Structural Optimization of Tanker with Double Hull System Based on Plastic Design

Abstract

This paper presents a practical method for the structural optimization of a tanker with a double hull and double bottom system by the Sequential Unconstrained Minimization Technique (SUMT) and the Multiplier Method. The weight of one tank hold length is taken as the objective function and the scantlings of the transverse and longitudinal members in the midship segment are chosen as the design variables. A lot of constraints such as plastic collapse of ship hull and of transverse frames, plastic collapse and buckling strength of longitudinal stiffeners and of plates, and buckling strength of transverse strut under the hogging and sagging loading conditions are considered. The minimum values of design variables are also included in the constraints. The focuses are attached on the variation of the optimized weight with the number of transverse ring spaces and the comparison between the SUMT method and the multiplier method on condition that the effective width of attached plates in transverse members is taken into consideration. A numerical example with 41 design variables and 118 constraints has been made and the results are presented.