Numerical Simulation of High-Speed Water Entry of Cone-Cylinder

Numerical method by solving Reynolds-averaged Navier-Stokes equations is presented to solve the vertical high-speed water entry problem of a cone-cylinder. The results of the trajectory and cavity shape agree well with the results obtained by the analytical model from literatures. The velocity of the projectile decays rapidly during the penetration,which is about 90% losing in 80D penetration depth. Pressure distributions are also discussed and the results show that the largest pressure appears on the tip of the cone and the lowest pressure occurs inside the cavity and causes vapor generation. For inside the cavity,there is always a supplement of air from outside before the splash closed,after that,the cavity is mainly filled with vapor.

Numerical simulation of the effect of waves on cavity dynamics for oblique water entry of a cylinder

The water entry process associated with complicated unsteady structures,with consideration of the influence of the waves,is not well studied.In the present work,the oblique water entry of a cylinder under different regular waves is numerically investigated.The volume of fluid(VOF)method and the sub-grid scale(SGS)stress model based on the large eddy simulation(LES)method are adopted for the 3-D simulation with six degrees of freedom.The present numerical model is based on a wave model,and as shown by the previous work that the predicted cavity evolution in the calm water agrees well with the experimental results.The present model is validated and it is shown that it could be used to predict the correct wave periods and fluctuations.The cavity evolution mechanism,the dynamic characteristics and the vortex structures are analyzed.The cavity of the water entry with waves closes more quickly than in the calm water case.Finally,several parametric studies of the water entry with different wave heights and water entry locations are carried out.The results provide insights into the effects of the waves on the cavity dynamics for oblique water entry problems.

Hydroelastic analysis of water entry of deformable spheres

This paper presents a numerical study of the hydroelastic coupling during the free-surface water entry of deformable spheres of different material densities.The focus is on the hydrodynamic forces,the stress loads,the sphere deformations,the wetted areas of the sphere and the cavity dynamics,including the impacting of the elastic spheres and the hydroelastic coupled behaviors in the free surface flows.It is shown that the elastic wave propagation in the sphere scales with the sphere density.For elastic spheres immersed in the water,the variation of the sphere deformations and its energy transformation mechanism are discussed.From the contact point positions of the cavity,it can be seen that the wetted area of the sphere is closely related with the sphere deformation.The first deformation cycle is a turning point in the relation between the wetted area and the sphere density.Based on the map of m*−ηsummarized in this work,the influence of the sphere deformation on the shape of the cavity can be roughly predicted from the material properties and the impact conditions.

Discussion on the extended form of internal solitary wave models between two typical stratification systems

The two-layer fluid system and the continuous density system are based on two typical simplified stratification conditions to support the propagation of the internal solitary waves(ISWs).The aim of this study is to establish several extension methods of the classical ISW models across the stratification systems in an attempt to find a simple ISW structure that can propagate more stably,and to determine whether the stable ISW structure in the two typical stratification systems can be expressed in terms of a consistent nonlinear model.For the constructed ISW structures,the propagation stability has been investigated by taking the Euler equations as the evolution equations.The results show that the ISW structure constructed from the Miyata-Choi-Camassa(MCC)model undergoes two stages of instability and the re-stable ISW has a larger available potential energy and a smaller kinetic energy than the initialized condition.This illustrates the limitation of the weakly dispersive assumption in the MCC model.In contrast,the ISW structure constructed from the Dubreil-Jacotin-Long(DJL)model for the two-layer fluid system is generally stable,due to the fact that the Boussinesq approximation introduced in the derivation of the DJL model will be automatically satisfied in this system.The initial condition interpolated from the DJL model with a thin pycnocline thickness can be regarded as an appropriate ISW structure for the two-layer system and is even more stable than that initialized by the MCC model.In addition,the effect of the Boussinesq approximation is also included in the discussion.The approximation can be considered equivalent to a weakly dispersive assumption and should not be ignored for the ISW problem in the continuous density system.