[Gmsh] wrong maximum-values in a contour plot coming from a .med-results-file

[Christophe Geuzaine]

On 07 Feb 2014, at 13:16, Johannes Ackva <johannes.ackva at code-aster.de> wrote:

> hello,
> 
> When opening a .med-file containing vmises-stresses for 5 loadcases,
> GMSH shows wrong maximum-values. I do it in this way:
> 
> - I open the .med-file with GMSH. The contour plot shows correctly the
> maximum value of the worst loadcase.
> 
> - to create a plot for each loadcase with the loadcase-specific max
> values, I do so: Options, highligth view (View[9]), in Tab General I
> cycle throug the time steps (0,1,2,3,4). I set "Range Mode" to Custom, I
> click onto "Max" (the value there should now be adjusted to the
> max-value of that loadcase).
> 
> But the max-values shown in the contour range bar seem me to be wrong.
> Because the differ from my printout which I made with Code-Aster. Also
> creating Contour-Plots with Salome (with the same .med-file ), Salome
> shows those maxima which are printed out by Code-Aster.
> 
> Strangle, the max-values of GMSH are all by a factor=1.235 smaller than
> those printed by Code-Aster.
> 
> I attach the .med file with this problem:
> bado_segment45_post_vmisesScrewTet_Quadratic_ToGMSHForum.rmed
> 
> I observe that this problem does not occur if I work with linear
> elements (no additional nodes at mid-edges). So it seems the problem
> occurs only with quadratic elements.
> 
> This was the Code-Aster command to create the med.-file:
> 
> IMPR_RESU(FORMAT='MED', UNITE=88,
>          RESTREINT=_F(GROUP_MA=('ScrewTet',),),
>          RESU=_F(RESULTAT=Result,
> INFO_MAILLAGE='NON',NOM_CHAM='SIEQ_NOEU',NOM_CMP='VMIS',NOM_CHAM_MED='VMises
> Screw, only Tetraeders',
>                INST=(1,2,3,4,5,),
>                ),);
> 
> "RESTREINT" means that I printed only a part of the mesh and the
> respective part of the field of vmises-values.
> 
> Can somebody please show me how to get the contour-plots with the
> correct max-values for each loadcase?
> 


Hi Johannes,

By default Gmsh uses a first order representation of the dataset. High-order representation can be obtained adaptively: just select "Adapt visualization grid" and choose the appropriate recursion level/error tolerance in the "General" option tab for the view.

I suspect that the maximum values returned by Aster and Salome are actually *not* the real maximum values of the field, but the *maximum nodal values* (the field being interpolated using 2nd order Lagrange elements).

Christophe



> Thank You
> 
> 
> -- 
> mit freundlichen Grüssen / Best regards
> 
> Johannes Ackva
> 
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine