ssc-367 - Ship Structure Committee

Wave informationis calculatedfrom wind, accountingfor direction,
duration and fetch. By integrating the weather conditions over
small time steps, a wind and wave history can be built. The
resulting records can be analyzed in a manner similar to that used
with actual wind and wave records to produce wave scatter diagrams
and wave exceedence curves.
6.1.2 Wave and Wind SDectra
Wave and wind spectra define the energy that is being applied to a
structure or vessel. There are many wave spectra formulations and
some of these are discussed in Appendix A. The most general and
therefore most useful wave spectrum formulation is the General
JONSWAP. The General JONSWAP spectra include the Bretschneider
spectra which in turn include the Pierson-Moskowitz spectra.
Reference 6.6 presents a summary of the various wind spectra. The
spectrum recommended in Reference 6,6 is defined as follows:
JONSWAP Wave SDectrum
The JONSWAP (JointNorth Sea Wave Project)spectrumwas derived from
wave measurements in the southern North Sea and is based on older
spectraformulations,Pierson-Moskowitz/Bretschneider/ISSCModified
P-M. The Mean JONSWAP spectrum has fixed parameters and represents
the waves measured during the project. The General JONSWAP
parameters can be varied so that the spectrum can represent either
fully developed seas or developing seas.
The formula for the JONSWAP spectrum is as follows:
s(f) = a (g2/f5)EXP[-1.25(f/fm)-4]qa
where
a = EXP[-.5 (f-fm)2/(sfm)2]
The Mean JONSWAP is defined with the following parameters.
6-5
l-u /J