Extended Narrow Band Weighted MultiFLIP for Two-Phase Liquid Simulation

Physically-based fluid simulation has been studied for many years in computer graphics. MultiFLIP is a powerful method to simulate two-phase liquid phenomena such as bubbles and the “glugging” effect of water pouring, which cannot be produced by the traditional Fluid Implicit Particle (FLIP) method. In contrast to FLIP where only the liquid phase is involved, MultiFLIP samples two respective grid velocities for both gas and liquid volumes. However, MultiFLIP produces some abnormal phenomena such as small liquid droplets getting carried around by gas. The abnormality is in fact produced by the reason that MultiFLIP uses the same weights for both gas and liquid when blending the velocities near the interface for divergence-free projection. To address this problem, we present a novel velocity coupling method, which uses different mass for gas and liquid particles when interpolating velocities of particles into the Eulerian grid. Besides, we apply a transition function to MultiFLIP method so that the two-phase liquid simulation can switch between a particle-based simulation and a grid-based simulation, which aims to reduce the number of particles and smooth the liquid-gas interface in the calm areas. Experiments show that our techniques can conserve the kinetic energy and tiny details of gas-liquid interface better, as well as reduce the number of gas and liquid particles.