Ansys Products

Discuss installation & licensing of our Ansys Teaching and Research products

Natural periods/frequencies for a structure with moorings to ANSYS AQWA.

• Greg Ioannou
Subscriber

Hello,how should we find the natural periods of the 6 DOF for a structure with or without moorings at ANSYS AQWA?How do we determine the calm water?And is it needed to check the Ansys Aqwa GS?

Thank you!

• Yu Bi
Ansys Employee

Hi, Aqwa Workbench can conduct the following calculation (no need to use AqwaGS).

1.  Model without mooring
In Hydrodynamic Diffraction analysis, the natural periods of the 6 DOF of a structure without mooring can be found from Solution -> Insert Results -> Natural Modes.
2.  Model with mooring
After running Hydrodynamic Diffraction, the natural periods of a structure with moorings could be found in Hydrodynamic Response -> Computation Type as Stability Analysis; Solution -> Insert Results -> Natural Modes.
The wave definitions in Hydrodynamic Diffraction are used for calculating the added mass and hydrodynamic damping, which are used to predict the natural periods of the freely floating structure in Hydrodynamic Diffraction analysis (calm water); the wave definition in Hydrodynamic Response -> Stability could be used to find out the equilibrium position of the structure, (if no wave is defined, then the analysis uses calm water), then the natural periods of the structure with mooring lines are calculated at the equilibrium position.

• Greg Ioannou
Subscriber

No matter if i use moorings or not,it cant calculate the natural modes and it appears the message below.Why can that happen?

• Yu Bi
Ansys Employee

Hi, this could be a localization problem. Could you ensure dot(".") is used for the decimal point in the regional format setting of your computer?

• Greg Ioannou
Subscriber

Thank you a lot.I will check it and come back.I also answered at one other thread that you answered(with the different layouts of moorings.I hope ,you will answer there too!

Thank you a lot again.

• Greg Ioannou
Subscriber

It worked...!!