How to attribute BC to Salomé exported UNV meshes?

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petroo
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Joined: 13 Jan 2010, 19:07
Location: Aachen, Germany

How to attribute BC to Salomé exported UNV meshes?

Post by petroo »

Hello @all,

being able to export UNV files with quite a lot of structures to be physically interpreted, I am wondering how to attribute BC to its elements in a non-visual fashion. The image below perhaps clarifies my problem: I want to calculate heat flows through structured walls and observe patterns on the outside originating from the internal wall structures. To do so, I created a "brick wall" in Salomé (by its multi-translation operation), consisting of a larger number of individual bricks with intermediate rims of mortar/cement between them and as covering on both wall sides:
Brick wall with hidden outer surface, one hidden brick surface and a highlighted brick side surface.
Brick wall with hidden outer surface, one hidden brick surface and a highlighted brick side surface.
brickwall.jpg (49.84 KiB) Viewed 7866 times
My intention now is to attribute the bricks and the mortar rims with values of heat capacity and conductance (as attributes of volume) and heat transfer coefficients (as attributes of the respective interfaces). But as you may understand from the image above, the visual attribution of individual BC via ElmerGUI is out of the question due to the very large number for a representative wall. To attribute the BC via a synthetic SIF file (to be written by a separate custom program) I would need the boundary (and volume) numbers, though. But I did not see a possibility to define them in Salomé or retrieve them for the entities.

Is there any suggestion on how to proceed in such case?

Kind regards,

Peter

P.S.: If my brick wall example should become feasible I'd love to elaborate it into another example for the tutorial!
petroo
Posts: 148
Joined: 13 Jan 2010, 19:07
Location: Aachen, Germany

Re: How to attribute BC to Salomé exported UNV meshes?

Post by petroo »

Well, responding to myself in order to help others with similar problems ...

My final path from Salomé (constructive geometry elements composition) to Elmer (simulation) was the following:
  • Definition of the individual volumes (bricks, heat introduction pad, mortar envelope) in Salomé (5.1.3)
  • Export of complete geometry as a BREP file
  • Import in Gmsh (2.4.2); re-export the geometry to a (for me) intelligible GEO file with lots of point, surface, and volume definitions
  • Creation of the computational grid in Gmsh, saved as a MSH file.
  • Elmergrid 14 2 meshfile.msh -autoclean
  • Visual inspection of the Elmer imported mesh/geometrical structure by selecting individual surfaces and comparing them to the numbering of the Gmsh GEO file.
  • Manual adaptation of a former SIF file by introducing lots of boundary condititions for the individual brick volumes, and respective definition of the important surface BC where deviating from adiabasis.
All in all it worked. But I reckon that there is lots of space for improvement of this process. With Salomé's own extensive potential of meshing facilities it would be highly desirable to directly export a mesh created there over to Elmer, but I could not find a way to assess surface/volume numbers assignments to the individual elements of my geometry and thus was not able to prepare the mandatory SIF input file appropriately.

For future applications I'd love to streamline this whole process, so feel free to suggest any improvements of it!

Kind regards,

Peter
raback
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Re: How to attribute BC to Salomé exported UNV meshes?

Post by raback »

Hi Peter

Thanx for reporting your endavour with this problem. I know that the workflow is far from optimal.

when you say that "I could not find a way to assess surface/volume numbers assignments to the individual elements of my geometry" do you mean that these numbers exist but you just cannot define them SALOME? Does the unv export from SALOME to Elmer otherwise work?

Personally I usually use ElmerGUI also for these complicated geometries. Often I define a first simple sif with proper BCs and bodies defined. When you do not join or divide geometric objects therein it is possible to use the same sif also for altered meshing parameters. Also BCs may be changed easily by string replacements. In ElmerGUI it is sometimes difficult to keep track of the already defined quantities. An option that would allow to choose defined/undefined quantities would be of use. Currently the undefined BCs are visible only in the postprocessing phase.

-Peter
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Re: How to attribute BC to Salomé exported UNV meshes?

Post by raback »

Another thing that came to my mind: Your periodic geometries might take use of the '-clone' feature of ElmerGrid. For example

Code: Select all

ElmerGrid 2 2 angle3d -clone 3 2 1 -out sixangles3d
This assumes that the nodes in left/right and up/down are on the same positions to allow merging of the cloned mesh. The body and BC flags remain unaltered.

-Peter
petroo
Posts: 148
Joined: 13 Jan 2010, 19:07
Location: Aachen, Germany

Re: How to attribute BC to Salomé exported UNV meshes?

Post by petroo »

Hello Peter,
raback wrote:when you say that "I could not find a way to assess surface/volume numbers assignments to the individual elements of my geometry" do you mean that these numbers exist but you just cannot define them SALOME?
No, I didn't find any numbering in the UNV output, but that may be accounted to my rather limited insight in the various geometry and mesh formats. In my understanding geometric objects are explicitly named in Salomé, but I assume that these names are not forwarded into the mesh files.
Does the unv export from SALOME to Elmer otherwise work?
I managed to import an UNV file into Elmer (ElmerGrid 8 2 ..., if I remember correctly), but staggered over the above stated problem of object attribution. While the surface numbering is still sensibly accessible in ElmerGUI (even though rather unattractive for larger numbers of surfaces) I failed to see a method to re-attribute the volume numbers for BC definition in the SIF file. I know there is a possiblity to display the node numbers and their volume assortment in ElmerGUI, but just try to envision this procedure for the shown geometry of my brick wall on a sensibly dense mesh.
Personally I usually use ElmerGUI also for these complicated geometries. Often I define a first simple sif with proper BCs and bodies defined. When you do not join or divide geometric objects therein it is possible to use the same sif also for altered meshing parameters.
Yes, this was about the same procedure I finally worked with in the end, re-using my old homogeneous wall SIF files. But my problem is that my geometries change frequently, as this is the main issue of my present calculational goals, to compare the heat spread differences of various wall constructions. So I'd strongly love to see a "streamlined" workflow from geometry definition to actual simulation.

In general I think your restriction to concentrate on the simulation issues while leaving the required mesh generation (mostly) to external programs is very good, but moving on from the simple functionality assessments to some more practice-oriented problems soon requires to revisit the overall workflow for practicability. Please don't get me wrong - I am not requesting that you create a complete and elaborated 4-d exchange matrix of {geometry creation, meshing, simulation, post-processing} programs. But just some documented path through the format jungle, from a sensible (csg) geometry definition program to a results inspection program, would be very helpful.

Judging from the screenshots of the various post-processors (like Gmsh or again Salomé, and maybe some others) it might even be sensible to resort to other freely available post-processing systems than ElmerPost or the VTK viewer iff the path to the result inspection is well documented and the cooperating program author would be willing to be so on a long-term basis.

Maybe some file transfer guru might take a deeper look into this workflow business and help out with some well-documented, more complex example where some of the procedural simplifications of the more simple test cases are no more applicable?

Kind regards,

Peter
petroo
Posts: 148
Joined: 13 Jan 2010, 19:07
Location: Aachen, Germany

Re: How to attribute BC to Salomé exported UNV meshes?

Post by petroo »

Hello Peter,
raback wrote:Another thing that came to my mind: Your periodic geometries might take use of the '-clone' feature of ElmerGrid. ...
Thanks for this suggestion, but I will rather soon have to migrate to non-regular geometries, so your suggestion might help in the present special case but not on the envisioned general cases.

Kind regards,

Peter
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