A FEM approximation of a two-phase obstacle problem and its a posteriori error estimate. (1st February 2017)

• Record Type: Journal Article
• Authors: Bozorgnia, Farid; Valdman, Jan
• Is Part Of: Computers & mathematics with applications. Volume 73:issue 3(2017)
• Page Start: 419
• Page End: 432
• Publication Date: 2017-02-01
• Subjects: A free boundary problem -- A posteriori error analysis -- Finite element method -- Dual problem -- Discretization -- Computer implementation; Electronic data processing -- Periodicals; Mathematics -- Data processing -- Periodicals; 510.28541
• DOI: 10.1016/j.camwa.2016.11.037
• Languages: English
• ISSNs: 0898-1221

Abstract

Abstract: This paper is concerned with the two-phase obstacle problem, a type of a variational free boundary problem. We recall the basic estimates of Repin and Valdman (2015) and verify them numerically on two examples in two space dimensions. A solution algorithm is proposed for the construction of the finite element approximation to the two-phase obstacle problem. The algorithm is not based on the primal (convex and nondifferentiable) energy minimization problem but on a dual maximization problem formulated for Lagrange multipliers. The dual problem is equivalent to a quadratic programming problem with box constraints. The quality of approximations is measured by a functional a posteriori error estimate which provides a guaranteed upper bound of the difference of approximated and exact energies of the primal minimization problem. The majorant functional in the upper bound contains auxiliary variables and it is optimized with respect to them to provide a sharp upper bound. A space density of the nonlinear related part of the majorant functional serves as an indicator of the free boundary.