Learning Forum

[javier.medina.galera]

Hi everybody!

I am trying to take into account the effect of an Anti-Roll tank in the RAO of a vessel. If you have any experience or ideas on this, please feel free to provide any comments!

I am using Ansys R22.1 and I have ran some time history analysis and got the vessel RAOs by performing some spectal analysis of the TH series. What I would like to do now is to introduce in the simulation the effects of the anti-roll tank. I was thinking in running some kind of script that during each time step of the simulation, calculates the anti-roll moment and applies it to the vessel. I was wondering if this is actually possible or if I only have the possibility of running a script before or after the simulation.

Normally I use AQWA inside workbench so I do not usually deal with .dat, .LIS files and AQWA GS. I am not aware if there is any specific option within this environment.

Another idea that comes into my mind is related to aero-servo-elastic models for floating offshore wind. The idea would be to use a coupled framework between the hydrodynamic analysis and the calculation of the anti-roll moment.

Thank you very much in advance!

 

[Mike Pettit]

Hello,

In Workbench you can directly model your anti-roll tank, and the Aqwa solver will include its effect on the vessel RAO motions in the Hydrodynamic Diffraction calculation (any any subsequent Hydrodynamic Response analyses).

In the geometry editor you should add the tank geometry to the vessel, and split the surface bodies at the tank mean fluid level (the split is not necessary in Release 2022 R2 onwards). Then you will probably need to flip the surface normals, so that they point inwards, into the anti-roll tank fluid.

Once you have (re-)imported the geometry into the Aqwa Workbench editor, you should right-click on the vessel in the Outline tree and Add > Internal Tank. Select the anti-roll tank surfaces as the Internal Tank Surfaces, and select an edge at the position of the mean tank fluid level for the Fluid Level Definition (you can define the Surface Height directly in 2022 R2, and a Fluid Volume in 2023 R1). Finally define the Fluid Density; you can also set a Permeability (0.0 to 1.0 as a volume fraction) to account for any unmodelled internal features that reduce the tank volume. The Damping Factor can be used to dampen the motion of the tank fluid surface, if necessary.

I hope this helps!

Mike