Two-dimensional wave tank tests in regular waves are carried out in order to clarify characteristics and a mechanism of generation of horizontal negative drift force acting on a floating OWC-type wave energy converter "Backward Bent Duct Buoy (BBDB)" in waves. Four kinds of experiments are carried out. The first experiment is a usual drift force testing for the BBDB moored by a soft mooring system. The second one is a drift force testing for the fixed BBDB. The third one is a drift force testing for the BBDB of which the surge motion is only possible. The fourth one is a forced pitch oscillation test in which the BBDB is rotated about the center of the air chamber. From these experiments, the mechanism of the generation of negative drift force acting on BBDB is discussed.
Recently, renewable energy has become of major interest in concerning depletion of petroleum and global warming in future. The utilization of the wave energy which is one of the renewable energy is also advanced in all over the world. The authors have been investigating a floating type wave energy converter (WEC) "Backward Bend Duct Buoy (BBDB)" proposed by Masuda (1986) (Nagata et al., 2006, Toyota et al., 2006, Nagata et al., 2007, Toyota et al., 2007). The BBDB is an oscillating water column (OWC) type wave energy converter. Fig.1 shows the concept of the BBDB. The BBDB consists of an air chamber, an L-shaped duct, a buoyancy module, a turbine and a generator. At first, the BBDB coverts the ocean wave energy into the pneumatic energy in a stage called primary conversion. Second, the turbine and generator module on the BBDB converts the pneumatic energy into electricity in a stage called secondary conversion. Compared with the conventional floating WEC, the BBDB has some advantages.
