Optimum Structural Design of Bulk Carrier by SUMT

Abstract

The authors try to develop an optimum design program by SUMT for the hold part construction of a bulk carrier. The program is so designed that user can apply to the practical design work in the initial stage. Some example calculations are carried out by the program. In this program the object of the optimization is the structure of a pair of loaded and empty hold, and the object function means mainly building cost per unit length including material cost, labour cost, and hatch cover production cost, but it can be easily changed to the steel weight by changing some of the input data. The program has 42 variables including dimensions presenting sectional form of the hold, scantlings of frames or longitudinals and thickness of plates. Users can easily specify arbitrary fixed values for any variables by the input data control, so that the confirmation calculations for the practical designs can easily be carried out. The program involves 87 design conditions represented by inequalities relating to the hold capacity, longitudinal strength, double bottom strength, hold frame strength and the local requirements by the NV rule. Zangwill's method is used for searching the minimum direction of the modified object function, and Fibonacci search is used to find out minimum point of the function towards given direction. Through this study the authors have reached the conclusion that in general SUMT is useful for this kind of design program especially including direct calculation even though there are still some problems. In the calculations about 70,000 t bulk carrier two kinds of optimum solutions are obtained, one of them is very close to the actual ship, and the other is very far from it and has some problems from the view point of the actual design.