A Condensed Constrained Nonconforming Mortar-based Approach for Preconditioning Finite Element Discretization Problems

Abstract

This paper presents and studies an approach for constructing auxiliary space preconditioners for finite element problems, using a constrained nonconforming reformulation that is based on a proposed modified version of the mortar method. The well-known mortar finite element discretization method is modified to admit a local structure, providing an element-by-element, or subdomain-bysubdomain, assembly property. This is achieved via the introduction of additional trace finite element spaces and degrees of freedom (unknowns) associated with the interfaces between adjacent elements (or subdomains). The resulting nonconforming formulation and a reduced (Schur complement), via static condensation on the interfaces, form of it are used in the construction of auxiliary space preconditioners for a given conforming finite element discretization problem. The properties of these preconditioners are studied and their performance is illustrated on model second order scalar elliptic problems, utilizing high order elements.