This paper presents a hybrid numerical method to solve efficiently a class of highly anisotropic elliptic problems. The anisotropy is aligned with one coordinate axis and its strength is described by a parameter ε ∈ (0, 1], which can largely vary in the study domain. Our hybrid model is based on asymptotic techniques and couples (spatially) an asymptotic-preserving model with its asymptotic limit model, the latter being used in regions where the anisotropy parameter ε is small. Adequate coupling conditions link the two models. The aim of this hybrid procedure is to reduce the computational time for problems where the region of small ε-values extends over a significant part of the domain, and this is due to the reduced complexity of the limit model.
Introduction.The present work is a contribution to the numerical resolution of highly anisotropic elliptic equations, the anisotropy being aligned with one coordinate axis and described by a perturbation parameter ε ∈ (0, 1], varying considerably in the study domain. The approach presented here is based on a coupling strategy, solving an asymptotic-preserving (AP) reformulation of the elliptic problem, where ε is nonnegligible, and solving the corresponding asymptotic limit model, where ε is quasi-vanishing. The strategy we propose is particularly well suited for physical systems in which the anisotropy parameter ε is very small in a large part of the study domain.Such types of directionally anisotropic diffusion systems are common in physical applications, such as plasma physics [4,13,14,16,25,26].The application which was at the origin of the present work comes from strongly magnetized ionospheric plasmas [1,15,21]. The problem we shall study here is extracted from the dynamo model and represents an elliptic equation for the computation of the electric potential in two-dimensions, i.e.,