ssc-367 - Ship Structure Committee

q = 3.3
s = 0.07, for f< fm
s = 0.09, for f > fm
The Bretschneider spectrum is a subset of the General JONSWAP;
setting the gamma parameter to 1.0 converts the JONSWAP spectrum
into the Bretschneideror ISSCModified P-M spectrum. Also setting
the alpha parameterto 0.0081 convertsthe JONSWAP spectrum intothe
Pierson-Moskowitzspectrum.
As a guideline, the JONSWAP spectrum with gamma = 2 would be an
applicablespectrum for confined regional areas. The Bretschneider
spectrum (JONSWAPwith gamma = 1) would be applicablefor open ocean
(Pacific or Atlantic) areas.
Ochi-Shin Wind Spectra
Ochi and Shin reviewed six wind spectra formulations currently in
use and have created an average wind spectrum to represent the
variation (gusts) of the wind about the mean value. The wind
spectrum represents the average of measured spectra and was
deliberately devised to accurately represent the low frequency
portion of the wind spectrum. The equation has three forms
depending upon the frequency range.
s(f*) =
{
583 f*
420 f*0”70/(l+f*O-3’) ”-5
838 f*/(l+f*0.3s)ll.s
with
f* = f z/uz,
where
f = frequency in Hz,
z = height above sea level in meters, and
Uz= mean wind speed at height z in meters/see.
6“6