Energy Dissipation Issue in Particle-Wall Collision Simulation with Small Spheres on the Surface

Hello everyone,

I am experiencing an unexpected issue in my MFIX-DEM simulations involving a 50μm polystyrene particle colliding with a silicon wall. Initially, I set the restitution coefficient to 0.5, the rebound velocity at an incident speed of 5 m/s is approximately 2.44 m/s, which aligns well with expectations, as shown in Fig. 1. However, when a small sphere is added to the surface, the larger particle’s energy dissipation during collision is significantly reduced, regardless of changes in restitution coefficients.

Upon exporting the force data from the collision process, I noticed that the damping force exerted on the large particle significantly decreases when a small sphere is present on the surface. leading to nearly identical force responses during both compression and rebound phases, thus minimizing energy loss, as shown in Fig. 2.

This is contrary to previous findings suggesting that submicron particle layers on surfaces could enhance energy dissipation.

Could anyone shed light on possible errors in my simulation setup or offer suggestions for adjustments? I’m eager to figure out the discrepancies in my simulation and align my results with expected outcomes.

I’ve attached my simulation program in the compressed package provided:
Particle-particle wall (29.7 MB)
Particle-wall (231.2 KB)

Thank you in advance for your help!

Can you post the results when you turn off cohesion and when you use LSD collision model?

Sure, this is the LSD results without cohesion and all coefficient of restitution is 0.5, while all other settings remain at their default values.

I think this is due to the damping coefficient being a function of the effective mass, which is very small here. I am wondering if the formulation is valid for such small particles.

I think the formula for damping coefficient should come from the formula 26 in article “Lagrangian numerical simulation of plug flow of damping less particles in a horizontal pipe”, it seems that there is no mention of the scope of application of this formula. Do you have any suggestions, Jeff.