Research On Dynamic Response Of Offshore Wind Turbine System Based On Semisubmersible-Spar Hybrid Floating Foundation

The energy obtained by our country is mainly from fossil fuels such as coal and oil,which has seriously affected the environment of our country.The wind energy has the advantages of cleaning,rich in quantity,relatively mature technology,wide distribution and so on,and gradually attracted people’s attention.The dynamical characteristic of the offshore floating wind turbine is studied in this paper.Based on Spar and semisub type foundation,a new type of floating foundation of semisub-Spar hybrid offshore wind turbine is designed,and its main technical parameters are determined.The hydrodynamic coefficients and RAOs of the foundation are calculated in the frequency domain based on the SESAM software.The system is modelled and the motion response of the system in time domain and frequency domain is calculated based on FAST software.Based on FLUENT the free decay motion is carried out in hydrostatic water,and the linear and nonlinear damping coefficients of the foundation in surge,heave and pitch are obtained.The rigid flexible coupling multibody dynamics model of whole system is established based on the Kane equation,and the generalized active force and generalized inertial force of floating foundation,tower,nacelle and blade are derivated,finally the fully coupled dynamic equation of the system is obtained.The numerical calculation is carried out by taking the OC4 subsemi floating foundation as an example,and the calculation results are verified by comparing with FAST.Considering the new semisub-Spar hybrid floating offshore wind turbine foundation designed in this paper,by solving the dynamic equations the motion response in time domain and frequency domain of the foundation,tower and blade of the floating wind turbine system in wind and wave combined environment is obtained,and the dynamic characteristics of different degrees of freedom are analyzed.The study shows that the hybrid floating foundation has good motion performance.The FAST calculation shows that the wave influences extreme value and standard deviation while the wind influences equilibrium position of the motion of the floating foundation.Under the rated wind speed,the thrust of the system is the largest and when the wind speed is greater than the rated wind speed,the variable pitch system will adjust the pitch angle of the blade,so that the thrust of the blade will be reduced,and the balance position in surge and pitch direction is reduced.By solving the dynamic equation,we can see that the extreme value of the foundation motion in irregular wave is larger than that in the regular wave,and the standard difference is smaller than that in the regular wave,and the mean value is basically the same.The frequency components of fore-aft vibration of the tower is wave frequency,the motion is affected by wave height and period.The frequency of the blade vibration is mainly the frequency of wave,the frequency of rotation,the sum of the frequency of rotation and the frequency of the wave,and the multifold frequency of rotation.