Study On The Deformation Of Free Surface And The Variation Of Fluid Loading During Water Exit Of A Revolving Body

Water entry and exit has been a topic of wide range of applications in naval architecture,ocean engineering and costal engineering,etc.For example,the missile exits water after being launched by the submerged submarine,and sunken ships are salvaged out of water by the floating crane.From the view of free surface,water exit can be very violent,especially for the high-speed water exit of a blunt body.The water-exit process of a blunt body may involve in complex physical phenomena such as large deformation and breakup of the free surface,sliding and detachment of the thin liquid layer and mixture of liquid and gas.The flow field is unsteady and highly nonlinear as a result.Due to the complexity of the water exit,the theoretical analysis and numerical simulation need to be studied more deeply.Taking potential applications of water exit in naval and ocean engineering as background,based on the theory of potential flow,this thesis explores the free surface and the body dynamic behaviors and loads characteristics during the whole water exit process by using model experiment and numerical simulation method,respectively.In the aspect of experiments,a set of water-exit equipment is designed independently.The experimental device is a new type of equipment with various water exit forms.Direction and speed of the water exit can be controlled.A series of experiment on water exit of various bodies are conducted at different conditions.Various models of different materials and shapes,such as sphere,ellipsoid and cone,are produced and tested.High-speed photographic technologies are adopted to capture the whole process of water exit and the large deformation of the free surface.Work was divided into forced water exit and free water exit.In the forced water exit,body is pushed out of water at a constant speed by the self-designed water exit experimental device.Based on whether an intersection line between body and free surfaces exiting initially or not,the forced water exit is divided into two categories: fully submerged and partially submerged ones.In the free water exit,an initially static body with a density smaller than water is released underwater by using an electromagnet.In the aspect of numerical simulation,equations about thin liquid film sliding down along the body surface are established,and a method is given for the breakup of free surface and detachment of free surface from the body based on the previous work.A numerical method based on boundary element method is developed.The mathematical model is established for modeling the whole process of water exit of a body: approaching to the free surface,penetrating through the free surface and detaching from the free surface.The numerical results are compared with experimental data and good agreements are obtained,which validates the numerical model.On this basis,the pressure on the body surface is given by the auxiliary function method,and the fluid force and the velocity are also calculated.The deformation of the free surface during the whole process of water exit is investigated as well as the spike of free surface,water column,the jet and so on.In this thesis,the influences of Froude number and the submergence parameter on the water exit are also discussed.