Modelling of Floating Offshore Wind Turbines (FOWTs) is challenging due to the strong coupling between the aerodynamics of the turbine and the hydrodynamics of the floating structure, which makes the dynamic response of the whole system highly complex. A variety of numerical approaches can be used to predict this response.

The frequency-domain method (FD) is chosen for further development. These methods are considered as efficient tools for analyzing first design iterations. Given the ongoing development of new concepts for FOWTs, the industry could benefit from such a tool. Currently, only one such open-sourced method is developed (RAFT), but the method still has room for improvements.

After enhancing RAFT's control modeling, the frequency-dependent aerodynamic added mass and damping coefficients are determined following RAFT's methodology. These coefficients are then implemented in a wave diffraction program to predict the surge, pitch, and mooring line tension response of FOWTs for four different design load cases (DLCs). These results are compared against time-domain (TD) simulations.

The method proved capable of predicting the surge and pitch motions well, but the mooring line tension prediction still needs improvements.