Response Analysis And Fragility Assessment Of Jacket Supported Offshore Wind Turbine Under Typhoon Environment

At present,China's offshore wind power industry is in the ascendant,gradually developing from shallow seas to more resource-rich deep seas,and the foundation form is also transitioning from the monopile suitable for shallow seas to jacket foundations.However,the frequent occurrence of typhoons along the southeast coast of China seriously threatens the safety of offshore wind turbines(OWTs).The ability of OWTs to resist typhoon disasters has become a bottleneck restricting the development of China's offshore wind power industry.Currently,the design of OWTs mainly relies on the development experience of onshore wind turbine and offshore oil or gas platforms.However,unlike traditional offshore oil/gas platforms,OWTs,as the wind-catching mechanism that utilizes wind energy,face more complex load conditions in harsh weather environments such as typhoons.Therefore,it is urgent to combine wind turbine design,marine structural mechanics,and disaster prevention and mitigation engineering disciplines to collaboratively tackle key problems,and carry out response analysis and fragility assessment of OWTs under typhoon environment in order to improve their survivability.Aiming at the anti-typhoon engineering of offshore wind turbines,this paper systematically analyzes the load and response characteristics of jacket supported large OWTs in typhoon environment.By simulating the failure conditions of the yaw control system that caused damage to the wind turbine,the corresponding strategies are discussed,and the typhoon resistance performance of the jacket platform is evaluated.Finally,a typhoon fragility analysis framework suitable for jacket supported OWTs is proposed.The main research progress is summarized as follows:(1)Based on the basic theories of wind and waves,combined with the characteristics of wind and waves in typhoon environment,using harmonic superposition and inverse fast Fourier transform methods,the environment load that can truly reflect the characteristics of the typhoon is simulated and generated.(2)In view of the failure of yaw control system that caused the destruction of the structure of OWT in the typhoon environment,the aero-hydro-servo-elastic tool FAST is used to calculate the dynamic response under the combined action of wind and wave loads.By considering and comparing the influence of the yaw angle and the parking position on the dynamic response of OWT,the best parking strategy to deal with the failure of yaw control system is proposed in order to reduce the damage probability of OWT.The results show that the responses of OWT are very sensitive to the yaw angle and the parking position,and the blade even appears aeroelastic instability phenomenon at certain yaw angles;based on the results of the whole yaw range,when the turbine is in an idling state or in a standstill state with 90°parking position,the response value of OWT is relatively small and it is most advantageous to deal with the yaw control system failure condition.(3)Considering the non-linear factors of material,geometry and load,the nonlinear static pushover analysis of the OWT under different load directions and yaw conditions in typhoon environment is carried out to evaluate the anti-typhoon performance of the jacket platform.The results show that the ductility performance and ultimate loadcarrying capacity of the jacket platform is the strongest in the 0° direction,and the weakest in the 45° diagonal direction;when the wind turbine yaw system fails,the loadbearing capacity of the jacket platform will be significant decline.In addition,in view of the shortcomings of the traditional pushover analysis method,the Incremental wind-wave analysis method(IWWA)is used and compared with the results of the traditional method to further verify the advanced nature of the method.(4)Based on the full probability decision-making framework of earthquake engineering and the aforementioned structural dynamic and static analysis methods,a typhoon fragility assessment method suitable for OWTs is proposed.First,Monte Carlo simulation is used to generate typhoon samples.Secondly,combined with dynamic response analysis,parameterized typhoon wind and wave field models are used to obtain the probability distribution of structural response.Then,considering the uncertainty of material properties and structural dimensions,the probability distribution characteristics of the load-bearing capacity are obtained by pushover analysis for OWT.Finally,through probability interference theory,the probability of structural failure of OWT under typhoon environment is calculated.