APPROXIMATE EXPRESSIONS FOR INTEGRAL PROPERTIES OF THE JONSWAP SPECTRUM.

Abstract

The JONSWAP spectrum proposed by Hasselman et al. has been conveniently used as a standard frequency spectrum of wind waves during wave growth. However, it is difficult to obtain the analytical integration for total wave energy and various kinds of mean wave period defined by the spectral moments with respect to frequency. In this paper, their approximate expressions are proposed as a function of peak shape parameter gamma under the assumption that the other parameters sigma //a and sigma //b are constant. All of the expressions have very high accuracy, and maximum error is less than 0. 3% respectively. It is also shown that the total wave energy-fetch relation estimated from the observed data by Hasselman et al. is inconsistent with the one derived from the other spectral parameter-fetch relations and the expression mentioned above in both the aspects of analytical form and numerical value.