ssc-367 - Ship Structure Committee

T~ = 0.9457*T P’
New
The first equation applies to original Bretschneider wave spectrum,
and the second is the result of recent wave studies (See Reference
A.I).
The peak period, Tp, is an unambiguous property of all common wave
spectra, and is therefore the preferred period to use in describing a
random sea.
A.2.2
CharacteristicWave Heiqhts
From the assumption that the wave elevations tend to follow a
Gaussian distribution, it is possible to show that the wave heights
follow a Rayleigh distribution. Since wave heights are measured from
a through to succeeding crest, wave heights are always positive which
agrees with the non-zero property of the Rayleigh probability
density. From the associated property that the wave heights follow a
Rayleigh distribution, the expected wave height, the significantwave
height, and extreme wave heights may be calculated. The equation for
the average height of the one-over-nth of the highest waves is as
follows.
—
where:
H,,n/ (mo) + = 2* [2*ln(n)]%+
n*(2~)%*{l-erf[(ln(n)}%l}
m
o
is the variance or the area under the energy
spectrum,
In
is the natural logrithm,
erf
is the error function, (the error function is
explained and tables of error function values are
available in mathematics table books.)
A-9