ssc-367 - Ship Structure Committee

The recommended form of displaying a wave spectrum is with an
ordinate of %*a2 and an abscissa of M, radial frequency. However,
since the engineer will encounter wave spectra equations in a number
of forms, using various bases and units, the applicable conversion
factors are provided in the following sections.
Suectrum Basis
The recommended spectrum basis is half amplitude squared or energy.
Often spectrum equations having a different basis are encountered.
Before any statistical calculations are performed with a spectrum
equation, the equation should be converted to the recommended basis.
For a “half amplitude” or “energy” spectrum, the basis is one-half
times the amplitude squared.
S(M) = **n*
S(m)dm = E / (pg)
where,
s
is the spectral ordinate,
(IJ
is the radial frequency,
is the wave amplitude of the constituent wave of
frequency,
E
is the energy content of the constituent wave of
frequency, M.
For an “amplitude” spectrum, the basis is amplitude squared.
A-3