Research On Mechanical Behavior Of Processing Technology For Special Structure Of Semi-submersible Lifting And Disassembling Platform

The structure of semi-submersible lifting and disassembly platform is complex,which is different from the conventional semi-submersible platform.It has different floating bodies and columns.There is no cross brace in the middle.It is only connected with the upper hull,which makes the construction difficult and requires high precision.In order to avoid structural stress concentration,the hyperboloid large arc plate structure is used to connect the column of semi-submersible lifting platform with the upper hull and the lower floating body.Surface plate requires high smoothness,large welding quantity and high precision.These special structures are the foundation to ensure the strength and function of the platform structure,and also the difficulty in the construction of the dismantling platform.Therefore,the forming of curved surface plate in the platform connection structure and the prediction of welding deformation have a great impact on the construction quality of the platform special structure.In this paper,the connecting structure of the platform is taken as the research object,and the forming shape and springback of the hyperboloid plate are simulated by the method of numerical simulation.Based on the thermo-elastic-plastic finite element method and the inherent deformation theory,the welding deformation of the connection structure in the platform is predicted,and the welding deformation is controlled by optimizing the welding sequence.It provides a theoretical basis for improving and optimizing the processing technology of the special structure of the platform and realizing the precision manufacturing of the platform structure.The main research content is as follows:(1)Change the maximum deflection of the single-curvature plate stamper,compare the error between the forming shape and the target shape of the single-curvature plate which are formed by different deflection stampers;and perform numerical simulation calculation on the springback problem is taken after forming the double-curvature plate.In the single-curvature sheet press forming,the maximum deflection of the stamper is larger than the forming deflection of the sheet,but the error of one-shot forming is large,which cannot fully meet the requirements of actual production;in the forming rebound of the double-curvature sheet,the amount of rebound in the edge portion of the sheet is greater than the amount of rebound in the middle of the sheet.It is difficult to achieve one-time forming for the press forming of the sheet,and the stamper can be improved by using a step-step pressing method and multiple pressing to form the steel sheet into a target shape.(2)Based on the thermoelastic-plastic finite element method,the numerical simulation of the flat butt welding of EH36 high-strength steel in the platform was carried out,and the variation law of residual stress and welding deformation of the butt joint of the flat plate was obtained.The finite element model of four T-joints with different web thickness and wing thickness was established.The effects of the webs on the residual stress and welding deformation of the webs with different thicknesses in the welded joints were studied.Both the transverse stress and the longitudinal stress in the weld and its vicinity show a large tensile stress.The longitudinal stress peak has exceeded the yield strength of the material and the material is in an irreversible deformation state.The butt joint is perpendicular to the weld direction,the edge portion of the base material is upturned,and the middle portion of the sheet is obviously sunk.When the thickness of the web and the flap is larger,the welding residual stress of the welded joint is larger;when the thickness of the web and the flap is larger,the welding deformation of the welded joint is smaller.(3)In the welding of the whole structure,the welding sequence has a great influence on the structural welding deformation.The finite element model of the whole structure is established.Through the study of three welding sequences,the deck and the horizontal and vertical members and the horizontal and vertical members are completed from left to right.The welding sequence between the connections has the least effect on the weld distortion.Therefore,it is preferred to weld the member with high rigidity to control the welding deformation effectively.The openings reduces the structural rigidity and makes the welding deformation larger.