A multi-scale model for simulating liquid-hair interactions

Abstract

Fig. 1. Hair is submerged in water and then rapidly flipped, resulting in wet locks and dripping.The diverse interactions between hair and liquid are complex and span multiple length scales, yet are central to the appearance of humans and animals in many situations. We therefore propose a novel multi-component simulation framework that treats many of the key physical mechanisms governing the dynamics of wet hair. The foundations of our approach are a discrete rod model for hair and a particle-in-cell model for fluids. To treat the thin layer of liquid that clings to the hair, we augment each hair strand with a height field representation. Our contribution is to develop the necessary physical and numerical models to evolve this new system and the interactions among its components. We develop a new reduced-dimensional liquid model to solve the motion of the liquid along the length of each hair, while accounting for its moving reference frame and influence on the hair dynamics. We derive a faithful model for surface tension-induced cohesion effects between adjacent hairs, based on the geometry of the liquid bridges that connect them. We adopt an empirically-validated drag model to treat the effects of coarse-scale interactions between hair and surrounding fluid, and propose new volume-conserving dripping and absorption strategies to transfer liquid between the reduced and particle-in-cell liquid representations. The synthesis of these techniques yields an effective wet hair simulator, which we use to animate hair flipping, an animal shaking itself dry, a spinning car wash roller brush dunked in liquid, and intricate hair coalescence effects, among several additional scenarios.

Robust handling of clumping and stiffness in wet hair animation

“…They proposed interactions between porous sand and water based on a continuum mixture theory and simulated the cohesion effects of sand according to the amount of absorbed water. Fei et al have proposed a multicomponent simulation framework that can physically represent water condensation, dripping, and clumping effects in wet hair. These techniques proposed cohesion modeling and hair–water interaction techniques based on continuum mechanics and physics.…”

Latent Space Physics: Towards Learning the Temporal Evolution of Fluid Flow

“…A good overview of fluid simulations for computer animation can be found in the book by R. Bridson [Bri15]. Aiming for more complex systems, other works have targeted coupled reduced order models, or sub‐grid coupling effects [TLK16, FMB∗17]. While we do not target coupled fluid solvers in our work, these directions of course represent interesting future topics.…”

A robust volume conserving method for character-water interaction

“…We embed hair particles in the KDSM and treat the hair using the KDSM as in [10] (we also refer the interested reader to [66], [67], [68], [69] for more discussion on hairwater interaction). Our hair-water approach is volumetric in nature, rasterizing multitude of hair representation into KDSM as opposed to [68], where they focus on a reduced model for individual hair strands. As a result, our method handles hair-water interaction with 540k hairs as opposed to 5k and 30k as given in [66] and [68], respectively.…”