Studying on the upper limit of the coarse-grained DEM model for simulating mixing processes in a rolling drum with complex wall boundary

Abstract

Compared with the original Discrete Element Method, the coarse-grained DEM significantly improves simulation efficiency. In CG DEM, the coarse-grained ratio is defined as the diameter of the coarse-grained particle divided by the diameter of the original particle. When the upper limit of coarse-grained ratio is used, the simulation is the most efficient. The upper value for simulating mixing process of spherical fuel particles was determined using a multi-level methodology. The adequacy of the upper value of the coarse-grained ratio was assessed by comparing the mixing characteristics and kinetic properties of the coarse-grained particle systems with those of the original particle systems in a rotating drum with blades. The impact of rotation speed and particle number on the upper value was examined and discussed. It was observed that the kinetic energy increases with an increase in the coarse-grained ratio, limiting the efficiency improvement. To ensure kinetic energy conservation, a scaling law for the restitution coefficient was proposed. Combined with the Reduced Particle Stiffness method, the simulation time of the coarse-grained case is only 1/3030 that of the original case (with a particle number of 2.3 million) when the upper limit of the coarse-grained ratio was used (12.0).