GPU-accelerated discontinuous Galerkin methods on hybrid meshes

We present a time-explicit discontinuous Galerkin (DG) solver for the time-domain acoustic wave equation on hybrid meshes containing vertex-mapped hexahedral, wedge, pyramidal and tetrahedral elements. Discretely energy-stable formulations are presented for both Gauss-Legendre and Gauss-Legendre-Lobatto (Spectral Element) nodal bases for the hexahedron. Stable timestep restrictions for hybrid meshes are derived by bounding the spectral radius of the DG operator using order-dependent constants in trace and Markov inequalities. Computational efficiency is achieved under a combination of element-specific kernels (including new quadrature-free operators for the pyramid), multi-rate timestepping, and acceleration using Graphics Processing Units.Comment: Submitted to CMAM

An efficient domain decomposition method with cross-point treatment for Helmholtz problems

National audienceThe parallel finite-element solution of large-scale time-harmonic scattering problems is addressed with a non-overlapping domain decomposition method. The efficiency of this method strongly depends on the transmission condition enforced on the interfaces between the subdomains. Conditions based on high-order local absorbing boundary conditions have proved well suited for configurations without cross points (i.e. points where more than two subdomains meet). In this work, we extend this approach to efficiently deal with cross points. Two-dimensional numerical results are presented

Corner treatments for high-order local absorbing boundary conditions in high-frequency acoustic scattering

International audienceThis paper deals with the design and validation of accurate local absorbing boundary conditions set on convex polygonal and polyhedral computational domains for the finite element solution of high-frequency acoustic scattering problems. While high-order absorbing boundary conditions (HABCs) are accurate for smooth fictitious boundaries, the precision of the solution drops in the presence of corners if no specific treatment is applied. We present and analyze two strategies to preserve the accuracy of Padé-type HABCs at corners: first by using compatibility relations (derived for right angle corners) and second by regularizing the boundary at the corner. Exhaustive numerical results for two- and three-dimensional problems are reported in the paper. They show that using the compatibility relations is optimal for domains with right angles. For the other cases, the error still remains acceptable, but depends on the choice of the corner treatment according to the angle

An efficient domain decomposition method with cross-point treatment for Helmholtz problems

International audienceThe parallel finite-element solution of large-scale time-harmonic scattering problems is addressed with a non-overlapping domain decomposition method (DDM). It is well known that the efficiency of this method strongly depends on the transmission condition enforced on the interfaces between the subdomains. Local conditions based on high-order absorbing boundary conditions (HABCs) are well suited for configurations without cross points (where more than two subdo-mains meet). In this work, we extend this approach to efficiently deal with cross points. Two-dimensional finite-element results are presented

An automatic PML for acoustic finite element simulations in convex domains of general shape

International audienceThis article addresses the efficient finite element solution of exterior acoustic problems with truncated computational domains surrounded by perfectly matched layers (PMLs). The PML is a popular nonreflecting technique that combines accuracy, computational efficiency, and geometric flexibility. Unfortunately, the effective implementation of the PML for convex domains of general shape is tricky because of the geometric parameters that are required to define the PML medium. In this work, a comprehensive implementation strategy is proposed. This approach, which we call the automatically matched layer (AML) implementation, is versatile and fully automatic for the end‐user. With the AML approach, the mesh of the layer is extruded, the required geometric parameters are automatically obtained during the extrusion step, and the practical implementation relies on a simple modification of the Jacobian matrix in the elementwise integrals. The AML implementation is validated and compared with other implementation strategies using numerical benchmarks in two and three dimensions, considering computational domains with regular and nonregular boundaries. A three‐dimensional application with a generally shaped domain generated using a convex hull is proposed to illustrate the interest of the AML approach for realistic industrial cases

An efficient domain decomposition method with cross-point treatment for Helmholtz problems

National audienceThe parallel finite-element solution of large-scale time-harmonic scattering problems is addressed with a non-overlapping domain decomposition method. The efficiency of this method strongly depends on the transmission condition enforced on the interfaces between the subdomains. Conditions based on high-order local absorbing boundary conditions have proved well suited for configurations without cross points (i.e. points where more than two subdomains meet). In this work, we extend this approach to efficiently deal with cross points. Two-dimensional numerical results are presented

An efficient domain decomposition method with cross-point treatment for Helmholtz problems

International audienceSolving high-frequency time-harmonic scattering problems using finite element techniques is challenging, as such problems lead to very large, complex and indefinite linear systems. Optimized Schwarz domain decomposition methods (DDMs) are currently a very promising approach, where subproblems of smaller sizes are solved in parallel using direct solvers, and are combined in an iterative procedure.It is well-known that the convergence rate of these methods strongly depends on the transmission condition enforced on the interfaces between the subdomains. Local transmission conditions based on high-order absorbing boundary conditions (HABCs) have proved well suited [Boubendir et al, 2012; Gander et al, 2002]. They represent a good compromise between basic impedance conditions (which lead to suboptimal convergence) and the exact Dirichlet-to-Neumann (DtN) map related to the complementary of the subdomain (which is expensive to compute). However, a direct application of this approach for domain decomposition configurations with cross-points, where more than two subdomains meet, does not provide satisfactory results.We present an improved DDM that efficiently addresses configurations with cross points. Noting that these points actually are corners for the subdomains, our strategy consists in incorporating a corner treatment developed for HABCs into the DDM procedure. After a presentation of the key aspects of the methods, the effectiveness of our approach is discussed with two-dimensional finite element results

A nodal discontinuous Galerkin method with high-order absorbing boundary conditions and corner/edge compatibility

International audienceWe present the coupling of a nodal discontinu-ous Galerkin (DG) scheme with high-order absorbing boundary conditions (HABCs) for the simulation of transient wave phenomena. The HABCs are prescribed on the faces of a cuboidal domain in order to simulate infinite space. To preserve accuracy at the corners and the edges of the domain, novel compatibility conditions are derived. The method is validated using 3D computational results