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

[Paul Cristini]

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; };

-- 
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  Paul CRISTINI  Charge de Recherche CNRS / CNRS Research Scientist
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  CNRS - Laboratoire de Mecanique et d'Acoustique (UPR 7051)

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  mailto: cristini at lma.cnrs-mrs.fr
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