Reseaches On Added Mass By 3-D Bem

The dynamic properties of a structure are related not only to its stiffness, but also to its mass. Therefore, it's very important to calculate correctly the added mass for underwater structures. It has been long accepted that the added mass is related only to the shape of bodies. Through numerical examples using 3-D boundary element method, it's proved in this paper that the fluid boundary, the member length and the T-joint may also have big affects on the value of added mass in many cases. The effects of these factors are analyzed in this paper through examples with square members and round members.3-D boundary element method is used in this paper to calculate the added mass for underwater structures. Quadrilateral elements with 8 nodes are used for all elements, which not only lead to higher accuracy, but also make a smooth connection among different elements. Effective methods are used to ensure an accurate numerical integration within each element. Continuity conditions for velocity potential are considered on the free surface, on the interface line of two boundary surfaces and at corner points, which have a significant affect on the stability of the numerical procedure.From the numerical results in this paper, it's concluded that besides body shapes for structure members, the fluid boundary, the member length and the T-joint may also have big affects on the value of added mass in many cases. The effects of these factors on the added mass are studied and given in this paper. The effects of member length, fluid boundary on added mass are studied for isolated poles. While for T-joints, numerical results for added mass are given and compared with those from simple poles. To get the numerical results, a 3-D boundary element method program has been used. Through comparison with previous results, better accuracy and stability are shown for our results which could be used for both engineering and fundamental researches.