This study examines the damping effects of two damping rings (DRs) applied on an offshore wind-turbine tower (a slender beam) subject to multiple external forces. The wind-turbine tower is simulated by a 3D nonlinear fixed-free elastic beam with a concentrated load applied on the beam tip. The multiple external forces include windward drag force, transverse induced force, the current force under the ocean surface, and the concentrated time-dependent load applied by the turbine on the free end of the tower. The Mindlin-Goodman method is applied to obtain the mode shape function of this beam. The method of multiple scales (MOMS) is employed to analyze the nonlinear problem. An 1:1 internal resonance was observed in this 3D elastic beam. The results indicate that in addition to placing one of the DRs at the maximum amplitude of the beam mode shape, adding the other set of DRs at the ocean currents and aerodynamic forces joint will produce better damping effects.
Journal of Chinese Society of Mechanical Engineers, Vol. 40, No.4, pp. 327-339.