In order to design a floating OWC-type wave energy converter such as Backward Bent Duct Buoy (BBDB), it is necessary to make clear the optimal hull shape which maximizes the generating electrical energy. In this paper, we have carried out two and three dimensional wave tank tests to obtaine the optimal hull shape of BBDB. Firstly, to make clear the effect of the length of the horizontal duct to the primary conversion efficiency, we have carried out two dimensional tank tests for three types of BBDB models. Secondly, we have investigated the effect of the duct length to the draft on the primary conversion efficiency by means of two types of BBDB models. Thirdly, we have investigated the effect of the direction of incident waves on the primary conversion efficiency. Finally, the three dimensional effect on the primacy conversion efficiency is investigated by comparing the difference between two dimensional tank tests and three dimensional tank tests.


Many types of wave energy converters (WECs) that are based on various concepts have been proposed in recent years (Cruz(2008)). Recently, authors are trying the research with the aim of the practical application of Backward Bent Duct Buoy(BBDB) which is one of floating oscillating water column (OWC) type WEC. This device was invented by Masuda(1986) and consists an air chamber, horizontal duct, buoyancy chamber and turbine as shown in Fig.1. This device has some advantages, that is,

  • the primary conversion efficiency is higher than other floating OWCs,

  • as the wavelength for which primary conversion efficiency is maximum is about four times the length of the BBDB, a longer floating structure is not required.

  • as BBDB slowly advances against wave propagation direction in particular wave frequency band, the mooring force and mooring cost are reduced in irregular sea.

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