[MOAB-dev] MOAB finding shells bounding closed regions in nonmanifold mesh
Steve Hughey
hugheyst at gmail.com
Wed Jan 22 12:16:23 CST 2025
Hi Paul,
Thank you for your response and suggestions!
In the terminology of the slides you sent, I am looking for a way to
construct from a raw mesh file the geometric Volumes, Surfaces, Curves, and
Nodes that make up the meshed geometry, similar to how CUBIT creates
mesh-based geometry from importing a mesh file. I've written a program that
uses the Skinner heavily to break the mesh down into connected meshed
Volumes, Surfaces, Curves, and Nodes; it also finds all of the
upward/downward adjacencies between these. If something equivalent to this
exists in MOAB, I am very interested to hear about it.
Regardless, the next step I need to take is to find the empty Volumes
bounded by any subset of Surfaces in my geometry. These are important in
boundary-element codes because materially homogeneous regions of space are
represented by their boundaries only. Boundary-element meshes can contain
many of these unmeshed volumes and non-manifold curves where different
materials abut each other.
I am hoping to take advantage of any extant machinery in MOAB for
addressing these problems. I have looked briefly at the CGM library, but
since it's no longer under development, I hesitate to adopt it.
Thank you,
Steve
On Wed, Jan 22, 2025 at 11:24 AM Paul Wilson <paul.wilson at wisc.edu> wrote:
> Hi Steve,
>
>
>
> The GeomTopoTool assumes that a mesh-based geometry follows the data model
> conventions described in slides 1-6 of this summary
> <https://urldefense.us/v3/__https://docs.google.com/presentation/d/10m8e6GN8DhLpNHHSOMniZ2pDU9DOAiD0xJF1Zyewzh8/edit*slide=id.g3b5f37914c_0_117__;Iw!!G_uCfscf7eWS!c1oZJ1JijGmIvdML0MotOwV3GWtr5fqBfxhmWMcy7yqyb53gbIG2AVFmXedMUDxrYu9Dm4Lak8QfebIWOqA9$ >,
> and assumes that the relationships defined there are embedded when the
> mesh-based geometry is created.
>
>
>
> I’m not sure I fully understand your question/use case, but you may also
> be interested in the MOAB skinner
> <https://ftp.mcs.anl.gov/pub/fathom/moab-docs/classmoab_1_1Skinner.html>
> that is designed to identify boundary elements.
>
>
>
> I hope this is somewhat helpful,
>
> Paul
>
>
>
> --
> -- ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ --
> Paul P.H. Wilson (he/him/his)
> Grainger Professor of Nuclear Engineering
> Chair, Department of Nuclear Engineering & Engineering Physics
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> paul.wilson at wisc.edu
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>
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>
>
>
>
> *From: *moab-dev <moab-dev-bounces at mcs.anl.gov> on behalf of Steve Hughey
> <hugheyst at gmail.com>
> *Date: *Wednesday, January 22, 2025 at 05:12
> *To: *moab-dev at mcs.anl.gov <moab-dev at mcs.anl.gov>
> *Subject: *[MOAB-dev] MOAB finding shells bounding closed regions in
> nonmanifold mesh
>
> Hello,
>
> I am using MOAB as the basis for a sort of mesh-based geometry model in a
> finite element/boundary element code. I must assume that the mesh
> connectivity and Exodus block specifications are the only information I
> have about the geometry. I have been able to use MOAB’s various adjacency
> queries to break the input mesh into connected components with adjacencies
> between them, largely along the lines of CUBIT’s mesh-based geometry
> engine. The meshes are pretty general, containing quads, tris, hexes, tets,
> prisms, and pyramids, and typically contain nonmanifold edges.
>
> However, I am now faced with the problem of finding closed regions. I have
> some ideas on how to do this based on concepts from half-facet data
> structures, but the MOAB classes FBEngine and GeomTopoTool caught my
> attention. I have tried reading the interface specification for these and
> have been unable to determine whether they could be useful for my closed
> regions problem. I have seen many allusions in the code to geometry and
> topology representation, but I haven’t been able to connect the dots. My
> hope is that someone has already thought through this problem and
> implemented a solution. I would appreciate any insight you can provide, and
> in the meantime I will continue testing things.
>
> Thanks,
> Steve
>
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