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gautcho August 10, 2011 12:22

How create a mesh with no "face-to-face"-cells?

I want to create a pretty simple mesh, but gmsh doesn't want me to do it. I want to have a mesh, in which for example 2 cells are connected to one face of another cell, so the one face from this cell is in contact to 2 faces and not just one.
As far as I got, gmsh doesn't allow meshes of this type. Do you have any idea how to do it anyway (perhaps with blockmesh?)?


nimasam August 10, 2011 18:47

do you want to share a face from one cell with two other cell's face?
as i know, its not possible! you can use block mesh to make this mesh! but when you run the case! it cant resolve phi in shared face! and it stops! then you are supposed to use merge patches! to merge that two faces

gautcho August 11, 2011 00:20

A colleague of mine does use a refinment alg and for him its possible to work with some mesh like this.

Perhaps my description was not good, I try to "paint" something ;):

| .............. |
|............... |
| .............. |
| ...... |..... |
| ...... | .... |

I want something like this. One cell on top, 2 cells under it (ignore the points!).

nimasam August 11, 2011 18:02

means one block share its face with two other block
make it in block mesh easily! use merge patches in block mesh to merge faces together

gautcho August 12, 2011 01:42

Okay, thank you. I thought about blockMesh but an other colleague told me, that this isnt possible with blockMesh.

gautcho August 15, 2011 08:26

Okay, I am very sorry. I didnt tell you, that I need a structured mesh. Can OpenFOAM even handle meshes like this?

wouter August 15, 2011 15:56

in faces the statement is:

Internal faces
Those faces that connect two cells (and it can never be more than two).
For each internal face, the ordering of the point labels is such that the face normal
points into the cell with the larger label, i.e. for cells 2 and 5, the normal points
into 5;

hope this helps

gautcho August 16, 2011 02:42

I have found that too, but I dont know if its because of my bad english, but I understand it otherwise.

It says, that one face can not connect more than two cells and I am fine with this. But it doesnt say, that tweo cells can not be connected by more than two faces.

Or it is at least not clear and both interpretations are possible...

What do you think?

val46 August 16, 2011 02:58


you can create such a mesh but as far as I know Openfoam can only handle conformal meshes (no hanging nodes).
You can try ggi-interface in dev-version (extend project) of Openfoam.

wouter August 16, 2011 03:15


In chapter Cells:

cells must not overlap
every cell must be convex, center inside the cell
the angle between the face area vector and the centre-to-centre vector must always be less than 90

So I do not think that one cell can have two faces in common with another cell.


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