抄録
Optimizing hull form design is playing a more important role in the shipbuilding industry, especially when regulations on the environmental protection and improvement of ship energy efficiency become more stringent than ever. Though the studies on design optimization of ship hull have a long history and achieved some significant results, studies on the stern shape optimization of a ship hull have been a few due to the complexity of flow field behind a transom stern. In this paper, a numerical method for optimizing the stern shape of a container ship based on a nonlinear programming method and a Navier-Stokes analysis is proposed. A CFD solver which solves the three-dimensional Reynolds Averaged Navier-Stokes (RANS) equations for incompressible flows is used for evaluation of an objective function and analysis of flow fields around ship hulls. The Sequential Quadratic Programming (SQP) method is utilized as an optimizer which automatically determines values of the design variables in such a way that the objective function is minimized subject to the given constraints. Design variables are selected so that the modified transom shapes are efficiently created during the optimization process. To demonstrate the applicability of the present method, transom stern of a container ship is optimized to minimize the pressure resistance coefficient at a model scale. In addition, the effects of the initial designs and of the frameline modification functions to the optimized results are examined in this paper. The optimized results show that the present optimization system is able to create a stern shape that decreases the pressure resistance coefficient; however, it turns out that special cares should be taken in selection of the initial designs and of the hull form modification functions since the optimization results strongly depend on these parameters.
