ssc-367 - Ship Structure Committee

Nm is the total number of waves in the design life, and
Nh is the
H.
number of occurances of waves with height exceeding
A.7 WAVE HISTOGRAM AND THE RAYLEIGH DISTRIBUTION
Actual wave height measurements can be plotted to show the number of
waves of a given height at equal wave height intervals. The
histogram obtained can be defined by a simple curve.
A simple curve that fits most wave histograms is the Rayleigh
distribution. Past work have shown that the Rayleigh distribution
often allows accurate description of observed wave height
distributions over a short term.
The Rayleigh distribution is typically given as,
,...,
p(Hi) = 2*Hi *EXP(-H12/~2) * (1/~2)
where
P(Hi)
is the wave height percentage of occurances,
Hi
is the wave heights at constant increments,
~ 2 is the average of all wave heights squared.
A.8 EXTREMEVALUESAND THE WEIBULL DISTRIBUTION
For design purposes an estimate of the maximum wave height (extreme
value) is required. The Rayleigh distribution provides such an
estimate over a short duration. However, in order to estimate the
extreme wave that may occur in say 100 years, the Weibull
distribution is often used.
A-22