Vibration Suppression of Offshore Wind Turbine Foundations using Tuned Liquid 2 Column Dampers and Tuned

4 5 Arash Hemmati, Erkan Oterkus, Mahdi Khorasanchi 6 Department of Naval Architecture, Ocean and Marine Engineering, University of Strathclyde, 100 Montrose Street, Glasgow G4 0LZ, UK 7 Department of Mechanical Engineering, Sharif University of Technology, Azadi Ave, Tehran, Iran 8 9 10 11 ABSTRACT 12 13 Highly dynamic nature of the applied loads on flexible and lightly damped offshore wind turbine (OWT) foundations affects the 14 lifetime and serviceability of the system. In this study, the excessive vibration responses of OWTs are minimized using tuned mass 15 dampers (TMD) and tuned liquid column dampers (TLCD). Due to high efficiency of TLCDs and TMDs for certain loading 16 conditions, a combined TLCD-TMD is also utilized to improve the overall performance in a wide range of loading conditions. First, a 17 parametric study was performed that highlights the sensitivity of these structural control devices. The effect of two devices on fixed 18 offshore wind turbine foundations for the benchmark 5MW NREL turbine in various loading patterns was investigated. Then, the 19 model was subjected to stochastically generated wind loading in operational, parked, startup, and shutdown conditions. The results 20 suggest that the standard deviation of the dynamic responses can be greatly reduced with all structural control devices. However, 21 TMDs are more efficient in operational conditions, whereas TLCDs show better performances in parked conditions. This highlights 22 the possibility and efficiency of a combined TLCD-TMD system in which the dynamic responses are minimized efficiently in a wider 23 selection of loading conditions. 24