On DEM simulation of loose packing behaviour of fine and cohesive particles

• Two commonly used force models are compared for simulating fine and cohesive particles. • Non-bonded force may not necessarily solely responsible for loose packing. • Cluster formation of free falling particles has a large impact on the packing fraction. • Simulation domain should be large enough to capture inter-cluster structures. • Equivalent inter-particle potential energy can give similar packing structures. While Discrete Element Method (DEM) is widely used to simulate fine and cohesive granular materials, accurately capturing real-life packing behaviour requires further investigation on the (i) types of attraction forces and (ii) cluster formation during free fall. In the present study, simulations of various scenarios have been performed to investigate the impacts of particle insertion methods on the resultant packing fraction. The results suggest that the introduction of initial vertical velocity fluctuations during stream insertion can lead to consistent formation of clusters of free falling particles, which is a key factor for achieving loose packing of cohesive particles. We then tested and compared two commonly used attraction force models: the JKR surface adhesion force and non-bonded van der Waals force models. It is revealed that the packing fractions and coordination numbers of the final beds are comparable across different attraction force models as long as the following two conditions are met at the same time: (i) the surface energy density is adjusted (by approximately 2.6 times) to match the total potential energy between a pair of particles and (ii) the initial vertical velocity fluctuations are assigned to form particle clusters during free fall.