ADAPTIVE SEMI-IMPLICIT INTEGRATOR FOR ARTICULATED RIGID-BODY SYSTEMS

This paper concerns the dynamic simulation of constrained rigid-body systems in the context of real-time applications and stable integrators. The goal is to adaptively find a balance between the stability of an over-damped implicit scheme and the energetic consistency of the symplectic, semi-implicit Euler scheme. As a starting point, we investigate in detail the properties of a new time stepping scheme proposed by Tournier et al., "Stable constrained dynamics", ACM transactions on Graphics, 2015, which approximates a full non-linear implicit solution with a single linear system without compromising stability. This introduces a geometric stiffness term that improves numerical stability up to a certain time step size, at the cost of large mechanical dissipation compared to the traditional formulation. Dissipation is sometimes undesirable from a mechanical point of view, especially if the dissipation is not quantified. In this paper, we propose to use an additional control parameter to regulate how "implicit" the Jacobian matrix is, and change the degree to which the geometric stiffness term contributes. For the selection of this parameter, adaptive schemes will be proposed based on the monitoring of energy drift. The proposed adaptive method is verified through the simulation of chain-like systems.