[Gmsh] Node ordering for quadratic elements

[Kris Van den Abeele]

Glad I could help!

Thanks for the quick replies,
Best,
Kris


On Wed, 2008-02-27 at 10:56 +0100, Christophe Geuzaine wrote:
> Hi Kris - I found the problem: there is indeed a nasty little bug for 
> higher order elements with nodes associated with faces, which occurs 
> only when we need to change the ordering of the nodes to guarantee a 
> positive Jacobian (this explains why some meshes were OK, while others 
> were not).
> 
> We will release a patched version as soon as possible (this will also 
> fix another annoying bug with high order elements in 2.1.0, which leads 
> to crashes with quad faces).
> 
> Many thanks for submitting the bug report!
> 
> Christophe
> 
> 
> (The reason it manifests itself only in one of your meshes is that the)
> 
> Kris Van den Abeele wrote:
> > Hi Christophe,
> > 
> > I verified the node ordering in the meshes I attached in my previous
> > email. The mesh for the sine bump (sineBumpHexaCurved3D.msh) has the
> > ordering you described. The mesh for the cilinder (halfcylinder_3D.msh)
> > has not. The nodes associated to the second and fourth face (1256 and
> > 2367) are swapped, as well as the nodes associated to the third and
> > fifth face (1458 and 3478).
> > 
> > Best regards,
> > Kris
> > 
> > 
> > On Sun, 2008-02-24 at 18:56 +0100, Christophe Geuzaine wrote:
> >> Kris Van den Abeele wrote:
> >>> Hi,
> >>>
> >>> My name is Kris Van den Abeele, I am a PhD student at VUB (research
> >>> group of Prof Lacor). I am working on the development high-order
> >>> Spectral Volume and Spectral Difference methods, which I implement in
> >>> the VKI COOLFluiD code. I've been using Gmsh (Version 2.0.8, on Linux)
> >>> as a mesh generator for a long time now and I am very happy with it.
> >>>
> >>> Lately, I've been creating meshes consisting of quadratic (27 nodes)
> >>> hexahedral elements, and I've encountered a problem. On the website, I
> >>> have not found the order in which the nodes of such a quadratic
> >>> hexahedron are written to the mesh file. I have two different meshes,
> >>> and it seems that for two different meshes, the order in which the nodes
> >>> are outputted differs (more specifically for the nodes that lie in the
> >>> center of a face).
> >> Hi Kris - The second order nodes are given in the following order: 
> >> first, the nodes associated with edges are given in the order of the 
> >> edges; then, the nodes associated with faces are given in the order of 
> >> the faces. The ordering of the edges and the faces is given here:
> >>
> >> http://geuz.org/gmsh/doc/texinfo/gmsh_10.html#SEC71
> >>
> >> Can you check if your meshes are consistent with the docs? If not, it's 
> >> a bug and we will fix it.
> >>
> >> Take care,
> >> Christophe
> >>
> >>
> >>> In attachment, I have included the .geo and .msh (Version 1.0) files
> >>> corresponding to the two meshes.
> >>>
> >>> Could you have a look at this, or maybe send me the order in which the
> >>> nodes are outputted?
> >>>
> >>> Thanks in advance!
> >>> Best regards,
> >>> Kris Van den Abeele
> >>>
> >>>
> >>>
> >>>
> >>> ------------------------------------------------------------------------
> >>>
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> >>> gmsh at geuz.org
> >>> http://www.geuz.org/mailman/listinfo/gmsh
> >>
> 
> 
-- 
Ir. Kris Van den Abeele

FWO Research Engineer

Vrije Universiteit Brussel

Dept. of Mechanical Engineering
 
Fluid Mechanics and Thermodynamics Research Group
 
Pleinlaan 2, 1050 Brussels, Belgium
 
Tel. : 02/629.23.99
 
Fax : 02/629.28.80