• wind energy;
  • floating offshore wind turbine;
  • spar-type;
  • edgewise vibration;
  • multiple tuned mass dampers;
  • passive control


This paper investigates the use of single and multiple tuned mass dampers (TMDs) for passive control of edgewise vibrations of nacelle/tower and spar of spar-type floating wind turbines (S-FOWTs). Uncontrolled and controlled mathematical models of the S-FOWT are developed by using Euler-Lagrangian energy formulations. In these models, the aerodynamic properties of the blade, variable mass and stiffness, gravity, the interactions among the blades, nacelle, spar and mooring system, the hydrodynamic effects, the restoring moment, and the buoyancy force are considered. The vibrations of the blades, nacelle, tower, and spar are coupled in all degrees of freedom and in all inertial, dissipative, and elastic components. In the controlled model, several set of horizontal TMDs are placed in the spar at various depths and the coupling of these TMDs with the nacelle and spar motions is considered. The control effectiveness is evaluated by the reduction of the root-mean-square and maximum response. The control feasibility is examined by using the spar sinking and the TMD maximum strokes. The investigations using nonlinear time–domain simulation show that a single TMD can reduce up to 40% of the nacelle sway displacement and the spar roll, and that the reduction observed with multiple TMDs is 50%. The influence of the spar TMD is more significant than that of the nacelle TMD. The spar TMDs are less effective when their positions are lower. In all the cases studied, good heave performance of the S-FOWT is maintained. Copyright © 2014 John Wiley & Sons, Ltd.