Role of the ratio of tangential to normal stiffness coefficient on the behaviour of vibrofluidised particles

TL;DR

This study investigates how the ratio of tangential to normal stiffness affects particle behavior in vibrofluidised beds, revealing significant impacts on contact regimes, velocity profiles, and the importance of realistic stiffness ratios.

Contribution

It provides new insights into the influence of the stiffness ratio on inter-particle contact behavior and flow properties in vibrofluidised granular materials.

Findings

The stiffness ratio significantly affects contact regimes and velocity distributions.

Using realistic stiffness ratios alters the predicted particle behavior.

The commonly used stiffness ratio of 2/7 differs from more realistic values in simulations.

Abstract

The selection of parameters in the contact law for inter-particle interactions affects the results of simulations of flowing granular materials. The present study aims to understand the effect of the ratio of tangential to normal spring stiffness coefficient ($\kappa$) on inter-particle contact behaviour in terms of the rotational coefficient of restitution determined using data obtained from multi-particle simulations. The effect of $\kappa$ on the profiles of the micro- and macroscopic properties of particles in a vibrofluidised bed is also investigated. The Discrete Element Method (DEM) is used to simulate a vertically vibrated fluidised bed using the open-source software LAMMPS. The inter-particle and wall-particle contact forces are determined using the linear spring-dashpot (LSD) model. The distribution of the mean co-ordination number, force during the contact, contact regimes, and rotational coefficient of restitution are determined from the data obtained from simulations. It was shown that $\kappa$ plays a significant role in the distribution of inter-particle contacts between different regimes and, thereby, the velocity distribution and profiles of statistically averaged properties of the vibrofluidised particles. Our results show that for particles with surface friction coefficient $\mu>0.1$, the commonly used value $\kappa=\frac{2}{7}$ results in quantitatively different results from those obtained using $0.67 \le \kappa < 1$, a range consistent with the realistic values of Poisson ratios for simple materials.