Removing mass leakage in non-equilibrium extrapolation method,a mass conservative boundary condition is proposed with improving non-equilibrium extrapolation method based on conservation of mass.Mass conservation of a system is ensured by defining an artificial density at solid boundary.Precision and stability of the new boundary condition are validated by simulating three classical flows (Poiseuille,Couette and Womersley).

Considering the fact that large deviatoric deformations are always localized in a small narrow region in hypervelocity impact problems,a method named subdomain computation for SPH(smoothed particle hydrodynamics) is developed.The entire computational domain is divided into several subdomains.In subdomains where large deformation is developed more particles are placed,and in subdomains where only small deformation is developed fewer particles are placed.Computational instability induced at interface of two subdomains is discussed and a method to handle the instability is proposed.Numerical simulations of a rod projectile penetrating into a thick target are carried out with the method and traditional SPH.It shows that computation accuracy as well as computation efficiency are improved.

A lattice Bohzmann model is established to describe liquid-vapor phase transitions using a model proposed by Shan instead of the R-K model. Evaporation from a higher density phase to a lower density phase is simulated. The model improves calculation efficiency and obtains good results. The model is also used to simulate phase transitions in porous media with a pore scale to demonstrate feasibility of the model for complicate phase transition problems.