Contact mechanics in multibody systems

Many applications of multibody dynamics to real-world systems require the modeling of contact mechanics. In order to simulate the contact in a multibody system it is necessary to determine the contact points and to model the contact forces. Contact points may be calculated analytically or numerically. Contact forces are modelled as applied forces and unilateral constraints. A new description is presented which comprises all possibilities of constrained and not constrained motion in one set of equations. The corresponding contact forces can be activated and deactivated easily. The procedure yields an advantage in finding a compatible set of constraints and applied forces after a contact event, resulting in a discontinuity. The contact events are indicated by switching functions. It is necessary to formulate the constraints on position, velocity, acceleration and velocity variation level. The first two choices are needed for the time-integration. The third option is required to calculate the discontinuities in the accelerations in the case of a transition from sliding to stiction and vice versa, The constraints on velocity variation level are used to calculate the discontinuities in the velocities caused by an impact. The structure-variant modeling of contact is implemented in the multibody program SIMPACK. The application is illustrated by the examples of a docking manoeuvre of spacecrafts and the gripping with a robot hand. For both examples a comparison is made between the structure-variant modeling and the usually used elastic contact approach. (C) 1998 Elsevier Science Ltd. All rights reserved.