Simple and scalable frictional contacts for thin nodal objects

Fig. 1. A virtual character going through a running cycle, letting his hair impact repeatedly the back and neck of his shirt. The groom consists of 54, 450 Discrete Elastic Rods, totalling 1.2M degrees of freedom, while the shirt mesh contains about 27, 000 vertices. This scene induces as much as 4.5M contacts, which are solved implicitly and with nonlinear Coulomb friction thanks to our proposed algorithm. © Weta Digital.

Frictional contacts are the primary way by which physical bodies interact, yet they pose many numerical challenges. Previous works have devised robust methods for handling collisions in elastic bodies, cloth, or fiber assemblies such as hair, but the performance of many of those algorithms degrades when applied to objects with different topologies or constitutive models, or simply cannot scale to high-enough numbers of contacting points.

In this work we propose a unified approach, able to handle a large class of dynamical objects, that can solve for millions of contacts with unbiased Coulomb friction while keeping computation time and memory usage reasonable. Our method allows seamless coupling between the various simulated components that comprise virtual characters and their environment. Furthermore, our proposed approach is simple to implement and can be easily integrated in popular time integrators such as Projected Newton or ADMM.