Learning Forum

[ahmadkhan]

Hi everyone.

I am doing a 2-way 3D FSI simulation and getting an error whenever I enable the "Structure" option in FLUENT.. (screenshot attached)

i am using Ansys 2020R1 student version.

I know it has something do with what i am doing in design modeler or meshing phase but I cant really figure it out..

In meshing, I am using contact detection along with 'contact sizing' and meshing method is 'tetrahedrons' with 'patch conforming' enabled.

The mesh interface in fluent has "coupled" and "matching" options enabled..

I was able to get it enabled previously but my harddisk crashed and had to reinstall Ansys 2020R1.. Have been facing this issue since then.

[Rob]

The text in the TUI is the clue here. You've got a non-conformal boundary between the fluid and solid zones. In DesignModeler you need to make a multibody part to avoid this. Note, it will increase your cell count.

[ahmadkhan]

Thanks a lot. so I combined the fluid and solid region into one part in DM..
I was able to get the structure running in fluent but here's the problem now.
1, contact is not getting detected during 'Meshing' (for contact sizing) even after manually defining contact zone.
2, If I continue to fluent and define mesh interface there, structure is getting disabled again with same error..
alternatively, If I dont define mesh interface in fluent, the structure remains enabled but no deformation takes place in solid part when I run simulation..

[Rob]

You need a conformal mesh between the solid & fluid parts. This means no contact regions, contact sizing etc.

[ahmadkhan]

but I've got it working before.. with contact regions defined.
Not able to recreate it now.
Here's a basic example of what i intend to do.. I recorded it a few months back.
https://entuedu-my.sharepoint.com/:v:/g/personal/ahmadabd003_e_ntu_edu_sg/ETI-xNA_N7FJv6mezsV7-UkB2RSz5qlpewFdSfAQBYvndg?e=KyJbM5
Pwd: 12345

Notice that "contact-region" is defined under 'mesh interface' option..

[ahmadkhan]

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So this the error i used to get when using non-conformal interface in fluent, previously. (notice the 2nd line in TUI)

I would just edit the interface as "coupled and matching" under 'mesh interface' option and could easily continue with FSI even with nonconformal interface..

Now i am getting a plain error that its not permissible. Have they disabled it or something?

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[ahmadkhan]

Hey, Thanks for the help.
I was able get structure enabled with non-conformal mesh (matching and coupling enabled) after doing a clean install of Ansys 2020R2..
some software glitch, i guess..
Regards. :)

[Rob]

Flow will work, the intrinsic FSI won't. As staff are not permitted to open or download files I cannot check what you did before.

[johnhavenar]

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In the documentation for 2021R1, there is a section in the structural model chapter for using non-conformal interfaces with two-way intrinsic FSI, but no matter what I try, as soon as the dynamic mesh needs to update, it fails with the error "Error at Node XX: cannot find node XXXX. no error."

You've stated here that fluid-solid interfaces shouldn't be non-conformal, but the documentation has a chapter on it. Is there something I'm missing? Thanks.

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[Rob]

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I think you've missed the model limitations https://ansyshelp.ansys.com/account/Secured?returnurl=/Views/Secured/corp/v221/en/flu_ug/flu_ug_fsi_sec_intro.html We can have non conformal interface between fluid and solid zones generally, but not with all of the models.

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