  We present theoretical predictions of granular flow in a conical hopper based
on a continuum theory employing a recently-developed constitutive model with
microstructure evolution by Sun and Sundaresan [1]. The model is developed for
strain rate-independent granular flows. The closures for the pressure and the
macroscopic friction coefficient are linked to microstructure through evolution
equations for the coordination number and fabric. The material constants in the
model are functions of particle-level properties. A salient prediction is the
variable stress ratio along the flow direction, in contrast to the constant
ratio employed in some widely-used plasticity theories, but supported by
results obtained from discrete element simulations. The model permits direct
interrogation of the influence of particle-particle friction as well as
normal-stress differences on the stress distribution and discharge rate.
Increasing particle friction leads to higher stress ratios, but lower normal
stress and flow rates, while considering normal-stress differences results in
the opposite effects.
