Effects of Forward Speed of a Ship on Added Resistance in Waves

摘要

Despite a large amount of work so far, it is said that the prediction accuracy in the area of added resistance is not enough, particularly in a range of short waves. For engineering purposes, application of the enhanced unified theory (EUT) seems promising for evaluating the wave-amplitude function, which is the most important term in Maruo's formula for the added resistance. To confirm the applicability of the EUT, measurements of the wave-induced ship motions and added resistance are carried out using a modified Wigley model at several Froude numbers, and obtained results are compared with computed ones. Discrepancy in the added resistance is observed at short wavelengths when forward speed is present, and the amount of this discrepancy tends to increase and then become constant as forward speed increases. This discrepancy may be attributed to hydrodynamic nonlinear effects in the wave diffraction at the bow, which may be intensified in the presence of forward speed. A practical factor for correcting this discrepancy, which is to be applied only to the component due to diffraction of an incident wave, is proposed in a form of mathematical function in the Froude number and the ratio of wavelength to ship length.