Pounding Tuned Mass Damper For Vibration Control Of Offshore Wind Turbine Subject To Combined Wind And Wave Excitation

With the continuous progress and development of society,the level of human energy development and utilization is getting higher than ever before.Conventional fossil energy reserves are limited and can cause serious problems such as environmental pollution.Among the emerging new energy technologies,wind power technology is most mature one.Besides,wind energy has the advantages of simple utilization,widespread distribution,and environmental friendliness.As the largest rotating structure on earth,offshore wind turbines need to support huge masses at the top.Because the wind,wave and seismic loads threaten the structural integrity and reliability of these energy infrastructures,the impact of multiple disasters on the structural performance of offshore wind turbines must be considered.In this paper,a5 MW benchmark single-pile offshore wind turbine is taken as the research object,in which a Pounding Tuned Mass Damper(PTMD)is proposed to reduce the excessive vibration of offshore single-pile wind turbines under various disasters.The principle of PTMD is to set a limit impact baffle at a certain distance on both sides of a traditional Tuned Mass Damper(TMD)oscillator to form a vibration damping damper that can limit the maximum travel of the oscillator and can also dissipate energy.This paper uses the Euler-Lagrangian equation to build a simplified model that considers blade,tower coupling,and pile-soil interaction.This simplified model greatly reduces the calculation consumption and retains the coupled dynamic characteristics of the fan blades and the tower to the greatest extent.Therefore,the proposed analytical model is quite suitable for the theoretical research of various control devices.The Kaimal spectrum in IEC 61400-3 is used in Turb Sim to simulate a random wind speed field.The aerodynamic load acting on the blades by wind turbulence is calculated using the phytokinetic theory considering Prandtl’s tip loss factor and Glauert correction.The time history of the random wave height based on the JONSWAP spectrum is simulated by the spectral representation method.The hydrodynamic load of the tower and its substructure is calculated by the wave theory and the Morison equation.In order to consider earthquake hazards,this study selects 15 representative ground motion records from the PEER ground motion database.Through numerical simulation,the dynamic response characteristics of the wind turbine under wind,wave and earthquake are analyzed with and without control devices.PTMD is used to control the forward and backward displacement of the nacelle of the offshore single pile wind turbine.Analysis shows that compared with TMD,the use of the viscoelastic material as pounding baffles makes PTMD more compact in the sense of stroke and more robust in the case of detuning.The fatigue analysis of the offshore under consideration is carried out in the last chapter of the thesis.Statistical analysis of the 20-year data measured from the actual offshore station is utilized to calculate the fatigue damage of the wind turbine tower via the rain flow method and the linear fatigue cumulative damage theory.The reduction levels of the fatigue damage of the wind turbine equipped with PTMD and TMD are investigated to show the effect of the proposed PTMD.