Resonance of steel wind turbines: Problems and solutions

This paper deals with an experimental and numerical dynamic characterization of two steel wind turbines currently located in Italy. The considered are onshore were originally built more than 20 years ago 65 m height (from the ground level to hub). Five ago, they unmounted reassembled present location. During this phase, due local national environmental prescriptions, shortened about 45 (hub height). Unfortunately, procedure generated a huge problem their structural behaviour: fundamental frequency vibration both “shorter” become close working rotors, causing resonance problem. To evaluate exactly turbine frequencies modal shapes, monitoring involving several accelerometers has been implemented. Then, finite element models (FEM) have developed investigate influence soil-structure interaction (SSI) on behaviour these structures. Finally, practical solutions overcome proposed discussed. Since investigated problems can arise for any worldwide turbine, general validity be extended many other different cases.