Hydrodynamic Study on Added Resistance by Means of Unsteady Wave Analysis (Mathematical aspects of nonlinear waves and their applications)

Abstract

It is known that the added resistance in waves can be computed from ship-generated unsteady waves through the unsteady wave-analysis method. In order to investigate the effects of nonlinear ship-generated unsteady waves and bluntness of the ship geometry on the added resistance, measurements of unsteady waves, wave-induced ship motions and added resistance are carried out using two different (blunt and slender) modified Wigley models. The ship-generated unsteady waves are also produced by the linear superposition using the waves measured for the diffraction and radiation problems and the complex amplitudes of ship motions measured for the motion-free problem in waves. Then a comparison is made among the values of the added resistance by the direct measurement using a dynamometer and by the wave-analysis method using the Fourier transform of measured and superposed waves. It is found that near the peak of the added resistance where ship motions become large, the degree of nonlinearity in the unsteady wave becomes prominent especially at the fore-front part of the wave. Thus the added resistance evaluated with measured waves at larger amplitude of incident wave becomes much smaller than the values by the direct measurement and by the wave analysis with superposed waves or measured waves at smaller amplitude of incident wave. Discussion is also made on the characteristics of the added resistance in the range of short incident waves.