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-   -   Do the cell IDs of a domain change on the fly? (https://www.cfd-online.com/Forums/openfoam-solving/122186-do-cell-ids-domain-change-fly.html)

HakikiCanakkaleli August 14, 2013 04:26
Do the cell IDs of a domain change on the fly?
 
Hi

== 1 ==

As the title indicates, I wonder whether the cell IDs of a computational domain do change or not while an OpenFOAM case is running on a single processor?

== 2 ==

* on multiple processors whilst a parallel job is executed?

Many thanks for your help.

romant August 15, 2013 04:38
They should not change while the case is running, as they are the ID's which you can read in the different file you see in constant/polymesh.

The ID of each cell/point/face ... is the line number which you can count from the beginning of each of these field, for example this face file

Code:
/*--------------------------------*- C++ -*----------------------------------*\
| =========                |                                                |
| \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox          |
|  \\    /  O peration    | Version:  2.2.0                                |
|  \\  /    A nd          | Web:      www.OpenFOAM.org                      |
|    \\/    M anipulation  |                                                |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version    2.0;
    format      ascii;
    class      faceList;
    location    "constant/polyMesh";
    object      faces;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //


268989
(
4(1 9 73 65)  // ID 1
4(8 72 73 9)  // ID 2
4(64 65 73 72) // ID 3
4(0 64 72 8)    // ID 4
...
)

HakikiCanakkaleli August 15, 2013 04:59
My personal experience suggests that:

== 1 ==

Once a case starts running -on a single processor or on many processors-, the cell IDs remain the same whilst constant/polyMesh files do not change. So, the cell IDs do not change on the fly.

== 2 ==

However, when a computational domain is decomposed by decomposePar, the cell IDs are no longer the same with the case executed by a single processor. Namely, each processor re-numbers the cells that it contains starting from 0.

Many thanks.

== 3 ==

But all these arise a new issue to me.

Is there any parameter -like cell coordinate, cell ID or whatsoever-, that I can flag a certain cell no matter what happens -like decomposing the computational domain or rotating region?

More precisely, is there any parameter that remains the same for cells no matter what happens so that I can easily identify this/these particular cell/cells?

elvis August 15, 2013 05:00
Hi,

you can use the command

renumberMesh

the command Renumbers the cell list in order to reduce the bandwidth, reading and renumbering all fields from all the time directories

http://www.openfoam.com/features/mesh-manipulation.php

usually the IDs do not change


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