# [Gmsh] 3D mesh where volumes share part of a boundary

Sat Aug 21 13:01:30 CEST 2010

```Hi,

I am having some problems meshing 3D shapes where parts of the
geometry include surfaces shared between different volumes. I start
with a 2D object comprising a number of surfaces and I extrude these
different surfaces by different amounts to produce a set of volumes. I
have tried making the 3D shape from a set of points rather than using
the extrude function and I get the same problem.

I guess it is an issue with the mesh overlapping at this boundary but
I have concluded I just don't understand gmsh well enough to work out
how I should get round this problem.

I have included a simple example of a geometry in which I see the
meshing problem. In this case it would be easy for me to make the
whole object one volume and not have the internal boundary. In the
actual  example I am working towards the boundaries are important as I
have different materials.

I am sorry if I have missed something really obvious and am taking up
others time.

Many thanks,

Matthew Suddards

Point(1) = {0, 0, 0};
Point(2) = {1, 0, 0};
Point(3) = {1, 1, 0};
Point(4) = {0, 1, 0};
Point(5) = {0, 2, 0};
Point(6) = {1, 2, 0};
Line(1) = {5, 4};
Line(2) = {4, 3};
Line(3) = {3, 6};
Line(4) = {6, 5};
Line(5) = {5, 4};
Line(6) = {1, 1};
Line(7) = {1, 4};
Line(8) = {1, 2};
Line(9) = {2, 3};
Line Loop(10) = {1, 2, 3, 4};
Plane Surface(11) = {10};
Line Loop(12) = {7, 2, -9, -8};
Plane Surface(13) = {12};
Extrude {0, 0, 0.5} {
Surface{11};
}
Extrude {0, 0, 0.25} {
Surface{13};
}

```