Study On Related Problems In Simulation Of Solid Entry Into Water

Fluid Simulation is an important branch of computer graphics,which is widely used in film and television special effects,game simulation,military simulation,medical imaging and so on.Solid entering water is a very common phenomenon in real life,and it is also an important subject in fluid simulation.At present,there are some problems in the simulation research of solid entry into water,such as unstable interface pressure of solid and fluid,rough simulation of fluid surface after being impacted by solid,and difficulty in simulating the evolution process of cavity formed by solid entry into water,have not been well solved.The research on the above problems has strong practical application value.In this thesis,the history and research status of solid boundary pressure treatment,fluid surface particle treatment and solid water cavity evolution treatment are firstly introduced.Then,the following work is carried out to solve the above three problems:Firstly,when the traditional boundary force method,virtual particle method or coupling force method is used to deal with the boundary treatment of solid entry into water,the fluid particle density at the interface between fluid and solid is discontinuous,which leads to unstable pressure at the interface,and some fluid particles penetrate or separate at the solid boundary.In this thesis,the solid wall boundary and moving solid boundary on both sides of the water tank are treated respectively in the process of simulating solid entry into water.The traditional virtual particle method combined with the improved virtual particle arrangement is used to deal with the solid wall boundary.Compared with the existing methods,the proposed method not only solves the problem of fluid particles penetrating solid boundary and separation of fluid particles from solid boundary,but also improves the simulation efficiency.For moving solid boundary,the traditional SPH method is improved,the support domain of boundary fluid particles is supplemented and perfected,the pressure formula is improved,and the pressure field is stabilized.Compared with the existing methods,the method in this thesis not only solves the phenomena of fluid particles penetrating solid boundary and separation between fluid particles and solid boundary,but also improves the computational accuracy and simulation efficiency.Then,solid enters water and impacts the water surface,causing large deformation of the water surface.When the traditional boundary force method,virtual particle method or coupling force method are used to simulate the water surface with large deformation,the simulated water surface is rough,or there is a large gap between the fluid particles and the solid particles,or a few fluid particles penetrate the solid boundary,etc.In order to solve the above problems,the position of particles on the fluid surface was corrected to make the particles on the fluid surface evenly distributed and the water surface flow naturally.Compared with the traditional method,the water surface simulated by the proposed method is relatively smooth,and there is no large gap between the fluid particles and solid particles,and a few fluid particles penetrate the solid boundary,and the simulation efficiency is improved.Finally,when the solid enters the water,the solid impinges on the surface of the fluid to form two jets.When a solid enters water,a symmetrical cavity appears below the free surface.In the simulation of solid entering water,the gas in the cavity has a great influence on the whole simulation process,but the interface pressure between the water phase and the gas phase in the cavity is unstable,the details of the jet flow are difficult to be truly displayed,and the evolution process of the air in the cavity is difficult to predict.Aiming at the above problems,an improved formula for calculating the pressure of two-phase flow is proposed in this thesis.The flow field of both water and gas phase is calculated in the governing equation.The simulation results show that,compared with the existing methods,the method presented in this paper improves the calculation accuracy,better displays the flow movement process and gas evolution process in the cavity,and the simulation of fluid surface jet flow is more consistent with the real effect.