BEM Analysis Of Added Mass, Water Entry&Water Exit Of A Two-dimensional Body

The phenomenon of water entry and exit widely occurs in the ship’s motions and ocean engineering. For example, the slamming between the structure of the ship and the water can be seen as water entry problem, while submarine-launched missile and the operation of the salvage ship face the water exit issue. This thesis solves the problem of the forces on two-dimensional bodies by calculating the added mass. The main contents are as follows:Firstly, two-dimensional Boundary Element Method (2D-BEM) is introduced and the establishment of the discrete equation is deduced in detail. The constant and linear boundary element methods are used to solve some basic potential flows to make a verification of the programs. And the two methods are compared on theoretical basis and the numerical accuracy.Secondly, vertical added mass of two-dimensional body is calculated both in infinite domain and the finite domain in the presence of free surface. The influence of the element’s size to the results is studied in the calculation of the added-mass in infinite domain. When free surface is taken into consideration, the results related on the length and height of the flow domain is studied and analyzed. The added mass matrix of multiple bodies are calculated by changing the horizontal spacing between the bodies.Thirdly, the impact force is calculated using the method of von Karman associated with non-linear free surface boundary condition. Wedge body with different dead rise angle, the U-shape body and the flare body are selected as models. The aim of this part is to study the impact force and the movement of the free surface when a body goes down with velocity V. The impact force results of wedge body agree well with present work. And the forces on the U-shape body and the flare body show different characters with time.Lastly, the water exit problem is studied with a model going up with velocity V. The forces and the movement of the free surface is calculated with non-linear free surface boundary condition. The results show that when a body exits from the water it not only gets buoyancy but also receives a force down into the water. The results are compared with other work and the differences are analyzed for viscodity being neglected.