The DDA, similar to the DEM, needs to address three key issues: (1) representation of contacts; (2)
representation of solid material; and (3) detection and revision of contacts during execution. The elements can be
convex or non-convex, and their shapes are determined by the location of their contacts with the neighboring
elements. Thus, blocks are represented by polyhedra, with the contacts between blocks consisting of edge to face,
edge to edge, or face to face.