COLLECTIVE FRICTION OF AN ARRAY OF PARTICLES - A CRUCIAL TEST FOR NUMERICAL ALGORITHMS

Using different simulation techniques, we study the influence of the f riction law governing interparticle and particle-plane contacts on the dynamics of a regular array of rigid parallel cylinders moving on a p lane. We find that the evolution of the system depends strongly on the simulation method. But both in simulations with a Contact Dynamics al gorithm, which prescribes the basic Coulomb's law of friction, and in simulations with molecular dynamics, which prescribes a regularized fo rm of Coulomb's law, a steady state with very similar collective rotat ion modes is reached. As long as the static and dynamic friction coeff icients are equal, the rotation modes are independent of the initial c onditions. We show that in all cases, the global steady-state coeffici ent of friction between the array and the plane is a function of the d riving force and the system size, and hence is not Coulombian.