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Old   August 16, 2001, 06:19
Default unmatched boundaries for sliding grids
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Markus
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I'm trying to model the flow for a small impeller in a cylindrical tank. I've defined the surfaces on the sliding inner part and the stationary outer part of the geometry as BLKBDY1 and BLKBDY2 respectively. They have the same size, the number of grid elements match and I've selected the right solids on both sides. In the command file, I have glued the unmatched boundaries correctly. But when I run the problem, I get the following error:

*** ERROR *** CONFLICTING SPECIFICATION OF PATCHES CANNOT DEFINE PATCH NAME PERD-PATCH---61LOW--J-BLK----1 OF TYPE BLKBDY. A PATCH OF TYPE BLKBDY HAS ALREADY BEEN DEFINED AT CONTROL VOLUME ( 2, 1, 1) IN BLOCK: BLOCK-NUMBER-1

*** ERROR *** CONFLICTING SPECIFICATION OF PATCHES CANNOT DEFINE PATCH NAME PERD-PATCH--133LOW--J-BLK----2 OF TYPE BLKBDY. A PATCH OF TYPE BLKBDY HAS ALREADY BEEN DEFINED AT CONTROL VOLUME ( 1, 1, 1) IN BLOCK: BLOCK-NUMBER-2

I have no idea how I could correct the boundaries or the solid model. I've been trying for nearly a week, but nothing I do solves this problem. Can anybody help me?

Thanx,

Markus
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Old   August 16, 2001, 19:06
Default Re: unmatched boundaries for sliding grids
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Glenn Horrocks
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Hi Markus,

Your problem is more likely to be from your geometry file than the command file. Your error message is saying that you are trying to make a boundary an unmatched grid where it is already an interblock boundary.

In my experience, this error is usually caused by nodes being equivalenced across unmatched grids in CFX-Build.

There are no simple ways of fixing this problem that I know of. The first thing to try is to redo the mesh of your geometry again, however this time mesh one block at a time. In CFX-Build, mesh one of the blocks, equivalence that block's mesh, hide the mesh, mesh the second block, equivalence the second block's mesh only (I think the option is "Equivalence List" and you can select the nodes to equivalence), and when you go "Analyse" make sure it does not equivalence before outputting the geometry file.

It would be nice if CFX-Build realised that you do not equivalence across unmatched boundaries, so equivalencing should be "turned off" at those nodes - this problem has caused me some grief too. Hopefully AEA can include this feature in future versions of CFX.

Alternatively, if you're feeling brave you can hack the geometry file directly. I won't go into details of how to do this unless you are really keen, but in short get a text editor and chop out the offending patches (the ones listed in you error above) from the geometry file, and rejig the file to update to the new patch list. Not for the feint hearted.

Hope this helps, Glenn
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