Research On Multi-phase Weakly-compressible SPH And Its Application To Water Entry

Multi-phase flows are common and significant for ship and ocean engineering.Smooth particle hydrodynamics(SPH)method is a Lagrangian particle method.Therefore,multi-phase interface can be directly captured based on particle physical property without interface tracking technology.At the same time the particle method is easy to deal with large deformation problems.In a word,SPH algorithm has unique advantages in solving multi-phase flow and large deformation problem.In this paper,we will conduct research on the multi-phase SPH model,and simulate the water entry problem by multi-phase SPH model.Here multi-phase flows are regarded as weakly-compressible flows.Thus,pressure of particles can be obtained by equation of state.For traditional SPH model,the discrete methods don't take an account of the discontinuity of physical property nearby interface,which can cause interface instability.In order to solve these problems,many people have presented multiphase SPH model.In our work,Chen et al' model is improved,including the improving discrete method and interface treatment.Rayleigh-Taylor instability,dam breaking and bubble rising,are simulated,which can prove that these improvement can make interface smoothed and stable.Thought Chen et al' model is quite simple and valid,the asymmetrical discrete form can conserve energy conservation.Besides that,they don't consider surface tension and physical viscous.Here,a generalized multi-phase model with Shelpter correction is proposed.Surface tension,viscous and particle shifting algorithm are introduced.The new multi-phase model can accuracy simulate surface tension and deal with large density ratio multi-phase with complex interface.Air is really important for plate structure water entry.In our work,a typical convex object during water entry are numerically investigated using Chen et al' model as the structures have large size.Two slamming processes,including the convex slamming and the structure slamming,are observed in simulations,with double-jetting pattern occurring after the structure slamming.Quantitatively,significant drop in pressure peak value is observed when the dimensionless width of the convex is large than 0.2.Among various shapes of convexes,the square shaped convex experiences the minimal local pressure peak value.