An approximate hard sphere method for densely packed granular flows

TL;DR

This paper introduces a modified approximate hard sphere method for simulating densely packed granular flows, which is faster and effective up to jamming compared to traditional molecular dynamics methods.

Contribution

The authors present a modification to an existing collision aggregation method, improving its accuracy and validating it on 2D granular Couette flow to demonstrate efficiency and reliability.

Findings

Successfully replicates previous results up to jamming

Operates ten times faster than comparable MD methods

Reduces overlap error in dense packing simulations

Abstract

The simulation of granular media is usually done either with event-driven codes that treat collisions as instantaneous but have difficulty with very dense packings, or with molecular dynamics methods that approximate rigid grains using a stiff viscoelastic spring. There is a little-known method that combines several collision events into a single timestep in order to retain the instantaneous collisions of event-driven dynamics but also be able to handle dense packings. However, it is poorly characterized as to its regime of validity and failure modes. We present a modification of this method to reduce the introduction of overlap error, and test it using the problem of 2D granular Couette flow, a densely packed system that has been well-characterized by previous work. We find that this method can successfully replicate the results of previous work up to the point of jamming, and that it can do so a factor of 10 faster than comparable MD methods.