General Mechanical

General Mechanical

The frequency domain analysis of a symmetrical body in AQWA

    • liangjb27
      Subscriber

      As I did use the AQWA to model and solve the dynamic response of the NAUTILUS-10 semi-submersible platform in frequency domain, e.g., the added mass and radiation damping,I found the non-zero values of these properties for the non-diagonal items, i.e., the coupling items on the direction of 45, 46, 56, as shown in the figure below. In these two figures, the“x454656_”represents the simulation data from the platform report and the other three curves are our simulations. As a platform with symmetric geometry and mooring line distribution, the coupling items should be zeros. We are curious why the non-zero values exist on these three coupling items. Can you help to find the problem and give your suggestions. Thank you!

    • Ingrid Machecler
      Ansys Employee

       

      Good morning, 

      Your stucture is indeed symmetrical but your mesh is not. So this is likely introducing small numerical errors. A way to check this is to generate the roll-roll and pitch-pitch damping and check that these above coefficients are small compared to the diagonal terms.

      A possible solution would be to model a 1/4 of the structure and mesh it and use the SYMX and SYMY. 

      Note that the wave directions should be within this quarter (ie, 0-90deg) and you won’t be able to visualize the pressure and motion but you can use AqwaGS instead.

      I hope this helps.

      Ingrid

       

      • liangjb27
        Subscriber

         

        Thanks for your reply!

        I have created a new model of the cube to make sure the mesh is indeed symmetrical. But the values of radiation damping and added mass for the non-diagonal items’45,46,56′ are still not zero.Can you give some advice again?

        Thank you!

         

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