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Anorky November 25, 2009 05:00

Mesh lines and points
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Hi everyone,

I have a short question.
I am making a fully hexagonal mesh in ICEM. Normally when you mesh the geometry, turn off the geomerty and check the lines and points of the mesh, these should represent the geometry curves and points. Is this correct?

In my mesh, two of these lines are missing.
Does anyone has any suggestions on how to solve this or what the problem might be?

I included two illustrations showing one of the missing lines.
The first picture are the geometry curves. The second illustrates the lines of the mesh.

The missing line is link bunched to another edge. Although I don't think this is the problem since I have linked bunched several other edges without problems.

Kind regards

PSYMN November 28, 2009 00:48

Associate edge to curve.
Lines (1D line elements) only form if the edge is associated to a curve. I am guessing that since the edge was straight and the edge already seemed to be in the right place, you didn't feel like you needed to associate it...

No association, no line elements.

However, you may not need to associate it. Does your solver need that line there? It may not. ICEM CFD is a patch independent mesher. You don't need to capture every line, only work to capture important feature curves (sharp edges, curves that help keep your mesh neat, etc.) Let the rest just follow the surface unless you have a strategic reason not to. many of these lines were just put there by the CAD system and you are under no obligation to respect them with your mesh.

Anorky November 30, 2009 08:10

Hi Simon,

Previously I didn't associate alle edges to curves of the geometry. But than I sometimes ended up having a mesh that didn't follow the geometry at f.e. sharp edges and so on as you said.

Since then, I associate all edges to curves when possible. Also here, I associated the edge to a curve, that is why I find it strange that the line does not show up...

I think the line is however needed. In the images you can see the two, straigth edges which are linked to a single edges, not showed here.
Near the missing line I get some negative volume elements and I think the missing line might be the problem.

Do you have any suggestions or ideas why this line might dissapear?

Could it be because I link bunch these two edges to a single edge of a different length? I mean the sum of the length of the two linked edges is not the same as the length to which they are linked.

Kind regards and thanks for helping me out.

PSYMN December 1, 2009 01:35

Hmm, I have never heard of link bunching affecting association, but you may be doing it wrong, so maybe...

Look in the help since I think I improved it in one of the more recent versions.

When you set up a linked bunching, it is critical that you select things in the right order...

Also, it can't link a shorter edge (fewer indices) to a longer one... Rather you select a single edge, but it really links everything parallel. Sorry if I am not explaining that right (it is past midnight here). But it is important that when you select the "shorter" edge, that you select the one aligned with the side 1 of the longer edge.

Again, please take another look at the instruction and make sure you are doing it correctly. It is easy to get it wrong. (we should improve that so selecting any of the parallel edges would be sufficient, I think there is already a request for that).

Other than that, I can't think of a good reason right now. To test your theory, please try turning off the linked bunching to see if you get the line elements...

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