A number of parametric shapes have been proposed to describe the frequency

distribution of wave energy. The spectral shapes were derived from long-term

field wave measurements and depend on factors such as wind duration, the

distance or fetch over which the wind blows, and water depth.

For fully-developed sea states in deep water where there is a local balance

between momentum transfer from the wind and wave breaking/nonlinear cross-

following wave spectrum:

*f *-4

α*g*

2

exp -β

(B1)

*f *

(2π) *f*

45

p

where α = 0.0081 is Phillips' constant, *g *is the gravitational acceleration, β =

0.74, *f*p = *g*/2π*U *19.5, and *U *19.5 is the wind speed at 19.5 m above the mean sea

level.

The Bretschneider spectrum (Bretschneider 1959) has the same shape as the

Pierson-Moskowitz spectrum but is defined in terms of the significant wave

written as:

1

References cited in this appendix are listed in the References at the end of the main text.

B1

Appendix B Description of Ocean Wave Spectra

Integrated Publishing, Inc. |