Study Of The Free Surface Effect On Water Entry Problem

Water entry problem is a very complex and non-linear impact dynamics problem with a broad research background and profound research significance.Based on the in-depth study of water entry problem and change rule of physical quantities in the water entry process,improved the internal structure or the outer surface line,in order to reduce the impact of the free surface and avoid the accidents of structural damage,Instrument failure,trajectory out of control,is the most important motivation to study the water entry problem.In this paper,the feasibility and accuracy of simulating the water entry problem using the computational fluid dynamics software STAR-CCM + is verified by comparing the experimental results with numerical results.The results show that STAR-CCM + can accurately and efficiently simulate the water entry problem.Then,a large number of simulations are carried out on the vertical free and the oblique free water entry problem with the three-dimensional cone.Emphasis is placed on the changes of slamming loads,accelerations and velocities of the cone by the free surface during vertical free water entry process,as well as the changes of the torques,angular velocities,horizontal and vertical physical components that the cone receives during the oblique free water entry process.The results show that cone density,deadrise angle,water entry velocity and water entry angle all have influence on the cone load,acceleration and other physical quantities.The cone received an impact of torque from free surface in oblique water entry process,with a macroscopic performance of rotating around the Y-axis.In addition,second slamming phenomenon occurs in the oblique free water entry problem,and the phenomenon becomes more obvious as the water entry angle increases.The cavitation phenomenon generated in the oblique uniform water entry process of three-dimensional wedges was also simulated.The research focused on the changes of free surface around the wedge,the development of cavitation in the back-flow zone,and the pressure distribution in the flow field around the wedge.The influence of the geometric asymmetry and the kinematic asymmetry on the type of oblique water entry problem of wedge is discussed.It turns out to be that according to asymmetry,the oblique water entry problem can be divided into the first type of slamming problem and the second type of slamming problem.The free surface,development of cavitation and flow field pressure distribution varies in the two types of slamming problems.