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An efficient method for restraining the large vibration displacements and loads of offshore floating wind turbines under harsh marine environment is proposed by putting tuned mass dampers in the cabin. A dynamics model for a barge-type offshore floating wind turbine with a fore-aft tuned mass damper is established based on Lagrange's equations; the nonlinear least squares Levenberg-Marquardt algorithm is employed to identify the parameters of the wind turbine; different parameter optimization methods are adopted to optimize tuned mass damper parameters by considering the standard deviation of the tower top longitudinal displacement as the objective function. Aiming at five typical combined wind and wave load cases under normal running state of the wind turbine, the dynamic responses of the wind turbine with/without tuned mass damper are simulated and the suppression effect of the tuned mass damper is investigated over the wide range of load cases. The results show that when the wind turbine vibrates in the state of damped free vibration, the standard deviation of the tower top longitudinal displacement is decreased approximately 60% in 100 s by the optimized tuned mass damper with the optimum tuned mass damper mass ratio 1.8%. The standard deviation suppression rates of the longitudinal displacements and loads in the tower and blades increase with the tuned mass damper mass ratio when the wind turbine vibrates under the combined wind and wave load cases. When the mass ratio changes from 0.5% to 2%, the maximum suppression rates vary from 20% to 50% correspondingly, which effectively reduce vibration responses of the offshore floating wind turbine. The results of this article preliminarily verify the feasibilities of using a tuned mass damper for restraining vibration of the barge-type offshore floating wind turbine.

Abstract. In recent years, offshore wind energy has become an attractive option due to the increased demand for the renewable energy. A method incorporating a tuned mass damper (TMD) in offshore wind turbine platform is proposed to demonstrate the improvement on structural dynamic performance in this investigation. The Lagrange's equations are applied to establish a limited degree-of-freedom (DOF) mathematical model for the barge-type offshore wind turbine. Genetic algorithm (GA) is then employed to find the globally optimum TMD design parameters. Numerical simulations based on FAST have been carried out to evaluate the effect of the passive control system. A changeable mass for the floating wind turbine will be brought for installing a heavy tuned mass damper in the platform. In this case, partial ballast is substituted for the equal mass of the tuned mass damper, and the vibration mitigation is simulated in five typical load cases. Results show that the passive control approaches can improve the dynamic responses of the barge-type wind turbine by placing a tuned mass damper in floating platform. Through replacing partial ballast with the equal mass of the tuned mass damper, a significant reduction of dynamic responses is also observed in simulation results for the barge-type floating structure.

This paper evaluates the application of a passive control technique with a tuned mass damper on platform for the barge-type offshore wind turbine. First of all, the three degrees of freedom mathematical model for the floating wind turbine is established based on Lagrange's equations, and the Levenberg-Marquardt algorithm is adopted to estimate the parameters of the wind turbine. Then, the method of frequency tuning which is utilized in engineering projects and genetic algorithm are employed respectively to simulate the optimum parameters of the tuned mass damper. The vibration mechanism about the phase-angle difference between tuned mass damper and floating platform is analyzed. Finally, the dynamic responses of floating wind turbine with/without tuned mass damper are calculated under five typical wind and wave load cases, and the vibration mitigation effects are researched in marine environment. Partial ballast is substituted by the equal mass of tuned mass damper due to the mass of floating platform with tuned mass damper would increase obviously, which would change the design of the wind turbine, and the vibration mitigation is also simulated in five typical load cases. The results show that the suppression rate of standard deviation of platform pitch is up to 47.95%, after substituting the partial mass of ballast, the suppression rate is 50%. Therefore, the dynamic responses of the barge-type floating wind turbine would be reduced significantly when the ballast is replaced by the equal mass of the tuned mass damper on floating platform.