Structural Strength Analysis And Optimum Design Of Pile Leg Of Self-elevating Offshore Platform

With the development of marine petroleum exploitation,Jack up drilling platform is the most commonly used mobile offshore platform.Offshore platform is the basic facilities for oil and gas resources.The marine environment which the offshore platform suffer from,including wind,waves,currents,earthquakes and other disasters threats the safety of the platform structure.The legs as a support structure for offshore platforms,affects the safety and stability of the platforms.When we optimize the legs with expensive materials,We should consider dynamic performance of legs,so take on a multiple-objective optimization to legs based on dynamic performance.Firstly,the static and dynamic analysis of jack up offshore platform should be done.The model of Jack up drilling platform is established in software.According to the angle of environment load,the article discuss 5 load case conditions on the static analysis.Boundary conditions are applied according to the specification and the loads are applied according to the deck load diagram.After the completion of the static analysis,select the most dangerous working condition to do dynamic analysis.In addition,it's necessary to check the leg yield and buckling strength.Secondly,the single objective optimization of the pile leg structure is carried out.The legs are segmented by leg thickness as design variables,dynamic displacement,dynamic stress and frequency as constraints.When optimization is carried out,quality is as the objective function.If we only consider the minimum value of quality,the thickness of the legs is the bias of lower design variables.However,the acceleration which is the feature of vibration of the platform becomes larger,so it is necessary to carry out multiple-objective optimization.Finally,the multiple-objective optimization of the pile leg is carried out.First,the sensitivity of the design variables to the acceleration of the pile leg is analyzed,and the same design variables and constraints are taken with the single objective optimization.The objective function is to minimize the mass and the acceleration.