Shear flow of non-Brownian suspensions close to jamming

The dynamical mechanisms controlling the rheology of dense suspensions close to jamming are investigated numerically, using a simplified model for the relevant dissipative forces. We show that the velocity fluctuations, which control the dissipation rate and therefore the effective viscosity of the suspension, are the same in quasi-static simulations as for the actual dissipative dynamics. We conclude that the statistical properties of grain trajectories -- in particular the critical exponent of velocity fluctuations with respect to volume fraction \phi --are largely independent of the dissipation mechanism. Rather they are determined by steric effects, which are the main driving forces in the quasistatic simulations. The critical exponent of the suspension viscosity (with respect to \phi) can then be deduced, and is consistent with experimental data