Energy monitoring in distinct element models of particle systems

This paper describes techniques for monitoring energy in discrete element method (DEM) simulations of granular flow. They have been applied to DMX a three-dimensional model of polydisperse cohesive spheres flowing into a cylindrical vessel, settling and then subject to vibration. The model takes account of gravitational potential energy, linear and tangential 'particle spring' potential energies and net work done by the particles, normal and angular kinetic energies, dissipated energies due to linear and tangential damping and friction, and the work done by the vibrating vessel on the particle system. Energy monitoring enhances understanding of the physics and further validates the program code. It was found that the numerical technique inherently introduces artificial energy components, but that these can be explicitly monitored. Energy conservation was thus verified and the artificial components explained. Simulations of various particle types and sizes were performed monitoring all the energy I components with time. The results show that explicit dissipated energy calculation is required and cannot be simplified as the remainder term of total minus potential and kinetic energies, and that energy is dissipated mainly in normal damping and gross sliding. Total energy dissipation is not sensitive to particle stiffness, but moderately sensitive to damping and friction. However, the maximum rate of energy dissipation is significantly affected by the damping coefficient and the particle stiffness, and only negligibly by the friction coefficient. Initial studies showed that in some low energy vibration the artificial energy component is not negligible and its effect must be considered in some DEM applications.