Floating Wind Turbine Platform in Waves: Computationally-Efficient Algorithm for Numerical Simulation

This study has developed a numerical tool capable of performing mooring design optimization analysis for floating wind turbine (FWT) platforms. The numerical model is capable of: i) correctly model the physical behavior of a moored FWT platform and ii) run at a low computational cost (i.e., faster than real-time) allowing for the evaluations of many different mooring configurations. The numerical model is based on the
Cummins-Ogilvie equation of motion. These hybrid frequency-time-domain approach, allows to perform fast time-domain simulation of floating bodies including external forces such as mooring lines or viscous effects. Firstly, the platform’s excitation force and hydrodynamic coefficients are obtained in the frequency domain utilizing a Boundary Element Method (BEM) solver. Secondly, the results from the BEM solver are converted to the time-domain via convolution integral of the impulse response functions to calculate the radiation force and inverse discrete Fourier transform to compute the excitation force. Thirdly, viscous effect are considered via the Morison Equation using empirical coefficients. Finally, the mooring lines are modelled according to the lumped-mass approach, omitting the coupling between internal nodes allowing the system to be transformed into numerous ordinary differential equations that are solved individually. The established numerical tool can be further coupled with a single and/or multi-objective optimization methods (e.g., genetic algorithm, particle swarm optimization, etc.) to perform a mooring design loop for an FWT platform achieving the optimal configuration in terms of platform motions, mooring line tensions and cost.