Jamming transition in a two-dimensional open granular pile with rolling resistance

TL;DR

This study uses molecular dynamics simulations to analyze the jamming and unjamming transition in two-dimensional granular piles with open boundaries, focusing on the effects of rolling resistance and orifice width.

Contribution

It introduces two models for rolling resistance in granular piles and examines their impact on the jamming transition through finite size analysis.

Findings

Finite orifice width thresholds exist for unjamming regardless of the model.

Rolling resistance increases the threshold width for unjamming.

The threshold depends on the specific rolling friction model used.

Abstract

We present a molecular dynamics study of the jamming/unjamming transition in two-dimensional granular piles with open boundaries. The grains are modeled by viscoelastic forces, Coulomb friction and resistance to rolling. Two models for the rolling resistance interaction were assessed: one considers a constant rolling friction coefficient, and the other one a strain dependent coefficient. The piles are grown on a finite size substrate and subsequently discharged through an orifice opened at the center of the substrate. Varying the orifice width and taking the final height of the pile after the discharge as the order parameter, one can devise a transition from a jammed regime (when the grain flux is always clogged by an arch) to a catastrophic regime, in which the pile is completely destroyed by an avalanche as large as the system size. A finite size analysis shows that there is a finite orifice width associated with the threshold for the unjamming transition, no matter the model used for the microscopic interactions. As expected, the value of this threshold width increases when rolling resistance is considered, and it depends on the model used for the rolling friction.