An analytical solution of Shallow Water system coupled to Exner equation

In this paper, an exact smooth solution for the equations modeling the bedload transport of sediment in Shallow Water is presented. This solution is valid for a large family of sedimentation laws which are widely used in erosion modeling such as the Grass model or those of Meyer-Peter & Muller. One of the main interest of this solution is the derivation of numerical benchmarks to valid the approximation methods

An entropy preserving relaxation scheme for ten-moments equations with source terms

International audienceThe present paper concerns the derivation of finite volume methods to approximate weak solutions of Ten-Moments equations with source terms. These equations model compressible anisotropic flows. A relaxation-type scheme is proposed to approximate such flows. Both robustness and stability conditions of the suggested finite volume methods are established. To prove discrete entropy inequalities, we derive a new strategy based on local minimum entropy principle and never use some approximate PDE's auxiliary model as usually recommended. Moreover, numerical simulations in 1D and in 2D illustrate our approach

Design of coupled finite volume schemes minimizing the grid orientation effect in reservoir simulation

In this paper, we propose an analysis method for the so-called grid orientation effect (GOE) in the numerical simulation of two-phase flows in porous media. The GOE, which occurs when using coupled finite volume schemes on structured grids, is well known to engineers. Several attempts, most of which are of empirical nature, have been put forward in order to alleviate this undesirable phenomenon. Here, our approach relies on a more rigorous notion of angular error for all directions, which in turn enables us via integration and minimization to single out the least anisotropic scheme within a given family of schemes depending on some tuning parameter(s). Numerical test problems testify to the improvement brought by the new construction. grid orientation effect; reservoir simulation; finite volume schemes; nine-point scheme

Satisfiability Modulo Free Data Structures Combined with Bridging Functions

International audienceFree Data Structures are finite semantic trees modulo equational axioms that are useful to represent classical data structures such as lists, multisets and sets. We study the satisfiability problem when free data structures are combined with bridging functions. We discuss the possibility to get a combination methodàmethod`methodà la Nelson-Oppen for these particular non-disjoint unions of theories. In order to handle satisfiability problems with disequalities, we investigate a form of sufficient surjectivity for the bridging functions

A Godunov-Type Solver for the Numerical Approximation of Gravitational Flows

International audienceWe present a new numerical method to approximate the solutions of an Euler-Poisson model, which is inherent to astrophysical flows where gravity plays an important role. We propose a discretization of gravity which ensures adequate coupling of the Poisson and Euler equations, paying particular attention to the gravity source term involved in the latter equations. In order to approximate this source term, its discretization is introduced into the approximate Riemann solver used for the Euler equations. A relaxation scheme is involved and its robustness is established. The method has been implemented in the software HERACLES and several numerical experiments involving gravitational flows for astrophysics highlight the scheme

A Local Entropy Minimum Principle for Deriving Entropy Preserving Schemes

International audienceThe present work deals with the establishment of stability conditions of finite volume methods to approximate weak solutions of the general Euler equations to simulate compressible flows. In oder to ensure discrete entropy inequalities, we derive a new technique based on a local minimum principle to be satisfied by the specific entropy. Sufficient conditions are exhibited to satisfy the required local minimum entropy principle. Arguing these conditions, a class of entropy preserving schemes is thus derived