Hello,
it is correct that the fluid viscosity is not explicitly taken into account in Aqwa.
However, the vortex shedding effect is accounted for by the program based on the roll motion, the Keulegan-Carpenter number and the roll natural frequency of the vessel. The bilge keel non-linear roll damping is based on the 2011 ITTC's recommended procedure and includes the K-C number in its calculation.
I hope this helps.
Kind regards,
Ingrid
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