Buckling Analysis And Experimental Study Of Variable Thickness Ellipsoidal Head

"Made in China 2025" requires accelerating research on marine engineering equipment and high-tech ship technology,which shows that the development of the marine economy plays a very important role in China’s economic growth.The submersible is an important tool for human exploration of the ocean,and the pressure shell is the most critical component of the submersible.In addition to the spherical pressure shell,other forms of sealed end of the shell often need to connect the head.Ellipsoidal heads have smooth and continuous warp radius of curvature,uniform stress distribution,and low edge stress.From the perspective of force,ellipsoidal heads are second only to hemispherical heads,and are superior to dish-shaped heads.For the ellipsoidal head under the action of internal pressure,there have been relatively perfect theoretical research results at home and abroad.However,there are few research results on top instability under external pressure.In this paper,a variable-thickness ellipsoid head is proposed,which has better buckling characteristics and material utilization.Based on theoretical calculation,numerical analysis and proportional model test,the buckling characteristics of the thickened ellipsoidal head are explored.The main research contents and conclusions of this paper are as follows:(1)Based on the Mushtari’s formula and the fourth strength theory,the thickening ellipsoid head is designed.When the main influencing factor of ellipsoidal head instability is buckling,the theoretical formula of equal buckling is derived to obtain the thickness expression,and when ρ=2,the thickness of equal buckling becomes thicker The minimum value of the thickness at the equator of the ellipsoidal head is about 35%of the thickness at the apex of the head;when (?),the main influencing factor of the instability of the ellipsoidal head is strength,the thickness formula is derived by deriving the equivalent strength theoretical formula and At this time,the minimum thickness at the equator of the equal-strength thickened ellipsoid head is about 68% of the thickness at the apex of the head.(2)The buckling characteristics of equistrength and shape optimization thickening ellipsoid head and equithickness ellipsoid head were compared.The results show that when the volume is equal and the modal defect value is 0.3mm(10%of the wall thickness),the nonlinear buckling critical load value of the iso-strength ellipsoid head is 1.16 times that of the iso-thickness ellipsoid head,and the nonlinear buckling critical load value of the shape optimization ellipsoid head is 1.1 times that of the iso-thickness ellipsoid head.The proportion model made by mechanical processing of Q345 material is difficult to ensure the accuracy due to the inevitable machining error,but the test results and the results of numerical analysis still have a high degree of similarity,equistrength thickening ellipsoid head are dimpled pits at the top.(3)The buckling characteristics of equistrength and shape optimization thickening ellipsoid head and equithickness ellipsoid head were compared.It is concluded that the linear elastic buckling load of the equistrength thickening ellipsoid head is about 1.49times that of the equistrength thickening ellipsoid head under the condition of ensuring equal volume.The linear elastic buckling load of shape optimized thickening ellipsoid head is about 1.62 times of that of isopymmetric ellipsoid head.The proportion model made by mechanical processing of Q345 material is difficult to guarantee the accuracy due to the inevitable machining error,but the test results still have a high degree of similarity with the results of numerical analysis.(4)The influence of geometric parameters of the frame on the head of ellipsoid was studied by orthogonal design.It is concluded that the radial ribbed Angle and rib height have greater influence on the critical load value of the ellipsoid head,while the circumferential ribbed arrangement has less influence on the critical load value of the ellipsoid head.The thickening ellipsoid head is better than the ribbed ellipsoid head in improving the buckling load under ideal conditions,but it is too sensitive to the initial defect,when the defect is too large,the buckling load is even lower than the ribbed ellipsoid head.