Effect of wave periods on added resistance and motions of a ship in head sea simulations

Given that the International Maritime Organization (IMO) recently introduced the Energy Efficiency Design Index (EEDI) for new ships and the Energy Efficiency Operational Indicator (EEOI) for ship operations, accurate prediction of the added resistance of ships advancing in waves has become necessary. In the present study, the open-source computational fluid dynamics library, OpenFOAM, was used to predict the added resistance with the motions of a ship. Unstructured grid using a hanging-node and cut-cell method was used to generate fine grid around a free-surface and ship. Five wavelengths from a short wavelength (λ/LPP=0.65) to a long wavelength (λ/LPP=1.95) were considered as head waves. The grid uncertainty was evaluated with respect to three grid systems for a wavelength of λ/LPP=1.15. The predicted added resistance and heave and pitch motions with various head waves were compared with the data from model experiments. The wave pattern around the ship and the motions of the ship were analyzed with respect to the wave encounter period. When the wavelength was similar to the ship length, the ship moved against the waves, and thus the added resistance was greater compared with other wavelengths.