| In recent years, along with the land resources consumed in large quantities, China has increased the intensity of the development of offshore oil and gas. However, offshore platforms as the infrastructures of development of offshore oil and gas are facing many problems in their service processes. Among them, the fatigue problem has attracted a lot of attentions, which is the main risk endangering the safety of the platform. Platform aging problem is emerging in recent years, which brings new challenges to the platform security. Therefore, it is of practical significance to study on fatigue strength of offshore platform.In this thesis,"The South China Sea II" semi submersible platform is the research object, the semi submersible platform hydrodynamic characteristics, fatigue damage, the resistance of extreme load under fatigue damage, detection and repair scheme and the continuation of life after maintenance were studied. Firstly, the motions and hydrodynamic distribution of "The South China Sea Ⅱ" semi submersible platform were calculated by the hydrodynamic analysis program AQWA. Then using the finite element structural analysis program ANSYS, the platform fatigue damage distribution was researched and the locations of hot spots were found. Fatigue damage reliability of the hot spot was calculated; and then getting the fatigue life of hot spot which has the enough guarantee. According to fatigue damage distribution of "The South China Sea Ⅱ " semi submersible platform, the detection and repair plan was established; according to the detecting and repair scheme, evaluating the continuation of life after maintenance. This paper discussed the fatigue life and safe life of the hot spot of the semi submersible platform, and the platform safety performance was assessed through the analysis of those, which provided the basis for the reasonable detection and repair scheme.Through the analysis we can conclude that:it’s not possible that the resonance happen for semi submersible platform in regular sea, and the heave performance than motions of other degrees relatively was poorer. The fatigue damage of connecting positions between column base and the rods in semi submersible platform which were positions of hot spots as well were most severe, the resistance of extreme load of semi submersible platform declines as the platform service life prolonged. After maintenance the performance of the semi submersible platform is improved, which can prolong the lifetime accordingly. |
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