Mike Pettit
Ansys Employee

Hi Greg,

The formulation used by Aqwa to estimate the nonlinear roll damping assumes that the vessel is 'ship-shaped' and symmetric, with a bilge radius and (optionally) symmetric bilge keels attached to the bilges at 45 degrees to the central line:

If you only want bilge keel effects to be included in the nonlinear roll damping estimate, I would recommend that you:

  • set the 'Depth to Bilge' value to be very small (0.01x) compared to the 'Offset of Bilge from Central Line' value; this forces the bilge vortex roll damping coefficient to be very small, i.e. turns off the bilge vortex shedding component of the roll damping.
  • change the 'Advanced Bilge Keel Options' detail from 'Program Controlled' to 'Manual Definition', which allows you to position the bilge keels independently of the bilges.

The graphical representation of the bilge keels in the Aqwa Workbench editor should hopefully give you an idea of when they are in the right place for your vessel.

Cheers, Mike