# Reference for coeff of restitution in Hertz-Mindlin with non-linear damping

I use the simple-

[Ip2_

[Law2_

and setting NewtonIntegrato

The scene is a sphere in free fall onto a box, then rebounding, falling down again etc, until all energy is dissipated. According to the documentation and source code, *en* is the normal coefficient of restitution, so I expect to see the energy quartered (1/4=.5^2) after each rebound. The sphere is originally with v=0 at z=2, entering in contact with the box when z=1.5. Therefore, after one rebound, it should fly up to about 1.625 etc, eventually approaching 1.5.

In the simulation, the sphere peaks at about z=1.55 after the first rebound. Considering that the equilibrium position will be at about z=1.45 due to still weight of the sphere in gravity, I still obtain coefficient of restitution of about sqrt((1.

The source (pkg/dem/

How reliable is this code in Yade? Has someone double-checked that it does what it should?

Cheers, Václav

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