Second-Order Wave Drift Loads |
 
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Second-Order Wave Drift Loads |
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The wave drift loads are calculated from user-specified Quadratic Transfer Function (QTF) coefficients according to the following equation:
(1)
where:
•FDG is one of the three wave drift loads applied to the body CoG, corresponding to FDy (surge), FDz (sway) or MDθ (yaw).
•QTFG(αk,ωk) is the QTF value for relative wave incidence αk (wave direction relative to the instantaneous body orientation) and frequency ωk for the load direction in question
•αk, ωk and ϕk are the amplitude, frequency and phase respectively of the kth wave harmonic
•sign(p) equals -1 if p < 0, 0 if p = 0, and 1 if p >0
The wave drift loads are calculated for every wave frequency present in the (discretised) wave spectrum and for every wave direction. A mean drift load is calculated in Static Mooring analyses to determine the mean body position, using the equation:
(2)
where:
•FDGMean is one of the three mean wave drift loads applied to the body CoG, corresponding to FDyMean (surge), FDzMean (sway) or MDθMean (yaw).
•Sηη(ωk) is the wave spectrum
and the remaining symbols have the same meanings as above.
•*QTF is used to specify Quadratic Transfer Functions (QTFs) that allow the second-order wave drift loads on a floating body to be determined.
If you would like to see an example of how this keyword is used in practice, refer to E02 - CALM Buoy - Complex.