Research On Motion Response And Structural Dynamic Response Of Floating Offshore Wind Turbine

As a pollution-free and inexhaustible renewable energy,offshore wind power has a great prospect in the era of rapid development of industrial productivity.The scale of the offshore wind power industry is gradually expanding,in order to obtain more abundant wind energy and more stable wind speed,the construction area of the offshore wind farm is also expanding to the deep water area,so the study of floating offshore wind turbine is of great help to the development of industrial society.The floating wind turbine is directly subjected to the action of wave load and ice load.Under the action of ice load,the tower of the floating wind turbine will vibrate.In addition,the wind turbine will also cause the tower to vibrate when working.Therefore,in the complex Marine environment,the support structure and tower of floating wind turbine are easy to produce serious fatigue damage,which affects the normal operation and service life of floating wind turbine.Therefore,this thesis selects OC4 Deepc Wind offshore floating wind turbine as the research object to study the motion response of the floating wind turbine under the action of wave load and the dynamic response of the structure under the action of ice load,and carries out research on the vibration control method of the floating wind turbine.In this thesis,based on the design parameters of NREL 5MW semi-submersible floating wind turbine,the three-dimensional model of floating wind turbine is established in SOLIDWORKS.Then,based on the theory of regular wave and three-dimensional potential flow in hydrodynamics,the motion response of the floating wind turbine was numerically calculated in Ansys workbench,and the RAO,added mass,radiation damping and first-order wave force of the floating wind turbine with six degrees of freedom under different wave angles were obtained.Secondly,the collision process between sea ice and floating wind turbine was simulated in LS-DYNA based on cohesive element method and sea ice elastoplastic constitutive model.The collision force,displacement and vibration acceleration at the top of the tower of the floating wind turbine are calculated by numerical simulation,and the extreme value of the collision force obtained by numerical calculation is compared with the extreme value of the static ice force formula at home and abroad to verify the accuracy of the numerical simulation.In addition,the influence of different cohesive element parameters and ice element parameters on the collision force,displacement and vibration acceleration at the top of the tower are considered,the numerical calculation and analysis are carried out.The floating wind turbine has a large response under the action of ice load,and it will produce violent vibration when the sea ice compresses.Finally,for the vibration control problem of floating offshore wind turbine,based on the characteristics of phononic crystal,the phononic crystal tower structure and the "inner wall attachment type" phononic crystal tower structure are proposed and designed.Two kinds of phononic crystal structure models were constructed by Comsol Multiphysics,and the band structure,displacement fields of eigenmodes,vibration transmission curve and structure displacement were calculated.The band gap characteristics of the structure were analyzed and the vibration reduction mechanism was revealed.The comparison of the vibration transmission curves between the phononic crystal tower and the tower without phononic crystal shows that the phononic crystal tower structure can control the vibration of the tower largely in the low frequency band.Compared with the phononic crystal tower structure,the "inner wall attachment type" phononic crystal tower structure has two different band gaps and saves more material.In addition,the effects of lead layer thickness,rubber thickness,lattice constant and oscillator height on the start frequency,cut-off frequency and band gap width of two phononic crystal structures are studied.