  In spite of many attempts to model dense granular flow, there is still no
general theory capable of describing different types of flows, such as
gravity-driven drainage in silos and wall-driven shear flows in Couette cells.
Here, we summarize our recent proposal of the Stochastic Flow Rule (SFR), which
is able to describe these cases in good agreement with experiments, and we
focus on testing the theory in more detail against brute-force simulations with
the discrete-element method (DEM). The SFR is a general rate-independent
constitutive law for plastic flow, based on diffusing spots of fluidization. In
the case of quasi-2D granular materials, we assume limit-state stresses from
Mohr-Coulomb plasticity and postulate that spots undergo biased random walks
along slip-lines, driven by local stress imbalances. We compare analytical
predictions of the SFR against DEM simulations for silos and Couette cells,
carrying out several parametric studies in the latter case, and find good
agreement.
