Hi Greg,
Hope all is well!
Is there any way/functionality to examine whether the generated hexahedral mesh is a conforming mesh?
Thanks for your help!
Karim
That’s a fantastic question! I’m not sure if Cubit has any built-in capabilities (though we should probably add some!) to verify conforming meshes directly. You can do things like draw surf with is_merged to find merged surfaces - which would then result in conforming meshes. Alternatively, you can export your mesh to an Exodus file and view it in ParaView using the GridConnectivity filter - which will find and color by connected (conforming) mesh regions:
Here’s an example:
Non-conforming
bri x 1
block 1 vol 1
webcut volume all with plane xplane offset 0
webcut volume all with plane yplane offset 0
webcut volume all with plane zplane offset 0
mesh vol all
set exodus netcdf4 off
set large exodus file on
export mesh "./non_conforming_mesh.e" overwrite
Conforming
bri x 1
block 1 vol 1
webcut volume all with plane xplane offset 0
webcut volume all with plane yplane offset 0
webcut volume all with plane zplane offset 0
merge vol all
mesh vol all
set exodus netcdf4 off
set large exodus file on
export mesh "./conforming_mesh.e" overwrite
Applying the GridConnectivity filter to both models, coloring by FragmentID shows us that there are 8 fragments (i.e. disconnected regions of conforming elements) on the non-conforming model, and only 1 fragment (i.e. one region of conforming elements) on the conforming model. Note that I’ve chosen to Interpret Volume As Categorization, but that’s not necessary.
Do you think this is a useful tool for visualizing & verifying conforming meshes? I think we could add this to our Mesh Quality tools pretty easily.
Post-script
As a side note, here’s what you’d get if you ran draw surf with is_merged in Cubit on the conforming model:
And here’s what you’d get if you did
draw block all
highlight surf with is_merged
But a shortcoming of these are that they only verify where the mesh is conforming, but don’t clearly identify where they are not conforming.
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Here a couple of other options as well.
- You can use Mesh/Node/Quality/Coincidence check. This will find nodes that are not within the given tolerance.
For example,
topology check coincident node node all tolerance 1e-06 draw brief result group
This image shows nodes within tolerance that are not merged. The model is the same 8 bricks as Greg’s above but with some surfaces that failed to merge correctly.
- You can use the highlighted toolbar icon to display curve valence or how many times a curve is connected to a surface. This is directly related to the merge status of the curves.
- Curves that are colored blue are connected to two surfaces. This is normal for curves on the exterior of a volume.
- Curves that are white are connected to more than two surfaces. This will happen for merged curves.
- Curves that are golden are non-manifold edges. There are used by only one surface. If you are doing volumetric modeling watch out for these!
The curve valence may be visualized best in wireframe graphics.
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Thanks Greg and Karl for the insight!
Cheers
Karim
@karim_gmSim - I know this is a long-time coming, but we recently started up a public GitHub repository for adding helpful Cubit utilities (e.g. Python scripts): https://github.com/coreformllc/coreform-cubit-utilities
I’ve added a script that goes through a volumetric mesh and finds connected (i.e. conforming) regions. The core functionality is pretty fast, though the final step of creating groups in Cubit for each region is a bit slow.
The result of the script is the construction of groups for each connected mesh region, which you can then select in the model-tree to highlight and/or draw. This will form the basis for a future built-in mesh-quality check, but wanted to get your feedback on the functionality. Does this (effectively) answer your original question?
Thanks so much Greg for your efforts! Much appreciated!
I will give it a try in the coming weeks and will let you know if something is not clear for me.
Cheers
Karim