  Dynamical behavior of steady granular flow is investigated numerically in the
inelastic hard sphere limit of the soft sphere model. We find distinctively
different limiting behaviors for the two flow regimes, i.e., the collisional
flow and the frictional flow. In the collisional flow, the hard sphere limit is
straightforward; the number of collisions per particle per unit time converges
to a finite value and the total contact time fraction with other particles goes
to zero. For the frictional flow, however, we demonstrate that the collision
rate diverges as the power of the particle stiffness so that the time fraction
of the multiple contacts remains finite even in the hard sphere limit although
the contact time fraction for the binary collisions tends to zero.
