Abstract
The prediction of the added resistance and attainable ship speed under actual weather conditions is essential to evaluate the true ship performance in operating conditions and assess environmental impact. In this study, a reliable methodology is proposed to estimate the ship speed loss of the S175 container ship in specific sea conditions of wind and waves. Firstly, the numerical simulations are performed to predict the added resistance and ship motions in regular head and oblique seas using three different methods; a 2-D and 3-D potential flow method and a Computational Fluid Dynamics (CFD) with an Unsteady Reynolds-Averaged Navier-Stokes (URANS) approach. Simulations of various wave conditions are compared with the available experimental data and these are used in a validation study. Secondly, following the validation study in regular waves, the ship speed loss is estimated using the developed methodology by calculating the resistance in calm water and the added resistance due to wind and irregular waves, taking into account relevant wave parameters and wind speed corresponding to the Beaufort scale, and results are compared with simulation results obtained by other researchers. Finally, the effect of the variation in ship speed and therefore the ship speed loss is investigated. This study shows the capabilities of the 2-D and 3-D potential methods and CFD to calculate the added resistance and ship motions in regular waves in various wave headings. It also demonstrates that the proposed methodology can estimate the impacts on the ship operating speed and the required sea margin in irregular seas.
Highlights
More than ever, the reduction of ship pollution and emissions, maximization of energy efficiency, enhancement of safety requirements and minimization of operational expenditure are key priorities
When a ship advances through a seaway, she requires additional power in comparison with the power required in calm water due to actual weather and ship operating conditions
The added resistance under ship motions is predicted in regular waves and the ship speed loss is estimated at the assumed design and other lower speeds by the proposed methodology
Summary
The reduction of ship pollution and emissions, maximization of energy efficiency, enhancement of safety requirements and minimization of operational expenditure are key priorities. When a ship advances through a seaway, she requires additional power in comparison with the power required in calm water due to actual weather and ship operating conditions. This degradation of the ship performance in a seaway, which is reported to be an addition of about 15–30% of the power required in calm water (Arribas, 2007) is accounted for by the application of a “Sea Margin” onto the total required engine power and a value of 15% is typically used. From a ship designer's point of view, the design could be seen as more competitive if the vessel is designed for better performance in a seaway, and for ship owners and officers, they could have safer ships in actual operation at sea
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