Research On Key Technologies For Multi-Purpose Jack-up Platform Structure Design

The topic of the research on key technologies for multi-purpose jack-up platform structure design is very complex and has practice significance, and it is beneficial to improve the design ability and research level of Chinese ocean engineering structure. In this thesis, taken the Chinese Qiongzhou strait bridge construction project as the research background, and considered the characteristics of bridge construction, the multi-purpose jack-up platform scheme design was completed according to the design theories and methods of offshore jack-up platform. Kinds of methods included theoretical research, model test and numerical simulation were used to research the key technologies of multi-purpose jack-up platform structure design such as the calculation method for the platform structure design, the ultimate load bearing capacity analysis method, the fatigue properties of tubular KK-joints of leg structure and the optimum lectotype design of leg structure. The main research contents of the thesis include:(1) According to the structural types and characteristics of existing jack-up platforms,based on the comprehensive reading of references and the thorough analysis of existing research results, the methods and related research on key technologies of jack-up platform structure design were digested, absorbed and summarized. On the basis of the construction condition and characteristics of Qiongzhou strait bridge construction project, the general design plan of multi-purpose jack-up platform was proposed. The multi-purpose jack-up platform should be able to complete a lot of bridge construction tasks, such as deep water pilling and foundationtrench leveling, in complex and harsh ocean environment safely and efficiently. The maximum operating water depth of the platform reaches80meters. The application of the modular technology made the general design plan of multi-purpose jack-up platform accord with the development trend of large marine engineering equipments, and the multi-purpose jack-up platform really have the characteristics of multi-purpose, versatility and good economy.(2) The structural types and offshore operation characteristics of multi-purpose jack-up platform were deeply analyzed and the structure design calculation methods of the platform were studied. On this basis, the multi-purpose jack-up platform structure strength analysis model were established by the finite element analysis software ANSYS as well as related marine platform design rules and construction rules. According to the research on calculation methods and principles of wind, wave and current to the platform, the worst environmental load calculation analysis method of the platform were put forward. The structure strength was analyzed under the conditions of survival, lift, normal operation and towage. According to the results, the mechanical characteristics of the platform under different conditions can be fully understood, the structure design calculation method offered by the thesis can be applied to the structure design, strength evaluation and structure optimization of the platform.(3) Based on the nonlinear finite element method, the ultimate load bearing capacity of multi-purpose jack-up platform were studied by static pushover analysis method. The ultimate bearing capacities of the platform were analyzed in both intact situation and damaged situations under the direction of0°,45°and90°environment load. The damaged situations contain collision injury, missing component, corrosion, marine growth attachment and pile foundation settlement. The worst cases of the ultimate load bearing capacity of the platform in different situations were obtained. The Reserve Strength Ratios (RSR) of the platform in different situations were calculated to evaluate the effects of the ultimate bearing capacities of the platform, and some valuable proposals were given.(4)Using the model test and numerical simulation methods, the fatigue properties of multi-planar tubular KK-joints which are the typical joint type in the truss legs of the multi-purpose jack-up platform was carried. The main tasks of experiment study are:testing the fatigue properties of KK-joints model under axial loading, obtaining the hot spot stress (HSS) distribution and the stress concentration factors(SCF) along the weld toe in the HSS region, finding the initial fatigue crack position and crack propagation law, etc.. Based on ANSYS software, the simulation models of the multi-planar tubular KK-joints were established to analyze the fatigue properties, and some geometric parameters which influence the fatigue properties of KK-joints were investigated. The proposals improved the fatigue properties of KK-joints were given.(5) Based on the finite element method, the methods of the lectotype optimization design of platform leg structure were studied. The platform leg optimization design model were established with ANSYS parametric design language in order to reduce weight and manufacturing cost, with the section sizes and shapes of the legs as the design variables, the strength, stiffness and stability of the design specifications as constraint conditions, and the optimized structural analysis program were compiled. The optimization results showed that optimized design scheme of legs can effectively reduce the structure weight and improve the economical efficiency of the platform, and, the use of reasonable leg structure can not only reduce the total steel quantity but also control stresses and displacement responses of the platform effectively.(6) In this thesis, the finite element analysis software ANSYS were chosen as the main calculation and analysis platform for the structure strength analysis, ultimate load bearing capacity analysis, tubular KK-joints numerical simulation analysis and leg structure optimum lectotype design of multi-purpose jack-up platform. According to the specific research contents and methods, the appropriate program modules were chosen and the reasonable analysis programs were compiled for the completion of related research work. The methods and ideas, which to study and solve the key technologies of multi-purpose jack-up platform structure design based on ANSYS platform were proposed.