ABSTRACT: Many analytical methods have been proposed to calculate hydroelastic responses of a very large pontoon-type floating structure in waves. In this paper, variational principles considering wave radiation condition at infinity related to motions of a plate in waves, which are very important in calculations of the elastic response of the pontoontype floating structure, are discussed. First, Sommerfeld radiation condition at infinity is extended to treat a case with an incident wave. Second, four kinds of variational principles related to motions of the elastic floating plate on a water surface considering the incident and radiated waves are proposed and clarified the mutual relationship of these variational principles. Third, numerical results for elastic response of a floating plate of rectangular and L-shaped plan geometry in waves, which are obtained by using these proposed variational principles, are shown. INTRODUCTION A Pontoon-type VLFS is one of the typical structural types of very large floating structures (VLFS). Various numerical methods have been proposed to predict the hydroelastic response of this structure in waves (Watanabe (2004); Chen (2006)). These methods are classified into the modal expansion method and the direct method. These analyses are carried out in the frequency domain or in the time domain. Finite element method is used for the structure in order to analyze actual complicated floating structure (Seto et al. (1998); Utsunomiya et al. (2002)). In relation to the elastic response of Pontoon-type VLFS in waves, four kinds of variational principles related to elastic motions of such a floating plate were derived and made clear the mutual relationship of them (Isshiki (2000), Isshiki and Nagata(2001)). However, in these variational principles, wave radiation condition at infinity was not included and the normal velocity on a vertical cylinder surface of finite size surrounding the plate was designated.

ABSTRACT: In this paper, from the viewpoint of thrust generation by waves, we discuss the fluid dynamics of two phenomena. One is a thrust generation by hydrofoil placed at the bow under water of a ship, and the other is a negative drift force acting on a floating oscillating water column (OWC) type wave energy converter "Backward Bent Duct Buoy (BBDB)" in particular wave frequency range. A foil among waves can produce thrust. This may be utilized into ship propulsion in waves and reduction of mooring force of an ocean platform. We discuss the possibility of applying this phenomenon to ship propulsion and reduction of mooring forces. In regard to BBDB, the mechanism of thrust generation and its characteristics are investigated by 2-D and 3-D tank tests and it is shown that this characteristic is very useful to reduce the wave drift force acting on BBDB in irregular waves. INTRODUCTION In this paper, from the viewpoint of thrust generation by waves, we discuss the fluid dynamics of two phenomena. One is a thrust generation by hydrofoil placed at the bow under water of a ship, and the other is a negative drift force acting on a floating oscillating water column (OWC) type wave energy converter "Backward Bent Duct Buoy (BBDB)" in particular wave frequency range. Generally speaking, resistance of a ship becomes bigger in waves than in calm water. This phenomenon is well known to naval architects as the resistance increase of a ship in waves. According to the contemporary report, he really built two boats of 13 ft and 24 ft in length named Autonaut as shown in Fig. l, and the boat could move of their own motions due to waves against wind and wave at a speed of three to four knots.