Irregular Wave RAO Computation |
 
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Irregular Wave RAO Computation |
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In the case of time domain irregular sea analyses, the procedure for computation of RAOs is as follows. Firstly a time history of the parameter of interest is generated. Then the parameter response spectrum is computed using the Fast Fourier Transform (FFT) algorithm. Similarly, the spectral density function for the wave elevation time history is generated. RAO amplitudes are then computed using the relation:
(1)
where RAO( f ) is the RAO amplitude (expressed as a function of frequency), Sn( f ) is the wave elevation spectrum and Sp( f ) is the spectrum of the parameter of interest.
The RAO phases are computed by algebraic subtraction of the phase angles determined from the FFT of the spectrum of the response parameter, and the phase angles determined from the FFT of the wave elevation. It should be noted that, in general, there is significant statistical error associated with this procedure for computation of phase angles, and the resulting phase angles are likely to be less accurate than those derived from regular sea analyses.
•*RAO is used to request the creation of RAO plots.