Research On Structural Strength Of Semi-Submersible Lifting And Dismantling Platform Considering Construction Defects

This paper takes the semi-submersible lifting and dismantling platform as the research object,and studies the strength problems of the two main defects of welding residual stress and deformation in the construction process of its structure.In this paper,starting from the sequential coupled thermo-elastoplastic finite element method,the residual stress and deformation of typical T-shaped plates under different constraints are studied;then based on the welding finite element simulation results,the buckling strength of typical T-shaped plates is measured by the load displacement loading method.Carry out analysis,and analyze its fatigue strength through Miner linear damage theory and fracture mechanics theory;finally,add different types of initial deformation and stress to the weld at the large arc transition structure of the platform,study its yield strength,and use the spectral fatigue analysis method at the same time Research on its fatigue strength in different sea areas and working conditions.The main research work of this paper is as follows:(1)Introduce the research background and significance of this article,briefly describe the research status of welding defects,buckling strength and fatigue strength;introduce the relevant theoretical basis used in this article,including the basic equations of welding temperature field and stress field,and buckling strength analysis Theory and fatigue cumulative damage theory.(2)Starting from the typical T-shaped structure,the welding temperature field is studied,and the residual stress and deformation of the T-shaped plate under different constrained boundaries are simulated.The results show that the temperature gradient distribution at the front end of the welding heat source moving direction is less,and the temperature distribution gradient at the rear end of the heat source is more obvious;the structural deformation is the largest in the free state,which is 7mm;the weld and its adjacent area appear as tensile residual stress close to the yield strength of the material,Is about 350 MPa.(3)Research on buckling strength and fatigue strength of T-shaped plates in ideal conditions and with initial defects.The results show that the buckling strength of the structure is reduced by 11.7% when the residual stress is considered,and the buckling strength of the structure is reduced by 4.7% when the residual deformation is considered.The fatigue strength of the structure is studied by applying different types of loads.The results show that the residual stress has a greater effect on the structure than the residual deformation.The fatigue strength has a greater impact.The fatigue strength of the structure is calculated through an empirical formula and the reason for the difference between it and the simulation is explained.Based on the theory of fracture mechanics,the remaining life of the T-shaped plate with initial defects is analyzed,and the results show that Paris The formula is more conservative than the Miner criterion.(4)For the welding seam of the large arc structure in the transition area between the column and the superstructure,different types of initial defects are added to study the yield strength.The results show that the structure has a maximum stress of 384 MPa at the welding seam position after the torsion deformation is added,which is lower than The allowable stress of the material,the structure will not yield failure;the influence of initial defects on the fatigue strength of the structure is considered by modifying the stress concentration factor at the weld position.The results show that the structure at the weld meets the 30-year life cycle of marine structures It is required that the structure will not suffer short-term fatigue failure.