Gratuitous goop

This video demonstrates a technique for animating the behavior of viscoelastic fluids, such as mucus, liquid soap, toothpaste, clay, or strange green goop, that exhibit a combination of both fluid and solid characteristics. The technique builds on prior Eulerian methods for animating incompressible fluids with free surfaces by including additional elastic terms in the basic Navier-Stokes equations. The elastic terms are computed by integrating and advecting strain rate throughout the fluid. Transition from elastic resistance to viscous flow is controlled by von Mises’ yield condition, and subsequent behavior is then governed by a quasi-linear plasticity model. PRODUCTION Modeling: Implicit surfaces defined with the particle levelset method. Rendering technique used most: Ray-marching using the opensource renderer, Pixie. Average CPU time for rendering per frame: 15-30 minutes. Total production time: approximately two months. Production highlight: This piece showcases a new simulation method for modeling visco-elastic fluids (a.k.a. goop). The method is described in a SIGGRAPH 2004 paper: A Method for Animating Viscoelastic Fluids by Goktekin, Bargteil, and O'Brien. Production work was done by two students.