We present here an algorithm to simulate the motion of rigid bodies subject to a non–overlapping constraint, and which tend to aggregate when they get close to each other. The motion is induced by external forces. Two types of forces are considered here: drift force induced by the action of a surrounding fluid whose motion is prescribed, and stochastic forces modelling random shocks of molecules on the surface of the bodies. The numerical approach fits into the general framework of granular flow modelling.