Dissertations / Theses on the topic 'Computational fluid-structure interactions'
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Pitman, Mark William. "An investigation of flow structure interactions on a finite compliant surface using computational methods." Thesis, Curtin University, 2007. http://hdl.handle.net/20.500.11937/625.
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A study of the interaction of one-sided flow over a compliant surface is presented. When fluid passes over a flexible surface the simultaneous interaction between the flow and structure gives rise to vibrations and instabilities on the surface as well as in the fluid. The fluid-structure interaction (FSI) has potential to be used in the control of boundary layer dynamics to achieve drag reduction through transition delay. The modelling and control of FSI systems apply to many fields of engineering beyond drag reduction, for example: the modelling and analysis of biomechanical systems; natural environmental systems; aero-elastics; and other areas where flow interacts moving or compliant boundaries. The investigation is performed through numerical simulation. This returns more detail than could be resolved through experiments, while also permitting the study of finite compliant surfaces that are prohibitively difficult, or impossible, to study with analytical techniques. In the present work, novel numerical modelling methods are developed from linear system analysis through to nonlinear disturbances and viscous effects.Two numerical modelling techniques are adopted to approach the analysis of the FSI system. A potential-flow method is used for the modelling of flows in the limit of infinite Reynolds numbers, while a grid-free Discrete Vortex Method (DVM) is used for the modelling of the rotational boundary-layer flow at moderate Reynolds numbers. In both inviscid and viscous studies, significant contributions are made to the numerical modelling techniques. The application of these methods to the study of flow over compliant panels gives new insight to the nature of the FSI system. In the linear inviscid model, a novel hybrid computational/theoretical method is developed that evaluates the eigenvalues and eigenmodes from a discretised FSI system. The results from the non-linear inviscid model revealed that the steady-state of the non-linear wall motion is independent of initial excitation. For the viscous case, the first application of a DVM to model the interaction of a viscous, rotational flow with a compliant surface is developed. This DVM is successfully applied to model boundary-layer flow over a finite compliant surface.
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Pitman, Mark William. "An investigation of flow structure interactions on a finite compliant surface using computational methods." Curtin University of Technology, Department of Mechanical Engineering, 2007. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=17209.
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A study of the interaction of one-sided flow over a compliant surface is presented. When fluid passes over a flexible surface the simultaneous interaction between the flow and structure gives rise to vibrations and instabilities on the surface as well as in the fluid. The fluid-structure interaction (FSI) has potential to be used in the control of boundary layer dynamics to achieve drag reduction through transition delay. The modelling and control of FSI systems apply to many fields of engineering beyond drag reduction, for example: the modelling and analysis of biomechanical systems; natural environmental systems; aero-elastics; and other areas where flow interacts moving or compliant boundaries. The investigation is performed through numerical simulation. This returns more detail than could be resolved through experiments, while also permitting the study of finite compliant surfaces that are prohibitively difficult, or impossible, to study with analytical techniques. In the present work, novel numerical modelling methods are developed from linear system analysis through to nonlinear disturbances and viscous effects.Two numerical modelling techniques are adopted to approach the analysis of the FSI system. A potential-flow method is used for the modelling of flows in the limit of infinite Reynolds numbers, while a grid-free Discrete Vortex Method (DVM) is used for the modelling of the rotational boundary-layer flow at moderate Reynolds numbers. In both inviscid and viscous studies, significant contributions are made to the numerical modelling techniques. The application of these methods to the study of flow over compliant panels gives new insight to the nature of the FSI system. In the linear inviscid model, a novel hybrid computational/theoretical method is developed that evaluates the eigenvalues and eigenmodes from a discretised FSI system. The results from the non-linear inviscid model revealed that the steady-state of the non-linear wall motion is independent of initial excitation. For the viscous case, the first application of a DVM to model the interaction of a viscous, rotational flow with a compliant surface is developed. This DVM is successfully applied to model boundary-layer flow over a finite compliant surface.
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Sheer, Francis Joseph. "Multi-Scale Computational Modeling of Fluid-Structure Interactions and Adhesion Dynamics in the Upper Respiratory System." The Ohio State University, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=osu1316287639.
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Li, Yuwei. "Coupled computational fluid dynamics/multibody dynamics method with application to wind turbine simulations." Diss., University of Iowa, 2014. https://ir.uiowa.edu/etd/4681.
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A high fidelity approach coupling the computational fluid dynamics method (CFD) and multi-body dynamics method (MBD) is presented for aero-servo-elastic wind turbine simulations. The approach uses the incompressible CFD dynamic overset code CFDShip-Iowa v4.5 to compute the aerodynamics, coupled with the MBD code Virtual.Lab Motion to predict the motion responses to the aerodynamic loads. The IEC 61400-1 ed. 3 recommended Mann wind turbulence model was implemented in this thesis into the code CFDShip-Iowa v4.5 as boundary and initial conditions, and used as the explicit wind turbulence for CFD simulations. A drivetrain model with control systems was implemented in the CFD/MBD framework for investigation of drivetrain dynamics. The tool and methodology developed in this thesis are unique, being the first time with complete wind turbine simulations including CFD of the rotor/tower aerodynamics, elastic blades, gearbox dynamics and feedback control systems in turbulent winds.
Dynamic overset CFD simulations were performed with the benchmark experiment UAE phase VI to demonstrate capabilities of the code for wind turbine aerodynamics. The complete turbine geometry was modeled, including blades and approximate geometries for hub, nacelle and tower. Unsteady Reynolds-Averaged Navier-Stokes (URANS) and Detached Eddy Simulation (DES) turbulence models were used in the simulations. Results for both variable wind speed at constant blade pitch angle and variable blade pitch angle at fixed wind speed show that the CFD predictions match the experimental data consistently well, including the general trends for power and thrust, sectional normal force coefficients and pressure coefficients at different sections along the blade.
The implemented Mann wind turbulence model was validated both theoretically and statistically by comparing the generated stationary wind turbulent field with the theoretical one-point spectrum for the three components of the velocity fluctuations, and by comparing the expected statistics from the simulated turbulent field by CFD with the explicit wind turbulence inlet boundary from the Mann model.
The proposed coupled CFD/MBD approach was applied to the conceptual NREL 5MW offshore wind turbine. Extensive simulations were performed in an increasing level of complexity to investigate the aerodynamic predictions, turbine performance, elastic blades, wind shear and atmospheric wind turbulence. Comparisons against the publicly available OC3 simulation results show good agreements between the CFD/MBD approach and the OC3 participants in time and frequency domains. Wind turbulence/turbine interaction was examined for the wake flow to analyze the influence of turbulent wind on wake diffusion.
The Gearbox Reliability Collaborative project gearbox was up-scaled in size and added to the NREL 5MW turbine with the purpose of demonstrating drivetrain dynamics. Generator torque and blade pitch controllers were implemented to simulate realistic operational conditions of commercial wind turbines. Interactions between wind turbulence, rotor aerodynamics, elastic blades, drivetrain dynamics at the gear-level and servo-control dynamics were studied, showing the potential of the methodology to study complex aerodynamic/mechanic systems.
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Conger, Michael Anthony. "Validation of CFD-MBD FSI for high-gidelity simulations of full-scale WAM-V sea-trials with suspended payload." Thesis, University of Iowa, 2015. https://ir.uiowa.edu/etd/1960.
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High-fidelity CFD-MBD FSI (Computational Fluid Dynamics - Multi Body Dynamics Fluid-Structure Interaction) code development and validation by full-scale experiments is presented, for a novel hull form, WAM-V (Wave Adaptive Modular Vessel). FSI validation experiments include cylinder drop with suspended mass and 33 ft WAM-V sea-trials. Calm water and single-wave sea-trails were with the original suspension, while the rough-water testing was with a second generation suspension. CFDShip-Iowa is used as CFD solver, and is coupled to Matlab Simulink MBD models for cylinder drop and second generation WAM-V suspension. For 1DOF cylinder drop, CFD verification and validation (V&V) studies are carried out including grid and time-step convergence. CFD-MBD results for 2DOF cylinder drop show that 2-way coupling is required to capture coupled physics. Overall, 2-way results are validated with an overall average error value of E=5.6%DR for 2DOF cylinder drop. For WAM-V in calm water, CFD-MBD 2-way results for relative pod angle are validated with E=14.2%DR. For single-wave, CFD-MBD results show that 2-way coupling significantly improves the prediction of the peak amplitude in pontoon motions, while the trough amplitudes in suspension motions are under-predicted. The current CFD-MBD 2-way results for single-wave are validated with E=17%DR. For rough-water, simulations are carried out in regular head waves representative of the irregular seas. CFD-MBD 2-way results are validation with E=23%D for statistical values and the Fourier analysis results, which is reasonable given the differences between simulation waves and experiments.
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Dombre, Emmanuel. "Modélisation non-linéaire des interactions vague-structure appliquée à des flotteurs d'éoliennes off-shore." Thesis, Paris Est, 2015. http://www.theses.fr/2015PEST1050/document.
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Cette thèse est consacrée à l'étude numérique des interactions non-linéaires entre des vagues et un corps rigide perçant la surface libre. La méthode développée repose sur un modèle d'éléments de frontière qui réduit la dimensionnalité du problème d'une dimension. Dans un premier temps, un modèle2D est appliqué à des géométries simples et permet de démontrer la pertinence de l'approche envisagée pour la prédiction des mouvements d'une structure flottante soumise à des vagues monochromatiques régulières. Dans un second temps, en nous inspirant d'un modèle potentiel non-linéaire 3D développé par Grilli textit{et al.}~cite{grilli2001fully}, nous proposons une généralisation de la méthode pour des maillages triangulaires non-structurés de surfaces 3D. Le modèle développé permet de traiter des configurations arbitraires de plusieurs cylindres verticaux en interaction avec les vagues. Nous présentons des cas de validation de nature académique qui permettent d'apprécier le comportement du modèle numérique. Puis nous nous tournons vers l'application visée par EDF R&D, qui concerne le dimensionnement d'éoliennes off-shore flottantes. Un flotteur de type semi-submersible est évalué à l'aide du modèle non-linéaireThis PhD work is devoted to the study of nonlinear interactions between waves and floating rigid structures. The developed model relies on a boundary element method which reduces the dimensionality of the problem by one. First, a 2D model is applied to basic geometries and allows us to demonstrate the validity of the method for predicting the motion of a floating structrure subject to incoming monochromatic regular waves. Secondly, getting inspired by the 3D fully nonlinear potential flow model of Grilli textit{et al.}~cite{grilli2001fully}, we propose a novel model which generalizes the method for unstructured triangular meshes of 3D surfaces. The proposed model is able to deal with arbitrary configurations of multiple vertical cylinders interacting with the waves. We present academic validation test cases which show how the model works and behaves. Finally, we study situations of interest for EDF R&D related to floating off-shore wind turbines. A semi-submersible platform is evaluated with the nonlinear model
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Vaterlaus, Austin C. "Development of a 3D Computational Vocal Fold Model Optimization Tool." BYU ScholarsArchive, 2020. https://scholarsarchive.byu.edu/etd/8468.
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One of the primary objectives of voice research is to better understand the biomechanics of voice production and how changes in properties of the vocal folds (VFs) affect voice ability and quality. Synthetic VF models provide a way to observe how changes in geometry and material property affect voice biomechanics. This thesis seeks to evaluate an approach of using a genetic algorithm to design synthetic VF models in three ways: first, through the development of a computationally cost-effective 3D vocal fold model; second, by creating and optimizing a variation of this model; and third, by validating the approach. To reduce computation times, a user-defined function (UDF) was implemented in low-fidelity 2D and 3D computational VF models. The UDF replaced the conventional meshed fluid domain with the mechanical energy equation. The UDF was implemented in the commercial finite element code ADINA and verified to produce results that were similar to those of 2D and 3D VF models with meshed fluid domains. Computation times were reduced by 86% for 2D VF models and 74% for 3D VF models while core vibratory characteristic changes were less than 5%. The results from using the UDF demonstrate that computation times could be reduced while still producing acceptable results. A genetic algorithm optimizer was developed to study the effects of altering geometry and material elasticity on frequency, closed quotient (CQ), and maximum flow declination rate (MFDR). The objective was to achieve frequency and CQ values within the normal human physiological range while maximizing MFDR. The resulting models enabled an exploration of trends between objective and design variables. Significant trends and aspects of model variability are discussed. The results demonstrate the benefit of using a structured model exploration method to create models with desirable characteristics. Two synthetic VF models were fabricated to validate predictions made by models produced by the genetic algorithm. Fabricated models were subjected to tests where frequency, CQ, and sound pressure level were measured. Trends between computational and synthetic VF model responses are discussed. The results show that predicted frequency trends between computational and synthetic models were similar, trends for closed quotient were inconclusive, and relationships between MFDR and sound pressure level remained consistent. Overall, while discrepancies between computational and synthetic VF model results were observed and areas in need of further study are noted, the study results provide evidence of potential for using the present optimization method to design synthetic VF models.
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Kessy, Edgard. "Décomposition de domaine et calcul parallèle distribué : application à la mécanique des fluides." Rouen, 1997. http://www.theses.fr/1997ROUES052.
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Ce travail concerne l'utilisation du parallélisme pour la résolution de certains problèmes de mécanique des fluides. La technique de décomposition de domaine a été appliquée pour résoudre en parallèle des problèmes basés aussi bien sur des schémas explicites qu'implicites. Elle a montré pour ce dernier cas la nécessité d'introduire un retard au niveau de la propagation de l'information lors de la gestion des interfaces entre sous-domaines. Deux exemples de problèmes couplés ont été résolus en parallèle. Le premier traite un problème de couplage fluide-structure appliqué au cas d'un propulseur de moteur fusée, le second exemple étant relatif à un couplage aérodynamique-chimie appliqué à une couche de mélange. La résolution parallèle a été faite sur différentes architectures MIMD à mémoire distribuée, avec l'utilisation des bibliothèques de communication PVM et MPI.
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Paton, Jonathan. "Computational fluid dynamics and fluid structure interaction of yacht sails." Thesis, University of Nottingham, 2011. http://eprints.nottingham.ac.uk/14036/.
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This thesis focuses on the numerical simulation of yacht sails using both computational fluid dynamics (CFD) and fluid structure interaction (FSI) modelling. The modelling of yacht sails using RANS based CFD and the SST turbulence model is justified with validation against wind tunnel studies (Collie, 2005; Wilkinson, 1983). The CFD method is found to perform well, with the ability to predict flow separation, velocity and pressure profiles satisfactorily. This work is extended to look into multiple sail interaction and the impact of the mast upon performance. A FSI solution is proposed next, coupling viscous RANS based CFD and a structural code capable of modelling anistropic laminate sails (RELAX, 2009). The aim of this FSI solution is to offer the ability to investigate sails' performance and flying shapes more accurately than with current methods. The FSI solution is validated with the comparison to flying shapes of offwind sails from a bespoke wind tunnel experiment carried out at the University of Nottingham. The method predicted offwind flying shapes to a greater level of accuracy than previous methods. Finally the CFD and FSI solution described here above is showcased and used to model a full scale Volvo Open 70 racing yacht, including multiple offwind laminate sails, mast, hull, deck and twisted wind profile. The model is used to demonstrate the potential of viscous CFD and FSI to predict performance and aid in the design of high performance sails and yachts. The method predicted flying shapes and performance through a range of realistic sail trims providing valuable data for crews, naval architects and sail designers.
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Yang, Liang. "An immersed computational framework for multiphase fluid-structure interaction." Thesis, Swansea University, 2015. https://cronfa.swan.ac.uk/Record/cronfa42413.
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The objective of this thesis is to further extend the application range of immersed computational approaches in the context of hydrodynamics and present a novel general framework for the simulation of fluid-structure interaction problems involving rigid bodies, flexible solids and multiphase flows. The proposed method aims to overcome shortcomings such as the restriction of having to deal with similar density ratios among different phases or the restriction to solve single-phase flows. The new framework will be capable of coping with large density ratios, multiphase flows and will be focussed on hydrodynamic problems. The two main challenges to be addressed are: - the representation, evolution and compatibility of the multiple fluid-solid interface - the proposition of unified framework containing multiphase flows, flexible structures and rigid bodies with possibly large density ratios First, a new variation of the original IBM is presented by rearranging the governing equations which define the behaviour of the multiple physics involved. The formulation is compatibile with the "one-fluid" equation for two phase flows and can deal with large density ratios with the help of an anisotropic Poisson solver. Second, deformable structures and fluid are modelled in a identical manner except for the deviatoric part of the Cauchy stress tensor. The challenging part is the calculation of the deviatoric part the Cauchy stress in the structure, which is expressed as a function of the deformation gradient tensor. The technique followed In this thesis is that original ISP, but re-expressed in terms of the Cauchy stress tensor. Any immersed rigid body is considered as an incompressible non-viscous continuum body with an equivalent internal force field which constrains the velocity field to satisfy the rigid body motion condition. The "rigid body" spatial velocity is evaluated by means of a linear least squares projection of the background fluid velocity, whilst the immersed force field emerges as a result of the linear momentum conversation equation. This formulation is convenient for arbitrary rigid shapes around a fixed point and the most general translation- rotation. A characteristic or indicator function, defined for each interacting continuum phase, evolves passively with the velocity field. Generally, there are two families of algorithms for the description of the interfaces, namely, Eulerian grid based methods (interface tracking). In this thesis, the interface capturing Level Set method is used to capture the fluid-fluid interface, due to its advantages to deal with possible topological changes. In addiction, an interface tracking Lagrangian based meshless technique is used for the fluid-structure interface due to its benefits at the ensuring mass preservation. From the fluid discretisation point of view, the discretisation is based on the standard Marker-and-Cell method in conjunction with a fractional step approach for the pressure/velocity decoupling. The thesis presents a wide range of applications for multiphase flows interacting with a variety of structures (i.e. rigid and deformable) Several numerical examples are presented in order to demonstrate the robustness and applicability of the new methodology.
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Yeh, Han Hung. "Computational analysis of fluid structure interaction in artificial heart valves." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44921.
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The development of heart valve stenosis and sclerosis can lead to the development of fatal complications such as congestive heart failure. Therefore, severe valve stenosis requires a surgical operation with artificial heart valve replacement. Given that the geometrical differences between artificial valves would significantly influence hemodynamic performance around the implanted valve, additional knowledge for the interactions between blood flow and the artificial valve is necessary. Therefore, in order to proceed, this study proposes an advanced computational fluid dynamics (CFD) simulation using a fluid-structure interaction (FSI) technique to investigate artificial valve leaflet motion under different physiological conditions.
Among various FSI technique, it is proposed to simulate the motion of the artificial heart valve with a fully-coupled algorithm and arbitrary Lagrangian-Eulerian formulation (ALE) using a monolithic solver. Models are constructed using a realistic aortic root for both the bileaflet and bioprosthetic valves with additional modifications and considerations for the flexible arterial wall. Normal physiological blood pressure and conditions are used to simulate healthy scenarios, which are compared with experiments. Validation is conducted by analysing particle image velocimetry (PIV) experimental data from ViVitro Lab. Hemodynamic performance analyses are conducted and found that both velocity and maximum von Mises stress are higher if calculated using a rigid wall model. The leaflet dynamics, on the other hand, is relatively the same for rigid or flexible wall model. Clinically relevant scenarios are also simulated for both mechanical and bioprosthetic valves. The clinical focus for the mechanical valve is on the malfunction of the valve due to leaflet restrictions. In addition, the clinical focus for the bioprosthetic valve is on the systolic deficiency due to different tissue properties.
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Hafezi, Farzaneh. "Computational modelling of fluid-structure interaction at nano-scale boundaries." Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42753.
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With the emergence of nano-devices and nano-scale research, gaining further understanding of the evolution of drag forces exerted by molecular flows, at low Knudsen numbers (-0.1-0.5), over nano-scaled objects with 20-100 nm size is a realistic expectation. The proposed research examines the fluid-structure interaction at nano-scales from first principles. It has also critically evaluated, and if necessary modified, the assumptions made during the development of a computational model. The research has provided new insights in modelling molecular interaction with continuum as well as molecular walls and calculation procedures for predicting macroscopic properties such as velocity, pressure and drag coefficients. The proposed formulation has been compared with the state of the art formulations as published in recent journals and verified on number numerical and molecular tests as experimental and analytical results are unavailable at this scale. The effect of various geometry configurations (slit pore, inclined and stepped wall) to model the pressure driven molecular flow through confined walls is studied for number of surface roughness and driving force values given by adjusting molecular accelerations. The molecular flow over diamond, circular and square shaped cylinders confined within parallel walls has also been modelled at various input conditions. It is expected that the proposed research will have impact in developing future nanoscale applications, in the field of drug delivery, surface cleaning and protein movement, where adsorption, drag resistance or, in general, understanding of the knowledge of fluid-structure interaction at 50-100nm scale is important. Some of the future research areas resulting from this research have also been identified.
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Behrndtz, Frandsen Jannette. "Computational fluid structure interaction applied to long-span bridge design." Thesis, University of Cambridge, 1999. https://www.repository.cam.ac.uk/handle/1810/272004.
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Cai, Shang-Gui. "Computational fluid-structure interaction with the moving immersed boundary method." Thesis, Compiègne, 2016. http://www.theses.fr/2016COMP2276/document.
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Dans cette thèse, une nouvelle méthode de frontières immergées a été développée pour la simulation d'interaction fluide-structure, appelée la méthode de frontières immergées mobiles (en langage anglo-saxon: MIBM). L'objectif principal de cette nouvelle méthode est de déplacer arbitrairement les solides à géométrie complexe dans un fluide visqueux incompressible, sans remailler le domaine fluide. Cette nouvelle méthode a l'avantage d'imposer la condition de non-glissement à l'interface d'une manière exacte via une force sans introduire des constantes artificielles modélisant la structure rigide. Cet avantage conduit également à la satisfaction de la condition CFL avec un pas de temps plus grand. Pour un calcul précis de la force induite par les frontières mobiles, un système linéaire a été introduit et résolu par la méthode de gradient conjugué. La méthode proposée peut être intégrée facilement dans des solveurs résolvant les équations de Navier-Stokes. Dans ce travail la MIBM a été mise en œuvre en couplage avec un solveur fluide utilisant une méthode de projection adaptée pour obtenir des solutions d'ordre deux en temps et en espace. Le champ de pression a été obtenu par l'équation de Poisson qui a été résolue à l'aide de la méthode du gradient conjugué préconditionné par la méthode multi-grille. La combinaison de ces deux méthodes a permis un gain de temps considérable par rapport aux méthodes classiques de la résolution des systèmes linéaires. De plus le code de calcul développé a été parallélisé sur l'unité graphique GPU équipée de la bibliothèque CUDA pour aboutir à des hautes performances de calcul. Enfin, comme application de nos travaux sur la MIBM, nous avons étudié le couplage "fort" d'interaction fluide-structure (IFS). Pour ce type de couplage, un schéma implicite partitionné a été adopté dans lequel les conditions à l'interface sont satisfaites via un schéma de type "point fixe". Pour réduire le temps de calcul inhérent à cette application, un nouveau schéma de couplage a été proposé pour éviter la résolution de l'équation de Poisson durant les itérations du "point fixe". Cette nouvelle façon de résoudre les problèmes IFS a montré des performances prometteuses pour des systèmes en IFS complexeIn this thesis a novel non-body conforming mesh formulation is developed, called the moving immersed boundary method (MIBM), for the numerical simulation of fluid-structure interaction (FSI). The primary goal is to enable solids of complex shape to move arbitrarily in an incompressible viscous fluid, without fitting the solid boundary motion with dynamic meshes. This novel method enforces the no-slip boundary condition exactly at the fluid-solid interface with a boundary force, without introducing any artificial constants to the rigid body formulation. As a result, large time step can be used in current method. To determine the boundary force more efficiently in case of moving boundaries, an additional moving force equation is derived and the resulting system is solved by the conjugate gradient method. The proposed method is highly portable and can be integrated into any fluid solver as a plug-in. In the present thesis, the MIBM is implemented in the fluid solver based on the projection method. In order to obtain results of high accuracy, the rotational incremental pressure correction projection method is adopted, which is free of numerical boundary layer and is second order accurate. To accelerate the calculation of the pressure Poisson equation, the multi-grid method is employed as a preconditioner together with the conjugate gradient method as a solver. The code is further parallelized on the graphics processing unit (GPU) with the CUDA library to enjoy high performance computing. At last, the proposed MIBM is applied to the study of two-way FSI problem. For stability and modularity reasons, a partitioned implicit scheme is selected for this strongly coupled problem. The interface matching of fluid and solid variables is realized through a fixed point iteration. To reduce the computational cost, a novel efficient coupling scheme is proposed by removing the time-consuming pressure Poisson equation from this fixed point interaction. The proposed method has shown a promising performance in modeling complex FSI system
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Kapor, Jarrad Stephen. "Novel computational methods for the study of compliant-wall fluid-structure interaction." Thesis, Curtin University, 2012. http://hdl.handle.net/20.500.11937/819.
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Applying compliant-wall coatings to otherwise rigid surfaces can delay the onset of laminar-turbulent transition and offer marked reductions in skin-friction drag and energy consumption, particularly in marine applications.However, the complex dynamics that result from the coupling of fluid and structure give rise to system instabilities that may prevent drag-reductions in engineering applications.A computational method is developed to study such systems and aid the design of compliant-wall technologies.
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Nagai, Toshiki. "Space-time Extended Finite Element Method with Applications to Fluid-structure Interaction Problems." Thesis, University of Colorado at Boulder, 2018. http://pqdtopen.proquest.com/#viewpdf?dispub=10844711.
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This thesis presents a space-time extended finite element method (space-time XFEM) based on the Heaviside enrichment for transient problems with moving interfaces, and its applications to the fluid-structure interaction (FSI) analysis. The Heaviside-enriched XFEM is a promising method to discretize partial differential equations with discontinuities in space. However, significant approximation errors are introduced by time stepping schemes when the interface geometry changes in time. The proposed space-time XFEM applies the finite element discretization and the Heaviside enrichment in both space and time with elements forming a space-time slab. A simple space-time scheme is introduced to integrate the weak form of the governing equations. This scheme considers spatial intersection configuration at multiple temporal integration points. Standard spatial integration techniques can be applied for each spatial configuration. Nitsche's method and the face-oriented ghost-penalty method are extended to the proposed space-time XFEM formulation. The stability, accuracy and flexibility of the space-time XFEM for various interface conditions including moving interfaces are demonstrated with structural and fluid problems. Moreover, the space-time XFEM enables analyzing complex FSI problems using moving interfaces, such as FSI with contact. Two FSI methods using moving interfaces (full-Eulerian FSI and Lagrangian-immersed FSI) are studied. The Lagrangian-immersed FSI method is a mixed formulation of Lagrangian and Eulerian descriptions. As solid and fluid meshes are independently defined, the FSI is computed between non-matching interfaces based on Nitsche's method and projection techniques adopted from computational contact mechanics. The stabilized Lagrange multiplier method is used for contact. Numerical examples of FSI and FSI-contact problems provide insight into the characteristics of the combination of the space-time XFEM and the Lagrangian-immersed FSI method. The proposed combination is a promising method which has the versatility for various multi-physics simulations and the applicability such as optimization.
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Miller, Samuel C. "Fluid-Structure Interaction of a Variable Camber Compliant Wing." University of Dayton / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1428575972.
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Scroggs, Richard A. "Validation of computational fluid-structure interaction models by comparison with collapsible tube experiments." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/14835/.
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The objective of this thesis was to assess the validity of the fluid-structure interaction (FSI) facilities in LS-DYNA for the analysis of highly deformable structures interacting with flowing viscous fluids. The collapsible tube experiment was chosen as a validation tool for FSI since its three-dimensional computational modelling would have been impossible if the viscous internal fluid flow were not considered. An explicit three-dimensional finite element model of a collapsible-tube was constructed and solved using LS-DYNA. The fully coupled model included internal fluid flow; external, inlet and outlet pressures; tube wall tension; pre-stressing; and contact. The finite element boundary conditions were taken as the recorded values of flow rate and pressure from a standard collapsible-tube experiment for both steady and unsteady flows. The predicted tube geometry in the steady LS-DYNA model showed good agreement with the experiment for operating points in the highly compliant region of the pressure-flow characteristic curve. The comparative position of the pinch at the outlet end differed by only 5.6% of the outlet diameter in the worst case. This analysis represents an advance on other published work in that previously no comparison with experiments have been drawn for FSI models involving high Reynolds number flowing viscous fluids interacting with highly deformable three dimensional structures. This analysis successfully made that comparison and the experimental and computational results have combined to form a more detailed picture of the collapsible-tube phenomenon by including detailed stress results of the tube walls and views of the internal fluid flow. The collapsible tube model exhibited uncertainty errors due to the use of a coarser than desirable mesh and a reduced fluid speed of sound. Although both these approximations caused significant error in the model both were necessary in order to achieve acceptable solution times. Because of these errors a thorough quantitative validation could not be achieved although LS-DYNA has been proven to be qualitatively accurate. Increases in computing speed are required before thorough quantitative validation of FSI can be achieved by comparison with the collapsible tube experiments.
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Mohnot, Anshul. "Solution of fluid-structure interaction problems using a discontinuous Galerkin technique." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43798.
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Thesis (S.M.)--Massachusetts Institute of Technology, Computation for Design and Optimization Program, 2008.Includes bibliographical references (p. 57-58).
The present work aims to address the problem of fluid-structure interaction using a discontinuous Galerkin approach. Starting from the Navier-Stokes equations on a fixed domain, an arbitrary Lagrangian Eulerian (ALE) approach is used to derive the equations for the deforming domain. A geometric conservation law (GCL) is then introduced, which guarantees freestream preservation of the numerical scheme. The space discretization is performed using a discontinuous Galerkin method and time integration is performed using either an explicit four stage Runge-Kutta scheme or an implicit BDF2 scheme. The mapping parameters for the ALE formulation are then obtained using algorithms based on radial basis functions (RBF) or linear elasticity. These strategies are robust and can be applied to bodies with arbitrary shapes and undergoing arbitrary motions. The robustness and accuracy of the ALE scheme coupled with these mapping strategies is then demonstrated by solving some model problems. The ability of the scheme to handle complex flow problems is demonstrated by analyzing the low Reynolds number flow over an oscillating circular cylinder.
by Anshul Mohnot.
S.M.
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Nave, Jr Gary Kirk. "Nonlinear Models and Geometric Structure of Fluid Forcing on Moving Bodies." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/84945.
Full textAbstract:
This dissertation presents useful nonlinear models for fluid forcing on a moving body in two distinct contexts, and methods for analyzing the geometric structure within those and other mathematical models. This manuscript style dissertation presents three works within the theme of understanding fluid forcing and geometric structure.
When a bluff body is free to move in the presence of an incoming bluff body wake, the average forcing on the body is dependent on its position relative to the upstream bluff body. This position-dependent forcing can be conceptualized as a stiffness, much like a spring. This work presents an updated model for the quasi-steady fluid forcing of a wake and extends the notion of wake stiffness to consider a nonlinear spring. These results are compared with kinematic experimental results to provide an example of the application of this framework.
Fluid force models also play a role in understanding the behavior of passive aerodynamic gliders, such as gliding animals or plant material. The forces a glider experiences depend on the angle that its body makes with respect to its direction of motion. Modeling the glider as capable of pitch control, this work considers a glider with a fixed angle with respect to the ground. Within this model, all trajectories in velocity space collapse to a 1-dimensional invariant manifold known as the terminal velocity manifold. This work presents methods to identify the terminal velocity manifold, investigates its properties, and extends it to a 2-dimensional invariant manifold in a 3-dimensional space.
Finally, in the search for manifolds such as the terminal velocity manifold, this dissertation introduces a new diagnostic for identifying the low dimensional geometric structure of models. The trajectory divergence rate uses instantaneous vector field information to identify regions of large normal stretching and strong normal convergence between nearby invariant manifolds. This work lays out the mathematical basis of the trajectory divergence rate and shows its application to approximate a variety of structures including slow manifolds and Lagrangian coherent structures.
This dissertation applies nonlinear theoretical and numerical techniques to analyze models of fluid forcing and their geometric structure. The tools developed in this dissertation lay the groundwork for future research in the fields of flow-induced vibration, plant and animal biomechanics, and dynamical systems.Ph. D.
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Pouplana, I. de (Ignasi de). "Development of new computational methods for fluid-structure interaction analysis of multi-fractured media." Doctoral thesis, Universitat Politècnica de Catalunya, 2018. http://hdl.handle.net/10803/461413.
Full textAbstract:
The objective of this thesis is the derivation and implementation of a robust Finite Element formulation for the solution of solid-pore fluid coupled problems in multi-fractured porous media.
A coupled displacement-pore pressure FEM formulation for solving solid-pore fluid interaction problems is first introduced. The interaction between both components is governed by two equations: the balance of momentum for the mixture solid-fluid and the mass balance for the pore fluid.
Under nearly undrained-incompressible conditions, such formulation suffers from instability problems because of the violation of Babuska-Brezzi conditions. In order to work with elements of equal order interpolation for the displacement and pore pressure, the formulation is stabilized by means of the Finite Increment Calculus method (FIC). The FIC-stabilized formulation is tested against stable elements with a higher order interpolation for the displacement field in 2D and 3D examples.
Continuum damage mechanics is the basis of the crack growth strategy for the proposed fracture propagation technique. The strain softening models used for quasi-brittle materials favour spurious strain localization and ill-posedness of the boundary value problem if the damage variable only depends on the strain state at the point under consideration.
An integral-type non-local damage model associated to a characteristic length parameter is presented as a method to control the size of the fracture process zone and fully regularize the problem. Two examples are solved assessing the robustness of the model in front of changes in the spatial discretization.
Quasi-zero-thickness interface elements are formulated to represent discontinuities in the porous domain. A bilinear cohesive fracture model is used to describe its mechanical behaviour, and a formulation derived from the cubic law models the fluid flow through the crack.
Finally, a new methodology for the simulation of fracture propagation processes in saturated porous media is presented. The non-local damage model is used in conjunction with the interface elements to predict the degradation pattern of the domain and insert new fractures followed by remeshing. Fluid-driven fracture propagation examples in 2D and 3D are presented to illustrate the accuracy of the proposed technique.El objetivo de esta tesis es la derivación e implementación de una formulación robusta de Elementos Finitos para la solución de problemas acoplados de sólido-fluido de poro en medios porosos multi-fracturados. Una formulación del MEF acoplada desplazamiento-presión de poro para resolver problemas de interacción solido-fluido de poro es primeramente introducida. La interacción entre ambos componentes es gobernada por dos ecuaciones: el balance de momento para la mezcla sólido-fluido y el balance de masa para el fluido de poro. Bajo condiciones de impermeabilidad e incompresibilidad, esta formulación sufre problemas de inestabilidad debido a la violación de las condiciones Babuska-Brezzi. Para poder trabajar con elementos de igual orden de interpolación para los desplazamientos y la presión de poro, la formulación es estabilizada mediante el método de Finite Increment Calculus (FIC). La formulación estabilizada con FIC es testeada contra elementos estables de mayor orden de interpolación para el campo de desplazamientos en ejemplos 2D y 3D. La mecánica del daño continua es la base de la estrategia de crecimiento de fisura para la técnica de propagación de fracturas propuesta. Los modelos de deformación con reblandecimiento utilizados para materiales cuasi-frágiles favorecen la localización espuria de las deformaciones y el mal condicionamiento del problema de valores en el contorno si la variable de daño depende únicamente del estado de deformación en el punto considerado. Un modelo de daño no-local de tipo integral asociado a un parámetro de longitud característica es presentado como un método para controlar el tamaño de la zona de fractura y regularizar totalmente el problema. Dos ejemplos son resueltos para evaluar la robustez del modelo frente a cambios en la discretización espacial. Elementos de interface de espesor cuasi-cero son formulados para representar discontinuidades en el dominio poroso. Un modelo de fractura cohesiva bilineal es utilizado para describir su comportamiento mecánico, y una formulación derivada de la ley cúbica modela el flujo de fluido a través de la fisura. Finalmente, una nueva metodología para la simulación de procesos de propagación de fractura en medios porosos saturados es presentada. El modelo de daño no-local es empleado juntamente con los elementos de interface para predecir el mapa de degradación del dominio e insertar nuevas fracturas seguido de un remallado. Ejemplos de fractura por fluido en 2D y 3D son presentados para ilustrar la precisión de la técnica propuesta.
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Chun, Sangeon. "Nonlinear Fluid-Structure Interaction in a Flexible Shelter under Blast Loading." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/29849.
Full textAbstract:
Recently, numerous flexible structures have been employed in various fields of industry. Loading conditions sustained by these flexible structures are often not described well enough for engineering analyses even though these conditions are important. Here, a flexible tent with an interior Collective Protection System, which is subjected to an explosion, is analyzed. The tent protects personnel from biological and chemical agents with a pressurized liner inside the tent as an environmental barrier. Field tests showed unexpected damage to the liner, and most of the damage occurred on tent's leeward side.
To solve this problem, various tests and analyses have been performed, involving material characteristics of the liner, canvas, and zip seals, modeling of the blast loading over the tent and inside the tent, and structural response of the tent to the blast loading as collaborative research works with others. It was found that the blast loading and the structural response can not be analyzed separately due to the interaction between the flexible structure and the dynamic pressure loading. In this dissertation, the dynamic loadings imposed on both the interior and the exterior sides of the tent structure due to the airblasts and the resulting dynamic responses were studied. First, the blast loadings were obtained by a newly proposed theoretical method of analytical/empirical models which was developed into a FORTRAN program. Then, a numerical method of an iterative Fluid-Structure Interaction using Computational Fluid Dynamics and Computational Structural Dynamics was employed to simulate the blast wave propagation inside and outside the flexible structure and to calculate the dynamic loads on it.
All the results were compared with the field test data conducted by the Air Force Research Laboratory. The experimental pressure data were gathered from pressure gauges attached to the tent surfaces at different locations. The comparison showed that the proposed methods can be a good design tool to analyze the loading conditions for rigid or flexible structures under explosive loads. In particular, the causes of the failure of the liner on the leeward were explained. Also, the results showed that the effect of fluid-structure interaction should be considered in the pressure load calculation on the structure where the structural deflection rate can influence the solution of the flow field surrounding the structure.Ph. D.
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Byrd, Alex W. "Fluid-Structure Interaction Simulations of a Flapping Wing Micro Air Vehicle." Wright State University / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=wright1401559891.
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Quintero, Igeño Pedro Manuel. "Characterization of Fluid Structure Interaction mechanisms and its application to vibroacoustic phenomena." Doctoral thesis, Universitat Politècnica de València, 2019. http://hdl.handle.net/10251/128412.
Full textAbstract:
[ES] La Interacción Fluido Estructura consiste en un problema físico en el
que dos materiales, gobernados por conjuntos de ecuaciones distintas, se
acoplan de diferentes formas.
La investigación en el campo de la Interacción Fluido Esructura
experimentó un importante desarrollo desde principios del siglo XX, de la
mano del campo de la aeroelasticdad. Durante el desarrollo de la industria
aeroespacial en el contexto de las guerras mundiales, el uso de materiales
más ligeros (y flexibles) comenzó a hacerse obligatorio para la obtención de
aeronaves con un comportamiento (y costes) aceptable.
A lo largo de los últimos años, el uso de materiales de construcción
cada vez más ligeros, se ha extendido al resto de campos de la industria.
A modo de ejemplo, podría servir el desarrollo de trackers en la producción
de energia solar; la utilización de materiales ligeros en ingeniería
civil o el desarrollo de elementos constructivos de plástico en la industria
del automóvil. Como consecuencia, la predicción con exactitud de las
deformaciones inducidas por un fluido y, si aplica, la influencia de estas
deformaciones en el propio flujo, ha adquirido una importancia vital.
Este documento intenta porporcionar, en primer lugar, una profunda
revisión de los métodos experimentales y computacionales que se han utilizado
en este contexto en la bibliografía, así como los análisis en problemas
de este tipo realizados por otros investigadores de cara a presentar una
primera aproximación a la Interacción Fluido Estructura.
Se verá cómo existe una importante cantidad de herramientas y
metodologías aplicables a cualquier tipo de problema y para cualquier
combinación de flujos y estructuras. Sin embargo, no existe una aproximación
general que, en función de valores de números adimensionales,
permita establecer cuáles de ellos son los de mayor importancia en este
tipo de problemas. En este sentido, se llevará a cabo un completo análisis
paramétrico durante el desarrollo del Capítulo 2 para establecer cuáles de
ellos son de mayor importancia.
Una vez se establezca la importancia de estos parámetros, se analizará
un caso que es de especial interés en la industria: la aerovibroacústica. Éste
es un caso particular de Interacción Fluido Estructura en el que, debido a
la combinación de parámetros adimensionales, la interacción se puede considerar
como prácticamente unidireccional, permitiendo extender estudios
mediante un conste computacional relativamente acotado. La Aerovibroacústica
y la vibroacústica se analizarán mediante la presentación de
dos casos de referencia, permitiendo proponer una metodología que se
podrá extender a otros problemas similares.[CAT] La Interacció Fluid Estructura consisteix en un problema físic en què dos materials, governats per conjunts d'equacions diferents, s'acoblen de diferents formes. La investigació en el camp de la Interacció Fluid Esructura va experimentar un important desenvolupament des de principis del segle XX, de la mà del camp de la aeroelasticdad. Durant el desenvolupament de la indústria aeroespacial en el context de les guerres mundials, l'ús de materials més lleugers (i flexibles) va començar a fer-se obligatori per a l'obtenció d'aeronaus amb un comportament (i costos) acceptable. Al llarg dels últims anys, l'ús de materials de construcció cada vegada més lleugers, s'ha estès a la resta de camps de la indústria. A tall d'exemple, podria servir el desenvolupament de textit trackers en la producció d'energia solar; la utilització de materials lleugers en enginyeria civil, el desenvolupament d'elements constructius de plàstic a la indústria de l'automòbil. Com a conseqüència, la predicció amb exactitud de les deformacions induïdes per un fluid i, si escau, la influència d'aquestes deformacions en el propi flux, ha adquirit una importància vital. Aquest document intenta porporcionar, en primer lloc, una profunda revisió dels mètodes experimentals i computacionals que s'han utilitzat en aquest context en la bibliografia, així com les anàlisis en problemes d'aquest tipus realitzats per altres investigadors de cara a presentar una primera aproximació a la Interacció Fluid Estructura. Es veurà com, encara que existeix una important quantitat d'eines i metodologies aplicables a qualsevol tipus de problema i per a qualsevol combinació de fluxos i estructures, no hi ha una aproximació general que, en funció de valors de nombres adimensionals, permeti establir quins d'ells són els de major importància en aquest tipus de problemes. En aquest sentit, es durà a terme una completa anàlisi paramètric durant el desenvolupament del Capítol 2 per a establir quins d'ells són de major importància. Un cop s'estableixi la importància d'aquests paràmetres, s'analitzarà un cas que és d'especial interès en la indústria: la aerovibroacústica. Això és un cas particular d'Interacció Fluid Estructura en què, a causa de la combinació de paràmetres adimensionals, la interacció es pot considerar com pràcticament unidireccional, permetent estendre estudis mitjançant un consti computacional relativament acotat. La Aerovibroacústica i la vibroacústica s'analitzaran mitjançant la presentació de dos casos de referència, permetent proposar una metodologia que es podrà estendre a altres problemes similars.
[EN] Fluid Structure Interaction is a physical problem where two different materials, governed by different set of fundamental equation, are coupled on different ways. The research on the field of Fluid Structure Interaction experienced a noticeable growth since the beginnings of the XXth century, by means of the field of aeroelasticity. During the development of the aerospace industry in the context of first and second Wolrd War, as the use of lighter (and softer) materials became mandatory for the correct behavior (and cost savings) of the produced aircrafts. During these past years, the use of use of increasingly lighter construction materials has extended to the rest of fields of the industry. As an example, it could be mentioned the use of solar trackers on the solar energy sector; the use of light materials on civil engineering or the use of plastic for some constructive elements in the context of the automotive field. As a consequence, the accurate prediction of the deformations induced to a fluid flow over a structure and, if needed, the influence of this deformation on the fluid flow itself is becoming of primal importance. This document intends to provide with a deep review of the computational and experimental reported methodologies already available on the literature and the previous works performed by other researches in order to infer a first approximation to the Fluid Structure Interaction Problem. It will be observed how an important amount of solving methodologies is available in order to face these problems regarding with the strength of the interaction. However, a general approximation allowing to predict this strength as a function of a set of dimensional number is rarely known. In this sense, a full parametric study will be performed during the development of Chapter 2 showing which of them are of higher importance. Once the influence of these parameters is determined, a case of special interest will be analyzed: aerovibroacoustics. This, is a particular case of Fluid Structure Interaction where, due to the combination of its nondimensional parameters, one directional coupling can be supposed for most of the cases. Aerovibroacoustics and vibroacoustics will be analyzed by means of two reference cases, allowing finally to propose a methodology which could be extended for other related problems.
Quintero Igeño, PM. (2019). Characterization of Fluid Structure Interaction mechanisms and its application to vibroacoustic phenomena [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/128412
TESIS
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Ramirez, Villalba Leidy catherine. "Towards an efficient modeling of Fluid-Structure Interaction." Thesis, Ecole centrale de Nantes, 2020. http://www.theses.fr/2020ECDN0029.
Full textAbstract:
Les applications industrielles FSI se caractérisent par des géométries et des matériaux complexes. Afin de prédire avec précision leur comportement, des coûts de calcul élevés sont associés, à la fois en temps et en ressources informatiques. Pour améliorer la qualité de la prédiction sans pénaliser le temps de calcul, et pour réduire le temps de calcul sans impacter la précision disponible aujourd'hui, deux axes principaux sont explorés dans ce travail. Le premier est l'étude d'un algorithme asynchrone qui pourrait permettre l'utilisation de modèles structurels complexes. Le second consiste à étudier la méthode des tranches en combinant l'utilisation d'un modèle RANS et d'un modèle FEM non linéaire. D'une part, l'étude de l'asynchronicité dans le domaine FSI a révélé différents aspect d'intérêt qui doivent être approfondis avant que l'approche puisse être utilisée industriellement. Cependant, un premier traitement des points mentionnés ci-dessus a montré des signe d'amélioration qui pourraient conduire à un algorithme prometteur, qui se situe naturellement entre l'algorithme explicite et l'algorithme implicite. D'autre part, il a été montré que la méthode des tranches développée dans ce travail conduit à une réduction significative du temps de calcul sans dégradation de la précisionFSI industrial applications are often described by complex geometries and materials. In order to accurately predict their behavior, high computational costs are associated, both in time and in computational resources. To improve the quality of the prediction without penalizing the computational time, and to reduce the computational time without impacting the accuracy that is available today, two main axes are explored in this work. The first one is the study of an asynchronous algorithm that could allow the use of complex structural models. The second axis consists of the study of the strip method while combining the use of a RANS model and a non-linear FEM model. On the one hand, the study of asynchronicity in the FSI domain revealed different aspects of interest that must be addressed before the approach can be used industrially. However, a first treatment of the limitations found showed signs of an improvement that could lead to a promising algorithm, one that naturally lies between the implicit external algorithm and the implicit internal algorithm. On the other hand, it was shown that the strip method developed in this work achieves a significant reduction in calculation time while maintaining excellent accuracy
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Lemmon, Jack David Jr. "Three-dimensional computational modeling of fluid-structure interaction : study of diastolic function in a thin-walled left heart model." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/15912.
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Mehra, Puneet. "Fluid-Structure Interaction Modeling of Human Upper Airway Collapse in Obstructive Sleep Apnea." University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563873512457421.
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Cole, Robert Edward. "Numerical Modeling of Air Cushion Vehicle Flexible Seals." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/83828.
Full textAbstract:
Air cushion vehicle flexible seals operate in a complex and chaotic environment dominated by fluid-structure interaction. An efficient means to explore interdependencies between various governing parameters that affect performance is through high fidelity numerical simulation. As previous numerical efforts have employed separate iterative partitioned solvers, or have implemented simplified physics, the approaches have been complex, computationally expensive, or of limited utility. This research effort performs numerical simulations to verify and validate the commercial multi-physics tool STAR-CCM+ as a stand-alone partitioned approach for fluid-structure interaction problems with or without a free surface. A dimensional analysis is first conducted to identify potential non-dimensional forms of parameters related to seal resistance. Then, an implicit, Reynolds-averaged Navier-Stokes finite volume fluid solver is coupled to an implicit, nonlinear finite element structural solver to successfully replicate benchmark results for an elastic beam in unsteady laminar flow. To validate the implementation as a seal parameter exploratory tool, a planer bow seal model is developed and results are obtained for various cushion pressures and inflow speeds. Previous numerical and experimental results for deflection and resistance are compared, showing good agreement. An uncertainty analysis for inflow velocity reveals an inversely proportional resistance dependency. Using Abaqus/Explicit, methodologies are also developed for a two-way, loosely coupled explicit approach to large deformation fluid-structure interaction problems, with and without a free surface. Following numerous verification and validation problems, Abaqus is ultimately abandoned due to the inability to converge the fluid pressure field and achieve steady state. This work is a stepping stone for future researchers having interests in ACV seal design and other large deformation, fluid-structure interaction problems. By modeling all necessary physics within a verified and validated stand-alone approach, a designer's ability to comprehensively investigate seal geometries and interactions has never been more promising.Ph. D.
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Heminger, Michael Alan. "Dynamic Grid Motion in a High-Order Computational Aeroacoustic Solver." University of Toledo / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1272550725.
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Gao, Hao. "Carotid plaque stress analysis by fluid structure interaction based on in-vivo MRI : implications to plaque vulnerability assessment." Thesis, Brunel University, 2010. http://bura.brunel.ac.uk/handle/2438/4731.
Full textAbstract:
Stroke is one of the leading causes of death in the world, resulting mostly from the sudden rupture of atherosclerotic plaques. From a biomechanical view, plaque rupture can be considered as a mechanical failure caused by extremely high plaque stress. In this PhD project, we are aiming to predict 3D plaque stress based on in-vivo MRI by using fluid structure interaction (FSI) method, and provide information for plaque rupture risk assessment. Fluid structure interaction was implemented with ANSYS 11.0, followed by a parameter study on fibrous cap thickness and lipid core size with realistic carotid plaque geometry. Twenty patients with carotid plaques imaged by in-vivo MRI were provided in the project. A framework of reconstructing 3D plaque geometry from in-vivo multispectral MRI was designed. The followed reproducibility study on plaque geometry reconstruction procedure and its effect on plaque stress analysis filled the gap in the literature on imaging based plaque stress modeling. The results demonstrated that current MRI technology can provide sufficient information for plaque structure characterization; however stress analysis result is highly affected by MRI resolution and quality. The application of FSI stress analysis to 4 patients with different plaque burdens has showed that the whole procedure from plaque geometry reconstruction to FSI stress analysis was applicable. In the study, plaque geometries from three patients with recent transient ischemic attack were reconstructed by repairing ruptured fibrous cap. The well correlated relationship between local stress concentrations and plaque rupture sites indicated that extremely high plaque stress could be a factor responsible for plaque rupture. Based on the 20 reconstructed carotid plaques from two groups (symptomatic and asymptomatic), fully coupled fluid structure interaction was performed. It was found that there is a significant difference between symptomatic and asymptomatic patients in plaque stress levels, indicating plaque stress could be used as one of the factors for plaque vulnerability assessment. A corresponding plaque morphological feature study showed that plaque stress is significantly affected by fibrous cap thickness, lipid core size and fibrous cap surface irregularities (curvedness). A procedure was proposed for predicting plaque stress by using fibrous cap thickness and curvedness, which requires much less computational time, and has the potential for clinical routine application. The effects of residual stress on plaque stress analysis and arterial wall material property characterization by using in-vivo MRI data were also discussed for patient specific modeling. As the further development, histological study of plaque sample has been combined with conventional plaque stress analysis by assigning material properties to each computational element, based on the data from histological analysis. This method could bridge the gap between biochemistry and biomechanical study of atherosclerosis plaques. In conclusion, extreme stress distributions in the plaque region can be predicted by modern numerical methods, and used for plaque rupture risk assessment, which will be helpful in clinical practice. The combination of plaque MR imaging analysis, computational modelling, and clinical study/ validation would advance our understandings of plaque rupture, prediction of future rupture, and establish new procedures for patient diagnose, management, and treatment.
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Gao, Haotian. "POD-Galerkin based ROM for fluid flow with moving boundaries and the model adaptation in parametric space." Diss., Kansas State University, 2018. http://hdl.handle.net/2097/38776.
Full textAbstract:
Doctor of PhilosophyDepartment of Mechanical and Nuclear Engineering
Mingjun Wei
In this study, a global Proper Orthogonal Decomposition (POD)-Galerkin based Reduced Order model (ROM) is proposed. It is extended from usual fixed-domain problems to more general fluid-solid systems with moving boundaries/interfaces. The idea of the extension is similar to the immersed boundary method in numerical simulations which uses embedded forcing terms to represent boundary motions and domain changes. This immersed boundary method allows a globally defined fixed domain including both fluid and solid, where POD-Galerkin projection can be directly applied. However, such a modified approach cannot get away with the unsteadiness of boundary terms which appear as time-dependent coefficients in the new Galerkin model. These coefficients need to be pre-computed for prescribed periodic motion, or worse, to be computed at each time step for non-prescribed (e.g. with fluid-structure interaction) or non-periodic situations. Though computational time for each unsteady coefficient is smaller than the coefficients in a typical Galerkin model, because the associated integration is only in the close neighborhood of moving boundaries. The time cost is still much higher than a typical Galerkin model with constant coefficients. This extra expense for moving-boundary treatment eventually undermines the value of using ROMs. An aggressive approach is to decompose the moving boundary/domain to orthogonal modes and derive another low-order model with fixed coefficients for boundary motion. With this domain decomposition, an approach including two coupled low-order models both with fixed coefficients is proposed. Therefore, the new global ROM with decomposed approach is more efficient. Though the model with the domain decomposition is less accurate at the boundary, it is a fair trade-off for the benefit on saving computational cost. The study further shows, however, that the most time-consuming integration in both approaches, which come from the unsteady motion, has almost negligible impact on the overall dynamics. Dropping these time-consuming terms reduces the computation cost by at least one order while having no obvious effect on model accuracy. Based on this global POD-Galerkin based ROM with forcing term, an improved ROM which can handle the parametric variation of body motions in a certain range is also presented. This study shows that these forcing terms not only represent the moving of the boundary, but also decouple the moving parameters from the computation of model coefficients. The decoupling of control parameters provides the convenience to adapt the model for the prediction on states under variation of control parameters. An improved ROM including a shit mode seems promising in model adaptation for typical problems in a fixed domain. However, the benefit from adding a shit mode to model diminishes when the method is applied to moving-boundary problems. Instead, a combined model, which integrates data from a different set of parameters to generate the POD modes, provides a stable and accurate ROM in a certain range of parametric space for moving-boundary problems. By introducing more data from a different set of parameters, the error of the new model can be further reduced. This shows that the combined model can be trained by introducing more and more information. With the idea of the combined model, the improved global ROM with forcing terms shows impressive capability to predict problems with different unknown moving parameters, and can be used in future parametric control and optimization problems.
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Hägglund, Jesper. "Simulated cerebrospinal fluid motion due to pulsatile arterial flow : Master Thesis Project." Thesis, Umeå universitet, Institutionen för fysik, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-182508.
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All organs, including the brain, need a pathway to remove neurotoxic extracellular proteins. In the brain this is called the glymphatic system. The glymphatic system works by exchanging proteins from interstitial fluids to cerebrospinal fluids. The extracellular proteins are then removed through the cerebrospinal fluid drains. The glymphatic system is believed to be driven by arterial pulsatility, cerebrospinal fluid production and respiration. Cerebrospinal fluids enters the brain alongside arteries. In this project, we investigate if a simulated pulsatile flow in a common carotid artery can drive cerebrospinal fluid flow running along the artery, using computational simulations of a linearly elastic and fluid-structure multiphysical model in COMSOL. Our simulations show that a heartbeat pulse increases the arterial radius of the common carotid artery by 6 %. Experimental data, assessed using 4D magnetic resonance imaging of a living human, show an increase of 13 %. Moreover, our results indicate that arterial displacement itself is not able to drive cerebrospinal fluid flow. Instead, it seems to create a back and forth flow that possibly could help with the protein exchange between the cerebrospinal and interstitial fluids. Overall, the results indicate that the COMSOL Multiphysics linearly elastic model is not ideal for approximations of soft non-linearly elastic solids, such as soft polydimethylsiloxane and artery walls work for stiffer materials. The long term aim is to simulate a part of the glymphatic system and the present work is a starting point to reach this goal. As the simulations in this work are simplified there are more things to test in the future. For example, using the same geometries a non-linear elastic model could be tested. The pulsatile waveform or the geometry could be made more complex. Furthermore the model could be scaled down to represent a penetrating artery in the brain instead of the common carotid artery.
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Benitez, Mendieta Jessica. "Patient-specific computational biomechanical analysis of carotid atherosclerotic plaques based on MRI." Thesis, Queensland University of Technology, 2021. https://eprints.qut.edu.au/213840/1/Jessica_Benitez%20Mendieta_Thesis.pdf.
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This thesis focuses on the biomechanical analysis of carotid atherosclerosis based on medical imaging. The rupture of carotid atherosclerotic plaques is the leading cause of acute cardiovascular events, such as stroke. For this analysis, patient-specific and image-based carotid models were developed for computational analysis to assess factors associated with plaque development and rupture. This study provided further knowledge in areas such as fluid dynamics of carotid arteries with stenosis, the role of the carotid plaque components, and a new technique for structural analysis of carotid plaques. These approaches will help clinicians in the diagnosis and treatment of carotid atherosclerosis.
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Nasar, Abouzied. "Eulerian and Lagrangian smoothed particle hydrodynamics as models for the interaction of fluids and flexible structures in biomedical flows." Thesis, University of Manchester, 2016. https://www.research.manchester.ac.uk/portal/en/theses/eulerian-and-lagrangian-smoothed-particle-hydrodynamics-as-models-for-the-interaction-of-fluids-and-flexible-structures-in-biomedical-flows(507cd0db-0116-4258-81f2-8d242e8984fa).html.
Full textAbstract:
Fluid-structure interaction (FSI), occurrent in many areas of engineering and in the natural world, has been the subject of much research using a wide range of modelling strategies. However, problems with high levels of structural deformation are difficult to resolve and this is particularly the case for biomedical flows. A Lagrangian flow model coupled with a robust model for nonlinear structural mechanics seems a natural candidate since large distortion of the computational geometry is expected. Smoothed particle Hydrodynamics (SPH) has been widely applied for nonlinear interface modelling and this approach is investigated here. Biomedical applications often involve thin flexible structures and a consistent approach for modelling the interaction of fluids with such structures is also required. The Lagrangian weakly compressible SPH method is investigated in its recent delta-SPH form utilising inter-particle density fluxes to improve stability. Particle shifting is also used to maintain particle distributions sufficiently close to uniform to enable stable computation. The use of artificial viscosity is avoided since it introduces unphysical dissipation. First, solid boundary conditions are studied using a channel flow test. Results show that when the particle distribution is allowed to evolve naturally instabilities are observed and deviations are noted from the expected order of accuracy. A parallel development in the SPH group at Manchester has considered SPH in Eulerian form (for different applications). The Eulerian form is applied to the channel flow test resulting in improved accuracy and stability due to the maintenance of a uniform particle distribution. A higher-order accurate boundary model is developed and applied for the Eulerian SPH tests and third-order convergence is achieved. The well documented case of flow past a thin plate is then considered. The immersed boundary method (IBM) is now a natural candidate for the solid boundary. Again, it quickly becomes apparent that the Lagrangian SPH form has limitations in terms of numerical noise arising from anisotropic particle distributions. This corrupts the predicted flow structures for moderate Reynolds numbers (O(102)). Eulerian weakly compressible SPH is applied to the problem with the IBM and is found to give accurate and convergent results without any numerical stability problems (given the time step limitation defined by the Courant condition). Modelling highly flexible structures using the discrete element model is investigated where granular structures are represented as bonded particles. A novel vector-based form (the V-Model) is identified as an attractive approach and developed further for application to solid structures. This is shown to give accurate results for quasi-static and dynamic structural deformation tests. The V-model is applied to the decay of structural vibration in a still fluid modelled using Eulerian SPH with no artificial stabilising techniques. Again, results are in good agreement with predictions of other numerical models. A more demanding case representative of pulsatile flow through a deep leg vein valve is also modelled using the same form of Eulerian SPH. The results are free of numerical noise and complex FSI features are captured such as vortex shedding and non-linear structural deflection. Reasonable agreement is achieved with direct in-vivo observations despite the simplified two-dimensional numerical geometry. A robust, accurate and convergent method has thus been developed, at present for laminar two-dimensional low Reynolds number flows but this may be generalised. In summary a novel robust and convergent FSI model has been established based on Eulerian SPH coupled to the V-Model for large structural deformation. While these developments are in two dimensions the method is readily extendible to three-dimensional, laminar and turbulent flows for a wide range of applications in engineering and the natural world.
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Wuilbaut, Thomas A. I. J. "Algorithmic developments for a multiphysics framework." Doctoral thesis, Universite Libre de Bruxelles, 2008. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210407.
Full textAbstract:
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.
Doctorat en Sciences de l'ingénieur
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Dobes, Jiri. "Numerical algorithms for the computation of steady and unsteady compressible flow over moving geometries: application to fluid-structure interaction." Doctoral thesis, Universite Libre de Bruxelles, 2007. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/210640.
Full textAbstract:
This work deals with the development of numerical methods for compressible flow simulation with application to the interaction of fluid flows and structural bodies.
First, we develop numerical methods based on multidimensional upwind residual distribution (RD) schemes. Theoretical results for the stability and accuracy of the methods are given. Then, the RD schemes for unsteady problems are extended for computations on moving meshes. As a second approach, cell centered and vertex centered finite volume (FV) schemes are considered. The RD schemes are compared to FV schemes by means of the 1D modified equation and by the comparison of the numerical results for scalar problems and system of Euler equations. We present a number of two and three dimensional steady and unsteady test cases, illustrating properties of the numerical methods. The results are compared with the theoretical solution and experimental data.
In the second part, a numerical method for fluid-structure interaction problems is developed. The problem is divided into three distinct sub-problems: Computational Fluid Dynamics, Computational Solid Mechanics and the problem of fluid mesh movement. The problem of Computational Solid Mechanics is formulated as a system of partial differential equations for an anisotropic elastic continuum and solved by the finite element method. The mesh movement is determined using the pseudo-elastic continuum approach and solved again by the finite element method. The coupling of the problems is achieved by a simple sub-iterative approach. Capabilities of the methods are demonstrated on computations of 2D supersonic panel flutter and 3D transonic flutter of the AGARD 445.6 wing. In the first case, the results are compared with the theoretical solution and the numerical computations given in the references. In the second case the comparison with experimental data is presented.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished
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Kadel, Saurav. "Computational Assessment of Aortic Valve Function and Mechanics under Hypertension." Wright State University / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=wright1594243694736478.
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Goddard, Aaron M. "A primarily Eulerian means of applying left ventricle boundary conditions for the purpose of patient-specific heart valve modeling." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6584.
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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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Akkaoui, Quentin. "Computational dynamics of geometrically nonlinear structures coupled with acoustic fluids in presence of sloshing and capillarity : uncertainty quantification." Thesis, Paris Est, 2019. http://www.theses.fr/2019PESC2001.
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Dans cette thèse, on s’intéresse à la modélisation et à la simulation numérique de systèmes couplés fluide-structure, constitués d'une structure élastique partiellement remplie d'un liquide avec une surface libre, tenant compte des effets de ballottement et de capillarité. Le fluide interne est considéré comme linéaire, acoustique, dissipatif et la structure, à comportement élastique linéaire, est soumise à de grands déplacements induisant des non-linéarités géométriques. Le travail présenté dans ce manuscrit s'intéresse tout d’abord à l’étude théorique de ce type de système couplé fluide-structure et s'attache à la construction et à l’implémentation du modèle numérique en utilisant un modèle réduit non linéaire adapté. Ce modèle réduit permet d'effectuer les calculs dynamiques non linéaires et permet également de mieux comprendre les phénomènes liés à chaque partie du système couplé. Plusieurs applications numériques sont ensuite développées permettant l’analyse de divers phénomènes liés aux différents couplages et transferts d’énergie dans le système. Le premier axe de développement consiste en la quantification et en la réduction du temps de calcul nécessaire à la construction de la base de projection du modèle réduit pour des modèles numériques de systèmes couplés fluide-structure de très grande dimension. Une nouvelle méthodologie est présentée permettant de réduire les coûts numériques induits par la résolution de trois problèmes généralisés aux valeurs propres ne pouvant être résolus sur les ordinateurs de puissance intermédiaire. Un second axe de développement concerne la quantification de l’influence de l'opérateur de couplage entre la structure et la surface libre du liquide interne permettant de prendre en compte la condition d’angle de contact capillaire au niveau de la ligne triple tout en considérant une structure déformable. Le troisième axe est basé sur des travaux expérimentaux publiés en 1962, dans le cadre de développements de la NASA pour les lanceurs, qui ont mis en évidence un phénomène inattendu de ballottement de grande amplitude en basses-fréquences pour le liquide interne lors de l’excitation moyenne-fréquence du réservoir. On propose de revisiter et d'expliquer les causes de ce phénomène inattendu au travers d’une simulation numérique prenant en compte les non-linéarités géométriques de la structure. Enfin, un dernier axe de développement est consacré à la propagation des incertitudes non paramétriques de la structure dans le système par les différents mécanismes de couplages. La modélisation stochastique non paramétrique est celle de l'approche probabiliste non paramétrique qui utilise la théorie des matrices aléatoires. Une méthodologie permettant l’identification de l'hyperparamètre est présentée, basée sur un ensemble de données expérimentales et sur la résolution d'un problème statistique inverse. Une validation numérique de cette méthode sur un ensemble de données expérimentales simulées est présentéeIn this thesis, we are interested in computationally modeling and simulating coupled fluid-structure systems constituted of an elastic structure partially filled with a fluid with a free surface, considering the effects of sloshing and capillarity. The internal fluid is linear, acoustic, dissipative, and the linear elastic structure is submitted to large displacements inducing geometrical nonlinearities. The work presented in this manuscript first details the theoretical study regarding such coupled fluid-structure systems and focuses on the construction and implementation of the computational model using an adapted nonlinear reduced-order model. This reduced-order model allows for performing the nonlinear dynamical simulations and for better understanding the phenomena related to each subset of the coupled system. Several numerical applications are then presented to analyze various phenomena related to the different coupling mechanisms and energy transfers in such fluid-structure system. The first development axis consists in quantifying and reducing the computational resources required for the construction of the projection basis of the reduced-order model when dealing with very-large dimension fluid-structure computational models. A new methodology is presented, which allows for reducing the computational costs required for solving three generalized eigenvalue problems that cannot be solved on medium-power computers. A second development axis is devoted to the quantification of the influence of the coupling operator between the structure and the free surface of the internal liquid allowing for taking into account the capillary contact angle condition on the triple line while considering a deformable structure. The third axis is based on experimental research published in 1962 in the framework of NASA researches for orbital launchers, which highlighted an unexpected phenomenon of large amplitude and low-frequency sloshing of an internal liquid for a medium-frequency excitation of the tank. We propose to revisit these experimental results and to explain the causes of such unexpected phenomenon through a numerical simulation taking into account the geometrical nonlinearities of the structure. Finally, the last development axis is devoted to the propagation of nonparametric uncertainties of the structure in the system by the different coupling mechanisms. The nonparametric stochastic model is the nonparametric probabilistic approach using the random matrix theory. A methodology for identifying the hyperparameter is presented, based on an experimental data set and on an inverse statistical problem. A numerical validation of this method on a simulated experimental data set is presented
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Gardner, Kevin Alexander. "Experimental Study of Air Blast and Water Shock Loading on Automotive Body Panels." The Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1468938824.
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Volpi, Silvia. "High-fidelity multidisciplinary design optimization of a 3D composite material hydrofoil." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6325.
Full textAbstract:
Multidisciplinary design optimization (MDO) refers to the process of designing systems characterized by the interaction of multiple interconnected disciplines. High-fidelity MDO usually requires large computational resources due to the computational cost of achieving multidisciplinary consistent solutions by coupling high-fidelity physics-based solvers. Gradient-based minimization algorithms are generally applied to find local minima, due to their efficiency in solving problems with a large number of design variables. This represents a limitation to performing global MDO and integrating black-box type analysis tools, usually not providing gradient information. The latter issues generally inhibit a wide use of MDO in complex industrial applications.
An architecture named multi-criterion adaptive sampling MDO (MCAS-MDO) is presented in the current research for complex simulation-based applications. This research aims at building a global derivative-free optimization tool able to employ high-fidelity/expensive black-box solvers for the analysis of the disciplines. MCAS-MDO is a surrogate-based architecture featuring a variable level of coupling among the disciplines and is driven by a multi-criterion adaptive sampling (MCAS) assessing coupling and sampling uncertainties. MCAS uses the dynamic radial basis function surrogate model to identify the optimal solution and explore the design space through parallel infill of new solutions.
The MCAS-MDO is tested versus a global derivative-free multidisciplinary feasible (MDF) approach, which solves fully-coupled multidisciplinary analyses, for two analytical test problems. Evaluation metrics include number of function evaluations required to achieve the optimal solution and sample distribution. The MCAS-MDO outperforms the MDF showing a faster convergence by clustering refined function evaluations in the optimum region.
The architecture is applied to a steady fluid-structure interaction (FSI) problem, namely the design of a tapered three-dimensional carbon fiber-reinforced plastic hydrofoil for minimum drag. The objective is the design of shape and composite material layout subject to hydrodynamic, structural, and geometrical constraints. Experimental data are available for the original configuration of the hydrofoil and allow validating the FSI analysis, which is performed coupling computational fluid dynamics, solving the Reynolds averaged Navier-Stokes equations, and finite elements, solving the structural equation of elastic motion. Hydrofoil forces, tip displacement, and tip twist are evaluated for several materials providing qualitative agreement with the experiments and confirming the need for the two-way versus one-way coupling approach in case of significantly compliant structures.
The free-form deformation method is applied to generate shape modifications of the hydrofoil geometry. To reduce the global computational expense of the optimization, a design space assessment and dimensionality reduction based on the Karhunen–Loève expansion (KLE) is performed off-line, i.e. without the need for high-fidelity simulations. It provides with a selection of design variables for the problem at hand through basis rotation and re-parametrization. By using the KLE, an efficient design space is identified for the current problem and the number of design variables is reduced by 92%.
A sensitivity analysis is performed prior to the optimization to assess the variability associated with the shape design variables and the composite material design variable, i.e. the fiber orientation. These simulations are used to initialize the surrogate model for the optimization, which is carried out for two models: one in aluminum and one in composite material. The optimized designs are assessed by comparison with the original models through evaluation of the flow field, pressure distribution on the body, and deformation under the hydrodynamic load. The drag of the aluminum and composite material hydrofoils is reduced by 4 and 11%, respectively, increasing the hydrodynamic efficiency by 4 and 7%. The optimized designs are obtained by evaluating approximately 100 designs. The quality of the results indicates that global derivative-free MDO of complex engineering applications using expensive black-box solvers can be achieved at a feasible computational cost by minimizing the design space dimensionality and performing an intelligent sampling to train the surrogate-based optimization.
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Lu, Zhaokuan. "Computationally-effective Modeling of Far-field Underwater Explosion for Early-stage Surface Ship Design." Diss., Virginia Tech, 2020. http://hdl.handle.net/10919/104996.
Full textAbstract:
The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a high-level of mesh refinement to prevent numerical dispersion from discontinuities. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach which has shown computational advantages in UNDEX problems, but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. This new meshing approach significantly saves time for mesh generation and allows the spectral element, which is confined to the hexahedral element, to be applied in practical ship problems. A further contribution of this dissertation is the development of a surrogate non-numerical approach to predict structural peak responses based on the shock factor concept. The regression analysis reveals a reasonably strong linear relationship between the structural peak response and the shock factor. The shock factor can be conveniently employed in the design aspects where the peak response is sufficient, using much less computational resources than numerical solvers.Doctor of Philosophy
The vulnerability of a ship to the impact of underwater explosions (UNDEX) and how to incorporate this factor into early-stage ship design is an important aspect in the ship survivability study. In this dissertation, attention is focused on the cost-efficient simulation of the ship response to a far-field UNDEX which involves fluid shock waves, cavitation, and fluid-structural interaction. Traditional fluid numerical simulation approaches using the Finite Element Method to track wave propagation and cavitation requires a highly refined mesh to deal with large numerical errors. Computation also becomes quite expensive for full ship-related problems due to the large fluid domain necessary to envelop the ship. The burden is aggravated by the need to generate a fluid mesh around the irregular ship hull geometry, which typically requires significant manual intervention. To accelerate the design process and enable the consideration of far-field UNDEX vulnerability, several contributions are made in this dissertation to make the simulation more efficient. First, a Cavitating Acoustic Spectral Element approach, which has shown computational advantages in UNDEX problems but not systematically assessed in total ship application, is used to model the fluid. The use of spectral elements shows greater structural response accuracy and lower computational cost than the traditional FEM. Second, a novel fully automatic all-hexahedral mesh generation scheme is applied to generate the fluid mesh. Along with the spectral element, the all-hex mesh shows greater accuracy than the all-tetrahedral finite element mesh which is typically used. A further contribution of this dissertation is the development of a non-numerical approach which can approximate peak structural responses comparable to the numerical solution with far less computational effort.
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Muddle, Richard Louden. "Parallel block preconditioning for multi-physics problems." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/parallel-block-preconditioning-for-multiphysics-problems(2efc63e4-f426-4be9-b48a-4016365e08b8).html.
Full textAbstract:
In this thesis we study efficient parallel iterative solution algorithms for multi-physics problems. In particular, we consider fluid structure interaction (FSI) problems, a type of multi-physics problem in which a fluid and a deformable solid interact. All computations were performed in Oomph-Lib, a finite element library for the simulation of multi-physics problems. In Oomph-Lib, the constituent problems in a multi-physics problem are coupled monolithically, and the resulting system of non-linear equations solved with Newton's method. This requires the solution of sequences of large, sparse linear systems, for which optimal solvers are essential. The linear systems arising from the monolithic discretisation of multi-physics problems are natural candidates for solution with block-preconditioned Krylov subspace methods.We developed a generic framework for the implementation of block preconditioners within Oomph-Lib. Furthermore the framework is parallelised to facilitate the efficient solution of very large problems. This framework enables the reuse of all of Oomph-Lib's existing linear algebra infrastructure and preconditioners (including block preconditioners). We will demonstrate that a wide range of block preconditioners can be seamlessly implemented in this framework, leading to optimal iterative solvers with good parallel scaling.We concentrate on the development of an effective preconditioner for a FSI problem formulated in an arbitrary Lagrangian Eulerian (ALE) framework with pseudo-solid node updates (for the deforming fluid mesh). We begin by considering the pseudo-solid subsidiary problem; the deformation of a solid governed by equations of large displacement elasticity, subject to a prescribed boundary displacement imposed with Lagrange multiplier. We present a robust, optimal, augmented-Lagrangian type preconditioner for the resulting saddle-point linear system and prove analytically tight bounds for the spectrum of the preconditioned operator with respect to the discrete problem size.This pseudo-solid preconditioner is incorporated into a block preconditioner for the full FSI problem. One key feature of the FSI preconditioner is that existing optimal single physics preconditioners (such as the well known Navier-Stokes Least Squares Commutator preconditioner) can be employed to approximately solve the linear systems associated with the constituent sub-problems. We evaluate its performance on selected 2D and 3D problems. The preconditioner is optimal for most problems considered. In cases when sub-optimality is detected, we explain the reasons for such behavior and suggest potential improvements.
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Ager, Christoph Franz [Verfasser], Wolfgang A. [Akademischer Betreuer] Wall, Wolfgang A. [Gutachter] Wall, and Marek [Gutachter] Behr. "Computational Methods for Fluid-Structure Interaction including Porous Media and Solid Contact / Christoph Franz Ager ; Gutachter: Wolfgang A. Wall, Marek Behr ; Betreuer: Wolfgang A. Wall." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1230985131/34.
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Auza, Gutierrez Rodrigo. "Prediction of Aerodynamically Induced Hood Vibration of Trailing Vehicles." The Ohio State University, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=osu1546472529004518.
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Subramaniam, Dhananjay Radhakrishnan. "Role of Elasticity in Respiratory and Cardiovascular Flow." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1522054562050044.
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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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Sanches, Rodolfo André Kuche. "Análise bidimensional de interação fluido-estrutura: desenvolvimento de código computacional." Universidade de São Paulo, 2006. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-06112006-145215/.
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O presente trabalho consiste no desenvolvimento de um código computacional baseado no método dos elementos finitos (MEF), para análise bidimensional de interação fluido-estrutura. Desenvolve-se um código bidimensional para dinâmica de fluidos compressíveis, viscosos ou não, em formulação Euleriana, com base no algoritmo CBS characteristic based split. Então o código desenvolvido é adaptado para poder ser acoplado a um programa de formulação Lagrangeana para análise dinâmica de estruturas, o que é feito através do emprego da descrição Lagrangeana - Euleriana arbitrária (ALE). Por fim procede-se o acoplamento com um código para análise de estruturas, de formulação posicional e não linear geométrica, baseado no método dos elementos finitos.The present work consists of the development of a computational code based on the element finite method for fluid-structure interaction analysis. A two-dimensional fluid dynamic Eulerian code is developed based on the CBS algorithm characteristic based split. Then, the computational code is modified to be coupled with a Lagrangean structures dynamical code by using the arbitrary Lagrangean Eulerian description (ALE). At the end, the coupling is made with a positional nonlinear geometrical structural dynamics code based on the finite element method.
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Acikgoz, Nazmiye. "Adaptive and Dynamic Meshing Methods for Numerical Simulations." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/14521.
Full textAbstract:
For the numerical simulation of many problems of engineering interest, it is desirable to have an automated mesh adaption tool. This is important especially for problems characterized by anisotropic features and require mesh clustering in the direction of high gradients. Another significant issue in meshing emerges in unsteady simulations with moving boundaries, where the boundary motion has to be accommodated by deforming the computational grid. Similarly, there exist problems where current mesh needs to be adapted to get more accurate solutions. To solve these problems, we propose three novel procedures.
In the first part of this work, we present an optimization procedure for three-dimensional anisotropic tetrahedral grids based on metric-driven h-adaptation. Through the use of topological and geometrical operators, the mesh is iteratively adapted until the final mesh minimizes a given objective function. We propose an optimization process based on an ad-hoc application of the simulated annealing technique, which improves the likelihood of removing poor elements from the grid. Moreover, a local implementation of the simulated annealing is proposed to reduce the computational cost.
Many challenging unsteady multi-physics problems are characterized by moving boundaries and/or interfaces. When the boundary displacements are large, degenerate elements are easily formed in the grid such that frequent remeshing is required. We propose a new r-adaptation technique that is valid for all types of elements (e.g., triangle, tet, quad, hex, hybrid) and deforms grids that undergo large imposed displacements at their boundaries. A grid is deformed using a network of linear springs composed of edge springs and a set of virtual springs. The virtual springs are constructed in such a way as to oppose element collapsing.
Both frequent remeshing, and exact-pinpointing of clustering locations are great challenges of numerical simulations, which can be overcome by adaptive meshing algorithms. Therefore, we conclude this work by defining a novel mesh adaptation technique where the entire mesh is adapted upon application of a force field in order to comply with the target mesh or to get more accurate solutions. The method has been tested for two-dimensional problems of a-priori metric definitions as well as for oblique shock clusterings.
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Braun, Alexandre Luis. "Simulação numérica na engenharia do vento incluindo efeitos de interação fluido-estrutura." reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2007. http://hdl.handle.net/10183/10592.
Full textAbstract:
O objetivo deste trabalho é estudar e desenvolver procedimentos numéricos adequados para a análise de problemas da Engenharia do Vento Computacional (EVC). O escoamento é analisado a partir das equações de Navier-Stokes para um fluido Newtoniano e de uma equação de conservação de massa considerando a hipótese de pseudo-compressibilidade, ambas em um processo isotérmico. Na presença de escoamentos turbulentos emprega-se a Simulação de Grandes Escalas (“LES”) com os modelos clássico e dinâmico de Smagorinsky para as escalas inferiores à resolução da malha. Dois modelos numéricos de Taylor-Galerkin para a análise do escoamento são estudados: o esquema explícito de dois passos e o esquema explícito-iterativo. O Método dos Elementos Finitos (MEF) é empregado para a discretização do domínio espacial utilizando o elemento hexaédrico trilinear isoparamétrico com integração reduzida das matrizes em nível de elemento. Em problemas envolvendo efeitos de interação fluido-estrutura emprega-se um esquema de acoplamento particionado com características superiores de conservação, permitindo, inclusive, o uso de subciclos entre as análises do fluido e da estrutura e de malhas não compatíveis na interface. A estrutura é considerada como um corpo deformável constituído de um material elástico linear com a presença de nãolinearidade geométrica. O MEF é também usado para a discretização da estrutura, empregando-se para tanto o elemento hexaédrico trilinear isoparamétrico com integração reduzida e controle de modos espúrios. A equação de equilíbrio dinâmico é integrada no tempo utilizando o método implícito de Newmark no contexto do método de estabilização α- Generalizado. Na presença de estruturas deformáveis, o escoamento é descrito através de uma formulação arbitrária Lagrangeana-Euleriana (ALE). Ao final, comparações com exemplos numéricos e experimentais são apresentadas para demonstrar a viabilidade dos algoritmos desenvolvidos, seguindo-se com as conclusões do trabalho e as sugestões para trabalhos futuros.Analysis and development of numerical tools to simulate Computational Wind Engineering (CWE) problems is the main goal of the present work. The isothermal flow is analyzed using the Navier-Stokes equations for viscous fluids and a mass conservation equation obtained according to the pseudo-compressibility assumption. Turbulent flows are simulated employing Large Eddy Simulation (LES) with the classical and dynamic Smagorinsky’s models for subgrid scales. Two Taylor-Galerkin models for the flow analysis are investigated: the explicit two-step scheme and the explicit-iterative scheme. The Finite Element Method (MEF) is employed for spatial discretizations using the eight-node hexahedrical isoparametric element with one-point quadrature. Fluid-structure interaction problems are analyzed with a coupling model based on a conservative partitioned scheme. The Finite Element Method (MEF) is employed for spatial discretizations using the eight-node hexahedrical isoparametric element with one-point quadrature. Fluid-structure interaction problems are analyzed with a coupling model based on a conservative partitioned scheme. Subcycling and nonmatching meshes for independent discretizations of the fluid and structure domains are also available. The structure is considered as a deformable body constituted by a linear elastic material with geometrically nonlinear effects. The FEM is used for the spatial discretization of the structure as well. Eight-node hexahedrical isoparametric elements with one-point quadrature and hourglass control are adopted in this process. The implicit Newmark algorithm within the framework of the α-Generalized method is employed for the numerical integration of the dynamic equilibrium equation. An arbitrary Lagrangean-Eulerian (ALE) description is adopted for the kinematic description of the flow when deformable structures are analyzed. Numerical and experimental examples are simulated in order to demonstrate the accuracy of the developed algorithms. Concluding remarks and suggestions for future works are pointed out in the last chapter of the present work.