| Global warning and environmental issues necessitate better energy efficiency in shipping industry. Therefore, International Maritime Organization(IMO) has proposed a series of codes and standards for energy efficiency, for example, the "Guidelines for voluntary use of Energy Efficiency Operational Indicators(EEOI)". In order to cope this guideline, a new approach by using running trim adjustment, aiming to reduce ship resistance and operational energy consumption has been attempted. Up to now, the optimum trim was mainly studied based on model tests and mathematical models. In this paper, a method based on numerical simulation which deals with ship models at different trims by offset transformation had been proposed. The wave-making resistance and total resistance of a container ship in still water are investigated based on Rankine Source method and CFD calculation, and added resistance due to regular waves is investigated based on three-dimensional panel method. The numerical results are validated by model tests in towing tank. Then the added resistance is predicted by using long term wave statistics, and the energy consumption has been calculated with respect to the actual navigation route. The loading conditions changes a lot when the container ship sails between different ports. Taking this situation into account, the resistance under the conditions of different water line has been calculated. Furthermore, optimizing the arrangement of ballast water to control the trim can be a good solution to reduce resistance and energy consumption. Finally, sample ship calculations are performed and the result shows the proposed method is helpful to guide ship energy efficiency design and can better guarantee the ship navigation performance at actual seas. |
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