CutFEM Based on Extended Finite Element Spaces

TL;DR

This paper introduces a general framework for constructing discrete extension operators in unfitted finite element methods, enabling stable and optimal approximation for complex PDEs with boundary intersections.

Contribution

It develops an abstract theory for extension operators applicable to various finite element spaces and PDE types, including high-order and interface problems.

Findings

Provides a unified approach for stabilization in unfitted FEM

Derives a priori error estimates for elliptic and parabolic PDEs

Demonstrates applicability to high-order and interface problems

Abstract

We develop a general framework for construction and analysis of discrete extension operators with application to unfitted finite element approximation of partial differential equations. In unfitted methods so called cut elements intersected by the boundary occur and these elements must in general by stabilized in some way. Discrete extension operators provides such a stabilization by modification of the finite element space close to the boundary. More precisely, the finite element space is extended from the stable interior elements over the boundary in a stable way which also guarantees optimal approximation properties. Our framework is applicable to all standard nodal based finite elements of various order and regularity. We develop an abstract theory for elliptic problems and associated parabolic time dependent partial differential equations and derive a priori error estimates. We finally apply this to some examples of partial differential equations of different order including the interface problems, the biharmonic operator and the sixth order triharmonic operator.