Numerical Simulation Of Water Entry Of A 3D Cone Under The Condition Of Vertically Free Fall Motion

The 21 st century is the century of the sea.The development of Marine resources and competition for space will be the focus of the world.With the continuous increase of new ships and Marine structures in the ocean development,the research on the problem of water slamming is becoming more and more important.The slamming between fluid and Marine engineering structures is one of the common engineering phenomena.For instance,during the voyage,the ship's bow and the surface of the water will collide frequently,causing a great slam load to cause structural damage;the plane landing on the water in aviation;the water entry and out of water of the boat and so on.When the slam occurs,it is often accompanied by drastic changes in the wet surface of the structure,the deformation of free surface,and fluid-solid coupling.The impact of the slamming is a big bang.The impact time is short but the peak is large enough to cause damage to the structure in a short period of time,or the repeated slamming can cause fatigue damage to the structure.Therefore,it is important to be able to accurately predict some important physical quantities in the slamming process during the design phase.The main research content of this paper is to simulate and track the parameters change in the water entry process of a cone.In the paper,the hydrodynamic problem of a cone entering the water through the free fall motion has been analyzed based on three dimensional(3D)velocity potential theory.The fully nonlinear boundary conditions are satisfied on the instantaneous free surface and the moving body surface,which are solved by a time stepping method.In the process of the cone entering water,the wet surface of the cone is expanding at a very rapid rate.So the time stepping method is used in the stretched coordinate system to make the computational domain change gently with time and the remeshing and the data transfer from the old mesh to the new mesh much easier.In each time step,the boundary element method is used to compute the unknown quantity of the domain surface.Remeshing and smoothing are applied to the free surface every time step to ensure grid quality.An improved Eulerian method is used to trace the free surface at a given azimuth in each plane of the cylindrical coordinate to obtain the position and the velocity potential on the new free surface.This paper verifies the correctness of the program by calculating the previous experiment and numerical simulation.On the basis of this study,we researched the influence of the gravity item in the dynamic boundary conditions of free surface during the free fall of the cone;we researched the influence of the initial velocity of the cone during the free fall of the cone;we researched the influence of the deadrise angle of the cone during the free fall of the cone.We also further studied the water entry of an elliptical cone,in which we carried out a numerical simulation of the entry of the elliptic cone into water and the parameters of the numerical simulation are analyzed and studied in detail.