Analysis of Instantaneous Ship Resistance-Increase in Waves with CFD URANS

Abstract To comply with the requirements set out by the International Maritime Organization (IMO) for reducing greenhouse gas (GHG) emissions, recent efforts have focused on investigating the parameters that affect the increase in ship resistance, with the aim of developing effective reduction methods. This research examines both the time-varying instantaneous characteristics of a ship’s resistance in waves, referred to as resistance-increase, and the mean resistance-increase, known as added resistance, using the computational fluid dynamics (CFD) method. The accuracy of the CFD method in predicting the instantaneous resistance-increase in waves is evaluated by comparing it with the experimental fluid dynamics (EFD) method. Overall, the CFD method is found to give reasonable predictions for the amplitude of resistance-increase; however, for waves with multiple oscillation frequencies, the CFD method predominantly captures a single frequency, called the encounter frequency, whereas the EFD method gives multiple frequencies. In addition, a parametric study of resistance-increase is conducted, which shows that the wavelength ratio significantly influences the pattern of resistance-increase, with a transition from a pure sine curve to a more irregular curve as the wavelength ratio shortens. Furthermore, with regard to the proportionality of the added resistance to the wave height, it is observed that the added resistance may be either much greater than or (sometimes) less than the square of the wave height. Finally, as the ship’s speed increases, the positive oscillation amplitude of the resistance-increase rises, while the negative amplitude tends to decrease, resulting in a significant increase in time-averaged added resistance. In summary, the wavelength ratio primarily governs both the added resistance and the resistance-increase in waves.