Fatigue Performance Of Offshore Wind Turbine Support Structure Under Wave And Wind Loads In Frequency Domain

Wind energy is abundant in the ocean.And offshore field is the ideal place to install the wind turbine.Support structure is the main load-bearing component of the offshore wind turbine,where suffers long-term random loads of wave and wind.It is easier to cause fatigue damage for support structure than the other components.In view of the fatigue problem,a frequency-domain fatigue assessment method is improved.And a 3 MW jacket-type support structure is taken as an example,the power spectrum density function of hot spot stress under wind load is obtained by the multi-input linear theory.And the power spectral density function of hot spot stress under wave load is obtained by SACS software.Then the total stress spectral density function is obtained based on the spectral superposition theory.On the basis of wind-wave scatter diagram and spectral fatigue statistical method,the total damage of the structure can be obtained.The proposed method is convenient and effective,which can be used for the fast fatigue assessment of support structure for offshore wind turbine.The main contents are as follows,(1)The spectral fatigue analysis method of offshore wind turbine support structure is studied.Respectively the method of calculating the power spectral density function of the hot-pot stress is studied under wind and wave loads.What's more,the linearization of the first principal stress under multi-loads is discussed.(2)The jacket support structure is taken as the research object.The spectrum of load under the spectrum of wind is calculated by Bladed software.And the stress response of the structure under per unit load is calculated by AN SYS software.The method to calculate stress spectral density function of support structure under wind load is established,including DNV method,plural-frequency response method.The effects of load correlation and structural damping on stress response are discussed.In addition,the stress spectral density function of the structure under the spectrum of wave is calculated by SACS software.(3)The reasonableness of the superposition theory of power spectral density function is discussed.And the total power spectral density function is obtained by superimposing the power spectral density function under wind as well as wave load alone.(4)The differences between different methods of spectral fatigue(narrowband approximation method,bandwidth correction method,Dirlik method,time domain transform method)for the estimation of the total stress spectral density function is discussed.