| The role of renewable energy is increasing over recent decades.Developing renewable energy is an important way to achieve emission reduction targets all over the world.The wind energy has obvious advantages in various clean energy sources and renewable energy sources.Using wind energy to meet power demand will be the development trend in the coming decades.Offshore wind energy resources are more abundant than onshore wind energy resources.In recent years,with the development of offshore technology,offshore wind power has flourished.China's offshore wind power has great potential for development with about a thousand megawatts of electricity resources.Total installed capacity and growth rate of offshore wind power in the Bohai Sea as an important area for research,development and utilization of offshore wind energy technology continue to increase in China.In winters,the sea ice in some areas of the Bohai will cause ice-induced vibration and iceinduced of fatigue of offshore structures.Especially for offshore wind turbines with a height of 50 m to 70 m,the impact of sea ice will be more significant.Therefore,the influence of sea ice should be considered in the design and operation of the offshore wind turbine structure in the Bohai ice area.This paper mainly studies the calculation method of fatigue damage of offshore wind turbine structure in the Bohai ice area under ice load.Due to the study of the anti-ice structure design of the offshore structure in the Bohai Sea area,the method of installing antiice cones is widely used to change the damage mode of sea ice and reduce the amplitude of ice load and the phenomenon of steady-state vibration.Therefore,this paper mainly considers the impact of random ice load generated by sea ice on the structure of offshore wind turbines.In the ice-induced vibration analysis,it is necessary to construct the fatigue environment of sea ice.The sea ice fatigue parameters adopted are based on long-term monitoring and statistics of the JZ20-2 sea area in the Bohai Sea.Fatigue parameters to be considered include ice age,ice thickness,ice speed,ice direction.As a result of the ice direction,the direction of the ice is concentrated only in a fixed direction.Therefore,when dividing the fatigue condition,the division of working conditions is based on the basis of ice speed and ice thickness.After obtaining the probability density function of the ice thickness ice speed,the joint probability distribution of the two is used as the probability of occurrence of the condition.For the ice load construction,the time history load and PDS load of the sea ice are calculated by the measured ice load time history formula and the ice load spectrum formula,respectively.In this paper,the time domain and frequency domain methods are used to calculate the hot spot position,hot spot stress time history curve,hot spot stress spectrum and damage of the offshore wind turbine under random ice load.Then use the Miner linear accumulation principle and the S-N curve method to calculate the fatigue life of the structure under random ice load.Finally,in terms of time domain and frequency domain methods,the calculation efficiency and calculation accuracy are compared when calculating the random ice-induced fatigue damage of offshore wind turbine structure.In the study of ice load,the discrete element method is a numerical method that can effectively simulate the damage process of sea ice and structure.Therefore,this paper uses the sphere to construct the sea ice discrete element model and the parallel particle model between the spherical particle units to construct the flat ice model and structure interaction.The ice load time history curve under different working conditions are obtained.Finally,the time domain fatigue damage results of the wind turbine structure based on the discrete element method are analyzed. |
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