  In this paper we review the simulation method of the non-smooth contact
dynamics. This technique was designed to solve the unilateral and frictional
contact problem for a large number of rigid bodies and has proved to be
especially valuable in research of dense granular materials during the last
decade. We present here the basic principles compared to other methods and the
detailed description of a 3D algorithm. We point out an artifact manifesting
itself in spurious sound waves and discuss the applicability of the method.
