Dear LAMMPS developers,

I have a question about the damping coefficient \eta_n in the Hertzian granular contact model. According to pair_style granular command — LAMMPS documentation, there are factors sqrt(5/6) and sqrt(3/2) in it. Where does this come from? The references cited just above (Tsuji et al. and Brilliantov et al.) don’t seem to have these factors. Can somebody provide a source?

Thanks and best regards

The key expression to solve should be in Brilliantov’s article, Eq. 18. This reference appears to outlines the process for Hooke Coefficient of restitution and linear–dashpot model revisited | Granular Matter and, without actually doing the algebra, Eq. 17 looks like it should yield what’s in the documentation. However, I’m not aware of a paper in the literature that reproduces the derivation for Hertz.

The coefficient of restitution damping model was recently added by Dhairya Vyas at Northwestern. Maybe he might know of an explicit reference?

Thanks! Yes, I understand the origin of the Hooke case, which actually goes back at least to a technical report of Jakubowski in 1964: https://apps.dtic.mil/sti/pdfs/AD0603711.pdf

I’ll try to reach out to Dhairya Vyas.

Just as an update, the model can be traced back to LIGGGHTS so far (gran model hertz model — LIGGGHTS v3.X documentation) but a derivation or primary source is still missing.