Experimental and Numerical Investigation on the Dynamic Response of Platform for a Spar-Type Floating Wind Turbine Under Aerodynamic and Hydrodynamic Forces

Abstract

Abstract Developing floating offshore wind turbines (FOWTs) operating in the deep sea is crucial for reducing carbon emissions and exploiting marine renewable energy. Compared with a fixed-bottom wind turbine, the FOWT with a moving floating platform faces more complex external environment and challenging operating conditions. Its 6-DOF motions with long periods and significant amplitudes will, in turn, affect the dynamic response and performance of FOWT. Therefore, it is necessary to take a deep insight into the dynamic response of floating platforms for FOWTs under aerodynamic and hydrodynamic forces. In this regard, the present study carried out a series of tank tests based on a scaled spar-type FOWT, employing AI-based software-in-the-loop hybrid testing method. Tests were performed in wave-only cases, wind-only cases and combined wind-wave cases to investigate the effect of wave frequency and wind speed on platform motions. Corresponding simulations were also conducted to compare with the test results. In this study, attention was focused on the law reflected by test results and evaluating the applicability and validity of the employed hybrid testing approach. Results show that the natural frequency of yaw can be affected by constant thrust force generated by fan. Wind speed rather than regular wave frequencies have a significant impact on the mean value of platform motions. The amplitude and standard deviation of motions are simultaneously controlled by wind speed and wave frequency. The spectral peak frequencies of surge, sway and yaw are wind-speed dependent in wind-only cases. With the increase of wave frequency, the spectral peak frequencies of 6-DOF motions gradually change from wave frequency into their own natural frequencies. Moreover, numerical calculations generally coincide with the testing results. This work attempts to provide reference and guide for understanding the dynamic response of FOWTs and develop a more reliable hybrid scaled testing method.