GENERAL FORM OF DIRECTIONAL SPECTRUM OF SWELL ALONG JAPAN COAST

Abstract

 The directional spectra expressed by a parametric function based on Goda et al. (1975) are commonly used to design use for multi-directional waves. It is proposed based on the extrapolation of parameters from wind wave observations, and the validity for swell conditions has not been confirmed yet. In this study, the validity of the directional spectrum proposed by Goda et al. (1975) was examined based on field observations. The dependence of the directional spreading on wave age and wave steepness was weak, and the directional spreading kept almost constant value. Compared with previous studies, the extrapolation of parameters from Hasselmann et al. (1980) to the swell region was the most consistent, whereas there were significant differences from Mitsuyasu et al. (1975), especially in the swell. On the other hand, the reference value by Goda et al. (1975) for the directional narrowness parameter generally covered the range of directional spreading observed in this study.