Ship Hull Optimization in Calm Water and Moderate Sea States

Abstract

Optimization is a human trait. Mathematically speaking, it is minimizing (or maximizing) one or several objectives within a set of constraints. Hull form optimization from a hydrodynamic performance point of view in calm water and in moderate sea states is an important aspect in preliminary ship design. The challenge of this work is getting a ship with lowest energy consumption in calm water and in different sea states by various optimization approaches. Several optimization approaches were used for a hull form improvement to maximize seakeeping performance (accelerations based criteria) and minimize the ship resistance at its given displacement and its service speeds. Different sea-states of operating routes and different speeds were taken into account for the analysis of seakeeping performance of a vessel. An academic container vessel (Duisburg Test Case developed and tested by the University of Duisburg-Essen) was taken for the study case. The parametric model of the vessel is developed by modifying the initial geometry with the use of CAESES 4.0. After getting a parametric model, it was simulated by GL Rankine, potential flow code developed by DNV GL and validated with experimental results from HSVA. After coupling GL Rankine solver with CAESES, different optimization approaches were done by using CAESES/Dakota interface. The optimization was focused on the changes of the forward part of the vessel (Bulbous bow). While performing optimization process, not only the main objectives to minimize the energy consumption of the vessel, also computational effort (how many number of CFD runs needed) and influence of slightly changes on the operational conditions were taken into account as major criteria. As the first approach, the optimal hull form was obtained in calm water condition by different optimization algorithms and was checked wave added resistance and seakeeping behavior in moderate sea states. In second approach, optimization process was done by considering calm water condition and also seakeeping performance in different operation profiles. Finally, the results of the optimal hull form were compared with original design.