SEISMIC PERFORMANCE ANALYSIS OF OFFSHORE WIND TURBINE SUPPORT STEEL STRUCTURE CONSIDERING CORROSION AND FATIGUE COUPLING DAMAGE

The coupled corrosion and fatigue calculations for existing offshore wind turbine structures usually only consider the effect of pitting or uniform corrosion on fatigue damage and, pay less attention to the interaction between corrosion and fatigue as well as the scenarios of coexistence of pitting and uniform corrosion, thusly leading to a large error in the estimation of residual performance of the structure and the analysis of corrosion and fatigue defects. Moreover, the offshore wind turbines are mostly highly flexible thin-walled structures that are sensitive to defects, and buckling failure often occurs due to the expansion of local defects. It shows that the insufficient consideration of the corrosion fatigue effect will reduce the reliability of the structural buckling failure mode identification and the seismic risk assessment. Therefore, this study aims to reveal the disaster mechanism and collapse risk evolution law of offshore wind turbine structures. Based on Faraday's law of electrochemistry and the principle of continuum damage mechanics, pitting corrosion and uniform corrosion damage calculation models were established. The structural cross-section division strategy is proposed to address the non-uniformity of fatigue damage caused by the directional effects of fatigue loading. Finally, based on the interactive coupling damage calculation theory of multi-environmental factors, calculated is the corrosion and fatigue coupling damage of offshore wind turbine structure, and analyzed is the influence of coupling damage on the failure mechanism and collapse risk of the structure. The results show that the buckling failure mode changes from overall bending buckling to local buckling which is prone to collapse after considering the coupling damage. By further quantifying the seismic collapse risk of the failure mode, it is found that long-term coupling damage will greatly increase the buckling collapse risk of the structure.