154
4 How to Determine Wave Parameters
mis, and fetch 100 < X < 300 km. The ratio wplw was assumed to be constant
and equal to 0.8.
Extended verification of the form (4.109) was reported by Krylov et al.
(1986). They collected the experimental spectra (about 200) from various
sources and constructed the averaged experimental spectrum (denoted by dots
in Fig. 4.28). The comparison of the experimental averaged spectrum with
the Strekalov-Massel spectrum shows a good agreement. It is recommended
that the spectrum (4.109) be used for the non-dimensional fetch range 10 2 ::;;
gX IV~ ::;; 10 4 .
Ochi and Hubble (1976) proposed another approximation for multipeak spectra. They represented each spectrum component in the form of a threeparameter formula:
( ) = (¥W:)A ~ [_(4).+1) (Wp)4]
S w
4f(>.) w4A+l exp
4
w
'
(4.112)
where Hs is a significant wave height and>' is a spectrum shape parameter.
By combining two sets of (4.112) spectra, one representing the low-frequency
component and the other the high-frequency component, they finally obtained
the following six-parameter spectral representation:
(4.113)
in which j = 1 and 2 represents the lower and higher frequency components,
respectively, and f is the gamma function. The parameters of spectrum (4.113)
should be determined numerically to best fit the observed spectra.