SOLVING PROBLEMS WITH UNILATERAL CONSTRAINTS BY DAE METHODS

We study trajectories of mechanical systems with unilateral constraint s under the additional assumption that always a given number of constr aints is active. A reformulation as a problem with bilateral condition s yields a drastic reduction in the number of constraints, but in gene ral, we are faced with regularity problems. We illustrate our approach in the special case of a dynamical rigid body contact problem. In par ticular, we present a regularization technique which leads to the defi nition of generalized solutions and a quite effective numerical method on the basis of algorithms for differential-algebraic systems. The re sults are applied to a wheel-rail contact problem of actual interest t o railway engineers. (C) 1998 IMACS/Elsevier Science B.V.