Abstract
In recent years, various countries worldwide have developed wind power as a clean energy source. In offshore regions, wind turbines other than the seabed-mounted type can also be developed; the floating-type wind turbine has been studied for expansion into deeper waters. Because offshore floating-type wind turbines are vibrated by wind, ocean currents, and waves-which varies the efficiency-the mechanical system is affected. This can be important for predicting sway. In this study, a spar-type floating offshore wind turbine was evaluated; likened to a pendulum in water, the angle is detected by a rotary encoder. The ratio of the period of the pendulum in air and in water and the sway of the pendulum were investigated in a water channel subjected to waves. The period ratio of the pendulum was found to increase in proportion to the aspect ratio of the immersed part of the weight. The period of the pendulum in the water was dependent on the moving speed, weight diameter, and pendulum mass. The ratio of the angular frequency of free vibration in water and the angular frequency of water waves in the vicinity of 1.05 was most upset.
