[Gmsh] R: Post-processing stress field

Thu Jan 31 09:40:27 CET 2019

I would be grateful if you could post a similar MSH2 example for a tetrahedron grid, with 1 data field assigned on nodes and another one assigned on cell centers...

A.

-----Messaggio originale-----
Da: gmsh [mailto:gmsh-bounces at ace20.montefiore.ulg.ac.be] Per conto di Christophe Geuzaine
Inviato: giovedì 31 gennaio 2019 09:37
A: Max Orok
Cc: gmsh at onelab.info; Gaetano Camarda
Oggetto: Re: [Gmsh] Post-processing stress field

> On 30 Jan 2019, at 23:58, Max Orok <morok at mevex.com> wrote:
> 
> Yes, the stresses belong in the $ElementData section for sure. 
> I think to correctly display it, you'll need to create rows of element data with 10 entries - 1 for the element number and 9 for the stress tensor values:
> 
> 1 sigx sigxy sigxz sigxy sigy sigyz sigxz sigyz sigz
> 
> I don't know if copying and pasting this pattern in ElementData will work without some tweaks...

That's correct. Here is a simple MSH2 example with 2 quads, with values [1 0 0, 2 0 0, 3 0 0] and [1 0.1 0.1, 0.1 2 0.1, 0.1 0.1 3]:

$MeshFormat
2.0 0 8
$EndMeshFormat
$Nodes
6
1 0.0 0.0 0.0
2 0.1 0.0 0.0
3 0.1 0.3 0.0
4 0.0 0.3 0.0
5 0.0 0.15 0.0
6 0.1 0.15 0.0
$EndNodes
$Elements
2
1000 3  2 6 100  1 2 6 5
1001 3  2 6 100  5 6 3 4
$EndElements
$ElementData
1
"stress field per element"
1
0.
3
0
9
2
1000  1 0 0 0 2 0 0 0 3
1001  1 0.1 0.1 0.1 2 0.1 0.1 0.1 3
$EndElementData

PS: the next release will improve the computation of the min/max for tensor fields. (Currently the min/max is computed using the default representation for tensors, i.e. Von-Mises. The next release will take the tensor visualization mode into account when explicitly requesting the calculation of min/max.)

Christophe

> (there is an InterpolationScheme section that I don't quite understand). If it were me, I would add the data using the gmsh API and it will handle the output format how it likes. 
> 
> Sincerely,
> Max
> 
> 
> On Wed, Jan 30, 2019 at 2:42 PM Gaetano Camarda <gaetano_18 at live.it> wrote:
> Thanks for your help, but I think I have not understood well. 
> I have a mesh all brick (8 nodes) and my stress field matrix is composed this way:
> 1 sigx sigy sigz sigxy sigyz sigxz
>    ...     ....    .....    .....    ......    .....
> 
> In each row is express the stress state of the element, I think I have to copy this matrix into .msh file as $ElementData, but I do not unsterstand well the input format, is that right this way? 
> 
> 
> Outlook per iOS
> Da: Max Orok <morok at mevex.com>
> Inviato: martedì, gennaio 29, 2019 7:14 PM
> A: Gaetano Camarda
> Cc: gmsh at onelab.info
> Oggetto: Re: [Gmsh] Post-processing stress field
>  
> Hello Gaetano,
> 
> Here is a short program to plot 3x3 tensor data using the C++ gmsh API (it shouldn't be too hard to port to Python or Julia if you're more comfortable there). It only plots data for one element, but can be extended for your case.
> 
> The "addModelData" call is expecting a vector of vectors with 9 entries each for this case.
> I think the vector ordering corresponding to the matrix is like this: 
> [elt11, elt12, elt13, elt21, elt22, ...]
> 
> I assume the stress matrix is symmetric and so only has 6 unique entries.
> Therefore your vector entries will look like [x xy xz xy y yz xz yz z] 
> The tricky part will be importing the data in a sensible way.
> 
> Perhaps you could parse a CSV using python and add entries to the data vector in a loop?
> Please find attached the program as well as example input mesh and output mesh files.
> 
> 
> 
> <image.png>
> 
> Sincerely,
> Max
> 
> On Tue, Jan 29, 2019 at 11:24 AM Gaetano Camarda <gaetano_18 at live.it> wrote:
> Hello everyone,
> 
> I’m having some difficult on post processing a mesh I created.
> 
> I create a mesh on Gmsh all Hexa (so a brick with 8 nodes), i use this 
> mesh and import it on Matlab,
> 
> there i run some analisys and find the stress matrix:
> 
> [sigx sigy sigz sigxy sigyz sigxz]
> 
> …..    …..    …..   …..    …..    …..
> 
>  
> 
> Now I would like to visualize the stress field on Gmsh, but I do not 
> find any way to do so, I can export the matrix,
> 
> I tried to generete a *.pos file, but I didn’t find a solution.
> 
>  
> 
> Inviato da Posta per Windows 10
> 
>  
> 
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> 
> 
> 
> --
> Max Orok
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>  
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> h=21dbbfec&f=y&p=y
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—
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science  https://urlsand.esvalabs.com/?u=http%3A%2F%2Fwww.montefiore.ulg.ac.be%2F~geuzaine&e=9895bfa0&h=408b631c&f=y&p=y 

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