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Le Barp, France

CEA/Cesta or simply Cesta is a French research facility dedicated to the design of nuclear weapons.The center was established in 1965 on the commune of Le Barp between Bordeaux and Arcachon.The center will host in the future the Megajoule laser , which will enable French nuclear scientists to validate models of nuclear explosion without having to conduct nuclear testing. The LMJ is the French equivalent of the National Ignition Facility. Wikipedia.

We present a one-step high-order cell-centered numerical scheme for solving Lagrangian hydrodynamics equations on unstructured grids. The underlying finite volume discretization is constructed through the use of the sub-cell force concept invoking conservation and thermodynamic consistency. The high-order extension is performed using a one-step discretization, wherein the fluxes are computed by means of a Taylor expansion. The time derivatives of the fluxes are obtained through the use of a node-centered solver which can be viewed as a two-dimensional extension of the Generalized Riemann Problem methodology introduced by Ben-Artzi and Falcovitz. © 2010 Elsevier Ltd. Source

Donohue J.T.,University of Bordeaux 1 | Gardelle J.,CEA Cesta
Applied Physics Letters | Year: 2011

The two-dimensional theory of the Smith-Purcell free-electron laser of Andrews and Brau [H. L. Andrews and C. A. Brau, Phys. Rev. ST Accel. Beams 7, 070701 (2004)] predicts that coherent Smith-Purcell radiation can occur only at harmonics of the frequency of the evanescent wave that is resonant with the beam. A particle-in-cell simulation shows that in a three-dimensional context, where the lamellar grating has sidewalls, coherent Smith-Purcell radiation can be copiously emitted at the fundamental frequency, for a well-defined range of beam energy. © 2011 American Institute of Physics. Source

Stupfel B.,CEA Cesta
IEEE Transactions on Antennas and Propagation | Year: 2013

For the solution of the time-harmonic electromagnetic scattering problem by inhomogeneous 3-D objects, a previously published one-way domain decomposition method (DDM) is considered: the computational domain is partitioned into concentric subdomains on the interfaces of which Robin-type transmission conditions (TCs) are prescribed, with an integral equation (IE) on the outer boundary of the computational domain (DDM-IE). On account of the large computing time required by the solution of the isolated IE system, in this paper the IE is replaced by the integral representations (IRs) of the fields that requires only a few matrix-vector products (adaptive absorbing boundary condition: AABC). The IRs necessitate the calculation of the electric and magnetic currents on some inner surface S that is chosen to be the interface between the last two subdomains. Taking advantage of the TCs, the unknown current on S (here the magnetic current) is obtained via a change of bases H(rot) to H(div) that allows the accurate computation of the IR integrals involving the surface divergence terms, and permits the separate solution of the FE systems in the last two subdomains. The matrix-vector products in the AABC are performed only once per DDM iteration. Numerical results are presented that illustrate the accuracy of the DDM-AABC and its superiority, in terms of computing time, over the DDM-IE. Also, some indications are given on how to estimate numerically the convergence rate of the DDM-AABC. © 1963-2012 IEEE. Source

Maire P.-H.,CEA Cesta | Breil J.,University of Bordeaux 1
Journal of Computational Physics | Year: 2012

In this paper, we describe a second-order accurate cell-centered finite volume method for solving anisotropic diffusion on two-dimensional unstructured grids. The resulting numerical scheme, named CCLAD (Cell-Centered LAgrangian Diffusion), is characterized by a local stencil and cell-centered unknowns. It is devoted to the resolution of diffusion equation on distorted grids in the context of Lagrangian hydrodynamics wherein a strong coupling occurs between gas dynamics and diffusion. The space discretization relies on the introduction of two half-edge normal fluxes and two half-edge temperatures per cell interface using the partition of each cell into sub-cells. For each cell, the two half-edge normal fluxes attached to a node are expressed in terms of the half-edge temperatures impinging at this node and the cell-centered temperature. This local flux approximation can be derived through the use of either a sub-cell variational formulation or a finite difference approximation, leading to the two variants CCLADS and CCLADNS. The elimination of the half-edge temperatures is performed locally at each node by solving a small linear system which is obtained by enforcing the continuity condition of the normal heat flux across sub-cell interface impinging at the node. The accuracy and the robustness of the present scheme is assessed by means of various numerical test cases. © 2011 Elsevier Inc. Source

We present a cell-centered discontinuous Galerkin discretization for the two-dimensional gas dynamics equations written using the Lagrangian coordinates related to the initial configuration of the flow, on general unstructured grids. A finite element discretization of the deformation gradient tensor is performed ensuring the satisfaction of the Piola compatibility condition at the discrete level. A specific treatment of the geometry is done, using finite element functions to discretize the deformation gradient tensor. The Piola compatibility condition and the Geometric Conservation law are satisfied by construction of the scheme. The DG scheme is constructed by means of a cellwise polynomial basis of Taylor type. Numerical fluxes at cell interface are designed to enforce a local entropy inequality. © 2012 Elsevier Ltd. Source

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