An Innovative Friction Base Restraint to Reduce Structural Demand to Wind Turbines

Abstract

This work proposes the use of an innovative base restraint to reduce the structural demand to wind turbine towers due to exceptional wind loads. The base of the tower has been designed as connected to the foundation thanks to (i) a hinge that allows rotation in one direction, (ii) a Rotational Friction Device (RFD) that dissipates energy when the external load overpasses the friction value, and (iii) a rotational spring able to re-center the tower during and after the history load case. The RFD and the rotational spring are placed in parallel. The effectiveness of such passive control system has been assessed comparing the structural demandbase bending moment and top displacementbetween the benchmark NREL 5 MW wind turbine in absence (i.e. fixed base) and in presence of control. The control strategy has turned out to be very promising. It leads, in fact, to a significant reduction of the bending moment at the base without involving an increasing in the displacement at the top. Moreover, it also favors the recentering of the tower after the end of the wind action.