Research On Particle-based 3D Real-time Fluid Simulation

Computational Fluid Dynamics has long been a hot spot in computer graphics.More virtual 3D scenes with high realism repeatedly come to the stage,i.e.movies and video games.Though grid-based Euler fluid simulations hold the advantage of highly detailed results,they in general can hardly reach real-time interactive rates.Smoothed Particle Hydrodynamics(SPH)is a Lagrangian method which can reduce the overall simulating complexity significantly.This thesis presents the formulation of particle-based SPH fluid simulation in detail,and makes some improvement against the flaw.In addition,the free surface rendering of fluid is of huge significance to the realism of virtual scene.This work takes the advantage of screen space rendering technique,which is popular among the computer graphics community in recent years.In contrast to traditional approaches,there is no request for explicit polygen meshes during the procedure,hence a great improvement in running efficiency is achieved.Specifically,the work of this thesis includes:(1)An introduction of computational fluid dynamics basics.We describe the formulation of Navier-Stokes equations,which drive the flow of incompressible fluid.An introduction of mesh-based Euler approach is presented,including the theory and process of development.Emphasis is put on the definition of SPH and the regarding kernels,which is important to the computation.(2)A through research to particle-based Lagrangian fluid.We formulate each force density in SPH equations,i.e.the internal forces such as pressure force and viscosity force.Besides,gravity and collision response as external forces are also covered.In addition,focused on the character of surface tension,we present a new threshold computation method that leads to a fast determination of particles to be involved in the evaluation of surface tension.A new control coefficient is proposed for surface tension,which enhances the effect during the fluid flow and also overcome the volume shrink phenomenon while the fluid approaches rest.A fast neighbor search algorithm is also presented and the comparison is stated between various numerical integration schemes.And a complete particle-based fluid simulation framework is presented in the end.(3)Screen space rendering for the final results.On the fundamental SPH fluid model,starting from the particles position,write the depth map and thickness map into two rendering targets respectively.Then we employ the idea of curvature flow to obtain the surface normal in eye space from each pixel on depth map.With the help of Fresnel equation,we finally generate a satisfactory realistic fluid with reasonable reflection and refraction.This thesis builds a particle-based fluid simulating and rendering framework.Emphasis is put on the modeling part,especially some innovation made on the surface tension.Generally,our methods lead to a realistic-looking fluid in an interactive rate.