Improved Velocity-Verlet Algorithm for the Discrete Element Method

TL;DR

This paper introduces an improved velocity-Verlet algorithm for the Discrete Element Method that maintains physical accuracy in granular flow simulations with large particle size ratios, addressing limitations of conventional methods.

Contribution

The authors develop and validate an enhanced velocity-Verlet integration scheme that ensures physically correct results for size ratios up to 100, surpassing previous limitations.

Findings

Improved algorithm maintains accuracy for size ratios up to 100.

Validated effectiveness through three-particle and granular flow simulations.

Provides guidelines for parameter selection in large particle ratio simulations.

Abstract

The Discrete Element Method is widely employed for simulating granular flows, but conventional integration techniques may produce unphysical results for simulations with static friction when particle size ratios exceed $R \approx 3$. These inaccuracies arise because some variables in the velocity-Verlet algorithm are calculated at the half-timestep, while others are computed at the full timestep. To correct this, we develop an improved velocity-Verlet integration algorithm to ensure physically accurate outcomes up to the largest size ratios examined ($R=100$). The implementation of this improved integration method within the LAMMPS framework is detailed, and its effectiveness is validated through a simple three-particle test case and a more general example of granular flow in mixtures with large size-ratios, for which we provide general guidelines for selecting simulation parameters and accurately modeling inelasticity in large particle size-ratio simulations.