Keynote Lecture – Vibration Mitigation Performance of On- and Off-shore Wind Turbine Tower
E. Sapountzakis, Professor, School of Civil Engineering & Vice Rector, National Technical University of Athens, Greece
The dynamic performance of on- and off-shore Wind Turbine (WT) towers is investigated adopting the vibration absorption concepts. The application of vibration absorbers to WTs has the potential to significantly improve the damping of the tower and the nacelle dynamic response, increasing the reliability of WTs. In this study, two vibration control alternatives are investigated. First the nacelle is released from the tower, using a low stiffness connection. This approach is related to the seismic isolation concept of structures. In the second approach, a passive vibration absorption concept is implemented, namely the KDamper , consisting of an additional mass, an artificial damper and both positive and negative stiffness elements.
The WTs are subjected to extreme environmental loads such as the wind loading while the off-shore WT are also subjected to the sea wave loading. The wind loading is taken into consideration by applying artificial time-histories according to the regulations of EC1, Part1,4 . In order to account for the WT blades’ motion an alternative aerodynamic time history is also investigated . The highly dynamic turbulent behaviour of waves is taken into account by simulating the sea body using Computational Fluid Dynamics based on the Control-Volume Finite-Element Method.
The vibration mitigation performance of the on- and off-shore WTs incorporating vibration control systems is illustrated. Numerical results demonstrate that the vibration control devices at hand, can bring a realistic alternative to the existing vibration absorption design options in wind turbine towers, enhancing the dynamic performance both nacelle and the tower.
 I. Antoniadis, S. Kanarachos, K. Gryllias, I. Sapountzakis, K-Damping: A Stiffness Based Vibration Absorption Concept, Journal of Vibration and Control, 2016.
 CEN/TC250, “Eurocode 1: Actions on structures-General actions-Part 1-4: Wind actions.” 2004.
 Y. Shkara, M. Cardaun, R. Schelenz, and G. Jacobs, “Aeroelastic response of a multi-megawatt upwind HAWT based on fluid-structure interaction simulation,” Wind Energy Sci., pp. 10–12, 2019.