Study On The Vibration Control Of Offshore Wind Turbines By Means Of Pendulum Damper

Wind power, as a kind of green and renewable energy, plays an important role in relieving the energy shortage without polluting environment. Compare to onshore wind turbines, offshore ones have many advantages. However, offshore wind turbines, installed in severe environment, are subject to various loads including wind, wave, current, ice, tidal and even earthquake. The structures will be fatigue damaged under normal operation in cycle. Therefore, it is necessary to take measures to control undesirable vibrations. The damping device enables not only reduction the Cost of Energy, but also extending service life.The study on dynamical analysis and vibration control is associated with lots of subjects such as Dynamics of Structure, Aerodynamics, Soil Mechanics, Wave Theory, fluid-solid coupling and so on. In this paper, after analyzing the dynamic responses under different loads, a pendulum damper is put forward to control the vibrations. This idea is based on the vibration control of turbines abroad, and rise structures domestic and foreign. For research and application on the vibration control of wind turbine is almost untouched interiorly, and not much abroad yet.(l)The three-dimensional finite element model consisting of blades-tower-pile is built, in which electromechanical devices are simplified. The blades are established using the design data. In general, the model is accurate, although some parts are simplified.(2)The blades rotate in cycle under rated wind, while the finite element model is still. To solve this problem, the changes of position are simulated by the varying wind loads. The method of HSM (harmony superposition method) is employed to synthesize the fluctuating wind velocity; wind loads are calculated according to the aerodynamic characteristics of the tower and blade. Based on the PM spectrum, the irregular wave is synthesized by the method of linear superposition first, and then the wave force acting on the pile is calculated by the Morison equation. The current load is calculated based on the volume-of-fluid theory; the seismic response is analyzed after inputting Taft wave.(3)Aimed at the high-rise structures'being sensitive to wind load, the pendulum damper is employed to control the resulting vibrations. SDOF model is applied to analyze the relationship between the parameters and the reduction affects. Tune parameters to achieve such a situation, that the frequency of the TMD is approach to the frequency of the first along-wind mode. Dynamic responses are carried out under different loads with the pendulum damper placed at the top of the tower. The feasibility and effectiveness are demonstrated by comparing the results with and without TMD.