Role of the ratio of tangential to normal stiffness coefficient in the behavior of vibrofluidized particles

The selection of parameters in the contact law for interparticle 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 (κ) on interparticle contact behavior in terms of the rotational coefficient of restitution determined using data obtained from multiparticle simulations. The effect of κ on the profiles of the micro- and macroscopic properties of particles in a vibrofluidized bed is also investigated. The discrete element method (DEM) is used to simulate a vertically vibrated fluidized bed using the open-source software LAMMPS. The interparticle 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 is observed that κ plays a significant role in the distribution of interparticle contacts between different regimes and, thereby, the velocity distribution and profiles of statistically averaged properties of the vibrofluidized particles. Our results show that for particles with surface friction coefficient μ>0.1, the commonly used value κ=2/7 results in quantitatively different results from those obtained using 0.67≤κ<1, a range consistent with the realistic values of Poisson ratios for simple materials.