Study On Nonlinear Buckling Properties Of Toroidal Pressure Hull And The Effects Of Parameters On Buckling

Developed on the basis of manned submersibles,the deep-sea space station is a new-generation platform for prolonged,residential deep-sea operations in situ,including scientific research and undersea military deterrence.The deep-sea space station has a large-scale pressure-resistant structure as its main structure and buoyancy unit,the form of this structure is crucial to work safety,positioning reliability and the three-dimensional steering of the deep-sea space station.The large-scale pressure shells that are presently in service are cylindrical shell and multi-ball junction shell,both of which are long column structure,and the lateral water resistance is large,which affects the steering and positioning reliability of the deep-sea space station.Column structure is sensitive to initial geometric defects,which leads to the decrease of compressive ability and poses a safety risk.The toroidal pressure shell is the mainstream design scheme for the deep-sea space station and a subject of considerable research currently.However,the toroidal pressure shell structure has positive and negative Gaussian curvature,and the instability mechanism is complicated,which is affected by the circumferential rotation angle,section parameters,section shape and defects.Accordingly,this study analyzed the nonlinear buckling properties of the toroidal pressure shell and the effects of the shell’s parameters on the buckling,as detailed in the following sections.(1)Comparative study on nonlinear buckling properties of toroidal and cylindrical shells.This study established finite element model of the toroidal shells and its equivalent cylindrical shells,analyzed the stress and buckling properties by using the linear perturbation method and nonlinear arc-length method.Three resin toroidal shells and three resin cylindrical shells were fabricated through additive manufacturing.The ultrasonic nondestructive thickness measurement,3D contour scanning and hydrostatic pressure tests were carried out respectively.By comparing the numerical and experimental results of toroidal shells and cylindrical shells,it was found that although the toroidal shells exhibited complex nonlinear buckling properties,it had lower defect sensitivity relative to the cylindrical shells.The average load-bearing capacity of the test model was 1.29 times that of the cylindrical shells,indicating superior compression performance.(2)Influence of circumferential rotation angle on buckling of the toroidal shell segments.The influence of circumferential rotation angle on the buckling of the toroidal shell segments was studied using the nonlinear arc-length method,and the defect sensitivity of the toroidal shell segments with typical circumferential rotation angle was analyzed.Twelve models of toroidal shells segments made of stainless steel were fabricated for numerical and experimental analysis.The results revealed that when the circumferential rotation angle was small,the toroidal pressure shell was sensitive to circumferential rotation angles,and the buckling load decreased rapidly as the rotation angle increased.The average buckling load of the experimental model of the toroidal shell segments with a circumferential rotation angle of 90° was approximately 75% that of the toroidal shell segments with a circumferential rotation angle of 45°.Both the collapse of the test models had the form of nonlinear elastoplastic collapse.(3)Influence of section parameters on buckling of the toroidal shells with elliptical cross-section.A number of finite element models of toroidal shells with different elliptic section parameters were established.The nonlinear arc-length method was used to analyze the influence of the length–to–minor axis ratio of the shell section parameters on the buckling of the toroidal shells with elliptical cross-section.A set of elliptic cross-section parameters were optimized.Two optimized resin toroidal shells with elliptical cross-section and two resin toroidal shells were fabricated.The ultrasonic nondestructive thickness measurement,3D scanning,hydrostatic pressure tests and numerical analysis were conducted respectively.As indicated by the results,the best compressive capacity was achieved when the ratio of the long axis to short axis of the shell section parameters was approximately at 1.27,where the buckling load of the optimized toroidal shells with elliptical cross-section was 1.72 times that of its equivalent toroidal shells.(4)Influence of the number of corrugations on the buckling of the corrugated cross-section toroidal shells.Based on the idea of "using straight instead of curved",several finite element models of corrugated cross-section toroidal shell with different corrugated section were established.Through the nonlinear analysis method of the ultimate strength of the pressure hull,the influence of the number of corrugations on the buckling load of the corrugated cross-section toroidal shells was studied.A corrugated cross-section toroidal shell was selected and compared with the toroidal shell.The results showed that with the increase of the number of corrugations,the buckling load of the corrugated cross-section toroidal shells gradually increased.When the number of corrugations increased to 12,the carrying capacity of the corrugated cross-section toroidal shell was as high as 98% of the toroidal shell.