Application of Multiplier Method to Ship Structural Optimization in View of the Discrete Values of Standard Plate Thickness

The multiplier method is applied to structural optimization of double hull tanker in this paper. The hull construction cost of one tank hold length in the midship segment of double hull tanker is taken as an objective function. Since there are standard values for plate thickness, the plate thickness can not be changed continuously. In order to solve this problem, two optimization processes are introduced to deal with those discrete design variables. In the first optimization process, it is assumed that all design variables vary continuously. After the first optimization process, the plate thickness is set to the nearest standard value and the rest of design variables is decided in the second optimization process. In this study, the effect of standard plate thickness on optimum design and the optimum values varied with fillet welding price rate as well as the influence of limiting value for longitudinal spaces on optimum design are investigated numerically.