No abstract

Originally developed for civil engineering applications, the tuned liquid column damper (TLCD) has been applied not only on tall buildings but also on floating offshore wind turbines (FOWTs) to minimize structural vibrations. This concept has also been adopted widely in navel architecture to reduce the roll motion. However, whether the damper will bring positive effects on mitigating the dynamic motions of FOWTs remains unknown. To this end, the paper studies the star-like three columns tuned liquid multi-column damper (TLMCD) impacts on the dynamic motions of a semi-submersible FOWT. The modelling is achieved by using a high-fidelity computational fluid dynamic (CFD) solver based on OpenFOAM. After the verification of the numerical model for the TLMCD system, it is extended to the modelling of the internal sloshing of TLMCD under prescribed pitch motions. A fully coupled floating-sloshing modelling is then conducted to simulate a semi-submersible FOWT with an integrated TLMCD under regular wave conditions. The study indicates that the passive-control TLMCD system has nearly no influence on the translational motions such as surge and heave. However, the pitch motions can be reduced significantly when the incident wave frequency is close to the natural pitch frequency of the platform. Apart from the natural pitch frequency, the TLMCD has a minor effect at other incident wave frequencies.

An accurate prediction of aerodynamic and hydrodynamic loads on an offshore floating wind turbine plays a critical role in determining its operational stability, fatigue life and survivability, as well as optimising its power control system. Therefore, it is essential to develop an integrated aerodynamics and hydrodynamics model, which is capable of capturing both loading on and dynamic response of an entire offshore wind turbine system with high accuracy and reliability. Prior to developing such an integrated model, aerodynamics and hydrodynamics models need to be systematically examined, individually. In this study, the performance of the overset mesh solver in OpenFOAM for modelling aerodynamics of a floating offshore wind turbine rotor is evaluated. A benchmark test on the rotor of the National Renewable Energy Laboratory (NREL) 5MW turbine, which is designed to be mounted on a semi-submersible platform is performed. The predicted power and thrust for cases of the rotor with its centre fixed and undergoing pitching motion are compared between the overset mesh solver, a frequency-domain Naiver-Stokes Computational Fluid Dynamics code and the open-source Blade Element Momentum theory code.