Oscillations in dense particle flow (quasi-static regime)

Hi everyone,

I try to simulate a problem similar to the binflow tutorial, i.e. I have a dense particle flow (quasi-static regime) with a high number of particles, permanent particle contacts and very low velocities. During my simulations I have experienced oscillations when particles are discharged at the bottom and others are fed in at the top.
I tried to find some references in the literature and I have found "Luding et al - Anomalous energy dissipation in molecular-dynamics simulations of grains: The 'detachment' effect". They say that for many particles in contact with each other the viscous disspation through particle contact is inefficient for long-wavelength modes.
Luding suggests in "Introduction to Discrete Element Methods" to indroduce an additional (velocity dependent) "Background friction". In LIGGGHTS this could be achieved through the "fix viscous" command. But I have found that the damping has to be rather large to damp the occuring oscillations and therefore could influence the solid flow.

Therefore I wanted to consult the LIGGGHTS community, maybe someone has faced similar problems and found a better solution and would like to discuss it here.

Best regards
Harald