Dissertations / Theses on the topic 'Problèmes Parabolique'
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Kaddouri, Isma. "Problèmes inverses pour des problèmes d'évolution paraboliques à coefficients périodiques." Thesis, Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4322/document.
This thesis consists in the study of two problems associated to inverse para-bolic equations with periodic coefficients. We are interested in identifying one coefficient by using two different methods. In the first part, we consider a parabolic equation with periodic coefficients and periodic initial condition. Our work consists to consider the case of coefficient with weak regularity and to minimize the constraints of observations which are required to establish our reconstruction result. We establish a result of existence and uniqueness of the solution in adequate energy space. Then we prove a maximum principle adapted to the hypothesis of the problem studied and we work with measurable and bounded coefficients. Finally, we reconstruct the potential by establishing a Carleman estimate. The identification result was achieved via an inequality of stability. In the second work, we are interested to determine a periodic coefficient of the reaction term defined in the whole space $mathbb{R}$. We establish a uniqueness result by using a new type of observations. The nature of the studied problem allowed us to use the notion of asymptotic speed of propagation. We prove the existence of this speed and we give its characterization. We overdetermin the inverse problem by choosing a family of initial conditions exponentially decaying. Our main result is that the coefficient is uniquely determined up to a symmetry, by the observation of a continuum of asymptotic speed of propagation
Seam, Ngonn. "Études de problèmes aux limites non linéaires de type pseudo-parabolique." Phd thesis, Université de Pau et des Pays de l'Adour, 2010. http://tel.archives-ouvertes.fr/tel-00523633.
Louis-Rose, Carole Julie. "Sur la contrôlabilité à zéro de problèmes d’évolution de type parabolique." Thesis, Antilles-Guyane, 2013. http://www.theses.fr/2013AGUY0609/document.
This thesis is devoted to the study of the null controllability of systems of parabolic partial differential equations, which we meet in physics, chemistry or in biology. In chemistry or in biology, the se systems model the evolution in time of a chemical concentration or the density of a population (of bacteria, cells). The aim of nu Il controllability is to lead the solution of the system to zero in a given time T, by acting on the system with a control. Thus we are looking for a control, of minimal norm, such as the associated solution y satisfies y(T)=O in the domain Omega under concern. We consider three types of null controllability problems in this thesis. At first, we are interested in the null controllability with afinite number of constraints on the normal derivative of the state, for the serni-Iinear heat equation. Then, we analyze the simultaneous null controllability with constraint on the control, for a linear system of two coupled parabolic equations. Our last study deals with the null controllability ofa non linear system oftwo coupled parabolic equations. We approach these controllability problems mainly by means of Carleman's inequalities. Indeed, the study of null controllability problems, and more generally exact controllability problems, is equivalent to obtain observability inequalities for the adjoint problem, consequences of Carleman's inequalities. We build the optimal controlusing the variationnal method and we characterize it by an optimality system
Kaddouri, Isma. "Problèmes inverses pour des problèmes d'évolution paraboliques à coefficients périodiques." Electronic Thesis or Diss., Aix-Marseille, 2014. http://www.theses.fr/2014AIXM4322.
This thesis consists in the study of two problems associated to inverse para-bolic equations with periodic coefficients. We are interested in identifying one coefficient by using two different methods. In the first part, we consider a parabolic equation with periodic coefficients and periodic initial condition. Our work consists to consider the case of coefficient with weak regularity and to minimize the constraints of observations which are required to establish our reconstruction result. We establish a result of existence and uniqueness of the solution in adequate energy space. Then we prove a maximum principle adapted to the hypothesis of the problem studied and we work with measurable and bounded coefficients. Finally, we reconstruct the potential by establishing a Carleman estimate. The identification result was achieved via an inequality of stability. In the second work, we are interested to determine a periodic coefficient of the reaction term defined in the whole space ℝ. We establish a uniqueness result by using a new type of observations. The nature of the studied problem allowed us to use the notion of asymptotic speed of propagation. We prove the existence of this speed and we give its characterization. We overdetermin the inverse problem by choosing a family of initial conditions exponentially decaying. Our main result is that the coefficient is uniquely determined up to a symmetry, by the observation of a continuum of asymptotic speed of propagation
Gisclon, Marguerite. "Etude des conditions aux limites pour des systèmes strictement hyperboliques, via l'approximation parabolique." Lyon 1, 1994. http://www.theses.fr/1994LYO10294.
Moutazaim, Fathallah. "EEtude de quelques problèmes inverses : parabolique et elliptique, à partir de données sur le bord d'un domaine borné." Compiègne, 1999. http://www.theses.fr/1999COMP1207.
Schweyer, Rémi. "Étude de l'existence et de la stabilité de dynamiques explosives pour des problèmes paraboliques critiques." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/1994/.
In this thesis, we have obtained a sharp description of blow-up dynamics (Universality of the bubble and the speed of the concentration, stability of the formation of the singularity) for three critical parabolic problems : harmonic heat flow in dimension two for the 1-corotational solutions, the energy critical semilinear heat flow in dimension four and the Patlak-Keller-Segel model in the parabolic-elliptic version, for supercritical mass solutions (M>8p). The first four chapters are devoted to the presentation of each problem, as well as the strategy of the proof. In the last three chapters have been placed submitted articles
Ben, slimene Byrame. "Comportement asymptotique des solutions globales pour quelques problèmes paraboliques non linéaires singuliers." Thesis, Sorbonne Paris Cité, 2017. http://www.theses.fr/2017USPCD059/document.
In this thesis, we study the nonlinear parabolic equation ∂ t u = ∆u + a |x|⎺⥾ |u|ᵅ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, ⍺ ∈ R, α > 0, 0 < Ƴ < min(2,N) and with initial value u(0) = φ. We establish local well-posedness in Lq(Rᴺ) and in Cₒ(Rᴺ). In particular, the value q = N ⍺/(2 − γ) plays a critical role.For ⍺ > (2 − γ)/N, we show the existence of global self-similar solutions with initial values φ(x) = ω(x) |x|−(2−γ)/⍺, where ω ∈ L∞(Rᴺ) is homogeneous of degree 0 and ||ω||∞ is sufficiently small. We then prove that if φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺ for |x| large, then the solution is global and is asymptotic in the L∞-norm to a self-similar solution of the nonlinear equation. While if φ(x)∼ω(x) |x| (x)|x|−σ for |x| large with (2 − γ)/α < σ < N, then the solution is global but is asymptotic in the L∞-norm toe t(ω(x) |x|−σ). The equation with more general potential, ∂ t u = ∆u + V(x) |u|ᵅ u, V(x) |x |⥾ ∈ L∞(Rᴺ), is also studied. In particular, for initial data φ(x)∼ω(x) |x| ⎺(²⎺⥾)/⍺, |x| large , we show that the large time behavior is linear if V is compactly supported near the origin, while it is nonlinear if V is compactly supported near infinity. we study also the nonlinear parabolic system ∂ t u = ∆u + a |x|⎺⥾ |v|ᴾ⎺¹v, ∂ t v = ∆v + b |x|⎺ ᴾ |u|q⎺¹ u, t > 0, x ∈ Rᴺ \ {0}, N ≥ 1, a,b ∈ R, 0 < y < min(2,N)? 0 < p < min(2,N), p,q > 1. Under conditions on the parameters p, q, γ and ρ we show the existence and uniqueness of global solutions for initial values small with respect of some norms. In particular, we show the existence of self-similar solutions with initial value Φ = (φ₁, φ₂), where φ₁, φ₂ are homogeneous initial data. We also prove that some global solutions are asymptotic for large time to self-similar solutions. As a second objective we consider the nonlinear heat equation ut = ∆u + |u|ᴾ⎺¹u - |u| q⎺¹u, where t ≥ 0 and x ∈ Ω, the unit ball of Rᴺ, N ≥ 3, with Dirichlet boundary conditions. Let h be a radially symmetric, sign-changing stationary solution of (E). We prove that the solution of (E) with initial value λ h blows up in finite time if |λ − 1| > 0 is sufficiently small and if 1 < q < p < Ps = N+2/N−2 and p sufficiently close to Ps. This proves that the set of initial data for which the solution is global is not star-shaped around 0
Mokrane, Abdelhafid. "Existence de solutions pour certains problèmes quasi linéaires elliptiques et paraboliques." Paris 6, 1986. http://www.theses.fr/1986PA066086.
Schweyer, Rémi. "Etude de l'existence et de la stabilité de dynamiques explosives pour des problèmes paraboliques critiques." Phd thesis, Université Paul Sabatier - Toulouse III, 2013. http://tel.archives-ouvertes.fr/tel-00969133.
Karimou, 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.
Hajj, Chehade Hana. "Contribution aux problèmes de diffusion non linéaire en hydrologie." Amiens, 2013. http://www.theses.fr/2013AMIE0103.
In this thesis, we model the interface (sharp interface) that exists naturally between sea water and fresh water in a homogenous confined coastal aquifer. We prove existence and uniqueness of some radial solutions. We consider then a fully nonlinear parabolic problem that generalizes the interface problem and prove a priori gradient estimates. Many applications are given such that the porous medium problem and the doubly nonlinear diffusion problem. For the last problem, we present too the self similar solutions and verify then the gradient estimates. Finally, we study existence of travelling waves for the interface equation with some source term
Rault, Jean-François. "Phénomène d'explosion et existence globale pour quelques problèmes paraboliques sous les conditions au bord dynamiques." Phd thesis, Université du Littoral Côte d'Opale, 2010. http://tel.archives-ouvertes.fr/tel-00554915.
Vohralík, Martin. "Méthodes numériques pour les équations elliptiques et paraboliques non linéaires : application à des problèmes d'écoulement en milieux poreux et fracturés." Paris 11, 2004. https://tel.archives-ouvertes.fr/tel-00008451.
We study numerical methods for the simulation of flow and contaminant transport in porous and fractured media. In Chapter 1 we propose a scheme allowing for efficient, robust, conservative, and stable discretizations of nonlinear degenerate parabolic convection–reaction–diffusion equations on unstructured grids in two or three space dimensions. We discretize the generally anisotropic diffusion term by means of the nonconforming finite element method and the other terms by means of the finite volume method and show the existence and uniqueness of a discrete solution and its convergence to a weak solution. We finally propose a version of this scheme for nonmatching grids and apply it to real simulations. In Chapter 2 we present a direct proof of the discrete Poincaré–Friedrichs inequalities and indicate optimal values of the constants in these inequalities. The results are important in the analysis of nonconforming numerical methods. In Chapter 3 we show that the lowest-order Raviart–Thomas mixed finite element method is equivalent to a particular multi-point finite volume scheme. This approach allows significant reduction of the computational time of the mixed finite element method without any loss of its high precision, which is confirmed by numerical experiments. Finally, in Chapter 4 we propose a version of the lowest-order Raviart–Thomas mixed finite element method for flow simulation in fracture networks that perturb rock massifs, prove that it is well posed, and study its relation to the nonconforming finite element method
Gombao, Sophie. "Equations de Hamilton-Jacobi-Bellman pour des problèmes de contrôle d'équations paraboliques semi-linéaires : approches théorique et numérique." Toulouse 3, 2004. http://www.theses.fr/2004TOU30027.
Karami, Fahd. "Limite singulière de quelques problèmes de Réaction Diffusion: Analyse mathématique et numérique." Phd thesis, Université de Picardie Jules Verne, 2007. http://tel.archives-ouvertes.fr/tel-00180724.
Vohralik, Martin. "Méthodes numériques pour des équations elliptiques et paraboliques non linéaires. Application à des problèmes d'écoulement en milieux poreux et fracturés." Phd thesis, Université Paris Sud - Paris XI, 2004. http://tel.archives-ouvertes.fr/tel-00008451.
Abourjaily, Chaouki. "Comparaison de deux problèmes paraboliques." Besançon, 1987. http://www.theses.fr/1987BESA2037.
Pincet, Mailly Gaëlle. "Explosion des solutions de problèmes paraboliques sous conditions au bord dynamiques." Littoral, 2001. http://www.theses.fr/2001DUNK0062.
This thesis deals with blow up phenomena for parabolic problems in a bounded domain under a dissipative dynamical boundary condition. Several problems are studied as well as reaction-diffusion equations and degenerate equations. The aim of this work is to establish the occurence of finite time blow up. So we are interested in various aspects. The comparison of solutions satisfying different boundary conditions as dynamical, Neumann and Dirichlet conditions underscores the monotonically dependance of the blow up time on the dynamical boundary condition and the damping of solutions. Thanks to comparison techniques, energy methods and spectral comparison, we obtain some lower and upper bounds of the blow up time, and sufficient conditions of finite time blow up. On the other hand, we study the asymptotic behaviour of solutions of some non-degenerate problems : we specify the growth order when approaching the blow up time. Then we caracterize the blow up set and we prove that it consists at most of a single point in the one-dimensional case
Lovat, Bruno. "Etudes de quelques problèmes paraboliques non locaux." Metz, 1995. http://docnum.univ-lorraine.fr/public/UPV-M/Theses/1995/Lovat.Bruno.SMZ9536.pdf.
In this work, we study a class of nonlocal, nonlinear parabolic problems. In these equations, the coefficients depend on the solution itself through global quantities like the total mass, the total flux or the total energy (for problems coming from physics) and the total density (for problems coming from mathematical methods of population biology). We study, not only, the existence and uniqueness of the solutions but also their longtime behaviour and their stability
Tahraoui, Yassine. "Problèmes paraboliques à contraintes, déterministes et stochastiques." Thesis, Pau, 2020. https://tel.archives-ouvertes.fr/tel-03126849.
In this thesis, our aim is to study elliptic and parabolic problems with constraints in theframe of deterministic and stochastic se3ngs. More precisely, we are interested in theexistence of solutions and the associated Lewy-Stampacchia (L-S) inequalities.In the 1rst chapter, we are interested in the proof of L-S inequalities associated with abilateral elliptic problem governed by a pseudomonotone operator in the frame of Sobolevspaces with variable exponents, we prove a result of existence of solutions sa sfying L-Sinequalities by using a technique of perturbation of the operator. In the second chapter, westudy a parabolic varia onal inequality with constraint where we prove a result of existenceof a solution sa sfying L-S inequalities; by a method of penalization of the constraint and atechnique of perturbation of the operator. In the last chapter, we are interested in astochas c parabolic obstacle problem governed by a T − monotone operator in the presenceof a stochastic reaction where we prove a result of existence and uniqueness of the solutionsa sfying L-S inequalities; by using a method of penalization of the constraint andperturbation of the stochastic reaction. Finally, we present some numerical illustrations ofthe previous problems in the one- dimensional space se3ng
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Autret, Laurent. "Vecteurs entiers et réversibilité des problèmes paraboliques." Poitiers, 1992. http://www.theses.fr/1992POIT2268.
Blanc, Thomas. "Etude mathématique des problèmes paraboliques fortement anisotropes." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0570.
This manuscript is devoted to the asymptotic analysis of parabolic equations with stiff terms. First, we perform the asymptotic analysis of a parabolic equation with stiff transport terms. An effective limit model is obtained by a two-scale analysis based on ergodic theory results. This effective system is again a parabolic system whose diffusion field is an average of the initial diffusion field along a group of unitary operators. The introduction of a corrector allows us to obtain a strong convergence result, with an order of convergence, for initial data not necessarily well prepared. We propose a numerical method to compute the effective diffusion field. This method is based on a Runge-Kutta scheme and a semi-Lagrangian scheme. The theoretically order of convergence is obtained numerically. We propose a numerical method based on operator splitting for the resolution of the parabolic system with stiff transport terms. Finally, we perform the asymptotic analysis of a strongly anisotropic parabolic problem. Under suitable smoothness hypotheses, an effective variational system is proposed. By using a suitable corrector, we obtain a strong convergence result and we are able to perform the error analysis. The arguments relate again to the two-scale analysis and the ergodic theory
Sbihi, Karima. "Etude de quelques E.D.P. non linéaires dans L^1 avec des conditions générales sur le bord." Phd thesis, Université Louis Pasteur - Strasbourg I, 2006. http://tel.archives-ouvertes.fr/tel-00110417.
Esteve, yague Carlos. "Étude qualitative de trois problèmes paraboliques non-linéaires." Thesis, Sorbonne Paris Cité, 2019. http://www.theses.fr/2019USPCD033.
This thesis is concerned with the study of three nonlinear parabolic problems : We start with a mathematical model for a micro-electro-mechanical system (MEMS) with variable dielectric permittivity. The model is based on a parabolic equation with singular nonlinearity which describes the dynamic deffection of an elastic plate under the effect of an electrostatic potential. We study the touchdown, or quenching, phenomenon. With the aim of controlling the touchdown set, we give results concerning the touchdownl ocalization in terms of the permittivity profile. In the second part of the thesis, we study a diffusive Hamilton-Jacobi equation in a bounded domain with zero Dirichlet boundary conditions. We analyze the gradient blow-up (GBU) that solutions can exhibit on the boundary of the domain. In a previous work, it was shown that single-point GBU solutions can be constructed in very particular domains, namely, locally fat domains and disks. We prove the existence of this kind ofsolutions for a large family of domains, for which the curvature of the domain may be nonconstant near the GBU point. In the last part of the thesis, we study the evolution problem associated to the j-th eigenvalue of the Hessian matrix. First, we show the existence of a (unique) viscosity solution, which can be approximated by the value function of a two-player zero-sumgame as the step length of the game goes to zero. Then, we show that solutions to this evolution problem converge exponentially fast to the unique stationary solution as t goes to ∞. Finally, we show that in some special cases (for affine boundary data) the solution coincides with the stationary solution in finite time
Falliero, Marc. "Comportement asymptotique de solutions de problèmes paraboliques dé́générés." Pau, 2002. http://www.theses.fr/2002PAUU3011.
The aim of this work is to study the long-time behaviour of solutions to the Dirichlet problem for non linear degenerate convection-reaction-diffusion equations. We look for some conditions leading to the existence of a bounded time global solution and to the uniqueness of the è-limit element which is a stationnary state. It is easier to study the existence and the asymptotic behaviour when the domain is a ball, and the solution radially symmetrical. Indeed the solution depends on one and only one space variable, the radial one. So the problem may be considered in one space dimension. Therefore the symmetrical case is first studied. Then symmetrisation techniques are used to deal with the non symmetrical case. In particular, when the domain is a ball, we prove that the è-limit element is radially symmetrical. Moreover, we point out conditions ensuring that the solution tends to zero
Wang, Chao. "Analyse de quelques problèmes elliptiques et paraboliques semi-linéaires." Phd thesis, Université de Cergy Pontoise, 2012. http://tel.archives-ouvertes.fr/tel-00809045.
Maghnouji, Abderrahman. "Problèmes elliptiques et paraboliques dans des domaines non-réguliers." Lille 1, 1992. http://www.theses.fr/1992LIL10161.
Bouhsiss, Fouzia. "Quelques résultats d'unicité pour des problèmes elliptiques et paraboliques." Besançon, 2001. http://www.theses.fr/2001BESA2048.
Redwane, Hicham. "Solutions normalisées de problèmes paraboliques et elliptiques non linéaires." Rouen, 1997. http://www.theses.fr/1997ROUES059.
Cohen, Laurent David. "Etude de quelques problèmes semi-linéaires paraboliques et elliptiques." Paris 6, 1986. http://www.theses.fr/1986PA066503.
Vasseur, Baptiste. "Étude de problèmes différentiels elliptiques et paraboliques sur un graphe." Thesis, Littoral, 2014. http://www.theses.fr/2014DUNK0400/document.
After a quick presentation of usual notations for the graph theory, we study the set of harmonic functions on graphs, that is, the functions whose laplacian is zero. These functions form a vectorial space. On a uniformly locally finite tree, we shaw that this space has dimension one or infinity. When the graph has an infinite number of cycles, this result change and we describe some examples showing that there exists a graph on which the harmonic functions form a vectorial space of dimension n, for all n. We also treat the case of a particular periodic graph. Then, we study more precisely the eigenvalues of infinite dimension. In this case, the eigenspace contains a subspace isomorphic to the set of bounded sequences. An inequality concerning the spectral is given when edges length is equal to one. Examples show that these inclusions are optimal. We also study the asymptotic behavior of eigenvalues for elliptic operators under dynamical Kirchhoff node conditions. We write the problem as a Sturm-Liouville operator and we transform it in a matrix problem. Then we find a characteristic equation whose zeroes correspond to eigenvalues. We deduce a formula for the asymptotic behavior. In the last chapter, we study the stability of stationary solutions for some reaction-diffusion problem whose the non-linear term is polynomial
Al, Sayed Waad. "Mesures réduites, grandes solutions et singularités de quelques problèmes paraboliques." Thesis, Tours, 2008. http://www.theses.fr/2008TOUR4021/document.
The thesis at hand is composed of three parts. The first part is devoted to present the notions of "good measure" and "reduced measure" for two non-linear parabolic problems. For each of these problems we construct a sequence, after a relaxation phenomenon, which converges to the "greatest" sub-solution of the given problem. Moreover, we look for "universal capacities" and we establish equivalence with Hausdorff measure. In the second part, we establish existence and uniqueness conditions for "large solutions" of parabolic problems whose non-linear term is an absorption one. Some boundary conditions will permit to prove uniqueness of solutions. In the last part we study the "singularities" of two non-linear parabolic problems
Mokrani, Amar. "Problèmes pseudo-paraboliques à vitesse asservie : Application en prospection pétrolière." Pau, 2008. http://www.theses.fr/2008PAUU3009.
This work deals with the mathematical analysis of a model initially proposed by the “Institut Français du Pétrole” (IFP). It concerns the evolution of a monolithological sedimentary basin with a maximum rate of erosion. We are led to consider a gravitational model where the flux of sediments is proportional to the gradient of the topography, following a dynamic law of type Darcy- Barenblatt, with a constraint. Then, a multiplier is introduced, playing the role of a flux-limiter, in order to reconcile a process of gravitational transport for the sedimentation and a mechanism maximum of erosion by autogeneous regulation. After a short presentation of this model “weather limited”, we present a method of compactness, based on a result of uniqueness for a non-standard nonlinear stationary problem, proving that a solution exists to the problem. Then, a result of existence of a sequence of solutions to an implicit time-discretisation of a differential inclusion is proved. By an alternative approach, based on the classical results of N. G. Meyers and J. Necas, it is possible to give a result of existence and uniqueness of the solution to slightly different model, for a regular initial condition. Then, thanks to some energy methods, locally hyperbolic aspects are proved. Some numerical simulations are also proposed in order to illustrate the theoretical aspects of the study and the influence of the different parameters of the equation. Finally, some conclusions and perspectives are proposed
Tayachi, Slim. "Solutions autosimilaires d'équations semi-linéaires paraboliques." Paris 13, 1996. http://www.theses.fr/1996PA132002.
El, Hachimi Abderrahmane. "Etude de quelques problèmes elliptiques et paraboliques liés au p-Laplacien." Doctoral thesis, Universite Libre de Bruxelles, 1993. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/212842.
Sauvy, Paul. "Étude de quelques problèmes elliptiques et paraboliques quasi-linéaires avec singularités." Thesis, Pau, 2012. http://www.theses.fr/2012PAUU3020/document.
This thesis deals with the mathematical field of nonlinear partial differential equations analysis. More precisely, we focus on quasilinear and singular problems. By singularity, we mean that the problems that we have considered involve a nonlinearity in the equation which blows-up near the boundary. This singular pattern gives rise to a lack of regularity and compactness that prevent the straightforward applications of classical methods in nonlinear analysis used for proving existence of solutions and for establishing the regularity properties and the asymptotic behavior of the solutions. To overcome this difficulty, we establish estimations on the precise behavior of the solutions near the boundary combining several techniques : monotonicity method (related to the maximum principle), variational method, convexity arguments, fixed point methods and semi-discretization in time. Throughout the study of three problems involving the p-Laplacian operator, we show how to apply this different methods. The three chapters of this dissertation the describes results we get :– In Chapter I, we study a singular elliptic absorption problem. By using sub- and super-solutions and variational methods, we prove the existence of the solutions. In the case of a strong singularity, by using local comparison techniques, we also prove that the compact support of the solution. In Chapter II, we study a singular elliptic system. By using fixed point and monotonicity arguments, we establish two general theorems on the existence of solution. In a second time, we more precisely analyse the Gierer-Meinhardt systems which model some biological phenomena. We prove some results about the uniqueness and the precise behavior of the solutions. In Chapter III, we study a singular parabolic absorption problem. By using a semi-discretization in time method, we establish the existence of a solution. Moreover, by using differential energy inequalities, we prove that the solution vanishes in finite time. This phenomenon is called "quenching"
Tort, Jacques. "Problèmes inverses pour des équations paraboliques issues de modèles de climat." Toulouse 3, 2012. http://thesesups.ups-tlse.fr/1649/.
This work aims at solving inverse issues in semilinear parabolic equations derived from the Budyko-Sellers climate model, which represents the evolution of the Earth's surface temperature during a long time period. A first step consists in studying an inverse problem in a one dimensional degenerate model on a meridian. In order to understand the consequences of boundary degeneracies, we have first investigated a one dimensional linear degenerate equation. We prove various Lipschitz stability results in the determination of a source term and a diffusive constant. We also solve an approximate controllability issue, putting a control at the degenerate boundary point. Eventually, we prove two Lipschitz stability results in the determination of the so-called insolation function, in both cases of the semilinear model on a meridian and the general semilinear equation posed on the Earth's surface
Seam, Ngonn. "Études de problèmes aux limites non linéaires de type pseudo-paraboliques." Pau, 2010. http://www.theses.fr/2010PAUU3005.
Canuto, Bruno. "Une contribution à l'étude de quelques problèmes inverses pour des équations paraboliques." Versailles-St Quentin en Yvelines, 1999. http://www.theses.fr/1999VERS0026.
Benhadid, Soumaia. "Semi-discrétisations en espace et approximation particulaire de problèmes hyperboliques et paraboliques." Lyon 1, 1990. http://www.theses.fr/1990LYO19001.
François, Gilles. "Comportement spectral asymptotique provenant de problèmes paraboliques sous conditions au bord dynamiques." Littoral, 2002. http://www.theses.fr/2002DUNK0083.
In this thesis, one studies the asymptotic behaviour of the eigenvalues associated with parabolic problems under dynamical boundary conditions. In the whole text, one puts our results on relation with the classical ones (e. G. Those related to the Dirichlet or Neumann boudary conditions). After obtaining a first result for the order of magnitude of the sequence (in the case of laplacian in an arbitrary domain), one considers two particular cases (the unit disc and the unit square in R2) and makes more explicit calculus for both domains. Then one extends the results of the first chapter to an elliptic operator with divergential form, and improves the order of magnitude of the sequence ina domaine of R2. Lastly, one makes a spectral analysis of a diffusion problem in a particular ramified space
Cocquebert, Cédric. "Méthodes de type "Waveform-FAC" pour la résolution numérique de problèmes paraboliques." Aix-Marseille 1, 1997. http://www.theses.fr/1997AIX11032.
Rouchon, Pierre. "Estimations à priori et critères d'exploxion pour les problèmes paraboliques non-linéaires." Paris 13, 2002. http://www.theses.fr/2002PA132017.
Sawangtong, Panumart. "Blow-up pour des problèmes paraboliques semi-linéaires avec un terme source localisé." Phd thesis, Université Montpellier II - Sciences et Techniques du Languedoc, 2010. http://tel.archives-ouvertes.fr/tel-00833171.
Feron, Pierre. "Schémas gradients appliqués à des problèmes elliptiques et paraboliques, linéaires et non-linéaires." Thesis, Paris Est, 2015. http://www.theses.fr/2015PESC1119/document.
The notion of gradient schemes, designed for linear and nonlinear elliptic and parabolic problems has the benefit of providing common convergence and error estimates results, which hold for a wide variety of numerical methods (finite element methods, nonconforming and mixed finite element methods, hybrid and mixed mimetic finite difference methods ...). Checking a minimal set of properties for a given numerical method suffices to prove that it belongs to the gradient schemes framework, and therefore that it is convergent on the different problems studied here. The study of the Stefan problem, the incompressible Stokes one and also the incompressible Navier-Stokes equations are presented in this thesis, where each one gets a convergence theorem set up with the gradient schemes framework. For Stokes and Navier-Stokes, we both provide the proof for the steady and the transient case dealing with some variational hypotheses which bring different convergence results. Finally, we also present four methods (Taylor-Hood, Crouzeix-Raviart, Marker-and-Cell, Hybrid Mixed Mimetic) for these two problems and we check that they enter in the gradient schemes framework
Alkhayal, Jana. "Équations paraboliques non linéaires pour des problèmes d'hydrogéologie et de transition de phase." Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS448/document.
The aim of this thesis is to study the existence of a solution for a class of evolution systems which are strongly coupled, as well as the singular limit of an advection-reaction-diffusion equation.In chapter 1, we describe briefly the derivation of a seawater intrusion model in confined and unconfined aquifers. For this purpose we combine Darcy's law with a mass conservation law and we neglect the effect of the vertical dimension.In chapter 2, we consider a system that generalizes the seawater intrusion model in unconfined aquifers. It is a strongly coupled nonlinear degenerate parabolic system. After discretizing in time, freezing and truncating the coefficients and finally regularizing the equations we apply Lax-Milgram theorem to prove the existence of a unique solution for the elliptic linear associated system. Then we apply a fixed point theorem to prove the existence of a solution for the nonlinear approximated problem. We obtain in addition an entropy estimate, which allows us in particular to prove the positivity of the solution. Finally, we pass to the limit in the system and the entropy in order to prove the existence of a solution for the initial problem.In chapter 3, we prove the existence of a solution for a system that contains in particular the seawater intrusion model in confined aquifers. This system is very similar to that introduced in chapter 2, only the pressure is a new unknown and we have the constraint that the sum of the unknown heights is a given function. The pressure is the Lagrange multiplier associated to the constraint. We obtain again an entropy estimate and we establish an estimate on the gradient of the pressure.In chapter 4, we are interested in the study of sharp interfaces that moves by a certain flow, by mean curvature flow for example. Singularities may occur in finite time which explains the necessity of having a differnet notion of surfaces. In this chapter, we introduce the notion of "varifolds" or generalized surfaces that extend the notion of manifolds. To these varifolds we associate a generalized mean curvature and a generalized normal velocity.In chapter 5, we consider an advection-reaction-diffusion equation arising from a chemotaxis-growth system proposed by Mimura and Tsujikawa. The unknown is the population density which is subjected to the effects of diffusion, of growth and to the tendency of migrating toward higher gradients of the chemotactic substance. When a small parameter tends to zero, the solution converges to a step function; the associated diffuse interface converges to a sharp interface which moves by perturbed mean curvature. We represent these interfaces by varifolds defined by the Lyapunov functional of the Allen-Cahn problem. We establish a monotonicity formula and we prove a property of equipartition of energy. We prove also the rectability of the varifold and that the multiplicity function is almost everywhere integer
Ould, el Mounir Abdallahi. "Comportement pour les grands temps pour les problèmes paraboliques dégénérés comportant des termes gradient." Besançon, 2002. http://www.theses.fr/2002BESA2063.
Bruyère, Nicolas. "Comportement asymptotique de problèmes posés dans les cylindres. Problèmes d’unicité pour les systèmes Boussinesq." Rouen, 2007. http://www.theses.fr/2007ROUES032.
The thesis is divided in two independent parts. In the first part, we investigate the asymptotic behaviour of elliptic and parabolic problems with L1 + W 1,p’ data (respectively with L1+ Lp (0, T ; W-1,p’) data in the parabolic case), in domaine becoming unbounded. Using the framework of renormalized solutions and the regularity results of the solutions for such data, we prove, under structural conditions on space variables, convergence results in spaces containing the solutions. In the second part, in the 2-dimensional case, we study Boussinesq type systems. These systems derive from fluid mechanics models and couple incompressible Navier-Stokes equations and heat equation. We focus our attention on studying the uniqueness of the solution, which is intricate because of the very nonlinear coupling of the equations. We consider weak solutions for the Navier-Stokes equations and renormalized solutions are used for the heat equation. We state regularity results for these equations and then we prove few existence and uniuqueness results of the solution of the system for small data
Sfaxi, Mourad. "Analyse asymptotique de problèmes d'évolution dégénérés dans des structures hétérogènes et anisotropes." Aix-Marseille 1, 2006. http://www.theses.fr/2006AIX11022.