Detection of Inelastic Collapse in 3-D Shear Flow

Inelastic collapse has been observed in a wide range of granular simulations. Very little work, however, has been done in the area of detection of inelastic collapse in couette flow hard sphere simulations. Only recently has the occurrence of inelastic collapse been investigated for such systems. That work has shown that the probability of detecting inelastic collapse increases with a decrease in the coefficient of restitution. In this paper we show that the traditional method for detection of inelastic collapse, based on separation distance, is too strict for couette flow systems. We show this by first performing a 3-D simulation of a granular system in planar shear where the traditional detection method finds what is considered to be inelastic collapse at a current time in the simulation. Unlike in previous work, the simulation is then allowed to continue beyond this point, and eventually reaches a steady state where inelastic collapse is not detected. Therefore the initial indication of inelastic collapse is a false positive, suggesting that the probability of inelastic collapse detection is too high. Furthermore, in a different granular system with a lower coefficient of restitution, however, when the simulation is allowed to continue beyond the detection of inelastic collapse, a steady state flow is not reached. Instead the system ceases to move forward in time. Based on the above results, we propose a new detection method for inelastic collapse in driven hard sphere simulations in order to avoid false positives.