Simple generalization of kinetic theory for granular flows of nonspherical, oriented particles

We generalize kinetic theory of inelastic spheres to uniaxial, nonspherical grains by including the orientational tensor as a state variable. The theory has three phenomenological parameters, with one parameter to account for the dependency of the stresses on the orientation, which is exactly one for frictionless cylinders, and the other two parameters to predict the orientational tensor. We model the competition between the alignment induced by shearing and the misalignment due to collisions in the evolution law for the orientational tensor. The theory can predict a significant reduction in the viscosity in response to alignment measured in discrete simulations of homogeneous shear flows of prolate and oblate frictionless cylinders.