Analysis Of Elastic And Plastic Stability Of Symmetrical Bi-cylindrical Shell

This paper presents a new pressure-hull structure of submarine, namely, symmetrical bi-cylindrical shell—a closed structure composed by two unclosed arch shells, and there is a vertical watertight longitudinal bulkhead fixed to reinforce the two shell-junctures. Based on the derived equations of plastic instability, the paper examines the structure's instable state under the conditions of assumed perfection and initial imperfection respectively. And the buckling law of the structure affected by circular-arc opening angle and buckling wave number in circumferential direction is then obtained through comparing its critical pressures with the existing results of experiments.The computational method of plastic stability of the structure is developed in this paper, on the basis of the classic plastic theory and orthodox method of the ring-stiffened cylindrical shell. The main contents of this paper are as follows:Firstly, the plastic instability coefficients of the ring-stiffened symmetrical bi-cylindrical shell are derived from the application of two classic plastic theories—incremental theory and deformation theory. And the stress-strain expressions of the two theories are given in some unified form.Secondly, the critical pressure formulas of the ring-stiffened symmetrical bi-cylindrical shell under hydrostatic pressure are derived by Ritz method when it buckles plastically in the small deflection situation. The calculations show that buckling wave number in circumferential direction is the key factor to the critical pressure; therefore, we should adjust structural parameter in the design process to avoid makingηclose to the (η)_min.Thirdly, considering Donnell initial imperfection, the critical pressure equations of the structure under hydrostatic pressure are derived on the basis of nonlinear large deflection theory. Through calculating, this paper obtains the law of buckling shape and critical pressure affected by initial imperfection and circular-arc opening angle. The lowest equilibrium value of the non-linear large deflection is not the critical pressure.