Jamming in granular hopper flow

TL;DR

This study uses large-scale molecular dynamics simulations to analyze how force and impulse distributions evolve as granular hopper flow approaches jamming, revealing that impulse distribution is a more reliable indicator of jamming than force distribution.

Contribution

It provides new insights into the microscopic force and impulse distributions near jamming in granular hopper flow, highlighting the importance of impulse distribution as an indicator.

Findings

Force distribution $P(f)$ changes little near jamming

Impulse distribution $P(i)$ increases in small impulses approaching jamming

Impulse distribution is a stronger indicator of jamming than force distribution

Abstract

Large-scale three dimensional molecular dynamics simulations of hopper flow are presented. The flow rate of the system is controlled by the width of the aperture at the bottom. As the steady-state flow rate is reduced, the force distribution $P(f)$ changes only slightly, while there is a large change in the impulse distribution $P(i)$. In both cases, the distributions show an increase in small forces or impulses as the systems approach jamming, the opposite of that seen in previous Lennard-Jones simulations. This occurs dynamically as well for a hopper that transitions from a flowing to a jammed state over time. The final jammed $P(f)$ is quite distinct from a poured packing $P(f)$ in the same geometry. The change in $P(i)$ is a much stronger indicator of the approach to jamming. The formation of a peak or plateau in $P(f)$ at the average force is not a general feature of the approach to jamming.