Improved synthesis capability for “T” ring-stiffened cylindrical shells under hydrostatic pressure☆☆☆

Abstract The new “Direct Search-Feasible Direction” (DSFD) nonlinear mathematical programming optimization algorithm is applied to the design of stiffened submersible shells. An automated design capability for this problem (SBSHL6) is described wherein the program will generate the least weight design by locating the optimal, or near optimal, values of skin thickness, web thickness and height, flange thickness and width, and stiffener spacing given the design parameters such as shell size, immersion pressure, shell eccentricity, materials properties, and minimum natural frequency. Constraint equations control, general, panel (between stiffener), web, and flange instability, skin and stiffener yielding, and minimum natural frequency. The DSFD procedure appears capable of reliably locating optimal designs whereas earlier attempts in investigations using other optimization methods, including the popular SUMT procedure, failed to provide optimal solutions to the same problem. This and an earlier detailed comparison study strongly suggest that SUMT is not a reliable procedure for structural optimization while DSFD seems to provide reasonably reliable performance. Designs generated by SBSHL6 are presented and compared with those of the earlier studies. The results of a series of synthesis runs from widely separated starting points are also presented. The designs developed by SBSHL6 are substantially lighter than those reported earlier. The multipath runs for each set of parameters studied all converged to similar designs of essentially identical weights demonstrating program reliability.

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