Évènements

The time-harmonic formulation of Maxwell’s equations presents several difficulties when the frequency is large. Here we propose a precise and efficient solution strategy that couples high order finite element discretizations with domain decomposition preconditioners. Finite elements suited for the approximation of the electric field are the curl-conforming (or edge) finite elements. Here, we revisit the classical degrees of freedom defined by Nédélec, in order to obtain a new more friendly expression in terms of the chosen high order basis functions. Moreover, we propose a general technique to restore duality between degrees of freedom and basis functions. We explicitly describe an implementation strategy, which we embedded in the open source domain specific language FreeFem++. In the second part, we focus on the preconditioning of the system resulting from the finite element discretization. In particular we investigate how two-level domain decomposition preconditioners recently analyzed for the Helmholtz equation work in the Maxwell case, both from the theoretical and numerical points of view. We apply these methods to the large scale problem arising from the modeling of a microwave imaging system, for the detection and monitoring of brain strokes. In this application accuracy and computing speed are indeed of paramount importance.

The objective of this work is the mathematical study for a Bresse system, consisting of coupled three wave equations in one dimensional open bounded domain. This system has its origin in the mechanics of structures and especially in the balance of elastic bars. We are interested in Bresse systems with three memories and three delays. The aim is the proof of the well-posedness and exponential stability of this system under some hypotheses.