[Gmsh] Node ordering for quadratic elements

[Christophe Geuzaine]

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