Improvement of the Coarse-Grained Discrete Element Method for Frictional Particles

The coarse-grained discrete element method (CGDEM) is promising for its ability to reduce computational cost. However, compared with discrete element method (DEM), CGDEM often overpredicts the granular temperature in simulations of systems with frictional particles. This is partially due to the fact that traditional coarsening strategies only account for the correction to energy dissipation due to inelastic collisions. This work proposes two types of new coarsening strategies that also make the correction to energy dissipation caused by the frictional force between particles. CGDEM simulations of homogeneous cooling systems (HCSs) and two bubbling fluidized beds are executed to evaluate the performance of the proposed strategies. It is found that, relative to CGDEM with traditional coarsening strategies, CGDEM with the proposed strategies gives a more accurate prediction of the instantaneous granular temperature in HCSs. They also better reproduce the time-averaged fields obtained by DEM simulations for the considered bubbling fluidized beds. This demonstrates the necessity of considering both inelastic and frictional origins of energy dissipation in the coarsening strategy.