Hertz-Mindlin Effective (Polyhedral)

This contact model is the same as the Hertz-Mindlin model used for spheres in EDEM, but the sphere radius is replaced with an effective sphere radius for each polyhedral. The effective radius is given by finding the radius of a sphere which has the same volume as the polyhedral particle: 

The penetration depth, d is then substituted directly for normal overlap, δ n.