SIMULATION OF DYNAMICS OF INTERACTING RIGID BODIES INCLUDING FRICTION .2. SOFTWARE SYSTEM-DESIGN AND IMPLEMENTATION

This is the second of two papers that deal with the problem of modeling contact (impact, sliding, rolling) between unconstrained rigid bodies, including friction. In a companion paper [1] we showed that the main underlying problem concerns the ability to do efficient contact mechanics when bodies interact through impact and/or sustained contact. Contact mechanics involves two aspects: detection of contact between bodies and estimation of contact forces. These forces are complicated in character and difficult to estimate because they depend on the material response of the contacting objects, on the duration of contact (very short duration impact, or more sustained contact), frictional interaction at the surfaces, geometry of contact, etc. In [1] we proposed a conceptual model in which linear elastic (springs) and viscous (dampers) elements acting at points of contact between objects generate all contact forces. In this paper we describe how the contact model has been implemented in the software of a working computer simulation system. The major aspects of this process are: formulation of a discrete version of the contact model; calculation of model parameters to reflect material properties; geometric representation of objects (in our system, objects are modeled as convex polyhedral); algorithms to detect and evaluate contacts among objects (a process called contact analysis); and estimation and control of model response of stable numerical integration of equations of motion. A graphical user interface displays a three-dimensional (3-D) perspective animation of the solution using full color shaded surface images. While the simulation may not be accomplished in real time, solutions can be saved in files for real-time visualization.