  The inertial number-based rheology, popularly known as the JFP model, is well
known for describing the rheology of granular materials in the dense flow
regime. While most of the recent studies focus on the steady-state rheology of
granular materials, the time-dependent rheology of such materials has received
less attention. Owing to this fact, we perform three-dimensional DEM
simulations of frictional inelastic spheres flowing down an inclined bumpy
surface varying over a wide range of inclination angles and restitution
coefficients. We show that steady, fully developed flows are possible at
inclinations much higher than those predicted from the JFP model rheology. We
show that, in addition to a modified effective friction law, the rheological
description also needs to account for the stress anisotropy by means of a first
and second normal stress difference law.
