Equivalent Regular Waves |
 
|
Equivalent Regular Waves |
|
Flexcom includes a capability to model a random sea as an equivalent regular wave. If you invoke this option, the approach adopted is as follows. The random sea is first discretised into component harmonics in the usual way, and equivalent regular wave properties are calculated from this discretisation. The equivalent regular wave height is got by multiplying the random sea significant wave height Hs (which is calculated from the moments of the discretised spectrum) by a user-specified factor. The equivalent regular wave period is got by multiplying the period at which the maximum value of the spectrum occurs (that is, the spectrum peak period) by a user-specified factor. Both factors (for wave period and wave height) are optional entries and suitable default values are provided (1.86 and 0.95, respectively) if not explicitly specified.
The program then calculates a response spectrum for each attached node in all degrees of freedom, by combining the wave spectrum with the vessel RAOs you input. From each response spectrum, sinusoidal boundary condition amplitudes are calculated in a similar manner to the above, and BC phase angles are estimated from the vessel RAOs. The period of the sinusoidal BCs is the wave period calculated above. These sinusoidal boundary conditions are then applied at the attached nodes in a regular wave dynamic analysis with the equivalent regular wave.
This facility can be invoked if the analysis includes two wave spectra. Each spectrum is handled separately using the procedure outlined above. In this case the dynamic analysis will have two independent regular waves, and sinusoidal BCs from the two spectra will be superposed or added together to define the motions of the attached node(s).
•*REGULAR WAVE EQUIVALENT is used to specify that Flexcom is to replace a random wave spectrum or spectra by an equivalent regular wave or waves, and to calculate equivalent sinusoidal boundary conditions for attached nodes.