Modelling particle contacts in distinct element simulations - Linear and non-linear approach

In numerical simulations using the Distinct Element Method (DEM) a major role in determining particles' trajectories is played by contact forces. In the present paper we thoroughly compare a commonly used linear force-displacement model and a recently proposed non-linear model. A discussion of the two mathematical formulations and the importance of the material parameters is presented first. Then, numerical simulations of a particle impacting oil a flat wall at various angles using the two approaches are compared. Macroscopically, experimental results are used as validation means. The evolution of the forces and velocities during the collisions are compared against rigourous results. Finally, the influence of choosing a contact model and the parameters is discussed for a bubble growth in a fluidized bed. The results show the degree of accuracy gain achievable using the non-linear model, in terms of the realistic material properties that can be used and correct reproduction of the force-displacement interaction. On the other hand, using the correct parameters and despite the strong assumptions, the linear model is capable of representing the kinematics of a collision as well as the macroscopic patterns in multi-particle simulations. Differences in the bubble dynamics are confined to a slight delay in the bed surface rise and evolution of secondary bubbles.