Dissertations / Theses on the topic 'LBM (Méthode de Lattice Boltzmann)'
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Wissocq, Gauthier. "Investigation of lattice Boltzmann methods for turbomachinery secondary air system simulations." Thesis, Aix-Marseille, 2019. http://www.theses.fr/2019AIXM0635.
This 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
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.
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
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.
Reducing 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
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.
In 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
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.
The 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
Abassi, Wafik. "Investigations expérimentales et modélisations numériques par la méthode de Lattice Boltzmann (LBM) pour l'étude des transferts dans les écoulements tourbillonnaires." Nantes, 2014. https://archive.bu.univ-nantes.fr/pollux/show/show?id=caaf67b3-c66e-4925-a786-000eb6287dea.
The numerical and experimental work focuses on the study of instabilities and transfers in two configurations of vortex flows: The wake behind an obstacle and Taylor-Couette flow. A numerical simulation based on the method of "Lattice Boltzmann" (LBM) has been developed to study the dynamics of the confined flow around an obstacle in a 2D and 3D geometry. An extension of this code was performed to enable the wall shear stress simulations (mass transfer). Thereafter, experimental investigations of the mass transfer mechanisms in the wake of an obstacle and in a Taylor-Couette flow were initiated. The results were compared to that obtained by simulation (LBM). The main objective is to check the validity of the developed code and to highlight the LBM performances. Experimental results, qualitative (visualizations) and quantitative (PIV and polarography) were performed to characterize the vortex flows studied. A post-processing of PIV measurements, using vortex detection criteria and POD method were has developed. The polarographic technique, through single probes and one tri-segmented sensor, has contributed to the determination of the wall shear stress. Synchronization between PIV measurements and polarography method, was carried out to understand the spatiotemporal interactions between vortices and the walls
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.
The 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
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.
The 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
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.
The 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
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.
In 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
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.
This 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
Nguyen, Khac Lan. "Modèles de champ de phase et modèles Lattice Boltzmann pour la segmentation 3D de tumeurs en imagerie ultrasons hautes fréquences." Thesis, La Rochelle, 2019. http://www.theses.fr/2019LAROS011.
In this thesis, we are interested in the problem of 3D segmentation of skin tumors in high frequency ultrasound images. We focus mainly on two questions: how best to estimate the volume of tumors (in accordance with references produced by dermatologists) and how to produce algorithms whose computation times are close to real time? First, we describe a new model, log-likelihood Cahn-Hilliard (LLCH), based on a variational formulation coupling a data attachment term computed from non-parametric estimates and a regularization term derived from a phase transition dynamic (Allen Cahn reaction diffusion equation). This model is tested with a first multigrid implementation using exact solutions calculated with a Lie splitting. Secondly, we are interested in the possibility of implementing the LLCH model using lattice Boltzmann methods (LBM). The underlying dynamic is not physical in nature, so this implementation is not direct and is subject to instability problems. We show that, due to the specificities of the data attachment term, the BGK schemes, with simple relaxation time, do not ensure sufficient stability. We then use MRT schemes, with multiple relaxation times, which allow us to gain stability by introducing additional parameters. The adjustment of the so-called quartic parameters makes it possible to obtain fourth-order exact schemes that are numerically stable. Tests performed on a clinical database with ground truth provided by dermatologists show that the results obtained with the two proposed implementations are much better than those obtained with level sets methods and that our model is a good alternative to overcome the problem of underestimation of tumor volume. The computation times, for 3D images of about 70 million voxels, are very short and well adapted for practical use in medical environments
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.
Renewable 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
Jurczuk, Krzysztof. "Calcul parallèle pour la modélisation d'images de résonance magnétique nucléaire." Thesis, Rennes 1, 2013. http://www.theses.fr/2013REN1S089.
This 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
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.
In 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
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.
Asta, Adelchi Jacques. "Listening to the electrical noise for nanofluidic sensing." Thesis, Sorbonne université, 2019. http://www.theses.fr/2019SORUS444.
Moving 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
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.
Over 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
Vogel, Laure. "Influence de l'hétérogénéité physique des microenvironnements du sol sur les transformations microbiennes du carbone : exploration à l'aide d'un modèle de Boltzmann sur réseau." Thesis, Paris, AgroParisTech, 2015. http://www.theses.fr/2015AGPT0061.
Heterotrophic microorganisms control soil organic matter (SOM) decomposition and may thus have a key importance in climate regulation. Heterogeneous abiotic conditions in soil microenvironments are thought to affect soil decomposers activity by controlling nutrient accessibility through solute transport (diffusion, advection) and sorption processes. Microhabitat – or pore – scale thus appears relevant to study biodegradation processes, but is also challenging to investigate by experimental means.A discrete model was created to explore the effect of abiotic conditions in soil microenvironments on biodegradation kinetics. It results from the coupling of a zero-dimensional soil carbon model and a lattice Boltzmann model (TRT-LBM [Ginzburg, 2005]). It simulates diffusion and biodegradation at the pore scale, as affected by explicitly described structural factors, such as the 3D pore architecture (approximated by discrete images), water distribution under unsaturated conditions and the spatial arrangement of substrates and decomposers – viewed here as immobile bacteria. The model was tested in a range of scenarios depicting contrasted abiotic conditions. The variability in biodegradation kinetics was analyzed to infer the contributions of physical factors. This source of variability was compared to uncertainties associated to biological metabolism description. Finally, experiments manipulating structural factors were performed to confront observed and simulated trends
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.
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.
Haughey, Kyle J. "Boundless Fluids Using the Lattice-Boltzmann Method." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/117.
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.
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.
Gokaltun, Seckin. "Lattice Boltzmann Method for Flow and Heat Transfer in Microgeometries." FIU Digital Commons, 2008. http://digitalcommons.fiu.edu/etd/64.
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.
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.
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.
Flüssigkeitsfilmströmungen 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
Dugast, Florian. "Optimisation topologique en convection thermique avec la méthode de Lattice Boltzmann." Thesis, Nantes, 2018. http://www.theses.fr/2018NANT4056/document.
Heat transfer enhancement is an important research area to improve the efficiency of energy systems, especially for heat exchangers. There are different ways of optimizing such systems as the choice of flow regime or the modification on the fluid channels geometry. This thesis is focused on the latter option with the development of a topology optimization method. The number of design parameters involved in this technique is important (several thousands) so a gradient-based method is employed. The calculation of the cost function gradient with respect to the design variables is done with an adjoint-state method. The forward problem is solved with the Lattice Boltzmann Method (LBM). The simple implementation of the LBM boundary conditions is an interesting feature for topology optimization. The LBM algorithm is also highly parallelizable and GPU cards have been used in this thesis to obtain fast computational times. The efficiency of the LBM is important because the forward problem must be solved at each optimization step. Then, the optimization domain is composed of either solid of fluid elements. This material distribution is defined by a Level-Set Function (LSF). This is a continuous function in which the zero contour defines the fluid/solid interface, allowing an accurate description of both domains. The proposed optimization method has been tested for different objectives (minimization of the mean temperature, maximization of heat transfer rate) and constraints (pressure drops limitation, fixed porosity)
Benamour, Malek. "Développement d'une méthode de pénalisation volumique en lattice Boltzmann : application aux domaines mobiles." Thesis, La Rochelle, 2015. http://www.theses.fr/2015LAROS017/document.
Flows around moving bodies are the subject of several numerical and experimental studies. The work presented in this document deals with the implementation of a volume penalization technique in a lattice Boltzmann model (LBM), in order to compute flows around moving obstacles. The LBM, which is accurate and easy to implement, has been successfully applied in fluid mechanics during the last decades. It was thus chosen in the present work, for flow computation. Furthermore, the volume penalization technique consists in introducing a volume penalization term into the equation that needs to be solved, in order to take into account the influence of the obstacle on the fluid domain. Since this equation is solved on both fluid and solid domains, the boundary conditions at the fluid-solid interface are naturally applied. Hence this technique seems easy to implement in a lattice Boltzmann framework. In the first chapter, the foundations and the main features of the lattice Boltzmann method are recalled, and several test cases that we simulated are presented. The second chapter deals with a literature review of the techniques developed for the simulation of fluid structure interaction problems in combination with the LBM. In the third chapter, the volume penalization method combined with the LBM was first applied to the one dimensional Burgers equation, considering motionless and moving obstacles (forced motion, and coupling between the fluid force calculated with the penalized Burgers equation and the motion of the obstacle). The combination of the volume penalization approach and the LBM was then employed to solve the incompressible NavierStokes equations, for cases of flows past motionless obstacles (flows over a square obstacle, and past a circular cylinder), and past an oscillating cylinder (where forced and free oscillations of the cylinder were simulated). Finally, this method was also applied to a symmetric Couette flow. For all these simulated cases, a good agreement with numerical results obtained with other techniques, and with results found in literature, was obtained
Kostenko, Romaric. "Simulation d'écoulements non-newtoniens en milieu poreux macroscopique par la méthode de lattice-Boltzmann." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLS561.
A non-newtonian fluid is a fluid which relation between it's shear rate and the stress under which it is put, is not linear. In a porous medium, the stress imposed to the fluid depends on the imposed pressure, but also on the pores size, and therefore on the macroscopic scale permeability. Some fluids have a rheology such that the fluid show a change of behaviour reaching a yield stress. If the pore size is random, then the fluid will present heterogeneous regime changes in the medium. The flow will then show a first regime where the whole fluid will be under the threshold, a regime where the whole fluid will be far above the threshold, and an intermediate regime for which both rheologies coexists. We are interested in intermediate regime for the flow of non-newtonian fluids in macroscopic porous media, and study it with numerical simulations. More particularly, we look at the flow of a Bingham fluid and that of a Carreau fluid. The Bingham fluid doesn't flow under a yield stress. Under the threshold, it behaves as a solid. Beyond, it's shear-rate/stress relation is an affine law. Carreau fluids have a shear-rate/stress relation that change regime between that of a newtonian fluid, and a power law. The macroscopic scale study is done simulating a Darcy-Brinkman law in a heterogeneous permeability field. We use for our simulations the lattice-Boltzmann method, on a regular node grid, and more specifically Irina Ginzburg two relaxation-time scheme. For each fluid, we study the flow-pressure relationship, as well as the geometric properties and the multi-scale properties in the fluid regions in the same flow regime (clusters), properties such as their size and shape. We also link these geometrical properties to the percolation theory, which studies the behaviour of randomly opening node maps and predicts fractal properties
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.
Ge, Fei. "The lattice Boltzmann method dedicated to image processing." Thesis, Lyon, 2020. http://www.theses.fr/2020LYSEI012.
Lattice 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
Suss, Alexandre. "Couplage des méthodes Navier-Stokes et Lattice Boltzmann pour les simulations aérodynamiques instationnaires." Electronic Thesis or Diss., Paris, HESAM, 2023. http://www.theses.fr/2023HESAC044.
Computational Fluid Dynamics has become an important design tool for the aeronautical industry. While most industrial simulations are carried out using a RANS (Reynolds Averaged Navier-Stokes) approach, this approach is showing its limitations when it comes to finely characterising unsteady turbulent flows or studying broadband aeroacoustic phenomena. In this context, manufacturers are increasingly looking for high-performance, high-fidelity simulation tools. Two numerical methods are showing particular promise for performing industrial-scale high-fidelity flow simulations in the near future: the Navier-Stokes method and the lattice Boltzmann method (LBM). These two approaches are often presented as competing, but each has its own specific features and requirements. The research carried out as part of this thesis has helped to provide a better understanding of the respective advantages and disadvantages of these two methods, revealing that the lattice Boltzmann and Navier-Stokes methods complement each other rather than compete. The study is divided into two main parts. Firstly, a comprehensive and rigorous comparison of the lattice Boltzmann and Navier-Stokes methods was conducted. The numerical methods were examined in various aspects, such as their intrinsic dissipation and dispersion, their performance in a parallel computing environment (HPC) and their ability to efficiently simulate various canonical LES problems at a given level of accuracy. This study has offered a new perspective on the properties of the lattice Boltzmann and Navier-Stokes methods, providing several decision aids to help the CFD community choose one method over the other based on the type of application and the fidelity level required. Secondly, this PhD explored the possibility of coupling the lattice Boltzmann and Navier-Stokes methods. Indeed, while the LBM offers many benefits, there are still some issues and inefficiencies, especially regarding the numerical treatment of the near-wall zone. The Cartesian shape of the meshes imposed by the method is one of the main reasons for this problem. In contrast, classical Navier-Stokes approaches are particularly effective in the vicinity of the wall thanks to the use of curvilinear meshes with very high aspect ratios and implicit time integration methods. Therefore, an innovative hybrid numerical method was developed based on a zonal coupling of the lattice Boltzmann and Navier-Stokes methods. This approach was then extended to the case of overset meshes (Chimera approach). Numerous validations have demonstrated the value of this strategy. In particular, this new hybrid method makes it possible to reduce the cost of direct aeroacoustic simulations while maintaining optimum accuracy
Shrestha, Kalyan. "Simulation of wall-bounded turbulent convective flows by finite volume Lattice Boltzmann method." Thesis, Lille 1, 2015. http://www.theses.fr/2015LIL10106/document.
Lattice Boltzmann Method (LBM) has become a viable alternative to Navier-Stokes Direct Numerical Simulations (DNS) in fluid dynamics research. The key of this success is the accuracy/simplicity and parallelization compliant property of the stream-collision algorithm. One shortcoming however, comes from the limitation to spatially uniform cubic grids. To overcome this, several LBM extension to non-homogeneous grids have been proposed. These techniques have been reviewed in this thesis. Such review suggests that a better refinement technique should fulfill some properties: obey conservation laws and be stable. This suggests a pathway to adopt Finite Volume approaches (FV LBM). A review on such volumetric approach to LBM concludes that although interesting, at present such methods suffer from several drawbacks. In this study, a new FV discretization method for the Lattice Boltzmann equation that combines high accuracy with limited computational cost is presented. In order to assess the performance of the FV method we carry out a systematic comparison, focused on accuracy and computational performances, with the standard streaming (ST) Lattice Boltzmann equation algorithm. In particular we aim at clarifying whether and in which conditions the proposed algorithm, and more generally any FV algorithm, can be taken as the method of choice in fluid-dynamics LB simulations. We report the first successful simulation of high-Rayleigh number convective flow performed by a Lattice Boltzmann FV based algorithm with wall grid refinement
Feng, Yongliang. "Multiscale Simulation Using Thermal Lattice Boltzmann Method with Turbulence Effects." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066254.
The simulation of fluid flows and heat transfer of multiscale phenomena orprocesses is one of the most challenging domains from the theoretical aswell as the numerical modeling point of view. It is difficult to model andsimulate multiscale problems using conventional computational fluid dynamicsmethods. As an approach based on the mesoscopic kinetic equationfor fluids and has many distinctive features, the lattice Boltzmann method(LBM) is a recently developed method for simulating fluid flows, heat transferand complicated physical phenomena. However, the applications of latticeBoltzmann method in actual multiscale problem are still in explorationstage. In order to enlarge the application scope of lattice Boltzmann methodfor multiscale simulation, the present work has conducted systematic researchon combination of LBM and macroscopic methods, thermal lattice Boltzmann models and turbulence simulation using LBM. The major contributions of this dissertation are summarized as follows: 1. A multiscale coupling LBM-FVM is constructed for unsteady fluid flows and a general reconstruction operator between LBM and FVMis proposed for information transfer. 2. A three-dimensional thermal lattice Boltzmann model is developed for thermal compressible flows with variable density in low Machnumber limit. Further more, a fully compressible lattice Boltzmann model with factorization symmetry is proposed for simulating high compressible flow. 3. An asymptotic preserving finite volume scheme LBM and a fractional propagation half step collision LBM are proposed for simulating high subsonic and transonic flows. 4. Large eddy simulation for turbulence is studied in framework of thermallattice Boltzmann method. Wall modeled LES using thermalLBM is developed for high Reynolds number flow
Grissa, Kods. "Numerical and Experimental Study of Heat Pipes Used in Solar Applications." Thesis, Chasseneuil-du-Poitou, Ecole nationale supérieure de mécanique et d'aérotechnique, 2018. http://www.theses.fr/2018ESMA0012/document.
Owing to the trend to development sustainability, solar systems (solar collector, solar concentrator, etc.) Are integrating (and asked to integrate even more) intensively residences and industries. In this context, two-phase systems like heat pipe seem highly effective because of their high heat transport capabilities and their passive operation in collectors’ technology. In view of the complexity of the heat pipes with a porous structure in this kind of application,most of the existing systems on the market use thermosyphons. Thus, the growing need of reliable and more efficient thermal control solutions is increasing for such systems. This thesis work focuses on the performance characterization of heat pipes with porous structure used in solar applications. A numerical study has been performed to model and simulate the behavior of a typical heat pipe using the Lattice Boltzmann method. An experimental study has also been done to characterize the performance of three prototypes tested under different conditions (condenser temperature, heat input and inclination angle). The effects induced by several parameters including the filling rate, working fluid and symmetry of the applied heat on the performance of these devices has also been investigated. In particular, heating asymmetry is found to induce dry-out earlier, all other things being equal. Optimal inclination is also determined where is balanced the maximum solar heat available and received by the heat pipe and the gravity-assisted liquid flow inside that device
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.
Pazdniakou, Aliaksei. "Lattice models in porous media studies." Paris 6, 2012. http://www.theses.fr/2012PA066116.
The thesis adresses the study of acoustic waves and multiphase flows in porous media. For the simulation of fluid flows, the lattice Boltzmann method is selected. The method is used for simulation of multiphase flows as well as for acoustic waves in a fluid. The method represents an alternative approach to the description of the fluid dynamics based on the kinetic theory of gases. In order to simulate acoustic waves in an elastic solid, the LSM (Lattice Spring model) is selected. In the framework of the LSM, the medium is replaced by a cubic lattice. The nodes of the lattice are connected by springs of two types. The obtained dynamic equations correspond to those of the theory of elasticity. The method is applied to calculate the compressional and shear wave velocities in reconstructed porous media for various frequencies and porosity values. The two models (LBM and LSM) are coupled by the boundary conditions in order to study acoustic waves in saturated porous media. Two principal approaches exist to simulate acoustic waves in saturated porous media using our coupled (LBM+LSM) model. The first is based on the homogenization theory and the second on the real time simulation of acoustic waves. The two methods are applied for calculation of the acoustic waves velocities in saturated reconstructed porous media. The results are systematically analysed. The codes are parallelized by using OpenMP in order to reduce significantly the program run time
Bechereau, Marie. "Élaboration de méthodes Lattice Boltzmann pour les écoulements bifluides à ratio de densité arbitraire." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLN059/document.
Two-fluid extensions of Lattice Boltzmann methods with free boundaries usually consider ``microscopic'' pseudopotential interface models. In this paper, we rather propose an interface-capturing Lattice Boltzmann approach where the mass fraction variable is considered as an unknown and is advected. Several works have reported the difficulties of LBM methods to deal with such two-fluid systems especially for high-density ratio configurations. This is due to the mixing nature of LBM, as with Flux vector splitting approaches for Finite Volume methods. We here give another explanation of the lack of numerical diffusion of Lattice Boltzmann approaches to accurately capture contact discontinuities. To fix the problem, we propose an arbitrary Lagrangian-Eulerian (ALE) formulation of Lattice-Boltzmann methods. In the Lagrangian limit, it allows for a proper separated treatment of pressure waves and advection phenomenon. After the ALE solution, a remapping (advection) procedure is necessary to project the variables onto the Eulerian Lattice-Boltzmann grid.We explain how to derive this remapping procedure in order to get second-order accuracy and achieve sharp stable oscillation-free interfaces. It has been shown that mass fractions variables satisfy a local discrete maximum principle and thus stay in the range $[0,1]$. The theory is supported by numerical computations of rising bubbles (without taking into account surface tension at this current state of development).Even if our methods are currently used for inviscid flows (Euler equations) by projecting the discrete distributions onto equilibrium ones at each time step, we believe that it is possible to extend the framework formulation for multifluid viscous problems. This will be at the aim of a next work
Tekitek, Mohamed Mahdi. "Identification de modèles et de paramètres pour la méthode de Boltzmann sur réseau." Phd thesis, Université Paris Sud - Paris XI, 2007. http://tel.archives-ouvertes.fr/tel-00207541.
La première partie introduit et analyse la méthode.
La deuxième partie décrit une approche variationnelle pour l'assimilation de paramètres relatifs à la méthode du gaz de Boltzmann sur réseau. Une méthode adjointe discrète en temps est développée. L'algorithme est d'abord testé sur un écoulement de type Poiseuille linéaire (problème de Stokes), puis il est appliqué à un problème non linéaire. Des résultats encourageants sont obtenus pour un et deux paramètres inconnus.
Finalement la troisième partie décrit une adaptation des couches absorbantes de Bérenger. Il en résulte un modèle d'automate de Boltzmann à neuf vitesses discrètes. Une analyse des ondes réfléchies est ensuite réalisée entre deux milieux de Boltzmann à une dimension, ce qui permet d'obtenir un équivalent des formules de Fresnel pour les schémas de Boltzmann et de proposer des modifications du schéma à l'interface pour annuler les ondes réfléchies. En deux dimensions, la même analyse d'ondes réfléchies met en évidence l'apparition de modes de Knudsen et des ondes transverses qui rendent l'analyse complexe.
Grondeau, Mikaël. "Modélisation des effets de sillage d'une hydrolienne avec la méthode de Boltzmann sur réseau." Thesis, Normandie, 2018. http://www.theses.fr/2018NORMC257/document.
In a global context where access to energy is a major problem, the exploitation of tidal currents with tidal turbines is of particular interest. Flows in areas with high energy potential suitable for the installation of tidal turbines are often highly turbulent. However, the ambient turbulence has a strong impact on the surrounding hydrodynamics and the turbine operation. A precise prediction of turbulence and wake is fundamental to the optimization of a tidal farm. A numerical model of the flow around the turbine must therefore be accurate and take into account the ambient turbulence. A tool based on the Lattice Boltzmann Method (LBM) is used for this purpose, in combination with a Large Eddy Simulation (LES) approach. The LBM is an unsteady method for modelling fluid flows. A synthetic turbulence method is implemented to take into account the ambient turbulence of tidal sites. Complex geometries, potentially in motion, are modelled using the Immersed Boundary Method (IBM). The implementation of a wall model is carried out in order to reduce the cost of the simulations. These tools are then used to model a turbine in a turbulent environment. The calculations, performed at two different turbulence rates, are compared with experimental and NS-LES results. The LBM-LES models are then used to analyze the wake of the turbine. In particular, it is observed that a low turbulence rate has a significant impact on the propagation of tip-vortices
Pepona, Marianna. "Modèle de frontières immergées pour la simulation d'écoulements de fluide en interaction avec des structures poreuses." Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4349/document.
A wide spectrum of engineering problems is concerned with fluid flows in interaction with porous structures, ranging from small length-scale problems to large ones. These structures, often of complex geometry, may move/deform in response to the forces exerted by the surrounding flow. Despite the advancements in computational fluid dynamics, the numerical simulation of such configurations - a valuable tool for the study of the flow physics involved - remains a challenging task.The aim of the present work is to propose a numerical model for the macroscopic simulation of fluid flows interacting with moving porous media of complex geometry, that is easy to implement and can be used in a range of applications. To achieve this, the Lattice Boltzmann method is employed for solving the flow in porous media at the representative elementary volume scale. For the implementation of the desired body motion, the concept of the Immersed Boundary method is adopted. In this context, a novel model is proposed for dealing with moving volumetric porous media, whose resistance to the surrounding flow obeys the Brinkman-Forchheimer-extended Darcy law. The algorithm is initially tested for flow past a static cylinder. The simplicity of this academic test case allows us to assess in detail the accuracy of the proposed method. The model is later used to simulate fluid flows around and through moving porous bodies, both in a confined geometry and in open space. We are able to demonstrate the Galilean invariance of the macroscopic volume-averaged flow governing equations. Excellent agreement with reference results is obtained in all cases
Hosseini, Seyed Ali. "Development of a lattice Boltzmann-based numerical method for the simulation of reacting flows." Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASC012.
The lattice Boltzmann (LB) method has emerged as an efficient alternative to classical methods for fluid flow simulation. It can also potentially be used for such complex flows as those involved in low Mach number combustion involving large numbers of field variables, temperature variations, variable properties and spanning multiple scales. Given the variations in diffusion parameters and existing stability issues in the LB, the choice of the collision operator is of the utmost importance. Furthermore, dilatation effects must be introduced as the original LB scheme was developed for isothermal flows. The flow solver has to be supplemented with components modeling balance equations for the energy and species mass fields.In the present work, first the LB solver (with plethora of collision operators) is analyzed using approaches like the von Neumann method. A variety of collision models including multiple relaxation, regularized, and equilibrium distribution functions, like different orders of the Hermite expansion, and the entropic equilibrium are considered. Then, two different approaches for introducing dilatation into the flow solver are proposed and validated. These approaches include one relying on a decomposition of pressure into a uniform thermodynamic and fluctuating hydrodynamic components, and a fully compressible formulation relying on a thermal Hermite expansion of the equilibrium. Appropriate collision operators, resulting on the widest stability domain for the latter are also proposed. In addition, minimalist LB solvers appropriate for the targeted flows are derived to model energy and species mass transport. Contrary to the classical passive scalar lattice Boltzmann models, the proposed formulations are not limited to constant specific heat capacity and/or density and include higher-order effects such as viscous dissipation heating. A variety of cases, covering premixed and diffusion flames, 1-, 2- and 3-D flows are then considered for validation of the overall solvers
Corre, Samuel. "Méthodes de Boltzmann sur réseau pour la simulation numérique de certains systèmes d'advection-réactiondiffusion provenant de la physique et de la biologie, et analyse mathématique et numérique de problèmes issus du domaine biomédical cardio-vasculaire." Thesis, Rennes, INSA, 2018. http://www.theses.fr/2018ISAR0022/document.
In this thesis, we develop and analyze numerical techniques based on the lattice Boltzmann method LBM) for solving systems of nonlinear advection-diffusion-reaction equations from physics and biology. Wi BM, problems relating to averaged quantities (density, potential, velocities, etc.) are expressed at the particle scale. We approach the solution of Boltzmann equation relating to the behavior of a particle field and then we recompose the averaged quantities solutions of treated systems. In the first part, we develop an appropriate general framework to deal with several types of non-linear systems (parabolic, elliptic, or coupled, with real or complex variables), with applications to models such as Burger-Fisher, fluid flow in a porous medium, Helmoltz, Patlar-Keller-Segel, or Schrodinger. For each problem, we analyze the asymptotic behavior of the method, when the number of Knudsen tends to zero (by the development of Chapman-Enskog) and we perform the numerical analysis of convergence and stability of the method. In the second part, we have taken an interest in a realistic problem of cardio-vascular electrophysiology. We adapt the developed LBM method to approach e solutions of a bidomain type system for simulating the behavior of electrical potentials and ionic interactions in myocardial region. The study and modeling of this type of problem is a major health issue in the treatment of pathologies related, for example, to cardiac arrhythmia. Since our goal is to obtain realistic behaviors, we introduce time-delay operators into this coupled system in order to take into account delay in signal transmissions. Once the existence and uniqueness of solution have been demonstrated, we propose a series of simulations with realistic physical and biological parameters to validate the proposed method
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.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Eng & Built Env
Science, Environment, Engineering and Technology
Full Text
Horstmann, Tobias. "Méthodes numériques hybrides basées sur une approche Boltzmann sur réseau en vue de l'application aux maillages non-uniformes." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC027/document.
Despite the inherent efficiency and low dissipative behaviour of the standard lattice Boltzmann method (LBM) relying on a two step stream and collide algorithm, a major drawback of this approach is the restriction to uniform Cartesian grids. The adaptation of the discretization step to varying fluid dynamic scales is usually achieved by multi-scale lattice Boltzmann schemes, in which the computational domain is decomposed into multiple uniform subdomains with different spatial resolutions. For the sake of connectivity, the resolution factor of adjacent subdomains has to be a multiple of two, introducing an abrupt change of the space-time discretization step at the interface that is prone to trigger instabilites and generate spurious noise sources that contaminate the expected physical pressure signal. In the present PhD thesis, we first elucidate the subject of mesh refinement in the standard lattice Boltzmann method and point out challenges and potential sources of error. Subsequently, we propose a novel hybrid lattice Boltzmann method (HLBM) that combines the stream and collide algorithm with an Eulerian flux-balance algorithm that is obtained from a finite-volume discretization of the discrete velocity Boltzmann equations. The interest of a hybrid lattice Boltzmann method is the pairing of efficiency and low numerical dissipation with an increase in geometrical flexibility. The HLBM allows for non-uniform grids. In the scope of 2D periodic test cases, it is shown that such an approach constitutes a valuable alternative to multi-scale lattice Boltzmann schemes by allowing local mesh refinement of type H. The HLBM properly resolves aerodynamics and aeroacoustics in the interface regions. A further part of the presented work examines the coupling of the stream and collide algorithm with a finite-volume formulation of the isothermal Navier-Stokes equations. Such an attempt bears the advantages that the number of equations of the finite-volume solver is reduced. In addition, the stability is increased due to a more favorable CFL condition. A major difference to the pairing of two kinetic schemes is the coupling in moment space. Here, a novel technique is presented to inject the macroscopic solution of the Navier-Stokes solver into the stream and collide algorithm using a central moment collision. First results on 2D tests cases show that such an algorithm is stable and feasible. Numerical results are compared with those of the previous HLBM
Vienne, Lucien. "Simulation of multi-component flows by the lattice Boltzmann method and application to the viscous fingering instability." Thesis, Paris, CNAM, 2019. http://www.theses.fr/2019CNAM1257/document.
The lattice Boltzmann method (LBM) is a specific discrete formulation of the Boltzmann equation. Since its first premises, thirty years ago, this method has gained some popularity and is now applied to almost all standard problems encountered in fluid mechanics including multi-component flows. In this work, we introduce the inter-molecular friction forces to take into account the interaction between molecules of different kinds resulting primarily in diffusion between components. Viscous dissipation (standard collision) and molecular diffusion (inter-molecular friction forces) phenomena are split, and both can be tuned distinctively. The main advantage of this strategy is optimizations of the collision and advanced collision operators are readily compatible. Adapting an existing code from single component to multiple miscible components is straightforward and required much less effort than the large modifications needed from previously available lattice Boltzmann models. Besides, there is no mixture approximation: each species has its own transport coefficients, which can be calculated from the kinetic theory of gases. In general, diffusion and convection are dealt with two separate mechanisms: one acting respectively on the species mass and the other acting on the mixture momentum. By employing an inter-molecular friction force, the diffusion and convection are coupled through the species momentum. Diffusion and convection mechanisms are closely related in several physical phenomena such as in the viscous fingering instability.A simulation of the viscous fingering instability is achieved by considering two species in different proportions in a porous medium: a less viscous mixture displacing a more viscous mixture. The core ingredients of the instability are the diffusion and the viscosity contrast between the components. Two strategies are investigated to mimic the effects of the porous medium. The gray lattice Boltzmann and Brinkman force models, although based on fundamentally different approaches, give in our case equivalent results. For early times, comparisons with linear stability analyses agree well with the growth rate calculated from the simulations. For intermediate times, the evolution of the mixing length can be divided into two stages dominated first by diffusion then by convection, as found in the literature. The whole physics of the viscous fingering is thus accurately simulated. Nevertheless, multi-component diffusion effects are usually not taken into account in the case of viscous fingering with three and more species. These effects are non-negligible as we showcase an initial stable configuration that becomes unstable. The reverse diffusion induces fingering whose impact depends on the diffusion between species
Louërat, Mathilde. "Modélisation par la méthode Lattice Boltzmann de la diffusion de chaleur et d’humidité dans des matériaux biosourcés à partir de leur morphologie 3D." Thesis, Université Paris-Saclay (ComUE), 2017. http://www.theses.fr/2017SACLC006/document.
As thermal performance of buildings is increasing, the simulation codes used during design require more accurate construction material data. Moreover, the use of bio-based materials which are hygroscopic (their moisture content balances with the ambient moist air) is booming. Their thermal conductivity and mass diffusivity must therefore be accurately characterized. A key factor affecting these properties is the microstructure of the materials. This work is dedicated to the prediction of macroscopic properties of spruce and fibreboards (heterogeneous and anisotropic materials) from their real 3D morphology. This is obtained by synchrotron X-ray microtomography, a powerful and nondestructive technique to characterize the internal structure of materials. Image processing allows the segmentation of the solid and gaseous phases. To model heat and mass diffusion, we choose the Lattice Boltzmann method because of its simple numerical development, suitability for parallel computing and easy processing of complex morphologies. The equivalent thermal conductivity and mass diffusivity are calculated in three orthogonal directions for each material. The results highlight the influence of the internal structure and the strong anisotropy of the materials studied (ratio of 2 between tangential and longitudinal directions of wood for heat diffusion and of 30 for mass diffusion). The transverse thermal conductivity of the lightweight board is about 0,04 W m−1 K−1
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.
This 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
Bertolaccini, Jonathan. "Modélisation et simulation des écoulements de contre-courant de l'hélium superfluide par la méthode Boltzmann sur réseau." Thesis, Lyon, École normale supérieure, 2015. http://www.theses.fr/2015ENSL1063/document.
The exceptional thermal properties of superfluid helium, or He-II, are exploited to the cryogenic refrigeration of high power installations, although the underlying physical mechanisms remain poorly understood. The He-II can be described macroscopically as the superposition of two fluids in interaction: a normal fluid behaves as an ordinary liquid, and a superfluid without viscosity. In the presence of a heat source, a counterflow established between these two components. The heat dissipation by this counterflow is limited by the occurrence of instabilities in misunderstood condition; the wide dispersion of experimental data does not allow to discriminate between the different theoretical models. This thesis examines using numerical simulations the role of boundary conditions and the mutual coupling between the two components of the He-II in triggering instabilities in counterflow.An innovative lattice Boltzmann type approach was developed to model the mesoscopic scale interaction between the two components of the He-II. A code reproducing counterflow in 2D and 3D conducts has been developed and validated. The results obtained indicate amplified entrance effects for superfluid component, which generate abnormally high pressure drops. The head of these entrance effects mechanism has been studied and it is shown that it can distort the detection of the transition threshold in too short pipes; This may partly explain the dispersion of experimental data.To illustrate the power of the approach in a complex geometry, the wake of an obstacle in a counterflow was simulated. The presence of recirculation areas on both sides of the obstacle, already observed experimentally, is found and explained by a new mechanism using "virtual walls"