NUMERICAL-INTEGRATION OF CONSTRAINED MECHANICAL SYSTEMS USING MEXX

MEXX (short for MEXanical systems eXtrapolation integrator) is a FORTR AN code for time integration of constrained mechanical systems. MEXX i s suited for direct integration of the equations of motion in descript or form. It is based on extrapolation of a timestepping method that is explicit in regard to differential equations and linearly implicit re garding nonlinear constraints. It requires only the solution of well-s tructured systems of linear equations whose solution requires computat ions that increase linearly with the number of bodies, in the case of multibody systems with few closed kinematic loops. Position and veloci ty constraints are enforced throughout the integration interval, where as acceleration constraints need not be formulated. MEXX has options f or time-continuous solution representation (useful for graphics) and f or the location of events such as impacts. The present article describ es MEXX and its underlying concepts.