Dissertations / Theses on the topic 'Problème de Convection-diffusion'
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Etchegaray, Christèle. "Modélisation mathématique et numérique de la migration cellulaire." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS428/document.
Collective or individual cell displacements are essential in fundamental physiological processes (immune response, embryogenesis) as well as in pathological developments (tumor metastasis). The intracellular processes responsible for cell motion have a complex self-organized activity spanning different time and space scales. Highlighting general principles of migration is therefore a challenging task.In a first part, we build stochastic particular models of migration. To do so, we describe key intracellular processes as discrete in space by using stochastic population models. Then, by a renormalization in large population, infinitesimal size and accelerated dynamics, we obtain continuous stochastic equations for the dynamics of interest, allowing a relation between the intracellular dynamics and the macroscopic displacement.First, we study the case of a leukocyte carried by the blood flow and developing adhesive bonds with the artery wall, until an eventual stop. The binding dynamics is described by a stochastic Birth and Death with Immigration process. These bonds correspond to resistive forces to the motion. We obtain explicitly the mean stopping time of the cell.Then, we study the case of cell crawling, that happens by the formation of protrusions on the cell edge, that grow on the substrate and exert traction forces. We describe this dynamics by a structured population process, where the structure comes from the protrusions' orientations. The limiting continuous model can be analytically studied in the 1D migration case, and gives rise to a Fokker-Planck equation on the probability distribution for the protrusion density. For a stationary profile, we can show the existence of a dichotomy between a non motile state and a directional displacement state.In a second part, we build a deterministic minimal migration model in a discoïdal cell domain. We base our work on the idea such that the structures responsible for migration also reinforce cell polarisation, which favors in return a directional displacement. This positive feedback loop involves the convection of a molecular marker, whose inhomogeneous spatial repartition is characteristic of a polarised state.The model writes as a convection-diffusion problem for the marker's concentration, where the advection field is the velocity field of the Darcy fluid that describes the cytoskeleton. Its active character is carried by boundary terms, which makes the originality of the model.From the analytical point of vue, the 1D model shows a dichotomy depending on a critical mass for the marker. In the subcritical and critical cases, it is possible to show global existence of weak solutions, as well as a rate-explicit convergence of the solution towards the unique stationary profile, corresponding to a non-motile state. Above the critical mass, for intermediate values, we show the existence of two additional stationary solutions corresponding to polarised motile profiles. Moreover, for asymmetric enough initial profiles, we show the finite time apparition of a blowup.Studying a more complex model involving activation of the marker at the cell membrane permits to get rid of this singularity.From the numerical point of vue, numerical experiments are led in 2D either in finite volumes (Matlab) or finite elements (FreeFem++) discretizations. They allow to show both motile and non motile profiles. The effect of stochastic fluctuations in time and space are studied, leading to numerical simulations of cases of responses to an external signal, either chemical (chemotaxis) or mechanical (obstacles)
Bouyssier, Julien. "Transports couplés en géométries complexes." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1929/.
This work interest is about stationary transfer and non-stationary transport by convection-diffusion onto complex geometries. For transport issues, complex refers to convection into flattened cavity of arbitrary transverse shape, slowly varying along the longitudinal direction. In the context of transfer, complex refers to non-axisymmetric domains of arbitrary transverse shape along which one or several parallel tubes convect heat or mass. For the transfer problem, this work extends the principle, validates the use, and illustrates the efficiency of Graetz modes decompositions for exchanges prediction in realistic exchangers configurations. This decomposition permits to formulate the initial 3D problem as a generalysed 2D eigenvalue problem, the numerical evaluation of which is drastically reduced. We generalyze Graetz modes solutions for arbitrary applied lateral boundary conditions. In the particular case of balanced exchangers, we bring to the fore a new neutral mode whose longitudinal variations are linear as opposed to classical Graetz modes displaying exponential decay. The numerical computation of those modes for semi-infinite configurations with lateral periodic boundary conditions shows that a few number of those provides a very good approximation for exchanges. In the case of finite exchangers coupled with inlet/oulet tubes, we show how to evaluate the amplitudes of Graetz modes in the various domains (inlet, exchanger, outlet) from functional minimization associated with input/output boundary conditions. The evaluation of these amplitudes permit a systematic parametric study of temperature fields, heat fluxes between fluid and solid, and hot/cold performance of a couple-tube exchanger. Our results indicate that the typical exchange length is governed by the first Graetz mode at large P\'eclet number. We also show that a symmetric exchanger has a symmetric spectrum and a upward/backward symmetric evolution. In the case transport we elaborate theoretically the conservative form of 3D Taylor dispersion equations into variable cavities which generalyzes the framework already known in 2D. We numerically implement these averaged dispersion equations with finite element, and validate in 2D the obtained results. We show that 3D longitudinal variations of a cavity has a strong impact on the longitudinal dispersion
Di, Pietro Daniele Antonio. "Méthodes non conformes pour des équations aux dérivées partielles avec diffusion." Habilitation à diriger des recherches, Université Paris-Est, 2010. http://tel.archives-ouvertes.fr/tel-00550230.
Aoun, Mirella. "Analyse et analyse numérique d'EDP issues de la thermomécanique des fluides." Electronic Thesis or Diss., Normandie, 2023. http://www.theses.fr/2023NORMR093.
In this thesis, we focus on nonlinear evolutionary systems derived from a non-isothermal solidification problem with melt convection. These systems consist of three partial differential equations. The first is the phase-field equation coupled with the heat equation and the incompressible Navier-Stokes equation. More precisely, we are interested in the existence of solutions for these types of systems in the two-dimensional and the three-dimensional cases, and in the convergence of a finite volume approximation. One of the particularities of this type of system is the presence of a term naturally in L^1 in the energy conservation equation, which requires special treatment.This thesis is divided into two parts.The first part is divided into two chapters and is devoted to the study of problems with L^1 data and Neumann-type boundary conditions. To deal with these problems, and with data that are not very regular, we use the framework of renormalized solutions.In the first chapter, we establish a convergence result for solutions approximated by the finite volume method to the unique renormalized solution with zero median in the case of an elliptic convection-diffusion equation. In the second chapter, we focus on a non-linear parabolic problem with non-homogeneous Neumann conditions and a convection term. For this problem, we provide a definition of a renormalized solution and we show the existence and uniqueness of such a solution.The second part is devoted to the study of the system in dimensions 2 and 3. The first chapter deals with the dimension 2 and defines the notion of weak--renormalized solutions. With the help of the existence and stability results established in the first part for the conservation of energy equation, we prove the existence of a weak--renormalized solution.The final chapter considers the trickier case of dimension 3. The absence of a general stability and uniqueness result for the 3-dimensional Navier-Sokes equation requires us to transform the system into a formally equivalent one. By approximation and passage to the limit, we prove the existence of a solution in a weak sense
Parvin, S. "Diffusion-convection problems in parabolic equations." Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382761.
Linß, Torsten. "Layer-adapted meshes for convection-diffusion problems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2008. http://nbn-resolving.de/urn:nbn:de:bsz:14-ds-1203582105872-58676.
Franz, Sebastian. "Uniform Error Estimation for Convection-Diffusion Problems." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-133017.
Linß, Torsten. "Layer-adapted meshes for convection-diffusion problems." Doctoral thesis, Technische Universität Dresden, 2006. https://tud.qucosa.de/id/qucosa%3A24058.
Tracey, John. "Stability analyses of multi-component convection-diffusion problems." Thesis, University of Glasgow, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.360157.
Wu, Wei. "Petrov-Galerkin methods for parabolic convection-diffusion problems." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.670384.
Duarte, Max Pedro. "Méthodes numériques adaptives pour la simulation de la dynamique de fronts de réaction multi-échelle en temps et en espace." Phd thesis, Ecole Centrale Paris, 2011. http://tel.archives-ouvertes.fr/tel-00737092.
Demirayak, Murat Neslitürk Ali İhsan. "Analysis Of Finite Difference Methods For Convection-Diffusion Problem/." [s.l.]: [s.n.], 2004. http://library.iyte.edu.tr/tezler/master/matematik/T000481.pdf.
Patel, Mayur K. "On the false-diffusion problem in the numerical modelling of convection-diffusion processes." Thesis, University of Greenwich, 1986. http://gala.gre.ac.uk/8697/.
Texier-Picard, Rozenn. "Problèmes de réaction-diffusion avec convection : Une étude mathématique et numérique." Phd thesis, Université Claude Bernard - Lyon I, 2002. http://tel.archives-ouvertes.fr/tel-00002038.
Texier, Picard Rozenn. "Problèmes de réaction-diffusion avec convection : une étude mathématique et numérique." Lyon 1, 2002. http://tel.archives-ouvertes.fr/docs/00/04/50/62/PDF/tel-00002038.pdf.
Pankratova, Iryna. "Convection-diffusion equation in unbounded cylinder and related homogenization problems." Licentiate thesis, Luleå : Luleå tekniska universitet, 2009. http://pure.ltu.se/ws/fbspretrieve/2579688.
Rees, M. D. "Moving point, particle and free-Lagrange methods." Thesis, University of Oxford, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235079.
Vu, Do Huy Cuong. "Méthodes numériques pour les écoulements et le transport en milieu poreux." Thesis, Paris 11, 2014. http://www.theses.fr/2014PA112348/document.
This thesis bears on the modelling of groundwater flow and transport in porous media; we perform numerical simulations by means of finite volume methods and prove convergence results. In Chapter 1, we first apply a semi-implicit standard finite volume method and then the generalized finite volume method SUSHI for the numerical simulation of density driven flows in porous media; we solve a nonlinear convection-diffusion parabolic equation for the concentration coupled with an elliptic equation for the pressure. We apply the standard finite volume method to compute the solutions of a problem involving a rotating interface between salt and fresh water and of Henry's problem. We then apply the SUSHI scheme to the same problems as well as to a three dimensional saltpool problem. We use adaptive meshes, based upon square volume elements in space dimension two and cubic volume elements in space dimension three. In Chapter 2, we apply the generalized finite volume method SUSHI to the discretization of Richards equation, an elliptic-parabolic equation modeling groundwater flow, where the diffusion term can be anisotropic and heterogeneous. This class of locally conservative methods can be applied to a wide range of unstructured possibly non-matching polyhedral meshes in arbitrary space dimension. As is needed for Richards equation, the time discretization is fully implicit. We obtain a convergence result based upon a priori estimates and the application of the Fréchet-Kolmogorov compactness theorem. We implement the scheme and present numerical tests. In Chapter 3, we study a gradient scheme for the Signorini problem. Gradient schemes are nonconforming methods written in discrete variational formulation which are based on independent approximations of the functions and the gradients. We prove the existence and uniqueness of the discrete solution as well as its convergence to the weak solution of the Signorini problem. Finally we introduce a numerical scheme based upon the SUSHI discretization and present numerical results. In Chapter 4, we apply a semi-implicit scheme in time together with a generalized finite volume method for the numerical solution of density driven flows in porous media; it comes to solve nonlinear convection-diffusion parabolic equations for the solute and temperature transport as well as for the pressure. We compute the solutions for a specific problem which describes the advance of a warm fresh water front coupled to heat transfer in a confined aquifer which is initially charged with cold salt water. We use adaptive meshes, based upon square volume elements in space dimension two
Nait, Slimane Younès. "Méthodes de volumes finis pour des problèmes de diffusion-convection non-linéaires." Paris 13, 1997. http://www.theses.fr/1997PA132015.
Sousa, Ercília. "Finite differences for the convection-diffusion equation : on stability and boundary conditions." Thesis, University of Oxford, 2001. http://ora.ox.ac.uk/objects/uuid:8369da31-2229-4e05-846c-de3072ac1a37.
Pankratova, Iryna. "L'homogénéisation d'équations de convection-diffusion singulières et de problèmes spectraux à poids indéfini." Phd thesis, Ecole Polytechnique X, 2011. http://pastel.archives-ouvertes.fr/pastel-00593511.
Michel, Anthony. "Convergence de schémas volumes finis pour des problèmes de convection diffusion non linéaires." Phd thesis, Université de Provence - Aix-Marseille I, 2001. http://tel.archives-ouvertes.fr/tel-00002553.
Nadukandi, Prashanth. "Stabilized finite element methods for convection-diffusion-reaction, helmholtz and stokes problems." Doctoral thesis, Universitat Politècnica de Catalunya, 2011. http://hdl.handle.net/10803/109155.
Presentamos tres nuevos metodos estabilizados de tipo Petrov- Galerkin basado en elementos finitos (FE) para los problemas de convecci6n-difusi6n- reacci6n (CDR), de Helmholtz y de Stokes, respectivamente. El trabajo comienza con un analisis a priori de un metodo de recuperaci6n de la consistencia de algunos metodos de estabilizaci6n que pertenecen al marco de Petrov-Galerkin. Hallamos que el uso de algunas de las practicas estandar (por ejemplo, la eoria de Matriz-M) para el diserio de metodos numericos esencialmente no oscilatorios no es apropiado cuando utilizamos los metodos de recu eraci6n de la consistencia. Por 10 tanto, con res ecto a la estabilizaci6n de conveccion, no preferimos tales metodos de recuperacion . A continuacion, presentamos el diser'io de un metodo de Petrov-Galerkin de alta-resolucion (HRPG) para el problema CDR. La estructura del metodo en 10 es identico al metodo CAU [doi: 10.1016/0045-7825(88)90108-9] excepto en la definicion de los parametros de estabilizacion. Esta estructura tambien se puede obtener a traves de la formulacion del calculo finito (FIC) [doi: 10.1 016/S0045- 7825(97)00119-9] usando una definicion adecuada de la longitud caracteristica. El prefijo de "alta-resolucion" se utiliza aqui en el sentido popularizado por Harten, es decir, tener una solucion con una precision de segundo orden en los regimenes suaves y ser esencialmente no oscilatoria en los regimenes no regulares. El diser'io en 10 se embarca en el problema de eludir el fenomeno de Gibbs observado en las proyecciones de tipo L2. A continuacion, estudiamos las condiciones de los parametros de estabilizacion para evitar las oscilaciones globales debido al ermino convectivo. Combinamos los dos resultados (una conjetura) para tratar el problema COR, cuya solucion numerica sufre de oscilaciones numericas del tipo global, Gibbs y dispersiva. Tambien presentamos una extension multidimensional del metodo HRPG utilizando los elementos finitos multi-lineales. fa. continuacion, proponemos un esquema compacto de orden superior (que incluye dos parametros) en mallas estructuradas para la ecuacion de Helmholtz. Haciendo igual ambos parametros, se recupera la interpolacion lineal del metodo de elementos finitos (FEM) de tipo Galerkin y el clasico metodo de diferencias finitas centradas. En 10 este esquema es identico al metodo AIM [doi: 10.1 016/0771 -050X(82)90002-X] y en 20 eligiendo el valor de 0,5 para ambos parametros, se recupera el esquema compacto de cuarto orden de Pade generalizada en [doi: 10.1 006/jcph.1 995.1134, doi: 10.1 016/S0045-7825(98)00023-1] (con el parametro V = 2). Seguimos [doi: 10.1 016/0045-7825(95)00890-X] para el analisis de este esquema y comparamos su rendimiento en las mallas uniformes con el de "FEM cuasi-estabilizado" (QSFEM) [doi: 10.1016/0045-7825 (95) 00890-X]. Presentamos expresiones genericas de los para metros que garantiza una precision dispersiva de sexto orden si ambos parametros son distintos y de cuarto orden en caso de ser iguales. En este ultimo caso, presentamos la expresion del parametro que minimiza el error maxima de fase relativa en 20. Tambien proponemos una formulacion de tipo Petrov-Galerkin ~ue recupera los esquemas antes mencionados en mallas estructuradas. Presentamos estudios de convergencia del error en la norma de tipo L2, la semi-norma de tipo H1 y la norma Euclidiana tipo I~ y mostramos que la perdida de estabilidad del operador de Helmholtz ("pollution effect") es incluso pequer'ia para grandes numeros de onda. Por ultimo, presentamos una coleccion de metodos FE estabilizado para el problema de Stokes desarrollados a raves del metodo FIC de primer orden y de segundo orden. Mostramos que varios metodos FE de estabilizacion existentes y conocidos como el metodo de penalizacion, el metodo de Galerkin de minimos cuadrados (GLS) [doi: 10.1016/0045-7825(86)90025-3], el metodo PGP (estabilizado a traves de la proyeccion del gradiente de presion) [doi: 10.1 016/S0045-7825(96)01154-1] Y el metodo OSS (estabilizado a traves de las sub-escalas ortogonales) [doi: 10.1016/S0045-7825(00)00254-1] se recuperan del marco general de FIC. Oesarrollamos una nueva familia de metodos FE, en adelante denominado como PLS (estabilizado a traves del Laplaciano de presion) con las formas no lineales y consistentes de los parametros de estabilizacion. Una caracteristica distintiva de la familia de los metodos PLS es que son no lineales y basados en el residuo, es decir, los terminos de estabilizacion dependera de los residuos discretos del momento y/o las ecuaciones de incompresibilidad. Oiscutimos las ventajas y desventajas de estas tecnicas de estabilizaci6n y presentamos varios ejemplos de aplicacion
Mbroh, Nana Adjoah. "On the method of lines for singularly perturbed partial differential equations." University of the Western Cape, 2017. http://hdl.handle.net/11394/5679.
Many chemical and physical problems are mathematically described by partial differential equations (PDEs). These PDEs are often highly nonlinear and therefore have no closed form solutions. Thus, it is necessary to recourse to numerical approaches to determine suitable approximations to the solution of such equations. For solutions possessing sharp spatial transitions (such as boundary or interior layers), standard numerical methods have shown limitations as they fail to capture large gradients. The method of lines (MOL) is one of the numerical methods used to solve PDEs. It proceeds by the discretization of all but one dimension leading to systems of ordinary di erential equations. In the case of time-dependent PDEs, the MOL consists of discretizing the spatial derivatives only leaving the time variable continuous. The process results in a system to which a numerical method for initial value problems can be applied. In this project we consider various types of singularly perturbed time-dependent PDEs. For each type, using the MOL, the spatial dimensions will be discretized in many different ways following fitted numerical approaches. Each discretisation will be analysed for stability and convergence. Extensive experiments will be conducted to confirm the analyses.
Krueger, Denise A. "Stabilized Finite Element Methods for Feedback Control of Convection Diffusion Equations." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11214.
Ph. D.
Apel, Thomas, and Gert Lube. "Local inequalities for anisotropic finite elements and their application to convection-diffusion problems." Universitätsbibliothek Chemnitz, 1998. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-199800625.
Zhu, Liang. "Robust a posteriori error estimation for discontinuous Galerkin methods for convection diffusion problems." Thesis, University of British Columbia, 2010. http://hdl.handle.net/2429/23337.
Baker, M. D. "A spectral Lagrange-Galerkin method for periodic/non-periodic convection-dominated diffusion problems." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240539.
Mishra, Sudib Kumar. "DEVELOPMENT OF A MULTISCALE AND MULTIPHYSICS SIMULATION FRAMEWORK FOR REACTION-DIFFUSION-CONVECTION PROBLEMS." Diss., The University of Arizona, 2009. http://hdl.handle.net/10150/194088.
Chalhoub, Nancy. "Estimations a posteriori pour l'équation de convection-diffusion-réaction instationnaire et applications aux volumes finis." Phd thesis, Université Paris-Est, 2012. http://pastel.archives-ouvertes.fr/pastel-00794392.
Mildner, Marcus. "Stabilité de l'équation d'advection-diffusion et stabilité de l'équation d'advection pour la solution du problème approché, obtenue par la méthode upwind d'éléments-finis et de volumes-finis avec des éléments de Crouzeix-Raviart." Phd thesis, Université du Littoral Côte d'Opale, 2013. http://tel.archives-ouvertes.fr/tel-00839524.
Ducrot, Arnaud. "Problèmes élliptiques dans des domaines non bornés et propagation d'ondes de réaction-diffusion." Ecully, Ecole centrale de Lyon, 2004. http://www.theses.fr/2004ECDL0025.
In this work we theorically and numerically study reaction-diffusion and reactiondiffusion-convection problems. The theorical part is interested in multi-dimensional travelling waves solutions for reaction-diffuion systems with linearly dependant reaction terms. We develop new approach to study such systems with non Fredholm operators. This approach essentially concists in a reformulation of the equations with an integro-differential operator. It allows us to derive sorne existence results. The numerical part is interested in the influence of natural convection on the ignition of a reaction front. We study numerically study two models based on reaction-diffusionconvection systems. It is shown that natural convection can influence the place where a frontal polymerization starts together with critical conditions of ignition
Sudirham, Janivita Joto. "Space-time discontinuous Galerkin methods for convection-diffusion problems application to wet-chemical etching /." Enschede : University of Twente [Host], 2005. http://doc.utwente.nl/50890.
Houston, Paul D. "Lagrange-Galerkin methods for unsteady convection-diffusion problems : a posteriori error analysis and adaptivity." Thesis, University of Oxford, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.337607.
Men, Han (Han Abby). "Efficient reduced-basis approximation of scalar nonlinear time-dependent convection-diffusion problems, and extension to compressible flow problems." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/39214.
Includes bibliographical references (p. 61-65).
In this thesis, the reduced-basis method is applied to nonlinear time-dependent convection-diffusion parameterized partial differential equations (PDEs). A proper orthogonal decomposition (POD) procedure is used for the construction of reduced-basis approximation for the field variables. In the presence of highly nonlinear terms, conventional reduced-basis would be inefficient and no longer superior to classical numerical approaches using advanced iterative techniques. To recover the computational advantage of the reduced-basis approach, an empirical interpolation approximation method is employed to define the coefficient-function approximation of the nonlinear terms. Next, the coefficient-function approximation is incorporated into the reduced-basis method to obtain a reduced-order model of nonlinear time-dependent parameterized convection-diffusion PDEs. Two formulations for the reduced-order models are proposed, which construct the reduced-basis space for the nonlinear functions and residual vector respectively. Finally, an offline-online procedure for rapid and inexpensive evaluation of the reduced-order model solutions and outputs, as well as associated asymptotic a posterior error estimators are developed.
(cont.) The operation count for the online stage depends only on the dimension of our reduced-basis approximation space and the dimension of our coefficient-function approximation space. The extension of the reduced-order model to a system of equations is also explored.
by Han Men.
S.M.
Belk, Michaël. "Stabilité structurelle de solutions invariantes par translation : application à des problèmes de réaction-diffusion avec convection." Lyon 1, 2003. http://www.theses.fr/2003LYO10260.
Cautres, René. "Discrétisation par volumes finis et méthodes de décomposition de domaine pour des problèmes de convection diffusion." Aix-Marseille 1, 2004. http://www.theses.fr/2004AIX10008.
Al-Bayati, Salam Adel. "Boundary element analysis for convection-diffusion-reaction problems combining dual reciprocity and radial integration methods." Thesis, Brunel University, 2018. http://bura.brunel.ac.uk/handle/2438/17071.
Vugrin, Eric D. "On Approximation and Optimal Control of Nonnormal Distributed Parameter Systems." Diss., Virginia Tech, 2004. http://hdl.handle.net/10919/11149.
Ph. D.
Atallah, Nabil. "Analyse des méthodes itératives par points pour les problèmes de diffusion-convection approchés par les schémas compacts." Toulouse 3, 2002. http://www.theses.fr/2002TOU30010.
Rodriguez, Erik. "A comparison of kansa and hermitian RBF interpolation techniques for the solution of convection-diffusion problems." Honors in the Major Thesis, University of Central Florida, 2010. http://digital.library.ucf.edu/cdm/ref/collection/ETH/id/1488.
Bachelors
Engineering and Computer Science
Mechanical Engineering
Rasoamiaramanana, Daniel. "Analyse numerique de schemas aux differences a deux et trois niveaux pour le probleme de diffusion convection non stationnaire." Toulouse 3, 1987. http://www.theses.fr/1987TOU30130.
Barros, Carlos Eduardo Rosado de. "Sequências monótonas aplicadas a um problema de cauchy para um sistema de reação-difusão-convecção." Universidade Federal de Goiás, 2015. http://repositorio.bc.ufg.br/tede/handle/tede/5543.
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Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq
In this work, mainly based on the articles, [1], [2] and [7], one studies a reactiondiffusion- convection system, related the propagation of a combustion front through a porous medium, giving origin a Cauchy problem. Such a problem has been approached by the methode of the monotone iterations, which leads to an unique time-global solution.
Nesse trabalho, baseado principalmente nos artigos [1], [2] e [7], estuda-se um sistema reação-difusão-convecção, relacionado à propagação de uma frente de combustão em um meio poroso, recaindo sobre um problema de Cauchy. Tal problema é abordado através do método de iterações monótonas, o qual conduz a uma única solução global no tempo.
Galbally, David. "Nonlinear model reduction for uncertainty quantification in large-scale inverse problems : application to nonlinear convection-diffusion-reaction equation." Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/43079.
Includes bibliographical references (p. 147-152).
There are multiple instances in science and engineering where quantities of interest are evaluated by solving one or several nonlinear partial differential equations (PDEs) that are parametrized in terms of a set of inputs. Even though well-established numerical techniques exist for solving these problems, their computational cost often precludes their use in cases where the outputs of interest must be evaluated repeatedly for different values of the input parameters such as probabilistic analysis applications. In this thesis we present a model reduction methodology that combines efficient representation of the nonlinearities in the governing PDE with an efficient model-constrained, greedy algorithm for sampling the input parameter space. The nonlinearities in the PDE are represented using a coefficient-function approximation that enables the development of an efficient offline-online computational procedure where the online computational cost is independent of the size of the original high-fidelity model. The input space sampling algorithm used for generating the reduced space basis adaptively improves the quality of the reduced order approximation by solving a PDE-constrained continuous optimization problem that targets the output error between the reduced and full order models in order to determine the optimal sampling point at every greedy cycle. The resulting model reduction methodology is applied to a highly nonlinear combustion problem governed by a convection-diffusion-reaction PDE with up to 3 input parameters. The reduced basis approximation developed for this problem is up to 50, 000 times faster to solve than the original high-fidelity finite element model with an average relative error in prediction of outputs of interest of 2.5 - 10-6 over the input parameter space. The reduced order model developed in this thesis is used in a novel probabilistic methodology for solving inverse problems.
(cont) The extreme computational cost of the Bayesian framework approach for inferring the values of the inputs that generated a given set of empirically measured outputs often precludes its use in practical applications. In this thesis we show that using a reduced order model for running the Markov
by David Galbally.
S.M.
Ahmed, Naveed, and Gunar Matthies. "Higher order continuous Galerkin−Petrov time stepping schemes for transient convection-diffusion-reaction equations." Cambridge University Press, 2015. https://tud.qucosa.de/id/qucosa%3A39044.
Rasoamiaramanana, Daniel. "Analyse numérique de schémas aux différences à deux et trois niveaux pour le problème de diffusion-convection non stationnaire." Grenoble 2 : ANRT, 1987. http://catalogue.bnf.fr/ark:/12148/cb37609190m.
Muller, Nicolas. "Études mathématiques et numériques de problèmes non-linéaires et non-locaux issus de la biologie." Thesis, Paris 5, 2013. http://www.theses.fr/2013PA05S016.
We investigate the influence of the environment on the behaviour of a cell in two different situations. In each of these situations, there is a non-linear coupling of the drift due to a non-local term coming from the boundary of the domain.The first part focuses on the modeling of cell polarisation during the mating of yeast. We use a convection-diffusion model with a non-linear and non-local drift. This model is similar to the Keller-Segel model, the source of the attractive potential comes from the boundary of the domain. We study the long time behaviour of the one-dimensional case by using logarithmic Sobolev and HWI inequalities.By relying on a heuristic, we reduce the study of our model in the two-dimensional case to the boundary of the domain. We validate the model with data provided by M. Piel. This validation requires adding a dynamical noise in our numerical simulations. We study then the cell discussion between yeast of opposite gender. In the second part we study the immune response in atherosclerosis. We build and then develop an age structured model in order to describe the inflammation. For specific parameters, we investigate the long time behaviour of our system by using a Lyapunov functional
Kunert, Gerd. "A posteriori error estimation for convection dominated problems on anisotropic meshes." Universitätsbibliothek Chemnitz, 2002. http://nbn-resolving.de/urn:nbn:de:bsz:ch1-200200255.
Franz, Sebastian [Verfasser], Hans-Görg [Akademischer Betreuer] Roos, Thomas [Akademischer Betreuer] Apel, and Martin [Akademischer Betreuer] Stynes. "Uniform Error Estimation for Convection-Diffusion Problems / Sebastian Franz. Gutachter: Hans-Görg Roos ; Thomas Apel ; Martin Stynes. Betreuer: Hans-Görg Roos." Dresden : Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://d-nb.info/1068445068/34.
Ludwig, Lars. "Analytical investigations and numerical experiments for singularly perturbed convection-diffusion problems with layers and singularities using a newly developed FE-software." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2014. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-137301.