ssc-367 - Ship Structure Committee

X(w) = A*RAO(w)*cos(wt+ O(W)).
When a spectral analysis is applied to the transfer function the
wave amplitudes, A, become a function of wave frequency, u, and
the X(U) is replaced by the differential slice of the response
power density spectrum.
SR(m)*dm = [A(W)*RAO(U)]2
or
SR(w)*dw = A2(u)*RA02(w)
or
SR(~)*dw = S(w)*du*RA02(w)
Thus, Sf(w) = S(U)*RA02(W)
The
the
response spectrum S(W)
RAO squared.
is therefore just the sea spectrum times
For multiple-degree-of-freedom systems, there is coupling between
some of the motions, such as pitch and heave. For example, to obtain
the motion or motion RAO for heave of a point distant from the center
of pitch rotation, the pitch times rotation arm must be added to the
structure heave. This addition must be added with proper
consideration of the relative phase angles of the pitch and heave
motions, and therefore, such addition must be performed at the
regular wave analysis stage. The combined heave (w/pitch) RAO can
then be used in a spectral analysis to obtain the heave spectrum and
heave response characteristicsat the point.
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