Experimental study of dynamic response and energy absorption of fixed circular cylindrical OWC columns in regular waves

Recently renewable energy has been recognized as the countermeasure against global warming and establishment of sustainable society. Therefore in the field of ocean engineering, development of energy converters including wave energy converter devices (Brooke, 2003) to extract energy from the ocean are active in the world. The authors have proposed a new type of floating wave power converter system with multiple columns (Yasuzawa and Nagashima, 2009). The wave power generation floating system is composed of deck structures and multiple columns underneath. Some columns are used as power generation units which are based on OWC (Oscillating Water Columns) principle and convert wave energy into electric energy, and the other columns have the function of buoyancy. In the present study, dynamic response characteristics of the fixed cylindrical OWC column in regular waves are investigated as basic information before estimation of the floating system. Acrylic cylinder models of the OWC have been designed and manufactured, and the experiment has been performed in the wave tank in Ocean Energy Institute of Saga University. In the experiment, amplitude of water level and pressure in the OWC have been measured to obtain energy absorption of the OWC. Horizontal shear force, vertical force, and pitching moment at the column root have been measured to clarify wave force acting on the columns simultaneously as well. The experiment has been conducted under several wave conditions and the columns with various dimensions to investigate frequency response and effect of column shape. Finally efficiency of primary energy conversion of the OWC columns has been calculated for various conditions based on experimental results on amplitude of water level and pressure in the OWC by using some theories and discussed.