Adaptive Solution of a Singularly-Perturbed Convection-Diffusion Problem Using a Stabilized Mixed Finite Element Method

We explore the applicability of a new adaptive stabilized dual-mixedfinite element method to a singularly-perturbed convection-diffusion equation withmixed boundary conditions. We establish the rate of convergence when the fluxand the concentration are approximated, respectively, by Raviart-Thomas/Brezzi-Douglas-Marini and continuous piecewise polynomials. We consider a simple a pos-teriori error indicator and provide some numerical experiments that illustrate theperformance of the method

Necking in 2D incompressible polyconvex materials: theoretical framework and numerical simulations

We show examples of 2D incompressible isotropic homogeneous hyperelastic materials with a poly-convex stored-energy function that present necking. The construction of the stored-energy function of amaterial satisfying all those properties requires a fine search. We used the software Algencan to perform numerical experiments and visualize necking for the examples constructed. The algorithm is based on minimization of the elastic energy under the nonconvex constraint of incompressibility

A modified discontinuous Galerkin method for solving efficiently Helmholtz problems

A new solution methodology is proposed for solving efficiently Helmholtz problems. The proposed method falls in the category of the discontinuous Galerkin methods. However, unlike the existing solution methodologies, this method requires solving (a) well-posed local problems to determine the primal variable, and (b) a global positive semi-definite Hermitian system to evaluate the Lagrange multiplier needed to restore the continuity across the element edges. Illustrative numerical results obtained for two-dimensional interior Helmholtz problems are presented to assess the accuracy and the stability of the proposed solution methodology

A Simulation Method for the Computation of the E

We propose a set of numerical methods for the computation of the frequency-dependent eff ective primary wave velocity of heterogeneous rocks. We assume the rocks' internal microstructure is given by micro-computed tomography images. In the low/medium frequency regime, we propose to solve the acoustic equation in the frequency domain by a Finite Element Method (FEM). We employ a Perfectly Matched Layer to truncate the computational domain and we show the need to repeat the domain a su cient number of times to obtain accurate results. To make this problem computationally tractable, we equip the FEM with non-fitting meshes and we precompute multiple blocks of the sti ffness matrix. In the high-frequency range, we solve the eikonal equation with a Fast Marching Method. Numerical results con rm the validity of the proposed methods and illustrate the e ffect of density, porosity, and the size and distribution of the pores on the e ective compressional wave velocity

Stabilization and a posteriori error analysis of a mixed FEM for convection–diffusion problems with mixed boundary conditions

We introduce a new augmented dual-mixed finite element method for the linear convection-diffusion equation with mixed boundary conditions. The approach is based on adding suitable residual type terms to a dual-mixed formulation of the problem. We prove that for appropriate values of the stabilization parameters, that depend on the diffusivity and the magnitude of the convective velocity, the new variational formulation and the corresponding Galerkin scheme are well-posed and a Céa estimate can be derived. We establish the rate of convergence when the flux and the concentration are approximated, respectively, by Raviart–Thomas/Brezzi–Douglas–Marini and continuous piecewise polynomials. In addition, we develop an a posteriori error analysis of residual type. We derive a simple a posteriori error indicator and prove that it is reliable and locally efficient. Finally, we provide some numerical experiments that illustrate the performance of the method.POCTEFA 2014–2020, Spain grant No. EFA362/19 - PIXI

A stable discontinuous Galerkin-type method for solving efficiently Helmholtz problems

We propose a stable discontinuous Galerkin-type method (SDGM) for solving efficiently Helmholtz problems. This mixed-hybrid formulation is a two-step procedure. Step 1 consists in solving well-posed problems at the element partition level of the computational domain, whereas Step 2 requires the solution of a global system whose unknowns are the Lagrange multipliers. The main features of SDGM include: (a) the resulting local problems are associated with small positive definite Hermitian matrices that can be solved in parallel, and (b) the matrix corresponding to the global linear system arising in Step 2 is Hermitian and positive semi-definite. Illustrative numerical results for two-dimensional waveguide and scattering problems highlight the potential of SDGM for solving efficiently Helmholtz problems in mid- and high-frequency regime