Numerical investigation of the coupled aero-hydrodynamic performances of a semi-submersible floating offshore wind turbine with inclined columns

Numerical investigations of floating platforms with different outer column inclined angles under two operating conditions of regular wave and irregular wave are presented in this paper. A coupled aero-hydrodynamic computational fluid dynamics in-house solver FOWT-UALM-SJTU is applied for the calculation. First, the validation for wave and wind generation are conducted to determine mesh distribution strategy. Based on these, the hydrodynamic motion response, aerodynamic performance and wake flow are analyzed to explore the impact of inclined angle. Conduct spectral analysis on the motion response under wave action, discuss the aerodynamic attack angle and inflow wind velocity along the blade spanwise direction in detail, reveal different trends in wake development and recovery. The results show that for the regular wave condition with the increase of inclined angles, the equilibrium position of surge motion is constantly rising, while pitch is decreasing. The maximum root mean square (rms) value occurs at angle = 30°, compared with the original OC4 FOWT, the rms in power and thrust increase 0.35%, 0.71%. And there are two low regions of attack angle and high regions of axial inflow velocity, corresponding to aerodynamic loads. The spectral analysis indicates that the natural frequency of pitch motion will increase with inclined angle. Besides, from the middle to far region of wake flow, the velocity recovery of FOWT with inclined angle will become faster, which is beneficial for downstream turbines to enhance more wind energy.