Fuel oil consumption of ships has been of great interest because of reinforced environmental regulations. The estimation of fuel consumption requires calculating the added resistance in actual irregular waves. However, most relevant research remains in regular waves because a nonlinear interaction in irregular waves is hard to include in numerical computation. In this paper, the added resistance in an irregular head sea has been investigated using Reynolds-averaged Navier-Stokes-based computational fluid dynamics. The results were compared with those from model tests conducted in Samsung Ship Model Basin. In the simulation, the irregular waves were generated by the linear superposition of a number of incoming wave components. Because the computation times are highly increased when a large number of waves are used, the total time window was divided into a number of partitions, and irregular waves were continuously generated by overlapping the neighboring windows. Three degrees of freedom were considered for the ship's motion: heave, pitch, and surge. Motion responses from the computation show fairly good agreement with those from the model test. In addition, the simulation predicts the added resistance at a similar level of accuracy to the experiment. The stepwise analysis is made, and key findings are discussed.
Recently, because of regulations of the Energy Efficiency Design Index, energy conservation and reduction of CO2 emissions have emerged as a major interest for ship design. In general, a ship is designed for a specific speed and draft based on her resistance and propulsion in a calm sea. However, when a ship sails in a seaway, it experiences added resistance, which is defined as an increased resistance as a result of environmental influence relative to that in a calm sea. Because the added resistance results in a speed loss of the sailing ship, the precise prediction of the added resistance is required to achieve economical sailing of the vessel.
