Techno-economic optimization of an LNG carrier with multicriteria in the preliminary design stage

Abstract

When economic optimization is considered in the preliminary design of a ship, required freight rate (RFR) is usually taken as the objective function because it is related to the building and the operating costs of a ship reflecting the interest of both the shipyard and the shipowner. However, the choice of RFR as the objective function sometimes has an adverse effect on the designer. For example, to analyze the effect on the objective function of change of the building and operating costs, a sensitivity analysis is required for each item. That is, the relative importance of the two costs, when constructing a design model, is not obvious as they are combined together. In order to overcome the limitation of single objective optimization, a multicriteria optimization method has been used. To solve the multicriteria optimization problem with efficiency a hybrid optimization solver is developed by coupling the genetic algorithm and the direct search method. Furthermore, to accelerate the searching speed of the solver in the design space, an Al (artificial intelligence) technique is applied to the hybrid optimization solver. It is applied to the optimum design of a liquified natural gas (LNG) carrier in the preliminary design stage. Through application to the ship design, the relative importance between the operating and building cost in the economic analysis of the ship design was manifested.