The antisymmetric wave-induced response of two types of VLFS (pontoon and semi-submersible), free-floating in oblique regular waves is predicted, using two-dimensional (in the case of the pontoon type only) and three-dimensional (for both VLFS) hydroelasticity theories. The term antisymmetric is used to denote coupled sway, yaw and roll motions and twisting distortions. A beam idealisation of the structure of the pontoon type VLFS and strip theory for the fluid-flexible structure interaction are used for the two-dimensional analysis. On the other hand, in three-dimensional analysis, the structures of the two VLFS are idealised using shell finite elements. The solution of the fluid-structure interaction problem is achieved through a pulsating source distribution over the mean wetted surface of the VLFS. Comparisons are carried out between the "dry" and "wet" hull dynamic characteristics of the two VLFS. In addition predictions obtained from both two- and threedimensional analyses are compared for the pontoon VLFS. The sensitivity to heading is also examined.
Geometrically, there are two distinctive types of VLFS that have been investigated, namely Pontoon and Semi-Submersible (SS). A pontoon type VLFS has a relatively simple geometrical shape. One distinctive feature of this type of VLFS is that it has very small draft compared to length and beam. As a result, when studying the hydroelastic behaviour of this type of structure it is treated as a mat like object of either "very thin" or "zero" thickness (Lemke, 1987; Ohkusu & Nanba, 1996; Ma & Hirayama, 1997; Kashiwagi, 1998a; Ohkusu, 2003; Greco et al., 2003). On the other hand a VLFS of semi-submersible type usually has a much bigger draft compared to mat like structures (Ma & Hirayama, 1997; Kashiwagi, 1998b; Murai et al., 1999; Murai & Kagemoto, 2003). In addition, its underwater shape is more complex.
