Page 122 - Introduction to Naval Architecture

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Figure 6.5 Motion energy spectrum

of the RAO for the motion concerned at the corresponding encounter
frequency. Take heave as an example. If the response amplitude
operator is F z(o> E) for encounter frequency (O E, then the energy
spectrum for the heave motions is:

where ,S^(a» E) is the wave energy spectrum.
2
This is illustrated in Figure 6.5 where AA = (AB) (AC).
Having created the motion spectrum, its area can be found and
various attributes of the motions deduced as they were for the wave
system itself. Thus if m ho is the area under the heave spectrum:
0 5
average heave amplitude = 1.25 (m ho) '
05
significant heave amplitude = 2 (m ho )
average amplitude of -fa highest heaves = 2.55 (m ho) 0-5