The jacket foundation steel pipe piles are the key structure that supports the upper wind turbine and bears the wind,wave,and current loads.Taking a multi-megawatt offshore wind turbine in a certain deep-water wind farm as an example,the dynamic characteristics of the jacket foundation models with different pile diameters are analyzed,and the development law of the frequency changing with the pile diameter is extracted.Meanwhile,the sensitivity analysis of the load-bearing performance of the main structure and the connection between the main structure and the piles is carried out using the SACS software,and the influence of the jacket foundation with different pile diameters on rock socketed is comprehensively compared.Based on this,the fatigue performance of the transition section at the pile top connection is studied,and the stress concentration factors under different pile diameters are obtained respectively,systematically evaluating the influence of the jacket foundation with different pile diameters on the fatigue damage.Finally,a new type of large-diameter jacket pile foundation that avoids rock socketed is formed,which is suitable for the shallow cover layer waters and the multi-megawatt wind turbine.The research results show that the sensitivity of the structural stress to the change of pile diameter is in the order from strong to weak:the strength of the grouted connection section>the strength of the pile top transition section>the strength of the jacket foundation>the fatigue performance of the pile top transition section>the pile length>the frequency.Under the premise of meeting the code requirements,increasing the pile diameter by 1.5 m in the site area can reduce the pile length by 4 m,greatly reducing the probability of the pile end being driven into the rock layer.
offshore wind turbinejacket foundationavoidance of rock socketedbearing capacityfatigue damagegrout connection section
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