[Gmsh] how to make a periodic cubic mesh

David Colignon david.colignon at ulg.ac.be
Wed Dec 14 15:29:48 CET 2016

```On 14/12/16 14:22, Aleksejs Fomins wrote:

> Dear Gmsh,
>
> I would like to create a cubic domain with a few complicated 3D shapes inside, and produce a corresponding tetrahedral mesh. The domain boundaries of the cube should be periodically conformal, e.g. each triangle on the surface with normal -x should be equivalent to a triangle on the surface with normal +x under translation along the x-axis.
>
> Using google I have found a solution proposed earlier on this list:
>
> http://onelab.info/pipermail/gmsh/2016/010305.html
>
> The .geo code suggested in the above link produces a conformal tetrahedral mesh of a cube using Transfinite surfaces and edges. It seems to work, but has a few problems:
> 1) It completely ignores the value of the characteristic lengthscale variable "lc", always splitting each edge in exactly 4 parts
> 2) The characteristic lengthscale changes depending on when index number of the Transfinite Line. Currently it is 5. If one would set it to 14, each edge would be split into exactly 25 segments. Why is that?

Hi,

see http://gmsh.info/doc/texinfo/gmsh.html#Structured-grids

Transfinite Line { expression-list } | "*" = expression < Using Progression | Bump expression >;

Selects the lines in expression-list to be meshed with the 1D transfinite algorithm. The expression on the right hand side gives the number of nodes that
will be created on the line (this overrides any other mesh element size prescription—see Specifying mesh element sizes).

5 nodes -> four segments

Regards,

Dave

--
David Colignon, Ph.D.
1er Logisticien de Recherche
Université de Liège
ACE - Applied & Computational Electromagnetics
Quartier POLYTECH 1 - Montefiore B28
Allée de la découverte 10
4000 Liège - BELGIQUE
Tél: +32 (0)4 366 37 32
http://www.ulg.ac.be/nic4
>
> GMSH version 2.13.2, Ubuntu 16.04
>
> Best regards,
> Aleksejs Fomins
> PhD student at Nanophotonics and Metrology Lab, EPF Lausanne, Switzerland
>
>
>
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```