Forewords
On a low Mach nuclear core model
We propose to formally derive a low Mach number model adapted to the modeling of a water nuclear core ( of PWR- or BWR-type) in the forced convection regime or in the natural convection regime by filtering out the acoustic waves in the compressible Navier-Stokes system. Then, we propose a monodimensional stationary analytical solution with regular and singular charge loss when the equation of state is a stiffened gas equation. Moreover, we show that...
High-frequency limit of the Maxwell-Landau-Lifshitz equations in the diffractive optics regime
We study the Maxwell-Landau-Lifshitz system for highly oscillating initial data, with characteristic frequencies (1 ) and amplitude (1), over long time intervals (1 ), in the limit → 0. We show that a nonlinear Schrödinger equation gives a good approximation for the envelope of the solution in the time interval under consideration. This extends previous results of Colin and Lannes [1]. This text is a short version of the article [5].
Homogenization of a Conductive-Radiative Heat Transfer Problem
This paper focuses on the contribution of the second order corrector in periodic homogenization applied to a conductive-radiative heat transfer problem. Especially, for a heat conduction problem in a periodically perforated domain with a non-local boundary condition modelling the radiative heat transfer, if this model contains an oscillating thermal source and a thermal exchange with the perforations, the second order corrector helps us to model the gradients which appear between the source area...
A coupled well-balanced and random sampling scheme for computing bubble oscillations
We propose a finite volume scheme to study the oscillations of a spherical bubble of gas in a liquid phase. Spherical symmetry implies a geometric source term in the Euler equations. Our scheme satisfies the well-balanced property. It is based on the VFRoe approach. In order to avoid spurious pressure oscillations, the well-balanced approach is coupled with an ALE (Arbitrary Lagrangian Eulerian) technique at the interface and a random sampling remap.
Hybrid finite volume scheme for a two-phase flow in heterogeneous porous media
We propose a finite volume method on general meshes for the numerical simulation of an incompressible and immiscible two-phase flow in porous media. We consider the case that can be written as a coupled system involving a degenerate parabolic convection-diffusion equation for the saturation together with a uniformly elliptic equation for the global pressure. The numerical scheme, which is implicit in time, allows computations in the case of a heterogeneous...
Iterative reconstruction methods for wave equations
Some new iterative techniques are defined to solve reversible inverse problems and a common formulation is explained. Numerical improvements are suggested and tests validate the methods.
A matrix-based numerical method for the simulation of the two-dimensional sine-Gordon equation,
This paper describes a numerical method for the two-dimensional sine-Gordon equation over a rectangular domain using differentiation matrices, in the theoretical frame of matrix differential equations.
Probabilistic Interpretation for the Nonlinear Poisson-Boltzmann Equation in Molecular Dynamics
The Poisson-Boltzmann (PB) equation describes the electrostatic potential of a biomolecular system composed by a molecule in a solvent. The electrostatic potential is involved in biomolecular models which are used in molecular simulation. In consequence, finding an efficient method to simulate the numerical solution of PB equation is very useful. As a first step, we establish in this paper a probabilistic interpretation of the nonlinear PB equation with Backward Stochastic Differential Equations...
Spline discrete differential forms
The equations of physics are mathematical models consisting of geometric objects and relationships between then. There are many methods to discretize equations, but few maintain the physical nature of objects that constitute them. To respect the geometrical nature elements of physics, it is necessary to change the point of view and using differential geometry, including the numerical study. We propose to construct discrete differential forms using B-splines and a formulation discrete for different...
An anti-diffusive Lagrange-Remap scheme for multi-material compressible flows with an arbitrary number of components
We propose a method dedicated to the simulation of interface flows involving an arbitrary number of compressible components. Our task is two-fold: we first introduce a -component flow model that generalizes the two-material five-equation model of [2,3]. Then, we present a discretization strategy by means of a Lagrange-Remap [8,10] approach following the lines of [5,7,12]. The projection step involves an anti-dissipative mechanism derived from [11,12]. This feature allows to prevent the numerical...
A problem of optimal control with free initial state
We are studying an optimal control problem with free initial condition. The initial state of the optimized system is not known exactly, information on initial state is exhausted by inclusions ∈ . Accessible controls for optimization of continuous dynamic system are discrete controls defined on quantized axes. The method presented is based on the concepts and operations of the adaptive method [9] of linear programming. The results are illustrated by a fourth order...
Stabilité sous condition CFL non linéaire
We present a basic althought little known numerical stability condition: for convection equations, the von Neumann stability constraint ∥ ∥ ≤ (1 + Δ) ∥ ∥ drives to the stability condition Δ ≤ Δ with where is an integer linked to the stability domain of the time scheme and ≥ an integer linked to the upwind property of the space discretization (in the...
Oscillatory limits with varying spectrum
High time frequency oscillations occur in many different physical cases: slightly compressible fluids, almost quasineutral plasmas, small electron mass approximation .... In many case, small parameters arise in fluids mechanics or plasma physics, leading to these oscillations as the small parameter goes to zero. The aim of this note is to detail how to obtain formal expansions and to give some indications on how to justify them.
Algebraic spectral gaps
For the one-dimensional Schrödinger equation, some real intervals with no eigenvalues (the spectral gaps) may be obtained rather systematically with a method proposed by H. Giacomini and A. Mouchet in 2007. The present article provides some alternative formulation of this method, suggests some possible generalizations and extensively discusses the higher-dimensional case.
Numerical Verification of Industrial Numerical Codes
Several approximations occur during a numerical simulation: physical effects mapy be discarded, continuous functions replaced by discretized ones and real numbers replaced by finite-precision representations. The use of the floating point arithmetic generates round-off errors at each arithmetical expression and some mathematical properties are lost. The aim of the numerical verification activity at EDF R&D is to study the effect of the round-off error propagation on the results of a numerical...
A well-balanced finite volume scheme for 1D hemodynamic simulations
We are interested in simulating blood flow in arteries with variable elasticity with a one dimensional model. We present a well-balanced finite volume scheme based on the recent developments in shallow water equations context. We thus get a mass conservative scheme which also preserves equilibria of = 0. This numerical method is tested on analytical tests.
Information issues in differential game theory
In this survey paper we present recent advances in some classes of differential game in which there is an asymmetry of information between the players. We explain that—under suitable structure conditions—these games have a value, which can be characterized in terms of (new) Hamilton-Jacobi equations.
Parallel Computing for the study of the focusing Davey-Stewartson II equation in semiclassical limit
The asymptotic description of the semiclassical limit of nonlinear Schrödinger equations is a major challenge with so far only scattered results in 1 + 1 dimensions. In this limit, solutions to the NLS equations can have zones of rapid modulated oscillations or blow up. We numerically study in this work the Davey-Stewartson system, a 2 + 1 dimensional nonlinear Schrödinger equation with a nonlocal term, by using parallel computing. This leads to the first results on the semiclassical limit for...
Cerebral blood flow simulations in realistic geometries
The aim of this work is to perform the computation of the blood flow in all the cerebral network, obtained from medical images as angiographies. We use free finite elements codes as FreeFEM++. We first test the code on analytical solutions in simplified geometries. Then, we study the influence of boundary conditions on the flow and we finally perform first computations on realistic meshes.
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