Effect of van der Waals force cut-off distance on adhesive collision parameters in DEM simulation

Abstract

Rapid advancement in computer technology makes it possible to perform simulations of large particulate systems using Discrete Element Method (DEM). However, it is still a challenge to adjust the DEM simulation parameters, especially the interparticle forces, in order to obtain rational results. Many of these forces diverge as the distance between particle surfaces approaches zero. Therefore, a cut-off distance needs to be considered in order to avoid such a problem. This work presents the results of the computational analysis of the influence of the cut-off distance, which is required to avoid the divergence of the van der Waals force, on the collision of a single particle against a flat surface. Hence, the effect of the cut-off distance on the coefficient of restitution, collision duration and maximum overlap has been studied. In addition, we have theoretically derived an expression for the minimum velocity under which the particle remains adhered to the surface (critical velocity) as a function of the cut-off distance. The simulation predictions of the critical velocity are within the range of experimental data published in the literature. We demonstrate that the cut-off distance has a profound influence on particle rebound and therefore, a careful selection of this parameter should take place when simulating bulk particle behaviour. Given that the hydrophobic force is usually simulated using the same expression as the van der Waals force, the results presented here could also be considered in the context of the simulation of the hydrophobic force.