ABSTRACT This paper describes the initial development phase of a finite element computer program, GEODYN, capable of simulating the three-dimensional transient dynamic response of a polycrystalline diamond compact (PDC) bit interacting with a non-uniform formation. The ability of GEODYN to simulate response variations attributable to hole size, hole bottom surface shapes, and formation material non-uniformities is demonstrated. Planned developmental phases will address the detailed response of a bottom-hole assembly (BHA), a drill ahead (rock penetration and removal) simulation, and ultimately, the response of the entire string.