Effects of ballast transfer on modeling and dynamic responses of a 15MW semi-submersible floating wind turbine

The total ballast accounts for more than 60% of displacement for large-megawatt floating wind turbines (FWT), including fixed and adjustable ballast. Properly using and controlling the variable ballast is attractive to optimize the dynamic performance but is not well studied yet. This study aims to demonstrate and quantify the effects of ballast transfer on the dynamic behavior and performance of FWTs. A 15 MW semi-submersible FWT equipped with an appropriate ballast transfer system is modeled and numerically analyzed. A hydrostatic model is first established to calculate inertial and hydrostatic properties of the FWT during the ballast transfer. Fully coupled time-domain simulations with and without ballast transfer are then carried out to predict the wind turbine performance, platform motion, and structural responses under various environmental conditions. The results indicate that ballast transfer can change the hydrostatic and hydrodynamic properties of the FWT, with an increase of approximately 3.5% in pitch hydrostatic stiffness. In addition, the ballast transfer can increase the average power generation, reduce platform pitch and roll motions, and significantly decrease the hub thrust and the tower base bending moment. The insights obtained serve as a foundation for the development of active ballast systems and the optimization of FWT operation.