| Offshore wind turbines are subjected to loads such as wind,waves,and currents for a long time,among which wind loads are dominant.The measured wind speed data show that the inflow wind field presents a certain non-Gaussian characteristic.The existing standards and studies mostly simplify the wind field to Gaussian distribution,so it is necessary to research the influence of the non-Gaussian characteristics of the wind field on the structure of the wind turbine.In this paper,the coupling effect of wind and wave loads is considered,and the influence of non-Gaussian characteristics of wind field on the extreme value and fatigue life of pile foundation is comparatively studied through numerical simulation.The main work and conclusions of this paper are as follows:(1)Based on the 5MW wind turbine model data of the National Renewable Energy Laboratory(NREL),a wind turbine support structure model that can consider the non-Gaussian characteristics of the wind field and pile-soil interaction is established,and the rationality of the model is verified.(2)Based on the time-history data of wind turbine structure stress obtained by numerical simulation,the time-domain characteristics and extreme value response analysis of wind turbine dynamic response were carried out on the tower base and the mudline of the pile.The results show that under the coupling action of wind and waves,the short-term and long-term extreme stress values of the pile foundation of the wind turbine are positively correlated with the kurtosis of the inflow wind.The stress extreme value response is sensitive to the change of the kurtosis of the inflow wind while skewness of the inflow wind has little effect.The softening properties of the wind field need to be taken into account in the analysis.Under the same average annual wind speed and probability of exceedance,the stress extreme value at the tower base is larger than that at the mudline of the pile foundation.The tower base is the extreme value control section of the wind turbine support structure.(3)Based on the stress time history data of the turbine structure obtained by numerical simulation,the fatigue analysis theory is used in the time domain to evaluate and analyze the fatigue crack formation life and crack propagation life of the turbine.The results show that,the crack initial life of pile foundation under the action of softening non-Gaussian wind and wave is shorter than that under the Gaussian wind and wave.The crack initial life is increased under the hardening non-Gaussian wind and wave.When considering the positive skew characteristic of the wind field,the fatigue initial life is reduced compared with the unbiased condition.The non-Gaussian characteristic of the wind field has little effect on the crack propagation life,and the difference under different wind speed is about 1%.Under the same average annual wind speed,the fatigue life of mudline of the pile foundation is smaller than that of the tower base.The mudline of the pile is the fatigue control section of the wind turbine supporting structure.(4)Based on two representative measured wind field data.Considering the joint distribution of inflow wind speed and wind direction,the influence of the inflow in full-direction on the fatigue life of wind turbine pile foundation is studied.The results show that it is conservative to determine the fatigue life of the turbine support structure based on a single wind direction.The fatigue life of a location with a relatively uniform incoming wind direction is nearly twice as long as that of a single wind direction.For a location with uneven inflow wind direction(with dominant wind direction),its fatigue life is also increased by about 25% compared with the fatigue life of a single inflow,and the position with shorter fatigue life is in the dominant wind direction and the opposite direction of the dominant wind direction. |
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