Fundamental Study on Phase Control for Air-Flow to Improve on Wave Power Absorption (2nd Report)

Abstract

We reported in 1st paper that the wave absorption efficiency of the air turbine (oscillating water column) type wave power generator was increased by phase control for air-flow in waves that period is longer than heaving natural period of the water column, and the optimum timing of phase control was found. But its experiment model was effected by 3 dimensional phenomenon, and the calculation method did not reappear with physical exactitude. So we performed some experiments by 2 dimensional air-chamber model in the same manner, and exact calculation to simulate the motion of the water column and the air power. Further we proposed the convencient calculation method in order to estimate the air power qualitatively. Results are, 1) Even in 2 dimensional condition, wave absorption efficiency increases by phase control for air-flow, but it does not exceed 50% because of the device absorbing by only heaving motion of the water column. 2) During the period when the valve is closed, we treate that the external force acts on the water column is due to air pressure in the air-chamber which is compressed and depressed by the motion of the water column. Results calculated by such simulation method reappears the motion of the water column and the air pressure. 3) Calculated value does not coincide experimental value, if the effect by unsteady phenomenon is not considered. 4) In oder to estimate the air power qualitatively, frequency response function method used equivalent sinusoidal force method is effective. 5) Value of optimum valve open timing obtained by 2 dimensional model is almost same as its value abtained by 3 dimensional model.