EACS 2016 paper - A semi-active rocking system for wind turbines under extreme wind loads

<div>EACS 2016 Paper No. 189</div><div><br></div><div>In the last decades, the negative impact of the use of fossil fuels on the environment has lead to a boom in the production of wind turbines. Then, wind turbine heights are progressively increasing in order to take advantage of the smoother winds at higher altitude. But, this has led to an increased demand to control tower forces. The application of a semi-active (SA) control system is herein proposed and discussed. Its aim is to limit bending moment demand at the base of a wind turbine by relaxing the base restraint of the turbine’s tower, without increasing the top displacement, thanks to the sharp increase of dissipated energy in selected intervals of time and a consequent change in tower dynamic properties. The proposed SA control system reproduces a variable restraint at the base that changes in real time its mechanical properties according to the instantaneous response of the turbine’s tower. This smart restraint is made of a central smooth hinge, elastic springs and SA magnetorheological dampers driven by a properly designed control algorithm. A commercial 105 m tall wind turbine has been assumed as a case study. Several numerical simulations have been performed with reference to an extreme load, aimed at establishing a procedure for the optimal calibration of the control algorithm according to the specific case, finally proving the actual potential of the proposed control technique in reducing the structural demand with respect to the “fixed base” structure.</div><div><br></div>