京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18938号 / 工博第3980号 / 新制||工||1613(附属図書館) / 31889 / 京都大学大学院工学研究科都市社会工学専攻 / (主査)教授 松岡 俊文, 教授 後藤 仁志, 准教授 村田 澄彦 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19681号 / 工博第4136号 / 新制||工||1638(附属図書館) / 32717 / 京都大学大学院工学研究科機械理工学専攻 / (主査)教授 西脇 眞二, 教授 稲室 隆二, 教授 松原 厚 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Micromechanics of solidluid interactions can play a key role controlling macro-scale engineering behavior of granular media. The main objective of this study is to numerically investigate the micromechanics involved in solidluid mixtures to develop a better understanding of the macroscopic behavior of granular media for different applications. This is accomplished by developing a numerical model coupling the Discrete Element Method (DEM) and the Lattice Boltzmann Method (LBM) and employing it to study three distinct yet interrelated applications throughout the course of this research. In the first application, the DEM model is used to provide a clear relationship between energy dissipated by micro-scale mechanisms versus the traditional engineering definition based on macro-scale (continuum) parameters to develop a better understanding for the frictional behavior of granular media. Macroscopic frictional behavior of granular materials is of great importance for studying several complex problems such as fault slip and landslides. In the second application, the DEM-LBM model is employed for studying the undrained condition of dense granular media. While the majority of previous modeling approaches did not realistically represent non-uniform strain conditions that exist in geomechanical problems, including the LBM in the proposed model offers a realistic approach to simulate the undrained condition since the fluid can locally conserve the system volume. For the third application, the DEM-LBM model is used to study discontinuous shear thickening in a dense solidluid suspension. Shear thickening in a fluid occurs when the viscosity of the fluid increases with increasing applied strain rate. The DEM-LBM results for discontinuous shear thickening were compared to experimental data and proved to be an accurate approach at reproducing this phenomenon. The validated DEM-LBM model is then used to develop a physics-based constitutive model for discontinuous shear thickening-shear thinning in granular medialuid suspension. A closedorm model is then calibrated using the DEM-LBM model and validated against existing experimental test results reported in the literature. Findings of this research demonstrate how micromechanical modeling can be employed to address challenging problems in granular media involving solidluid interaction.

In this work, a two-phase lattice Boltzmann method (LBM) approach is implemented to investigate the hydrodynamic behavior of a single droplet impingement on a dry surface. LBM is a recently developed powerful technique to compute a wide range of fluid flow problems, especially in applications involving interfacial dynamics and complex geometries. Instead of solving the non-linear Navier-Stokes equations, which are complicated partial differential equations, LBM solves a set of discretized linear equations, which are easy to implement and parallelize. The fundamental idea of LBM is to recover the macroscopic properties of the fluid which obeys Navier-Stokes equations, by using simplified kinetic equations that incorporate the essential physics at the microscopic level. Considering the numerical instability induced by large density difference between two phases during the LBM simulations, the particular LBM scheme used in this study has its benefits when dealing with high density ratios. All the simulations are conducted for density ratio up to 50 in a three-dimensional Cartesian coordinate system, and three important dimensionless numbers, namely Weber number, Reynolds number and Ohnesorge number, are used for this study. To validate this multiphase LBM approach, several benchmark tests are conducted. First, the angular frequency of an oscillating droplet is calculated and compared with the corresponding theoretical value. Errors are found to be within 6.1% for all the cases. Secondly, simulations of binary droplet collisions are conducted in the range of 20

Computational fluid dynamics, abbreviated CFD, is a valuable tool for several engineering applications. Applications such as heating, cooling or drying are some examples of areas where CFD is used. The Lattice Boltzmann method, abbreviated LBM, is a popular method for CFD simulations due to its fast simulation time in comparison to traditional methods like the finite volume method. ESS is a company that has supplied LBM simulation software aimed at perfecting the baking process of car carrosserie. The aim of this thesis is to verify and validate their software against earlier works, to ensure that the solver can capture the physical reality of an impinging jet. The verification and validation are conducted over three different cases: experimental free jet, direct numerical simulation and a large eddy simulation of an impinging jet. Identical digital models were created for each case and then simulated with similar conditions for comparison. All three cases were tested with Richardson extrapolation to ensure grid convergence. The Richardson method showed that the highest error among the cases was 2.02 %. The results shows that the LBM solver can accurately predict the flow and thermal field compared to the three cases. The LBM solver is considered verified and validated for flowfield and thermal simulations. / Numeriska strömningsberäkningar är ett värdefullt verktyg för flera ingenjörsapplikationer. Applikationer som uppvärmning, kylning eller torkning är några exempel på områden där CFD används. Lattice Boltzmann-metoden, förkortat LBM, är en populär metod för CFD-simuleringar på grund av dess snabba simuleringshastighet jämfört med traditionella metoder som finita volymsmetoden. ESS är ett företag som har skapat LBM- simuleringsprogramvaran med målet att förbättra bakningsprocessen för bilkarosserier. Målet med denna avhandling är att verifiera och validera deras programvara mot tidigare arbeten för att säkerställa att lösningsmetoden kan fånga den fysiska verkligheten hos en påverkande jetstråle.Verifieringen och valideringen utförs över tre olika fall: Experimentell fri stråle, Direkt numerisk simulering och en Large eddy-simulering av en påverkande jetstråle. Identiska digitala modeller skapades för varje fall och simulerades sedan under liknande förhållanden för att kunna jämföra resultaten. Alla tre fall testades med Richardson-extrapolation för att säkerställa nätkonvergens. Richardson-metoden visade att den högsta felet bland fallen var 2,02 %. Resultaten visar att LBM-lösaren kan förutsäga flödes och termiska fältet noggrant jämfört med de tre fallen. LBM-lösaren anses vara verifierad och validerad för flödesfälts- och termiska simuleringar.

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En esta tesis se investigaron modelos de simulación en tiempo real para animaciones de superficies líquidas, basados en un modelo de Lattice Boltzmann de la física de aguas superficiales. La implementación de dichos modelos permitió implementar un motor físico capaz de producir escenas de estanques o aguas abiertas, cuya superficie reacciona a las perturbaciones introducidas interactivamente por el usuario. Estas perturbaciones pueden ser por ejemplo la agitación provocada por un objeto movible (hélice, barco u otro objeto definido mediante una triangulación arbitraria), u otro tipo de perturbaciones externas, como por ejemplo efectos de lluvia. Un aspecto significativo del modelo investigado fue el tratamiento de bordes y obstáculos internos móviles, que intervienen como condiciones de contorno en el esquema numérico. Se implementó para ello un modelo completo de interacción fluido-objeto que simula en forma flexible escenarios de ondas producidas por embarcaciones, reflejos del frente de onda en puentes, y otras situaciones de interés en animación, tanto para la animación de efectos especiales como para simuladores de entrenamiento náutico. En particular, se propuso una estrategia novedosa para el cálculo de la fuerza de flotabilidad basada en la integral de la presión del fluido sobre la superficie sumergida del objeto. El método propuesto es más versátil y exacto que otros esquemas que estiman el volumen y aproximan el centro de carena, y es muy fácil de incorporar a cualquier implementación de simulación de fluidos basada en grillas. Los tiempos de cálculo obtenidos son razonables y permiten utilizar el método en aplicaciones de computación gráfica interactivas con una adecuada tasa de cuadros por segundo en equipos de cómputo convencionales. La validación se realizó con escenarios tridimensionales, mostrando muy buena concordancia con otras simulaciones y métodos numéricos más sofisticados y que consumen muchos más recursos. El modelo completo de simulación está disponible en Internet1 para ser utilizado como biblioteca y ha sido descargado más de 4.000 veces con visitas de Croacia, EEUU, Rusia y Turquía. Adicionalmente, los videos generados a partir de esta tesis, han conseguido más de 21.000 visitas en el sitio Youtube. La facilidad de uso del módulo ha hecho que se utilice en aplicaciones de campos tan variados como el arte escénico, la domótica o los videojuegos. Clasificación (ACM CSS 1998): I.3.5 Computer Graphics - Computational Geometry and Object Modeling, Physically based modeling. I.3.7 Computer Graphics - Three-Dimensional Graphics and Realism, Animation. Palabras clave: LBM, Animación basada en física, Computación Gráfica, Simulación de superficies de fluido / This thesis presents the research results of real-time algorithms for interactive liquid surfaces animation, based on a Lattice Boltzmann model which represents the surface-water interface equations. These results are developed and thoroughly tested, resulting in a physical engine able to produce dynamic scenes of ponds or open waters, with surfaces that react to the perturbations introduced interactively by the users. Examples of these perturbations are the agitation induced by moving objects (ships, propellers, or any specific object defined by an arbitrary triangulation), or other type of external perturbation, like rain drops. A major topic developed in this work was the treatment of fixed and dynamic borders, like bridges’ columns or boats, which are represented as dynamic boundary conditions or external forces that interact with the numeric simulation. The solution led to a complete model for fluid-structure interaction (i.e., fluid-to-structure and structure-to fluid) that provides flexible representations of waves produced by boats, wave reflections in bridges, and other situations of interest in computer animation, either for the creation of special effects or in the graphic support of nautical training simulators. In particular, a novel strategy for the calculation of the buoyancy force was introduced, based in the integration of the hydrostatic pressure over the solid immersed surfaces. The proposed method is more versatile and accurate than other schemes based on the tracking of the center of buoyancy, and it is very easy to implement in grid based representations. Even though the main purpose of this work was aimed to produce physically and visually accurate simulations, the resulting implementation achieves reasonable calculation times. Thus, the application of this model in interactive computer graphics achieves an adequate frame rate using conventional desktop computers without losing accuracy, using more efficiently the computational resources than other more sophisticated numerical methods. The engine is freely available on the Internet2 as a library, which was downloaded more than 4,000 times including visits from Croacia, USA , Russia and Turkey. Additionally, the videos generated using the product of the present thesis have been viewed by more than 21,000 visits in YouTube. The flexibility of the engine was demonstrated in the variety of applications generated from it, like scenic art, domotics and videogames. Clasification (ACM CSS 1998): I.3.5 Computer Graphics - Computational Geometry and Object Modeling, Physically based modeling. I.3.7 Computer Graphics - Three-Dimensional Graphics and Realism, Animation. Keywords: LBM, Physics based animation, Computer Graphics, Surface waters.

Yes / We present the OpenLB package, a C++ library providing a flexible framework for lattice Boltzmann simulations. The code is publicly available and published under GNU GPLv2, which allows for adaption and implementation of additional models. The extensibility benefits from a modular code structure achieved e.g. by utilizing template meta-programming. The package covers various methodical approaches and is applicable to a wide range of transport problems (e.g. fluid, particulate and thermal flows). The built-in processing of the STL file format furthermore allows for the simple setup of simulations in complex geometries. The utilization of MPI as well as OpenMP parallelism enables the user to perform those simulations on large-scale computing clusters. It requires a minimal amount of dependencies and includes several benchmark cases and examples. The package presented here aims at providing an open access platform for both, applicants and developers, from academia as well as industry, which facilitates the extension of previous implementations and results to novel fields of application for lattice Boltzmann methods. OpenLB was tested and validated over several code reviews and publications. This paper summarizes the findings and gives a brief introduction to the underlying concepts as well as the design of the parallel data structure.