High-order Accurate Implicit-Explicit Time-Stepping Schemes for Wave Equations on Overset Grids

TL;DR

This paper introduces high-order implicit-explicit time-stepping schemes for wave equations on overset grids, improving stability and efficiency for complex geometries and large time-steps in 2D and 3D problems.

Contribution

It develops novel second and fourth-order accurate implicit-explicit schemes with stability and efficiency benefits for wave equations on overset grids.

Findings

Implicit schemes achieve high-order accuracy and stability.

Partitioned implicit-explicit schemes are significantly faster.

Numerical results confirm the schemes' effectiveness.

Abstract

New implicit and implicit-explicit time-stepping methods for the wave equation in second-order form are described with application to two and three-dimensional problems discretized on overset grids. The implicit schemes are single step, three levels in time, and based on the modified equation approach. Second and fourth-order accurate schemes are developed and they incorporate upwind dissipation for stability on overset grids. The fully implicit schemes are useful for certain applications such as the WaveHoltz algorithm for solving Helmholtz problems where very large time-steps are desired. Some wave propagation problems are geometrically stiff due to localized regions of small grid cells, such as grids needed to resolve fine geometric features, and for these situations the implicit time-stepping scheme is combined with an explicit scheme: the implicit scheme is used for component grids containing small cells while the explicit scheme is used on the other grids such as background Cartesian grids. The resulting partitioned implicit-explicit scheme can be many times faster than using an explicit scheme everywhere. The accuracy and stability of the schemes are studied through analysis and numerical computations.