Learning Forum

[jcapper]

Can someone please direct me to some resources that explain how to create external lids in ANSYS AQWA? I have been looking at the AQWA user manual, but there is not a lot of information.nI am trying to create an external lid between two bodies because I think that there is hydrodynamic interaction occurring in the gap between the bodies, leading to unrealistic hydro-diffraction results like added mass and radiation damping. I tried to create a surface in the space between the two bodies and set the structure type as abstract geometry to create the external lid. I tried running the model without a point mass for the lid and received an error message. I tried adding a point mass and received a different error message.nWithout point mass:nWith point mass:nn

[Yu Bi]

Hi, the external lid surface needs to belong to one of the hydrodynamic interacting structures, i.e. Side Buoy 1 or Side Buoy 2 in your case. n

[jcapper]

Would I need to create 2 external lids (one for each structure) with equivalent values for damping factor and gap size? If I just make a lid for one of the structures, could that make the results asymmetric?n

[Yu Bi]

Just one external lid located between the two structures is enough. You can put the external lid surface in either of the structures.n

[jcapper]

I did as you suggested, but I am getting an illegal connectivity error message when I try to run the model now. Do you know what may be causing the error?.nn

[Yu Bi]

The external lid should not connect with or too close to the buoy surface. Please ensure there is a gap between the external lid surface and buoy structure surfaces. n

[jcapper]

If I create a gap, I end up with two surface bodies for the lid because the two buoys come together at the center. I'm don't know how to create a single lid from the two surface bodies. Do you have any recommendations?nnn

[Yu Bi]

You can create multiple external lids. n

[Tianyuan Wang]

 

 

Dear Yu:

I would like build a coaxial double buoy in AQWA workbench, but I am a little confused about the lid method in AQWA.

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Q1:

In workbench, does the structural surface of the floating body on the SWL need to be preserved? I am not sure if the structural surfaces on the SWL are involved in the calculations.

This essentially relates to the principle of the internal lid method. If I turn on the internal lid method, does AQWA generate additional lid elements that are duplicated with the structural surface meshes on the SWL.

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Q2:

For a torus with a moon pool, assume that the structural surface on the SWL is deleted in the DM, does the internal lid method just generate the internal lid of the toroidal surface, or generate the lid including the toroidal surface and moon pool?

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Q3:

As for a coaxial double buoy, how could I generate a external lid of the narrow gap between inner and outer bodies? I creat a lid in DM. As you mention, A or B is desirable. I found AQWA USER MANUAL highlights that lid normal should be pointing up (away from the fluid). Do all the lids have to meet this requirement? And this operation needs to be done in DM?

A. a lid attached to inner body

(1) Internal lid on the SWL is reserved, with 'Generate internal lid' being No (2) Internal lid is removed, with 'Generate internal lid' being YES (3) Internal lid is reserved, with 'Generate internal lid' being No, and external lid has a gap between inner and outer bodies(4) Internal lid is removed with 'Generate internal lid' being YES, and external lid has a gap between inner and outer bodies
   

B. a lid attached to outer body

(1) Internal lid on the SWL is reserved, with 'Generate internal lid' being No (2) Internal lid is removed, with 'Generate internal lid' being YES (3) Internal lid is reserved, with 'Generate internal lid' being No, and external lid has a gap between inner and outer bodies(4) Internal lid is removed with 'Generate internal lid' being YES, and external lid has a gap between inner and outer bodies

C. a separate lid

(1) Internal lid on the SWL is reserved, with 'Generate internal lid' being No (2) Internal lid is removed, with 'Generate internal lid' being YES (3) Internal lid is reserved, with 'Generate internal lid' being No, and external lid has a gap between inner and outer bodies(4) Internal lid is removed with 'Generate internal lid' being YES, and external lid has a gap between inner and outer bodies

According to the discussion above, configuration A(3), A(4), B(3) or B(4) is correct. The internal and external lids must be manually specified for A(3) and B(3), and the lid normal should be pointing up.

Do you think so? 

Looking forwards to hearing from you

Best regards,

Tianyuan?