Learning Forum

[w.s.syafruddin2]

Hi all

Would it be possible to use autopilot or something similar to control the path of the ship in Aqwa without restricting the sway and yaw motions? I'm conducting a 6DoF simulation in the stern/following waves, but it seems like the ship is moving excessively sideways.

Thank you in advance.

[Shuangxing Du]

You can define a PID course controll system by employing USERFORCE.DLL (see your Ansys installation folder\aqwa\doc\user_force.c or user_force.f90) or Aqwa socket user force (see your Ansys installation folder\aqwa\utils\ExternalForceCalculation). Alternativey you can define four fenders fixed on the ship to restrict the motions in sway and yaw, as shown below

[w.s.syafruddin2]

Thank you very much for your help. 👍

[Shuangxing Du]

You are welcome.

[w.s.syafruddin2]

I have more questions.
Will the ship forward speed that has been configured in the GUI be automatically disregarded when employing external/user force? requiring us to input the thrust force in addition to the rudder force/autopilot.

Thank you.

[Shuangxing Du]

If the forward speed is defined in Hydrodynamic Diffraction analysis, it is recommended to define an opposite current (i.e. opposite direction and the same magnitude of forward speed in HD) in the time domain analysis. You could use a PID in x direction to keep the ship's x-position (nearly constant as your frame is moving with the ship's forward speed in the time domain analysis, as the opposite current is defined). 

[w.s.syafruddin2]

Many thanks for the answer.

Just to make sure, if I define the thrust from the user force while using the forward velocity in hydrodynamic diffraction (HD), should I also have to define the counter current at the same magnitude? So, if I don't use the thrust in user force to push the ship, is determining forward velocity in HD sufficient (and with no current)?

Thank you.

[Shuangxing Du]

It is fine to define the thrust by the user force and let the ship with the specified forwarded speed. By doing so, there is no need to define the counter current.

[w.s.syafruddin2]

Many thanks for the answer

I have a question again, since we run the user force simulation in batch mode, is it possible to see the animation? 
If possible, please let me know how to do that.

Thank you