| As the hydrocarbon resources inland is unceasingly decreasing, the exploitation ofthose resources is transferring to the ocean, and the marine energy is becoming the majorenergy resources in the future. Nowadays, the semi-submersible drilling platforms haveplayed key roles in the deep-sea exploitation, and still, with a lot of scope of development.Firstly, as to hydrodynamic performance, for instance, reducing the heave motion of thesemi-submersible platform can bring more time for drilling; decreasing the amplitude of rolland pitch can contribute to platform operation and transportation; studying on furtherhydrodynamic performance will benefit to the development of the dynamic positioning, etc.Secondly, since structural strength analysis is treated as the priority of maintaining theplatform in good condition, the further research on it is of great significance. Moreover, dueto the effect of cyclic loading, we should take fatigue assessment into consideration whenwe get down to analysis. Additionally, in the stage of structure design, we should pay moreattention to the construction level and economic returns instead of the mechanicalproperties.The analysis of structural strength analysis, hydrodynamic analysis, and fatiguereliability analysis of a hotspot location for aimed semi submersible platform will be carriedout by DNV.SESAM software, which are based on ABS specifications. So the followingproblems are emphatically investigated.1) In this paper, the development history and current status for the deep-watersemi-submersible drilling platform will be introduced as well as the analysis of structure andtechnical characteristics. Besides, the status quo of wave loads and fatigue reliability inChina and abroad will be summarized.2) The basic theory of hydrodynamic analysis is represented which includes solutionfor3D potential theory at zero speed, solution for wave force in any location which be basedon Morison theory, physical significance of hydrodynamic parameter for platform, andtheoretical derivation of long-term forecast for wave load. With the requirements of ABSGuide for the Fatigue Assessment of Offshore Structures, the spectral-based fatigue analysisapproach is derived theoretically by using S-N curve and Miner’s rule in accordance. Thecomplete process of the spectral fatigue reliability analysis for hotspots is summarized.3) With the calculation of wave load and comparative analysis of hydrodynamic performance for three semi submersible platforms, it was deduced that the third platform indiagonal brace has the minimum heave RAO swing motion response and the changes ofbrace structural make very little difference on1st order wave exciting force.4) The method and process of analysis for structural strength of semi submersibleplatform is summarized. The design wave parameters of three semi submersible platformsare determined by using random design wave method, thus the conclusion that the waveload in the state of longitudinal shear force between pontoons is the worst is put forward.Meanwhile, we can reach the conclusion that the minimum von Mises stresses of thirdplatform in diagonal brace except for the number of hot spots of fatigue with the yieldingcheck which is carried out for the same key joints of three semi submersible platforms onthe base of ABS Rule. As a result, the space-crossing braces are highly recommended. Inaddition, the welding technology of the horizontal brace and the influence of the bracestructural changes on platform construction are analyzed to obtain that the weldingtechnology of fabrication on diagonal brace is complex.5) The fatigue life of the external brackets at the brace end of the aimed platformmeets the requirements of ABS Rule. By means of the spectral fatigue analysis, we got thepredicted value that the fatigue life was sufficient for the required20years, and thereliability was beyond97.13%. |
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