Single- and multiobjective optimization of a welded stringer-stiffened cylindrical shell

This paper presents the single- and multiobjective optimization of a welded stringer-stiffened cylindrical steel shell. A column fixed at the bottom and free on the top is constructed of stringer-stiffened cylindrical shell and loaded by axial compression as well as by a horizontal force acting on the top. Halved rolled I-section stringers are welded outside of the shell by longitudinal fillet welds. The shell is loaded by a compression force N_F and a horizontal force H_F. The horizontal displacement of the top (w) is limited. The stiffening is economic when the shell thickness can be decreased in such a measure that the cost savings caused by this decreasing is higher than the additional cost of stiffening material and welding. Variables are the shell thickness as well as dimension and number of stringers. We have considered three objective functions: (1) material cost, (2) cost of forming the shell elements into the cylindrical shape, assembly and welding, (3) painting cost. The original Particle Swarm Optimization (PSO) algorithm was modified to handle multiobjective optimization techniques and to find discrete values of design variables. It was built into a program system, where several singleobjective and multiobjective techniques like min-max, different versions of global criterion, weighted min-max, weighted global criterion, pure and normalized weighting techniques are available.

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