Numerical simulation of wind wave surface profiles with tuned phase spectra

Abstract

It is known that the phases of the individual harmonic components in a linear narrow band wave spectrum are uniformly random. It has been suggested by some workers that some sort of phase coupling and `locking' between the different spectral components would lead to nonlinear surface waves. Conventional methods of wave recording and analysis inherently fail to record or to bring out the exact quantitative picture of nonlinear interactions due to recording and sampling limitations in relation to nonlinear waves with vertical and horizontal asymmetries especially in the case of breaking and shoaling waves. Hence, the inverse method of computing the surface profile from a known autospectrum using transformed (tuned) phase spectrum with coupling of different natures is tried and the results are presented here. Increased wave groupiness is found for higher spectral peak periods with phase coherency at the peak. Abnormally high breaking waves (freak waves) are generated when frequency dependent (by Normal probability law) phase spectrum is used. The results suggest that external factors like currents, wind, boundaries (bottom) and other waves systems can cause changes in the phase spectrum to give rise to nonlinear processes.