Selected Frequencies |
 
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Selected Frequencies |
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The procedure for discretising a random sea into component harmonics (described earlier in Spectrum Discretisation) in the frequency domain is identical to that performed in the time domain. However, there is one additional option available in the frequency domain – you may optionally specify selected (exact) frequencies which Flexcom must include in the range of solution harmonics. This feature can potentially be quite important in terms of ensuring the accuracy of a frequency domain simulation. It might typically be invoked to guarantee that Flexcom includes a solution at any natural frequency of the structure which occurs in the range of harmonics. Unlike time domain simulations, structural excitation at a natural frequency may not be captured in the frequency unless one of the component harmonics corresponds exactly to the natural frequency. In terms of the discretisation itself, Flexcom searches for the harmonic nearest the selected frequency, sets the component frequency equal to the specified frequency, and adjusts the adjacent segment areas appropriately.
•*WAVE-GENERAL is used to specify miscellaneous parameters to wave loading. Specifically, the FREQUENCIES= input is used to specify selected frequencies that Flexcom must include in the range of solution harmonics.