This paper addresses the recovery of piecewise smooth functions from their discrete data.Reconstruction methods using both pseudo-spectral coefficients andphysical space interpolants have been discussed extensively in theliterature, and it is clear that an a priori knowledge of the jumpdiscontinuity location is essential for any reconstruction techniqueto yield spectrally accurate results with high resolution near thediscontinuities. Hence detection of the jump discontinuities iscritical for all methods. Here we formulate a new localized reconstruction method adapted from themethod developed in Gottlieb and Tadmor (1985) and recently revisited in Tadmor and Tanner (in press). Our procedure incorporates the detection of edges into the reconstruction technique. The methodis robust and highly accurate, yielding spectral accuracy up to a smallneighborhood of the jump discontinuities. Results are shown inone and two dimensions.

Different effective boundary conditions or wall laws for unsteady incompressible Navier-Stokes equations over rough domains are derived in the laminar setting. First and second order unsteady wall laws are proposed using two scale asymptotic expansion techniques. The roughness elements are supposed to be periodic and the influence of the rough boundary is incorporated through constitutive constants. These constants are obtained by solving steady Stokes problems and so they are calculated only once. Numerical tests are presented to validate and compare the proposed boundary conditions.

The numerical solution of the flow of a liquid crystal governedby a particular instance of the Ericksen–Leslie equations is considered.Convergence results for this system rely crucially upon energyestimates which involve H2 (Ω) norms of the director field. Weshow how a mixed method may be used to eliminate the need forHermite finite elements and establish convergence of the method.

In this paper, we are interested in finding the optimal shapeof a magnet. The criterion to maximize is the jump of theelectromagnetic field between two different configurations.We prove existence of an optimal shape into a natural classof domains. We introduce a quasi-Newton type algorithm whichmoves the boundary. This method is very efficient to improvean initial shape. We give some numerical results.

In this paper we combine the dual-mixed finite element method with a Dirichlet-to-Neumann mapping(given in terms of a boundary integral operator) to solve linear exterior transmission problems inthe plane. As a model we consider a second order elliptic equation in divergence form coupled withthe Laplace equation in the exterior unbounded region. We show that the resulting mixed variationalformulation and an associated discrete scheme using Raviart-Thomas spaces are well posed, and derivethe usual Cea error estimate and the corresponding rate of convergence. In addition, we develop twodifferent a-posteriori error analyses yielding explicit residual and implicit Bank-Weiser typereliable estimates, respectively. Several numerical results illustrate the suitability of theseestimators for the adaptive computation of the discrete solutions.

This article is devoted to the numerical study of a flame ball model, derived by Joulin, which obeys to a singular integro-differential equation. The numerical scheme that we analyze here, is based upon a one step method, and we are interested in its long-time behaviour. We recover the same dynamics as in the continuous case: quenching, or stabilization of the flame, depending on heat losses, and an energy input parameter.

In this paper we consider the Maxwell resolvent operator and its finite elementapproximation. In this framework it is natural the use of the edge elementspaces and to impose the divergence constraint in a weaksense with the introduction of a Lagrange multiplier, followingan idea by Kikuchi [14].We shall review some of the known properties for edge elementapproximations and prove some new result. In particular we shall prove auniform convergence in the L 2 norm for the sequence of discrete operators.These results, together with a general theory introduced by Brezzi, Rappaz andRaviart [8], allow an immediate proof of convergence for thefinite element approximation of the time-harmonicMaxwell system.

We consider a new formulation for finite volume element methods, which is satisfied byknown finite volume methods and itcan be used to introduce new ones. This framework results by approximating the test function in theformulation of finite element method.We analyze piecewise linear conforming or nonconforming approximations on nonuniform triangulations andprove optimal order H 1-norm and L 2-norm errorestimates.

The aim of this work is to deduce the existence of solutionof a coupled problem arising in elastohydrodynamiclubrication. The lubricant pressure and concentration aremodelled by Reynolds equation, jointly with the free-boundaryElrod-Adams model in order to take into account cavitationphenomena. The bearing deformation is solution of Koitermodel for thin shells. The existence of solution to thevariational problem presents some difficulties: the coupledcharacter of the equations, the nonlinear multivaluedoperator associated to cavitation and the fact of writing theelastic and hydrodynamic equations on two different domains.In a first step, we regularize the Heaviside operator.Additional difficulty related to the differentdomains is circumvented by means of prolongation andrestriction operators, arriving to a regularized coupledproblem. This one is decoupled into elastic and hydrodynamicparts, and we prove the existence of a fixed point for theglobal operator. Estimations obtained for theregularized problem allow us to prove the existence ofsolution to the original one. Finally, a numerical method is proposed in orderto simulate a real journal-bearing device and illustrate the qualitative andquantitative properties of the solution.

This paper is devoted to the study of a turbulentcirculation model. Equations are derived from the “Navier-Stokes turbulentkinetic energy” system. Some simplifications are performed but attentionis focused on non linearities linked to turbulent eddy viscosity  $\nu _{t}$ . The mixing length $\ell $ acts as a parameter which controls theturbulent part in $\nu _{t}$ . The main theoretical results that we haveobtained concern the uniqueness of the solution for bounded eddy viscositiesand small values of $\ell $ and its asymptotic decreasing as $\ell\rightarrow \infty $ in more general cases. Numerical experimentsillustrate but also allow to extend these theoretical results: uniqueness isproved only for $\ell $ small enough while regular solutions are numericallyobtained for any values of $\ell $ . A convergence theorem is proved forturbulent kinetic energy: $k_{\ell }\rightarrow 0$ as $\ell \rightarrow\infty ,$ but for velocity $u_{\ell }$ we obtain only weaker results.Numerical results allow to conjecture that $k_{\ell }\rightarrow 0,$ $\nu_{t}\rightarrow \infty $ and $u_{\ell }\rightarrow 0$ as $\ell \rightarrow\infty .$ So we can conjecture that this classical turbulent model obtainedwith one degree of closure regularizes the solution.