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1
Falagkaris, Emmanouil. "Lattice Boltzmann method and immersed boundary method for the simulation of viscous fluid flows." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/33165.
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Most realistic fluid flow problems are characterised by high Reynolds numbers and complex boundaries. Over the last ten years, immersed boundary methods (IBM) that are able to cope with realistic geometries have been applied to Lattice- Boltzmann methods (LBM). These methods, however, have normally been applied to low Reynolds number problems. In the present work, an iterative direct forcing IBM has been successfully coupled with a multi-domain cascaded LBM in order to investigate viscous flows around rigid, moving and wilfully deformed boundaries at a wide range of Reynolds numbers. The iterative force-correction immersed boundary method of (Zhang et al., 2016) has been selected due to the improved accuracy of the computation, while the cascaded LB formulation is used due to its superior stability at high Reynolds numbers. The coupling is shown to improve both the stability and numerical accuracy of the solution. The resulting solver has been applied to viscous flow (up to a Reynolds number of 100000) passed a NACA-0012 airfoil at a 10 degree angle of attack. Good agreement with results obtained using a body-fitted Navier-Stokes solver has been obtained. At moving or deformable boundary applications, emphasis should be given on the influence of the internal mass on the computation of the aerodynamic forces, focusing on deforming boundary motions where the rigid body approximation is no longer valid. Both the rigid body and the internal Lagrangian points approximations are examined. The resulting solver has been applied to viscous flows around an in-line oscillating cylinder, a pitching foil, a plunging SD7003 airfoil and a plunging and flapping NACA-0014 airfoil. Good agreement with experimental results and other numerical schemes has been obtained. It is shown that the internal Lagrangian points approximation accurately captures the internal mass effects in linear and angular motions, as well as in deforming motions, at Reynolds numbers up to 4 • 104. Finally, an expanded higher-order immersed boundary method which addresses two major drawbacks of the conventional IBM will be presented. First, an expanded velocity profile scheme has been developed, in order to compensate for the discontinuities caused by the gradient of the velocity across the boundary. Second, a numerical method derived from the Navier-Stokes equations in order to correct the pressure distribution across the boundary has been examined. The resulting hybrid solver has been applied to viscous flows around stationary and oscillating cylinders and examined the hovering flight of elliptical wings at low Reynolds numbers. It is shown that the proposed scheme smoothly expands the velocity profile across the boundary and increases the accuracy of the immersed boundary method. In addition, the pressure correction algorithm correctly expands the pressure profile across the boundary leading to very accurate pressure coefficient values along the boundary surface. The proposed numerical schemes are shown to be very efficient in terms of computational cost. The majority of the presented results are obtained within a few hours of CPU time on a 2.8 GHz Intel Core i7 MacBook Pro computer with a 16GB memory.
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Madani, Kermani Seyed Hossein. "Application of immersed boundary method to flexible riser problem." Thesis, Brunel University, 2014. http://bura.brunel.ac.uk/handle/2438/9605.
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In the recent decades the Fluid-Structure Interaction (FSI) problem has been of great interest to many researchers and a variety of methods have been proposed for its numerical simulation. As FSI simulation is a multi-discipline and a multi-physics problem, its full simulation consists of many details and sub-procedures. On the other hand, reliable FSI simulations are required in various applications ranging from hemo-dynamics and structural engineering to aero-elasticity. In hemo-dynamics an incompressible fluid is coupled with a flexible structure with similar density (e.g. blood in arteries). In aero-elasticity a compressible fluid interacts with a stiff structure (e.g. aircraft wing) or an incompressible flow is coupled with a very light structure (e.g. Parachute or sail), whereas in some other engineering applications an incompressible flow interacts with a flexible structure with large displacement (e.g. oil risers in offshore industries). Therefore, various FSI models are employed to simulate a variety of different applications. An initial vital step to conduct an accurate FSI simulation is to perform a study of the physics of the problem which would be the main criterion on which the full FSI simulation procedure will then be based. In this thesis, interaction of an incompressible fluid flow at low Reynolds number with a flexible circular cylinder in two dimensions has been studied in detail using some of the latest published methods in the literature. The elements of procedures have been chosen in a way to allow further development to simulate the interaction of an incompressible fluid flow with a flexible oil riser with large displacement in three dimensions in future. To achieve this goal, a partitioned approach has been adopted to enable the use of existing structural codes together with an Immersed Boundary (IB) method which would allow the modelling of large displacements. A direct forcing approach, interpolation / reconstruction, type of IB is used to enforce the moving boundary condition and to create sharp interfaces with the possibility of modelling in three dimensions. This provides an advantage over the IB continuous forcing approach which creates a diffused boundary. And also is considered as a preferred method over the cut cell approach which is very complex in three dimensions with moving boundaries. Different reconstruction methods from the literature have been compared with the newly proposed method. The fluid governing equation is solved only in the fluid domain using a Cartesian grid and an Eulerian approach while the structural analysis was performed using Lagrangian methods. This method avoids the creation of secondary fluid domains inside the solid boundary which occurs in some of the IB methods. In the IB methods forces from the Eulerian flow field are transferred onto the Lagrangian marker points on the solid boundary and the displacement and velocities of the moving boundary are interpolated in the flow domain to enforce no-slip boundary conditions. Various coupling methods from the literature were selected and improved to allow modelling the interface and to transfer the data between fluid and structure. In addition, as an alternative method to simulate FSI for a single object in the fluid flow as suggested in the literature, the moving frame of reference method has been applied for the first time in this thesis to simulate Fluid-Structure interaction using an IB reconstruction approach. The flow around a cylinder in two dimensions was selected as a benchmark to validate the simulation results as there are many experimental and analytical results presented in the literature for this specific case.
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Lai, Xin. "Modeling and Numerical Simulations of Active and Passive Forces Using Immersed Boundary Method." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1334.
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This thesis uses the Immersed Boundary Method (IBM) to simulate the movement of a human heart. The IBM was developed by Charles Peskin in the 70’s to solve Fluid-Structure Interaction models (FSI). The heart is embedded inside a fluid (blood) which moves according to the Navier-Stokes equation. The Navier-Stokes equation is solved by the Spectral Method. Forces on the heart muscle can be divided into two kinds: Active Force and Passive Force. Passive includes the effect of curvature (Peskin’s model), spring model, and the torsional spring (or beam) model. Active force is modeled by the 3-element Hill model, which was used in the 30’s to model skeletal muscle. We performed simulations with different combinations of these four forces. Numerical simulations are performed using MATLAB. We downloaded Peskin’s code from the Internet and modified the Force.m file to include the above four forces. This thesis only considers heart muscle movement in the organ (macroscopic) scale.
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Gerych, Walter. "Versatile Anomaly Detection with Outlier Preserving Distribution Mapping Autoencoders." Digital WPI, 2019. https://digitalcommons.wpi.edu/etd-theses/1345.
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State-of-the-art deep learning methods for outlier detection make the assumption that outliers will appear far away from inlier data in the latent space produced by distribution mapping deep networks. However, this assumption fails in practice,because the divergence penalty adopted for this purpose encourages mapping outliers into the same high-probability regions as inliers. To overcome this shortcoming,we introduce a novel deep learning outlier detection method, called Outlier Preserving Distribution Mapping Autoencoder (OP-DMA), which succeeds to map outliers to low probability regions in the latent space of an autoencoder. For this we leverage the insight that outliers are likely to have a higher reconstruction error than inliers. We thus achieve outlier-preserving distribution mapping through weighting the reconstruction error of individual points by the value of a multivariate Gaussian probability density function evaluated at those points. This weighting implies that outliers will result in an overall penalty if they are mapped to low-probability regions. We show that if the global minimum of our newly proposed loss function is achieved,then our OP-DMA maps inliers to regions with a Mahalanobis distance less than \delta, and outliers to regions past this \delta, \delta being the inverse ChiSquared CDF evaluated at 1−\alpha with \alpha the percentage of outliers in the dataset. We evaluated OP-DMA on 11 benchmark real-world datasets and compared its performance against 7 different state-of-the-art outlier detection methods, including ALOCC and MO-GAAL. Our experiments show that OP-DMA outperforms the state-of-the-art methods on 7 of the datasets, and performs second best on 3 of the remaining 4 datasets, while no other method won on more than 1 dataset.
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Rowlatt, Christopher Frederick. "Modelling flows of complex fluids using the immersed boundary method." Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/63680/.
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This thesis is concerned with fluid-structure interaction problems using the immersed boundary method (IBM). Fluid-structure interaction problems can be classified into two categories: a remeshing approach and a fixed-grid approach. Both approaches consider the fluid and structure separately and then couple them together via suitable interface conditions. A common choice of remeshing approach is the Arbitrary-Eulerian-Lagrangian (ALE) technique. Whilst the ALE method is a good choice if deformations are small, it becomes computationally very expensive if deformations are large. In such a scenario, one turns to a fixed-grid approach. However, the issue with a fixed-grid approach is the enforcement of the interface conditions. An alternative to the remeshing and fixed-grid approach is the IBM. The IBM considers the immersed elastic structure to be part of the surrounding fluid by replacing the immersed structure with an Eulerian force density. Therefore, the interface conditions are enforced implicitly. This thesis applies the finite element immersed boundary method (IBM) to both Newtonian and Oldroyd-B viscoelastic fluids, where the fluid variables are approximated using the spectral element method (hence we name the method the spectral element immersed boundary method (SE-IBM)) and the immersed boundary variables are approximated using either the finite element method or the spectral element method. The IBM is known to suffer from area loss problems, e.g. when a static closed boundary is immersed in a fluid, the area contained inside the closed boundary decreases as the simulation progresses. The main source of error in such a scenario can be found in the spreading and interpolation phases. The aim of using a spectral element method is to improve the accuracy of the spreading and interpolation phases of the IBM. We illustrate that the SE-IBM can obtain better area conservation than the FE-IBM when a static closed boundary is considered. Also, the SE-IBM obtains higher order convergence of the velocity in the L2 and H1 norms, respectively. When the SE-IBM is applied to a viscoelastic fluid, any discontinuities which occur in either the velocity gradients or the pressure, introduce oscillations in the polymeric stress components. These oscillations are undesirable as they could potentially cause the numerics to break down. Finally, we consider a higher-order enriched method based on the extended finite element method (XFEM), which we call the eXtended Spectral Element Method (XSEM). When XSEM is applied to the SE-IBM with a viscoelastic fluid, the oscillations present in the polymeric stress components are greatly reduced.
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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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Schwarz, Stephan. "An immersed boundary method for particles and bubbles in magnetohydrodynamic flows." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-142500.
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This thesis presents a numerical method for the phase-resolving simulation of rigid particles and deformable bubbles in viscous, magnetohydrodynamic flows. The presented approach features solid robustness and high numerical efficiency. The implementation is three-dimensional and fully parallel suiting the needs of modern high-performance computing.
In addition to the steps towards magnetohydrodynamics, the thesis covers method development with respect to the immersed boundary method which can be summarized in simple words by From rigid spherical particles to deformable bubbles. The development comprises the extension of an existing immersed boundary method to non-spherical particles and very low particle-to-fluid density ratios. A detailed study is dedicated to the complex interaction of particle shape, wake and particle dynamics.
Furthermore, the representation of deformable bubble shapes, i.e. the coupling of the bubble shape to the fluid loads, is accounted for. The topic of bubble interaction is surveyed including bubble collision and coalescence and a new coalescence model is introduced.
The thesis contains applications of the method to simulations of the rise of a single bubble and a bubble chain in liquid metal with and without magnetic field highlighting the major effects of the field on the bubble dynamics and the flow field. The effect of bubble coalescence is quantified for two closely adjacent bubble chains.
A framework for large-scale simulations with many bubbles is provided to study complex multiphase phenomena like bubble-turbulence interaction in an efficient manner.
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Bürger, Markus [Verfasser]. "An Immersed Boundary Method for Arbitrarily Shaped Lagrangian Bodies / Markus Bürger." Düren : Shaker, 2021. http://d-nb.info/1225654211/34.
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Park, Hee Sung. "Immersed Boundary Method for High Reynolds Number Computation of Rotorcraft Aerodynamics." Thesis, The University of Sydney, 2020. https://hdl.handle.net/2123/22441.
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In this research, an Immersed Boundary Method (IBM) is developed and implemented into a finite-volume based incompressible, Navier-Stokes solver within OpenFOAM for efficient full rotorcraft simulations. Given a geometry definition, a simple Cartesian mesh generated through a fully automated process can be used for an IBM since it is a non-body-conformal mesh approach which incorporates geometrical complexities using momentum forcing to enforce its boundary condition onto the flow field. Detached Eddy Simulation is employed for the turbulence modelling, and an appropriate wall function for the Spalart-Allmaras turbulence model is defined and implemented as needed for efficient high Reynolds number computations. Also, it is demonstrated that a Total Variation Diminishing reconstruction must be used to give physically reasonable results. Finally, an Actuator Surface Model (ASM) is integrated with the IBM solver, concluding the overall IBM-ASM methodology to address rotorcraft problems. Detailed verification and validation of the IBM solver are demonstrated for three test cases: (i) low Reynolds number flow over a fixed cylinder to inspect its capability in fully resolved simulations, (ii) a zero-pressure-gradient turbulent boundary layer flow over a flat plate to verify the tangential velocity profile modelled by a wall function, and (iii) high Reynolds number flow over a fixed cylinder to validate for unsteady flow over curved surfaces using a wall function. Lastly, the integrated IBM-ASM solver is validated against experimental measurements for the flow around a simplified airframe developed by Georgia Institute of Technology. Unsteady rotor-wake/fuselage interactions in a forward flight condition are analysed. Results are competitive with existing best methods using a fraction of the setup and computational effort of the body conforming method.
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Linnick, Mark Nicholas. "A high-order immersed boundary method for unsteady incompressible flow calculations." Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/290009.
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A high-order immersed boundary method (IBM) for the computation of unsteady, incompressible fluid flows on two-dimensional, complex domains is proposed, analyzed, developed and validated. In the IBM, the equations of interest are discretized on a fixed Cartesian grid. As a result, domain boundaries do not always conform to the (rectangular) computational domain boundaries. This gives rise to 'immersed boundaries', i.e., boundaries immersed inside the computational domain. A new IBM is proposed to remedy problems in an older existing IBM that had originally been selected for use in numerical flow control investigations. In particular, the older method suffered from considerably reduced accuracy near the immersed boundary surface where sharp jumps in the solution, i.e., jump discontinuities in the function and/or its derivatives, were smeared out over several grid points. To avoid this behavior, a sharp interface method, originally developed by LeVeque & Li (1994) and Wiegmann & Bube (2000) in the context of elliptic PDEs, is introduced where the numerical scheme takes such discontinuities into consideration in its design. By comparing computed solutions to jump-singular PDEs having known analytical solutions, the new IBM is shown to maintain the formal fourth-order accuracy, in both time and space, of the underlying finite-difference scheme. Further validation of the new IBM code was accomplished through its application to several two-dimensional flows, including flow past a circular cylinder, and T-S waves in a flat plate boundary layer. Comparison of results from the new IBM with results available in the literature found good agreement in all cases.
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Suzuki, Kosuke. "An immersed boundary-lattice Boltzmann method for moving boundary flows and its application to flapping flight." 京都大学 (Kyoto University), 2014. http://hdl.handle.net/2433/188584.
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Vasyliv, Yaroslav V. "Development of general finite differences for complex geometries using immersed boundary method." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54425.
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In meshfree methods, partial differential equations are solved on an unstructured cloud of points distributed throughout the computational domain. In collocated meshfree methods, the differential operators are directly approximated at each grid point based on a local cloud of neighboring points. The set of neighboring nodes used to construct the local approximation is determined using a variable search radius. The variable search radius establishes an implicit nodal connectivity and hence a mesh is not required. As a result, meshfree methods have the potential flexibility to handle problem sets where the computational grid may undergo large deformations as well as where the grid may need to undergo adaptive refinement. In this work we develop the sharp interface formulation of the immersed boundary method for collocated meshfree approximations. We use the framework to implement three meshfree methods: General Finite Differences (GFD), Smoothed Particle Hydrodynamics (SPH), and Moving Least Squares (MLS). We evaluate the numerical accuracy and convergence rate of these methods by solving the 2D Poisson equation. We demonstrate that GFD is computationally more efficient than MLS and show that its accuracy is superior to a popular corrected form of SPH and comparable to MLS. We then use GFD to solve several canonic steady state fluid flow problems on meshfree grids generated using uniform and variable radii Poisson disk algorithm.
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Shui, Pei. "Novel immersed boundary method for direct numerical simulations of solid-fluid flows." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10050.
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Solid-fluid two-phase flows, where the solid volume fraction is large either by geometry or by population (as in slurry flows), are ubiquitous in nature and industry. The interaction between the fluid and the suspended solids, in such flows, are too strongly coupled rendering the assumption of a single-way interaction (flow influences particle motion alone but not vice-versa) invalid and inaccurate. Most commercial flow solvers do not account for twoway interactions between fluid and immersed solids. The current state-of-art is restricted to two-way coupling between spherical particles (of very small diameters, such that the particlediameter to the characteristic flow domain length scale ratio is less than 0.01) and flow. These solvers are not suitable for solving several industrial slurry flow problems such as those of hydrates which is crucial to the oil-gas industry and rheology of slurries, flows in highly constrained geometries like microchannels or sessile drops that are laden with micro-PIV beads at concentrations significant for two-way interactions to become prominent. It is therefore necessary to develop direct numerical simulation flow solvers employing rigorous two-way coupling in order to accurately characterise the flow profiles between large immersed solids and fluid. It is necessary that such a solution takes into account the full 3D governing equations of flow (Navier-Stokes and continuity equations), solid translation (Newton’s second law) and solid rotation (equation of angular momentum) while simultaneously enabling interaction at every time step between the forces in the fluid and solid domains. This thesis concerns with development and rigorous validation of a 3D solid-fluid solver based on a novel variant of immersed-boundary method (IBM). The solver takes into account full two-way fluid-solid interaction with 6 degrees-of-freedom (6DOF). The solid motion solver is seamlessly integrated into the Gerris flow solver hence called Gerris Immersed Solid Solver (GISS). The IBM developed treats both fluid and solid in the manner of “fluid fraction” such that any number of immersed solids of arbitrary geometry can be realised. Our IBM method also allows transient local mesh adaption in the fluid domain around the moving solid boundary, thereby avoiding problems caused by the mesh skewness (as seen in common mesh-adaption algorithms) and significantly improves the simulation efficiency. The solver is rigorously validated at levels of increasing complexity against theory and experiment at low to moderate flow Reynolds number. At low Reynolds numbers (Re 1) these include: the drag force and terminal settling velocities of spherical bodies (validating translational degrees of freedom), Jeffrey’s orbits tracked by elliptical solids under shear flow (validating rotational and translational degrees of freedom) and hydrodynamic interaction between a solid and wall. Studies are also carried out to understand hydrodynamic interaction between multiple solid bodies under shear flow. It is found that initial distance between bodies is crucial towards the nature of hydrodynamic interaction between them: at a distance smaller than a critical value the solid bodies cluster together (hydrodynamic attraction) and at a distance greater than this value the solid bodies travel away from each other (hydrodynamic repulsion). At moderately high flow rates (Re O(100)), the solver is validated against migratory motion of an eccentrically placed solid sphere in Poisuelle flow. Under inviscid conditions (at very high Reynolds number) the solver is validated against chaotic motion of an asymmetric solid body. These validations not only give us confidence but also demonstrate the versatility of the GISS towards tackling complex solid-fluid flows. This work demonstrates the first important step towards ultra-high resolution direct numerical simulations of solid-fluid flows. The GISS will be available as opensource code from February 2015.
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He, Long. "Study of Fluid Forces and Heat Transfer on Non-spherical Particles in Assembly Using Particle Resolved Simulation." Diss., Virginia Tech, 2018. http://hdl.handle.net/10919/91400.
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Gas-solid flow is fundamental to many industrial processes. Extensive experimental and numerical studies have been devoted to understand the interphase momentum and heat transfer in these systems. Most of the studies have focused on spherical particle shapes, however, in most natural and industrial processes, the particle shape is seldom spherical. In fact, particle shape is one of the important parameters that can have a significant impact on momentum, heat and mass transfer, which are fundamental to all processes. In this study particle-resolved simulations are performed to study momentum and heat transfer in flow through a fixed random assembly of ellipsoidal particles with sphericity of 0.887. The incompressible Navier-Stokes equations are solved using the Immersed Boundary Method (IBM). A Framework for generating particle assembly is developed using physics engine PhysX. High-order boundary conditions are developed for immersed boundary method to resolve the heat transfer in the vicinity of fluid/particle boundary with better accuracy. A complete framework using particle-resolved simulation study assembly of particles with any shape is developed. The drag force of spherical particles and ellipsoid particles are investigated. Available correlations are evaluated based on simulation results and recommendations are made regarding the best combinations. The heat transfer in assembly of ellipsoidal particle is investigated, and a correlation is proposed for the particle shape studied. The lift force, lateral force and torque of ellipsoid particles in assembly and their variations are quantitatively presented and it is shown that under certain conditions these forces and torques cannot be neglected as is done in the larger literature.Ph. D.
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Argyropoulos, Christos. "A combined immersed boundary/phase-field method for simulating two-phase pipe flows." Thesis, Imperial College London, 2015. http://hdl.handle.net/10044/1/51089.
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The investigation of the flow in a pipe is a major issue for the pipeline capacity but also plays an important role for the control and prevention of phenomena that could damage the pipe, such as corrosion, erosion, and the potential formation of wax or their deposits. Therefore, the characterization of the flow patterns is also a major issue for the prediction of the distribution over the cross-section of the pipe, in order to understand any problems that may interrupt or shut down the operation of the production line. The main purpose of the present effort is to develop an appropriate numerical method for simulating two-phase pipe flows. Advanced Computational Fluid Dynamics (CFD) methods are employed as Navier-Stokes solver, while a Phase-Field method is used to simulate the interfacial region between the two fluids. A Ghost-Cell Immersed Boundary Method (GCIBM) was developed and implemented for the reconstruction of smooth rigid boundaries (pipe wall) based on the work of Tseng and Ferziger (2003). The method was also modified in order to incorporate appropriate boundary conditions for coupling the Phase-Field and Navier-Stokes solvers for two-phase pipe flows. Tseng and Ferziger (2003) used the GCIBM for turbulent single-phase flows; the present modified version comprises a continuation of the method for handling two-phase pipe flows. The computational model is capable of handling large density and viscosity ratios with good accuracy. The developed GCIBM algorithm was validated against analytical solutions for single and two-phase pipe flow, presenting very good agreement. The computational model was compared to available experimental data from the literature for single rising bubbles and bubble coalescence in vertical pipe also with good agreement. The numerical method was used to investigate the lateral wall effects of a 3-D single bubble in a viscous liquid for different pipe diameters and bubble flow regimes. The dynamics of 3-D Taylor bubbles was also examined in vertical pipes for different properties of fluids (e.g. air-water system) and dimensionless parameters relevant to the problem (e.g. ReB, Eo, Mo). The numerical results were compared with available experimental and numerical data from the literature, presenting good agreement.
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Kang, Seongwon. "An improved immersed boundary method for computation of turbulent flows with heat transfer /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Brehm, Christoph. "Novel Immersed Interface Method for Solving the Incompressible Navier-Stokes Equations." Diss., The University of Arizona, 2011. http://hdl.handle.net/10150/202770.
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For simulations of highly complex geometries, frequently encountered in many fields of science and engineering, the process of generating a high-quality, body-fitted grid is very complicated and time-intensive. Thus, one of the principal goals of contemporary CFD is the development of numerical algorithms, which are able to deliver computationally efficient, and highly accurate solutions for a wide range of applications involving multi-physics problems, e.g. Fluid Structure Interaction (FSI). Immersed interface/boundary methods provide considerable advantages over conventional approaches, especially for flow problems containing moving boundaries.In the present work, a novel, robust, highly-accurate, Immersed Interface Method (IIM) is developed, which is based on a local Taylor-series expansion at irregular grid points enforcing numerical stability through a local stability condition. Various immersed methods have been developed in the past; however, these methods only considered the order of the local truncation error. The numerical stability of these schemes was demonstrated (in a global sense) by considering a number of different test-problems. None of these schemes used a concrete local stability condition to derive the irregular stencil coefficients. This work will demonstrate that the local stability constraint is valid as long as the DFL-number does not reach a limiting value. The IIM integrated into a newly developed Incompressible Navier-Stokes (INS) solver is used herein to simulate fully coupled FSI problems. The extension of the novel IIM to a higher-order method, the compressible Navier-Stokes equations and the Maxwell's equations demonstrate the great potential of the novel IIM.In the second part of this dissertation, the newly developed INS solver is employed to study the flow of a stalled airfoil and steady/unsteady stenotic flows. In this context, a new biglobal stability analysis approach based on solving an Initial Value Problem (IVP), instead of the traditionally used EigenValue Problem (EVP), is presented. It is demonstrated that this approach based on an IVP is computationally less expensive compared to EVP approaches while still capturing the relevant physics.
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Yin, Y. "Turbulence model and immersed boundary method development in TELEMAC-3D for offshore structure modelling." Thesis, University of Liverpool, 2017. http://livrepository.liverpool.ac.uk/3006448/.
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In recent years, increased evidences suggest that offshore structures such as wind farms, tidal turbine farms, piles of bridge and breakwater have great impact on the hydrodynamics and hence may have a strong influence on the sediment transport at a site. The open-source hydrodynamic suite of software TELEMAC has been used for the study of such environmental influence around Unite Kingdom. However, the use of the 3-D version of the software, TELEMAC-3D is restricted by how structures are accounted for in the meshes, as water columns have the same number of layers all over the domain. Moreover, a large scale farm has a large impact on turbulence mixing in the coastal regional scale, and this is not properly understood. The PhD project focuses on 3-D hydrodynamics and development of an 3-D unstructured capability using an immersed boundary method to account for obstacles in the flow. Two large eddy simulation models (the 2eddy LES model and the Wall-adapted Large Eddy model) have been incorporated into TELEMAC-3D to get a more realistic and effective representation of the turbulence mixing and to account for the unsteadiness of the flow past the structures. The simulations have been performed using High Performance Computing to enable large scale applications using TELEMAC-3D and fine spatial and temporal resolutions in 3-D. The implementations carried out in the code are fully parallel. The numerical models have been validated for two laboratory scale cases, including the flow around a circular cylinder and the flow over a submerged structure. Then a far-field simulation at the southern North Sea has been carried out, where the hydrodynamics and morphological impacts of the London Array offshore wind turbine farm have been investigated. The numerical results of turbulence model implementation indicate that both turbulence models have good performance in the representation of the flow past a cylinder in laboratory scale. However in the large scale application, only the 2eddy LES model is successfully applied because the WALE model relies on a very fine mesh in the vertical direction. The implementation of IBM suggested that when dealing with an obstacle going from the bottom though the surface of the water, the immersed boundary method offers good accuracy in the prediction of surrounding flow structures. For the submerged obstacles, they can be simulated by TELEMAC-3D by implementing the Immersed Boundary method. Although the accuracy is limited currently, qualitative analysis can still be performed.
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Gordon, Eric Duane. "Using the penalty immersed boundary method to model the interaction between filiform hairs of crickets." Thesis, Montana State University, 2011. http://etd.lib.montana.edu/etd/2011/gordon/GordonE0811.pdf.
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Fluid-structure interactions are important in a wide range of applications and, due to their complexity, need extensive experimental and computational research. One such example comes from crickets, which have evolutionarily developed an excellent micro-air-flow sensory system. Understanding principles of the cricket' micro-air-flow sensor will help design and manufacture artificial sensors. This thesis focuses on improving and validating a Penalty Immersed Boundary (PIB) model of the cricket sensory system, which consists of hundreds of filiform hairs. Previous efforts by others have modeled the filiform hair as a rigid inverted pendulum. Advantages to the PIB approach over previous models include a flexible fluid solver (previous models used an idealized, analytical flow field), the filiform hairs are not required to be completely rigid, and, most importantly, the entire cerci and all the filiform hairs can be modeled. The first goal was to improve the precision and accuracy of modeling a single filiform hair by adjusting model parameters so that the model predictions more accurately fit experimental data. A second goal was to model a portion of a full cercus based on filiform hair data from a real cricket and use the model to determine the interactions occurring between multiple hairs and identify any evolutionary optimization of the cercal system.
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Bomminayuni, Sandeep Kumar. "Large eddy simulation of turbulent flow over a rough bed using the immersed boundary method." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34821.
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Study of turbulent flow over a rough bed is highly important due to its numerous applications in the areas of sediment transport and pollutant discharge in streams, rivers and channels. Over the past few decades, many experimental studies have been conducted in this respect to understand the underlying phenomenon. However, there is a scarcity in the number of computational studies conducted on this topic. Therefore, a Large Eddy Simulation (LES) of turbulent flow over a rough channel bed was conducted to contribute further understanding of the influence of bed roughness on turbulent flow properties. For this purpose, an efficient, second order accurate 'immersed boundary method' was implemented into the LES code Hydro3d-GT, and validated for flow past bluff bodies.
LES results from the present study showed excellent agreement with previous experimental studies on flow over rough beds. An in-depth analysis of time varying turbulent quantities (like the velocity fluctuations) revealed the presence of coherent structures in the flow. Also, a three dimensional visualization of the turbulent structures provided a good picture of the flow, especially in the near bed region, which is quite difficult to accomplish using experimental studies.
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Hsu, Chia-Yu. "A 3D bacterial swimming model coupled with external fluid mechanics using the immersed boundary method." Online access for everyone, 2007. http://www.dissertations.wsu.edu/Dissertations/Summer2007/c_hsu_080207.pdf.
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Ni, Mong-Tang. "Analysis of fluid structure interaction problem using immersed boundary method with a finite element approach /." May be available electronically:, 2008. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
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Navarro, Jiménez José Manuel. "Contact problem modelling using the Cartesian grid Finite Element Method." Doctoral thesis, Universitat Politècnica de València, 2019. http://hdl.handle.net/10251/124348.
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[ES] La interacción de contacto entre sólidos deformables es uno de los fenómenos más complejos en el ámbito de la mecánica computacional. La resolución de este problema requiere de algoritmos robustos para el tratamiento de no linealidades geométricas. El Método de Elementos Finitos (MEF) es uno de los más utilizados para el diseño de componentes mecánicos, incluyendo la solución de problemas de contacto. En este método el coste asociado al proceso de discretización (generación de malla) está directamente vinculado a la definición del contorno a modelar, lo cual dificulta la introducción en la simulación de superficies complejas, como las superficies NURBS, cada vez más utilizadas en el diseño de componentes.
Esta tesis está basada en el "Cartesian grid Finite Element Method" (cgFEM). En esta metodología, encuadrada en la categoría de métodos "Immersed Boundary", se extiende el problema a un dominio de aproximación (cuyo mallado es sencillo de generar) que contiene al dominio de análisis completamente en su interior. Al desvincular la discretización de la definición del contorno del problema se reduce drásticamente el coste de generación de malla. Es por ello que el método cgFEM es una herramienta adecuada para la resolución de problemas en los que es necesario modificar la geometría múltiples veces, como el problema de optimización de forma o la simulación de desgaste.
El método cgFEM permite también crear de manera automática y eficiente modelos de Elementos Finitos a partir de imágenes médicas. La introducción de restricciones de contacto habilitaría la posibilidad de considerar los diferentes estados de integración implante-tejido en procesos de optimización personalizada de implantes.
Así, en esta tesis se desarrolla una formulación para resolver problemas de contacto 3D con el método cgFEM, considerando tanto modelos de contacto sin fricción como problemas con rozamiento de Coulomb. La ausencia de nodos en el contorno en cgFEM impide la aplicación de métodos tradicionales para imponer las restricciones de contacto, por lo que se ha desarrollado una formulación estabilizada que hace uso de un campo de tensiones recuperado para asegurar la estabilidad del método. Para una mayor precisión de la solución, se ha introducido la definición analítica de las superficies en contacto en la formulación propuesta.
Además, se propone la mejora de la robustez de la metodología cgFEM en dos aspectos: el control del mal condicionamiento del problema numérico mediante un método estabilizado, y la mejora del campo de tensiones recuperado, utilizado en el proceso de estimación de error.
La metodología propuesta se ha validado a través de diversos ejemplos numéricos presentados en la tesis, mostrando el gran potencial de cgFEM en este tipo de problemas.[CAT] La interacció de contacte entre sòlids deformables és un dels fenòmens més complexos en l'àmbit de la mecànica computacional. La resolució d'este problema requerix d'algoritmes robustos per al tractament de no linealitats geomètriques. El Mètode dels Elements Finits (MEF) és un dels més utilitzats per al disseny de components mecànics, incloent la solució de problemes de contacte. En este mètode el cost associat al procés de discretització (generació de malla) està directament vinculat a la definició del contorn a modelar, la qual cosa dificulta la introducció en la simulació de superfícies complexes, com les superfícies NURBS, cada vegada més utilitzades en el disseny de components. Esta tesi està basada en el "Cartesian grid Finite Element Method" (cgFEM). En esta metodologia, enquadrada en la categoria de mètodes "Immersed Boundary", s'estén el problema a un domini d'aproximació (el mallat del qual és senzill de generar) que conté al domini d'anàlisi completament en el seu interior. Al desvincular la discretització de la definició del contorn del problema es reduïx dràsticament el cost de generació de malla. És per això que el mètode cgFEM és una ferramenta adequada per a la resolució de problemes en què és necessari modificar la geometria múltiples vegades, com el problema d'optimització de forma o la simulació de desgast. El mètode cgFEM permet també crear de manera automàtica i eficient models d'Elements Finits a partir d'imatges mèdiques. La introducció de restriccions de contacte habilitaria la possibilitat de considerar els diferents estats d'integració implant-teixit en processos d'optimització personalitzada d'implants. Així, en esta tesi es desenvolupa una formulació per a resoldre problemes de contacte 3D amb el mètode cgFEM, considerant tant models de contacte sense fricció com a problemes amb fregament de Coulomb. L'absència de nodes en el contorn en cgFEM impedix l'aplicació de mètodes tradicionals per a imposar les restriccions de contacte, per la qual cosa s'ha desenvolupat una formulació estabilitzada que fa ús d'un camp de tensions recuperat per a assegurar l'estabilitat del mètode. Per a una millor precisió de la solució, s'ha introduït la definició analítica de les superfícies en contacte en la formulació proposada. A més, es proposa la millora de la robustesa de la metodologia cgFEM en dos aspectes: el control del mal condicionament del problema numèric per mitjà d'un mètode estabilitzat, i la millora del camp de tensions recuperat, utilitzat en el procés d'estimació d'error. La metodologia proposada s'ha validat a través de diversos exemples numèrics presentats en la tesi, mostrant el gran potencial de cgFEM en este tipus de problemes.
[EN] The contact interaction between elastic solids is one of the most complex phenomena in the computational mechanics research field. The solution of such problem requires robust algorithms to treat the geometrical non-linearities characteristic of the contact constrains. The Finite Element Method (FE) has become one of the most popular options for the mechanical components design, including the solution of contact problems. In this method the computational cost of the generation of the discretization (mesh generation) is directly related to the complexity of the analysis domain, namely its boundary. This complicates the introduction in the numerical simulations of complex surfaces (for example NURBS), which are being increasingly used in the CAD industry. This thesis is grounded on the Cartesian grid Finite Element Method (cgFEM). In this methodology, which belongs to the family of Immersed Boundary methods, the problem at hand is extended to an approximation domain which completely embeds the analysis domain, and its meshing is straightforward. The decoupling of the boundary definition and the discretization mesh results in a great reduction of the mesh generation's computational cost. Is for this reason that the cgFEM is a suitable tool for the solution of problems that require multiple geometry modifications, such as shape optimization problems or wear simulations. The cgFEM is also capable of automatically generating FE models from medical images without the intermediate step of generating CAD entities. The introduction of the contact interaction would open the possibility to consider different states of the union between implant and living tissue for the design of optimized implants, even in a patient-specific process. Hence, in this thesis a formulation for solving 3D contact problems with the cgFEM is presented, considering both frictionless and Coulomb's friction problems. The absence of nodes along the boundary in cgFEM prevents the enforcement of the contact constrains using the standard procedures. Thus, we develop a stabilized formulation that makes use of a recovered stress field, which ensures the stability of the method. The analytical definition of the contact surfaces (by means of NURBS) has been included in the proposed formulation in order to increase the accuracy of the solution. In addition, the robustness of the cgFEM methodology is increased in this thesis in two different aspects: the control of the numerical problem's ill-conditioning by means of a stabilized method, and the enhancement of the stress recovered field, which is used in the error estimation procedure. The proposed methodology has been validated through several numerical examples, showing the great potential of the cgFEM in these type of problems.
Navarro Jiménez, JM. (2019). Contact problem modelling using the Cartesian grid Finite Element Method [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/124348
TESIS
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Moon, Jiyoung. "Rheological Behavior of Complex Fluid with Deformable and Rigid Particles." Thesis, The University of Sydney, 2017. http://hdl.handle.net/2123/17106.
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Predicting the rheological properties of particles in matrix is one of the most challenging and complicated problems in material and fluid sciences. The complication is arisen by the particles collision and interactions with the surrounding fluid. A full description of the rheology of particles requires a complete understanding of the interactions between particles, interaction between the particles and the matrix fluid, and interactions between channel and particles. Thus consideration of above factors can lead to a better understanding of the rheological behavior of suspensions with particles flow. In this thesis, fluid with deformable particle and fluid with rigid particles are considered. A combination model of the three dimensional lattice Boltzmann method (LBM) and the immersed boundary method (IBM) are used to simulate these suspension systems. For the single particle deformation in the flow, the boundary thickness and value on transit time in a microchannel was analyzed. To see the physics behind the single particle in a micro channel, the path selection (navigation) of a single moving particle in a microfluidic channel network was analyzed. To see the interaction between wall property and suspension flow, deformable particles in hydrophobic and hydrophilic surface microfluidic channels was analyzed. To see the effect of particle roughness on rheology, the results of measuring the viscometric flow of concentrated rigid-sphere suspensions with constant-viscosity matrices, both Newtonian (silicone oil) and non-Newtonian were presented. Finally, the rough particle was analyzed by lattice Boltzmann method to find the physics behind the experimental results.
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He, Long. "A Study of Immersed Boundary Method in a Ribbed Duct for the Internal Cooling of Turbine Blades." Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/78069.
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In this dissertation, Immersed Boundary Method (IBM) is evaluated in ribbed duct geometries to show the potential of simulating complex geometry with a simple structured grid. IBM is first investigated in well-accepted benchmark cases: channel flow and pipe flow with circular cross-section. IBM captures all the flow features with very good accuracy in these two cases. Then a two side ribbed duct geometry is test using IBM at Reynolds number of 20,000 under fully developed assumption. The IBM results agrees well with body conforming grid predictions. A one side ribbed duct geometry is also tested at a bulk Reynolds number of 1.5⨉10⁴. Three cases have been examined for this geometry: a stationary case; a case of positive rotation at a rotation number (Ro=ΩDₕ/U) of 0.3 (destabilizing); and a case of negative rotation at Ro= -0.3 (stabilizing). Time averaged mean, turbulent quantities are presented, together with heat transfer. The overall good agreement between IBM, BCG and experimental results suggests that IBM is a promising method to apply to complex blade geometries. Due to the disadvantage of IBM that it requires large amount of cells to resolve the boundary near the immersed surface, wall modeled LES (WMLES) is evaluated in the final part of this thesis. WMLES is used for simulating turbulent flow in a developing staggered ribbed U-bend duct. Three cases have been tested at a bulk Reynolds number of 10⁵: a stationary case; a positive rotation case at a rotation number Ro=0.2; and a negative rotation case at Ro=-0.2. Coriolis force effects are included in the calculation to evaluate the wall model under the influence of these effects which are known to affect shear layer turbulence production on the leading and trailing sides of the duct. Wall model LES prediction shows good agreement with experimental data.Master of Science
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Oh, Tae Kyung. "Strongly-Coupled Conjugate Heat Transfer Investigation of Internal Cooling of Turbine Blades using the Immersed Boundary Method." Thesis, Virginia Tech, 2019. http://hdl.handle.net/10919/90894.
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The present thesis focuses on evaluating a conjugate heat transfer (CHT) simulation in a ribbed cooling passage with a fully developed flow assumption using LES with the immersed boundary method (IBM-LES-CHT). The IBM with the LES model (IBM-LES) and the IBM with CHT boundary condition (IBM-CHT) frameworks are validated prior to the main simulations by simulating purely convective heat transfer (iso-flux) in the ribbed duct, and a developing laminar boundary layer flow over a two-dimensional flat plate with heat conduction, respectively. For the main conjugate simulations, a ribbed duct geometry with a blockage ratio of 0.3 is simulated at a bulk Reynolds number of 10,000 with a conjugate boundary condition applied to the rib surface. The nominal Biot number is kept at 1, which is similar to the comparative experiment. As a means to overcome a large time scale disparity between the fluid and the solid regions, the use of a high artificial solid thermal diffusivity is compared to the physical diffusivity. It is shown that while the diffusivity impacts the instantaneous fluctuations in temperature, heat transfer and Nusselt numbers, it has an insignificantly small effect on the mean Nusselt number. The comparison between the IBM-LES-CHT and iso-flux simulations shows that the iso-flux case predicts higher local Nusselt numbers at the back face of the rib. Furthermore, the local Nusselt number augmentation ratio (EF) predicted by IBM-LES-CHT is compared to the body fitted grid (BFG) simulation, experiment and another LES conjugate simulation. Even though there is a mismatch between IBM-LES-CHT prediction and other studies at the front face of the rib, the area-averaged EF compares reasonably well in other regions between IBM-LES-CHT prediction and the comparative studies.Master of Science
The present thesis focuses on the computational study of the conjugate heat transfer (CHT) investigation on the turbine internal ribbed cooling channel. Plenty of prior research on turbine internal cooling channel have been conducted by considering only the convective heat transfer at the wall, which assumes an iso-flux (constant heat flux) boundary condition at the surface. However, applying an iso-flux condition on the surface is far from the realistic heat transfer mechanism occurring in internal cooling systems. In this work, a conjugate heat transfer analysis of the cooling channel, which considers both the conduction within the solid wall and the convection at the ribbed inner wall surface, is conducted for more realistic heat transfer coefficient prediction at the inner ribbed wall. For the simulation, the computational mesh is generated by the immersed boundary method (IBM), which can ease the mesh generation by simply immersing the CAD geometry into the background volume grid. The IBM is combined with the conjugate boundary condition to simulate the internal ribbed cooling channel. The conjugate simulation is compared with the experimental data and another computational study for the validation. Even though there are some discrepancy between the IBM simulation and other comparative studies, overall results are in good agreement. From the thermal prediction comparison between the iso-flux case and the conjugate case v using the IBM, it is found that the heat transfer predicted by the conjugate case is different from the iso-flux case by more than 40 percent at the rib back face. The present study shows the potential of the IBM framework with the conjugate boundary condition for more complicated geometry, such as full turbine blade model with external and internal cooling system.
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Nicolaou, Fernandez Laura. "A robust immersed boundary method for flow in complex geometries : study of aerosol deposition in the human extrathoracic airways." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9288.
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The flow and the transport of particles in the human respiratory system dictate the effectiveness of therapeutic aerosols used in inhaled drug delivery. The aerosol particles are generally inhaled through the mouth, passing by the throat before reaching the targeted areas in the lungs. Therefore, knowledge of the particle deposition in the mouth-throat region is critical in the design of effective inhalation devices for optimum delivery to the lungs. Numerical simulations offer a non-invasive and cost-effective alternative to in vivo and in vitro tests. However, accurate prediction remains a challenge for numerical models due to the complexity of the flow in the extrathoracic airways. A robust immersed boundary method for flow in complex geometries is proposed. This greatly simplifies the task of grid generation and eliminates the problems associated with grid quality that exist for boundary-fitted grid techniques. The proposed method is an extension to the momentum forcing approach onto curvilinear coordinates and applies an iterative procedure to compute the forcing term implicitly, which stabilizes the scheme for higher Reynolds numbers. The use of a curvilinear grid minimizes the number of unused cells outside the geometry and increases the efficiency of the numerical scheme. The method is validated against numerical and experimental data in the literature for a number of test cases on both Cartesian and curvilinear grids. The results show good agreement with previous studies. Direct numerical simulations were performed in a number of realistic mouth and throat geometries obtained from MRI scans. A Lagrangian particle tracking scheme was employed to advance the particles dynamically, and total and regional deposition efficiencies were determined and compared to in vitro data. The effect of inflow turbulence and intersubject variation on deposition was studied. Geometric variation has a large impact on total deposition whereas the effect of inflow turbulence is confined to oral deposition.
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Taira, Kunihiko Colonius Timothy E. Colonius Timothy E. "The immersed boundary projection method and its application to simulation and control of flows around low-aspect-ratio wings /." Diss., Pasadena, Calif. : California Institute of Technology, 2008. http://resolver.caltech.edu/CaltechETD:etd-05232008-124342.
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O'Connor, Joseph. "Fluid-structure interactions of wall-mounted flexible slender structures." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/fluidstructure-interactions-of-wallmounted-flexible-slender-structures(1dab2986-b78f-4ff9-9b2e-5d2181cfa009).html.
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The fluid-structure interactions of wall-mounted slender structures, such as cilia, filaments, flaps, and flags, play an important role in a broad range of physical processes: from the coherent waving motion of vegetation, to the passive flow control capability of hair-like surface coatings. While these systems are ubiquitous, their coupled nonlinear response exhibits a wide variety of behaviours that is yet to be fully understood, especially when multiple structures are considered. The purpose of this work is to investigate, via numerical simulation, the fluid-structure interactions of arrays of slender structures over a range of input conditions. A direct modelling approach, whereby the individual structures and their dynamics are fully resolved, is realised via a lattice Boltzmann-immersed boundary model, which is coupled to two different structural solvers: an Euler-Bernoulli beam model, and a finite element model. Results are presented for three selected test cases - which build in scale from a single flap in a periodic array, to a small finite array of flaps, and finally to a large finite array - and the key behaviour modes are characterised and quantified. Results show a broad range of behaviours, which depend on the flow conditions and structural properties. In particular, the emergence of coherent waving motions are shown to be closely related to the natural frequency of the array. Furthermore, this behaviour is associated with a lock-in between the natural frequency of the array and the predicted frequency of the fluid instabilities. The original contributions of this work are: the development and application of a numerical tool for direct modelling of large arrays of slender structures; the characterisation of the behaviour of slender structures over a range of input conditions; and the exposition of key behaviour modes of slender structures and their relation to input conditions.
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Tschisgale, Silvio. "A numerical method for fluid-structure interactions of slender rods in turbulent flow." TUDpress - Thelem Universitätsverlag, 2018. https://tud.qucosa.de/id/qucosa%3A38706.
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This thesis presents a numerical method for the simulation of fluid-structure interaction (FSI) problems on high-performance computers. The proposed method is specifically tailored to interactions between Newtonian fluids and a large number of slender viscoelastic structures, the latter being modeled as Cosserat rods. From a numerical point of view, such kind of FSI requires special techniques to reach numerical stability. When using a partitioned fluid-structure coupling approach
this is usually achieved by an iterative procedure, which drastically increases the computational effort. In the present work, an alternative coupling approach is developed based on an immersed boundary method (IBM). It is unconditionally
stable and exempt from any global iteration between the fluid part and the structure part.
The proposed FSI solver is employed to simulate the flow over a dense layer of vegetation elements, usually designated as canopy flow. The abstracted canopy model used in the simulation consists of 800 strip-shaped blades, which is the
largest canopy-resolving simulation of this type done so far. To gain a deeper understanding of the physics of aquatic canopy flows the simulation data obtained are analyzed, e.g., concerning the existence and shape of coherent structures.
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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.
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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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Schwarz, Stephan [Verfasser], Jochen [Akademischer Betreuer] Fröhlich, and Thomas [Akademischer Betreuer] Boeck. "An immersed boundary method for particles and bubbles in magnetohydrodynamic flows / Stephan Schwarz. Gutachter: Jochen Fröhlich ; Thomas Boeck. Betreuer: Jochen Fröhlich." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://d-nb.info/1068446498/34.
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Gokhale, Nandan Bhushan. "A dimensionally split Cartesian cut cell method for Computational Fluid Dynamics." Thesis, University of Cambridge, 2019. https://www.repository.cam.ac.uk/handle/1810/289732.
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We present a novel dimensionally split Cartesian cut cell method to compute inviscid, viscous and turbulent flows around rigid geometries. On a cut cell mesh, the existence of arbitrarily small boundary cells severely restricts the stable time step for an explicit numerical scheme. We solve this `small cell problem' when computing solutions for hyperbolic conservation laws by combining wave speed and geometric information to develop a novel stabilised cut cell flux. The convergence and stability of the developed technique are proved for the one-dimensional linear advection equation, while its multi-dimensional numerical performance is investigated through the computation of solutions to a number of test problems for the linear advection and Euler equations. This work was recently published in the Journal of Computational Physics (Gokhale et al., 2018). Subsequently, we develop the method further to be able to compute solutions for the compressible Navier-Stokes equations. The method is globally second order accurate in the L1 norm, fully conservative, and allows the use of time steps determined by the regular grid spacing. We provide a full description of the three-dimensional implementation of the method and evaluate its numerical performance by computing solutions to a wide range of test problems ranging from the nearly incompressible to the highly compressible flow regimes. This work was recently published in the Journal of Computational Physics (Gokhale et al., 2018). It is the first presentation of a dimensionally split cut cell method for the compressible Navier-Stokes equations in the literature. Finally, we also present an extension of the cut cell method to solve high Reynolds number turbulent automotive flows using a wall-modelled Large Eddy Simulation (WMLES) approach. A full description is provided of the coupling between the (implicit) LES solution and an equilibrium wall function on the cut cell mesh. The combined methodology is used to compute results for the turbulent flow over a square cylinder, and for flow over the SAE Notchback and DrivAer reference automotive geometries. We intend to publish the promising results as part of a future publication, which would be the first assessment of a WMLES Cartesian cut cell approach for computing automotive flows to be presented in the literature.
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Alex, Alvisi, and Perez Adalberto. "Analysis of wall-mounted hot-wire probes." Thesis, KTH, Strömningsmekanik och Teknisk Akustik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-289564.
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Flush-mounted cavity hot-wire probes have been around since two decades, but have typically not been applied as often compared to the traditional wall hot-wires mounted several wire diameters above the surface. While the latter suffer from heat conduction from the hot wire to the substrate in particular when used in air flows, the former is belived to significantly enhance the frequency response of the sensor. The recent work using a cavity hotwire by Gubian et al. (2019) came to the surprising conclusion that the magnitute of the fluctuating wall-shear stress τ+w,rms reaches an asymptotic value of 0.44 beyond the friction Reynolds number Re τ ∼ 600. In an effort to explain this result, which is at odds with the majority of the literature, the present work combines direct numerical simulations (DNS) of a turbulent channel flow with a cavity modelled using the immersed boundary method, as well as an experimental replication of the study of Gubian et al. in a turbulent boundary layer to explain how the contradicting results could have been obtained. It is shown that the measurements of the mentioned study can be replicated qualitatively as a result of measurement problems. We will present why cavity hot-wire probes should neither be used for quantitative nor qualitative measurements of wall-bounded flows, and that several experimental short-comings can interact to sometimes falsely yield seemingly correct results.
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Jadidi, Mansoor. "Numerical and Experimental Model of Healthy and Damaged Red Blood Cell Trajectories in Micro-channels." Thesis, Griffith University, 2023. http://hdl.handle.net/10072/421347.
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Motivation: Red blood cells (RBCs) are the most common cells in the blood due to their high concentration. The RBC has a deformable membrane enclosing a jelly-like fluid known as the cytosol. For many years, the dynamics of RBCs has attracted growing interest both numerically and experimentally in various fields of research on biological systems. Owing to their high deformability, RBCs exhibit complex dynamic behaviours in micro-vessels where Reynolds numbers (Re) are less than unity (Re < 1). First, a healthy RBC at a low shear rate or a high viscosity contrast (λ - defined as the ratio of viscosities between RBC cytosol and external fluid), may tumble, i.e., the whole RBC rotates continuously in the original shape like a rigid body. Second, at a high shear rate or a low viscosity contrast (λ), the RBC may exhibit a tank-treading motion, i.e., its membrane rotates around the cytosol which maintains a fixed angle with respect to the flow direction. Finally, a healthy RBC migrates in the lateral direction towards the micro-vessel axis while moving in the longitudinal direction (downstream) of a micro-vessel.
Under physiological conditions, the RBC experiences a varying range of shear stresses (typically in the range of 1-10 Pa) in the circulatory system without exhibiting any physical signs of mechanical damage. Upon exposure to high shear stresses, such as those present within mechanical circulatory support, RBCs exhibit irreversible functional impairment called sub-haemolytic/sub-lethal damage. Sub-haemolytically damaged RBCs exhibit impaired mechanical properties that substantially alter bulk flow behaviour when compared with healthy RBCs. However, there has been little attention directed toward characterizing sub-haemolytic damage in literature. For better understanding, it is necessary to have a reliable model to predict the dynamics of sub-haemolytically damaged RBCs in micro-vessels in comparison with healthy RBCs.
Methods: Highly-efficient numerical approaches have been developed to investigate blood flow, with particular emphasis on the motion and deformation of RBCs under shear flow. Among these methods, the integration of the lattice Boltzmann method (LBM) and immersed boundary method (IBM) has received considerable attention. In this dissertation, a 2D in-house generated algorithm based on the LBM-IBM was utilised for the numerical simulations. Moreover, a spring-based model was applied to simulate the elastic behaviour of the RBC membrane. Finally, a microfluidic experimental system including flow control, image capture, and data acquisition was established to validate the numerical results with the experimental results.
Goal: The main focus of this dissertation was to establish a 2D LBM-IBM coupled with a spring-based model to simulate the trajectory of both healthy RBC and damaged RBC in Poiseuille flow in low Reynolds numbers (Re < 1), in which the numerical results are compared with the experimental ones to allow for model validation. The second aim of this study was to numerically simulate the tumbling and tank-treading-like motion of a single RBC (healthy and damaged) in a micro-channel. Finally, the third aim was to numerically simulate the effect of the viscosity contrast (λ) on the trajectory of an RBC in a micro-channel. λ is one of the important factors that can severely affect RBC dynamics and cell deformation in a shear flow. Because of computational complexity, little effort has been made to numerically model the effect of λ on RBC dynamics in flow in the literature, for this reason, most of the current simulation studies assume for simplicity the viscosity contrast of unity.
Results: Overall, the numerical results indicated a reasonable agreement with the observed experimental results. However, the numerical simulation predicts a larger migration (1.81 μm for the healthy RBC and 0.96 μm for the damaged RBC) compared to the experimental tests (1.20 μm for the healthy RBC and 0.41 μm for the damaged RBC). Moreover, the experimental results showed that at a certain distance from the entrance of the micro-channel, the RBCs have a rolling motion like a wheel but without lateral migration. Due to the deformability of the RBCs, this motion is unstable so that later on, the RBCs migrate laterally toward the centreline of the micro-channel. The results also showed that the distance at which rolling motion happens is greater for the damaged RBCs (~ 150 μm) compared to the healthy RBCs (~ 25 μm) because the damaged cells deform less. The numerical results confirm this result. It can be seen from the numerical results that the healthy RBC experiences the tank-treading motion compared to the damaged RBC that exhibits the tumbling motion. Furthermore, the numerical results indicated a significant impact on the RBC trajectory when λ = 5 compared to λ = 1. The higher viscosity contrast of 5 has less lift (5.06 μm) in comparison with the lower viscosity contrast of 1 (6.56 μm). In addition, for a fixed viscosity contrast λ of 10, as the rigidity of the RBC increases, its final lateral and longitudinal displacements decrease.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
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Ren, Qinlong, and Qinlong Ren. "GPU Accelerated Study of Heat Transfer and Fluid Flow by Lattice Boltzmann Method on CUDA." Diss., The University of Arizona, 2016. http://hdl.handle.net/10150/621746.
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Lattice Boltzmann method (LBM) has been developed as a powerful numerical approach to simulate the complex fluid flow and heat transfer phenomena during the past two decades. As a mesoscale method based on the kinetic theory, LBM has several advantages compared with traditional numerical methods such as physical representation of microscopic interactions, dealing with complex geometries and highly parallel nature. Lattice Boltzmann method has been applied to solve various fluid behaviors and heat transfer process like conjugate heat transfer, magnetic and electric field, diffusion and mixing process, chemical reactions, multiphase flow, phase change process, non-isothermal flow in porous medium, microfluidics, fluid-structure interactions in biological system and so on. In addition, as a non-body-conformal grid method, the immersed boundary method (IBM) could be applied to handle the complex or moving geometries in the domain. The immersed boundary method could be coupled with lattice Boltzmann method to study the heat transfer and fluid flow problems. Heat transfer and fluid flow are solved on Euler nodes by LBM while the complex solid geometries are captured by Lagrangian nodes using immersed boundary method. Parallel computing has been a popular topic for many decades to accelerate the computational speed in engineering and scientific fields. Today, almost all the laptop and desktop have central processing units (CPUs) with multiple cores which could be used for parallel computing. However, the cost of CPUs with hundreds of cores is still high which limits its capability of high performance computing on personal computer. Graphic processing units (GPU) is originally used for the computer video cards have been emerged as the most powerful high-performance workstation in recent years. Unlike the CPUs, the cost of GPU with thousands of cores is cheap. For example, the GPU (GeForce GTX TITAN) which is used in the current work has 2688 cores and the price is only 1,000 US dollars. The release of NVIDIA's CUDA architecture which includes both hardware and programming environment in 2007 makes GPU computing attractive. Due to its highly parallel nature, lattice Boltzmann method is successfully ported into GPU with a performance benefit during the recent years. In the current work, LBM CUDA code is developed for different fluid flow and heat transfer problems. In this dissertation, lattice Boltzmann method and immersed boundary method are used to study natural convection in an enclosure with an array of conduting obstacles, double-diffusive convection in a vertical cavity with Soret and Dufour effects, PCM melting process in a latent heat thermal energy storage system with internal fins, mixed convection in a lid-driven cavity with a sinusoidal cylinder, and AC electrothermal pumping in microfluidic systems on a CUDA computational platform. It is demonstrated that LBM is an efficient method to simulate complex heat transfer problems using GPU on CUDA.
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Tseng, Yu-chieh, and 曾鈺傑. "Numerical study of immersed boundary method." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/29507190803969141685.
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碩士國立清華大學
數學系
98
In this thesis, we introduce the fundamental concepts of the immersed boundary method and also apply it to the simulation of two-dimensional interfacial flows. The governing equations are written in a usual immersed boundary formulation where a mixture of Eulerian flow and Lagrangian interfacial variables are used, and the linkage between these two set of variables is provided by the Dirac delta function which is constructed under certain postulates. A new type of smooth delta functions is compared with the original ones. The incompressible viscous Navier-Stokes equations are solved by a semi-implicit second-order projection method, and the interface moves by the velocity which is interpolated from the fluid velocity. In numerical results, we first verify several facts of the immersed boundary method and then consider a bubble immersed in an two-dimensional incompressible fluid. We observe the deformation of a bubble with different Capillary number in a shear flow. Moreover, we take the advantage of an equi-distributed technique to control the distribution of the Lagrangian markers uniformly. As expected, the numerical experiments with marker control technique have better performance in the area preservation than the case without it.
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Yu, Chien-Ting, and 余建廷. "Numerical Study on an Immersed Boundary Method." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/47764384779040641599.
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碩士國立暨南國際大學
土木工程學系
95
The study will propose a practical calculation numerical method that is simple and accurate, calculate an arbitrary geometric border flow with Nested Cartesian grid. Cavity Flow is investigated to verify Fractional Step Method, and Wannier Flow to Immersed Boundary Method. The accuracy of numerical methods in this paper can be discussed by studying the flow through the cylindrical vortex shedding. Further, we discuss the characteristics of suppression of the vortex shedding flow acting in downstream cylinder flow field, including vortex shedding frequency, and the drag force and lift force repeated shocks acting on the cylinder, by using Immersed Boundary Method. Then, the accuracy will be investigated by comparing and discussing the numerical results solved by distinguishing between the fluid and the structure in the flow, and those from results of experiments in the past. Next the discussion in this study, about an ellipse with an angle of attack and two circular cylinders with different diameters in the flow, the aim of this study is investigated for the ability of the present numerical method by solving the suppression of the vortex shedding flow behind the two-cylinder system which was kind of difficult to reach by a Cartesian grid method. In this study, the suppression of the vortex shedding flow is tested to solve a uniform flow past through two different diameter cylindrical in the flow field with Fractional Step Method and Immersed Boundary Method.The numerical method which we investigated is showed that the results of the problem is appropriable in other literatures.
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Li, Jia-Yang, and 李佳陽. "Fluid-Structure Interaction Method Development with Immersed Boundary Method." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/n9r62u.
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碩士國立清華大學
動力機械工程學系
105
The interaction between the elastic solid structure and the fluid field it immersed in is of great concern in many areas including wind turbine designing and upper nasal treatments. A new fluid-structure interaction method based on immersed boundary method is developed. Multigrid scheme is applied to trace the interface more accurately. Preliminary validation has been done in a fully developed tube flow model. The result is reasonable in trend, yet has obvious difference from the analytic solution. Advanced research is needed to improve the behavior of the computational program, especially where the two mesh domains transfer information that interacting with Poisson equation solving.
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Su, S. W., and 蘇紳瑋. "Numerical simulation for complex boundary flow with immersed boundary method." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/39246557184256991044.
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碩士國立清華大學
動力機械工程學系
91
Abstract This thesis reports the simulations using the immersed boundary method (IBM) with complex environments. Based on the IBM simulation on the fixed and moving boundary problems, it was found that the position restoring force formulation performs better than that of spring and bending force method to achieve stable computation. Due to the adoption of the dirac delta force redistribution function, the IBM tends to produce a diffusive flow field near the interface boundary. Part of the efforts was aiming improving this deficiency. A modification, which ensures the fiber marker to move in the normal direction, does reduce this diffusive effect. However, across the boundary an induced secondary motion was also predicted. This was attributed to the inaccurate treatment of diffusive flux across the boundary. Finally, a circular object falling from resting position due to gravity was simulated with the immersed boundary method, where the mass of the fiber is represented via the variation of the density field.
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謝先皓. "Matrix Factorization Method for the Immersed Boundary problem." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/42764060404517226300.
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碩士國立交通大學
應用數學系所
96
The immersed boundary method is a model to simulate a viscous incompressible fluid with immersed massless boundary. It comes from the Navier-Stokes equation of viscous incompressible fluid with the interaction term between the immersed boundary and the fluid. The matrix factorization method is a formulation of immersed boundary method, and the idea is the fractional step method for Navier-Stokes equation. The immersed boundary problem could be factorized to three steps, and the conjugate gradient method can be applied to solve the first and second step. In this paper, we use the matrix factorization method simulate the flow past stationary or movable immersed object, including the flow past a stationary and a moving cylinder, the flow past two stationary cylinders, and the flow past a winglike object.
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廖廷暉. "Numerical simulations of flow with elastic boundary using immersed boundary method." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/93204768659176471727.
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碩士國立清華大學
動力機械工程學系
95
This thesis presents two methods for simulating flows over or inside complex elastic boundary. Scheme A is based on the feedback forcing concept, and scheme B is based on the immersed interface method. The immersed boundary generally dose not coincide with the grid point and these forcing procedures involve an interpolation scheme, since the boundary condition can be implemented on Eulerian grid directly. Scheme A is a more convenient method to simulate the elastic boundary problem. Its advantage is that the forcing value can be directly obtained form Lagrangian makers, but there is a smearing phenomenon on pressure field near interface. The smearing phenomenon will cause incorrect velocity at interface. Scheme B can determine the sharp flow field, especially for pressure field. For leakage problem, scheme B always has better performance, because the velocity near interface can be evaluated more correctly. A smooth curve is an important effect on stability. If the Lagrangian makers distribution isn't uniform, the force distribution can't be evaluated well. Here, we use periodic cubic spline to reconstruct Lagrangian makers with constant arc length and Fourier fitering to smooth the curve throughout each time step after moving boundary location. Numerical experiments also show that the stability limit can be improved if the distribution of Lagrangian makers is uniform. Four different test problems are simulated using present schemes, and scheme B has better performance.
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Chang, Ching-Hsiung, and 張景雄. "Tsunami simulation by combining Immersed Boundary Method and Level Set Method." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/37544973589889779472.
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碩士逢甲大學
水利工程與資源保育學系
102
Tsunami simulation by combining immersed boundary method and level set method to resolve the flow problems between the free surface and structures. Respectively, in space and time discretization using the fifth-order WENO method and the third-order Runge-Kutta method to calculate the function of , and then solve the pressure Poisson equation such that the continuity equation satisfies. This research considers two kind of tsunami causing conditions to divide into case one and case two. Case one is a rigid rectanglar body sliding into water and case two is a rigid triangular body sliding down an incline. Observe interaction between the free surface and rigid structures under two different situations. Case three to five are model simulations of solitary wave in which generated solitary waves process as tsunami propagates by using 2D numerical simulation. When solitary wave contacts different structures, the free surface will run up along the slope or even run over the top of structure. For investigating aforementioned phenomenon, setting several observation points to measure solitary wave height and print out the data, and then applying graphics software to present the result of 2D numerical simulation. Key words: immersed boundary method, level set method, free surface, WENO method, Runge-Kutta method, solitary wave
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Liao, Chuan-Chieh, and 廖川傑. "Simulating dynamic and thermal flows with moving rigid boundary using immersed-boundary method." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/69451381306321277829.
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黃蔚荏. "Numerical Simulations for Insect Flight with the Immersed Boundary Method." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/23078761228193912286.
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碩士國立清華大學
動力機械工程學系
94
Abstract This thesis reports the simulations of insect flight using the immersed boundary. The major advantage of the IBM is that the computations can be performed within the Cartesian framework to mimic the complex geometry of the insect wing. Both the inertial and non-inertial coordinate systems are adopted in the computations and the predicted lift and drag coefficients are examined. In comparisons with the benchmark solutions of Wang, the non-inertial frame simulation was observed to produce more accurate results than those generated by the inertial frame. When examining the predicted vorticity fields, the wake capture and delayed stall phenomena were captured by the present predictions The influences of the Reynolds number and the phase differences on the lift and drag were also examined. The ranges of the Reynolds numbers investigated are from 78.5 to 314. It was shown that the insect can not generate enough lift force to support its flight when the Reynolds number was smaller than 78.5. The lift and drag were also shown to increase in tandem with the Reynolds number. The computations of the variations of the phase angles, , and , show that the delayed rotation produces the negative lift force. On the other hand, both the lift and drag forces generated by the advanced rotation are approximately 40% higher than those generated by the symmetric rotation.
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陳帝嘉. "Immersed boundary method based LBM to simulate complex geometry flows." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/tkjnqq.
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碩士國立清華大學
動力機械工程學系
93
In this thesis, the lattice Boltzmann method is combined with the immersed boundary technique to simulate complex geometry flows both with stationary and moving boundaries. The complex geometry is represented by Lagrangian markers and forces are exerted at the Lagrangian markers in order to satisfy exactly the prescribed velocity of the boundary. This force at the Lagrangian markers is then distributed to the Eulerian grid by a well-chosen discretized delta function. With the known force field in the Eulerian grid to mimic the boundary, the lattice Boltzmann method is used to compute the flow field where the complex geometry is immersed inside the Cartesian computational domain. The proposed method is examined by computing decaying vortex flow, lid driven cavity flow, rotating cylinder flow and flows over both stationary and moving cylinder. All the numerical results agree reasonably well with the analytical solution or the benchmark solution, and the Galilean invariance is satisfied. The influences of the Lagrangian marker spacing on the solution accuracy are also examined. It was observed that the error on the Eulerian grid increases when reducing the Lagrangian marker spacing. The predicted results also show a discontinuous pressure field across the immersed boundary, a phenomenon to be clarified in future study.
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Lee, Tzu Jung, and 李紫榕. "Simulations of flow and structure interaction using Immersed Boundary Method." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/43854489062264133251.
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碩士國立清華大學
動力機械工程學系
104
In the present study, the problems of solid-fluid interaction using the immersed boundary strategy are investigated. The DKT phenomenon of two sedimenting spheres is presented. The DS phenomenon is observed in the case that the larger sphere is at the bottom. The duration of drafting term in the smallest initial gap in DS phenomenon is investigated at different diameter ratio in the case. On the other hand, in order to simulate the complex-shape object, the method of finding the boundary with the triangular facet surface is added into the numerical method. The triangular facet surface of the object is performed in Standard Tessellation Language (STL) format. In the STL format, the normal vector and three positions of points are recorded in x, y, z-directions. The STL files for the different objects are designed by using CAD. The characteristic of the STL format triangular facet surface is used in the identification of the points around and inside the solid object. The forcing points, decided by using the STL-format triangular facets, is tested in the sphere case and the location of the forcing points are matched with the location found by employing the equation of sphere surface. The parallel computing and altering position of shape are used and validated with the case of rotating ellipsoid. Then, the case of the viscous flow past a sphere is presented. Finally, the case of a rotating turbine with a static fluid domain is performed.
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Karachun, Kateryna Morris Philip J. "Analysis of ducted fan flows using an immersed boundary method." 2008. http://www.etda.libraries.psu.edu/theses/approved/WorldWideIndex/ETD-3161/index.html.
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Kang, Shin Kyu. "Immersed Boundary Methods in the Lattice Boltzmann Equation for Flow Simulation." Thesis, 2010. http://hdl.handle.net/1969.1/ETD-TAMU-2010-12-8710.
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In this dissertation, we explore direct-forcing immersed boundary methods (IBM) under the framework of the lattice Boltzmann method (LBM), which is called the direct-forcing immersed boundary-lattice Boltzmann method (IB-LBM).
First, we derive the direct-forcing formula based on the split-forcing lattice Boltzmann equation, which recovers the Navier-Stokes equation with second-order accuracy and enables us to develop a simple and accurate formula due to its kinetic nature. Then, we assess the various interface schemes under the derived direct-forcing formula. We consider not only diffuse interface schemes but also a sharp interface scheme. All tested schemes show a second-order overall accuracy. In the simulation of stationary complex boundary flows, we can observe that the sharper the interface scheme is, the more accurate the results are.
The interface schemes are also applied to moving boundary problems. The sharp interface scheme shows better accuracy than the diffuse interface schemes but generates spurious oscillation in the boundary forcing terms due to the discontinuous change of nodes for the interpolation. In contrast, the diffuse interface schemes show smooth change in the boundary forcing terms but less accurate results because of discrete delta functions. Hence, the diffuse interface scheme with a corrected radius can be adopted to obtain both accurate and smooth results.
Finally, a direct-forcing immersed boundary method (IBM) for the thermal lattice Boltzmann method (TLBM) is proposed to simulate non-isothermal flows. The direct-forcing IBM formulas for thermal equations are derived based on two TLBM models: a double-population model with a simplified thermal lattice Boltzmann equation (Model 1) and a hybrid model with an advection-diffusion equation of temperature (Model 2). The proposed methods are validated through natural convection problems with stationary and moving boundaries. In terms of accuracy, the results obtained from the IBMs based on both models are comparable and show a good agreement with those from other numerical methods. In contrast, the IBM based on Model 2 is more numerically efficient than the IBM based on Model 1.
Overall, this study serves to establish the feasibility of the direct-forcing IB-LBM as a viable tool for computing various complex and/or moving boundary flow problems.
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Chang, Yu-Wei. "Implementation of the immersed boundary method for flow in complex geometry." 2006. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0016-0109200613413497.
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