Vessel Motions – Equivalent Airy Wave |
 
|
Vessel Motions – Equivalent Airy Wave |
|
This option is provided to allow you to specify a sinusoidal vessel response to the multiple order stream function wave. To invoke this facility you specify an equivalent Airy wave amplitude when you are inputting the Stream Function data; you can optionally specify an equivalent wave period. What then happens is the following. The Dean’s Stream Function wave height, period and direction are used in the normal way in calculating water particle kinematics and ultimately wave forces. The equivalent Airy wave parameters on the other hand are combined with the vessel RAOs and phase angles to calculate vessel motions. This ensures a sinusoidal response. You can specify an equivalent Airy wave amplitude without inputting a corresponding period, in which case the Dean’s Stream Function wave period is used by default.
The high frequency response 
of the vessel reference point in local degree of freedom i to a Dean’s Stream Function wave when you nominate the Equivalent Airy Wave option is defined by:
(1)
where:
•
is the vessel RAO in degree of freedom i, which is a function of wave heading 
and equivalent wave frequency 
•ωe is the equivalent Airy wave circular frequency 
•
is the period of equivalent Airy wave
•Ae is the amplitude of equivalent Airy wave
•
is the vessel phase angle in degree of freedom i, which is also a function of 
and 
Remaining symbols are as previously.