  Macroscopic and microscopic properties of dense granular layers flowing down
inclined planes are obtained from Discrete-Element-Method simulations for both
frictionless and frictional grains. Three fundamental observations for dense
granular flows are recovered, namely the occurrence of a critical stress, the
Bagnold velocity profile, as well as well-defined friction and dilatancy laws.
The microscopic aspects of the grain motion highlight the formation of
transient clusters. From this microscopic picture, we derive a theoretical
scaling model without any empirical input that explains quantitatively the
fundamental laws of dense granular flows in incline plane and shear geometries.
The adequacy between the model and the observed results suggests that granular
flows can be viewed as flows from thermal fluids of hard spheres.
