Page 46 - Marine Structural Design

Chapter 2 Wave Loads for Ship Design and Classification 23

Mitsuyasu Spectrum
Ochi-Hubble Spectrum
The Pierson-Moskowitz (p-M) spectra for hlly developed seas may be analytically expressed
as:

where,
S(w) = spectral ordinate in cm’sec
g = acceleration of gravity in cm/sec2
w = frequency in radians/sec
a =0.00810
V, = wind speed in cndsec (1 9.5 m above the sea level)

The Bretschnerder spectrum is a two-parameter family that permits period and wave height to
be assigned separately and has the form:

S(w) = 0.1687Hf “:.xp[- ws 0.675(ws /w4] (2.6)

where the two parameters A and B depend on the modal fiequency w, and the variance, E.
2a
0, =-
TS
T, = 0.946T0

where T, and To are significant wave period and peak period respectively. H, is significant
wave height. The JONSWAP spectrum can be written by modifying the P-M spectrum as:

(2.9)
where,
y =3.3

o = 0.07 and 0.09 for w < w, and w > w, respectively
a = 0.076X-0.22
3.5 x-0.33
g
w, =2n TI
“ w10
Vwl0= wind speed 10 m above the sea level