An overview of MEXX: Numerical Software for the Integration of Multibody Systems

Abstract

MEXX (short for MEXanical systems eXtrapolation integrator) is a Fortran code for time integration of constrained mechanical systems, which was developed at the University of Innsbruck and the Konrad-Zuse-Center Berlin. It is suited for direct integration of the equations of motion in descriptor form, and has the following features:

• Time stepping by a half-explicit extrapolation method, allowing for the accurate and robust computation of position, velocity, acceleration, and constraint forces.

• Only position and velocity constraint functions are evaluated, acceleration constraints need not be formulated.

• Both position and velocity constraints remain satisfied throughout the integration interval.

• Uses well-structured linear algebra, enabling the use of O(n) recursive elimination, among other full and sparse linear algebra options.

• Time-continuous solution representation (e.g., for graphics)

• Root-finding options (e.g., for impact and Coulomb friction problems)

MEXX encourages the use of large, sparse descriptor formulations, but can also efficiently handle near-statespace kinematic formulations of multibody systems. A detailed description of MEXX and the underlying concepts is given in [5]. In the present short note we provide a brief overview.