Dissertations / Theses on the topic 'LBM (Lattice Boltzmann Method)'
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1
Chang, Qingming. "LATTICE BOLTZMANN METHOD (LBM) FOR THERMAL MULTIPHASE FLUID DYNAMICS." Case Western Reserve University School of Graduate Studies / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=case1133469811.
2
Haughey, Kyle J. "Boundless Fluids Using the Lattice-Boltzmann Method." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/117.
Abstract:
Computer-generated imagery is ubiquitous in today's society, appearing in advertisements, video games, and computer-animated movies among other places. Much of this imagery needs to be as realistic as possible, and animators have turned to techniques such as fluid simulation to create scenes involving substances like smoke, fire, and water. The Lattice-Boltzmann Method (LBM) is one fluid simulation technique that has gained recent popularity due to its relatively simple basic algorithm and the ease with which it can be distributed across multiple processors. Unfortunately, current LBM simulations also suffer from high memory usage and restrict free surface fluids to domains of fixed size. This thesis modifies the LBM to utilize a recursive run-length-encoded (RLE) grid data structure instead of the standard fixed array of grid cells, which reduces the amount of memory required for LBM simulations as well as allowing the domain to grow and shrink as necessary to accomodate a liquid surface. The modified LBM is implemented within the open-source 3D animation package Blender and compared to Blender's current LBM simulator using the metrics of memory usage and time required to complete a given simulation. Results show that, although the RLE-based simulator can take several times longer than the current simulator to complete a given simulation, the memory usage is significantly reduced, making an RLE-based simulation preferable in a few specific circumstances.
3
Walther, Édouard. "Contribution de la Lattice Boltzmann Method à l’étude de l’enveloppe du bâtiment." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN004/document.
Abstract:
Les enjeux de réduction des consommations d’énergie, d’estimation de la durabilité ainsi que l’évolution des pratiques constructives et réglementaires génèrent une augmentation significative du niveau de détail exigé dans la simulation des phénomènes physiques du Génie Civil pour une prédiction fiable du comportement des ouvrages. Le bâtiment est le siège de phénomènes couplés multi-échelles, entre le microscopique (voire le nanoscopique) et le macroscopique, impliquant des études de couplages complexes entre matériaux, à l’instar des phénomènes de sorption-désorption qui influent sur la résistance mécanique, les transferts de masse, la conductivité, le stockage d’énergie ou la durabilité d’un ouvrage. Les méthodes numériques appliquées permettent de résoudre certains de ces problèmes en ayant recours aux techniques de calcul multi-grilles, de couplage multi-échelles ou de parallélisation massive afin de réduire substantiellement les temps de calcul. Dans le présent travail, qui traite de plusieurs simulations ayant trait à la physique du bâtiment, nous nous intéressons à la pertinence d’utilisation de la méthode "Lattice Boltzmann". Il s’agit d’une méthode numérique construite sur une grille – d’où l’appellation de lattice – dite "mésoscopique" qui, à partir d’un raisonnement de thermodynamique statistique sur le comportement d’un groupes de particules microscopiques de fluide, permet d’obtenir une extrapolation consistante vers son comportement macroscopique. Après une étude les avantages comparés de la méthode et sur le comportement oscillatoire qu'elle exhibe dans certaines configurations, on présente :- une application au calcul des propriétés diffusives homogénéisée des matériaux cimentaires en cours d'hydratation, par résolution sur le cluster du LMT.- une application à l'énergétique du bâtiment avec la comportement d'une paroi solaire dynamique, dont le calcul a été porté sur carte graphique afin d'en évaluer le potentielReducing building energy consumption and estimating the durability of structures are ongoing challenges in the current regulatory framework and construction practice. They suppose a significant increase of the level of detail for simulating the physical phenomena of Civil Engineering to achieve a reliable prediction of structures.Building is the centre of multi-scale, coupled phenomena ranging from the micro (or even nano) to the macro-scale, thus implying complex couplings between materials such as sorption-desorption process which influences the intrinsic properties of matter such as mechanical resistance, mass transfer, thermal conductivity, energy storage or durability.Applied numerical methods allow for the resolution of some of these problems by using multi-grid computing, multi-scale coupling or massive parallelisation in order to substantially reduce the computing time.The present work is intended to evaluate the suitability of the “lattice Boltzmann method” applied to several applications in building physics. This numerical method, said to be “mesoscopic”, starts from the thermodynamic statistical behaviour of a group of fluid particles, mimicking the macroscopic behaviour thanks to a consistent extrapolation across the scales.After having studied the comparative advantages of the method and the oscillatory behaviour it displays under some circumstances, we present - An application to the diffusive properties of cementitious materials during hydration via numerical homogenization and cluster-computing numerical campaign - An application to building energy with the modeling of a solar active wall in forced convection simulated on a graphical processing unit
4
Koosukuntla, Narender Reddy. "Towards Development of a Multiphase Simulation Model Using Lattice Boltzmann Method (LBM)." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1321629685.
5
Gokaltun, Seckin. "Lattice Boltzmann Method for Flow and Heat Transfer in Microgeometries." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/64.
Abstract:
Recent technological developments have made it possible to design various microdevices where fluid flow and heat transfer are involved. For the proper design of such systems, the governing physics needs to be investigated. Due to the difficulty to study complex geometries in micro scales using experimental techniques, computational tools are developed to analyze and simulate flow and heat transfer in microgeometries. However, conventional numerical methods using the Navier-Stokes equations fail to predict some aspects of microflows such as nonlinear pressure distribution, increase mass flow rate, slip flow and temperature jump at the solid boundaries. This necessitates the development of new computational methods which depend on the kinetic theory that are both accurate and computationally efficient. In this study, lattice Boltzmann method (LBM) was used to investigate the flow and heat transfer in micro sized geometries. The LBM depends on the Boltzmann equation which is valid in the whole rarefaction regime that can be observed in micro flows. Results were obtained for isothermal channel flows at Knudsen numbers higher than 0.01 at different pressure ratios. LBM solutions for micro-Couette and micro-Poiseuille flow were found to be in good agreement with the analytical solutions valid in the slip flow regime (0.01 < Kn < 0.1) and direct simulation Monte Carlo solutions that are valid in the transition regime (0.1 < Kn < 10) for pressure distribution and velocity field. The isothermal LBM was further extended to simulate flows including heat transfer. The method was first validated for continuum channel flows with and without constrictions by comparing the thermal LBM results against accurate solutions obtained from analytical equations and finite element method. Finally, the capability of thermal LBM was improved by adding the effect of rarefaction and the method was used to analyze the behavior of gas flow in microchannels. The major finding of this research is that, the newly developed particle-based method described here can be used as an alternative numerical tool in order to study non-continuum effects observed in micro-electro-mechanical-systems (MEMS).
6
BOCANEGRA, CIFUENTES JOHAN AUGUSTO. "Lattice Boltzmann Method: applications to thermal fluid dynamics and energy systems." Doctoral thesis, Università degli studi di Genova, 2021. http://hdl.handle.net/11567/1060259.
Abstract:
In many energy systems fluids play a fundamental role, and computational simulations are a valuable tool to
study their complex dynamics. The Lattice Boltzmann Method (LBM) is a relatively new numerical method
for computational fluid dynamics, but its applications can be extended to physical phenomena beyond fluid
flows. This thesis presents applications of the LBM to thermal fluid dynamics and energy systems. Specific
applications considered are: application to nuclear reactor engineering problems; thermal fluid dynamic
behavior of a Natural Circulation Loop; nanoparticles gravitational sedimentation; acoustical problems.
The main original contributions derived from this work are: first, the systematic description of the current
status of LBM applications to nuclear reactors problems, including test cases and benchmark simulations;
second, the development and validation of a LBM model for a single-phase natural circulation loop; third,
the development and validation of a LBM model for gravitational sedimentation of nanoparticles, and fourth,
the systematic description of the current status of LBM applications to acoustics, including simulations of
test cases. The development of this thesis was not limited to simulations; experimental studies in parallel
connected natural circulation loops of small inner diameter were conducted, showing the wide applicability
of the one-dimensional theoretical models used to validate the LBM results. Additional contributions derived
from this work: 1. the applicability of the method to study neutron transport and nuclear waste disposal using
porous materials was shown. 2. changes in the thermophysical performance of the natural circulation loop
when the loop reached a non-laminar (transition) regime were found at a Reynolds number lower than the
typical range. 3. variable diffusion and sedimentation parameters were effective to model the experimental
sedimentation curves. In conclusion, this work shows that the LBM is a versatile and powerful computational
tool that can be used beyond the common Computational Fluid Dynamics applications.In many energy systems fluids play a fundamental role, and computational simulations are a valuable tool to study their complex dynamics. The Lattice Boltzmann Method (LBM) is a relatively new numerical method for computational fluid dynamics, but its applications can be extended to physical phenomena beyond fluid flows. This thesis presents applications of the LBM to thermal fluid dynamics and energy systems. Specific applications considered are: application to nuclear reactor engineering problems; thermal fluid dynamic behavior of a Natural Circulation Loop; nanoparticles gravitational sedimentation; acoustical problems. The main original contributions derived from this work are: first, the systematic description of the current status of LBM applications to nuclear reactors problems, including test cases and benchmark simulations; second, the development and validation of a LBM model for a single-phase natural circulation loop; third, the development and validation of a LBM model for gravitational sedimentation of nanoparticles, and fourth, the systematic description of the current status of LBM applications to acoustics, including simulations of test cases. The development of this thesis was not limited to simulations; experimental studies in parallel connected natural circulation loops of small inner diameter were conducted, showing the wide applicability of the one-dimensional theoretical models used to validate the LBM results. Additional contributions derived from this work: 1. the applicability of the method to study neutron transport and nuclear waste disposal using porous materials was shown. 2. changes in the thermophysical performance of the natural circulation loop when the loop reached a non-laminar (transition) regime were found at a Reynolds number lower than the typical range. 3. variable diffusion and sedimentation parameters were effective to model the experimental sedimentation curves. In conclusion, this work shows that the LBM is a versatile and powerful computational tool that can be used beyond the common Computational Fluid Dynamics applications.
7
Wissocq, Gauthier. "Investigation of lattice Boltzmann methods for turbomachinery secondary air system simulations." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0635.
Abstract:
Ce manuscrit présente une étude du potentiel des méthodes lattice Boltzmann pour traiter des écoulements circulant dans les systèmes de refroidissement des turbomachines. La combinaison de phénomènes physiques complexes donne naissance à des structures instationnaires, non-axisymmétriques et de période a priori inconnue. Leur bonne modélisation représente un défi pour la simulation numérique en mécanique des fluides. Ce travail peut être divisé en trois sous-parties. Une étude physique des instabilités à l'origine des structures tourbillonnaires est d'abord effectuée par analyse de stabilité linéaire des écoulements. Ensuite, les méthodes lattice Boltzmann sont introduites et leurs problèmes de stabilités numériques sont étudiés via des analyses basées sur l'approche de von Neumann. Enfin, la méthode est évaluée sur des simulations académiques de complexité croissante représentatives des systèmes d'air secondaire, nécessitant des simulations à flux de chaleur conjuguésThis thesis provides an investigation on the use of lattice Boltzmann methods to treat turbomachinery secondary cooling systel flows. The combination of complex physical phenomena (rotating environment with high temperature fluctuations) gives rise to unsteady, non-axisymmetric structures with a priori unknown periodicity. Their modelling, required for a correct heat transfer prediction, represents a challenge for numerical simulations in fluid mechanics. This work can be divided into three sub-sections. A physical study of the instabilities at the origin of unsteady structures is first carried out by analyzing the linear stability of the flows. Lattice Boltzmann methods are then introduced and their numerical stability issues are studied through analyses based on the von Neumann approach. Finally, the method is assessed on academic simulations of increasing complexity representative of secondary air systems, requiring conjugate heat transfer simulations
8
Caiazzo, Alfonso. "Asymptotic Analysis of lattice Boltzmann method for Fluid-Structure interaction problems." Doctoral thesis, Scuola Normale Superiore, 2007. http://hdl.handle.net/11384/85682.
Abstract:
The lattice Boltzmann method (LBM) is a numerical solver for the Navier-Stokes
equation, based on an underlying molecular dynamic model. Recently, it has
been extended towards the simulation of complex
fluids.
In this thesis, we use the asymptotic expansion technique to investigate the standard
scheme, the initialization problem and possible developments towards moving
boundary and
fluid-structure interaction problems. At the same time, it will
be shown how the mathematical analysis can be used to understand and improve
the algorithm.
First of all, we elaborate the tool "asymptotic analysis", explaining the methods
and the strategy we use for the investigation. A first application to the LBM is described,
recovering the approximation of the Navier-Stokes solution starting from
the lattice Boltzmann equation. As next, we extend the analysis, to investigate
the origin and the dynamic of initial layers. A class of initialization algorithms to
generate accurate initial values within the LB framework is described in detail.
Then we study the features of a simple moving boundary LBM. In particular, we
concentrate on the initialization of new
uid nodes created by the variations of
the computational
fluid domain.
Finally, to set up an LBM for
uid structure interaction, efficient routines to
evaluate forces are required. We describe the Momentum Exchange algorithm
(MEA). Precise accuracy estimates are derived, and the analysis leads to the
construction of an improved method to evaluate the interface stresses.
In conclusion, we test the defined code and validate the results of the analysis on
several simple benchmarks.
9
Banete, Olimpia. "TOWARDS MODELING HEAT TRANSFER USING A LATTICE BOLTZMANN METHOD FOR POROUS MEDIA." Thesis, Laurentian University of Sudbury, 2014. https://zone.biblio.laurentian.ca/dspace/handle/10219/2200.
Abstract:
I present in this thesis a fluid flow and heat transfer model for porous media using the lattice Boltzmann method (LBM). A computer simulation of this process has been developed and it is written using MATLAB software. The simulation code is based on a two dimensional model, D2Q9. Three physical experiments were designed to prove the simulation model through comparision with numerical results. In the experiments, physical properties of the air flow and the porous media were used as input for the computer model. The study results are not conclusive but show that the LBM model may become a reliable tool for the simulation of natural convection heat transfer in porous media.
Simulations leading to improved understanding of the processes of air flow and heat transfer in porous media may be important into improving the efficiency of methods of air heating or cooling by passing air through fragmented rock.
10
Cao, Weijin. "Investigation of the applicability of the lattice Boltzmann method to free-surface hydrodynamic problems in marine engineering." Thesis, Ecole centrale de Nantes, 2019. http://www.theses.fr/2019ECDN0011/document.
Abstract:
La simulation numérique des écoulements à surface libre pour les applications du génie maritime est un problème qui présente de grands défis dans le domaine de la dynamique des fluides numérique (CFD). On propose dans cette thèse une solution, qui consiste à utiliser la méthode de Boltzmann sur réseau régularisée (RLBM) avec un modèle de surface libre basé sur le volume-de-fluide (VOF), et on étudie sa faisabilité et sa fiabilité. Les connaissances théoriques de la méthode de Boltzmann sur réseau (LBM) sont présentées dans un premier temps, sur la base d'un développement polynomial d'Hermite et d'une analyse de Chapman-Enskog. De cette perspective, l’idée de la RLBM se résume comme étant la régularisation d'Hermite des fonctions de distribution. Dans les cas tests suivants du vortex de Taylor-Green et de la cavité entraînée, il est vérifié que la RLBM posse possède une précision de second ordre et une stabilité améliorée. On a alors ensuite implémenté le modèle de surface libre dans la RLBM. Sur la simulation d'une onde de gravité visqueuse stationnaire et d'un écoulement de dambreak, il est montré que la régularisation stabilise fortement le calcul en réduisant les oscillations de pression, ce qui est très bénéfique pour obtenir des écoulements à surface libre précis, et que la RLBM n'introduit pas non plus de dissipation numérique supplémentaire. De plus, une nouvelle méthode de reconstruction des fonctions de distribution à la surface libre est proposée. Le modèle proposé est ainsi plus consistent avec la RLBM, ce qui offre un moyen efficace pour simuler des écoulements à surface libre à un grand nombre de Reynolds en génie maritimeThe numerical simulation of the freesurface flows for marine engineering applications is a very challenging issue in the field of computational fluid dynamics (CFD). In this thesis, we propose a solution, which is to use the regularized lattice Boltzmann method (RLBM) with a volume-of-fluid (VOF) based single-phase free-surface lattice Boltzmann (LB) model, and we investigate its feasibility and its reliability. The theoretical insights of the lattice Boltzmann method (LBM) are given at first, through the Hermite expansion and the Chapman-Enskog analysis. From this perspective, the idea of the RLBM is summarized as the Hermite regularization of the distribution functions. On the test-cases of the Taylor-Green vortex and the lid-driven cavity flow, the RLBM is verified to have a 2nd-order accuracy and an improved stability. The adopted free-surface model is then implemented into the RLBM and validated through simulating a viscous standing wave and a dambreak flow problems. It is shown that the regularization not only strongly stabilizes the calculation by reducing spurious pressure oscillations, which is very beneficial for obtaining accurate free-surface motions, but also does not introduce any extra numerical dissipation. Furthermore, a new reconstruction method for the distribution functions at the free-surface is proposed. The present model is more consistent with the RLBM, which provides an effective way for simulating high-Reynoldsnumber free-surface flows in marine engineering
11
Hantsch, Andreas. "A lattice Boltzmann equation model for thermal liquid film flow." Doctoral thesis, Technische Universitaet Bergakademie Freiberg Universitaetsbibliothek "Georgius Agricola", 2013. http://nbn-resolving.de/urn:nbn:de:bsz:105-qucosa-130098.
Abstract:
Liquid film flow is an important flow type in many applications of process engineering. For supporting experiments, theoretical and numerical investigations are required. The present state of the art is to model the liquid film flow with Navier--Stokes-based methods, whereas the lattice Boltzmann method is employed here. The final model has been developed within this treatise by means of a two-phase flow and a heat transfer model, and boundary and initial conditions. All these sub-models have been applied to simple test cases. It could be found that the two-phase model is capable of solving flow phenomena with a large density ratio which has been shown impressively in conjunction with wall boundary conditions. The heat transfer model was tested against spectral method results with a transient non-uniform flow field. It was possible to find optimal parameters for computation. The final model has been applied to steady-state film flow, and showed very good agreement to OpenFOAM simulations. Tests with transient film flow demonstrated that the model is also able to predict these flow phenomenaFlüssigkeitsfilmströmungen kommen in vielen verfahrenstechnischen Prozessen zum Einsatz. Zur Unterstützung von Experimenten sind theoretische und numerische Untersuchungen nötig. Stand der Technik ist es, Navier--Stokes-basierte Modelle zu verwenden, wohingegen hier die Lattice-Boltzmann-Methode verwendet wird. Das finale Modell wurde unter Verwendung eines Zweiphasen- und eines Wärmeübertragungsmodell entwickelt und geeignete Rand- und Anfangsbedingungen formuliert. Alle Untermodelle wurden anhand einfacher Testfälle überprüft. Es konnte herausgefunden werden, dass das Zweiphasenmodell Strömungen großer Dichteunterschiede rechnen kann, was eindrucksvoll im Zusammenhang mit Wandrandbedingungen gezeigt wurde. Das Wärmeübertragungsmodell wurde gegen eine Spektrallösung anhand eines transienten und nichtuniformen Strömungsproblemes getestet. Stationäre Filmströmungen zeigten sehr gute Übereinstimmungen mit OpenFOAM-Lösungen und instationäre Berechungen bewiesen, dass das Model auch solche Strömungen abbilden kann
12
Mudrich, Jaime. "Development of a Coupling Model for Fluid-Structure Interaction using the Mesh-free Finite Element Method and the Lattice Boltzmann Method." FIU Digital Commons, 2013. http://digitalcommons.fiu.edu/etd/964.
Abstract:
In the presented thesis work, the meshfree method with distance fields was coupled with the lattice Boltzmann method to obtain solutions of fluid-structure interaction problems. The thesis work involved development and implementation of numerical algorithms, data structure, and software. Numerical and computational properties of the coupling algorithm combining the meshfree method with distance fields and the lattice Boltzmann method were investigated. Convergence and accuracy of the methodology was validated by analytical solutions.
The research was focused on fluid-structure interaction solutions in complex, mesh-resistant domains as both the lattice Boltzmann method and the meshfree method with distance fields are particularly adept in these situations. Furthermore, the fluid solution provided by the lattice Boltzmann method is massively scalable, allowing extensive use of cutting edge parallel computing resources to accelerate this phase of the solution process. The meshfree method with distance fields allows for exact satisfaction of boundary conditions making it possible to exactly capture the effects of the fluid field on the solid structure.
13
Rehhali, Khaoula. "Simulations de la convection naturelle couplée au rayonnement surfacique par la méthode de Boltzmann sur réseau : cas des chauffages variable et discret." Electronic Thesis or Diss., Amiens, 2019. http://www.theses.fr/2019AMIE0001.
Abstract:
Cette thèse s'inscrit dans le cadre d'une étude numérique visant à étudier les phénomènes de couplage de la convection naturelle et du rayonnement surfacique dans des cavités carrées dont les parois sont soumises à des chauffages discrets ou non-uniformes. En effet, la première étude réalisée s'intéresse à un problème de couplage convection-rayonnement dans une cavité carrée inclinée et remplie d'air, ayant d'un côté une paroi chauffée à une température constante et du côté opposé, une paroi chauffée linéairement. Les parois restantes sont considérées adiabatiques. Dans la seconde étude, la cavité a des parois verticales partiellement chauffées (symétriquement et asymétriquement), une paroi supérieure refroidie et une paroi inférieure adiabatique. L'objectif de ces études numériques réside dans l'analyse de l'effet du rayonnement surfacique et des différents paramètres gouvernants (mode de chauffage, nombre de Rayleigh, angle d'inclinaison, différence de température) sur la structure d'écoulement et le transfert de chaleur. Le second objectif de cette thèse consiste à tester la performance du schéma à temps de relaxation multiple (MRT) de la méthode Lattice Boltzmann (LBM) en présence du couplage convection-rayonnement. Les résultats de ce travail ont révélé que les paramètres de contrôle considérés ont un effet important sur la structure de l'écoulement et le transfert de chaleur à travers la cavitéIn this thesis, a numerical study is carried out on the coupling phenomena between natural convection and surface radiation in square cavities whose walls are subjected to discrete or non-uniform temperatures. Indeed, the first study carried out is concerned with a problem of convection-radiation coupling in a square cavity inclined and filled with air, having on one side a wall heated at a constant temperature and on the opposite side, a wall heated linearly. The remaining walls are considered adiabatic. In the second study, the cavity has partially heated vertical walls (symmetrically and asymmetrically), a cooled upper wall and an adiabatic bottom wall. The objective of these numerical studies is to analyze the effect of surface radiation and the different governing parameters (heating mode, Rayleigh number, angle of inclination, temperature difference) on the flow structure and the heat transfer. The second objective of this thesis is to test the performance of the multiple relaxation time (MRT) scheme of the Lattice-Boltzmann method (LBM) in the presence of convection radiation coupling. The results of this study revealed that the considered governing parameters have a significant effect on the flow structure and heat transfer through the cavity
14
Cheylan, Isabelle. "Optimisation de forme avec la méthode adjointe appliquée aux équations de Lattice-Boltzmann en aérodynamique." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0119.
Abstract:
Cette thèse a pour objectif le développement d’un solveur adjoint dans ProLB, le logiciel d’aérodynamique basé sur la méthode de Lattice-Boltzmann utilisé chez Renault. Ce solveur adjoint permet de calculer les sensibilités surfaciques des efforts aérodynamiques sur un obstacle, typiquement un véhicule, par rapport à la forme de celui-ci. L’objectif final est de le déformer, par des techniques de morphing basées sur une méthode de descente du gradient à pas constant, afin de réduire sa traînée aérodynamique. Dans un premier temps, l’étude de cas 2D laminaires permet de détailler le développement du solveur adjoint étape par étape. Le choix de la formulation de la force de traînée est un point important. Une étude a montré qu’il est plus judicieux de calculer cette force dans le sillage de l’objet plutôt que sur l’objet lui-même. L’objectif étant de minimiser la force de traînée moyenne, il a été montré que le meilleur compromis entre l’effort de calcul et la précision des gradients est obtenu en moyennant en temps le champ direct instationnaire. Dans un second temps, l’étude de cas 3D turbulents à grandes échelles a permis de montrer que les algorithmes fonctionnant sur des cas 2D laminaires ne sont pas suffisamment stables pour être utilisés dans ce contexte beaucoup plus complexe. Des modifications ont donc été apportées au solveur adjoint afin de pouvoir l’utiliser dans un contexte industriel. Il permet d’obtenir une cartographie des sensibilités sur tout le véhicule dans un écoulement à Reynolds élevé. Une boucle d’optimisation complète a été réalisée, avec une étape de lissage des sensibilités, et a permis de réduire la force de traînée de 5%This work aims at developing an adjoint solver in ProLB, the aerodynamic software based on the Lattice-Boltzmann method used by Renault. The adjoint solver makes it possible to calculate the surface sensitivities of the aerodynamic forces acting on an obstacle, such as a vehicle, with respect to its shape. The final purpose is to deform it, using morphing techniques based on a fixed step gradient descent method, in order to reduce its drag. First, the step by step development process of the adjoint solver is shown through 2D laminar test cases. The choice of the drag force expression is important because it has an impact on the complexity of the adjoint equations and on the gradient calculation. It is shown that calculating the drag force in the wake of the obstacle is more adequate than calculating it on the obstacle directly. The aim being to minimize the time-averaged drag force, it is demonstrated that the best trade-off between the gradients accuracy and the computation cost is obtained by time-averaging the unsteady direct field. Then, the study of 3D large-scale turbulent cases shows that the algorithms used for the 2D laminar cases are not stable enough to be used in this more complicated context. Changes have therefore been brought to the adjoint solver, in order to use it in an industrial context. Every assumption used for the development of the adjoint solver is justified and referenced. The adjoint solver is finally applied to an industrial test case. It gives a sensitivity map on a vehicle in a high Reynolds number flow. A complete optimization loop is performed, using a smoothing step on the sensitivities, and gives a 5% reduction of the drag force
15
Maquignon, Nicolas. "Vers un modèle multiphases et multicomposants (MPMC) de type Lattice Boltzmann Method (LBM) pour la simulation dynamique d'un fluide cyogénique dans l'eau." Thesis, Littoral, 2015. http://www.theses.fr/2015DUNK0426/document.
Abstract:
Au cours de cette thèse, un modèle LBM MPMC avec échanges thermiques est développé. Des tests d'assimilation de données et des mesures par flot optique sont réalisés en vue d'une validation. Le cadre d'application de cette thèse est celui du mélange d'un fluide cryogénique avec l'eau. Dans une première partie, un travail bibliographique rappelant l'équation de Boltzmann, ses diverses hypothèses et simplifications, ainsi que l'aspect algorithmique de la LBM sont exposés. Une comparaison entre opérateur de collision SRT et MRT est réalisée, et une simulation de phénomènes turbulents à différents nombres de Reynolds est étudiée, notamment avec le benchmark de l'instabilité de Von Karman. Dans une seconde partie, le modèle MPMC de Shan & Cehn est rappelé puis étendu au cas où les échanges thermiques entre composants sont présents. Des validations quantitatives sont faites, notamment avec le benchmark du fluide de Couette à deux phases ou à deux composants, du test de cohérence vis-à-vis de la loi de Laplace, ou encore par rapport à un benchmark faisant intervenir la conduction thermique. Des tests qualitatifs de condensation en milieu multicomposants sont proposés pour valider l'aspect des échanges thermiques entre composants en présence d'une transition de phase. Dans la troisième partie de cette thèse, une méthode de validation par assimilation de données est introduite, avec le filtrage de Kalman d'ensemble. Un test d'estimation d'état d'un fluide di-phasique est réalisé, et la compatibilité du filtrage de Kalman d'ensemble par rapport au modèle LBMMPMC est évaluée. Pour la validation du comportement du modèle d'un point de vue de la présence de deux composants, un fluide de substitution (non-cryogénique) au GNL, le butane, a été choisi pour permettre des observations dans des conditions expérimentales accessibles. Puis, une plateforme expérimentale d'injection de butane liquide dans une colonne d'eau sous pression est présentée. Des images d'ombroscopie issues d'expériences de remontée de butane liquide dans de l'eau sont exposées et un algorithme de calcul de flot optique est appliqué à ces images. Une évaluation qualitative des champs de vitesses obtenus par application de cet algorithme est réaliséeIn this thesis, a LBM MPMC model with heat exchange is developed. Data assimilation tests and optical flow measurements are made in order to validate the model. The application context of this thesis is the mixture of a cryogenic fluid with water. In the first part, a bibliographical work reminding the Boltzmann equation and its various assumptions and simplifications, as well as the algorithmic aspect of the LBM are exposed. A comparison between SRT and MRT collision operator is performed, and a simulation of turbulent phenomena at different Reynolds numbers is studied, especially with the benchmark of the instability from Von Karman. In the second part, the MPMC model from Shan & Chen is reminded and extended to the case of the inter-component heat exchanges. Quantitative validations are made, especially with the benchmark of a two-phase or two-component Couette fluid. Consistency is tested against Laplace's law rule, or against a benchmark involving heat conduction. Qualitative testing of condensations in a multi-component medium are proposed to validate the heat exchange between components in the presence of a phase transition. In the third part of this thesis, a validation method for data assimilation is introduced, with the ensemble Kalman filter. A state estimation test of a bi-phase fluid is realized, and compatibility of the ensemble Kalman filtering to the LBM MPMC model is assessed. For validation of the behavior of the model for a two-component case, a substitution fluid (non-cryogenic) for LNG, butane, was selected to permit observations in experimental conditions which are accessible. Then, an experimental platform of injection of liquid butane in a pressurised water column is presented. Shadowgraph images from liquid butane experiments in water are exposed and an optical flow calculation algorithm is applied to these images. A qualitative assessment of the velocity field obtaines by application of this algorithm is performed
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Tran, Duc Kien. "Modélisation numérique discrète de l'érosion interne par renard hydraulique dans les barrages ou digues en terre." Thesis, Lyon, 2016. http://www.theses.fr/2016LYSEC055/document.
Abstract:
Le travail présenté dans ce mémoire de thèse porte sur la modélisation discrète de l’évolution régressive du front d’un conduit d’érosion qui peut se produire dans les barrages ou digues en remblai. Des outils numériques ont été développés en se basant sur le couplage entre la méthode des éléments discrets (DEM) et la méthode de Boltzmann sur réseau (LBM) pour la description, respectivement, des phases solide et fluide. L’implémentation de la méthode DEM suit une approche standard de type dynamique moléculaire (DM) et les interactions intergranulaires sont modélisées par des contacts unilatéraux visco-élastiques frottants ou bilatéraux (ponts solides) viscoélastiques, afin de permettre la modélisation d’un sol légèrement cohésif. La méthode LBM est implémentée ici avec des temps de relaxation multiples (MRT) et une condition de rebondissement interpolée pour les frontières solides en mouvement, afin d’améliorer la stabilité numérique des calculs. Le schéma du couplage entre les deux méthodes, ainsi que les critères pour le choix des paramètres numériques des deux méthodes. Pour étudier le phénomène visé, un échantillon représentatif de sol granulaire situé au front d’un conduit d’érosion est d’abord assemblé par une procédure de préparation “à sec”, puis testé dans des conditions saturées sous un chargement hydraulique monotone croissant. L’érosion régressive se produit par amas de grains au niveau du front d’érosion ayant subi au préalable une dégradation due à de nombreuses ruptures de ponts solides en traction. L’autre phénomène important observé est la présence d’arcs associés a` des chaines de forces en compression qui parviennent à maintenir parfois totalement, parfois partiellement l’intégrité du matériau non érodéThe work reported in this thesis consists in a discrete modelling of the backward front propagation of an erosion pipe, as can take place in embankment dams or dikes. Some numerical tools have been developed to this end, based on the coupling between the Discrete Element Method (DEM) and the Lattice Boltzmann Method (LBM) for the representation of the solid and uid phases, respectively. The implementation of DEM follows a standard molecular dynamics approach and the interaction among grains are regulated by unilteral frictional visco-elastic and breakable visco-elastic bonds, in order to take into account a slightly cohesive soil behaviour. The LBM was implemented according to the Multiple Relaxation Time (MRT) scheme along with an interpolated non-slip conditions for moving boundaries, in order to improve the numerical stability of the calculations. The coupling scheme is described along with the criteria for the numerical parameters of the two methods. A representative specimen of a granular soil located at the front of an erosion pipe is first assembled by a \dry" preparation precedure and then tested under fully-saturated conditions and increasing hydraulic load over time. Backward erosion is takes place in the form of clusters of grain being eroded at the erosion front after a degradation of the material due to the breakage of tensile bonds. The other interesting feature that was observed is the creation of arches of compressive force chains. These arches enabled the specimen to maintain a stable or metastable configuration under the increasing hydraulic load
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Sjölund, Johannes. "Real-time Thermal Flow Predictions for Data Centers : Using the Lattice Boltzmann Method on Graphics Processing Units for Predicting Thermal Flow in Data Centers." Thesis, Luleå tekniska universitet, Institutionen för system- och rymdteknik, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-70530.
Abstract:
The purpose of this master thesis is to investigate the usage of the Lattice Boltzmann Method (LBM) of Computational Fluid Dynamics (CFD) for real-time prediction of indoor air flows inside a data center module. Thermal prediction is useful in data centers for evaluating the placement of heat-generating equipment and air conditioning. To perform the simulation a program called RAFSINE was used, written by Nicholas Delbosc at the University of Leeds, which implemented LBM on Graphics Processing Units (GPUs) using NVIDIA CUDA. The program used the LBM model called Bhatnagar-Gross-Krook (BGK) on a 3D lattice and had the capability of executing thermal simulations in real-time or faster than real-time. This fast rate of execution means a future application for this simulation could be as a predictive input for automated air conditioning control systems, or for fast generation of training data sets for automatic fault detection systems using machine learning. In order to use the LBM CFD program even from hardware not equipped with NVIDIA GPUs it was deployed on a remote networked server accessed through Virtual Network Computing (VNC). Since RAFSINE featured interactive OpenGL based 3D visualization of thermal evolution, accessing it through VNC required use of the VirtualGL toolkit which allowed fast streaming of visualization data over the network. A simulation model was developed describing the geometry, temperatures and air flows of an experimental data center module at RISE SICS North in Luleå, Sweden, based on measurements and equipment specifications. It was then validated by comparing it with temperatures recorded from sensors mounted in the data center. The thermal prediction was found to be accurate on a room-level within ±1° C when measured as the average temperature of the air returning to the cooling units, with a maximum error of ±2° C on an individual basis. Accuracy at the front of the server racks varied depending on the height above the floor, with the lowest points having an average accuracy of ±1° C, while the middle and topmost points had an accuracy of ±2° C and ±4° C respectively. While the model had a higher error rate than the ±0.5° C accuracy of the experimental measurements, further improvements could allow it to be used as a testing ground for air conditioning control or automatic fault detection systems.
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Gendre, Félix. "Développement de méthodes de Boltzmann sur réseau en maillages non-uniformes pour l'aéroacoustique automobile." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0196/document.
Abstract:
L’objectif de ce travail est d’étudier les capacités de la méthode de Boltzmann sur réseau (LBM) dans un cadre numériquement contraignant : celui de la simulation aéroacoustique en maillage non-uniforme, à très haut nombre de Reynolds et à nombre de Mach non négligeable (Ma > 0.1), appliquée à l’automobile. La problématique industrielle est celle du calcul du bruit intérieur d’origine aérodynamique, dont le calcul du champ de pression pariétal instationnaire sur le vitrage conducteur est la première étape décisive. Il a été constaté qu’un manque de précision sur la faible part acoustique du champ de pression total sur le vitrage, provenant très probablement d’erreurs au niveau des transitions de résolution du maillage, était la cause d’une surestimation du bruit intérieur. Nous présentons d’abord une construction cohérente et unifiée de la méthode de Boltzmann sur réseau à partir de l’équation de Boltzmann, dans un cadre athermal faiblement compressible. Nous étudions ensuite en détail les propriétés aéroacoustiques de la LBM, en parcourant toutes les grandes familles d’opérateurs de collision de la littérature. Une variante de modèle à temps de relaxation multiples, utilisable pour l’aéroacoustique, est présentée et testée. Un modèle alternatif simplifié de filtrage sélectif, rapide et compact, est développé et validé. La problématique des maillages non-uniformes est abordée. Un recensement exhaustif des études LBM menées dans ce cadre dans la littérature montre qu’aucune ne correspond à nos contraintes. Des algorithmes alternatifs aux transitions sont développés. Enfin, des applications industrielles sont réalisées à l’aide des modèles développés dans le mémoireThe main goal of this work is to study the capacities of the Lattice Boltzmann Method in a constrained numerical framework : that of numerical simulation in automotive aeroacoustics with non-uniform meshes, at high Reynolds number and non egligible Mach number (Ma > 0.1). The industrial problem is the computation of the interior aerodynamic noise, which includes as its first decisive step the computation of the unsteady wall pressure field on the car windows. It was observed that a lack of precision on the weak acoustic part of the total pressure field on the driver-side window, which is most probably due to errors at mesh refinement interfaces, caused an overestimation of the interior noise. We first present a coherent and unified construction of the Lattice BoltzmannMethod from the Boltzmann equation, in an athermal weakly compressible framework. Then, we study in details the aeroacoustic properties of the LBM by reviewingall the main families of collisional operators that exist in the literature. A variant of multiple relaxation time operator that can be used for aeroacoustics is presented and tested. A simplified alternative selective filter, fast and compact, is developped and numerically validated. The problem of non-uniform meshes is discussed. An exhaustive review of the LBM studies that have been carried out within that framework shows that none of them corresponds to our constraints. Alternative transition nodes algorithms are developed. Finally, all the developed models of this work are applied to industrial cases
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Stockinger, Claudius. "Study and analysis οf Sοοt Filter Regeneratiοn by using the Lattice Bοltzmann Μethοd." Electronic Thesis or Diss., Normandie, 2024. http://www.theses.fr/2024NORMIR07.
Abstract:
La maîtrise des émissions de noir de carbone est une tâche importante dans de nombreux domaines d'application, le secteur des transports étant l'un des domaines les plus importants. Les moteurs diesel, encore largement utilisés dans le monde entier, sont l'une des principales sources d'émissions anthropiques de noir de carbone. Afin de contrer l'effet néfaste du noir de carbone sur la santé humaine, le traitement des gaz d'échappement est au centre de la recherche depuis de nombreuses décennies. Les filtres à suie de pointe utilisent une structure en nid d'abeille en céramique, agissant comme des filtres à flux mur. Ces filtres nécessitent une régénération périodique une fois qu'une contre-pression de filtre critique est atteinte. La régénération est effectuée soit sous forme de régénération active à des températures élevées (>600 °C), soit en continu, sous forme de régénération passive à des températures à partir de 300 °C. La température nécessaire des gaz d'échappement pour la régénération active entraîne une pénalité en carburant, rendant le contrôle précis du processus de régénération impératif. Des travaux antérieurs ont suggéré que la morphologie mésoscopique de la suie et son évolution pendant la combustion de la suie influencent la réactivité, affectant ainsi le processus de régénération. Par conséquent, le contrôle du système de régénération nécessite une connaissance précise des phénomènes physiques et chimiques en jeu, nécessitant des simulations du processus de régénération. Dans cette thèse, un cadre de simulation pour modéliser l'écoulement de gaz, composé des différentes espèces réactives, en tenant compte des interactions solide-gaz, est créé. De plus, le transfert de chaleur conjugué, les réactions hétérogènes et la libération de chaleur de réaction à l'interface entre les phases solide et gazeuse sont traités. À cette fin, la méthode de Boltzmann sur réseau (LBM), en raison de sa nature mésoscopique, est choisie comme un excellent outil pour modéliser la combustion hétérogène à l'échelle des pores. Dans cette thèse, un cadre LBM est créé et des méthodes appropriées pour modéliser la combustion de la suie sont choisies et largement validées. Une procédure d'utilisation des données de microscopie électronique à balayage par faisceau ionique focalisé (FIB-SEM) de véritables échantillons de suie pour la simulation de combustion est mise en œuvre. De plus, les régimes de combustion sont analysés en fonction de la variation du nombre de Péclet, du nombre de Damköhler et de la fraction molaire d'oxygène dans le flux gazeux d'entrée. Des simulations avec des géométries de suie réalistes sont réalisées et les résultats sont comparés avec des résultats expérimentaux. Il est constaté que l'évolution de la surface réactive spécifique, telle que reçue des simulations LBM, n'est pas comparable aux résultats expérimentaux. L'analyse par microscopie électronique à transmission (TEM) et les spectres Raman de la suie avant et après les expériences de combustion ont révélé que la combustion affecte les particules primaires à l'échelle nanométrique. Pour cette raison, un modèle séparé pour décrire les particules primaires hétérogènes et leur combustion a été créé. Ensuite, les premières simulations avec couplage d'échelle ont été menées, en reliant les simulations LBM mésoscopiques avec la conception des particules primaires à l'échelle nanométrique. Il est démontré qu'une augmentation plus réaliste de la surface spécifique peut être obtenue dans les simulations en couplant le modèle LBM mésoscopique avec un modèle de particules primaires à l'échelle nanométriqueThe control of the emission of carbon black is an important task in many fields of application, with the transport sector being one of the most important domains. Diesel engines, still being extensively used worldwide, are one of the main contributors to the anthropogenic emission of carbon black. In order to counteract the detrimental effect of carbon black on human health, exhaust gas treatment has been the focal point of research for many decades.State of the art soot filters use a ceramic honey-comb structure, acting as wall flow filters. These filters require periodic regeneration once a critical filter back-pressure is reached. Regeneration is conduced either as active regeneration at elevated temperatures (>600 °C) or continuously, as passive regeneration at temperatures starting from 300 °C. The necessary exhaust gas temperature of active regeneration results in a fuel penalty, making the precise control of the regeneration process imperative. Previous works suggested that the mesoscopic morphology of soot and its evolution during soot combustion influence the reactivity, thus affecting the regeneration process. Hence, the control of the regeneration system requires precise knowledge of the physical and chemical phenomena at hand, necessitating simulations of the regeneration process.In this thesis, a simulation framework to model gas flow, consisting of the different reactive species, taking into account solid-gas interactions, is created. Furthermore, conjugate heat transfer, heterogeneous reactions and the release of reaction heat at the interface between the solid and gas phases is treated. For this purpose, the lattice Boltzmann method (LBM), due to its mesoscopic nature, is chosen as an excellent tool to model the heterogeneous combustion on the pore scale. Within this thesis, a LBM framework is created and appropriate methods to model soot combustion are chosen and extensively validated. A procedure to use focused ion beam scanning electron microscopy (FIB-SEM) data of realistic soot samples for the combustion simulation is implemented. Furthermore, the combustion regimes are analysed based on variation of Péclet number, Damköhler number, and oxygen mass fraction in the inlet gas stream. Simulations with realistic soot geometries are performed and the results are compared with experimental results. It is found that the evolution of the specific reactive surface, as received from LBM simulations, is not comparable to the experimental results. Transmission electron microscopy (TEM) analysis and Raman spectra of the soot before and after combustion experiments revealed that combustion affects the primary particles on the nano-scale. For this reason, a separate model to describe the heterogeneous primary particles and their combustion was created. Subsequently, first simulations with scale-coupling were conducted, by connecting the mesoscopic LBM simulations with the primary particle design on the nano-scale. It is shown that a more realistic increase in specific surface could be achieved in simulations by coupling the mesoscopic LBM model with a nano-scale primary particle model
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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.
Abstract:
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
Full Text
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Mercier, Philippe. "Modélisation de la turbulence engendrée par la morphologie du fond dans le Raz Blanchard : approche locale avec la LBM-LES." Thesis, Normandie, 2019. http://www.theses.fr/2019NORMC206/document.
Abstract:
Le développement des énergies renouvelables passe par l’exploitation de nouvelles sources d’énergie. La filière hydrolienne, dédiée à la récupération de l’énergie des courants de marée, est proche de l’industrialisation. Cependant, les conditions hydrodynamiques turbulentes des sites hydroliens sont encore mal connues. Cette thèse propose d’examiner à l’échelle locale l’effet des rugosités du fond marin sur la génération de tourbillons hautement énergétiques par la simulation numérique en mécanique des fluides de type méthode de Boltzmann sur réseau. Cette méthode est particulièrement adaptée à la simulation d’écoulements instationnaires sur un domaine de simulation complexe. Dans un premier temps, les phénomènes physiques de détachements tourbillonnaires sur des macro-rugosités canoniques sont décrits. L’appariement de structures tourbillonnaires est mis en évidence dans le processus de formation de tourbillons hautement énergétiques. Dans un deuxième temps, la simulation permet d’observer de tels phénomènes dans le cas d’écoulements environnementaux intégrant une bathymétrie réelle. Ces simulations, validées par rapport à des mesures in situ, mènent à une meilleure compréhension des effets du fond marin sur la turbulence en milieu hydrolien. En particulier, l’importance des failles géologiques dans la génération de turbulence dans la zone d’étude est mise en évidenceRenewable energy development calls for exploitation of new energy resources. Tidal stream power harvesting is now close to the industrialisation step. Still, turbulent hydrodynamic conditions at tidal sites are not well understood. This thesis aims to investigate the local scale effect of sea bottom roughnesses on energetic vortex generation with computational fluid simulations using the lattice Boltzmann method. This method is highly indicated for unsteady flow simulations of complex domains. First, the physical phenomena involved in vortex emission around canonical macroroughnesses are described. Vortex merging is identified in the generation process of energetic vortices. Then, such physical events are reproduced in the case of environmental flow simulations using a real seabed morphology. These simulations are validated on in situ measured data, and lead to a better understanding of the sea bottom effect on tidal stream site turbulence. They demonstrate the role of geological faults on the local turbulence
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Jurczuk, Krzysztof. "Calcul parallèle pour la modélisation d'images de résonance magnétique nucléaire." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S089.
Abstract:
L'objet de cette thèse est la modélisation computationnelle de l'Imagerie par Résonance Magnétique (IRM), appliquée à l'imagerie des réseaux vasculaires. Les images sont influencées par la géométrie des vaisseaux mais aussi par le flux sanguin. Par ailleurs, outre la qualité des modèles développés, il est important que les calculs soient performants. C'est pourquoi, le calcul parallèle est utilisé pour gérer ce type de problèmes complexes. Dans cette thèse, trois solutions sont proposées. La première concerne les algorithmes parallèles pour la modélisation des réseaux vasculaires. Des algorithmes dédiés à différentes architectures sont proposés. Le premier est basé sur le modèle de « passage de messages » pour les machines à mémoires distribuées. La parallélisation concerne l'irrigation de nouvelles zones de tissu par les vaisseaux existants. Le deuxième algorithme est dédié aux machines à mémoire partagée. Il parallélise également le processus de perfusion mais des processeurs différents se chargent de gérer les différents arbres vasculaires. Le troisième algorithme est une combinaison des approches précédentes offrant une solution pour les architectures parallèles hybrides. Les algorithmes proposés permettent d'accélérer considérablement la croissance des réseaux vasculaires complexes, ce qui rend possible la simulation de structures vasculaires plus précises, en un temps raisonnable et aide à améliorer le modèle vasculaire et à tester plus facilement différents jeux de paramètres. Une nouvelle approche de modélisation computationnelle des flux en IRM est également proposée. Elle combine le calcul de flux par la méthode de Lattice Boltzmann, la simulation IRM par le suivi temporel de magnétisations locales, ainsi qu'un nouvel algorithme de transport des magnétisations. Les résultats montrent qu'une telle approche intègre naturellement l'influence du flux dans la modélisation IRM. Contrairement aux travaux de la littérature, aucun mécanisme additionnel n'est nécessaire pour considérer les artéfacts de flux, ce qui offre une grande facilité d'extension du modèle. Les principaux avantages de cette méthode est sa faible complexité computationnelle, son implémentation efficace, qui facilitent le lancement des simulations en utilisant différents paramètres physiologiques ou paramètres d'acquisition des images. La troisième partie du travail de thèse a consisté à appliquer le modèle d'imagerie de flux à des réseaux vasculaires complexes en combinant les modèles de vaisseaux, de flux et d'acquisition IRM. Les algorithmes sont optimisés à tous les niveaux afin d'être performants sur des architectures parallèles. Les possibilités du modèle sont illustrées sur différents cas. Cette démarche de modélisation peut aider à mieux interpréter les images IRM grâce à l'intégration, dans les modèles, de connaissances variées allant de la vascularisation des organes jusqu'à la formation de l'image en passant par les propriétés des flux sanguinsThis PhD thesis concerns computer modeling of magnetic resonance imaging (MRI). The main attention is centered on imaging of vascular structures. Such imaging is influenced not only by vascular geometries but also by blood flow which has to been taken into account in modeling. Next to the question about the quality of developed models, the challenge lies also in the demand for high performance computing. Thus, in order to manage computationally complex problems, parallel computing is in use. In the thesis three solutions are proposed. The first one concerns parallel algorithms of vascular network modeling. Algorithms for different architectures are proposed. The first algorithm is based on the message passing model and thus, it is suited for distributed memory architectures. It parallelizes the process of connecting new parts of tissue to existing vascular structures. The second algorithm is designed for shared memory machines. It also parallelizes the perfusion process, but individual processors perform calculations concerning different vascular trees. The third algorithm combines message passing and shared memory approaches providing solutions for hybrid parallel architectures. Developed algorithms are able to substantially speed up the time-demanded simulations of growth of complex vascular networks. As a result, more elaborate and precise vascular structures can be simulated in a reasonable period of time. It can also help to extend the vascular model and to test multiple sets of parameters. Secondly, a new approach in computational modeling of magnetic resonance (MR) flow imaging is proposed. The approach combines the flow computation by lattice Boltzmann method, MRI simulation by following discrete local magnetizations in time and a new magnetization transport algorithm together. Results demonstrate that such an approach is able to naturally incorporate the flow influence in MRI modeling. As a result, in the proposed model, no additional mechanism (unlike in prior works) is needed to consider flow artifacts, what implies its easy extensibility. In combination with its low computational complexity and efficient implementation, the solution is a user-friendly and manageable at different levels tool which facilitates running series of simulations with different physiological and imaging parameters. The goal of the third solution is to apply the proposed MR flow imaging model on complex vascular networks. To this aim, models of vascular networks, flow behavior and MRI are combined together. In all the model components, computations are adapted to be performed at various parallel architectures. The model potential and possibilities of simulations of flow and MRI in complex vascular structures are shown. The model aims at explaining and exploring MR image formation and appearance by the combined knowledge from many processes and systems, starting from vascular geometry, through flow patterns and ending on imaging technology
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Asta, Adelchi Jacques. "Listening to the electrical noise for nanofluidic sensing." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS444.
Abstract:
Le passage de la microfluidique, qui est aujourd'hui un domaine bien établi, à la nanofluidique nécessite le développement de techniques numériques. En utilisant la méthode de Lattice Boltzmann sur réseau électrocinétique (LBE), nous pouvons coupler l'équation de Navier-Stokes avec la théorie de Poisson-Nernst Planck et ainsi étudier les fluides confinés et chargés à l'échelle nanométrique. Les électrochimistes ont commencé à utiliser les fluctuations électriques qui en découlent pour extraire des informations sur les phénomènes interfaciaux et donc sur les processus microscopiques sous-jacents (par exemple: la détection de molécules uniques ou l’adsorption/désorption). Ceci nécessite de pouvoir modéliser des nanocondensateurs avec une différence de potentiel constante entre les deux électrodes, ce qui est la principale nouveauté ajoutée à l'algorithme LBE. Enfin, en couplant cette méthode à la méthode de propagation des moments, nous avons été en mesure de fournir un outil de calcul efficace, capable d'analyser les effets hydrodynamiques, électrocinétiques, d'adsorption/désorption et de taille finie dans des fluides confinés à l'échelle nanométrique, pour des géométries arbitraires, en régime linéaire et non linéaire, ainsi que dans les régimes transitoires et stationnaires. Dans le contexte du bruit électrique, la réponse temporelle de la charge à une perturbation de tension peut être liée à l'impédance et donc aux fluctuations électriques. A l'avenir, nous pourrons également étudier la réponse électrocinétique liée à la réponse de corrélation croisée entre la masse et les courants électriquesMoving from microfluidics, which is now a well-established field, to nanofluidics requires the development of computational tools. Using the Lattice Boltzmann Electrokinetics (LBE) method, we can couple the Navier-Stokes equation with the Poisson-Nernst Planck theory and thus study charged confined fluids at the nanoscale. Electrochemists have begun to use the electrical fluctuations arising from them to extract information on the interfacial phenomena and thus the underlying microscopic processes (e.g. single molecule detection, adsorption/desorption). This requires to be able to model nanocapacitors with a constant potential difference between the two electrodes, which was the main novelty added to the LBE algorithm. Finally by coupling this method with the moment propagation method, we have been able to provide an efficient computational tool capable to analyse, hydrodynamic, electrokinetic, adsorption/desorption and finite size effects in fluids confined at the nanoscale, for arbitrary geometries, in both linear and non-linear regimes, as well as in the transient and steady state regimes. Within the context of electrical noise, the temporal charge response to a voltage perturbation can be linked to the impedance and thus to the electrical fluctuations. In the future we will also be able to study the electrokinetic response related to the cross correlation response between mass and electric currents
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Obrecht, Christian. "High performance lattice Boltzmann solvers on massively parallel architectures with applications to building aeraulics." Phd thesis, INSA de Lyon, 2012. http://tel.archives-ouvertes.fr/tel-00776986.
Abstract:
With the advent of low-energy buildings, the need for accurate building performance simulations has significantly increased. However, for the time being, the thermo-aeraulic effects are often taken into account through simplified or even empirical models, which fail to provide the expected accuracy. Resorting to computational fluid dynamics seems therefore unavoidable, but the required computational effort is in general prohibitive. The joint use of innovative approaches such as the lattice Boltzmann method (LBM) and massively parallel computing devices such as graphics processing units (GPUs) could help to overcome these limits. The present research work is devoted to explore the potential of such a strategy. The lattice Boltzmann method, which is based on a discretised version of the Boltzmann equation, is an explicit approach offering numerous attractive features: accuracy, stability, ability to handle complex geometries, etc. It is therefore an interesting alternative to the direct solving of the Navier-Stokes equations using classic numerical analysis. From an algorithmic standpoint, the LBM is well-suited for parallel implementations. The use of graphics processors to perform general purpose computations is increasingly widespread in high performance computing. These massively parallel circuits provide up to now unrivalled performance at a rather moderate cost. Yet, due to numerous hardware induced constraints, GPU programming is quite complex and the possible benefits in performance depend strongly on the algorithmic nature of the targeted application. For LBM, GPU implementations currently provide performance two orders of magnitude higher than a weakly optimised sequential CPU implementation. The present thesis consists of a collection of nine articles published in international journals and proceedings of international conferences (the last one being under review). These contributions address the issues related to single-GPU implementations of the LBM and the optimisation of memory accesses, as well as multi-GPU implementations and the modelling of inter-GPU and internode communication. In addition, we outline several extensions to the LBM, which appear essential to perform actual building thermo-aeraulic simulations. The test cases we used to validate our codes account for the strong potential of GPU LBM solvers in practice.
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Yehya, Alissar. "Contribution to the experimental and numerical characterization of phase-change materials : consideration of convection, supercooling, and soluble impurities." Thesis, Artois, 2015. http://www.theses.fr/2015ARTO0207/document.
Abstract:
Au cours des deux dernières décennies, le contexte économique a changé de manière significative en raison de la hausse des prix de l'énergie. Le bâtiment étant devenu le principal secteur consommateur d'énergie, la réduction de celle-ci est devenue un objectif économique, sociétal et environnemental. Ce sujet mobilise de nombreux travaux de recherche. Les Matériaux à Changement de Phase (MCP) représentent une solution innovante qui pourrait contribuer à améliorer la performance énergétique des bâtiments. Ils sont principalement utilisés pour la régulation de température, et leur forte capacité de stockage est un moyen de réduire la consommation d'énergie. Notre étude vise à caractériser, via une approche expérimentale et numérique, le comportement d'un PCM (l’Octadécane). Pour cela, nous avons développé et mis en œuvre un modèle numérique qui corrobore les résultats expérimentaux, et ainsi améliore la prédiction de la performance du MCP considéré.Dans ce travail, notre principale préoccupation est de mettre en évidence les erreurs ou simplifications présentes dans le modèle numérique traditionnel pouvant entraîner un écart global par rapport au comportement réel du MCP. Ces différences conduisent à une estimation erronée des temps de fusion et de la quantité d'énergie stockée. L'amélioration significative de notre modèle est la prise en compte de la convection naturelle, de la surfusion, et l'utilisation des courbes réelles d'enthalpie du MCP considéré. La relation température-enthalpie réelle tient compte de la présence d'une fraction d'impuretés solubles dans le matériau. L’originalité de ce travail est de traiter ces phénomènes physiques via la méthode de Boltzmann réseau (connue sous l'acronyme LBM) avec des fonctions de distribution doubles couplée à une formulation enthalpique. Une telle approche permet de passer outre la non-linéarité des équations régissant l'écoulement et le transfert de chaleur. Sa simplicité de mise en œuvre et son caractère local permettent d'affiner le modèle. Ainsi, on peut couvrir les problèmes de changement de phase, y compris ceux pouvant avoir lieu dans des matrices poreuses ou fibreuses. Ce dernier point a été couvert dans cette thèse.Enfin, il s'est avéré que l'approche numérique adoptée ici pour traiter les problèmes de changement de phase corrobore à la fois nos résultats expérimentaux et ceux disponibles dans la littératureOver the past two decades, the economic context has changed significantly due to the rise in energy prices. The building sector has become the main consumer of energy. Thereby, reducing the latter is now an economic, societal and environmental necessity. Accordingly, this topic mobilizes many researches. Phase Change Materials (PCMs) represent an innovative solution, which could improve buildings' energy performance. They are primarily used for temperature regulation, and their high storage capacity can reduce energy consumption.Our study aims at characterizing, via a complementary approach of experimental and numerical simulation, the behavior of a PCM (n-Octadecane). For this, we have developed and implemented a numerical model that corroborates the experimental results, and hence improves the prediction of the PCM performance.In this work, our main concern is to highlight the common errors or simplifications taken in the traditional numerical model, which can result in an overall discrepancy compared to the actual behavior of PCMs. Those discrepancies lead to wrong estimation of the fusion times and amount of energy stored. The major improvement of our model is the consideration of the natural convection, the supercooling, and the use of real enthalpy curves of the considered PCM. The actual temperature-enthalpy relationship takes into account the presence of a fraction of soluble impurities in the material. The originality of this work is to handle these physical phenomena via a lattice Boltzmann method (known by the acronym LBM), which leans on double distribution functions and coupled with the enthalpy formulation. Such an approach overcomes the non-linearity in the governing equations of fluid flow and heat transfer. Its simplicity and local character allow adding complexity to the model. Thereby, one can cover up the phase change problems, including those, which may occur in heterogeneous matrices. This last point has been also covered in this thesis.Finally, it turned out that the approach implemented here for phase change problems supports both, our experimental results and those available in the literature
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Adia, Jean-Luc. "Modélisation multi échelle des phénomènes de retrait et de fluage dans les matériaux cimentaires : approches numériques couplant les éléments finis et la méthode de Lattice-Boltzmann." Thesis, Paris Est, 2017. http://www.theses.fr/2017PESC1013/document.
Abstract:
Dans les structures en béton précontraint, les phénomènes de fluage et de retrait tendent à réduire les efforts de précontrainte initialement prévus pour maintenir le béton dans un état minimisant les forces de traction et donc la fissuration. La compréhension et la prédiction de ces phénomènes par le biais de modèles sont donc primordiales pour la conception et la maintenance à long terme des ouvrages du génie civil tels que les enceintes de confinement des centrales nucléaires.L’objectif de cette thèse est d’élaborer un cadre de modélisation micromécanique pour décrire de manière unifiée le retrait et le fluage dans les matériaux cimentaires. Pour cela, l’étude se base sur l’échelle de la microstructure poreuse du gel de C-S-H où les mécanismes intrinsèques de ces déformations différées du béton opèrent. Une approche d’homogénéisation numérique modélisant ces phénomènes dans des microstructures poreuses à morphologies quelconques est développée. Une description explicite du réseau poreux ainsi que de la phase liquide de l’eau pendant les processus de séchage/humidification est prise en compte. Les mécanismes concernant lesdéformations différées dans la phase solide sont modélisés par la théorie de la microprécontrainte-solidification (MPS). Les simulations à l’échelle microscopique sont réalisées par une approche originale couplant la méthode de Lattice Boltzmann (LBM) et la méthode des éléments finis (FEM). La LBM est utilisée pour décrire la distribution du liquide capillaire à l’échelle du pore,tandis que la FEM est employée pour simuler la déformation du squelette solide sous l’action combinée de l’eau dans l’espace poreux et d’un chargement macroscopique.La démarche proposée permet, au travers des simulations, de mieux comprendre les mécanismes liés à la non saturation et aux effets capillaires dans les milieux poreux. En particulier, la prise en compte de morphologies réalistes de microstructures et des ménisques formés conduit à différents régimes de retrait/gonflement. Ainsi les effets de l’intensité de la pression capillaire,de la tension de surface et des surfaces de chargement sur la réponse élastique du squelette solide sont évalués. Enfin, nous proposons une extension des approches précédentes au cas d’un squelette viscoélastique se déformant sous les effets de la pression capillaire et des tensions de surface. A partir des observations numériques réalisées, nous proposons un modèle pour décrire le fluage et le retrait du gel de C-S-H de manière unifiéeIn pre-stressed concrete structures, creep and shrinkage tend to reduce the pre-stress forces which are initially produced so as to maintain concrete in a state minimizing traction forces and then cracks. Understanding and predicting these phenomena through models are thus highly important for the design and durability of civil engineering structures, such as containment buildings in nuclear power plants.The objective of this thesis is to develop a micromechanical modeling framework to describe shrinkage and creep in cementitious materials in a unified manner. For this purpose, the study focuses on the scale of the porous structure of the C-S-H gel where the intrinsic mechanisms of delayed strains are active. A computational homogenization approach is developed to model these phenomena in porous structures with arbitrary morphologies. An explicit description of the porous network and of the liquid phase of water during the drying/humidification process is taken into account. The mechanisms related to delayed strains in the solid phase are modeled by the microprestress-solidification theory (MPS). The simulations at the microscale are conductedbased on an original approach coupling the Lattice Boltzmann method (LBM) and the finite element method (FEM). The LBM is used to describe the distribution of capillary water in the porous structure, whereas the FEM serves as modeling the strain of the solid skeleton under the capillary water effets and a macroscopic load.The proposed method allows, by means of the simulations, to better understand the mechanisms related to the capillary effects in the porous structure. More specifically, taking into account realistic morphologies of microstructures and of the formed menisci lead to different regimes of shrinkage/swelling. Then, the effects of capillary pressure intensity, of surface tension and of morphologies of capillary surfaces on the elastic response of the solid skeleton are evaluated. Finally, the above approaches are extended to the case of a viscoelastic solid deformed under the action of the capillary water. From numerical observations, we propose a model is proposed to describe the creep and shrinkage of C-S-H gel in a unified way
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Ducasse, Marie laure. "Mélange d'un scalaire dans un jet turbulent : influence d'un obstacle." Thesis, Aix-Marseille, 2012. http://www.theses.fr/2012AIXM4094/document.
Abstract:
Cette étude s'intéresse aux risques associés à la formation d'une ATmosphère EXplosive (ATEX) née d'une fuite d'hydrogène et de sa dispersion dans l'air ambiant. La fuite a été modélisée par un jet turbulent à densité variable libre, impactant sur une sphère de diamètre 20mm ou sur une plaque plane. Dans un premier temps, les champs de vitesses et de concentration ont été obtenus expérimentalement en proche sortie grâce à des mesures de Vélocimétrie par Images de Particules (PIV) et de Fluorescence Induite par Plan Laser sur l'acétone (PLIF). La turbulence et le mélange ont été caractérisés pour le cas d'un jet libre ou en présence d'un obstacle. A partir de ces mesures, la structure générale de l'écoulement a été étudiée à partir des champs moyens et fluctuants par comparaison avec les données de la bibliographie. Puis, les données issues des fluctuations ont été analysées statistiquement par l'étude des fonctions de densité de probabilité du scalaire. Ces travaux se sont poursuivis avec la mise en relation des résultats expérimentaux avec ceux obtenues par des simulations numériques DNS (Direct Numerical Simulation) utilisant la méthode Boltzmann sur Réseau (LBM) d'un scalaire passif dans un jet d'air. Cette étude a permis de recueillir et d'analyser des données supplémentaires sur le mélange d'un jet à masse volumique variable libre ou impactant. Ces données sont directement applicables à la maitrise des risques liés aux fuites d'hydrogèneThis study examines the risks associated with the formation of an explosive atmosphere from a hydrogen leak and its dispersion into the air. We considered the leak as a turbulent jet with density variable, free and impinging a $20,mm$ diameter sphere or a flat plate. Firstly, velocity and scalar fields have been measured experimentally in the near field through Particle Image Velocimetry (PIV) and acetone Planar Laser Induced Fluorescence (LIF). Turbulence and mixing have been defined in the case of free jet and impinging jet. From this measurements, the flow structure has been presented from the mean and fluctuating flow measurements by comparison with literature data. Next, the fluctuation scalar fields are studied with the probability density function method. Finally, a comparison has been conducted between the experiments and direct numerical simulation (DNS) of turbulence based on the lattice Boltzmann method (LBM) for passive scalar in air jet. This study is gathering and analyzing data on the mixing of jet with density variable, free and impinging jet. Such data is directly useful to identify and control risks incurred due to hydrogen leak
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Abbaspour, Nima. "Approche numérique et expérimentale des écoulements au sein des piles à combustible : innovations liées aux conditions aux limites." Thesis, Avignon, 2020. http://www.theses.fr/2020AVIG0507.
Abstract:
La présente thèse fait partie d’un projet destiné à améliorer l’efficacité et la stabilité des piles à combustible à membrane à échange de protons. Elle présente des expériences et des simulations visant à faire évoluer en ce sens la géométrie de canaux véhiculant des fluides à travers les plaques bipolaires à l’anode et à la cathode. En effet, l’electricité produite dépend en particulier d’écoulements diphasiques couplés avec divers phénomènes physiques et très impactés par les forces interfaciales sur les surfaces solides qui les limitent. Nous avons utilisé des codes indutriels ainsi que la méthode des réseaux de Boltzmann pour simuler les sytèmes complexes en jeu. Le chapitre 1 rappelle le principe de base des piles à combustible ainsi que le rôle des fluides s’écoulant dans les canaux des plaques bipolaires. En partant de piles standard,nousjetonslesbasesdesmodificationsétudiéesici. Lechapitre2détailleunmodèle classique du fonctionnement des piles à combustible en régime stationnaire, supposant des écoulements monophasiques dans les canaux. Une expérience réalisée sur une unique pile de ce type valide la formulation mathématique du modèle ainsi que l’outil numérique (Comsol). La simulation met en évidence l’hétérogénéité des flux dans les différents canaux, alors qu’on connait l’influence négative de cette hétérogéneité. Cependant le modèle utilisé ne tient pas compte de la possibilité d’avoir de l’eau en phase liquide (et pas uniquement gaseuze) dans les écoulements. Pour y remédier, le chaptitre 3 décrit un code LBM fondé sur le modèle du gradient de couleur pour les écoulements diphasiques. Ce code est validé à partir d’une expérience réalisée sur une jonction en T, un dispositif applicable bien au delà du contextedespilesàcombustible. Lechapitre4restedanslecadred’écoulementsstationnaires gazeux dans des canaux parallèles, mais cependant différents de ceux de piles standard. Un algorithme uniformise automatiquement les écoulements des différents canaux en modifiant leur géométrie, dans certaines limites cependant. Il fait pour cela varier des paramètres comme le nombere de canaux et leurs largeurs. Les dispositifs répartissant ou collectant le fluide entre les différents canaux à l’entrée ou à la sortie influencent aussi le résultat. Nous proposons des géométries uniformisant les écoulements des divers canaux. Hélas le résultat n’est pas satisfaisant en terles de production électrique . Le chapitre 5 décrit les déplacements dirigés et spontanés de gouttes d’eau sur des structures métalliques pourvues de canaux d’axes parallèles, mais dont la forme rappelle des nageoires: une expérience met en évidence une direction nettementprivilégiée pour l’étalement des gouttes. Les simulations tri-dimensionnelles en LBM et par la méthode du volume de fluide corroborent la tendance observée tout en révélant à plus petite échelle des détails qui échappent aux visualisations mises en oeuvre: l’effet des forces capillaires est clairement dominant, et s’exerce dans des régions bien précises du dispositif, alors que dans d’autres régions l’inertie est essentielle aussi. Les simulations d’écoulements diphasiques décrits aux chapitres 3 et 5 représentent les résultats principauxThis thesis is part of a wider project that aims at improving proton exchange membrane fuel cell (PEMFC) efficiency and stability. Our contribution aims at improving the geometry and structure of channels in anode and cathode bipolar plates (BPP) using experiments and simulations. The operation of a PEMFC involves multiphase flows and multiphysics phenomenon such as reactant concentration and electron exchange between the components. To simulate such a complex system employed industrial codes as well as Lattice Boltzmann Method. Chapter 1 reminds the basic principle of PEM fuel cell and the role of the fluids that flow through BPP channels. We describe a standard version of the latter and the modifications which we consider here. Chapter 2 details a classical model that describes PEM fuel cell operation in steady regime and assumes single phase flows in channels. The underlying equations and their simulation (using COMSOL) are validated by an experiment performed on standard single cell. The simulation evidences channels exhibiting unequal fluid fluxes while the literature points the negative effects of such heterogeneity. Since the used models disregards the possibility of having water in two phases, Chapter 3 describes a LBMcolorgradientcodefortwophaseflows. Wevalidateitagainstanexperimentperformed of a T-junction, a device that has applications beyond fuel cell. Chapter 4, differently, is devoted to steady gas flows in parallel channels that differ from standard fuel cell. An algorithm automatically homogenizes the fluid flow by modifying domain geometry within definite limits. It applies to diverse settings, and manages parallel channels by varying parameters as channel number and widths. However, the distributing channels that span the fluid between channels at BPP inlet and recollect it at outlet also matter. The author thus proposes designs that equalize channel flows. The author creates a new design to study the manufacturing feasibility of BPP. Chapter 5 describes water drop directional spreading on metallic structures decorated with fin shaped channels of parallel axis: experiments reveal almost total spreading only in one direction. Three dimensional LBM and Volume of Fluid simulationsretrievetheobservedtrendandcapturesmallerscaledetailssuggestingsubsetsof the fluid domain where capillary forces or inertia dominate. Most significant results are two phase flows simulations. They describe the different regimes of films or drops at the outlet of a T-junction whose other branches are fed with immiscible wetting and non-wetting fluids. Moreover, they describe how water drops spread on a microscopic relief which results into skewed capillary force
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Nakamura, Masamichi, and Kazuhiro Yamamoto. "Simulation of heat conduction and soot combustion in diesel particulate filter." Inderscience publishers, 2012. http://hdl.handle.net/2237/20055.
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Reis, Tim. "Lattice Boltzmann method for complex flows." Thesis, Cardiff University, 2007. http://orca.cf.ac.uk/55060/.
Abstract:
This thesis presents the extension of the lattice Boltzmann equation (LBE) to several well-known flows. First, the flow over a cylinder is studied using the LBE and the numerical predictions are shown to compare well with those obtained using a stylised finite volume method. A clear and formal perturbation analysis of the generalised LBE is also presented. A LBE for axisymmetric flows is developed, the precise form of which is derived through a Chapman-Enskog analysis so that the additional axisymmetric contributions to the Navier-Stokes equation are furnished when written in the cylindrical polar coordinate system. Stokes' flow over a sphere is studied and excellent agreement is found between the numerical and analytical predictions. A lattice Boltzmann model for immiscible binary fluids with variable viscosities and density ratio is developed. In the macroscopic limit this model is shown to recover the Navier-Stokes equations for two phase flow. A theoretical expression for surface tension is determined. The validity of this analysis is confirmed by comparing numerical and theoretical predictions of surface tension as a function of density. A number of numerical simulations are presented and shown to be in good agreement with analytical results. Finally, an axisymmetric multiphase lattice Boltzmann model has been proposed. This model is easy to implement and some test cases have been performed to demonstrate its capabilities. A review of the extension of the lattice Boltzmann equation to viscoelasticity is also presented.
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Kaehler, Goetz August. "Fluctuations in the Lattice Boltzmann Method." Diss., North Dakota State University, 2012. https://hdl.handle.net/10365/26865.
Abstract:
The implementation of fluctuations in the lattice Boltzmann method has made significant progress in the last 10 years. The significance of incorporating noise to all non-conserved degrees of freedom was a significant recent discovery that was based on a simplified Langevin treatment of the linarized Boltzmann equation. However, for non-vanishing mean velocities significant deviations in the correlation functions were observed. In this thesis we show how we can largely alleviate these deviations by incorporating fully velocity dependent moment transforms and thus recover a fluctuation dissipation theorem that is valid for a larger range of velocities. Furthermore we show that the remaining deviations can be attributed to the collision operator of the linearized Boltzmann equation not being identical to the one of the BGK collision which forms the basis of most modern lattice Boltzmann applications. Finally we show that the locally velocity dependent transforms significantly improve the stability of fluctuating lattice Boltzmann simulations at low particle densities.
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Prasianakis, Nikolaos I. "Lattice Boltzmann method for thermal compressible flows /." Zürich : ETH, 2008. http://e-collection.ethbib.ethz.ch/show?type=diss&nr=17739.
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Viggen, Erlend Magnus. "The lattice boltzmann method with applicationsin acoustics." Thesis, Norwegian University of Science and Technology, Department of Physics, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-6345.
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YAMAMOTO, Kazuhiro, Xiaoyi HE, and Gary D. DOOLEN. "Combustion Simulation Using the Lattice Boltzmann Method." The Japan Society of Mechanical Engineers, 2004. http://hdl.handle.net/2237/9002.
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Mao, Wenbin. "Modeling particle suspensions using lattice Boltzmann method." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50349.
Abstract:
Particle suspensions are common both in nature and in various technological applications. The complex nature of hydrodynamic interactions between particles and the solvent makes such analysis difficult that often requires numerical modeling to understand the behavior of particle suspensions. In this dissertation, we employ a hybrid computational model that integrates a lattice spring model for solid mechanics and a lattice Boltzmann model for fluid dynamics. We use this model to study several practical problems in which the dynamics of spherical and spheroidal particles and deformable capsules in dilute suspensions plays an important role. The results of our studies yield new information regarding the dynamics of solid particle in pressure-driven channel flows and disclose the nonlinear effects associated with fluid inertia leading to particle cross-stream migration. This information not only give us a fundamental insight into the dynamics of dilute suspensions, but also yield engineering guidelines for designing high throughput microfluidic devices for sorting and separation of synthetic particles and biological cells.
We first demonstrate that spherical particles can be size-separated in ridged microchannels. Specifically, particles with different sizes follow distinct trajectories as a result of the nonlinear inertial effects and secondary flows created by diagonal ridges in the channel. Then, separation of biological cells by their differential stiffness is studied and compared with experimental results. Cells with different stiffness squeeze through narrow gaps between solid diagonal ridges and channel wall, and migrate across the microchannel with different rates depending on their stiffness. This deformability-based microfluidic platform may be valuable for separating diseased cells from healthy cells, as a variety of cell pathologies manifest through the change in mechanical cell stiffness. Finally, the dynamics of spheroid particles in simple shear and Poiseuille flows are studied. Stable rotational motion, cross-stream migration, and equilibrium trajectories of non-spherical particles in flow are investigated. Effects of particle and fluid inertia on dynamics of particles are disclosed. The dependence of equilibrium trajectory on particle shape reveals a potential application for shape based particle separation.
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Viggen, Erlend Magnus. "The lattice Boltzmann method: Fundamentals and acoustics." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2014. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-24085.
Abstract:
The lattice Boltzmann method has been widely used as a solver for incompressible flow, though it is not restricted to this application. More generally, it can be used as a compressible Navier-Stokes solver, albeit with a restriction that the Mach number is low. While that restriction may seem strict, it does not hinder the application of the method to the simulation of sound waves, for which the Mach numbers are generally very low. Even sound waves with strong nonlinear effects can be captured well. Despite this, the method has not been as widely used for problems where acoustic phenomena are involved as it has been for incompressible problems. The research presented this thesis goes into three different aspects of lattice Boltzmann acoustics. Firstly, linearisation analyses are used to derive and compare the sound propagation properties of the lattice Boltzmann equation and comparable fluid models for both free and forced waves. The propagation properties of the fully discrete lattice Boltzmann equation are shown to converge at second order towards those of the discrete-velocity Boltzmann equation, which itself predicts the same lowest-order absorption but different dispersion to the other fluid models. Secondly, it is shown how multipole sound sources can be created mesoscopically by adding a particle source term to the Boltzmann equation. This method is straightforwardly extended to the lattice Boltzmann method by discretisation. The results of lattice Boltzmann simulations of monopole, dipole, and quadrupole point sources are shown to agree very well with the combined predictions of this multipole method and the linearisation analysis. The exception to this agreement is the immediate vicinity of the point source, where the singularity in the analytical solution cannot be reproduced numerically. Thirdly, an extended lattice Boltzmann model is described. This model alters the equilibrium distribution to reproduce variable equations of state while remaining simple to implement and efficient to run. To compensate for an unphysical bulk viscosity, the extended model contains a bulk viscosity correction term. It is shown that all equilibrium distributions that allow variable equations of state must be identical for the one-dimensional D1Q3 velocity set. Using such a D1Q3 velocity set and an isentropic equation of state, both mechanisms of nonlinear acoustics are captured successfully in a simulation, improving on previous isothermal simulations where only one mechanism could be captured. In addition, the effect of molecular relaxation on sound propagation is simulated using a model equation of state. Though the particular implementation used is not completely stable, the results agree well with theory.
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Mossige, Endre Joachim. "Curved Boundary Conditions for the Lattice Boltzmann Method." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for energi- og prosessteknikk, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14667.
Abstract:
The lattice Boltzmann method is a modern method in computational fluid dynamics. Its primary use is the simulation of incompressible flows. It has computational advantages over conventional methods like the finite volume method. However, the implementation of boundary conditions is still an unsolved topic for this method. The method is defined on a Cartesian grid such that curved walls need special treatment as they are generally not aligned with the grid lines. We investigated a number of straight and curved boundary conditions and performed four different benchmark tests to verify these. Based on a formulation for curved walls with no-slip from the literature, we showed that this method could be extended to simulate flows with arbitrary velocity boundary conditions. Our scheme conserved the second order accuracy of the lattice Boltzmann method in time and space.
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Viggen, Erlend Magnus. "The lattice Boltzmann method with applications in acoustics." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 2009. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-6345.
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Jin, Kang Meir Amnon J. "On the Lattice Boltzmann method implementation and applications /." Auburn, Ala, 2008. http://repo.lib.auburn.edu/EtdRoot/2008/FALL/Mathematics_and_Statistics/Dissertation/Jin_Kang_9.pdf.
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Doolen, Gary D., Xiaoyi He, and Kazuhiro Yamamoto. "Simulation of Combustion Field with Lattice Boltzmann Method." Springer, 2002. http://hdl.handle.net/2237/20030.
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Wagner, Alexander. "Theory and applications of the lattice Boltzmann method." Thesis, University of Oxford, 1997. http://ora.ox.ac.uk/objects/uuid:882b9026-22cd-4e77-95e5-aca62f93df11.
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Chin, Jonathan. "Mesoscale fluid simulation with the lattice Boltzmann method." Thesis, Queen Mary, University of London, 2005. http://qmro.qmul.ac.uk/xmlui/handle/123456789/1776.
Abstract:
This thesis describes investigations of several complex fluid effects., including hydrodynamic spinodal decomposition, viscous instability. and self-assembly of a cubic surfactant phase, by simulating them with a lattice Boltzmann computational model. The introduction describes what is meant by the term "complex fluid", and why such fluids are both important and difficult to understand. A key feature of complex fluids is that their behaviour spans length and time scales. The lattice Boltzmann method is presented as a modelling technique which sits at a "mesoscale" level intermediate between coarse-grained and fine-grained detail, and which is therefore ideal for modelling certain classes of complex fluids. The following chapters describe simulations which have been performed using this technique, in two and three dimensions. Chapter 2 presents an investigation into the separation of a mixture of two fluids. This process is found to involve several physical mechanisms at different stages. The simulated behaviour is found to be in good agreement with existing theory, and a curious effect, due to multiple competing mechanisms, is observed, in agreement with experiments and other simulations. Chapter 3 describes an improvement to lattice Boltzmann models of Hele-Shaw flow, along with simulations which quantitatively demonstrate improvements in both accuracy and numerical stability. The Saffman-Taylor hydrodynamic instability is demonstrated using this model. Chapter 4 contains the details and results of the TeraGyroid experiment, which involved extremely large-scale simulations to investigate the dynamical behaviour of a self-assembling structure. The first finite- size-effect- free dynamical simulations of such a system are presented. It is found that several different mechanisms are responsible for the assembly; the existence of chiral domains is demonstrated, along with an examination of domain growth during self-assembly. Appendix A describes some aspects of the implementation of the lattice Boltzmann codes used in this thesis; appendix B describes some of the Grid computing techniques which were necessary for the simulations of chapter 4. Chapter 5 summarises the work, and makes suggestions for further research and improvement.
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Ge, Fei. "The lattice Boltzmann method dedicated to image processing." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI012.
Abstract:
La méthode de Boltzmann sur réseau est un outil de simulation numérique dont la formulation à l'échelle mésoscopique permet d'éviter la résolution d'une équation différentielle, et repose sur des mécanismes de propagation et de collision au cours du temps, de distributions de particules se propageant sur un réseau régulier. Si les lois de conservation sont imposées en chaque nœud du réseau, alors la solution générée correspondra à la modélisation de phénomènes physiques à l'échelle macroscopique. Dans ce contexte la méthode de Boltzmann est tout à fait adaptée pour résoudre un problème de mécanique des fluides qui équivaut à résoudre indirectement l'équation de Navier-Stokes. Récemment des travaux en traitement d'images ont été réalisés en adaptant la méthode de Boltzmann sur réseau à des opérations de segmentation, de dé bruitage, etc. Par ailleurs la méthode Boltzmann est intrinsèquement adaptée au calcul parallèle sur cartes graphiques permettant ainsi d'optimiser les temps de calculs. Dans ce cadre, l'objectif de cette thèse est de développer une stratégie générale de segmentation multi-seuils appliquée à des données 3D. L'élaboration d'une fonction de collision originale couplée à un algorithme des k-moyennes réalisant une division en "K" partitions ("clusters") des niveaux de gris de l'image considérée, permet une segmentation efficace à seuils multiples. La précision et l’efficacité de la solution proposée ont été validées sur des images de références et sur des séquences d'imagerie médicale traitant d’anévrismes cérébraux. Egalement la méthode proposée couplant la méthode de Boltzmann et la méthode des k-moyennes, a été testée sur cartes graphiques n’VIDIA attestant que la méthode proposée permet une accélération des calculs d'un facteur au moins supérieur à cent et avec une précision identique relevée notamment lors de la segmentation de la paroi d'anévrismes intracrâniensLattice Boltzmann Method (LBM) is a numerical tool for solving partial differential equation, LBM being a mesoscopic model dealing with the material containing a quantity of particles in order to simulate macroscopic phenomenon. As a numerical tool LBM has proved its capability to simulate complex fluid flow behaviours and more recently to process medical images. In the framework of image analysis, LBM is implemented to perform de-noising operation, image boundary detection and image segmentation. In addition, LBM has advantage of strong amenability to parallel computing, especially on low-cost, powerful graphics hardware (GPU).In this direction, the main purpose of this thesis is to develop a general parallel computational segmentation algorithm. We have proved the efficiency of the proposed original method through the segmentation of the wall of an aneurysm and associated with parent blood vessels, whole cerebral data-set and stent-assisted aneurysm. The parallel segmentation algorithm has been run on nVIDIA graphic card, and demonstrates that the speedup has been improved by more than 100 times under the same precision
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Rannou, Guillaume. "Lattice-Boltzmann method and immiscible two-phase flow." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26560.
Abstract:
Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2009.Committee Chair: Cyrus K. Aidun; Committee Member: Marc K. Smith; Committee Member: S. Mostafa Ghiaasiaan. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Mazhari, Seyed Babak. "An assessment of lattice Boltzmann method for swallowing simulations." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/58288.
Abstract:
Lattice Boltzmann is a fixed grid particle based method originated from molecular dynamics which uses a kinetic-based approach to simulate fluid flows. The fixed grid nature and simplicity of lattice Boltzmann algorithm makes it an appealing approach for preliminary swallowing simulations. However, the issues of compressibility effect and boundary/initial condition implementation can be the source of instability and inaccuracy especially at high Reynolds simulations. The current work is an assessment of the lattice Boltzmann method with respect to high Reynolds number flow simulations, compressibility effect of the method, and the issue of boundary and initial condition implementation. Here we investigate the stability range of the lattice Boltzmann single relaxation and multi relaxation time models as well as the issue of consistent boundary/initial condition implementation. The superior stability of multi relaxation time (MRT) model is shown on the lid-driven cavity flow benchmark as a function of Reynolds number. The computational time required for the SRT model to simulate the li-driven cavity flow at Re=3200 is about 14 times higher than the MRT model and it’s shown that computational time is related to the third power of lattice resolution. It is suggested that single relaxation time model is inefficient for simulations with moderately high Reynolds number Re>1000 and the use of multi relaxation time model becomes necessary. Compressibility effect is the next topic of study where the incompressible lattice Boltzmann method is introduced. The compressibility error of the method surpasses the spatial discretization error and becomes the dominant source of error as the flow Reynolds number increases. It is shown on a 2D Womersley flow benchmark that the physical time step required for LBM is about 300 times larger than the physical time step of the finite volume implicit solver while generating results with the same order of accuracy at Re=2000. Due to the compressibility error inherent to the method, lattice Boltzmann is not recommended for preliminary swallowing simulations with high Reynolds number, since implicit time advancement methods can generate results with the same order of accuracy in noticeably less computational time.Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate
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Carvalho, Junior Paulo Roberto de. "GPU Communication Performance Engineering for the Lattice Boltzmann Method." reponame:Repositório Institucional da UFPR, 2016. http://hdl.handle.net/1884/45773.
Abstract:
Orientador : Prof. Dr. Daniel WeingaertnerDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Exatas, Programa de Pós-Graduação em Informática. Defesa: Curitiba, 10/08/2016
Inclui referências : f. 59-62
Área de concentração: Ciência da computação
Resumo: A crescente importância do uso de GPUs para computação de propósito geral em supercomputadores faz com que o bom suporte a GPUs seja uma característica valiosa de frameworks de software para computação de alto desempenho como o waLBerla. waLBerla é um framework de software altamente paralelo que suporta uma ampla gama de fenômenos físicos. Embora apresente um bom desempenho em CPUs, testes demonstraram que as suas soluções de comunicação para GPU têm um desempenho ruim. Neste trabalho são apresentadas soluções para melhorar o desempenho, a eficiência do uso de memória e a usabilidade do waLBerla em supercomputadores baseados em GPU. A infraestrutura de comunicação proposta para GPUs NVIDIA com suporte a CUDA mostrou-se 25 vezes mais rápida do que o mecanismo de comunicação para GPU disponíveis anteriormente no waLBerla. Nossa solução para melhorar a eficiência do uso de memória da GPU permite usar 55% da memória necessária por uma abordagem simplista, o que possibilita executar simulações com domínios maiores ou usar menos GPUs para um determinado tamanho de domínio. Adicionalmente, levando-se em consideração que o desempenho de kernels CUDA se mostrou altamente sensível ao modo como a memória da GPU é acessada e a detalhes de implementação, foi proposto um mecanismo de indexação flexível de domínio que permite configurar as dimensões dos blocos de threads. Além disso, uma aplicação do Lattice Boltzmann Method (LBM) foi desenvolvida com kernels CUDA altamente otimizados a fim de se realizar todos os experimentos e testar todas as soluções propostas para o waLBerla. Palavras-chave: HPC, GPU, CUDA, Comunicação, Memória, Lattice Boltzmann Method, waLBerla.
Abstract: The increasing importance of GPUs for general-purpose computation on supercomputers makes a good GPU support by High-Performance Computing (HPC) software frameworks such as waLBerla a valuable feature. waLBerla is a massively parallel software framework that supports a wide range of physical phenomena. Although it presents good performance on CPUs, tests have shown that its available GPU communication solutions perform poorly. In this work, we present solutions for improving waLBerla's performance, memory usage e_ciency and usability on GPUbased supercomputers. The proposed communication infrastructure for CUDA-enabled NVIDIA GPUs executed 25 times faster than the GPU communication mechanism previously available on waLBerla. Our solution for improving GPU memory usage e_ciency allowed for using 55% of the memory required by a naive approach, which makes possible for running simulations with larger domains or using fewer GPUs for a given domain size. In addition, as CUDA kernel performance showed to be very sensitive to the way data is accessed in GPU memory and kernel implementation details, we proposed a flexible domain indexing mechanism that allows for configuring thread block sizes. Finally, a Lattice Boltzmann Method (LBM) application was developed with highly optimized CUDA kernels in order to carry out all experiments and test all proposed solutions for waLBerla. Keywords: HPC, GPU, CUDA, Communication, Memory, Lattice Boltzmann Method, waLBerla.
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Axner, Lilit. "High performance computational hemodynamics with the Lattice Boltzmann method." [S.l. : Amsterdam : s.n.] ; Universiteit van Amsterdam [Host], 2007. http://dare.uva.nl/document/54726.
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TORQUATO, MARIANA LUISA DE LIMA. "EMULSION FLOW THROUGH CONSTRICTED CAPILLARY USING LATTICE-BOLTZMANN METHOD." PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2015. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=25700@1.
Abstract:
PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIROA injeção de emulsão em meio poroso como método de recuperação avançada pode se tornar realidade na operação de campos de petróleo devido à maior rigidez no descarte de água produzida e aos potenciais ganhos na produção de óleo. Para entender o comportamento macroscópico desta técnica de EOR, é necessário compreender o fenômeno microscópico. Com este objetivo, fez-se a modelagem numérica do escoamento de uma gota imersa em fase contínua escoando em capilar restrito utilizando o método de Lattice-Boltzmann. Este método foi escolhido devido à sua facilidade de ser aplicado em geometrias complexas de rocha e fluido e ao bom compromisso na representação dos fenômenos de microescala. Para entender a influência de cada parâmetro, foram realizadas diversas simulações em domínio tridimensional, alterando a velocidade do fluxo, a razão de viscosidades dos fluidos, a relação entre os diâmetros da gota e do tubo e a magnitude da tensão interfacial. Observou-se que a passagem da gota pela restrição causa uma redução na mobilidade do escoamento, representada por um aumento na perda de carga, pela conjunção dos efeitos viscosos e capilares. Obteve-se correlação negativa do fator redutor de mobilidade com a razão de viscosidade e com o tamanho da gota, assim como fora determinado numericamente por Roca-Reyes (2011) com o método level-set. Foi notada uma pequena sensibilidade de ao número de capilaridade, assim como estabelecido experimentalmente por Robles-Castillo (2011). Verificou-se a importância de se determinar o conjunto adequado de parâmetros do sistema para ter sucesso na implantação de injeção de emulsões.
Emulsion injection in porous medium as an Enhanced Oil Recovery method can turn out to be reality in the operation of onshore and offshore fields, due to increasing rigidity in the disposal of produced water and also due to the potential additional oil production. In order to understand macroscopic behavior of this EOR method, it is necessary to understand the microscopic phenomenon. With this objective, it was performed the numerical modeling of the flow of a droplet immerse in continuous phase through a constricted capillary using the Lattice-Boltzmann method. This method was chosen due to its simplicity on being applied to complex rock geometries and multiphasic flow and due to its good commitment in representing microscopic phenomena. Focusing on understanding the influence of each parameter on flow behavior, several simulation studies were performed altering flow velocity, viscosity ratio, ratio between droplet s and pipe s diameter and interfacial tension. A reduction in mobility is observed as the droplet passes through the restriction caused by the conjunction of viscous and capillary effects. A negative correlation of mobility reduction factor in relation to the viscosity ratio and to droplet size was noticed, as it had been observed before by Roca-Reyes (2011) in a numerical implementation of level-set method. Weak correlation between and capillary number was determined, as in previous experimental essay performed by Robles-Castillo (2011). In this study, it was verified the importance of determining the appropriate set of system parameters, in order to achieve success in the implementation of emulsion injection.
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De, Anindya Kanti. "Numerical Modeling of Microscale Mixing Using Lattice Boltzmann Method." Diss., Virginia Tech, 2008. http://hdl.handle.net/10919/27425.
Abstract:
Recent advancements in microfabrication technology have led to the development of micro-total analytical systems (μ-TAS), more popularly known as lab-on-a-chip (LOC) devices. These devices have a relatively small size and are capable of performing sample and reagent handling steps together with analytical measurements. Rapid mixing is essential in such microfluidic systems for various applications e.g., biochemical analysis, sequencing or synthesis of nucleic acids, and for reproducible biological processes that involve cell activation, enzyme reactions, and protein folding.
In this work a numerical model is developed using a lattice Boltzmann method (LBM) to study microscale mixing. The study involves two mixing methods, namely, electroosmotic mixing and magnetic assisted mixing. A single component LBM model is developed to study electroosmotic flow in a square cavity. Mixing is studied by introducing two types of tracer particles in the steady electroosmotic flow and characterized by various mixing parameters. The results show that rapid mixing can be achieved by using a steady electric field and a homogeneous zeta potential.
A multicomponent LBM method is also developed to study magnetic assisted mixing in a channel configuration. The ferrofluid flow is influenced by two magnets placed across a microchannel. The interacting field induced by these magnets promotes cross-stream motion of the ferrofluid, which induces its mixing with the other nonmagnetic fluid. Two fluids, one magnetic and another non-magnetic fluid, are introduced in a channel, when two magnets are placed across it at a distance apart. In the presence of the magnetic field, the magnetic fluid tries to follow a zig-zag motion generating two rolls of vortices thereby enhancing mixing. A parametric study characterizes the effects of diffusivity, magnetic field strength, and relative magnet positions on a mixing parameter. Mixing is enhanced when the magnetic field strength and diffusivity are increased. However, contrary to the observed trend, placing the magnets very close to each other axially results in local ferrofluid agglomeration rather than promoting mixing.Ph. D.
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Jones, Bruce. "Characterisation of porous media using the lattice Boltzmann method." Thesis, Swansea University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678453.