Improved Implementation of Approximate Full Mass Matrix Inverse Methods into Material Point Method Simulations

TL;DR

This paper presents an improved, stable, and efficient implementation of approximate full mass matrix inverse methods for the material point method, enhancing accuracy and compatibility with other MPM features.

Contribution

The paper introduces a revised, simplified FMPM(k) implementation that resolves conflicts with common MPM features and discusses stability and efficiency improvements.

Findings

Revised FMPM(k) implementation simplifies integration into MPM codes.

Modified FMPM(k) enhances compatibility with other MPM features.

Analysis shows stability issues at high order k and discusses efficiency options.

Abstract

Approximate full mass matrix methods for the material point method, known as FMPM(k) of order k, can improve the calculation of grid velocities from grid momentum. It can be implemented in any MPM code by inserting a new calculation task whenever grid velocities are needed. The implementation recommended in this paper only needs these calculations once per time step just before when updating particle positions and velocities. FMPM implementation issues arise, however, when its methods are mixed with other MPM feature that rely on lumped mass calculations. Some common lumped-mass MPM features are grid-based, velocity boundary condition, multimaterial contact calculations, crack contact calculations, and imperfect interfaces. This paper first derives a revised FMPM(k) implementation that both simplifies and clarifies the "FMPM Loop" that can be added to MPM codes. Next, that loop is modified to allow FMPM(k) to work well even in simulations that need other MPM features that previously caused conflicts. Two other FMPM(k) issues are apparent loss of stability at very higher order k and inherent computational cost. These issues are discussed in an analysis of temporal stability as a function of order k and in consideration of options to improve efficiency.