Assessment On The Ice-Resistant Capacity And Operation Adaptability For Jack Up Platforms

The dissertation is supported by China Industry and Information Technology project named “research on Anti-ice capability of Jack up platform”.Specific to the oil and gas exploratory development in the Ice zone,research on the key technology of ice operations for Jack up truss leg platform is conducted.A systematic research including the interaction mechanism between sea ice and Jack up platform,anti-ice ability of structure,Ice adaptability evaluation method and Anti-ice strategy,which can provide technical support and operational guidance for the safety management of ice operation for Jack up truss leg platform.It has important theoretical value and good engineering application prospect.The main achievements are as follows.(1)Study on the interaction mechanism between sea ice and Jack up platformStudy on mechanical properties of sea ice,the interaction model between sea ice and vertical or conical structures.Analysis of Quasi-static vibration model,Steady-state vibration model and Random-vibration model.The finite element model of Jack up truss leg platform is established by ANSYS,then modal analysis and horizontal static stiffness analysis of Jack up platform are carried out.The influence of different ship lift height on the static performance of the structure was researched to provide the basis for the following analysis and adaptability evaluation.(2)Study on anti-ice characteristics of self elevating platformThe effect of environment load on the dynamic response of structure is researched by ANSYS.The respective effects of wind load,current load and ice load are obtained.The static / dynamic ice analysis of Jack up platform are carried out,the issue of structure static pushover under extreme ice load is researched by elastic plastic analysis method,and the relationship between the maximum displacement and the base shear force or ice thickness is obtained.According to the different breakup models of sea ice,the ice-induced dynamic response of jack up platform under three typical dynamic ice force models are researched,especially the ice induced response under the steady-state vibration,the amplitude distribution of displacement and acceleration are analyzed.(3)Study on the evaluation of ice adaptability for Jack up platformThe evaluation of ice adaptability for Jack up truss leg platform is established.Design method for stiffness / strength of platform in ice zone is formed,including the analysis of overall strength and stiffness of truss leg,transverse local strength / stiffness analysis and longitudinal local strength / stiffness analysis.The distribution of stress and displacement of truss legs under different ice thickness,direction and depth are researched.Overall stability evaluation of truss leg is researched,and fatigue damage and life assessment process for truss leg platform in ice zone is formed.Fatigue sub condition is based on the probability distribution of ice thickness and velocity in a specific area,the MATLAB program is based on Miner criterion and rain flow counting method to conduct fatigue life assessment of truss leg platform.(4)Research on anti-ice strategy based on anti-ice performance of jack up platformIce-induced vibration suppression of offshore structure is researched,the ice induced vibration mitigation strategy for jack up platform is proposed which is combined with the characteristics of self elevating truss leg platform,that is the main hull lift method.The dynamic ice force at different frequencies are applied to structure under the depth of 20 m,the resonance height of the structure is researched by dynamic magnification factor.Two schemes which are increasing and decreasing the main hull are proposed,the damping effect of two schemes are analysized based on the ice induced dynamic response of structure,and the ice induced vibration reduction strategy is established.