Sloshing dynamics of a tuned liquid multi-column damper for semi-submersible floating offshore wind turbines

In this paper, sloshing inside a novel passive control device termed tuned liquid multi-column damper (TLMCD) for mitigating rotational motions of a semi-submersible floating offshore wind turbine (FOWT) is numerically modelled using a high-fidelity CFD approach. Test cases of the device under various external excitations including single degree surge and pitch as well as combined surge/pitch are presented and analysed to reveal its damping mechanisms and performance. Through analysing the results of the predicted sloshing induced mo-ments on the TLMCD structure and their phases under a range of external excitation frequencies, it was found that although the maximum moments always occur at or very close to the resonance excitations, their phases may not be exactly opposite to those of the wave-induced moments on a FOWT platform, which has important implications to the optimal design of the TLMCD system for floating wind turbine applications. The study also shows that the performance of the TLMCD is not significantly affected by the change of the relative angular (yaw) position of the device under pitch excitations and would potentially be more robust than the traditional U-shaped TLCDs, applied in isolation or in combination.