Research On Stability And Reliability Of Cylindrical Shell Structure

Manned submersibles are important tools for offshore resource exploration,accident handling,and maritime military means.The safe navigation of submersibles in the deep sea is a prerequisite for normal operations.The ring-ribbed pressure-resistant cylindrical shell and the cone-column combined cylindrical shell structure are the main structures of common submarines,and the strength and stability of the structure should also be paid attention to.We must consider whether to increase the structural weight,change the structural thickness of some parts of the pressure-resistant shell structure and the structural form of the rib to increase the structural strength and stability,and thus improve the utilization of structural materials.The main failure mode of the cylindrical shell is buckling instability,and the occurrence of instability is generally abrupt.Therefore,the buckling problem of the cylindrical shell has been receiving much attention.When the submarine is working at a safe depth,the reliability method is used to determine the reliability of the design method of the pressure-resistant casing structure to ensure that the design size can make the pressure-resistant casing have high safety.Therefore,it is of great significance to study the stability and reliability of the pressure-resistant cylindrical shell.In this paper,the main ship's pressure-resistant cylindrical shell structure is taken as the research object,and the stability of the submarine structure is studied by combining theoretical analysis with nonlinear finite element method.On this basis,the structural reliability of the structure under the stability failure mode is discussed.The specific research contents are as follows:(1)The critical pressure theory results of the overall instability of the cylindrical shell structure and the local instability of the shell are obtained by the energy method.The numerical simulation of the experimental model is carried out by nonlinear finite element method,and the theoretical calculation,numerical simulation and experimental results are compared.The results show that the numerical analysis method is in good agreement with the theoretical calculations and experimental results,and the calculation method is reliable and applicable.(2)On the basis of reasonable selection of grid size and boundary conditions,the stability of cylindrical shell structure is analyzed by nonlinear finite element method.The effects of single-variable changes in the thickness of the shell shell,the thickness of the rib web and the height of the rib web on the structural stability of the cylindrical pressure shell were studied.The analysis results show that changing the size of the structure will affect the instability of the structure;compared with the thickness of the shell and the thickness of the rib web,the influence of the height of the rib web on the stability of the cylindrical shell is more obvious.(3)Under the same quality conditions,the influence of several common rib types on the stability of cylindrical shell structure was analyzed.Compared with flat steel,when the rib type is unequal angle steel and T-shaped material,the stability of the cylindrical shell structure is better.On this basis,the influence of different initial deflection amplitudes on the stability of cylindrical shell structures with different failure modes is analyzed.The results show that the initial deflection amplitude affects the critical pressure of the cylindrical shell structure,but does not change the failure buckling mode of the structure;the overall instability of the cylindrical shell structure is more sensitive to the initial deflection than the local instability.(4)The stability of the cone-column combined cylindrical shell structure was studied.The effects of initial deflection amplitude and initial deformation of different regions on structural stability were analyzed.With the increase of the initial deflection amplitude,the instability mode of the structure remains as the local shell plate instability;compared with the structure of the initial deformation of each part added separately,the structure is stable when the cone-colum combination cylindrical shell is applied with the initial deformation as a whole.The worst is the worst,and the most unstable failure occurs in the conical shell and the large-diameter cylindrical shell.On this basis,the influence of the thickness of the shell,the half cone angle of the cone shell and the radius of the large and small cylindrical shells on the stability of the cone-column combined cylindrical shell structure is analyzed.The results show that increasing the thickness of the cone and the large cylindrical shell and the appropriate half cone angle can improve the stability of the cone-column combined cylindrical shell structure.The closer the radius of the large and small cylindrical shells is,the more the structure can withstand the failure.The greater the ultimate bearing capacity,that is,the higher the structural stability.(5)Based on the theoretical formula and finite element software,the reliability analysis of the stability of the cylindrical pressure shell structure is carried out by FORM method and Monte-Carlo method.The failure probability of the cylindrical shell under large depth is discussed.The influence of the geometric correction coefficient of the model and the variation coefficient of the physical correction coefficient on the structural failure probability is analyzed.The reliability analysis of the cone-column combined shell structure is carried out,and the safe working depth of the structure is calculated according to the target reliability.The results show that the reliability of the cylindrical shell structure based on the theoretical formula is more conservative than that calculated by the finite element software.