Computing RAOS with AQWA
 

Hi everyone,

I'm trying to compute RAOs of a FPSO using Ansys AQWA. But it seems I'm doing something wrong because the RAOs of some degrees of freedom are completely out of range (27 deg/m in roll, while 5 deg/m expected) even if the general allure of the curves are fine (with pic periods corresponding).

I thougth I was doing everything right, step by step :

1. Selecting hydrodynamic diffraction module
2. Define geometry, add point mass and generate mesh
3. Analysis setting : GOON option enabled, calculate full QTF disabled
4. Selecting wave directions and frequencies
5. Inserting results "RAO distance/rotation vs frequency"
6. Run calculation

I'm pretty my geometry and mass/inertia distribution are okay because hydrostatics are fine.

Does anyone know if AQWA's output must be dimensionalized by some factor, or if I forgot any option during calculation, or something else ?

Thank you.
Regards,
Antoine

It seems that I must define an additional damping due to viscosity. After a quick search, I read that the FIDD could suffice, but I didn't really understood how to use it. Please could someone explain it ?