High-frequency aware PIC/FLIP in liquid animation

We present a simple extension to PIC/FLIP(Particle-in-Cell/Fluid-Implicit- Particle) for animating liquid with enhanced behaviors such as pushing or eddying (Figure 1), which we call HFA/PIC/FLIP (High-frequency aware PIC/FLIP). As a fundamental approach we use PIC/FLIP [Brackbill and Ruppel 1986] and compute approximate low-frequency part and high-frequency part of particles velocities. Low-frequency velocities are entirely projected onto divergence free and high-frequency field is partially projected onto divergence free to achieve realistic liquid animations. In contrast to the PIC/FLIP proposed by Zhu and Bridson [Zhu and Bridson 2005]; our approach facilitates "pushing" or "curly" features whereas their approach disperses the momentum towards noisy directions, resulting in dispersion. Recently similar approach has been done with coarse to fine mesh grid [Lentine et al. 2010], we refined directly with particles. We produced several footage of liquid animation and compared with competitive alternatives to show the benefits of the proposed algorithm.