(87b) DEM Simulation with Reduced Particle Stiffness

In Discrete Element Method (DEM), the time step required for stable calculation is inversely proportional to the square of the stiffness of particles, that is, the spring constant for the linear (Hookean) contact model and the Young’s modulus for the non-linear (Hertzian) model. Therefore, the stiffness of particles is often reduced artificially from the real material property to increase the time step and decrease the calculation cost. This approach is widely accepted for dry and coarse particles where only contact force is dominant. However, Kobayashi et al. [1] recently reported that the powder behaviour changes drastically with reducing the particle stiffness if constant cohesion force is exerted on the particles. The present study generalises this problem and provides a solution, which is named as the Reduced Particle Stiffness (RPS) scaling. The RPS scaling laws for both linear and non-linear contact models are developed based on the dimensionless equation of motion where additional forces, e.g. liquid bridge, cohesion and electrostatic forces, are exerted on particles. It is proven that, using the RPS scaling law, particles with reduced stiffness show similar sticking/rebound behaviour and bulk velocity as those of the original (stiff) particles.

[1] T. Kobayashi et al., Powder Technol., 248, 143-152 (2013).