Study On The Fluid-solid Boundary And Liquid Surface Treatment Algorithm In SPH-based Fluid Simulation

As an important branch of computer graphics,fluid simulation has been widely used in special effects,military simulation,animation production,medicine and other fields,however there are still many problems to be studied,such as solid wall boundary treatment of fluid,surface tension calculation,moving boundary treatment of solid into water,etc.The research on these problems is not only of theoretical significance,but also of strong practical application value.This thesis studies the above problems on the basis of reading and analyzing a large number of relevant literature materials.We first introduce the historical background and research status of the solid-wall boundary treatment,surface tension calculation,moving boundary treatment of solid into water,and then do the following three aspects of work:Firstly,boundary force method and virtual particle methods are common methods to deal with fluid-solid boundary.The boundary force method prevents particles from penetrating by applying repulsive forces to particles laid on the boundary,but the calculation of boundary forces limits the simulation speed.The virtual particle method generates virtual particles at the boundary,but as the number of particles increases,the number of virtual particles is increased,resulting in a decrease in computational speed,and the phenomenon of fluid separation from the boundary occurs.For this reason,this thesis proposes a boundary processing method by using symmetric region,which meets the real-time requirements under the premise of ensuring fidelity,and with the increase of the number of fluid particles,the time-consuming growth of the method is obviously slower than that of other traditional methods,which is more suitable for simulation of complex scenes,while avoiding the phenomenon of fluid and boundary separation at the boundary.Secondly,the CSF(continue surface tension)method is a common method for dealing with surface tension.It takes the surface tension as volume force to calculate the surface tension,which greatly reducing the effect of surface shape on curvature calculation,when in fact curvature is only related to the shape of the surface.For solving this problem,the CSF method is improved and a surface tension calculation method based on surface particle extraction is proposed,which reduces the error of the traditional CSF method to calculate curvature,and improves the calculation speed.Thirdly,the problem of solid entering water can be divided into high-speed and low-speed problems.The traditional virtual particle method is a common method to deal with this problem.The traditional virtual particle method prevents the fluid from penetrating the solid by generating virtual particles inside the solid.For simple boundary,such as circular boundary,the virtual particles are evenly distributed inside the boundary,so the treatment effect is good;but for complex boundary,such as sharp corner,because the virtual particles cannot be evenly distributed inside the boundary,the repulsive force generated by the virtual particles is not the same everywhere in the solid boundary.The phenomenon of uneven gap between the fluid and the solid and fluid penetrating the solid at the sharp corner will occur,and the calculation of the virtual particle method is large.Due to the difference of simulation results(whether there is splashing water or not)between solid high-speed entering water and solid entering low-speed water,this thesis improves the virtual particle method for solid highspeed entering water and solid low-speed entering water respectively.At first,aiming at the problem of high-speed entering water,this thesis proposes an improved virtual particle method.The improved virtual particle method solves the above problems with the same simulation time as that of the traditional virtual particle method,and is more suitable for the treatment of complex boundaries.Then,in order to solve the problem of solid low-speed entering water,this thesis proposes a pressure calculation method of inverse interpolation,which can effectively deal with the interaction between moving boundary and fluid without generating virtual particles.This method improves the simulation efficiency while ensuring the fidelity.There is no gap between solid and fluid,and it is suitable for complex moving boundary,and it can guarantee the conservation of momentum.