![]() ![]() We started there, and progressively reached all the other goals with more simplified models, and finally our framework came out. ![]() The actor in this photo is Raymond Yun Fei, the first author.īased on these observations and some literature, we decide to focus only on our picked effects, and built liquid (that may suffer from strong accelerations and surface tension) on hair surface, which is different with all of the previous work. The major effects we try to simulate in liquid-hair interaction: flow along hairs, liquid dripping, and hair cohesion. The previous methods have no way to simulate such effects. We noticed that in previous work people assume the wet hairs as sponge and simulate slow non-inertial flow inside hairs, which contradicts with our experiment on pulling hairs out of water, where we shall see liquid flows down rapidly in seconds, and may suffer from drastic acceleration when people do hair flip. With support from experiments we found several pieces that may construct a wet-hair effect that is promising, which include liquid flowing along hairs, dripping/capturing, and cohesion between hairs. We never expect we would use this model to succeed but just to learn the goals that we should focus on. I restarted by modeling everything in the simplest, most naive, most costly and most brute-force way as first trial (such as using smoothed particle hydrodynamics to model the liquid between hairs which has width of only several micrometers, or explicitly model the liquid-air interface with dense triangle mesh and performing huge non-linear optimizations to minimize the surface energy). We optimize the positions of the blue and black dots to minimize surface energy. Red circles are the core of hair strands and blue region indicates the liquid. Left: a very early version of SPH brute-force simulation of the liquid-hair interaction Right: a very early version of brute-force simulation of the cross-section of six hairs being sticked together by liquid. The project was stuck after 6 months of building fancy models so I decided to take a detour, and return to the wet hair project 9 month after. But since the goal is unclear (and what’s worse is that we didn’t realize our goal was unclear) and there are too many literatures each of which focus on a different specific case, we didn’t find anything unified that is working for the simulation of wet-hair in practical scale. We began with investigation of different models where researchers in physics and chemistry engineering implemented for very simple cases such as liquid flowing on infinite long cylinders, and solid particles dragging the fluids. I was interested in the project though I have no idea about how to do it in the beginning. For sometime these studios wanted a workflow that can simulate wet hairs realistically for their new movies but they didn’t know how to do it with the existing methods, and so they found us and see if there were any hope to do this. Eitan Grinspun when he met with some technical directors in VFX and animation studios such as Weta Digital, Disney, and Pixar. I started this project as my first project during my PhD study. In this project, we have Henrique Maia, another PhD student in our lab focusing on hair collision Christopher Batty, assistant professor in University of Waterloo, who is a professional in fluid simulation Changxi Zheng, assistant professor in Columbia University, my co-adviser and an expert in physics simulation and numerical analysis and Eitan Grinspun, associate professor in Columbia University, my adviser and an expert in physics simulation and geometry processing.Ī Multi-Scale Model for Simulating Liquid-Hair Interactions Before the wet hair project I worked on projects including fast voxelization on GPU, real-time rendering, image stylization, high quality offline rendering, interactive sound synthesis and 3D-printed metallophone. Attracted by game industry I started my first project in real-time rendering and GPU acceleration. I began research in computer graphics when I was a sophomore. ![]() Previously I complete my undergraduate study in Tsinghua University, and got my M. I am a third year PhD student specialized in physics simulation. ![]()
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