter des données additionnelles fournies par ce modèle pour mieux planifier le moment idéal pour l'intervention chirurgicale dans la région de la valve aortique pathologique.
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Yeh, Han Hung. "Computational analysis of fluid structure interaction in artificial heart valves." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44921.
Testo completoAbstract (sommario):
The development of heart valve stenosis and sclerosis can lead to the development of fatal complications such as congestive heart failure. Therefore, severe valve stenosis requires a surgical operation with artificial heart valve replacement. Given that the geometrical differences between artificial valves would significantly influence hemodynamic performance around the implanted valve, additional knowledge for the interactions between blood flow and the artificial valve is necessary. Therefore, in order to proceed, this study proposes an advanced computational fluid dynamics (CFD) simulation using a fluid-structure interaction (FSI) technique to investigate artificial valve leaflet motion under different physiological conditions.
Among various FSI technique, it is proposed to simulate the motion of the artificial heart valve with a fully-coupled algorithm and arbitrary Lagrangian-Eulerian formulation (ALE) using a monolithic solver. Models are constructed using a realistic aortic root for both the bileaflet and bioprosthetic valves with additional modifications and considerations for the flexible arterial wall. Normal physiological blood pressure and conditions are used to simulate healthy scenarios, which are compared with experiments. Validation is conducted by analysing particle image velocimetry (PIV) experimental data from ViVitro Lab. Hemodynamic performance analyses are conducted and found that both velocity and maximum von Mises stress are higher if calculated using a rigid wall model. The leaflet dynamics, on the other hand, is relatively the same for rigid or flexible wall model. Clinically relevant scenarios are also simulated for both mechanical and bioprosthetic valves. The clinical focus for the mechanical valve is on the malfunction of the valve due to leaflet restrictions. In addition, the clinical focus for the bioprosthetic valve is on the systolic deficiency due to different tissue properties.
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TEUMA-MELAGO, Eric. "A FLUID STRUCTURE INTERACTION MODEL OF INTRACORONARY ATHEROSCLEROTIC PLAQUE RUPTURE." Doctoral diss., University of Central Florida, 2006. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/2359.
Testo completoAbstract (sommario):
Plaque rupture with superimposed thrombosis is the primary cause of acute coronary syndromes of unstable angina, myocardial infarction and sudden death. Although intensive studies in the past decade have shed light on the mechanism that causes unstable atheroma, none has directly addressed the clinical observation that most myocardial infarction (MI) patients have moderate stenoses (less than 50%). Considering the important role the arterial wall compliance and pulsitile blood flow play in atheroma rupture, fluid-structure interaction (FSI) phenomenon has been of interest in recent studies. In this thesis, the impact is investigated numerically of coupled blood flow and structural dynamics on coronary plaque rupture. The objective is to determine a unique index that can be used to characterize plaque rupture potential. The FSI index, developed in this study for the first time derives from the theory of buckling of thin-walled cylinder subjected to radial pressure. Several FSI indices are first defined by normalizing the predicted hemodynamic endothelial shear stress by the structural stresses, specifically, by the maximum principal stress (giving the ratio ), and the Von Mises stress (giving the ratio ). The predicted at the location of maximum (i.e { }) denoted , is then chosen to characterize plaque rupture through systematic investigation of a variety of plaque characteristics and simulated patient conditions. The conditions investigated include varying stenosis levels ranging from 20% to 70%, blood pressure drop ranging from 3125 Pa/m to 9375 Pa/m, fibrous cap thickness ranging from to , lipid pool location ranging from the leading to the trailing edge of plaque, lipid pool volume relative to stenosis volume ranging from 24% to 80%, Calcium volume relative to stenosis volume ranging from 24% to 80% and arterial remodeling. The predicted varies with the stenosis severity and indicates that the plaques investigated are prone to rupture at approximately 40-45% stenosis levels. It predicts that high pressure significantly lowers the threshold stenosis rate for plaque rupture. In addition, the plaque potential to rupture increases for relatively thin fibrous cap, lipid core located near the leading plaque shoulder, and dramatically for relative lipid pool volume above 60%. However, calcium deposit has marginal effect on plaque rupture. Overall, the predicted results are consistent with clinical observations, indicating that the has the potential to characterize plaque rupture when properly established. In the appendix, the unsteady flow in a collapsible tube model of a diseased artery is solved analytically. The novelty of our approach is that the set of governing equations is reduced to a single integro-differential equation in the transient state. The equation was solved using the finite difference method to obtain the pressure and compliant wall behavior. The analytical approach is less computer-intensive than solving the full set of governing equations. The predicted membrane deflection is quite large at low inlet velocity, suggesting possible approach to breakdown in equilibrium. As the transmural pressure increases with wall deflection, bulges appear at the ends of the membrane indicating critical stage of stability, consistent with previous studies. An increase in wall thickness reduces the wall deflection and ultimately results in its collapse. The collapse is due to breakdown in the balance of wall governing equation. An increase in internal pressure is required to maintain membrane stability.<br>Ph.D.<br>Department of Mechanical, Materials and Aerospace Engineering;<br>Engineering and Computer Science<br>Mechanical Engineering
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Conner, Ryan P. "Fluid Structure Interaction Effects on Composites Under Low Velocity Impact." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/7324.
Testo completoAbstract (sommario):
In this study composite materials were tested in different fluid environments to determine the role of Fluid Structure Interaction with these composites under a lower velocity impact. The purpose of this research is to develop a better understanding of possible marine applications of composite materials. This was done using a low velocity impact machine and two composite types. The first composite is made from a multi-ply symmetrical plain weave 6 oz. E-glass skin. The test area of the composites is 12 in by 12 in (30.5 cm by 30.5 cm) with clamped boundary conditions. The testing was done using a drop weight system to impact the center of the test area. A Plexiglas box in conjunction with the impact machine was used to keep the top of the composite sample dry while it was submerged in approximately 15 inches (38.10 cm) of water. The second composite type was constructed using the same methods, but was made from a Carbon Fiber Reinforced Polymer (CFRP) instead of the E-glass skin. These samples were pre-cracked and tested using the same impact machine in 15 inches (38.10 cm) of water. The overall size of these samples was 42 cm long and 3 cm wide forming a long thin rectangular shape. The test area of these samples was a 20 cm long section of the sample with the outsides being clamped to achieve the desired boundary conditions. Two variations of these samples were tested. The first was reinforced with Multi-Walled Carbon Nanotubes (MWCNTs) and the second had no reinforcements at the interface layer in front of the pre-cracks. Output from both tests was recorded using strain gauges and a force impact sensor. The results show that an added mass from the water plays a large role in the Fluid Structure Interaction with composites due to the similar densities of water and the composites.