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Artykuły w czasopismach na temat "Méthode de Boltzmann sur réseau – Aérodynamique"
MARTIN, Sylvain, i Olivier BONNEFOY. "Méthode de Boltzmann sur réseau - Application à la mécanique des fluides". Mathématiques, grudzień 2019. http://dx.doi.org/10.51257/a-v1-bm5220.
Pełny tekst źródłaRozprawy doktorskie na temat "Méthode de Boltzmann sur réseau – Aérodynamique"
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.
Pełny tekst źródłaComputational 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
Hekmati, Abbas. "Analyse des évènements aérodynamiques à l'origine des émissions sonores à partir de simulations numériques". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2011. http://tel.archives-ouvertes.fr/tel-00734572.
Pełny tekst źródłaLestang, Thibault. "Numerical simulation and rare events algorithms for the study of extreme fluctuations of the drag force acting on an obstacle immersed in a turbulent flow". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN049/document.
Pełny tekst źródłaThis thesis discusses the numerical simulation of extreme fluctuations of the drag force acting on an object immersed in a turbulent medium.Because such fluctuations are rare events, they are particularly difficult to investigate by means of direct sampling. Indeed, such approach requires to simulate the dynamics over extremely long durations.In this work an alternative route is introduced, based on rare events algorithms.The underlying idea of such algorithms is to modify the sampling statistics so as to favour rare trajectories of the dynamical system of interest.These techniques recently led to impressive results for relatively simple dynamics. However, it is not clear yet if such algorithms are useful for complex deterministic dynamics, such as turbulent flows.This thesis focuses on the study of both the dynamics and statistics of extreme fluctuations of the drag experienced by a square cylinder mounted in a two-dimensional channel flow.This simple framework allows for very long simulations of the dynamics, thus leading to the sampling of a large number of events with an amplitude large enough so as they can be considered extreme.Subsequently, the application of two different rare events algorithms is presented and discussed.In the first case, a drastic reduction of the computational cost required to sample configurations resulting in extreme fluctuations is achieved.Furthermore, several difficulties related to the flow dynamics are highlighted, paving the way to novel approaches specifically designed to turbulent flows
Marié, Simon. "Etude de la méthode Boltzmann sur Réseau pour les simulations en aéroacoustique". Phd thesis, Université Pierre et Marie Curie - Paris VI, 2008. http://tel.archives-ouvertes.fr/tel-00311293.
Pełny tekst źródłaDans un premier temps, les élements historiques et théoriques de la LBM sont présentés ainsi que le développement permettant de passer de l'équation de Boltzmann aux équations de Navier-Stokes. La construction des modèles à vitesses discrètes est également décrite. Deux modèles basés sur des opérateurs de collision différents sont présentés : le modèle LBM-BGK et le modèle LBM-MRT. Pour l'étude des capacités aéroacoustiques de la LBM, une analyse de von Neumann est réalisée pour les modèles LBM-BGK et LBM-MRT ainsi que pour l'équation de Boltzmann à vitesse discrète (DVBE). Une comparaison avec les schémas Navier-Stokes d'ordre élevé est alors menée. Pour remédier aux instabilités numériques de la méthode Boltzmann sur Réseau intervenant lors de la propagation dans des directions particulières à M>0.1, des filtres sélectifs sont utilisés et leur effet sur la dissipation est étudié.
Dans un second temps, le code de calcul L-BEAM est présenté. La structure générale et les différentes techniques de calculs sont décrites. Un algorithme de transition de résolution est développé. La modélisation de la turbulence est abordée et le modèle de Meyers-Sagaut est implémenté dans le code. Enfin, des cas tests numériques sont utilisés pour valider le code et la simulation d'un écoulement turbulent complexe est réalisée.
Thandavamoorthy, Gayathiri. "Modélisation des phénoménes transitoire lents avec la méthode de Boltzmann sur réseau". Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066210/document.
Pełny tekst źródłaA new three-dimensional CFD solver, LaBS, based on the lattice Boltzmann alogorithms has been developed in a framework of university and industry consortium. In this thesis, this solver is used to simulate thermal flows, with a new thermal boundary condition for immersed solid boundary. The new proposed thermal boundary condition is based on the reconstruction method of the distribution function and is evaluated for immersed solid with coincident and non-coincident wall on the case of diffusion and natural convection phenomena.Renault case study, deals with a vehicle moving at constant speed (highway) that suddently slows down and stops (with or without a cut off contact). In such situation the cooling of the engine compartment first driven by forced convection during taxiing stage, abruptly switches to natural convection in low velocity stages. As natural convection is a slow process, it can take several minutes to remove the accumulated heat in the engine compartment. Such duration could be damaging for some components of the engine compartement which do not tolerate high temperature.In order to anticipate overheating of the engine compartment, where a lot of automotive parts with complex geometry are present and to avoid the above mentioned damages, the phenomenon of natural convection is here studied with the new thermal boundary condition.%The new proposed thermal boundary condition is first tested on academic case studies for validation, and then applied to the case of a real car.The modelling of thermal flows with the lattice Boltzmann method (LBM) can be classified into three categories: the multispeed approach, the hybrid approach and the double-distribution-function (DDF) approach. The multispeed approach, uses only one equation to resolve velocity, density and temperature field, which is solved by the LBM. Whereas the hybrid approach and the DDF approach utilize two sets of equations, one to resolve velocity field and density field and another to resolve temperature field. The hybrid approach solves velocity field and density field by the LBM method and the temperature field by finite-different or finite-volume methods. On the other hand the DDF approach solves the two equations with LBM.The thermal model used in the solver LaBS is based on the coupled DDF approach. In this model, the flow field is solved by a D3Q19 velocity model while the temperature field is solved by a D3Q19 or a D3Q7 velocity model. The coupling between the momentum and the energy transport is made by the boussinesq approximation. The new proposed thermal boundary condition decomposes the distribution function at the boundary node into its equilibrium and non-equilibrium part. The non-equilibrium part is calculated from the theoretical solution based on Chapman-Enskog developement.LaBS thermal model based on the coupled DDF approach is evaluated on a set of cases with increasing complexity. The results obtained with LaBS are compared with analytical solutions or with reference articles and are in a good agreement with the results expected. Results show that the model D3Q19/D3Q7 is qualitatively as good as the model D3Q19/D3Q19 but quantitatively the model D3Q19/D3Q19 remains the best
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.
Pełny tekst źródłaLa 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.
Wang, Yan. "Etude de la méthode de Boltzmann sur réseau pour la segmentation d'anévrismes cérébraux". Thesis, Lyon, INSA, 2014. http://www.theses.fr/2014ISAL0078/document.
Pełny tekst źródłaCerebral aneurysm is a fragile area on the wall of a blood vessel in the brain, which can rupture and cause major bleeding and cerebrovascular accident. The segmentation of cerebral aneurysm is a primordial step for diagnosis assistance, treatment and surgery planning. Unfortunately, manual segmentation is still an important part in clinical angiography but has become a burden given the huge amount of data generated by medical imaging systems. Automatic image segmentation techniques provides an essential way to easy and speed up clinical examinations, reduce the amount of manual interaction and lower inter operator variability. The main purpose of this PhD work is to develop automatic methods for cerebral aneurysm segmentation and measurement. The present work consists of three main parts. The first part deals with giant aneurysm segmentation containing lumen and thrombus. The methodology consists of first extracting the lumen and thrombus using a two-step procedure based on the LBM, and then refining the shape of the thrombus using level set technique. In this part the proposed method is also compared with manual segmentation, demonstrating its good segmentation accuracy. The second part concerns a LBM approach to vessel segmentation in 2D+t images and to cerebral aneurysm segmentation in 3D medical images through introducing a LBM D3Q27 model, which allows achieving a good segmentation and high robustness to noise. The last part investigates a true 4D segmentation model by considering the 3D+t data as a 4D hypervolume and using a D4Q81 lattice in LBM where time is considered in the same manner as for other three dimensions for the definition of particle moving directions in the LBM model
Tekitek, Mohamed-Mahdi. "Identification de modèles et de paramètres pour la méthode de Boltzmann sur réseau". Paris 11, 2007. https://tel.archives-ouvertes.fr/tel-00207541.
Pełny tekst źródłaThis thesis is composed of three parts. Firstly a study of Lattice Boltzmann scheme (LBE) is performed. Then Adjoint Lattice Boltzmann scheme (ALBE) is introduced for parameters identification. Finally a new Lattice Boltzmann scheme (BRB) is proposed to modelise B\'erenger's Perfectly Matched Layer (PML) method. The first part introduces and analyzes the LBE method. The second part describes a variational approach for parameters identification adapted to LBE. A time discrete adjoint method is developed. At first the ALBE method is applied to Stokes' problem and then to a nonlinear problem. Good results have been obtained in the cases of one or tow unknown parameters. Finally the third part describes an adaptation of PML for LBE. The LB scheme is obtained with 9 discretes velocities. An analysis of reflected waves between two one dimensional LB media is performed. It provides us an equivalent for the Fresnel formula for LBE interface. That gives us same ideas to modify the LB scheme at the interface to vanish reflected waves. In the two dimensional case, the same analysis of reflected waves shows the existence of Knudsen modes and transverse waves, which make the analysis more difficult
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.
Pełny tekst źródłaIn 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
Marcou, Olivier. "Modélisation et contrôle d’écoulements à surface libre par la méthode de Boltzmann sur réseau". Perpignan, 2010. http://www.theses.fr/2010PERP1001.
Pełny tekst źródłaThis PhD work considers the general problem of modelling and simulation of complex systems and deals with the domain of control and management of water resources. We propose here an original approach based on Lattice Boltzmann models (LB) for modelling free surface flows in irrigation canals, usually described with the non-linear shallow water equations. We adapted a bi-fluid model and studied the boundary conditions which allow to reproduce the geometry of a free-surface irrigation canal. Methods for estimating the desired hydraulic quantities were developed. We studied the behavior of submerged underflow gates, and we show that the model is able to spontaneously and correctly describe how the gates function in quite different situations. Validations were realized by comparing results from simulations and experimentations performed on a laboratory micro-canal facility. We also introduced sedimentation phenomena in the model and studied the influence of a sedimentation deposit on the flow. Comparisons between experimental and simulation results were also performed and converged