[Gmsh] 3D Periodic Boundary Conditions with test.

[Gustavo Charles Peixoto de Oliveira]

Dear all,

I've read your discussion about 3D PBC here

http://www.geuz.org/pipermail/gmsh/2013/008054.html

and I'd like to give some contribution. I'm a GMSH newbie and my need seems
similar to yours.

I've been trying to generate 3D PBC meshes for simple geometries like
square, triangular and rectangular channels with the Periodic Surface
command by using the version 2.7.0. However, before running my code, I had
to write a function to verify if the periodicity really was being satisfied
like Dorin did. It's surprisingly that the test fails for 1 point for some
refined meshes. However, it succeeds for coarser meshes of the same kind. I
didn't know why...

For instance, my script test outputs something like that for an x-extrusion:

Warning! Left and right y-components are not equal.
Entry: 72
yU = 0.5; yV = 0.625
Warning! Left and right z-components are not equal.
Entry: 72
zU = 0.25; zV = 0.625

As you can see, the y-coordinate is "slightly" different, whereas
z-component is a bit more. In the end, both differs, but for an unique
point! Although the error is small, it is problematic for my purposes.

I didn't test the output with Transfinite option.

Dorin, I will test your suggestion to use Extrude + Transfinite, but have
you already found some solution concerning extrusion for further directions?

Would be this case a bug of the Periodic Surface function?

Kind regards,

-- 
Gustavo Oliveira, Ph.D. Student
Graduate Program in Mechanical Engineering
State University of Rio de Janeiro
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