Optimum structural design of tankers using multi-objective optimization technique

Abstract

While designing a ship's structure, the material cost of hull's weight and the overall cost of construction processes should be minimized considering safety and reliability. In the past, the minimum weight design has focused mainly on reducing material cost and increasing dead weight, which reflects the interests of a ship's owner. But, in the past experience, the minimum weight design has inevitably led to increasing the construction cost, making it necessary for ships' structural designers to consider both structural weight and construction cost. From this point of view, this study proposes a multi-objective optimization technique for designing ships' structures. According to the proposed algorithm, the results of optimization were compared to the structural design of an existing very large crude oil carrier. Objective functions were weight cost and construction cost of the very large crude oil carrier, and evolution strategies, one of the stochastic search methods, was used as an optimization solver. For the scantlings of members and the estimations of objectives, the classification rule was adopted for longitudinal members, and the direct calculation method, generalized slope deflection method, was adopted for transverse members. To choose the most economical design point among the results of Pareto optimal set, the required freight rate was evaluated for each Pareto point, and compared to the required freight rate of the actual ship.