Vibration suppression of offshore wind turbine foundations using tuned liquid column dampers and tuned mass dampers

Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed offshore wind turbine foundations for the benchmark 5 MW NREL turbine in various loading patterns was investigated. Then, the model was subjected to stochastically generated wind loading in operational, parked, startup, and shutdown conditions. The results suggest that the standard deviation of the dynamic responses can be greatly reduced with all structural control devices. However, TMDs are more efficient in operational conditions, whereas TLCDs show better performances in parked conditions. This highlights the possibility and efficiency of a combined TLCD-TMD system in which the dynamic responses are minimized efficiently in a wider selection of loading conditions.