[Gmsh] eigenvalue + eigenvectors

[Christophe Geuzaine]

Emmanuel ROBBE wrote:
> 
> hello,
> 
> following to my previous mail, i've found a solution that could be 
> eaysily done (maybe?) :
> is there a way (plugins) which can only keep the  values > 0 of a scalar 
> results and replace the others by 0. ? Same for the values <0 ?

Yes, you could use the CutMap plugin (with A=0 and ExtractVolume=1 or 
-1) to split the view (or the ExtractElements if you do not want to 
split the elements)


> this way by using this plugin on the eigenvalues, you can create to 
> results : one for the positiv values, the others fot the negativ ones. 
> And then by using the "evaluate" plugin and multiply theses fields with 
> the eigenvectors,  you can create two fields of eigenvectors 
> corresponding to the positive values and negatives values.
> 
> regards,
> 
> Emmanuel ROBBE
> 
> ----- Réacheminé par Emmanuel ROBBE/CNEH/DE/EDFGDF/FR le 17/10/2008 
> 17:21 -----
> 	*Emmanuel ROBBE*
> 
> 17/10/2008 16:41
> 
> 	       
>         Pour :        gmsh at geuz.org
>         cc :        
>         Objet :        eigenvalue + eigenvectors
> 
> 
> 
> hello,
> 
> I'm currently working with gmsh in order to view the results of some 
> mechanicals problems solved with Code_Aster. First of all, i want to 
> congratulate you for the very good job you've done with you software : 
> every time I'm using it, I 'm impressed with the hign number of ways to 
> draw and use the results of the calculation.
> 
> In order to understand the behaviour of some concrete structure, i'm 
> using the plugins "eigenvalues" and "eigenvectors" in order to view the 
> main stress direction / vectors in the structure. Usually, i run the 
> eigenvectors plugins on the stress tensor with the option 'scale by 
> eigenvalue' but unfortunatly, with this methode, you can not know 
> anymore if the value is positiv or negativ, wich is very interesting for 
> us in order to know if there is traction or not.
> 
> The idea is to be able to represent the eigenvectors with a line with 
> the followings properties
>  - the direction is the one of the vectors (which is already given by 
> eigenvectors)
>  - the size is related to the value
>  - the colors depends of the value : for exemple green color for positiv 
> value, and red for negativ. This last point can ben easily done by 
> choosing a custom ange with 2 intervals
> So, it's a sort of mix between eigenvectors and eigenvalue : this last 
> option is keeping the information of the sign of the value.
> I'm currently trying to use some operation with the plugins existing in 
> order to do it, without success for the moment.
> 
> With this tool, you can very easily and quicky see the way the force are 
> crossing the structure and where are the weak point.
> 
> I hope you will me able to help me. Sorry for the poor english, it would 
> have be more easy for me to write in french. :)
> 
> regards,
> 
> Emmanuel ROBBE
> 
> ps : actually, i've got some others questions about this type of 
> results's visualization  . Let me know if you are interesting.
> 
> 
> 
> 
> 
> 
> 
> 
> ------------------------------------------------------------------------
> 
> _______________________________________________
> gmsh mailing list
> gmsh at geuz.org
> http://www.geuz.org/mailman/listinfo/gmsh


-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science
http://www.montefiore.ulg.ac.be/~geuzaine