A high accuracy nonconforming finite element scheme for Helmholtz transmission eigenvalue problem

TL;DR

This paper introduces a novel cubic nonconforming finite element scheme for the Helmholtz transmission eigenvalue problem, achieving high accuracy and robustness, with explicit basis functions and proven convergence rates.

Contribution

The paper develops a new nonconforming finite element scheme with explicit basis functions and demonstrates its effectiveness for transmission eigenvalue problems.

Findings

Achieves b1h^2b1 approximation for eigenspaces

Achieves b1h^4b1 approximation for eigenvalues

Numerical tests confirm high accuracy and robustness

Abstract

In this paper, we consider a cubic $H^2$ nonconforming finite element scheme $B_{h0}^3$ which does not correspond to a locally defined finite element with Ciarlet$'$s triple but admit a set of local basis functions. For the first time, we deduce and write out the expression of basis functions explicitly. Distinguished from the most nonconforming finite element methods, $(\delta\Delta_h\cdot,\Delta_h\cdot)$ with non-constant coefficient $\delta>0$ is coercive on the nonconforming $B_{h0}^3$ space which makes it robust for numerical discretization. For fourth order eigenvalue problem, the $B_{h0}^3$ scheme can provide $\mathcal{O}(h^2)$ approximation for the eigenspace in energy norm and $\mathcal{O}(h^4)$ approximation for the eigenvalues. We test the $B_{h0}^3$ scheme on the vary-coefficient bi-Laplace source and eigenvalue problem, further, transmission eigenvalue problem. Finally, numerical examples are presented to demonstrate the effectiveness of the proposed scheme.