[Gmsh] Elements with negative jacobian after extrusion of a spline

[Christophe Geuzaine]

Hi Paul,

Apparently we broke this (again) in 2.6. (It works fine in 2.5.)

We will investigate.

Thanks for the report,

Christophe


On 25 Oct 2012, at 17:44, Paul Cristini <cristini at lma.cnrs-mrs.fr> wrote:

> Hello all,
> 
> I am just trying to do the extrusion of a spline and depending on the position of a point of the spline I got 2 elements with a negative jacobian.
> 
> Here is the .geo file. If Point(3) = { -L/2,  l+dl/2, 0, lc}; is changed to Point(3) = { -L/2,  l+dl/3, 0, lc}; ,which means that one point is lowered, then no problem.
> 
> I am generating all quads meshes and  I am also using second order elements. I noticed that if I use first order or incomplete second order element there is no element with a negative jacobian.
> 
> Any idea of what's going on ?
> 
> Thanks
> 
> Paul
> 
> // Gmsh project created on Sat Apr 10 19:26:34 2010
> lambda = 30;
> lc=lambda/4;
> //
> L  = 10 * lambda; // Width
> l  =  8 * lambda; // Height
> dl =  2 * lambda; // Decalage
> 
> Point(1) = { L, l+dl, 0, lc};
> Point(2) = {-L,    l, 0, lc};
> //
> Point(3) = { -L/2,  l+dl/2, 0, lc};
> Point(4) = { 0,  l+dl/3, 0, lc};
> Point(5) = { L-L/4,  l+dl/2, 0, lc};
> 
> //lx1 = newl; Line(lx1) = {cx2, cx1};
> lx1 = newl; Spline(lx1) = {2, 3, 4, 5, 1};
> Extrude {0,1.5*lambda,0} {Line{lx1}; Layers{3};Recombine; };
> 
> -- 
> *--------------------------------------------------------------------------*
> Paul CRISTINI  Charge de Recherche CNRS / CNRS Research Scientist
> --------
> CNRS - Laboratoire de Mecanique et d'Acoustique (UPR 7051)
> 
> 31 chemin Joseph Aiguier, F-13402 Marseille Cedex 20 - France
> mailto: cristini at lma.cnrs-mrs.fr
> phone number: +33 (0)4 91 16 42 89
> fax number: +33 (0)4 91 16 44 81
> http://www.lma.cnrs-mrs.fr/
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-- 
Prof. Christophe Geuzaine
University of Liege, Electrical Engineering and Computer Science 
http://www.montefiore.ulg.ac.be/~geuzaine