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Postresp
SESAM
B-6
15-DEC-2007
Program version 6.2
where
4λ j + 1
(B.26)
λ̃ j = ----------------4
and where index j = 1 corresponds to the lower frequency components and j = 2 to the higher frequency
components. Hsj, ω0j, λj are significant wave height, modal frequency of the spectral peak and shape factor
of component j, respectively. The spectrum is illustrated in Figure B.3.
If in either spectral component the values of the parameters Hsj and ω0j are held constant, λj controls the
shape, or, in particular the sharpness of the spectral peak. Thus, λj is called the spectral shape parameter. If
λ1 = 1 and λ2 = 0, we obtain the Pierson-Moskowitz spectrum model. In the general formulation of Equation
(B.25), the equivalent significant height Hs is obtained from
Hs =
2
2
H s1 + H s2
(B.27)
B.2on the assumption of narrowbandedness of the entire spectrum. Generally, the value of λ1 is much higher
than that of λ2.
B.3
Figure B.3 Ochi-Hubble double peaks spectrum model
B 1.7
Torsethaugen Spectrum
The sea state is described by superposing a part according to locally wind generated sea on another part
according to swell. Each of the parts is described by a generalized Jonswap spectrum. The generalized Jonswap spectrum S, as a function of the orbital frequency ω has the form:
–N
S ( ω ) = G0ω e
N ω –M
– ----- ⎛ ------⎞
M ⎝ w p⎠
a
γ
(B.28)