Crank-Nicolson Finite Element Discretizations for a 2D Linear Schr\"odinger-Type Equation Posed in a Noncylindrical Domain

TL;DR

This paper develops and analyzes a finite element Crank-Nicolson scheme for a 2D Schrödinger-type equation in variable domains, providing stability, regularity results, and optimal error estimates validated by numerical experiments.

Contribution

It introduces a stable finite element discretization for Schrödinger equations in noncylindrical domains with proven regularity and error estimates, advancing numerical methods for complex geometries.

Findings

Proved a global elliptic regularity theorem for mixed boundary conditions.

Derived optimal order $L^2$-error estimates for the scheme.

Numerical experiments confirmed the theoretical convergence rates.

Abstract

Motivated by the paraxial narrow-angle approximation of the Helmholtz equation in domains of variable topography that appears as an important application in Underwater Acoustics, we analyze a general Schr\"odinger-type equation posed on two-dimensional variable domains with mixed boundary conditions. The resulting initial- and boundary-value problem is transformed into an equivalent one posed on a rectangular domain and is approximated by fully discrete, $L^2$-stable, finite element, Crank--Nicolson type schemes. We prove a global elliptic regularity theorem for complex elliptic boundary value problems with mixed conditions and derive $L^2$-error estimates of optimal order. Numerical experiments are presented which verify the optimal rate of convergence.