Non-linear roll damping

[w.s.syafruddin2]

Hi,

I am currently running a hydrodynamic response simulation of a ship in AQWA and I’m trying to include a nonlinear (quadratic) roll damping coefficient. However, it’s not entirely clear to me what this coefficient physically represents in the software.

From the interface, it looks like a “coefficient,” but the unit seems to correspond to a damping moment rather than a nondimensional ratio. When I input the quadratic term obtained from my roll-decay curve fitting (≈ 0.0179), there is almost no visible damping effect on the roll response. When I input a value of 1, the maximum roll amplitude decreases from about 15° to 5°, indicating a very strong damping effect.

Could you please let me know how AQWA interprets this nonlinear damping coefficient (e.g., dimensional units, scaling, ratio or normalization method)?
Also, is it possible to suppress or override the bilge damping defined in the “After” and “Forward” end settings when specifying the nonlinear damping coefficient, so that the bilge damping can be fully represented within the nonlinear term instead?

Many thanks in advance for your help and clarification.