Introduction and implementation of fluid forces in a DEM code for simulating particle settlement in fluids

Abstract

Simulations of a problem involving particles and fluid usually require coupling a discrete element method (DEM) with computational fluid dynamics (CFD) or smoothed particle hydrodynamics (SPH). The former suffers from the accuracy or even reliability problem induced by mesh size while the latter suffers from small size model and high computation time and cost. To overcome part of these problems, fluid forces have been formulated and directly implemented in a DEM code, resulting in a new model, named f-EDEM. Using this model, the settlement of particles in a fluid can be simulated by a single DEM code without the need of coupling with a CFD or SPH solver. In this study, the formulation and implementation of fluid forces into the DEM code are presented. The proposed f-EDEM model is first validated against an analytical solution. The applicability and ability of the f-EDEM model are examined by reproducing and predicting some laboratory results. The comparisons between the numerical, analytical and experimental results indicate that the f-EDEM model is successfully validated and has the required capacity for simulating the settlement of single and multiple particles in both Newtonian and some of non-Newtonian (Bingham plastic) fluids. The results also indicate that the time step recommended by most DEM manuals can be excessively small, resulting in a high computational cost. It is thus necessary to perform sensitivity analysis of time step to obtain an optimal numerical model, which ensures stable and reliable numerical result with the shortest time of computation.