Rolling friction as a technique for modelling particle shape in DEM

Shape is a computationally expensive property to model in DEM, and so rolling friction is often employed in order to simulate its effects. However, the precise way in which rolling friction models shape has never been properly outlined. This paper presents an attempt to do so by estimating the coefficient of rolling friction for simplified shapes using a simple geometric argument based on the eccentricity of contact. This method was tested by running a series of back-to-back simulations of a simple angle of repose test with clumped particles (simulating shape) and idealised spherical particles with rolling friction. Some similarities were observed, however, quantitatively, there was a significant discrepancy. Approximately half as much rolling friction was required to reproduce the effects of an equivalent amount of shape estimated by the method. This discrepancy is thought to be due to the fact that shape can cause rotation as well as resist it, while rolling friction always acts to oppose rolling motion.