Gradient recovery for elliptic interface problem: II. Immersed finite element methods

This is the second paper on the study of gradient recovery for elliptic interface problem. In our previous work [H. Guo and X. Yang, 2016, arXiv:1607.05898], we developed a novel gradient recovery technique for finite element method based on body-fitted mesh. In this paper, we propose new gradient recovery methods for two immersed interface finite element methods: symmetric and consistent immersed finite method [H. Ji, J. Chen and Z. Li, J. Sci. Comput., 61 (2014), 533–557] and Petrov-Galerkin immersed finite element method [T.Y. Hou, X. H. Wu and Y. Zhang, Commun. Math. Sci., 2 (2004), 185–205, and S. Hou and X. D. Liu, J. Comput. Phys., 202 (2005), 411–445]. Compared to bodyfitted mesh based gradient recover methods, immersed finite element methods provide a uniform way of recovering gradient on regular meshes. Numerical examples are presented to confirm the superconvergence of both gradient recovery methods. Moreover, they provide asymptotically exact a posteriori error estimators for both immersed finite element methods.