ssc-367 - Ship Structure Committee

Awhite noise function-may be used to represent a very broad banded
input spectrum, if the response spectrum is narrow banded.
The extreme response can be calculated from a given extreme wave, or
the extreme response may be statistically derived from a set of
spectral analyses.
The sea spectra used in the computation of random sea response can be
reduced in number by selecting a smaller family of representative
spectra, or by creating a set of mean spectra.
0.1.3 m
The purpose of this appendix is to provide a background of the
spectral analysis method and to clarify the concept of a response
spectrum and how its properties are derived.
P,
B.2 RESPONSE TO RANDOM WAVES
The spectral analysis method is a means of taking the known response
of an offshore structure to regular waves and determining the
structure’s response to a random sea. The input to the spectral
analysis method is the response amplitude per unit wave amplitude (or
equally, the response double amplitude per unit wave height) for a
range of periods or frequencies of regular waves. These ratios of
response amplitude to wave amplitude are known as “Response Amplitude
Operators” or just “RAOS.” The response of the offshore structure is
first obtained for a set of unit amplitude, regular, sinusiodal
waves. The regular wave response may be obtained either from model
tests or from empirical or theoretical analyses.
A wave energy spectrum is selected to represent the random sea. Wave
spectra are described in Appendix A. The wave spectrum represents
the distribution of the random sea’s energy among an infinite set of
regular waves that when added together create the random character of
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