# [Gmsh] periodic mesh

Josefin Ahlkrona josefin.ahlkrona at it.uu.se
Tue Feb 2 20:59:48 CET 2016

```Hi,

I have a cuboid (x,y,z) domain for which i have created tetrahedral,
structured mesh.  Now, I want to apply periodic boundary conditions in
x, and y direction and in order to do that I need the mesh to be
identical for the x=0 and x=xmax surfaces, as well as for the y=0 and
y=ymax surfaces. It is not sufficient for only the nodes to match but I
also want the edges to match!

I have tried to use the "Periodic Surface" command without success. I
have seen several posts on using the "Periodic Surface" commands without
finding a solution for my problem.

Could anyone help me?

My geofile looks like this:

cl=1.0;
//cuboid which is 8000,8000,1000 big

Point(1) = {0,0,0,cl};
Extrude {8000,0,0} {
Point{1}; Layers{10};
}
Extrude {0,8000,0} {
Line{1}; Layers{10};
}
Extrude {0,0,1000} {
Surface{5}; Layers{5};
}

boundMaster[] = Boundary{26};
boundSlave[] = Boundary{-8}; //tried plus and minus sign here..
boundMaster2[] = Boundary{22};
boundSlave2[] = Boundary{-14};  //tried plus and minus sign here..

Periodic Surface 18 {boundSlave[]} = 26 {boundMaster[]};
Periodic Surface 14 {boundSlave2[]} = 22 {boundMaster2[]};

Physical Surface(28) = {14};   //y=y0
Physical Surface(29) = {18};   //x=xmax
Physical Surface(30) = {22};   //y=ymax
Physical Surface(31) = {26};   //x=x0
Physical Surface(32) = {5};    //top
Physical Surface(33) = {27};   //bottom

Physical Volume(34) = {1};

Best,

Josefin

```