On a Method of Wave Analysis Based on Two Dimensional Spectra of Ship Wave Patterns

Abstract

It has been realized that the spectrum of measured wave profile along a longitudinal cut and the wave-making resistance estimated from them are considerably dependent on the distance between the course of the ship and the longitudinal cut. This fact differs from the conclusion of the linearized theory of wave-making resistance of ships, and has been thought caused by the defect of the correction of the truncation of reflected waves on side walls or by the effect of local wave on the longitudinal cut. But, the conclusions of recent investigations on these fields are not enongh to explain the difference of the results on the cuts of different distance. The authors thought that the application of the linearized theory of wave-making as it is to real wave patterns created by the ship or by the model may be the main reason of this defect of wave analysis. Then, starting from two dimensional Fourier analysis, the two dimensional wave spectrum can be estimated from the measured wave pattern. And, when one investigates this two dimensional spectrum of the real wave pattern comparing to one dimensional spectra derived from the ordinary longitudinal cut method and to properties of the theoretical ship wave system based on the linearized theory, the characteristics of the actual wave pattern generated by ships may be distinctly grasped and the above mentioned defect of the ordinary longitudinal cut method 〓 wave analysis must be improved. Considering thus, the authors deduced the theory of wave analysis based on two dimensional wave spectra and applied it to the wave profiles of 2m Wigley model measured on six longitudinal cuts in the towing tank. The results showed that two dimensional spectra of real wave patterns are remarkably different from the spectra of the linearized theory.