[Gmsh] Trouble Exporting Physical Entity Tags for Surface Elements and Volume Elements in .msh File

[Robbie Jaeger]

Thank you for your prompt assistance, Christophe. That was exactly my issue.

Best regards,
Robert Jaeger

On Thu, Dec 27, 2018 at 11:42 AM Christophe Geuzaine <cgeuzaine at uliege.be>
wrote:

>
> My guess is that you have selected "Save all elements" (or have
> "Mesh.SaveAll = 1" in your option file). In the MSH2 format, this option
> discards the physical group definitions. (The MSH4 format's behaviour is
> more intuitive - it keeps the physical groups.)
>
> Christophe
>
> > On 27 Dec 2018, at 20:21, Robbie Jaeger <rjaeger at gmail.com> wrote:
> >
> > Hi,
> >
> > I'm having difficulty exporting a .msh ASCII file (format version 2)
> that includes the physical entity tags for elements. I've created a box
> volume and have assigned the 6 surfaces and volume to separate physical
> groups. I'd like to export the mesh as a .msh ASCII file (format version 2)
> as an input for a finite element program. As such, I am using the physical
> groups to identify regions where boundary conditions apply and where
> material types are assigned. I'm using gmsh version 4.0.7 Win64 on Windows
> 10.
> >
> > The .geo commands for the box are as follows:
> >
> > SetFactory("OpenCASCADE");
> > Box(1) = {0, 0, 0, 10, 10, 5};
> > Physical Surface("DS") = {2};
> > Physical Surface("US") = {1};
> > Physical Volume("Solid") = {1};
> > Physical Surface("Other Surface") = {3, 5, 6, 4};
> >
> > I created 1d, 2d, and 3d meshes using the GUI. When I export this to a
> .msh file (format version 2), the elements are exported with their
> elementary tags rather than their physical tags. For example, here is the
> line from the .msh file for element 500 which falls on elementary surface 6
> and physical surface 4:
> > 500 2 2 0 6 15 247 237
> >
> > Three-dimensional elements are similarly exported using their elementary
> surface tags. Here is a 4-node tetrahedron within elementary volume 1 and
> physical volume 5:
> > 924 4 2 0 1 169 306 196 293
> >
> > Based on the documentation, I expected the first tag after the number of
> tags to be the physical entity tag:
> >
> > number-of-tags
> > gives the number of integer tags that follow for the n-th element. By
> default, the first tag is the tag of the physical entity to which the
> element belongs; the second is the tag of the elementary geometrical entity
> to which the element belongs;...
> >
> > However, I'm receiving a zero tag for all elements. Am I
> misunderstanding the documentation or is this the intended behavior? Is
> there a way to export a .msh with the physical entity tags or do I need to
> go about this in a different way?
> >
> > Best regards,
> > Robert Jaeger
> > _______________________________________________
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> > gmsh at onelab.info
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>
> —
> Prof. Christophe Geuzaine
> University of Liege, Electrical Engineering and Computer Science
> http://www.montefiore.ulg.ac.be/~geuzaine
>
> Free software: http://gmsh.info | http://getdp.info | http://onelab.info
>
>
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