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Converting wave energy from fluid-elasticity interactions / Convertir l’énergie des vagues à partir d’interactions fluide-élasticitéNové-Josserand, Clotilde 01 October 2018 (has links)
Le développement des systèmes houlomoteurs ainsi que la gestion du littoral reposent sur une bonne compréhension des mécanismes liés aux interactions houle-structure. Dans cette thèse, nous nous intéressons à l'étude d'un champ de structures flexibles soumises à des ondes de surface, en vue de développer un système qui puisse à la fois atténuer les vagues et absorber l'énergie qui leur est associée de manière efficace. Les résultats présentés se basent autour d'expériences réalisées dans des installations de petite échelle, dans lesquelles la disposition spatiale des objets flexibles est le principal paramètre étudié. Dans un premier temps, nous caractérisons notre champ modèle afin d'évaluer l'influence de divers paramètres (configuration, flexibilité, fréquences des vagues) sur la distribution de l'énergie dans le système. Sur la base de ces résultats, nous développons ensuite un modèle d'interférences permettant de décrire les observations globales du système à partir de paramètres locaux connus, associés à une portion unitaire du champ. Ce modèle nous sert ensuite d'outil pour l'exploration d'une multitude de configurations spatiales, afin de déterminer le choix optimal vis-à-vis de l'atténuation et de l'absorption des vagues incidentes. Enfin, une campagne de mesures supplémentaire est utilisée afin d'expliquer les résultats obtenus avec le modèle et d'identifier les principes sous-jacents à cette optimisation / Understanding the mechanisms involved in wave-structure interactions is of high interest for the development of efficient wave energy harvesters as well as for coastal management. In this thesis, we study the interactions of surface waves with a model array of slender flexible structures, in view of developing an efficient system for both attenuating and harvesting wave energy. The presented results are based around experimental investigations, by means of small scale facilities, in which the spatial arrangement of the flexible objects is the key parameter of study. The model array is first characterised by evaluating the role played by various parameters (configuration, flexibility, wave frequency) on the energy distribution in our system. Following these first observations, an interference model is then developed in order to describe the observed global effects of the array on both the wave field and the blade dynamics, based on known local parameters of a unit item of the array. This model then serves as a tool for exploring many possible array configurations, in order to determine the optimal choice regarding both the attenuation and the absorption of the imposed waves. A final experimental study is presented, in which the key results from the interference model are evaluated and the underlying principles of array optimisation are identified
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A parallelized diffuse interface solver with applications to meso scale simulation of suspensionsMohaghegh, Fazlolah 15 December 2017 (has links)
The ultimate goal of this research is to develop the capability of direct numerical simulation of a flow containing numerous rigid finite size particles. In order to reach this goal, we have implemented the smoothed profile method (SPM) in the University of Iowa in-house solver, pELAFINT3D and overcame several challenges related to the method. This includes a proposed formulation for the interface thickness and many validations and comparisons with experimental data as well as with a second-order accurate sharp interface method. As one of the issues related to low-density particles is the instability, SPM has been improved by developing to a fully implicit scheme. Moreover, use of higher order integration formulation and implementation of Euler parameters have been shown to be helpful in stabilization of the calculations.
To preserve the efficiency when the number of the particles increases, local mesh refinement is shown to be a very effective tool. A revised version of SPM that has only one projection step is proposed to improve the efficiency of the method. A comprehensive efficiency study is performed and it has been shown that the new method is less expensive in problems with high added mass effect when strongly coupled fluid-structure interaction schemes are used. Moreover, the code is massively parallelized using MPI and PETSc libraries. The parallelization includes I/O, operations leading to construction of the linear solver as well as the solver itself.
Simulation of a particle laden flow involves particles collisions. Two novel collision models are suggested which are able to avoid particle overlapping for arbitrary shape particles. The methods are efficient as they are not involved with extra grid refinement related to implementing lubrication forces. The issue of handling continuously changing number of particles in a particle laden flow is solved by implementation of a linked list data structure for the particles.
By studying a flow over a constricted region we showed that the platelets’ activation is more likely to happen for the particles that pass from the middle of the upper bump region because those particles will have longer exposure time to the high shear flow behind the bump. PDF contour of particles’ presence show the more concentrated presence of the particles near the bump. Moreover, the interaction of RBCs and platelets pushes the platelets toward the wall after the bottom wall.
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A primarily Eulerian means of applying left ventricle boundary conditions for the purpose of patient-specific heart valve modelingGoddard, Aaron M. 01 December 2018 (has links)
Patient-specific multi-physics simulations have the potential to improve the diagnosis, treatment, and scientific inquiry of heart valve dynamics. It has been shown that the flow characteristics within the left ventricle are important to correctly capture the aortic and mitral valve motion and corresponding fluid dynamics, motivating the use of patient-specific imaging to describe the aortic and mitral valve geometries as well as the motion of the left ventricle (LV). The LV position can be captured at several time points in the cardiac cycle, such that its motion can be prescribed a priori as a Dirichlet boundary condition during a simulation. Valve leaflet motion, however, should be computed from soft-tissue models and incorporated using fully-coupled Fluid Structure Interaction (FSI) algorithms. While FSI simulations have in part or wholly been achieved by multiple groups, to date, no high-throughput models have been developed, which are needed for use in a clinical environment. This project seeks to enable patient-derived moving LV boundary conditions, and has been developed for use with a previously developed immersed boundary, fixed Cartesian grid FSI framework. One challenge in specifying LV motion from medical images stems from the low temporal resolution available. Typical imaging modalities contain only tens of images during the cardiac cycle to describe the change in position of the left ventricle. This temporal resolution is significantly lower than the time resolution needed to capture fluid dynamics of a highly deforming heart valve, and thus an approach to describe intermediate positions of the LV is necessary. Here, we propose a primarily Eulerian means of representing LV displacement. This is a natural extension, since an Eulerian framework is employed in the CFD model to describe the large displacement of the heart valve leaflets. This approach to using Eulerian interface representation is accomplished by applying “morphing” techniques commonly used in the field of computer graphics. For the approach developed in the current work, morphing is adapted to the unique characteristics of a Cartesian grid flow solver which presents challenges of adaptive mesh refinement, narrow band approach, parallel domain decomposition, and the need to supply a local surface velocity to the flow solver that describes both normal and tangential motion. This is accomplished by first generating a skeleton from the Eulerian interface representation, and deforming the skeleton between image frames to determine bulk displacement. After supplying bulk displacement, local displacement is determined using the Eulerian fields. The skeletons are also utilized to automate the simulation setup to track the locations upstream and downstream where the system inflow/outflow boundary conditions are to be applied, which in the current approach, are not limited to Cartesian domain boundaries.
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Fluid flow during continental reworking : a study of shear zones in the Arunta Inlier, central AustraliaRead, Caroline M. (Caroline Margaret), 1972- January 2002 (has links)
Abstract not available
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Algorithmic Developments for a Multiphysics FrameworkWuilbaut, Thomas 17 December 2008 (has links)
In this doctoral work, we adress various problems arising when dealing with multi-physical simulations using a segregated (non-monolithic) approach. We concentrate on a few specific problems and focus on the solution of aeroelastic
flutter for linear elastic structures in compressible fl
ows, conjugate heat transfer for re-entry vehicles including thermo-chemical reactions and finally, industrial electro-chemical plating processes which often include
stiff source terms. These problems are often solved using specifically developed
solvers, but these cannot easily be reused for different purposes. We have therefore considered the development of a
flexible and reusable software platform for the simulation of multi-physics problems. We have based this
development on the COOLFluiD framework developed at the von Karman Institute in collaboration with a group of partner institutions.
For the solution of fl
uid fl
ow problems involving compressible
flows, we have used the Finite Volume method and we have focused on the application of the method to moving and deforming computational domains using the Arbitrary Lagrangian Eulerian formulation. Validation on a series of testcases (including turbulent flows) is shown. In parallel, novel time integration
methods have been derived from two popular time discretization methods.
They allow to reduce the computational effort needed for unsteady fl
ow computations.
Good numerical properties have been obtained for both methods.
For the computations on deforming domains, a series of mesh deformation techniques are described and compared. In particular, the effect of the stiffness definition is analyzed for the Solid material analogy technique. Using
the techniques developed, large movements can be obtained while preserving a good mesh quality. In order to account for very large movements for which mesh deformation techniques lead to badly behaved meshes, remeshing is also considered.
We also focus on the numerical discretization of a class of physical models that are often associated with
fluid fl
ows in coupled problems. For the elliptic problems considered here (elasticity, heat conduction and electrochemical
potential problems), the implementation of a Finite Element solver is presented. Standard techniques are described and applied for a variety of problems, both steady and unsteady.
Finally, we discuss the coupling of the
fluid flow solver with the finite element solver for a series of applications. We concentrate only on loosely and strongly coupled algorithms and the issues associated with their use and implementation. The treatment of non-conformal meshes at the interface between two coupled computational domains is discussed and the problem
of the conservation of global quantities is analyzed. The software development of a
flexible multi-physics framework is also detailed. Then, several coupling algorithms are described and assessed for testcases in aeroelasticity and conjugate heat transfer showing the integration of the
fluid and solid solvers within a multi-physics framework. A novel strongly coupled algorithm, based on a Jacobian-Free Newton-Krylov method is also presented and applied to stiff coupled electrochemical potential problems.
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Finite element modelling of hydroelasticity in hull-water impactsStenius, Ivan January 2006 (has links)
<p>The work in this thesis focuses on the use of explicit finite element analysis (FEA) in the modelling of fluid-structure interaction of panel-water impacts. Paper A, considers modelling of a two-dimensional rigid wedge impacting a calm water surface. From analytical methods and results of a systematic parameter study a generalised approach for determination of fluid discretization and contact parameters in the modelling of arbitrary hull-water impact situations is developed and presented. In paper B the finite element modelling methodology suggested in paper A is evaluated for elastic structures by a convergence study of structural response and hydrodynamic load. The structural hydroelastic response is systematically studied by a number of FE-simulations of different impact situations concerning panel deadrise, impact velocity and boundary conditions. In paper B a tentative method for dynamic characterization is also derived. The results are compared with other published results concerning hydroelasticity in panel water impacts. The long-term goal of this work is to develop design criteria, by which it can be determined whether the loading situation of a certain vessel type should be regarded as quasi-static or dynamic, and which consequence on the design a dynamic loading has.</p>
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Algorithmen zur Kopplung und Interpolation in der Aerelastik / Algorithms for Coupling and Interpolation in the AeroelasticAhrem, Regine 19 December 2005 (has links)
No description available.
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Nonlinear fluid-structure interaction : a partitioned approach and its application through component technologyKassiotis, Christophe 20 November 2009 (has links) (PDF)
A partitioned approach is studied to solve strongly coupled nonlinear fluid structure interaction problems. The stability, convergence and performance of explicit and implicit coupling algorithms are explored. The partitioned approach allows to re-use existing codes in a more general context. One purpose of this work is to be able to couple them as black-boxes. To that end, the scientific software component framework CTL is considered. Therefore a fluid and a structure component based on existing software are developed and coupled with a master code approach. Computational performance of different remote calls and parallel implementation of components are also depicted herein. The re-use of existing software allows to couple advanced models developed for both sub-problems. In this work, the structure part is solved by the Finite Element Method, with the possibility to use different non-linear and large deformation behaviors. For the fluid part, examples modeled with an arbitrary Lagrangian Eulerian formulation are considered, solved with a finite volume method. The models used are first transient incompressible flows described by the Navier-Stokes equation, then free surface flows. With the latter, the impact of sloshing and breaking waves on model structures can be computed
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Boundary Element-finite Element Acoustic Analysis Of Coupled DomainsIrfanoglu, Bulent 01 August 2004 (has links) (PDF)
This thesis studies interactions between coupled acoustic domain(s) and enclosing rigid or elastic boundary. Boundary element-finite element (BE-FE) sound-structure interaction models are developed by coupling frequency domain BE acoustic and FE structural models using linear inviscid acoustic and elasticity theories.
Flexibility in analyses is provided by discontinuous triangular and quadrilateral elements in the BE method (BEM), and a rectangular plate and a triangular shell element in the FE method (FEM).
An analytical formulation is developed for an extended fundamental sound-structure interaction problem that involves locally reacting sound absorptive treatment on interior elastic boundary. This new formulation is built upon existing analytical solutions for a configuration known as the cavity-backed-plate problem. Results from developed analytical formulation are compared against those from independent BE-FE analyses.
Analytical and BE-FE analysis results for a selection of cavity-plate(s) interaction cases are given.
Single- and multi-domain BE analyses of cavity-Helmholtz resonator interaction are provided as an alternative to modal method of acoustoelasticity.
A discrete-form of the existing BE acoustic particle velocity formulation is presented and demonstrated on a basic case study. Both the existing and the discretized BE acoustic particle velocity formulations could be utilized in acoustic studies.
A selection of case studies involving fundamental configurations are studied both analytically and computationally (by BE or BE-FE methods). These studies could provide a basis for benchmark case development in the field of acoustics.
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Using foam-extend to assess the influence of fluid-structure interaction on the rupture of intracranial aneurysms /Oliveira, Iago Lessa January 2017 (has links)
Orientador: José Luiz Gasche / Resumo: 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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