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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.
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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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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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Gallagher, Timothy. "Towards multi-scale reacting fluid-structure interaction: micro-scale structural modeling." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53483.
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The fluid-structure interaction of reacting materials requires computational models capable of resolving the wide range of scales present in both the condensed phase energetic materials and the turbulent reacting gas phase. This effort is focused on the development of a micro-scale structural model designed to simulate heterogeneous energetic materials used for solid propellants and explosives. These two applications require a model that can track moving surfaces as the material burns, handle spontaneous formation of discontinuities such as cracks, model viscoelastic and viscoplastic materials, include finite-rate kinetics, and resolve both micro-scale features and macro-scale trends. Although a large set of computational models is applied to energetic materials, none meet all of these criteria. The Micro-Scale Dynamical Model serves as the basis for this work. The model is extended to add the capabilities required for energetic materials. Heterogeneous solid propellant burning simulations match experimental burn rate data and descriptions of material surface. Simulations of realistic heterogeneous plastic-bound explosives undergoing impact predict the formation of regions of localized heating called hotspots which may lead to detonation in the material. The location and intensity of these hotspots is found to vary with the material properties of the energetic crystal and binder and with the impact velocity. A statistical model of the hotspot peak temperatures for two frequently used energetic crystals indicates a linear relationship between the hotspot intensity and the impact velocity. This statistical model may be used to generate hotspot fields in macro-scale simulations incapable of resolving the micro-scale heating that occurs in heterogeneous explosives.
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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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Yang, Qing. "SPH Simulation of Fluid-Structure Interaction Problems with Application to Hovercraft." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/26785.
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A Computational Fluid Dynamics (CFD) tool is developed in this thesis to solve complex fluid-structure interaction (FSI) problems. The fluid domain is based on Smoothed Particle Hydro-dynamics (SPH) and the structural domain employs large-deformation Finite Element Method (FEM). Validation tests of SPH and FEM are first performed individually. A loosely-coupled SPH-FEM model is then proposed for solving FSI problems. Validation results of two benchmark FSI problems are illustrated (Antoci et al., 2007; Souto-Iglesias et al., 2008). The first test case is flow in a sloshing tank interacting with an elastic body and the second one is dam-break flow through an elastic gate. The results obtained with the SPH-FEM model show good agreement with published results and suggest that the SPH-FEM model is a viable and effective numerical tool for FSI problems.
This research is then applied to simulate a two-dimensional free-stream flow interacting with a deformable, pressurized surface, such as an ACV/SES bow seal. The dynamics of deformable surfaces such as the skirt/seal systems of the ACV/SES utilize the large-deformation FEM model. The fluid part including the air inside the chamber and water are simulated by SPH. A validation case is performed to investigate the application of SPH-FEM model in ACV/SES via comparison with experimental data (Zalek and Doctors, 2010). The thesis provides the theory of the SPH and FEM models incorporated and the derivation of the loosely-coupled SPH-FEM model. The validation results have suggested that this SPH-FEM model can be readily applied to skirt/seal dynamics of ACV/SES interacting with free-surface flow.Ph. D.
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Engels, Thomas. "Numerical modeling of fluid-structure interaction in bio-inspired propulsion." Thesis, Aix-Marseille, 2015. http://www.theses.fr/2015AIXM4773/document.
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Les animaux volants et flottants ont développé des façons efficaces de produire l'écoulement de fluide qui génère les forces désirées pour leur locomotion. Cette thèse est placée dans ce contexte interdisciplinaire et utilise des simulations numériques pour étudier ces problèmes d'interaction fluides-structure, et les applique au vol des insectes et à la nage des poissons. Basée sur les travaux existants sur les obstacles mobiles rigides, une méthode numérique a été développée, permettant également la simulation des obstacles déformables et fournissant une polyvalence et précision accrues dans le cas des obstacles rigides. Nous appliquons cette méthode d'abord aux insectes avec des ailes rigides, où le corps et d'autres détails, tels que les pattes et les antennes, peuvent être inclus. Après la présentation de tests de validation détaillée, nous procédons à l'étude d'un modèle de bourdon dans un écoulement turbulent pleinement développé. Nos simulations montrent que les perturbations turbulentes affectent les insectes volants d'une manière différente de celle des avions aux ailes fixées et conçues par l'humain. Dans le cas de ces derniers, des perturbations en amont peuvent déclencher des transitions dans la couche limite, tandis que les premiers ne présentent pas de changements systématiques dans les forces aérodynamiques. Nous concluons que les insectes se trouvent plutôt confrontés à des problèmes de contrôle dans un environnement turbulent qu'à une détérioration de la production de force. Lors de l‘étape suivante, nous concevons un modèle solide, basé sur une équation de barre monodimensionnelle, et nous passons à la simulation des systèmes couplés fluide–structureFlying and swimming animals have developed efficient ways to produce the fluid flow that generates the desired forces for their locomotion. These bio-inspired problems couple fluid dynamics and solid mechanics with complex geometries and kinematics. The present thesis is placed in this interdisciplinary context and uses numerical simulations to study these fluid--structure interaction problems with applications in insect flight and swimming fish. Based on existing work on rigid moving obstacles, using an efficient Fourier discretization, a numerical method has been developed, which allows the simulation of flexible, deforming obstacles as well, and provides enhanced versatility and accuracy in the case of rigid obstacles. The method relies on the volume penalization method and the fluid discretization is still based on a Fourier discretization. We first apply this method to insects with rigid wings, where the body and other details, such as the legs and antennae, can be included. After presenting detailed validation tests, we proceed to studying a bumblebee model in fully developed turbulent flow. Our simulations show that turbulent perturbations affect flapping insects in a different way than human-designed fixed-wing aircrafts. While in the latter, upstream perturbations can cause transitions in the boundary layer, the former do not present systematical changes in aerodynamic forces. We conclude that insects rather face control problems in a turbulent environment than a deterioration in force production. In the next step, we design a solid model, based on a one--dimensional beam equation, and simulate coupled fluid--solid systems
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Hendry, Stephen R. "Projectile impact of fluid backed metal beams and plates : experiments and numerical simulation." Thesis, University of Aberdeen, 1985. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU356814.
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The growth of the nuclear power industry has provided a considerable stimulus for investigations into fluid-structure interaction problems. The safety case for nuclear reactors requires an understanding of the impact response of structures enclosing or surrounded by fluids. In many cases the structural response is in excess of that which can be predicted by elastic analyses and both material and geometrical non-linearities must be considered. The understanding of the interaction between the structure and the contained fluid poses additional problems which, in the extreme loading conditions envisaged, have received little attention. There is a lack of data relating to basic fluid-structure interaction problems involving dynamic plastic structural impact. Two sets of experiments are described which were carried out to provide some such data. The first set of experiments considered beams, both fully clamped (leading to large membrane forces) and partially clamped (preventing rotational and transverse motion while allowing the beam material to be fed in from the supports), struck centrally by a projectile. The second set of experiments considered a circular plate clamped around its periphery, sealing a volume of fluid, and struck centrally by a projectile. The shape of the plates and beams as they deformed were recorded, as were the pressure variations during the tests. In both sets of experiments the main contribution of the fluid to the beam or plate response was to localise the deformations. The early deformation of the beams was limited to the centre half span and the deformation only spread to the ends of the beams as the supporting effect of the fluid was lost due to the fluid escaping. In the plate experiments, where a good seal could be achieved, the deformation throughout was localised compared with a similar plate in air. The deformation in these cases was limited to a central disc of approximately half the plate diameter. The pressures recorded during the tests suggest that the fluid response was predominantly incompressible. A finite element program was written to model the response of beams and circular plates (axisymmetric problems). A brief history of the finite element method, the background theory and the development of the method to treat non-linear, large displacement, dynamic problems are given. The results are presented for a number of beam and plate problems, both those described above and other problems for which data was available. The finite element program was found to give good predictions of the deforming shapes of both the beams and the plates. No detailed analysis of the fluid was carried out, but two types of approximation to the effect of the fluid were investigated. Firstly a time varying pressure pulse (based on the measured pressure pulses) or a pressure loading derived from the beam velocity (acoustic and incompressible fluid approximations) were used to represent the loading on the beam due to the fluid. Secondly a mass was added to the plate mass to represent the inertia of the fluid. The applied pressure loading worked to a limited extent for the beams but no one pressure pulse shape gave good results for both end fixities. The best results for the plate problem were achieved with the added mass approach. Finally a number of areas of experimental and computational work are identified, which it is felt would benefit from further study.
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Aliabadi, Ardavan. "Numerical simulation of fluid-structure interaction for tilting-disk mechanical heart valves." Thesis, Wichita State University, 2013. http://hdl.handle.net/10057/6803.
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According to the United States Department of Health and Human Services, 27.1 million non-institutionalized adults were diagnosed with heart disease in 2010. The number of deaths associated with heart disease in 2009 was reported to be 599,413, claiming the lives of 195 out of every 100,000 people, which makes heart disease the number one killer in the U.S. Even though mechanical heart valves (MHVs) have proven to save lives in many of these cases, they are still not perfect, and complications arising from their design have reduced their application. To better understand the important factors and pursue remedies, numerous experimental investigations have been conducted; however, despite impressive improvements, small-scale studies suffer from lower levels of accuracy and sometimes are very costly to conduct. As in many other areas of research, numerical simulations can be helpful in reducing costs and supplementing such experimental work.
The computational effort in this thesis focused on the numerical analysis of current tilting-disk MHVs. In this work, an implicit fluid-structure interaction (FSI) simulation of the Bjork-Shiley design was carried out using in-house codes implemented in the commercial code software FLUENT. In-house codes in the form of journal files, schemes, and user-defined functions (UDFs) were integrated to automate the inner iterations and enable communication between the fluid and the moving disk at the interfaces. Based on the investigation of the current simulations, a new design aiming at improving the hemodynamic performance is suggested. The hemodynamics of flow in current tilting-disk valves was compared with the suggested design, and it is concluded that the suggested design has a better hemodynamic performance in terms of shear stress values and residence times.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Aerospace Engineering
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Paik, Kwang Jun. "Simulation of fluid-structure interaction for surface ships with linear/nonlinear deformations." Diss., University of Iowa, 2010. https://ir.uiowa.edu/etd/569.
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The present research develops a numerical fluid-structure interaction (FSI) code based on CFDShip-Iowa version 4, a general-purpose URANS/DES overset fluid solver. Linear and nonlinear FSI methods are developed to compute structural responses on surface ships or marine structures. The modal superposition transient analysis and the nonlinear FEM structure solver are used for small and large deformation FSI problems, respectively.
The gluing method is applied to transfer the forces and displacements on non-matching grids for fluid and structure domains. The linear FEM solver is applied to deform the boundary layer grid with large deformation in the fluid domain, while the deformation is ignored in small deformation problems. Deformation of an interior point in the boundary layer grid is obtained using linear interpolation in both linear and nonlinear deformation problems.
The S175 containership is studied in regular waves as an application example for the linear problem. Heave and pitch responses are compared with the experiments, showing good agreement. Time histories of vertical bending moment (VBM) are calculated using rigid model, one-way coupling, and two-way coupling approaches. The elastic models are able to capture the ringing of the VBM induced by slamming, while the rigid model shows a peak at the moment of slamming without further fluctuations. The two-way coupling method shows the effects of hull deformation on the amplitude and phase of VBM as well as the accelerations of heave and pitch.
For the nonlinear deformation problem three sloshing tanks with an elastic bar clamped to its bottom or top are simulated and compared with the experiments and other numerical simulation results. The present simulation results show reasonable agreement with the experiments for bar deformation and free surface elevation. A secondary wave on the free surface is creadted by the vorticity generated from the free surface. The effect of the bar on the sloshing impact is studied comparing dynamic pressure acting on the tank wall without bar, with an elatic bar, and with a rigid bar.
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Ross, Mike R. "Coupling and simulation of acoustic fluid-structure interaction systems using localized Lagrange multipliers." Diss., Connect to online resource, 2006. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3219206.
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Doradoux, Adrien. "Simulation numérique d’écoulements diphasiques autour d’un solide mobile." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0582/document.
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Les méthodes de domaines fictifs permettent de simuler numériquement des écoulements autour de structures complexes et/ou mobiles à l’aide de maillages simples. L’objet solide est alors « immergé » dans un domaine de calcul englobant le fluide et le solide. Dans un premier temps, on étudie une méthode de pénalisation, qui consiste à ajouter un terme dans l’équation de conservation de la quantité de mouvement du fluide afin d’imposer la vitesse du solide. Grâce à des développements asymptotiques, on obtient une estimation de l’erreur induite par cette approche lorsque le solide est en mouvement. Ce procédé est ensuite couplé avec un schéma de projection vectorielle permettant d’imposer la contrainte d’incompressibilité. La convergence du schéma ainsi obtenu, vers les équations de Navier-Stokes, est établie. Dans un second temps,une approche originale capable de traiter des écoulements multiphasiques est développée : la méthode de porosité variable. L’idée principale est de considérer le solide comme un milieu sans masse. La discrétisation des bilans massiques de chaque phase est alors modifiée, de sorte que le volume total occupé par l’ensemble des phases fluides soit égal au volume laissé libre parle solide. Cette méthode est validée numériquement sur un ensemble varié de cas test comprenantd es écoulements monophasiques incompressibles et compressibles ainsi que des écoulements diphasiquesFictitious domain methods allow to simulate flows around complex and/or moving bodies with simple meshes. The object is "immersed" in a domain that contains fluid and solid volumes. The penalization method, which consists in adding a term in the momentum balance equation, in order to impose the solid velocity, is studied in a first part. Thanks to asymptotic expansions, the order of the error induced by this method is computed for moving bodies. This approach is then coupled with a Vector Penalty Projection scheme that permits to impose the incompressibility constraint. The convergence of the penalized scheme towards the Navier-Stokes equations is established. In a second part, an original approach, able to treat multiphase flowsis presented: the Time and Space Dependent Porosity method. The key idea is to consider the solid as a medium without mass. The discretization of the mass balance equation is modified,so that the total volume occupied by all fluid phases and the solid is equal to the total volume.This method is numerically validated on a set of various test cases including incompressible or compressible single phase flows and two-phase flows
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Pittard, Matthew T. "Large eddy simulation based turbulent flow-induced vibration of fully developed pipe flow /." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd295.pdf.
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Badiane, Doudou. "Simulation numérique et étude expérimentale d'un viscosimètre à principe vibrant." Thesis, Orléans, 2012. http://www.theses.fr/2012ORLE2057/document.
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La connaissance de la viscosité est un défi majeur dans les technologies de pointe (biomédical, pétrochimie, imprimerie, cosmétique, agroalimentaire, etc). Cette étude présente un capteur de viscosité qui exploite la vibration transversale forcée d’une poutre mince. L’amortissement induit par le fluide permet d’évaluer sa viscosité et sa masse volumique par la seule connaissance des caractéristiques à la résonance de la poutre (amplitude et fréquence). Cette mesure est réalisée par un circuit électromagnétique. Dans ce travail, la simulation numérique et l’étude expérimentale du viscosimètre sont réalisées en vue de mieux cerner les paramètres influençant le fonctionnement du capteur. Les différentes investigations menées dans ce travail sont d’une grande importance pour l’optimisation du viscosimètre d’une part. D’autre part, c’est une contribution à l’ensemble des études qui traitent de l’aspect du couplage fluide-structure-électromagnétismeKnowing the viscosity becomes increasingly a major challenge in leading-edge technologies (biomedical, petrochemical, printing, cosmetic, food industry, etc). This study presents a viscosity sensor based on a thin beam immersed in a newtonian fluid and subjected to transverse vibrations due to an electromechanical excitation system. The damped vibration can be used to evaluate the fluid viscosity and density by measuring the beam’s resonance characteristics (amplitude, frequency). This measurement is done by an electromagnetic feedback circuit. In this work, numerical model and experimental studies of the vibrating viscometer are conducted to better understand the influencing factors of the sensor’s operation. The different investigations carried out in this work are of great importance for the viscometer optimization on one hand. On the other hand, it’s a contribution to all studies dealing with the aspect of fluid-structure-electromagnetism coupling
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Doyle, Matthew Gerard. "Simulation of Myocardium Motion and Blood Flow in the Heart with Fluid-Structure Interaction." Thesis, Université d'Ottawa / University of Ottawa, 2011. http://hdl.handle.net/10393/20166.
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The heart is a complex organ and much is still unknown about its mechanical function. In
order to use simulations to study heart mechanics, fluid and solid components and their
interaction should be incorporated into any numerical model. Many previous studies have
focused on myocardium motion or blood flow separately, while neglecting their interaction.
Previous fluid-structure interaction (FSI) simulations of heart mechanics have made
simplifying assumptions about their solid models, which prevented them from accurately
predicting the stress-stain behaviour of the myocardium. In this work, a numerical model
of the canine left ventricle (LV) is presented, which serves to address the limitations of previous studies. A canine LV myocardium material model was developed for use in conjunction with a commercial finite element code. The material model was modified from its original form to make it suitable for use in simulations. Further, numerical constraints were imposed when calculating the material parameter values, to ensure that the model would be strictly convex. An initial geometry and non-zero stress state are required to start cardiac cycle simulations. These were generated by the static inflation of a passive LV model to an end-diastolic pressure. Comparisons with previous measurements verified that the calculated geometry was representative of end diastole. Stresses calculated at the specified end diastolic pressure showed complex spatial variations, illustrating the superiority
of the present approach over a specification of an arbitrary stress distribution to an
end-diastolic geometry. In the third part of this study, FSI simulations of the mechanics
of the LV were performed over the cardiac cycle. Calculated LV cavity pressures agreed
well with previous measurements during most of the cardiac cycle, but deviated from them
during rapid filling, which resulted in non-physiological backflow. This study is the first one to present a detailed analysis of the temporal and spatial variations of the properties of both the solid and the fluid components of the canine LV. The observed development of non-uniform pressure distributions in the LV cavity confirms the advantage of performing FSI simulations rather than imposing a uniform fluid pressure on the inner surface of the myocardium during solid-only simulations.
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Ali, Awais [Verfasser], Michael [Akademischer Betreuer] Schäfer, and Johannes [Akademischer Betreuer] Janicka. "On the Simulation of Turbulent Fluid-Structure Interaction / Awais Ali ; Michael Schäfer, Johannes Janicka." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1125627557/34.
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Alimi, Aria [Verfasser]. "Modeling and Numerical Simulation of Fluid-Structure Interaction in Circle of Willis / Aria Alimi." Kassel : Kassel University Press, 2019. http://d-nb.info/1206954078/34.
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Bloxom, Andrew Lawrence. "Numerical Simulation of the Fluid-Structure Interaction of a Surface Effect Ship Bow Seal." Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/50592.
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Numerical simulations of fluid-structure interaction (FSI) problems were performed in an effort to verify and validate a commercially available FSI tool. This tool uses an iterative partitioned coupling scheme between CD-adapco's STAR-CCM+ finite volume fluid solver and Simulia's Abaqus finite element structural solver to simulate the FSI response of a system. Preliminary verification and validation work (VandV) was carried out to understand the numerical behavior of the codes individually and together as a FSI tool.
Verification and Validation work that was completed included code order verification of the respective fluid and structural solvers with Couette-Pouiselle flow and Euler-Bernoulli beam theory. These results confirmed the 2nd order accuracy of the spatial discretizations used. Following that, a mixture of solution verifications and model calibrations was performed with the inclusion of the physics models implemented in the solution of the FSI problems. Solution verifications were completed for fluid and structural stand-alone models as well as for the coupled FSI solutions. These results re-confirmed the spatial order of accuracy but for more complex flows and physics models as well as the order of accuracy of the temporal discretizations. In lieu of a good material definition, model calibration is performed to reproduce the experimental results. This work used model calibration for both instances of hyperelastic materials which were presented in the literature as validation cases because these materials were defined as linear elastic.
Calibrated, three dimensional models of the bow seal on the University of Michigan bow seal test platform showed the ability to reproduce the experimental results qualitatively through averaging of the forces and seal displacements. These simulations represent the only current 3D results for this case. One significant result of this study is the ability to visualize the flow around the seal and to directly measure the seal resistances at varying cushion pressures, seal immersions, forward speeds, and different seal materials. SES design analysis could greatly benefit from the inclusion of flexible seals in simulations, and this work is a positive step in that direction. In future work, the inclusion of more complex seal geometries and contact will further enhance the capability of this tool.Ph. D.
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Doyle, Matthew G. "Simulation of blood flow in a ventricular assist device with fluid-structure interaction effects." Thesis, University of Ottawa (Canada), 2004. http://hdl.handle.net/10393/26630.
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Numerical simulations combining solid and fluid models and fluid-structure interaction effects were performed for a diaphragm-type ventricular assist device (VAD). These simulations include an open loop configuration, in which the VAD inlet and outlet tubes are open to the surroundings, and a closed loop configuration, in which the VAD is connected to an idealized model of the circulatory system.
Comparisons have been made between the open loop case and previous experimental and numerical results for a similar VAD designed by a group at Brunel University. Differences between the two models can be partially accounted for by differences in flow forcing. Even with these differences, this comparison validates this method as a tool for the design and optimization of VADs.
For the closed loop case, results were limited by the required use of a slightly compressible fluid model. Further relaxation of this requirement is needed to fully explore closed loop simulations.
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Kara, Mustafa Can. "Fluid-structure interaction (FSI) of flow past elastically supported rigid structures." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/51931.
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Fluid-structure interaction (FSI) is an important physical phenomenon in many applications and across various disciplines including aerospace, civil and bio-engineering. In civil engineering, applications include the design of wind turbines, pipelines, suspension bridges and offshore platforms. Ocean structures such as drilling risers, mooring lines, cables, undersea piping and tension-leg platforms can be subject to strong ocean currents, and such structures may suffer from Vortex-Induced Vibrations (VIV's), where vortex shedding of the flow interacts with the structural properties, leading to large amplitude vibrations in both in-line and cross-flow directions. Over the past years, many experimental and numerical studies have been conducted to comprehend the underlying physical mechanisms. However, to date there is still limited understanding of the effect of oscillatory interactions between fluid flow and structural behavior though such interactions can cause large deformations. This research proposes a mathematical framework to accurately predict FSI for elastically supported rigid structures. The numerical method developed solves the Navier-Stokes (NS) equations for the fluid and the Equation of Motion (EOM) for the structure. The proposed method employs Finite Differences (FD) on Cartesian grids together with an improved, efficient and oscillation-free Immersed Boundary Method (IBM), the accuracy of which is verified for several test cases of increasing complexity. A variety of two and three dimensional FSI simulations are performed to demonstrate the accuracy and applicability of the method. In particular, forced and a free vibration of a rigid cylinder including Vortex-Induced Vibration (VIV) of an elastically supported cylinder are presented and compared with reference simulations and experiments. Then, the interference between two cylinders in tandem arrangement at two different spacing is investigated. In terms of VIV, three different scenarios were studied for each cylinder arrangement to compare resonance regime to a single cylinder. Finally, the IBM is implemented into a three-dimensional Large-Eddy Simulation (LES) method and two high Reynolds number (Re) flows are studied for a stationary and transversely oscillating cylinder. The robustness, accuracy and applicability of the method for high Re number flow is demonstrated by comparing the turbulence statistics of the two cases and discussing differences in the mean and instantaneous flows.
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Anderson, Peter J. "Modeling the fluid-structure interaction of the upper airway : towards simulation of obstructive sleep apnea." Thesis, University of British Columbia, 2014. http://hdl.handle.net/2429/50162.
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Obstructive Sleep Apnea (OSA) is a syndrome in which the human Upper Airway (UA) collapses during sleep leading to frequent sleep disruption and inadequate air supply to the lungs. OSA involves Fluid-Structure Interaction (FSI) between a complex airflow regime and intricate mechanics of soft and hard tissue, causing large deformation of the complicated UA geometry. Numerical simulations provide a means for understanding this complex system, therefore, we develop a validated FSI simulation, composed of a 1D fluid model coupled with a 3D FEM solid solver (Artisynth), that is applied to a parameterized airway model providing a fast and versatile system for researching FSI in the UA.
The 1D fluid model implements the limited pressure recovery model of Cancelli and Pedley [28] using a dynamic pressure recovery term, area function corrections allowing complete closure and reopening of fluid geometries, and discretization schemes providing robust behavior in highly-uneven geometries. The fluid model is validated against 3D fluid simulations in static geometries and simple dynamic geometries, and proves reliable for predicting bulk flow pressure. Validation of simulation methods in Artisynth is demonstrated by simulating the buckling, complete collapse, and reopening of elastic tubes under static pressure which compare well with experimental results.
The FSI simulation is validated against experiments performed for a collapsible channel (a "2D" Starling resistor) designed to have geometry and characteristics similar to the UA. The observed FSI behaviors are described and compared for both experiment and simulation, providing a quantitative validation of the FSI simulation. The simulations and experiments agree quite well, exhibiting the same major FSI behaviors, similar progression from one behavior to another, and similar dynamic range.
A parameterized UA model is designed for fast and consistent creation of geometries. Uniform pressure and dynamic flow FSI simulations are performed with this model for numerous parameters associated with OSA. Uniform pressure simulations compare well to clinical data. Dynamic flow results demonstrate airflow limitation and snoring oscillations. The simulations are fast, simulating 1 s of FSI in 30 minutes. This model is a powerful tool for understanding the complex mechanics of OSA.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Salman, Huseyin Enes. "Investigation Of Fluid Structure Interaction In Cardiovascular System From Diagnostic And Pathological Perspective." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614388/index.pdf.
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Atherosclerosis is a disease of the cardiovascular system where a stenosis may develop in an artery which is an abnormal narrowing in the blood vessel that adversely affects the blood flow. Due to the constriction of the blood vessel, the flow is disturbed, forming a jet and recirculation downstream of the stenosis. Dynamic pressure fluctuations on the inner wall of the blood vessel leads to the vibration of the vessel structure and acoustic energy is propagated through the surrounding tissue that can be detected on the skin surface. Acoustic energy radiating from the interaction of blood flow and stenotic blood vessel carries valuable information from a diagnostic perspective. In this study, a constricted blood flow is modeled by using ADINA finite element analysis software together with the blood vessel in the form of a thin cylindrical shell with an idealized blunt constriction. The flow is considered as incompressible and Newtonian. Water properties at indoor temperature are used for the fluid model. The diameter of the modeled vessel is 6.4 mm with 87% area reduction at the throat of the stenosis. The flow is investigated for Reynolds numbers 1000 and 2000. The problem is handled in three parts which are rigid wall Computational Fluid Dynamics (CFD) solution, structural analysis of fluid filled cylindrical shell, and Fluid Structure Interaction (FSI) solutions of fluid flow and vessel structure. The pressure fluctuations and consequential vessel wall vibrations display broadband spectral content over a range of several hundred Hz with strong fluid-structural coupling. Maximum dynamic pressure and vibration amplitudes are observed around the reattachment point of the flow near the exit of the stenosis and this effect gradually decreases along downstream of flow. Results obtained by the numerical simulations are compared with relevant studies in the literature and it is concluded that ADINA can be used to investigate these types of problems involving high frequency pressure fluctuations of the fluid and the resulting vibratory motion of the surrounding blood vessel structure.
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Deparis, Simone. "Numerical analysis of axisymmetric flows and methods for fluid-structure interaction arising in blood flow simulation /." [S.l.] : [s.n.], 2004. http://library.epfl.ch/theses/?display=detail&nr=2965.
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Al-Manthari, Maimouna S. "Numerical simulation of selected two-dimensional and three-dimensional fluid-structure interaction problems using OpenFOAM technology." Thesis, Swansea University, 2018. https://cronfa.swan.ac.uk/Record/cronfa40949.
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Fluid-structure interaction (FSI) problems are increasing in various engineering fields. In this thesis, different cases of FSI in two- and three-dimensions (2D and 3D) are simulated using OpenFOAM and foam-extend. These packages have been used to create a coupling between fluid and solid. The vortex-induced vibration (VIV) phenomenon of flow past a circular cylinder is studied using PIMPLE algorithm for pressure-velocity coupling. This VIV study is restricted to incompressible flow simulation at a Reynolds number (Re) of 100. The changes of drag and lift coefficient values depend on the study case and the spring-mass-damper system for the flow past a free oscillatory cylinder. The free vibrating cylinder examined in one-degree-of-freedom (1DOF) and two-degrees-of-freedom (2DOF) systems with linear damping and spring properties. Both will affect the behaviour of the cylinder within the flow with some noticeable differences. The response time of the cylinder and the drag coefficient are the most affected by the spring and damper. Besides the vortex-induced vibration test cases, the two-dimensional and three-dimensional fluid-structure interaction benchmarking is also studied. A partitioned solution method for strongly coupled solver with independent fluid and solid meshes for transient simulation has been applied. The fluid domain dynamics is governed by the incompressible Navier-Stokes equations; however, the structural field is described by the nonlinear elastodynamic equations. Fluid and solid domains are discretised by finite volume method (FVM) in space and time. A strong coupling scheme for partitioned analysis of the thin-walled shell structure exposed to wind-induced vibration (WIV) is presented. The achievement of the 3D membrane roof coupling scheme is studied by applying the 2D model. Additionally, numerical models for the slender shell structures coupling and the 3D flows indicate possible applications of the presented work. The computational fluid dynamics (CFD) simulation results revealed that even the flow is considered as a laminar, turbulence modelling or more refined meshes should be used to capture the generation and release of vortices. A partitioned solution procedure for FSI problems in the building aeroelasticity area is also studied. An illustrative real-world model on the coupled behaviour of membrane structure under wind flow influence is given. A four-point tent subjected to wind motion is a typical application of this work applying with various physical factors that are a necessity for the thin membrane structure. The fluid domain is described by the incompressible Navier-Stokes equations at a Reynolds number of Re = 3,750. However, the motion of the solid field is modeled by total Lagrangian strategy for nonlinear elastic deformation. The FSI simulation, particularly 3D problems require in very long calculation time. Some limitations of the FSI solver in foam-extend package called fsiFoam is discussed. All solvers that used in this thesis are considered to be applied to a wide use of the implementation of FSI models, despite some problems in parallelisation, particularly in the latest FSI solver version. The analysis results are presented to demonstrate accuracy, convergence, and stability.
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Sourdille, Etienne. "Numerical simulation and control of a fluid structure interaction for a plate in a transverse flow." Thesis, University of Southampton, 2006. https://eprints.soton.ac.uk/47114/.
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The control of a moving structure in an unbounded flow has numerous applications in engineering, such as the aileron on an airplane. Here an approach is proposed where a CFD method is coupled with a controller to provide a qualitative flow model, and a tool for the development and the validation of the control scheme. A rotating rigid flat plate in transverse flow is considered. For the CFD, a discrete vortex method is used due to its relevance for separated flows, which implies approximating the flat plate by a thin ellipse. The simulation for a fixed plate has been completed with a plate approximated by a 20:1 ellipse and placed in an inviscid flow. A comparison with an image method is also undertaken. The results show encouraging features for modelling the vortex street, but also problems in the transient behaviour of the flow. The control method is based on fuzzy logic, and has shown a remarkable ability to adapt to the nonlinear nature of the force generated by the flow/structure system. Comparison is made with more classical schemes such as a controller based on optimal control theory using an intermediary flow/structure model, similar to a gain scheduling model, instead of the full simulation.
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Hermange, Corentin. "Simulation des interactions fluide-structure dans le problème de l’aquaplaning." Thesis, Ecole centrale de Nantes, 2017. http://www.theses.fr/2017ECDN0014/document.
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Le problème de l’hydroplannage a fait l’objet de peu de travaux de simulation jusqu’à présent du fait de sa complexité : couplage fluide-structure, complexité de la structure du pneu du fait des matériaux en présence, contact avec l’asphalte, complexité de l’écoulement fluide résultant (interface extrêmement complexe,assèchement de la route, ventilation, développement éventuel de la turbulence et de cavitation). Dans ce contexte, Michelin, Centrale Nantes et NextFlowSoftware ont cherché récemment à évaluer la capacité du solveur SPH développé par ces deux derniers pour classifier des pneumatiques en fonction de la géométrie de leurs structures surfaciques, sans prendre en compte la phase gazeuse. Cela a permis de démontrer la faisabilité de telles simulations par méthode SPH, et même d’obtenir de bons résultats avec pour avantages de s’absoudre des difficultés liées au maillage. L’autre avantage conséquent d’utiliser la méthode SPH pour modéliser le fluide dans ce contexte est apparu dans sa capacité à se coupler relativement aisément à des solveurs classiques de type Eléments Finis pour le problème structurel. L’objectif du doctorat est triple, poursuivre la qualification du couplage SPH–Eléments Finis, en particulier en termes énergétiques, développer des schémas permettant d’assurer un bon compromis stabilité / précision / temps de calcul. Deuxièmement quantifier l’influence des différents phénomènes physiques en jeu pour déterminer lesquels doivent être modélisés. Enfin adapter des modélisations SPH permettant de prendre en compte simultanément les différents phénomènes influant pour réaliser des simulations du problème completThe aquaplaning problem has been the topic of simulation works emphasizing its complexity: fluid structure interactions, structures modelling, materials involved, contact with asphalt and the complexity of the resulting fluid flow (extremely complex interface, drying up the road, ventilation, possible development of turbulence and cavitation). As additional difficulty, the tire is a highly deformable body and fluid-structure interaction effects should be considered, leading to a challenging problem for the numerical modelling. Then Michelin, Ecole Centrale Nantes and NextFlow Software have recently tested the ability of the SPH solver developed by the two latter to classify tires based on their surface structure geometries, without considering the gas phase. In this context, the interest of SPH for modelling efficiently the aquaplaning flow has been underlined. The meshless and Lagrangian feature of SPH naturally avoid the problem of fluid/solid grid compatibility. The other significant advantage of the SPH method, in this context, appears in its ability to be relatively easily coupled to with conventional Finite Element solvers. The aim of this workis three fold. First, qualify the SPH-FE coupling strategy, especially in terms of energy and then develop schemes to ensure a good compromise among stability, accuracy and computation time. Second, quantify the influence of different involved physical phenomena to determine which should be modelled. Finally, adapt SPH models to simultaneously consider different phenomena and to performe simulations of the complete problem
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Oliveira, Iago Lessa [UNESP]. "Using foam-extend to assess the influence of fluid-structure interaction on the rupture of intracranial aneurysms." Universidade Estadual Paulista (UNESP), 2017. http://hdl.handle.net/11449/151490.
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Les anévrismes sont des anomalies formées sur certaines régions du système vasculaire humain et sont caractérisés par des régions dilatées de la paroi artérielle, avec une petite épaisseur. L’un des types les plus communs se produit à l’intérieur des artères de la base du cerveau, dans le cercle de Willis. Ces cas d’anévrismes intracrâniens sont extrêmement dangereux car ils peuvent provoquer une hémorragie sous-arachnoïdienne en cas de rupture, avec la mort ou la présence d’un dommage définitif pour le patient. Les causes d’anévrismes sont étudiées depuis longtemps et des recherches reconnaissent que les effets hémodynamiques jouent un rôle clé dans la formation, la croissance, et la rupture des anévrismes intracrâniens. Cependant, les procédures expérimentales pour mieux comprendre les caractéristiques de l’écoulement du sang dans l’anévrisme sont encore difficiles à réaliser. Avec le développement de techniques des images du système vasculaire cérébral, il a été possible d’obtenir la géométrie des anévrismes, donc des méthodes numériques ont commencé à être utilisées pour la solution de l’écoulement dans les anévrismes, et alors plusieurs recherches ont étudié l’influence des variables biologiques et hémodynamiques sur la rupture de l’anévrisme. Cependant, ce n’est que dans la dernière décennie que l’influence de l’interaction fluide-structure, due à la flexibilité de la paroi de l’artère, sur ces variables a été étudiée. Dans ce contexte et à l’aide de géométries d’anévrismes spécifiques des patients, des simulations numériques ont été effectuées avec le logiciel open-source foam-extend, qui utilise une méthodologie partitionnée pour résoudre numériquement le problème d’interaction fluide-structure. En comparant les paramètres qui peuvent conduire à la rupture – tels que le cisaillement sur la paroi et l’indice d’oscillation du cisaillement – entre les résultats des simulations avec l’hypothèse de la paroi rigide et élastique, nous avons évalué l’influence de la flexibilité de la paroi de l’anévrisme sur ces paramètres, en concluant que cette flexibilité change les valeurs de ces paramètres, donc l’option de traitement peut changer si le médecin les utilise pour décider de traiter le patient.
Aneurismas são anormalidades formadas em algumas partes do sistema vascular humano e se caracterizam por regiões dilatadas e finas da parede arterial. Um dos tipos mais comuns ocorre no interior das artérias que chegam ao cérebro, no chamado círculo de Willis. Estes casos de aneurismas intracranianos são extremamente perigosos, pois em caso de rompimento podem ocasionar hemorragia cerebral, com consequente morte ou presença de sequelas permanentes no paciente. As causas dos aneurismas vêm sendo investigadas há tempos, e os pesquisadores concordam que os fenômenos hemodinâmicos têm papel fundamental na formação, crescimento e ruptura do aneurisma cerebral. Entretanto, os procedimentos experimentais para se conhecer melhor as características do escoamento de sangue no interior do aneurisma ainda são de difícil realização. A partir do desenvolvimento de técnicas de mapeamento do sistema vascular cerebral, pôde-se obter a geometria de aneurismas de modo que métodos numéricos na solução de problemas de escoamento passaram a ser utilizados. A partir de então, diversas pesquisas vêm sendo feitas visando a investigação da influência das variáveis biológicas e hemodinâmicas na ruptura do aneurisma. Entretanto, apenas recentemente foi dado foco na influência da interação fluido-estrutura que existe neste problema, devido a flexibilidade da parede da artéria. Assim, usando geometrias de aneurismas específicos de pacientes, simulamos o escoamento sanguíneo utilizando o pacote open-source foam-extend, que possui uma metodologia particionada implementada para resolver numericamente o problema de interação fluido-estrutura. Através de comparação dos parâmetros que podem levar a ruptura -- tensão de cisalhamento na parede e índice de oscilação do cisalhamento -- entre os resultados das simulações considerando as hipóteses de parede rígida e flexível, avaliamos a influência da flexibilidade da parede em tais parâmetros, concluindo que tal flexibilidade tem influência nos parâmetros que podem levar à ruptura do aneurisma a ponto de alterar a decisão de tratamento, caso ela fosse feita baseada em tais parâmetros.
Aneurysms are abnormalities formed in some regions of the human vascular system and are characterized by dilated and thin regions of the arterial wall. One of the most common types occurs inside the brain arteries in the so-called circle of Willis. These intracranial aneurysms are extremely dangerous, because in case of rupture they can cause sub-arachnoid hemorrhage, with consequent death or presence of permanent damage to the patient. Causes of aneurysms have been investigated for a long time, and researchers agree that hemodynamic effects play a key role in the formation, growth, and rupture of brain aneurysms. However, the experimental procedures to better understand the characteristics of blood flow within the aneurysm are still difficult to perform. With the development of scanning techniques of the cerebral vascular system, it has been possible to obtain the geometry of aneurysms and then with that numerical methods for the solution of blood flow have begun to be used. Since then, several researchers have been investigating the influence of biological and hemodynamic variables on aneurysms rupture. However, it has been only in the last decade that the influence of fluid-structure interaction, due to the flexibility of the artery wall, on those variables has been investigated. In this context and using patient-specific aneurysm geometries, we simulated the blood flow using the opensource library foam-extend, which uses a partitioned methodology to numerically solve the fluid-structure interaction problem. By comparing the parameters that can lead to rupture – wall shear stress and oscillatory shear index – between the results of the simulations considering the rigid and flexible walls hypotheses, we evaluated the influence of wall flexibility on such parameters, concluding that the flexibility influences the parameters that can lead to rupture, changing the decision of treatment if made using those parameters.
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Oliveira, Iago Lessa. "Using foam-extend to assess the influence of fluid-structure interaction on the rupture of intracranial aneurysms /." Ilha Solteira, 2017. http://hdl.handle.net/11449/151490.
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Orientador: José Luiz GascheResumo: Aneurismas são anormalidades formadas em algumas partes do sistema vascular humano e se caracterizam por regiões dilatadas e finas da parede arterial. Um dos tipos mais comuns ocorre no interior das artérias que chegam ao cérebro, no chamado círculo de Willis. Estes casos de aneurismas intracranianos são extremamente perigosos, pois em caso de rompimento podem ocasionar hemorragia cerebral, com consequente morte ou presença de sequelas permanentes no paciente. As causas dos aneurismas vêm sendo investigadas há tempos, e os pesquisadores concordam que os fenômenos hemodinâmicos têm papel fundamental na formação, crescimento e ruptura do aneurisma cerebral. Entretanto, os procedimentos experimentais para se conhecer melhor as características do escoamento de sangue no interior do aneurisma ainda são de difícil realização. A partir do desenvolvimento de técnicas de mapeamento do sistema vascular cerebral, pôde-se obter a geometria de aneurismas de modo que métodos numéricos na solução de problemas de escoamento passaram a ser utilizados. A partir de então, diversas pesquisas vêm sendo feitas visando a investigação da influência das variáveis biológicas e hemodinâmicas na ruptura do aneurisma. Entretanto, apenas recentemente foi dado foco na influência da interação fluido-estrutura que existe neste problema, devido a flexibilidade da parede da artéria. Assim, usando geometrias de aneurismas específicos de pacientes, simulamos o escoamento sanguíneo utilizando o pacote open-source... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: Aneurysms are abnormalities formed in some regions of the human vascular system and are characterized by dilated and thin regions of the arterial wall. One of the most common types occurs inside the brain arteries in the so-called circle of Willis. These intracranial aneurysms are extremely dangerous, because in case of rupture they can cause sub-arachnoid hemorrhage, with consequent death or presence of permanent damage to the patient. Causes of aneurysms have been investigated for a long time, and researchers agree that hemodynamic effects play a key role in the formation, growth, and rupture of brain aneurysms. However, the experimental procedures to better understand the characteristics of blood flow within the aneurysm are still difficult to perform. With the development of scanning techniques of the cerebral vascular system, it has been possible to obtain the geometry of aneurysms and then with that numerical methods for the solution of blood flow have begun to be used. Since then, several researchers have been investigating the influence of biological and hemodynamic variables on aneurysms rupture. However, it has been only in the last decade that the influence of fluid-structure interaction, due to the flexibility of the artery wall, on those variables has been investigated. In this context and using patient-specific aneurysm geometries, we simulated the blood flow using the opensource library foam-extend, which uses a partitioned methodology to numerically solve the ... (Complete abstract click electronic access below)
Résumé: Les anévrismes sont des anomalies formées sur certaines régions du système vasculaire humain et sont caractérisés par des régions dilatées de la paroi artérielle, avec une petite épaisseur. L’un des types les plus communs se produit à l’intérieur des artères de la base du cerveau, dans le cercle de Willis. Ces cas d’anévrismes intracrâniens sont extrêmement dangereux car ils peuvent provoquer une hémorragie sous-arachnoïdienne en cas de rupture, avec la mort ou la présence d’un dommage définitif pour le patient. Les causes d’anévrismes sont étudiées depuis longtemps et des recherches reconnaissent que les effets hémodynamiques jouent un rôle clé dans la formation, la croissance, et la rupture des anévrismes intracrâniens. Cependant, les procédures expérimentales pour mieux comprendre les caractéristiques de l’écoulement du sang dans l’anévrisme sont encore difficiles à réaliser. Avec le développement de techniques des images du système vasculaire cérébral, il a été possible d’obtenir la géométrie des anévrismes, donc des méthodes numériques ont commencé à être utilisées pour la solution de l’écoulement dans les anévrismes, et alors plusieurs recherches ont étudié l’influence des variables biologiques et hémodynamiques sur la rupture de l’anévrisme. Cependant, ce n’est que dans la dernière décennie que l’influence de l’interaction fluide-structure, due à la flexibilité de la paroi de l’artère, sur ces variables a été étudiée. Dans ce contexte et à l’aide de géométries d’anévri... (Résumé complet accès életronique ci-dessous)
Mestre
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Mosquera, Michaelsen Pablo [Verfasser], and M. [Akademischer Betreuer] Gabi. "A Fluid-Structure-Interaction Simulation tool for application in rotating machinery / Pablo Mosquera Michaelsen. Betreuer: M. Gabi." Karlsruhe : KIT-Bibliothek, 2015. http://d-nb.info/1078420688/34.
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Blauert, Florian [Verfasser], and H. [Akademischer Betreuer] Horn. "Investigating biofilm deformation using optical coherence tomography and fluid-structure interaction simulation / Florian Blauert ; Betreuer: H. Horn." Karlsruhe : KIT-Bibliothek, 2017. http://d-nb.info/1132997801/34.
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Gaugain, Fabien. "Analyse expérimentale et simulation numérique de l’interaction fluide-structure d’un hydrofoil élastique en écoulement subcavitant et cavitant." Thesis, Paris, ENSAM, 2013. http://www.theses.fr/2013ENAM0054/document.
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Le développement de structures portantes flexibles dans le domaine naval, telles que les hélices ou les safrans, pose de nouveaux problèmes de dimensionnement. Cette thèse a pour but de développer une méthode de dimensionnement validée par des essais pour des structures portantes déformables soumises à des écoulements, éventuellement diphasiques de type cavitant. Les essais sont réalisés sur un hydrofoil de type NACA66-312(mod.), fabriqué en polyacetate, au sein du tunnel hydrodynamique de l'Institut de Recherche de l'Ecole Navale. Lors des essais, des mesures de déformations du profil portant ainsi que de niveaux vibratoires sont réalisées. Une méthode numérique couplant un code structure éléments finis (ANSYS Mechanical) avec un code fluide volumes finis (ANSYS CFX) par une méthode partitionnée, itérative, synchrone et séquentielle, laquelle est validée en terme de prédiction du déplacement et des contraintes pour des écoulements subcavitants dans un premier temps, puis pour des écoulements cavitants stables et instablesThe design of flexible lifting bodies in the naval industry, such as propelleror rudders, create some new design problems. This thesis proposes a numerical method validated by experimental comparison for solving the case of lifting bodies loaded by flow with or whitout cavitation. The tests are carried out in the hydrodynamic tunnel of the French Naval Academy Research Institute, on a polyacetate flexible hydrofoil NACA66-312 (mod.). During tests, strains and vibrations are measured for comparisons with numerical results. The numerical method uses a sequential synchrone iterative partitionned coupling betweena structural finite-element code (ANSYS Mechanical) and a finite-volume code (ANSYS CFX). Good agreement between numerical and experimental results for displacements, and stresses of the structure is highlighted. For the cavitating flow, a good agreement for the cavitation dynamic is observed and the stresses are evaluated with satisfying accuracy
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Benguigui, William. "Modélisation de la réponse dynamique d’une paroi solide mise en vibration par un écoulement fluide diphasique." Thesis, Université Paris-Saclay (ComUE), 2018. http://www.theses.fr/2018SACLY014/document.
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Les tubes des générateurs de vapeur des centrales nucléaires vibrent sous l'effet d'écoulement eau/vapeur. Pour appréhender ce phénomène et le comprendre, des expériences à échelles réduites sont réalisées. La simulation numérique a montré son habilité à reproduire l'interaction fluide-structure sur ce type de géométrie pour des écoulements monophasiques. L'objectif est désormais de faire de même en écoulement diphasique et de caractériser les propriétés physiques du mélange liquide/gaz influant sur la vibration.Pour se faire, un code CFD avec une approche bi-fluide est utilisé. Une méthode dite de "Discrete forcing" est implémentée pour permettre le mouvement imposé de corps solides au sein d'un écoulement à plusieurs phases. Celle-ci est alros validée sur des cas simples et intégraux avec une comparaison systématique à des résultats expérimentaux ou théoriques.En se basant sur un algorithme implicite existant dans la littérature, un couplage fluide-structure utilisant cette méthode de suivi d'interface est implémenté. Validé sur des cas monophasiques et diphasiques, ce couplage offre désormais la possibilité de déplacer un solide en fonction des forces fluides diphasiques qui lui sont appliquées.Les différentes méthodes numériques présentes dans NEPTUNE_CFD sont ensuite évaluées pour un écoulement fréon/fréon au travers d'un faisceau de tubes inclinés. La nécessité d'utiliser des modèles dit "multi-régime" est mis en avant.Afin de déterminer l'influence sur l'écoulement des différentes propriétés physiques d'un mélange diphasique, plusieurs cas simples sont réalisés.Finalement, l'application industrielle cible, un écoulement eau/fréon dans un faisceau de tubes à pas carré, est simulée et comparée à un écoulement en conditions réelles (eau/vapeur à 70 bar). Les vibrations induites par écoulement monophasique puis diphasique sont correctement reproduites sur des cas dit de "faisabilité"In nuclear power plants, steam generator tubes vibrate because of steam/water cross-flows. In order to understant this phenomenon, reduced-scale experiments are performed. Numerical simulations have shown their ability to accurately reproduce the vibration induced by a single phase flow in a tube bundle. The aim of the present work is to do the same with two-phase flow and to characterize the effect of the mixture physical properties on vibration.To do so, a CFD code based on a two-fluid approach is used. A "discrete forcing" method is implemented in order to allow solid body motion in a two-phase flow. The validation is performed with simple and industrial cases using experimental and theoretical results.Using an existing implicit algorithm, a fluid-structure coupling based on the developed interface tracking method is implemented. Validated for single and two-phase flows, it is now possible to have solid motion induced by fluid forces.The different numerical models dedicated to two-phase flows are then evaluated on a freon/freon flow across an inclined tube bundle. The use of a multi-regime model is required. In order to investigate the role of the different physical properties on the vibration, three simple studies are performed.Finally, the industrial application, a freon/water flow across a square pitch tube bundle, is performed. First, it is compared to a steam/water flow in order to characterize the discrepancies when we are using a modeling mixture. Then, the vibration induced by single- and two-phase flows is reproduced by the developed method on feasibility test cases
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Partimbene, Vincent. "Calcul haute performance pour la simulation d'interactions fluide-structure." Phd thesis, Toulouse, INPT, 2018. http://oatao.univ-toulouse.fr/20524/1/PARTIMBENE_Vincent.pdf.
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Cette thèse aborde la résolution des problèmes d'interaction fluide-structure par un algorithme consistant en un couplage entre deux solveurs : un pour le fluide et un pour la structure. Pour assurer la cohérence entre les maillages fluide et structure, on considère également une discrétisation de chaque domaine par volumes finis. En raison des difficultés de décomposition du domaine en sous-domaines, nous considérons pour chaque environnement un algorithme parallèle de multi-splitting (ou multi-décomposition) qui correspond à une présentation unifiée des méthodes de sous-domaines avec ou sans recouvrement. Cette méthode combine plusieurs applications de points fixes contractantes et nous montrons que, sous des hypothèses appropriées, chaque application de points fixes est contractante dans des espaces de dimensions finies normés par des normes hilbertiennes et non-hilbertiennes. De plus, nous montrons qu'une telle étude est valable pour les résolutions parallèles synchrones et plus généralement asynchrones de grands systèmes linéaires apparaissant lors de la discrétisation des problèmes d'interaction fluide-structure et peut être étendue au cas où le déplacement de la structure est soumis à des contraintes. Par ailleurs, nous pouvons également considérer l’analyse de la convergence de ces méthodes de multi-splitting parallèles asynchrones par des techniques d’ordre partiel, lié au principe du maximum discret, aussi bien dans le cadre linéaire que dans celui obtenu lorsque les déplacements de la structure sont soumis à des contraintes. Nous réalisons des simulations parallèles pour divers cas test fluide-structure sur différents clusters, en considérant des communications bloquantes et non bloquantes. Dans ce dernier cas nous avons eu à résoudre une difficulté d'implémentation dans la mesure où une erreur irrécupérable survenait lors de l'exécution ; cette difficulté a été levée par introduction d’une méthode assurant la terminaison de toutes les communications non bloquantes avant la mise à jour du maillage. Les performances des simulations parallèles sont présentées et analysées. Enfin, nous appliquons la méthodologie présentée précédemment à divers contextes d'interaction fluide-structure de type industriel sur des maillages non structurés, ce qui constitue une difficulté supplémentaire.
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Ndiaye, Moctar. "Stabilisation et simulation de modèles d'interaction fluide-structure." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30323/document.
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L'objet de cette thèse est l'étude de la stabilisation de modèles d'interaction fluide-structure par des contrôles de dimension finie agissant sur la frontière du domaine fluide. L'écoulement du fluide est décrit par les équations de Navier-Stokes incompressibles tandis que l'évolution de la structure, située à la frontière du domaine fluide, satisfait une équation d'Euler-Bernoulli avec amortissement. Dans le chapitre 1, nous étudions le cas où le contrôle est une condition aux limites de Dirichlet sur les équations du fluide (contrôle par soufflage/aspiration). Nous obtenons des résultats de stabilisation locale du système non-linéaire autour d'une solution stationnaire instable de ce système. Dans les chapitres 2 et 3, nous nous intéressons au cas où le contrôle est une force appliquée sur la structure (contrôle par déformation de paroi). Dans le chapitre 2, nous considérons un modèle simplifié, où l'équation d'Euler-Bernoulli pour la structure est remplacée par un système de dimension finie. Nous construisons des lois de contrôle pour les systèmes de dimension infinie, ou pour leurs approximations semi-discrètes, capables de stabiliser les systèmes linéarisés avec un taux de décroissance exponentielle prescrit, et localement les systèmes non-linéaires. Nous présenterons des résultats numériques permettant de vérifier l'efficacité de ces lois de contrôlesThe aim of this thesis is to study the stabilization of fluid-structure interaction models by finite dimensional controls acting at the boundary of the fluid domain. The fluid flow is described by the incompressible Navier-Stokes equations while the displacement of the structure, localized at the boundary of the fluid domain, satisfies a damped Euler-Bernoulli beam equation. First, we study the case where the control is a Dirichlet boundary condition in the fluid equations (control by suction/blowing). We obtain local feedback stabilization results around an unstable stationary solution of this system. Chapters 2 and 3 are devoted to the case where control is a force applied to the structure (control by boundary deformation). We consider, in chapter 2, a simplified model where the Euler-Bernoulli equation for the structure is replaced by a system of finite dimension. We construct feedback control laws for the infinite dimensional systems, or for their semi-discrete approximations, able to stabilize the linearized systems with a prescribed exponential decay rate, and locally the nonlinear systems. We present some numerical results showing the efficiency of the feedback laws
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Wick, Thomas [Verfasser], and Rolf [Akademischer Betreuer] Rannacher. "Adaptive Finite Element Simulation of Fluid-Structure Interaction with Application to Heart-Valve Dynamics / Thomas Wick ; Betreuer: Rolf Rannacher." Heidelberg : Universitätsbibliothek Heidelberg, 2011. http://d-nb.info/1179783395/34.
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Bruckner, Robert Jack. "Simulation and Modeling of the Hydrodynamic, Thermal, and Structural Behavior of Foil Thrust Bearings." Case Western Reserve University School of Graduate Studies / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=case1089304186.
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Ben, Ayed Samah. "Analysis, Simulation and Control of Peak Pressure Loads on Low-Rise Structures." Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/23671.
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Wind storms pose dangerous threats to human lives and are an enormous drain on the economy. Their damage to buildings usually starts with the failure of structural components that are subjected to excessive wind loads. In this dissertation, we investigate the characteristics of extreme loads on low-rise structures through analysis of full-scale and numerical data. We also use numerical simulations to evaluate different approaches to control the separated flow over a surface-mounted prism with the objective of reducing extreme pressure coefficients or loads on its surface.In the first part, we use a probabilistic approach to characterize peak loads as measured on a subject house during Hurricane Ivan on 2004. Time series of pressure coefficients collected on the roof of that house are analyzed. Rather than using peak values, which could vary due to the stochastic nature of the data, a probabilistic analysis is used to determine the probability of non-exceedence of specific values of pressure coefficients and associated wind loads. The results show that the time series of the pressure coefficients follow a three-parameter Gamma distribution, while the peak pressure follows a two-parameter Gumbel distribution. The results of the analysis are contrasted with the design values.
In the second part, we perform numerical simulations of the flow over a surface-mounted prism as a simplified example for the flow over a low-rise structure. A Direct Numerical Simulation (DNS) code is developed to solve the unsteady two-dimensional incompressible Navier-Stokes equations of the flow past the prism. The pressure coefficients are then computed on the prism surface in order to assess the wind loads. The code is written on a parallel platform using the Message Passing Interface (MPI) library. We use the simulations to study the effects of inflow disturbances on the extreme loads on structures. The sensitivities of peak loads on a surface mounted prism to variations in incident gust parameters are determined. Latin Hypercube Sampling (LHS) is applied to obtain different combinations of inflow parameters. A non-intrusive polynomial chaos expansion is then applied to determine the sensitivities. The results show that the gust enhances the destabilization of the separation shear layer, forces it to break down and moves it closer to the roof of the prism. As for the sensitivities, the results show that the extreme loads are most sensitive to the transverse amplitude of the disturbance.
Because the separated flow over sharp edges is responsible for the extreme pressure peaks, we investigate the use of active and passive control strategies to reduce wind loads. The studied active flow control strategies include blowing, suction, and synthetic jets. We implement them by using different flux injections, different slot locations and different angles. Investigation of the possible peak pressure reduction for two Reynolds numbers is performed. For Re = 1000, a reduction by nearly 50% of the peak pressure is obtained. For Re = 10, 000, the highest achieved reduction is nearly 25%. For passive control, we mount a flexible membrane on the top of the prism. In a two-dimensional framework, the membrane equation is modeled by a forced string equation. This mechanical equation is coupled with the DNS solver and integrated in time using a fourth order Hamming predictor corrector scheme. The results show that this strategy is as efficient as the active control approach, in terms of reducing extreme loads, for Re = 10, 000.
Ph. D.
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Pittard, Matthew Thurlow. "Large Eddy Simulation Based Turbulent Flow-induced Vibration of Fully Developed Pipe Flow." Diss., CLICK HERE for online access, 2003. http://contentdm.lib.byu.edu/ETD/image/etd295.pdf.
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Hartig, Maximilian [Verfasser], and T. [Akademischer Betreuer] Schulenberg. "Numerical Simulation of Fluid-Structure Interaction during the Expansion Phase in Sodium Cooled Fast Reactors / Maximilian Hartig ; Betreuer: T. Schulenberg." Karlsruhe : KIT-Bibliothek, 2019. http://d-nb.info/120047130X/34.
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Taraconat, Pierre. "Application of numerical simulation for a better characterization of red blood cells by impedance measurement." Thesis, Montpellier, 2020. http://www.theses.fr/2020MONTS006.
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Le comptage et la volumétrie des cellules sanguines est réalisé par l'analyse des signatures électriques provenant de leur passage dans un micro-orifice polarisé.Cependant, les mesures peuvent être altérées par des dynamiques et déformations complexes de la cellule lorsque la trajectoire empruntée est proche des parois de l'orifice.Dans cette thèse, des dynamiques de Globules Rouges (GRs) dans un compteur Coulter et les signatures électriques correspondantes sont simulées.La prise en compte de la déformabilité des GRs implique de se confronter au caractère multi-échelle de ce type de configuration.Une méthode est proposée pour contourner cette difficulté de modélisation.En particulier, le calcul de la dynamique et de la perturbation électrique est fractionné en une séquence de simulations spécifiques, et le coût de calcul est réduit d'un ordre de grandeur.La méthode proposée est utilisée pour simuler des signaux de sphères rigides et de GRs, et les résultats sont validés par comparaisons avec des données expérimentales.L'association des signaux expérimentaux à des dynamiques de GRs dans l'orifice fournit une compréhension inédite des mécanismes en jeu dans les signatures complexes observées lorsque la cellule emprunte une trajectoire proche-paroi.Cette connaissance nouvelle des signatures a permis l'élaboration d'une nouvelle approche de tri permettant d'isoler les pulses associées aux passages en bord, non adaptés pour la volumétrie des cellules.La méthode introduite retrouve la distribution symétrique attendue pour le volume des GRs et donne des résultats comparables à la focalisation hydrodynamique, une implémentation plus complexe du principe Coulter.Les résultats ainsi obtenus ouvrent la voie à une mesure des paramètres hématologiques plus précise tout en conservant la simplicité et le coût modéré d'un système classique.L'impact des paramètres morphologiques et rhéologiques des cellules sur les signatures correspondants à des passages proche paroi est illustré.En modifiant la déformabilité et la sphéricité des GRs dans une approche expérimentale, les mesures diffèrent d'une normalité préétablie.De plus, des modélisations par réseaux de neurones sont réalisées dans le but d'accéder aux propriétés du GR à partir du pulse électrique.Parmi les traitements proposés, une classification des GRs normaux, rigides et sphériques est réalisée.Enfin, la modélisation du problème inverse des simulations numériques est effectuée afin d'évaluer de manière quantitative les paramètres mécaniques des GRsIn Coulter counters, cells counting and volumetry is achieved by monitoring their electrical print when they flow through a polarized micro-orifice.However, the volume measurement may be impaired when the trajectory of the cell is in the vicinity of the aperture edges due to complex dynamics and deformations of the cell.In this thesis, numerical simulations of the dynamics and electrical signature of red blood cells (RBCs) in a Coulter counter are presented, accounting for the deformability of the cells.In particular, a specific numerical pipeline is developed to overcome the challenge of the multi-scale nature of the problem.It consists in segmenting the whole computation of the cell dynamics and electrical response in a series of dedicated computations, with a saving of one order of magnitude in computational time.This numerical pipeline is used with rigid spheres and deformable red blood cells in an industrial Coulter counter geometry and compared with experimental measurements.The simulations not only reproduce electrical signatures typical of those measured experimentally, but also provide an understanding of the key mechanisms at play in the complex signatures induced by RBCs following a near-wall trajectory.Based on this new understanding provided by numerical simulations, a filtering strategy is introduced, which allows the filtering of pulses induced by near-wall paths which are irrelevant for the cells sizing.The method is shown to retrieve the expected symmetrical distribution of RBCs and provides results comparable to hydrodynamical focusing, a more intricate implementation of the Coulter principle.Such a result paves the way for a robust assessment of haematological parameters with a cheaper and simpler implementation, compared to hydrofocused devices.The impact of the cell morphology and rheology on the electrical print is evidenced for near-wall trajectories.Indeed, by altering the cell deformability and sphericity, the electrical pulses are proven to differ from predefined normality of measurements.Furthermore, neural network modellings are performed in the aims of assessing such RBC properties.Among the proposed processing, classification of normal, stiffened and spherical RBCs is provided.Finally, the inverse problem of numerical simulations is achieved, thus allowing the evaluation of the mechanical parameters of RBCs
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Kondratyuk, Anastasia [Verfasser], Michael [Akademischer Betreuer] Schäfer, and Suad [Akademischer Betreuer] Jakirlić. "Investigation of the Very Large Eddy Simulation Model in the Context of Fluid-Structure Interaction / Anastasia Kondratyuk ; Michael Schäfer, Suad Jakirlic." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2017. http://d-nb.info/1135385971/34.
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Marcel, Thibaud. "Simulation numérique et modélisation de la turbulence statistique et hybride dans un écoulement de faisceau de tubes à nombre de Reynolds élevé dans le contexte de l'interaction fluide-structure." Thesis, Toulouse, INPT, 2011. http://www.theses.fr/2011INPT0109/document.
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La prédiction des instabilités fluide-élastique qui se développent dans un faisceau de tubes est importante pour la conception des générateurs de vapeur dans les centrales nucléaires, afin de prévenir les accidents liés à ces instabilités. En effet, ces instabilités fluide-élastique, ou flottements, conduisent à une fatigue vibratoire des matériaux, voire à des chocs entre les tubes, et par la suite, à des dégâts importants. Ces aspects sont d'une grande complexité pour les applications scientifiques impliquant l'industrie nucléaire. Le présent travail est issu d'une collaboration entre l'EDF, le CEA et l'IMFT. Elle vise à améliorer la simulation numérique de cette interaction fluide- structure dans le faisceau de tubes, en particulier dans la gamme de paramètres critiques favorisant l'apparition d'un amortissement négatif du système et de l'instabilité fluide-élastiqueThe prediction of fluid-elastic instabilities that develop in a tube bundle is of major importance for the design of modern heat exchangers in nuclear reactors, to prevent accidents associated with such instabilities. The fluid-elastic instabilities, or flutter, cause material fatigue, shocks between beams and damage to the solid walls. These issues are very complex for scientific applications involving the nuclear industry. This work is a collaboration between EDF, CEA and IMFT. It aims to improve the numerical simulation of the fluid-structure interaction in the tube bundle, in particular in the range of critical parameters contribute to the onset of damping negative system and the fluid-elastic instability
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Deborde, Julien. "Modélisation et simulation de l’interaction fluide-structure élastique : application à l’atténuation des vagues." Thesis, Bordeaux, 2017. http://www.theses.fr/2017BORD0606/document.
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Une méthode complètement Eulérienne reposant sur un modèle 1-fluide est présentée afinde résoudre les problèmes d’interaction fluide-structure élastique. L’interface entre le fluideet la structure élastique est représentée par une fonction level-set, transportée par le champde vitesse du fluide et résolue par un schéma d’ordre élevé WENO 5. Les déformationsélastiques sont calculées sur la grille eulérienne à l’aide des caractéristiques rétrogrades.Nous utilisons différents modèles d’hyperélasticité, afin de générer puis d’intégrer les forcesélastiques comme terme source des équations de Navier Stokes. Le couplage vitesse/pressionest résolu par une méthode de correction de pression et les équations sont discrétisées parla méthode des volumes finis sur la grille eulérienne. La principale difficulté réside dansles grands déplacements de fluide autour du solide, source d’instabilités numériques. Afind’éviter ces problèmes, nous effectuons périodiquement une redistanciation de la level-setet une extrapolation linéaire des caractéristiques rétrogrades. Dans un premier temps,nous effectuons la vérification et la validation de notre approche à l’aide de plusieurs castests comme celui proposé par Turek. Ensuite, nous appliquons notre méthode à l’étudedu phénomène d’atténuation des vagues par des structures élastiques. Il s’agit d’une desvoies possibles pour réduire l’impact des fortes houles sur notre littoral. De plus dans lalittérature et à notre connaissance, seules des structures élastiques rigides ou élastiquesmais monodimensionnelles ont été utilisées pour réaliser ces études. Nous proposons deplacer des structures élastiques sur les fonds marins et analysons leur capacité d’absorptionde l’énergie produite par les vaguesA fully Eulerian method is developed to solve the problem of fluid-elastic structure interactionsbased on a 1-fluid method. The interface between the fluid and the elastic structureis captured by a level set function, advected by the fluid velocity and solved with a WENO5 scheme. The elastic deformations are computed in an Eulerian framework thanks to thebackward characteristics. We use the Neo Hookean or Mooney Rivlin hyperelastic modelsand the elastic forces are incorporated as a source term in the incompressible Navier-Stokesequations. The velocity/pressure coupling is solved with a pressure-correction methodand the equations are discretized by finite volume schemes on a Cartesian grid. The maindifficulty resides in that large deformations in the fluid cause numerical instabilities. Inorder to avoid these problems, we use a re-initialization process for the level set and linearextrapolation of the backward characteristics. First, we verify and validate our approachon several test cases, including the benchmark of FSI proposed by Turek. Next, we applythis method to study the wave damping phenomenon which is a mean to reduce thewaves impact on the coastline. So far, to our knowledge, only simulations with rigid orone dimensional elastic structure has been studied in the literature. We propose to placeelastic structures on the seabed and we analyse their capacity to absorb the wave energy
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Jedouaa, Meriem. "Une méthode efficace de capture d'interface pour la simulation de suspensions d'objets rigides et de vésicules immergées dans un fluide." Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAM042/document.
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Dans ce travail, nous nous sommes intéressés à la simulation numérique de suspensions denses d'objets immergés dans un fluide. En s'inspirant d'une méthode de segmentation d'image, nous avons développé une méthode efficace de capture d'interface permettant d'une part de localiser les structures immergées et d'autre part de gérer les contacts numériques entre les structures.Le domaine fluide/structure est représenté à l'aide de trois fonctions labels et deux fonctions distances qui permettent de localiser chaque structure et son plus proche voisin.Les interfaces sont capturées par une seule fonction level set, celle-ci est ensuite transportée par la vitesse du fluide ou par la vitesse de chaque structure. Un algorithme de multi-label fast marching permet de réinitialiser à chaque pas de temps les fonctions labels et distances dans un périmètre proche des interfaces.La gestion des contacts numériques est effectuée grâce à une force répulsive à courte portée prenant en compte l'interaction entre les objets les plus proches.Dans un premier temps, la méthode est appliquée à l'évolution de solides rigides immergés.Un modèle de pénalisation global couplé aux fonctions labels permet de calculer en une seule fois l'ensemble des vitesses des structures rigides. Les résultats obtenus montrent l'efficacité de la méthode à gérer un grand nombre de solides.Nous avons ensuite appliqué la méthode des suspensions de vésicules immergées. Ce type de simulation requiert le calcul des forces élastiques et de courbures exercées sur les membranes. Grâce au modèle proposé, seulement une force élastique et une force de courbure sont calculées pour l'ensemble des membranes à l'aide de la fonction level set et des fonctions labelsIn this work, we propose a method to efficiently capture an arbitrary number of fluid/solid or fluid/fluid interfaces, in a level-set framework. This technique, borrowed from image analysis, is introduced in the context of the interaction of several bodies immersed in a fluid. A configuration of the bodies in the fluid/structure domain is described by three label maps providing the first and second neighbours, and their associated distance functions. Only one level set function captures the union of all interfaces and is transported with the fluid velocity or with a global velocity field which takes into account the velocity of each structure. A multi-label fast marching method is then performed in a narrow-band around the interfaces allowing to update the label and distance functions. Within this framework, the numerical treatment of contacts between the structures is achieved by a short-range repulsive force depending on the distance between the closest bodies.The method is validated through the simulation of a dense suspension of rigid bodies immersed in an incompressible fluid. A global penalization model uses the label maps to follow the solid bodies altogether without a separate computation of each body velocity. Consequently, the method shows its efficiency when dealing with a large number of rigid bodies. We also investigate the numerical simulation of vesicle suspensions for which a computation of elastic and bending forces on membranes is required. In the present model, only one elastic and bending force is computed for the whole set of membranes according to the level set function and the label maps
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Kemp, Iain Henry. "Development,testing and fluid interaction simulation of a bioprosthetic valve for transcatheter aortic valve implantation." Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71710.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: Bioprosthetic heart valves (BHVs) for transcatheter aortic valve implantation (TAVI) have been rapidly developing over the last decade since the first valve replacement using the TAVI technique. TAVI is a minimally invasive valve replacement procedure offering lifesaving treatment to patients who are denied open heart surgery. The biomedical engineering research group at Stellenbosch University designed a 19 mm balloon expandable BHV for TAVI in 2007/8 for testing in animal trials. In the current study the valve was enlarged to 23 mm and 26 mm diameters. A finite element analysis was performed to aid in the design of the stents. New stencils were designed and manufactured for the leaflets using Thubrikar‟s equations as a guide. The 23 mm valve was manufactured and successfully implanted into two sheep. Fluid structure interaction (FSI) simulations constitute a large portion of this thesis and are being recognized as an important tool in the design of BHVs. Furthermore, they provide insight into the interaction of the blood with the valve, the leaflet dynamics and valve hemodynamic performance. The complex material properties, pulsating flow, large deformations and coupling of the fluid and the physical structure make this one of the most complicated and difficult research areas within the body. The FSI simulations, of the current valve design, were performed using a commercial programme called MSC.Dytran. A validation study was performed using data collected from a cardiac pulse duplicator. The FSI model was validated using leaflet dynamics visualisation and transvalvular pressure gradient comparison. Further comparison studies were performed to determine the material model to be used and the effect of leaflet free edge length and valve diameter on valve performance. The results from the validation study correlated well, considering the limitations that were experienced. However, further research is required to achieve a thorough validation. The comparative studies indicated that the linear isotropic material model was the most stable material model which could be used to simulate the leaflet behaviour. The free edge length of the leaflet affects the leaflet dynamics but does not greatly hinder its performance. The hemodynamic performance of the valve improves with an increase in diameter and the leaflet dynamics perform well considering the increased surface area and length. Many limitations in the software prevented more accurate material models and flow initiation to be implemented. These limitations significantly restricted the research and confidence in the results. Further investigation regarding the implementation of FSI simulations of a heart valve using the commercial software is recommended.
AFRIKAANSE OPSOMMING: Bio-prostetiese hartkleppe (Bioprosthetic Heart Valves - BHVs) wat gebruik word vir transkateter aortaklep-inplantings (Transcatheter Aortic Valve Implantation - TAVI) het geweldig vinnige ontwikkeling getoon in die afgelope tien jaar sedert die eerste klepvervanging wat van die TAVI prosedure gebruik gemaak het. TAVI is ʼn minimaal indringende klepvervangingsprosedure wat lewensreddende behandeling bied aan pasiënte wat ope-hart sjirurgie geweier word. Die Biomediese Ingenieurswese Navorsingsgroep (BERG) by Stellenbosch Universiteit het in 2007/8 ʼn 19 mm ballon-uitsetbare BHV vir TAVI ontwerp vir eksperimente met diere, en hierdie tesis volg op die vorige projekte. In die huidige studie is die klep vergroot na 23 mm en 26 mm in deursnee. ʼn Eindige element analise is gedoen om by te dra tot die ontwerp van die rekspalke vir die klep. Nuwe stensils is ontwerp en vervaardig vir die klepsuile, deur gebruik te maak van Thubrikar se vergelykings. Die 23 mm klep is vervaardig en suksesvol in twee skape ingeplant. Vloeistruktuur interaksie (Fluid Structure Interaction (FSI)) simulasies vorm ‟n groot deel van die tesis en word gesien as ʼn noodsaaklike hulpmiddel in die ontwerp van BHVs. Die simulasies verskaf ook insig in die interaksie van die bloed met die klep, die klepsuil-dinamika en die klep se hemodinamiese werkverrigting. Die komplekse materiaal eienskappe, polsende vloei, grootskaalse vervorming, die verbinding van die vloeistof en die fisiese struktuur maak van hierdie een van die mees gekompliseerde voorwerpe om te simuleer. Die FSI simulasies van die huidige ontwerp, is uitgevoer deur van kommersiële sagteware, MSC.Dytran, gebruik te maak. ʼn Geldigheidstudie wat data gebruik het vanaf die hartklop-nabootser, is uitgevoer. Die FSI model word geverifieer deur klepsuil dinamika visualisering en ʼn vergelyking van die drukgradiënt gebruik te maak. Verdere vergelykende studies is uitgevoer om te bepaal watter materiaal model om te gebruik, asook die uitwerking van die klepsuil-vrye rand en klepdeursnee op die klep se werkverrigting. Die resultate van die studie korreleer goed, in ag genome die beperkings wat ervaar is. Verdere navorsing is egter nodig vir ʼn volledige geldigheidstudie. Vergelykende studies het getoon dat die liniêre isotropiese materiaalmodel die meer stabiele materiaalmodel is wat kan gebruik word om klepsuilgedrag te simuleer. Die vrye-rand lengte van die klepsuil affekteer die dinamika van die klepsuil, maar belemmer nie die werkverrigting grootliks nie. Die hemodinamiese werkverrigting van die klep verbeter met die toename in deursnee en die klepsuil-dinamika vertoon goed in ag genome die verhoogde oppervlak area en lengte. Die vele beperkings in die sagteware het die implementering van meer akkurate materiaalmodelle verhoed. Hierdie beperkings het ʼn verminderde vertroue in die resultate tot gevolg gehad. Verdere ondersoek rakende die implementering van die FSI simulasies van ʼn hartklep deur kommersieel beskikbare sagteware te gebruik, word aanbevel.
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Touboul, Eric. "Simulation numérique tridimensionnelle d'un problème de fracturation hydraulique." Ecully, Ecole centrale de Lyon, 1986. http://www.theses.fr/1986ECDL0004.
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On présente ici un modèle numérique de fracturation hydraulique dans un milieu tridimensionnel, base sur un couplage entre : une suite d'états d'équilibre élastique, l'écoulement du fluide à l'intérieur de la fracture, et le phénomène de rupture. Pour l'élasticité, une formulation intégro-variationnelle permet de se ramener à un problème bidimensionnel tout en évitant les singularités classiques. La résolution numérique se fait par éléments finis sur un maillage mobile. On résout d'abord le problème d'équilibre. Les résultats numériques pour l'ouverture et les facteurs d'intensité de contrainte sont en très bon accord avec des solutions analytiques disponibles pour des géométries simples. Puis le couplage et la propagation sont réalisés. Les résultats sont compares a ceux obtenus par des modèles plus simples dans l'industrie pétrolière.
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Pauthenet, Martin. "Macroscopic model and numerical simulation of elastic canopy flows." Thesis, Toulouse, INPT, 2018. http://www.theses.fr/2018INPT0072/document.
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On étudie l'écoulement turbulent d'un fluide sur une canopée, que l'on modélise comme un milieu poreux déformable. Ce milieu poreux est en fait composé d'un tapis de fibres susceptibles de se courber sous la charge hydrodynamique du fluide, et ainsi de créer un couplage fluide-structure à l'échelle d'une hauteur de fibre (honami). L'objectif de la thèse est de développer un modèle macroscopique de cette interaction fluide-structure, afin d'en réaliser des simulations numériques. Une approche numérique de simulation aux grandes échelles est donc mise en place pour capturer les grandes structures de l'écoulement et leur couplage avec les déformations du milieu poreux. Pour cela nous dérivons les équations régissant la grande échelle, au point de vue du fluide ainsi que de la phase solide. À cause du caractère non-local de la phase solide, une approche hybride est proposée. La phase fluide est décrite d'un point de vue Eulerien, tandis que la description de la dynamique de la phase solide nécessite une représentation Lagrangienne. L'interface entre le fluide et le milieu poreux est traitée de manière continue. Cette approche de l'interface fluide/poreux est justifiée par un développement théorique sous forme de bilan de masse et de quantité de mouvement à l'interface. Ce modèle hybride est implémenté dans un solveur écrit en C$++$, à partir d'un solveur fluide disponible dans la librairie CFD \openfoam. Un préalable nécessaire à la réalisation d'un tel modèle macroscopique est la connaissance des phénomènes de la petite échelle en vue de les modéliser. Deux axes sont explorés concernant cet aspect. Le premier consiste à étudier les effets de l'inertie sur la perte de charge en milieu poreux. Un paramètre géométrique est proposé pour caractériser la sensibilité d'une microstructure poreuse à l'inertie de l'écoulement du fluide dans ses pores. L'efficacité de ce paramètre géométrique est validée sur une diversité de microstructures et le caractère général du paramètre est démontré. Une loi asymptotique est ensuite proposée pour modéliser les effets de l'inertie sur la perte de charge, et comprendre comment celle-ci évolue en fonction de la nature de la microstructure du milieu poreux. Le deuxième axe d'étude de la petite échelle consiste à étudier l'effet de l’interaction fluide-structure à l'échelle du pore sur la perte de charge au niveau macroscopique. Comme les cas présentent de grands déplacements de la phase solide, une approche par frontières immergées est proposée. Ainsi deux méthodes numériques sont employées pour appliquer la condition de non-glissement à l'interface fluid/solide: l'une par interface diffuse, l'autre par reconstitution de l'interface. Cela permet une validation croisée des résultats et d'atteindre des temps de calcul acceptables tout en maîtrisant la précision des résultats numériques. Cette étude permet de montrer que l'interaction fluide-structure à l'échelle du pore a un effet considérable sur la perte de charge effective au niveau macroscopique. Des questions fondamentales sont ensuite abordées, telles que la taille d'un élément représentatif ou la forme des équations de transport dans un milieu poreux soupleWe study the turbulent flow of a fluid over a canopy, that we model as a deformable porous medium. This porous medium is more precisely a carpet of fibres that bend under the hydrodynamic load, hence initiating a fluid-structure coupling at the scale of a fibre's height (honami). The objective of the thesis is to develop a macroscopic model of this fluid-structure interaction in order to perform numerical simulations of this process. The volume averaging method is implemented to describe the large scales of the flow and their interaction with the deformable porous medium. An hybrid approach is followed due to the non-local nature of the solid phase; While the large scales of the flow are described within an Eulerian frame by applying the method of volume averaging, a Lagrangian approach is proposed to describe the ensemble of fibres. The interface between the free-flow and the porous medium is handle with a One-Domain- Approach, which we justify with the theoretical development of a mass- and momentum- balance at the fluid/porous interface. This hybrid model is then implemented in a parallel code written in C$++$, based on a fluid- solver available from the \openfoam CFD toolbox. Some preliminary results show the ability of this approach to simulate a honami within a reasonable computational cost. Prior to implementing a macroscopic model, insight into the small-scale is required. Two specific aspects of the small-scale are therefore studied in details; The first development deals with the inertial deviation from Darcy's law. A geometrical parameter is proposed to describe the effect of inertia on Darcy's law, depending on the shape of the microstructure of the porous medium. This topological parameter is shown to efficiently characterize inertia effects on a diversity of tested microstructures. An asymptotic filtration law is then derived from the closure problem arising from the volume averaging method, proposing a new framework to understand the relationship between the effect of inertia on the macroscopic fluid-solid force and the topology of the microstructure of the porous medium. A second research axis is then investigated. As we deal with a deformable porous medium, we study the effect of the pore-scale fluid-structure interaction on the filtration law as the flow within the pores is unsteady, inducing time-dependent fluidstresses on the solid- phase. For that purpose, we implement pore-scale numerical simulations of unsteady flows within deformable pores, focusing for this preliminary study on a model porous medium. Owing to the large displacements of the solid phase, an immersed boundary approach is implemented. Two different numerical methods are compared to apply the no-slip condition at the fluid-solid interface: a diffuse interface approach and a sharp interface approach. The objective is to find the proper method to afford acceptable computational time and a good reliability of the results. The comparison allows a cross-validation of the numerical results, as the two methods compare well for our cases. This numerical campaign shows that the pore-scale deformation has a significant impact on the pressure drop at the macroscopic scale. Some fundamental issues are then discussed, such as the size of a representative computational domain or the form of macroscopic equations to describe the momentum transport within a soft deformable porous medium
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Boëdec, Gwenn. "Modélisation d'une vésicule sous forçage hydrodynamique." Thesis, Aix-Marseille 3, 2011. http://www.theses.fr/2011AIX30025.
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Les vésicules sont des gouttes immergées dans un fluide externe visqueux, dont le rayon vautquelques dizaines de micromètres et entourées par une membrane imperméable constituée de lipides, dont l’épaisseur est approximativement 4 nm. La membrane d’une vésicule est un systèmeoriginal du point de vue mécanique : celle-ci présente à la fois des propriétés fluides (les lipidespeuvent s’écouler librement le long de la membrane, mais la surface est incompressible locale-ment) et des propriétés solides (la membrane résiste à la flexion). Les propriétés spécifiques de lamembrane rendent ce système à la fois très déformable et très contraint.Ce manuscrit s’intéresse à la modélisation d’une vésicule soumise à des efforts extérieurs d’o-rigine hydrodynamique, dans le régime de Stokes. Une attention particulière est consacrée à lasituation d’une vésicule qui sédimente. Cette situation est étudiée analytiquement dans le régimedes faibles déformations. Il est montré que plusieurs familles de solutions stationnaires non triv-iales existent, grâce aux propriétés spécifiques de la membrane. L’étude de la sédimentation d’unevésicule est poursuivie par le développement d’un code numérique capable de simuler de grandesdéformations. Pour cela, des méthodes numériques originales de calcul de prise en compte de laflexion et de l’incompressibilité surfacique sont développées. Ce code permet d’étudier la forma-tion d’un tube à l’arrière d’une vésicule en sédimentation. Ces tubes sont de fins (rapport d’aspecttypique longueur/rayon ∼ 100) cylindres connectés à la vésicule d’origine. Il est montré que cesformes tubes sont des formes stationnaires. Un modèle théorique est proposé et comparé auxsimulations numériques. Ce modèle met en lumière l’importance particulière de la tension dansces formes. Une modélisation mécanique basée sur un milieu de Cosserat surfacique courbé estégalement présentée, et permet d’identifier la contribution de la flexion au tenseur des contraintes.Cette contribution est un ingrédient indispensable pour comprendre les formes tubesVesicles are drops of radius of a few tens micrometers, bounded by an impermeable lipidmembrane of approximately 4 nm thickness, and embedded in an external viscous fluid. Thevesicle membrane is an original system from the mechanical point of view : it presents bothincompressible fluid properties (the lipids can flow freely along the membrane, but membraneis incompressible locally) and solid properties (the membrane resists to bending). The specificproperties of the membrane make the system very deformable and very constrained at the sametime.This manuscript deals with the modelisation of a vesicle subjected to external stresses of hydrodynamical origin, in the Stokes regime. A particular attention is paid to the situation of asettling vesicle. This situation is studied analytically in the small deformation regime. It is foundthat several families of non-trivial stationnary shapes exist, owing to the specific properties ofthe membrane. The study of a settling vesicle is pursued by the development of a numerical codeable to deal with large deformations. Original numerical methods are developped to deal with thecomputation of the bending and with the surface incompressibility constraint. This code permitsto study the formation of tether at the rear of a settling vesicle. These tethers are thin (typicalaspect ratio : length/radius ∼ 100) cylinders of membrane connected to the original vesicle. Itis shown that these tethered shapes are stationary shapes. A theoretical model is proposed andcompared to numerical simulations. This model shows the particular importance of tension inthese shapes. A mechanical modelling based on a curved Cosserat surface is also presented, andpermits to identify the bending contribution to the stress tensor. This contribution is a salientingredient to understand tethered shapes
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Razzaq, Mudassar Verfasser], Stefan [Akademischer Betreuer] Turek, and Heribert [Akademischer Betreuer] [Blum. "Finite element simulation techniques for incompressible fluid structure interaction with applications to bioengineering and optimization / Mudassar Razzaq. Betreuer: Stefan Turek. Gutachter: Heribert Blum." Dortmund : Universitätsbibliothek Dortmund, 2011. http://d-nb.info/1096224798/34.
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Li, Zhe. "Développement d'une méthode de simulation de couplage fluide-structure à l'aide de la méthode SPH." Thesis, Ecully, Ecole centrale de Lyon, 2013. http://www.theses.fr/2013ECDL0036/document.
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L’Interaction Fluide-Structure (IFS) est un sujet d’intérêt dans beaucoup de problèmes pratiques aussi bien pour les recherches académiques ainsi que pour les applications industrielles. Différents types d’approches de simulation numérique peuvent être utilisés pour étudier les problèmes d’IFS afin d’obtenir de meilleurs conceptions et d’éviter des incidents indésirables. Dans ce travail, le domaine du fluide est simulé par une méthode hybride sans maillage (SPH-ALE), et la structure est discrétisée par la méthode d’ ´ Eléments Finis (EF). Considérant le fluide comme un ensemble de particules, on peut suivre l’interface entre le fluide et la structure d’une manière naturelle. Une stratégie de couplage conservant l’énergie est proposée pour les problèmes d’IFS transitoires où différents intégrateurs temporels sont utilisés pour chaque sous-domaine: 2nd ordre schéma de Runge-Kutta pour le fluide et schéma de Newmark pour le solide. En imposant la continuité de la vitesse normale à l’interface, la méthode proposée peut assurer qu’il n’y a ni injection d’énergie ni dissipation d’énergie à l’interface. L’énergie de l’interface est donc nulle (aux erreurs de troncature près) durant toute la période de simulation numérique. Cette méthode de couplage assure donc que la simulation de couplage est numériquement stable en temps. Les expérimentations numériques montrent que le calcul converge en temps avec l’ordre de convergence minimal des schémas utilisés dans chaque sous-domaine. Cette méthode proposée est d’abord appliquée `a un problème de piston mono-dimensionnel. On vérifie sur ce cas qu’elle ne dégrade pas l’ordre de précision en temps des schémas utilisés. On effectue ensuite les études des phénomènes de propagation d’ondes de choc au travers de l’interface fluide-structure. Un excellent accord avec la solution analytique est observé dans les cas de teste de propagation d’onde en 1-D. Finalement, les exemples multi-dimensionnels sont présentés. Ses résultats sont comparés avec ceux obtenus par d’autres méthodes de couplageThe Fluid-Structure Interaction (FSI) effects are of great importance for many multi-physical problems in academic researches as well as in engineering sciences. Various types of numerical simulation approaches may be used to investigate the FSI problems in order to get more reliable conception and to avoid unexpected disasters. In this work, the fluid sub-domain is simulated by a hybrid mesh-less method (SPH-ALE), and the structure is discretized by the Finite Element (FE) method. As the fluid is considered as a set of particles, one can easily track the fluid structure interface. An energy-conserving coupling strategy is proposed for transient fluid-structure interaction problems where different time integrators are used for each sub-domain: 2nd order Runge-Kutta scheme for the fluid and Newmark time integrator for the solid. By imposing a normal velocity constraint condition at the interface, this proposed coupling method ensures that neither energy injection nor energy dissipation will occur at the interface so that the interface energy is rigorously zero during the whole period of numerical simulation. This coupling method thus ensures that the coupling simulation shall be stable in time, and secondly, the numerical simulation will converge in time with the minimal convergence rate of all the time integrators chosen for each sub-domain. The proposed method is first applied to a mono-dimensional piston problem in which we verify that this method does not degrade the order of accuracy in time of the used time integrators. Then we use this coupling method to investigate the phenomena of propagation of shock waves across the fluidstructure interface. A good agreement is observed between the numerical results and the analytical solutions in the 1-D shock wave propagation test cases. Finally, some multi-dimensional examples are presented. The results are compared with the ones obtained by other coupling approaches
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Fleischer, Mario. "Mehrfeldmodellierung und Simulation der äußeren Haarsinneszelle der Cochlea." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-100717.
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Das Innenohr des Säugetieres ist ein hochspezialisiertes sensorisches System, das durch ein komplexes mechanisches Verhalten gekennzeichnet ist. Neben der komplizierten Morphometrie und Geometrie kommen auch dem richtungsabhängigen Materialverhalten eine wesentliche Bedeutung zu. Es zeigt sich, daß im Cortischen Organ mit der äußeren Haarsinneszelle ein Zelltyp vorliegt, der durch seine physikalischen Eigenschaften das Gesamtverhalten des Innenohres maßgeblich beeinflußt. Wie jede tierische Zelle weist die äußere Haarsinneszelle als biomechanisches System eine heterogene Mikrostruktur auf. Vom mechanischen Standpunkt aus gesehen, ist neben der mehrschichtigen basolateralen Zellwand jede Einzelzelle durch ein viskoses inneres Fluid (Zellplasma) und einen Zellkern (Nukleus) gekennzeichnet. Die resultierenden mechanischen Eigenschaften des Gesamtsystems ”äußere Haarsinneszelle” können durch Experimente und eine geeignete Modellierung determiniert werden.
In dieser Arbeit wird ein neuer Ansatz zur Bestimmung der viskoelastischen Materialeigenschaften der basolateralen Wand vorgestellt. Durch Anwendung einer effektiven Fluid-Struktur-Interaktion wird das Gesamtsystem geschlossen untersucht und eine umfangreiche Materialparameterstudie durchgeführt. Dabei werden im Rahmen der Kontinuumsmechanik gültige Materialgesetze angewendet. Das durch partielle Differentialgleichungen formulierte mechanische Feldproblem wird im Rahmen der Finiten-Elemente-Methode approximiert, was zu einem linearen Gleichungssystem führt. Auf dieser Grundlage wird ein Finite-Elemente-Modell der äußeren Haarsinneszelle entwickelt. Die zur Beschreibung notwendigen Systemmatrizen – insbesondere die Dämpfungsmatrix – basieren dabei vollständig auf einem viskoelastischen Materialgesetz. Die benutzte Methodik läßt weiterhin eine effiziente Berechnung im Frequenzbereich zu.
Es zeigt sich, daß eine spezielle Dämpfungsformulierung die experimentell bestimmten dynamischen Eigenschaften der Zelle adäquat widerspiegelt. Eine Analyse auf Materialgesetzebene zeigt, daß dafür reine Schubdämpfung und damit eine spezielle Anisotropie im Viskositätstensor verantwortlich ist. Diese Eigenschaft bestimmt das dynamische Verhalten der äußeren Haarsinneszelle bis mindestens 10 kHz und liegt damit im Hörbereich.
Der Modellierung der Zelle geht eine angepaßte Auswertung der experimentell ermittelten Daten voraus. Die mechanisch geeignete Auswertung der zugrundeliegenden Experimente weist dabei auf mögliche Fehlerquellen bei der Analyse der Rohdaten hin. Das hat zur Konsequenz, daß der experimentellen Umgebung die gleiche Aufmerksamkeit geschenkt werden muß wie dem Meßobjekt selbst. Nur so kann eine geeignete Extraktion der für das Meßobjekt spezifischen Eigenschaften erfolgen.