Structural Analysis And Optimization Of Jack Up Multifunctional Platforms In Ice Free Period

Jack-up platforms have a wide range of uses,and the environmental load conditions of jack-up platforms for different purposes are also very different.Under normal circumstances,the design conditions of jack-up platforms should consider complex marine environmental conditions including ice loads,but some multi-functional platforms have a single purpose and do not work in ice areas.Therefore,this article does not consider ice areas for platform use.Specific marine environmental conditions are used to determine the self-existing working conditions,and conduct strength analysis and structural optimization of the platform structure,thereby improving structural strength or reducing construction costs.Firstly,a three-dimensional finite element model of a jack up multi-functional platform for aquaculture is established.According to the angle of incidence of wind,wave and current loads,the platform does not consider ice load.After the static analysis of the platform is completed,the most dangerous working condition is selected for dynamic analysis,and the stress and displacement of leg under extreme conditions are calculated.Secondly,The legs are divided into 6 segments,take leg thickness,leg diameter and height at the segment as design variables.The maximum dynamic stress and maximum dynamic displacement before the optimization of the leg are taken as the constraint conditions.The minimum material mass of the leg and the minimum acceleration under the self-contained condition are the objective functions.Multi Island genetic algorithm(MIGA)and gradient optimization algorithm(NLPQL)are used to optimize the leg of jack up platform.The total weight of the leg is reduced,the stress distribution is more uniform,and the requirements of strength and stiffness are met.Finally,the main platform is optimized.The deck thickness,web height,thickness and flange width and thickness of T-beam and L-beam are taken as design variables,and the maximum dynamic displacement and stress before the optimization of the platform and the maximum stress of the beam are taken as constraints.The objective function is to minimize the total mass of deck,T-beam and L-beam and to minimize the acceleration under self-contained condition.The results show that the strength analysis and structural optimization of the leg and main body of the jack-up platform are carried out under the condition of meeting the requirements of the specification.Without reducing the overall structural performance,the total mass of the platform is significantly reduced,more materials can be saved,and the stress distribution is more uniform.This method can provide a useful reference for the design and construction of such platforms.