Physically-based Fluid Animation

Close-up scenes of fluid phenomena such as stormy oceans,curly rising smokes and droplet splashes are amongst the most spectacular visual effects both in the real life and in the special effects industry.Photographers,movie makers and game developers all try their best to catch these moments of beauty(e.g.the famous photograph "milk crown" and the movie "Poseidon").It is obvious that the realistic fluid animation is getting more and more demanding as people have higher and higher requirements on the visual effects of movies and games.However,the extreme complexity of fluid dynamics renders it impossible for the artists to animate fluid effects frame by frame.Thus,physicallybased methods are now becoming the widely used techniques for generating realistic fluid animations.In this paper,we give an up-to-date survey on physically-based fluid animation research. As one of the most popular approaches to simulate realistic fluid effects,physicallybased fluid animation has spurred a large number of new results in recent years.We classify and discuss the existing methods within three categories:Lagrangian method, Eulerian method and Lattice-Boltzmann method.We then introduce techniques for seven different kinds of special fluid effects.Finally we review the latest hot research areas and point out some future research trends,including surface tracking,fluid control,hybrid method,model reduction,etc.The purpose of this article is to provide readers with a rapid refence of the topic so that experienced users might easily identify the best or the most commonly used methods for a particular task and point out their strengths and deficiencies.Similarly,the beginners will hopefully find a gentle and up-to-date review of this field,get acquaint to the concepts of physically-based fluid animation without wasting time and effort in looking for the original re%fences.In addition,we present a new method to address some long-lasting problems of Eulerian method used in fluid animations by solving Navier-Stokes equations on multiple layers of grids with different resolutions or discretizations.The governing equations are solved on different layers in successive passes.The velocity and pressure fields are synchronized between adjacent layers through the processes of prolongation and restriction.Although the multi-layer approach does not generally increase the numerical accuracy,it makes it possible to combine the respective advantages of various grid types(discretizations),to catch the multi-scale behavior of fluids and to optimize the computational resources.Two simple examples,the regular-tetrahedral and the coarse-fine bi-layer grids,are given to illustrate the power of the multi-layer framework.