Directional growth of wind generated waves

Abstract

The Spectral Ocean Wave Model (SOWM) is a numerical wave prediction model which calculates directional wave spectra from input wind fields. As do the majority of wave models, it uses a point spectral growth mechanism, i.e., it applies the energy balance equation in a directionally integrated form. The directionality of its growth is obtained from an assumed spreading function on the wind direction.

In this study, the energy balance equation is applied in directional form using directional atmospheric energy source functions. The B function of Miles’ instability mechanism is derived following the analysis of Phillips and it is tuned to the directionally integrated form used in the SOWM. Two infinite ocean wave models are used to compare the behavior of the point and directional growth mechanisms under various wind conditions. The directional form shows more flexibility in responding to directionally varying winds while the point spectral form creates excess energy spread widely over direction when operating in the presence of swell.