Is there a way to add a force and a variable velocity to a group of rigid grains?
I am modelling planar shear between two walls (modelled as two groups of grains, same as the particles in the shear layer). I would like to add a confining pressure to the top wall, and set its velocity (which is variable in time). The bottom layer is stationary. I believe I need to use 'fix rigid', 'fix move variable' and 'fix addforce' however, when I put these together, the simulation doesn't run as intended since the particles are time integrated more than once. I understand there is the aveforce command which seems like it was built for this sort of a situation, but I don't like how the layer slowly diffuses and deforms over time - grains start leaking out.
I've been getting around these problems by applying the force to the bottom wall, but it's not the implementation I prefer. Is there a way to apply a pressure and variable velocity in this manner?