| The Arctic has been attracting more and more attentions from many relevant countries,due to the very huge oil and gas reserves in this area.Conventional offshore drilling platform is an indispensable mean for offshore oil and gas exploration and development.However,a series of great challenges should be conquered when drilling offshore platform is applied in the development of offshore oil and gas resources in the arctic.Conventional offshore drilling platform should be upgraded with special design and consideration,to ensure its safe and efficient operation in arctic waters.These challenges and key technology can be summarized as:? the statistical data about marine environment in arctic ice region are few and the design sea state conditions is not formed clearly;? the research on the ice load of large offshore platforms in arctic is still immature,and almost no effective ice load prediction model was established;? due to the extreme cold temperature and ice-rich marine environment,anti-ice capability,operational reliability,positioning performance and structural material strength of the drilling platform should be carefully considered.The main research work in this thesis can be summarized as the following:(1)The ice,wind,wave,current,water depth and temperature in the Kara Sea and Barents Sea are investigated and compared with the data of other similar sea areas in existing codes.The design sea state conditions of these two sea areas are established with probability statistics method.(2)The interaction mechanism of sea ice with large-scale vertical structure,large-scale inclined plane structure and slender flexible structure is studied.The ice load calculation method suitable for polar semi submersible platform column large-scale inclined structure and drilling riser slender flexible structure is modified and proposed.The analysis results of discrete element method(DEM)are compared with those of standard analysis method and ice basin model tests or field observation data,and verified The value of discrete element method in engineering optimization is discussed.(3)To carry out the innovative design of the overall structure of semi submersible drilling platform,the ice load is taken as the control design load of the platform,and the environmental loads such as wind,wave and current are comprehensively considered to establish the optimization model of the drilling platform,comprehensively evaluate the motion performance,ice resistance performance,functional requirements and positioning ability of the platform,and optimize the optimal design scheme of the ice resistant semi submersible drilling platform,partly verification was carried out in the model basin.(4)In view of the positioning requirements of semi submersible drilling platform in the ice sea area and the special sea conditions that are difficult to avoid in the Arctic sea area,the fast release and re-connection scheme of mooring system is proposed innovatively,and the positioning ability and feasibility of the scheme are analyzed and verified,and the optimization design of some parameters is carried out,and the optimization direction is analyzed and summarized.At the same time,the influence of ice load on the dynamic positioning system is studied,and the control strategy of the dynamic positioning system is proposed and verified to ensure the positioning ability of the dynamic positioning system in ice area.(5)Considering the mechanical properties of sea ice and the interaction between sea ice and pipe string structure in typical sea area,the finite element numerical simulation of local collision between sea ice and riser under different working conditions is carried out,and then the overall dynamic response analysis model of drilling riser in polar ice area is established,and the ultimate strength evaluation method of drilling riser system under crushing ice load is studied,and the critical evaluation of drilling riser system in ice area is proposed The accuracy of the evaluation method is verified by laboratory tests. |
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