Tesis sobre el tema "Conditions aux limites de Ventcel"
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Auvray, Alexis. "Contributions à l'amélioration de la performance des conditions aux limites approchées pour des problèmes de couche mince en domaines non réguliers". Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEC018/document.
Texto completoTransmission problems with thin layer are delicate to approximate numerically, because of the necessity to build meshes on the scale of the thin layer. It is common to avoid these difficulties by using problems with approximate boundary conditions — also called impedance conditions. Whereas the approximation of transmission problems by impedance problems turns out to be successful in the case of smooth domains, the situation is less satisfactory in the presence of corners and edges. The goal of this thesis is to propose new impedance conditions, more efficient, to correct this lack of performance. For that purpose, the asymptotic expansions of the various models -problems are built and studied to locate exactly the origin of the loss, in connection with the singular profiles associated to corners and edges. New impedance conditions are built, of multi-scale Robin or Venctel types. At first studied in dimension 2, they are then generalized in certain situations in dimension 3. Simulations have been carried out to confirm the efficiency of the theoretical methods to some
Ghantous, Joyce. "Prise en compte de conditions aux bords d'ordre élevé et analyse numérique de problèmes de diffusion sur maillages courbes à l'aide d'éléments finis d'ordre élevé". Electronic Thesis or Diss., Pau, 2024. http://www.theses.fr/2024PAUU3024.
Texto completoThis thesis focuses on the numerical analysis of partial differential equations involving high-order boundary conditions of the Ventcel type using the finite element method. To define the Laplace-Beltrami operator involved in the boundary condition, the domain is assumed to be smooth: thus, the meshed domain does not correspond to the initial physical domain, resulting in a geometric error. We then use curved meshes to reduce this error and define a lift operator that allows comparing the exact solution defined on the initial domain with the approximate solution defined on the discretized domain. We obtain a priori error estimates, expressed in terms of finite element approximation error and geometric error. We study problems with source terms and spectral problems, as well as scalar equations and vector equations of linear elasticity. Numerical experiments in 2D and 3D validate and complement these theoretical results, particularly highlighting the optimality of the obtained errors. These simulations also identify a super-convergence of the errors on quadratic meshes
Lemrabet, Keddour. "Justification des modèles de problèmes aux limites de Ventcel en élasticité linéaire". Nice, 1987. http://www.theses.fr/1987NICE4111.
Texto completoLemrabet, Keddour. "Justification des modèles de problèmes aux limites de Ventcel en élasticité linéaire". Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37607318z.
Texto completoSaikali, Elie. "Numerical modelling of an air-helium buoyant jet in a two vented enclosure". Thesis, Sorbonne université, 2018. http://www.theses.fr/2018SORUS023/document.
Texto completoWe present numerical results from large eddy simulations (LES) and coarse direct numerical simulations (DNS) of an air-helium buoyant jet rising in a two vented cavity. The geometrical configuration mimics the helium release experimental set-up studied at CEA Saclay in the framework of security assessment of hydrogen-based systems with an indoor usage. The dimension of the enclosure was chosen to ensure a laminar-turbulent transition occurring at about the middle height of the cavity. This study focuses mainly on three key points : the influence of the boundary conditions on the jet development and its interaction with the exterior environment, the validity of the numerical model which is analyzed by comparing the numerical velocity distribution versus the measured particle image velocimetry (PIV) ones, and finally understanding the distribution of air-helium and the stratification phenomenon that takes place inside the cavity. We observe at first that applying constant pressure outlet boundary conditions directly at the vent surfaces underestimates the volumetric flow rate of air entering the enclosure and thus overestimate the helium mass inside the cavity. On the contrary, modelling an exterior region in the computational domain better predicts the air flow-rate entrance and numerical results matches better with the experimental PIV data. It has been figured out that the coarse DNS predictions match better with the velocities PIV measurements, compared to the LES. Numerical prediction of the helium field depicts a homogeneous layer formed at the top of the cavity, with a concentration in good agreement with the theoretical model of Linden et al. 1990. However, the position and the thickness of the layer do not correspond to the theory. This is mainly due to the direct interactions between the buoyant jet and both the solid boundaries of the cavity and the exterior environment. Statistical analysis regarding the buoyancy production of the turbulent kinetic energy (TKE) served to identify the limits of the buoyant jet
Gonzalez, Thierry. "Contributions aux conditions d'interface et conditions aux limites pour le systeme d'equations euler compressible". Paris 6, 2000. http://www.theses.fr/2000PA066512.
Texto completoBrouillat, Sébastien. "Conditions aux limites absorbantes d'ordre élevé en électromagnétisme". Bordeaux 1, 1996. http://www.theses.fr/1996BOR10608.
Texto completoEl, Ouaraini Rachida. "Sensibilité des assimilations d'ensemble globales et régionales aux conditions initialites et aux conditions limites latérales". Phd thesis, Toulouse, INPT, 2016. http://oatao.univ-toulouse.fr/15999/1/ElOuaraini.pdf.
Texto completoUzan, Jean-Philippe. "Defauts topologiques et conditions aux limites en cosmologie primordiale". Paris 11, 1998. http://www.theses.fr/1998PA112143.
Texto completoSesques, Muriel. "Conditions aux limites artificielles pour le système de Maxwell". Bordeaux 1, 1990. http://www.theses.fr/1990BOR10606.
Texto completoBergeret, Pascale. "Systèmes de lois de conservation, effets non linéaires des conditions aux limites : traitement numérique des conditions aux limites et des jonctions dans un réseau de pipelines". Lyon 1, 1995. http://www.theses.fr/1995LYO10004.
Texto completoMachrouki, Hicham. "Incompressibilité et conditions aux limites dans la méthode Smoothed particle hydrodynamics". Poitiers, 2012. http://theses.univ-poitiers.fr/25282/2012-Machrouki-Hicham-These.pdf.
Texto completoA numerical particle method for solving the Bavier-Stokes equations in velocity-pressure formulation for two dimensional incompressible flows is presented. The basis of the method is the Smoothed particle hydrodynamics (SPH) formulation for the moment transport. On advantage of this meshless method is an easy treatment of computational domains with complex boundaries. The pressure is computed by solving a poisson equation that ensures the flow incompressibility and the boundary conditions are imposed by using a boundary integral method (BIM). This last method, is known to be strongly CPU time consuming. To overcome this difficulty, the source term of the poisson equation was solved by introducing a cartesian grid and by using finite differences. The same treatment has been applied to the generalize Helmholtz equation for the velocity field as well. The different steps were validated by studying several academic cases including a driven cavity low, a dam break and an impulsively started flow around a circular cylinder. Aditionaly to this standard use for flow numerical modelling, the method was also applied for rebuilding the pressure and velocity fields from velocity fields experimentally measured by a PIV method. The method was then applied to the flow around a moving NACA profile
TAJCHMAN, MARC. "Conditions aux limites absorbantes pour des fluides viscoélastiques de type différentiel". Paris 11, 1994. http://www.theses.fr/1994PA112100.
Texto completoBarucq, Hélène. "Etude asymptotique du système de Maxwell avec conditions aux limites absorbantes". Bordeaux 1, 1993. http://www.theses.fr/1993BOR10620.
Texto completoCroizet, Cédric. "Modelisation cinetique d'une suspension et conditions aux limites sur une paroi". Paris 6, 2000. http://www.theses.fr/2000PA066499.
Texto completoPrat, Marc. "Modélisation des transferts en milieux poreux : changement d'échelle et conditions aux limites". Toulouse, INPT, 1989. http://www.theses.fr/1989INPT067H.
Texto completoLohéac, Jean-Pierre. "Conditions aux limites artificielles pour des modèles de la mécanique des fluides". Lyon 1, 1989. http://www.theses.fr/1989LYO19009.
Texto completoDarblade, Gilles. "Méthodes numériques et conditions aux limites pour les modèles Shallow-Water multicouches". Bordeaux 1, 1997. http://www.theses.fr/1997BOR10588.
Texto completoChalindar, Bruno. "Conditions aux limites absorbantes appliquées à des problèmes hyperboliques intervenant en sismique". Saint-Etienne, 1988. http://www.theses.fr/1988STET4013.
Texto completoHouari, Menouar. "Etude des conditions aux limites dans un modèle numérique d'agitation de houle". Marne-la-vallée, ENPC, 2002. http://www.theses.fr/2002ENPC0209.
Texto completoCORNUBERT, REMI. "Conditions aux limites des modeles cinetiques discrets : couche de knudsen et obstacles". Paris 6, 1991. http://www.theses.fr/1991PA066450.
Texto completoChalindar, Bruno. "Conditions aux limites absorbantes appliquées à des problèmes hyperboliques intervenant en sismique". Grenoble 2 : ANRT, 1988. http://catalogue.bnf.fr/ark:/12148/cb37612449h.
Texto completoKarimou, Gazibo Mohamed. "Etudes mathématiques et numériques des problèmes paraboliques avec des conditions aux limites". Phd thesis, Université de Franche-Comté, 2013. http://tel.archives-ouvertes.fr/tel-00950759.
Texto completoTourrette, Loïc. "Conditions aux limites artificielles pour les équations de Navier-stokes compressibles linéarisées". Palaiseau, Ecole polytechnique, 1990. http://www.theses.fr/1990EPXX0006.
Texto completoEl, Hamdani Driss. "Application de la théorie de l'homogénéisation aux problèmes aux limites : À conditions périodiques, en formulation intégrale". Besançon, 1990. http://www.theses.fr/1990BESA2005.
Texto completoFavraud, Gael. "Acoustique dans les écoulements cisaillés : conditions limites de géométries complexes, application à l’acoustique et aux couches limites visqueuses". Thesis, Le Mans, 2012. http://www.theses.fr/2012LEMA1024/document.
Texto completoThe first part is a study of the interactions between acoustic and vorticity perturbations in linear incompressible shear flows, which can decomposed as a sum of a hyperbolic part and of a rigid rotation part. The plane Couette flow is an example of such flows. By using the non-modal approach, the equations governing the evolution of compressible perturbations reduce to an ODE of dimension three in time, which depends on a dimensionless parameter ε representing the ratio between the shear rate of the flow and the frequency of the perturbations. For small ε values, the WKB method allows us to exhibit naturally three modes (two acoustic modes and one vorticity mode) and to highlight couplings between these modes. These couplings are exponentially small in 1/ε, and cannot be taken into account by an asymptotic method. They seem to be linked to the hyperbolic part of the flow.The second part deals with the reflection of a wave by a geometrically complex surface. A conformal mapping allows us to transform a complex boundary into a plane boundary, but makes appear varying coefficients in the bulk equations. These equations are then solved with the multimodal impedance matrix method, which reduce the problem to a Riccati equation for the impedance matrix. A method to find geometries allowing for the existence of trapped modes is proposed. Then the solving method is applied to the modeling of the viscous boundary layer of a fluid oscillating near a periodical rough surface. A perturbative solution is proposed. The presence of recirculation areas is studied
Favraud, Gael. "Acoustique dans les écoulements cisaillés : conditions limites de géométries complexes, application à l'acoustique et aux couches limites visqueuses". Phd thesis, Université du Maine, 2012. http://tel.archives-ouvertes.fr/tel-00821059.
Texto completoLamarque, Nicolas Poinsot Thierry. "Schémas numériques et conditions limites pour la simulation aux grandes échelles de la combustion diphasique dans les foyers d'hélicoptère". Toulouse : INP Toulouse, 2008. http://ethesis.inp-toulouse.fr/archive/00000593.
Texto completoDuprat, Véronique. "Conditions aux limites absorbantes enrichies pour l'équation des ondes acoustiques et l'équation d'Helmholtz". Phd thesis, Université de Pau et des Pays de l'Adour, 2011. http://tel.archives-ouvertes.fr/tel-00817506.
Texto completoMeslameni, Mohamed. "Équations de Stokes et d'Oseen en domaine extérieur avec diverses conditions aux limites". Thesis, Pau, 2013. http://www.theses.fr/2013PAUU3002/document.
Texto completoIn this work, we study the linearized Navier-Stokes equations in an exterior domain or in the whole space at the steady state, that is, the Stokes equations and the Oseen equations. We give existence, uniqueness and regularity of solutions. The case of very weak solutions is also treated. We consider not only the Dirichlet boundary conditions but also the Non Standard boundary conditions, on some components of the velocity field, vorticity and also on the pressure. Since the domain is not bounded, the classical Sobolev spaces are not adequate. Therefore, a specific functional framework is necessary which also has to take into account the behaviour of the functions at infinity. Our approach rests on the use of weighted Sobolev spaces
Gisclon, Marguerite. "Etude des conditions aux limites pour des systèmes strictement hyperboliques, via l'approximation parabolique". Lyon 1, 1994. http://www.theses.fr/1994LYO10294.
Texto completoVovelle, Julien. "Prise en compte des conditions aux limites dans les équations hyperboliques non-linéaires". Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11059.
Texto completoMondoloni, Antoine. "Existence d'une solution faible d'une équation d'onde quasi-linéaire avec conditions aux limites". Corte, 2000. http://www.theses.fr/2000CORT3052.
Texto completoKadri, Harouna Souleymane. "Ondelettes pour la prise en compte de conditions aux limites en turbulence incompressible". Grenoble, 2010. http://www.theses.fr/2010GRENM050.
Texto completoThis work concerns wavelet numerical methods for the simulation of incompressible turbulent flow. The main objective of this work is to take into account physical boundary conditions in the resolution of Navier-Stokes equations on wavelet basis. Unlike previous work where the vorticity field was decomposed in term of classical wavelet bases, the point of view adopted here is to compute the velocity field of the flow in its divergence-free wavelet series. We are then in the context of velocity-pressure formulation of the incompressible Navier-Stokes equations, for which the boundary conditions are written explicitly on the velocity field, which differs from the velocity-vorticity formulation. The principle of the method implemented is to incorporate directly the boundary conditions on the wavelet basis. This work extends the work of the thesis of E. Deriaz realized in the periodic case. The first part of this work highlights the definition and the construction of new divergence-free and curl-free wavelet bases on [0,1]n, which can take into account boundary conditions, from original works of P. G. Lemarie-Rieusset, K. Urban, E. Deriaz and V. Perrier. In the second part, efficient numerical methods using these new wavelets are proposed to solve various classical problem: heat equation, Stokes problem and Helmholtz-Hodge decomposition in the non-periodic case. The existence of fast algorithms makes the associated methods more competitive. The last part is devoted to the definition of two new numerical schemes for the resolution of the incompressible Navier-Stokes equations into wavelets, using the above ingredients. Numerical experiments conducted for the simulation of driven cavity flow in two dimensions or the issue of reconnection of vortex tubes in three dimensions show the strong potential of the developed algorithms
Tonnoir, Antoine. "Conditions transparentes pour la diffraction d'ondes en milieu élastique anisotrope". Palaiseau, École nationale supérieure de techniques avancées, 2015. http://www.theses.fr/2015ESTA0016.
Texto completoThis thesis is motivated by the numerical simulation of Non Destructive Testing by ultrasonic waves. It aims at designing a method to compute by Finite Element (EF) the diffraction of elastic waves in time-harmonic regime by a bounded defect in an anisotropic plate. The goal is to take into account an infinite plate and to restrict the FE calculations to a bounded area. This point is difficult due to the anisotropy and, in particular, methods such as perfectly matched layers fail. In this thesis, we have mainly considered two-dimensional cases that enabled us to implement the main ingredients of a method designed for the three-dimensional case of the plate. The first part deals with the diffraction problem in an infinite strip. The classical approach consists in writing transparent conditions by matching on a boundary the displacement and the axial stress using a modal expansion in the safe part of the plate, and the FE representation in the perturbed area. We have shown the interest of imposing these matching conditions on two separated boundaries, by introducing an overlap between the modal domain and the FE domain. Thus, we can take advantage of the bi-orthogonality relations valid for general anisotropy, and also improve the rate of convergence of iterative methods of resolution. In the second part, that represents the main part of the thesis, we discuss the diffraction problem in an anisotropic medium infinite in the two directions. The key idea is that we can express the solution (via the Fourier transform) in a half-plane given its trace on the boundary. Therefore, the approach consists in coupling several analytical representations of the solution in half-planes surrounding the defect (at least 3) with the FE representation. The difficulty is to ensure that all these representations match, in particular in the infinite intersections of the half-planes. It leads to a formulation which couples, via integral operators, the solution in a bounded domain including the defect, and its traces on the edge of the half-planes. The approximation releases a truncation and a discretization both in space and Fourier variables. For each of these two parts, the methods have been implemented and validated with a C++ code developed during the thesis, first in the scalar acoustic case, and then in the elastic case
Vezinet, René. "Conditions aux limites absorbantes d'ordre élevé appliquées aux équations de Maxwell dans le vide et en milieu conducteur". Limoges, 1993. http://www.theses.fr/1993LIMO0225.
Texto completoAbbaspour, 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.
Texto completoThis 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
Rejaiba, Ahmed. "Equations de Stokes et de Navier-Stokes avec des conditions aux limites de Navier". Thesis, Pau, 2014. http://www.theses.fr/2014PAUU3050/document.
Texto completoThis thesis is devoted to the study of the Stokes equations and Navier-Stokes equations with Navier boundary conditions in a bounded domain of . The work contains three chapters: In the first chapter, we consider the stationary Stokes equations with Navier boundary condition. We show the existence, uniqueness and regularity of the solution in the Hilbert case and in the -theory. We prove also the case of very weak solutions. In the second chapter, we focus on the Navier-Stokes equations with the Navier boundary condition. We show the existence of the weak solution in , with by a fixed point theorem over the Oseen equation. We show also the existence of the strong solution in . In chapter three, we study the evolution Stokes problem with Navier boundary condition. For this, we apply the analytic semi-groups theory, which plays a crucial role in the study of existence and uniqueness of solution in the case of the homogeneous evolution problem. We treat the case of non-homogeneous problem through imaginary powers of the Stokes operator
Pilon, Dominic. "Influence des conditions aux limites sur les mesures acoustiques au tube à ondes stationnaires". Mémoire, Université de Sherbrooke, 2002. http://savoirs.usherbrooke.ca/handle/11143/1172.
Texto completoOuarzazi, Mohamed-Najib. "Bifurcations associées à des imperfections des conditions aux limites pour des problèmes de convection". Lille 1, 1993. http://www.theses.fr/1993LIL10147.
Texto completoAbdelmoula, Radhi. "Flambage des coques cylindriques sous pression : influence des conditions aux limites et des défauts". Metz, 1989. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1989/Abdelmoula.Radhi.SMZ8913.pdf.
Texto completoAstruc, Dominique. "Instabilité de Kelvin-Helmholtz en régime subsonique : développement spatial et conditions aux limites ouvertes". Toulouse, INPT, 1993. http://www.theses.fr/1993INPT131H.
Texto completoLeclercq, Marie-Pierre. "Résolution des équations d'Euler par des méthodes multigrilles : conditions aux limites en régime hypersonique". Saint-Etienne, 1990. http://www.theses.fr/1990STET4010.
Texto completoRosier, Carole. "Étude numérique des équations bi-dimensionnelles de Navier-Stokes avec conditions aux limites périodiques". Paris 11, 1989. http://www.theses.fr/1989PA112234.
Texto completoThe aim of this work is to describe a new numerical method, well suited for computing the solution of the Navier-Stokes equations over large time intervals. Introduced by Foias, Manley and Temam, this method corresponds to a projection of the equations on a nonlinear subspace, while the usual Galerkin method can be interpreted as a projection on a linear space; this is why it is called "The nonlinear Galerkin method". The work is organized as follows. In the first chapter a description of the problem is presented and some theoretical results concerning the behavior as it goes to infinity of the solutions are recalled. The second chapter is devoted to a comparative study of schemes based on different time discretizations of the Navier-Stokes equations. Our study shows that the predictor-corrector or Runge-Kutta schemes are better suited to the Galerkin approximation than a projection scheme or the Adams-Bashforth-Crank Nicholson scheme. These schemes are used in the numerical calculations. In the third chapter, a theoretical motivation of the nonlinear Galerkin method is presented. We define manifolds, the approximate inertial manifolds, which approximate the strange attractor, and which describe the interaction between the small and large eddies of the flow. Numerical tests are given in the last chapter
Dhifaoui, Anis. "Équations de Stokes en domaine extérieur avec des conditions aux limites de type Navier". Thesis, Bourgogne Franche-Comté, 2020. http://www.theses.fr/2020UBFCD009.
Texto completoIn this manuscript, we study the three-dimensional stationary Stokes equations set in a exterior domain. The problem describes the flow of a viscous and incompressible fluid past a bounded obstacle. The distinctif feature here relies on the fact that the obstacle is assumed to a rough boundary. As a result, the fluid may slip on the boundary of the obstacle and, to take into account this property, we use the Navier boundary conditions. On the one hand, They model the impermeability of the obstacle, and on the other hand, the fact that the tangential component of the fluid velocity on the obstacle is proportional to the stress tensor. This problem has been well studied when set in a bounded domain. The standard Sobolev spaces provides, in this case, an adequate functional framework for a complete study. Since in our case, the domain is unbounded, these spaces are not adapted since it is necessary to describe the behaviour of the solutions to infinity. Therefore, we choose to set the problem in weighted Sobolev spaces where the weights describe the behaviour at infinity of the function (growth or decay).In this work, we first start by performing the mathematical analysis in the Hilbert setting. The key point here is to establish variant weighted Korn’s inequalities in order to get the coercivity of the bilinear form associated to the variational formulation. Next, we proved the existence, uniqueness of strong and very weak solutions. Finally, we study the extension of some of thses results to a weightedL^p-theory
BOSSEUR, FREDERIC. "Determination de conditions aux limites en mer ouverte par une methode de controle optimal". Corte, 1998. http://www.theses.fr/1998CORT3035.
Texto completoPilon, Dominic. "Influence des conditions aux limites sur les mesures acoustiques au tube à ondes stationnaires". Sherbrooke : Université de Sherbrooke, 2002.
Buscar texto completoAbdelmoula, Radhi Potier-Ferry Michel. "Flambage des coques cylindriques sous pression influence des conditions aux limites et des défauts /". Metz : Université Metz, 2008. ftp://ftp.scd.univ-metz.fr/pub/Theses/1989/Abdelmoula.Radhi.SMZ8913.pdf.
Texto completoDelzant, Pierre-Olivier. "Refusion sous vide d’alliages de titane : comportement de l’arc électrique et conditions aux limites". Thesis, Université de Lorraine, 2018. http://www.theses.fr/2018LORR0020/document.
Texto completoIn the vacuum arc remelting process, the structure and dynamics of the electric arc are responsible for the spatial distributions of energy and current at the top of the remelted ingot. Those distributions strongly impact the ingot temperature field and the liquid metal velocity field, which govern the ingot solidification conditions, hence the final product quality. A study based on the optical measurement of the electric arc dynamics at a long time-scale during vacuum arc remelting of titanium alloys was undertaken. This analysis was performed either qualitatively using melt video recordings, or quantitatively by a new specifically developed diagnostic technique based on the use of photodiodes. The analysis of the electric arc dynamics confirmed the presence of an ensemble arc motion during vacuum arc remelting of titanium alloys and showed a strong correlation between the observed dynamics and the magnitude of the imposed electromagnetic stirring. Furthermore, our results allow to predict the arc dynamics in non-studied conditions and to propose possible origins for the observed behaviors. Finally, a first simulation of the influence of the arc behavior is proposed in order to study its impact on the ingot solidification. This work comprises also a detailed modelling of the thermal radiation at the ingot top, based on the radiosity method
Le, Hardy David. "Traitement des conditions aux limites spéculaires pour l'étude du transfert radiatif dans des matériaux à géométrie complexe". Thesis, Nantes, 2017. http://www.theses.fr/2017NANT4016/document.
Texto completoThis dissertation considers the development of numerical tools for the solution of the radiative transfer equation within threedimensional media with complex geometries, combined with the accurate treatment of specular boundary conditions. Numerical developments rely on the Discrete Ordinate Method, combined with SUPG-type stabilized Finite Elements. A very novel partitioning method has been developped for accurate treatment of specularity on borders. Also, some Gauss– Seidel type and GMRES parallel solvers have been used to deal with huge size matrix systems, due to fine discretization in both space and angles, needed for such considered geometrical complexity. Finally, all developped numerical tools have been tested for the modelling of radiative transport within a micro-tomographied ceramic ligament, extracted from a real open-cell foam