Fundamental Study on the Influence of Pitch Control of Twin- VAWT on the Gyration Motion of a Single Point Mooring Floating

- Numerical Modeling of Gyration Motion under Wind Alone

Abstract

　This study proposes a new concept for floating offshore wind power generation facilities: a single-point mooring with twin vertical-axis turbines with a variable pitch mechanism. The goal of this concept is to control the direction of thrust by pitch control and to function as an assist to the wind tracking effect of the floating structure. As a first step, a numerical model of the gyration motion of a single-point mooring with pitch control of a variable pitch vertical axis wind turbine was developed, and the effect of pitch control on the gyration motion of the floating structure was examined in conjunction with the results of wind-alone experiments. In the numerical model, it was confirmed that periodic motion, which did not appear in the experimental results, occurred. It was confirmed that this phenomenon can be reduced by introducing a damping force coefficient that depends on the angular rate of gyration, as has been shown in existing studies. It is necessary to develop an estimation method for these fluid forces in the future. Although changes in the direction and magnitude of the thrust can be calculated by modeling the pitch control in the two-stage multiple flow control theory, it is necessary to calculate the thrust as an external force that varies from time to time depending on the blade arrangement. As inferred from the experimental results, the direction of thrust is changed by the pitch control, and it is confirmed that the thrust can be used as an assist mechanism for the floating body to follow the wind.