On the influence of contact models on friction forces in discrete element method simulations

The discrete element method (DEM) is an important tool to simulate granular systems with high accuracy. Depending on the application, it is often unclear which model is more appropriate for the calculation of collision forces: the Hertzian approach is generally considered more accurate, but it makes the simulation significantly slower than the Hookean one. In this work, these two approaches are compared in two different situations: the stress distribution of static particles in a cylindrical column (DEM) and the onset of water fluidisation for a completely segregated mixture (CFD-DEM). In both cases, particle contact forces are of great relevance to determine the output. It is found that in the first case the Hookean approach does not produce the expected asymptotical stress trend and does not even respond satisfyingly to friction mobilisation. Conversely, in the fluidisation simulations the results are virtually identical, pointing out that the more complex Hertzian approach may be unnecessary in that case.