[Gmsh] post procssing using the .msh file format
Antoine Dechaume
boolegue at gmail.com
Sat Jul 5 12:32:35 CEST 2008
Hi Shi,
paraview does it, by splitting each elements into 4 first order
elements though.
Antoine.
On 5-Jul-08, at 2:50 AM, Shi Jin wrote:
> Hi there,
>
> I am trying to use gmsh to visualize my FEM simulation results. The
> reason I want to use gmsh is that it is the only visualization
> software I found that is able to visualize 2nd order Taylor-Hood
> tetrahedral elements. (if you happen to know any other tools to do
> this, free or commercial, please let me know).
>
>> From the tutorials, I learned to visualize with the View
>> "string" { string < ( expression-list ) > { expression-
>> list }; ... }; postprocessing command. However, as mentioned in
>> the manaul,"However this "parsed format" is read by Gmsh's script
>> parser, which
> makes it inefficient if there are many elements in the dataset. Also,
> there is no connectivity information in parsed views and all the
> elements are independent (all fields can be discontinuous), so a lot
> of
> information can be duplicated. For large datasets, you should thus use
> the mesh-based post-processing file format described in 9. File
> formats, or use one of the standard formats like MED.
> "
>
> Therefore, I decided to try with the mesh-based file format, i.e.,
> the .msh file. Following the manual, I was able to get the post-
> processing window to show the views and the color map, however, my
> results does not seem to get visualized as it should.
> Here is my .msh file.
> $MeshFormat
> 2 0 8
> $EndMeshFormat
> $Nodes
> 39
> 12 1.00000 0.00000 0.00000
> 13 0.00000 1.00000 0.00000
> 14 -1.00000 0.00000 0.00000
> 15 -0.00000 -1.00000 0.00000
> 16 1.00000 0.00000 1.00000
> 17 0.00000 1.00000 1.00000
> 18 -1.00000 0.00000 1.00000
> 19 -0.00000 -1.00000 1.00000
> 20 -0.00000 0.00000 0.00000
> 21 -0.00000 0.00000 1.00000
> 22 -0.00000 0.00000 0.50000
> 23 0.50000 0.00000 0.50000
> 24 0.50000 0.00000 0.00000
> 26 -0.00000 -0.50000 0.50000
> 27 -0.00000 -0.50000 0.00000
> 29 0.50000 -0.50000 0.00000
> 32 -0.00000 -1.00000 0.50000
> 33 -0.00000 -0.50000 1.00000
> 35 0.50000 -0.50000 0.50000
> 36 0.50000 0.00000 1.00000
> 38 0.50000 -0.50000 1.00000
> 41 1.00000 0.00000 0.50000
> 44 -0.50000 0.00000 0.50000
> 45 -0.50000 0.00000 0.00000
> 47 -0.00000 0.50000 0.50000
> 48 -0.00000 0.50000 0.00000
> 50 -0.50000 0.50000 0.00000
> 53 -0.50000 0.50000 0.50000
> 54 -0.00000 0.50000 1.00000
> 56 -1.00000 0.00000 0.50000
> 57 -0.50000 0.00000 1.00000
> 59 -0.50000 0.50000 1.00000
> 62 0.00000 1.00000 0.50000
> 65 0.50000 0.50000 0.00000
> 68 0.50000 0.50000 0.50000
> 70 0.50000 0.50000 1.00000
> 74 -0.50000 -0.50000 0.00000
> 77 -0.50000 -0.50000 0.50000
> 79 -0.50000 -0.50000 1.00000
> $EndNodes
> $Elements
> 12
> 1 11 3 4 1 0 20 21 12 15 22 23 24 27 29 26
> 2 11 3 4 1 0 21 15 19 16 26 32 33 36 38 35
> 3 11 3 4 1 0 16 21 15 12 36 26 35 41 29 23
> 4 11 3 4 1 0 20 21 14 13 22 44 45 48 50 47
> 5 11 3 4 1 0 21 14 17 18 44 53 54 57 59 56
> 6 11 3 4 1 0 21 13 17 14 47 62 54 44 53 50
> 7 11 3 4 1 0 13 21 12 20 47 23 65 48 24 22
> 8 11 3 4 1 0 17 12 21 16 68 23 54 70 36 41
> 9 11 3 4 1 0 17 13 21 12 62 47 54 68 23 65
> 10 11 3 4 1 0 15 21 14 20 26 44 74 27 45 22
> 11 11 3 4 1 0 19 14 21 18 77 44 33 79 57 56
> 12 11 3 4 1 0 19 15 21 14 32 26 33 77 44 74
> $EndElements
> $NodeData
> 0
> 0
> 0
> 12 80.00000
> 13 80.00000
> 14 80.00000
> 15 80.00000
> 16 0.00000
> 17 0.00000
> 18 0.00000
> 19 0.00000
> 20 80.00000
> 21 0.00000
> $EndNodeData
>
> The key uncertainty I have is about the use of tags.
> 1. For the $Elements section, I use "3 4 1 0" following a .msh file
> generated by gmsh. However, I don't know whether they play any role
> since I don't have any physical names defined. Can i simply use "0"
> as the tag. It does not seem to matter for me in this case.
> 2. In the $NodeData section, there are three tags required: string,
> float and integer. I give them all 0s. Is this a correct way?. If I
> want to give a name to the field, I might do
> 1
> "pressure"
> 0
> 0
> as the three tags. Do I need to give any other tags?
> 3. What shall I do if I want to visualize a velocity vector field?
> Just like
> node-number vx vy vz ?
> 4. I still can't see the visualized field. Please help me. It would
> be great if there is any example/tutorial on post-processing with
> the .msh file.
> Thank you very much.
>
>
> Shi
> --
> Shi Jin, PhD
>
>
>
>
>
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