[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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