Jérôme Pousin

Farshid Dabaghi, Pavel Krejci, Adrien Petrov et al.

This paper deals with a one-dimensional wave equation being subjected to a unilateral boundary condition. An approximation of this problem combining the finite element and mass redistribution methods is proposed. The mass redistribution method is based on a redistribution of the body mass such that there is no inertia at the contact node and the mass of the contact node is redistributed on the other nodes. The convergence as well as an error estimate in time are proved. The analytical solution associated with a benchmark problem is introduced and it is compared to approximate solutions for different choices of mass redistribution. However some oscillations for the energy associated with approximate solutions obtained for the second order schemes can be observed after the impact. To overcome this difficulty, an new unconditionally stable and a very lightly dissipative scheme is proposed.

Olivier Besson, Martine Picq, Jérôme Pousin

This work originates from a heart's images tracking which is to generate an apparent continuous motion, observable through intensity variation from one starting image to an ending one both supposed segmented. Given two images $ρ_0$ and $ρ_1$, we calculate an evolution process $ρ(t,\cdot)$ which transports $ρ_0$ to $ρ_1$ by using the optical flow. In this paper we propose an algorithm based on a fixed point formulation and a space-time least squares formulation of the transport equation for computing a transport problem. Existence results are given for a transport problem with a minimum divergence for a dual norm or a weighted $H^1_0$-semi norm, for the velocity. The proposed transport is compare with the transport introduced by Dacorogna-Moser. The strategy is implemented in a 2D case and numerical results are presented with a first order Lagrange finite element, showing the efficiency of the proposed strategy.

Jérôme Pousin, Eric Zeltz, Gérard Debicki

L'objectif de cette note est de proposer un modèle mathématique simple permettant de comprendre l'arrêt de la pénétration d'un flux de vapeur d'eau condensable sur un mur de béton, observé expérimentalement (voir par exemple les différentes expériences d'injection de vapeur dans du béton présentées dans [11], et [7]). Un modèle homogénéisé simple d'injection dans un milieu poreux est proposé, donnant une borne pour la position asymptotique en temps du front de pénétration. The aim of this paper is to propose a simple mathematical model to understand the decision of the penetration of a stream of water vapor condensing on a concrete wall, observed experimentally (see for example the situations described in [11], and [7]). A simple homogenized model for the injection in a porous medium is proposed, giving a bound for the asymptotic-time position at the front of penetration.