[MOAB-dev] canonical face connectivity from 10-nodded tet mesh

[Julien Vignollet]

Thank you for your answers. Yes you are right, I actually meant nodes 8 and 9  (starting from 0).


Julien


On 1 Jun 2010, at 14:31, Jason Kraftcheck wrote:

> Julien Vignollet wrote:
>> Dear Moab developers,
>> 
>> I am a new (and very modest!) moab user experiencing difficulties when
>> trying to retrieve the canonical face connectivities in a mesh of 10
>> nodded tetrahedrons (order based on Tautges system from the paper
>> "Canonical numbering systems for finite-element codes") . I am trying to
>> use moab in a 3D finite element code to model multi-phasic hyperelastic
>> elements. I am using Gmsh and Paraview for pre- and post-processing.
>> Attached is the basic mesh I am using to get started.
>> 
>> Apart from a small problem when importing the gmsh file (it seems nodes
>> 7 and 8 are swapped), 
> 
> Are you certain that it is nodes 7 and 8 that are swapped?  I reviewed the
> MOAB code for loading Gmsh files and there is a bug.  It appears that the
> last two nodes for a 10-node tetrahedron will be in the swapped.  That is,
> either nodes 8 and 9 are swapped or nodes 9 and 10 are swapped, depending on
> whether you're counting from 0 or 1.
> 
>> my main difficulty arises when I try to access the
>> faces connectivity (see extract of code at the end of this message).
>> This technique worked successfully to obtain the element connectivities
>> (i.e. the 10 nodes of the tets in a canonical order) when I loop over
>> the elements, but it fails when I loop over the faces. The handle conn
>> gets populated with the correct 6 face nodes but not in a canonical
>> order. The vertex nodes are in the right order, but the mid-nodes are
>> not and I don't see any consistent pattern.
>> 
> 
> This is most likely a side effect of the above bug.  Because the tetrahedra
> have incorrect node order, the triangles generated for the faces of the
> tetrahedra are also incorrect.
> 
> - jason
> 
>