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Old   July 22, 2012, 02:39
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  #41
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Hi,

I've not yet looked at Case2 posted.
The problem I am facing is when using a more refined mesh the section where the curve stops and joins with a straight line becomes very skewed and stretched which leads to the solver being unstable.- When running checkMesh it finds a large number of "severely non-orthogonal faces". I tried to change the nonOrthogonal corrector to 3 to see if it would affect stability but it was unsuccessful!

How would you recommend would be a good way to overcome this issue?

Kind Regards
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Old   October 8, 2012, 06:55
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sivakumar selvaraju
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Hi Niels and Matt,
I have a problem while converting the mesh (.msh) file to foam.
here is the steps which I followed,
1) copied .msh file to polymesh folder
2) then fluent3DMeshToFoam
3) checkMesh (there is no error message)
4) i have edited the createPatchDict
5) createPatch
6) while trying to view the mesh, I am getting the following error.

--> FOAM FATAL ERROR:
More than six unsigned transforms detected:
6(((0 0 0) (1 1.57813e-06 -0.000193506 -0.000137946 0.707107 -0.707107 0.000135714 0.707107 0.707107) 1) ((0 0 0) (0.999999 3.64383e-05 -0.00152133 -0.00110151 0.707109 -0.707104 0.00104998 0.707105 0.707108) 1) ((0 0 0) (0.999996 7.7863e-05 -0.00275828 -0.00200544 0.707113 -0.707098 0.00189536 0.7071 0.707111) 1) ((0 0 0) (0.999992 0.000140037 -0.00401223 -0.00293604 0.70712 -0.707087 0.00273811 0.707093 0.707115) 1) ((0 0 0) (1 -0.000137946 0.000135714 1.57813e-06 0.707107 0.707107 -0.000193506 -0.707107 0.707107) 1) ((0 0 0) (0.999999 -0.00110151 0.00104998 3.64383e-05 0.707109 0.707105 -0.00152133 -0.707104 0.707108) 1))

From function void Foam::globalIndexAndTransform::determineTransforms ()
in file primitives/globalIndexAndTransform/globalIndexAndTransform.C at line 225.

my boundary file looks as follows,

FoamFile
{
version 2.0;
format ascii;
class polyBoundaryMesh;
location "1/polyMesh";
object boundary;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

12
(
fan
{
type wall;
nFaces 2800;
startFace 1357300;
}
top2
{
type wall;
nFaces 5600;
startFace 1360100;
}
top1
{
type wall;
nFaces 800;
startFace 1365700;
}
top0
{
type wall;
nFaces 2800;
startFace 1366500;
}
center1
{
type wall;
nFaces 5600;
startFace 1369300;
}
center0
{
type wall;
nFaces 2800;
startFace 1374900;
}
outlet
{
type patch;
nFaces 2000;
startFace 1377700;
}
inlet
{
type patch;
nFaces 2000;
startFace 1379700;
}
ILR0
{
type cyclic;
nFaces 3500;
startFace 1381700;
matchTolerance 0.001;
neighbourPatch ILR1;
}
ILR1
{
type cyclic;
nFaces 3500;
startFace 1385200;
matchTolerance 0.001;
neighbourPatch ILR0;
}
OLR0
{
type cyclic;
nFaces 7000;
startFace 1388700;
matchTolerance 0.001;
neighbourPatch OLR1;
}
OLR1
{
type cyclic;
nFaces 7000;
startFace 1395700;
matchTolerance 0.001;
neighbourPatch OLR0;
}
)

Can you guys help me to solve the problem?
please tell me what are the steps I need to follow further.


Thanks and Regards,
Sivakumar
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Old   October 8, 2012, 08:13
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Hi sivakumar,

I was getting this error also, but never determined what was causing the issues..

As Niels recommend I used the autoPatch method which was quite robust and seems to work very well- this is my preferred method! Follow the thread below Niels has outlined the process clearly.

Also I thought that the .msh file should be placed in the case dir not in constant/polyMesh? Seems like you're getting a mesh out of the conversion anyway so not sure that this would cause you problems? Maybe worth a try.

It also could be to do with the .msh file- are there any named patches n the .msh file? If so try removing named selections in fluent/ansys and converting a mesh with no boundary patches defined. Then you can define them after you convert the mesh.

Hope this helps!
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Old   October 8, 2012, 12:46
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sivakumar selvaraju
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hello Matt,

Follow the thread below Niels has outlined the process clearly
you mean this steps

Go to the mesh module.

Mesh -> create mesh -> assign a set of hypotheses -> 2d: Automatic quadrangulation -> specify number of segments -> apply and close

Mesh -> Compute

Modification -> extrusion -> select triangle at top -> tick select whole mesh, submesh or group (select mesh if not already selected in the tree) -> Extrusion to distance -> Z = 0.01 -> Number of steps = 15 -> Apply and close

if so, can you please tell me where it is located?

with regards,
Siva
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Old   October 8, 2012, 19:01
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Those are he steps for Salome meshing..

Try this instead:
Convert .msh file

Then run autoPatch 5 ( might have to play with the parametr here unil you gt all your faces)

View the mesh in paraview (do not chose to load any fields with the mesh as they will not have correctly specified patches and it will crash). You can use paraFoam or open paraview and load your ontrolDict file here

Note all the patches auto0, auto1,... and what they are meant to be (your patch names)

Change the corresponding entries in 0.001?/constant/polyMesh/boundary to have the correct tach names

Move he new polyMesh folder to the correct location ie constant dir. (Rename your old polyMesh dir first as a back up if something goes wrong)

Hope that's clear!
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Old   October 9, 2012, 11:02
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sivakumar selvaraju
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Hi There,

I have a simple problem, I have generated the mesh using gambit,
I followed the steps to convert the mesh is:
1) fluent3DMeshToFoam
2) createPatch for my cyclic boundary

I am able to see the mesh in paraView.

Now I want to use MRFSimpleFoam.
for my sample case I used blockMesh, there I dindt get any problem to run MRFSimpleFoam, because blockMesh creates cellSet cellZone and all the necessary files.

my questions are:

1) Do we need to define the regions in the gambit itself?
or can we create the cellSet and cellZone using some other option?

2) If it is possible to use some other option, what are the option?
can you guys please explain, what are the steps I need to do to make my case to run?

thanks,
Sivakumar
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Old   October 12, 2012, 22:28
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I have never used gambit so cannot comment here..
I think your problem is being caused by the way that mesh boundaries are being labeled?

I think this was the problem for me. Is it possible to remove all patch names etc from the gambit mesh and only import the mesh into OF? Then use autoPatch to name the patches individually then createPatch to make your cyclic patches?
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Old   October 13, 2012, 03:54
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Hi Matt,
thanks for reply, I am also suspecting the same like you. but I dont have any idea about generating only mesh file in gambit, because I am 3 weeks old for gambit.
I will try your idea then i will let you know if it works.

thanks matt,

Sivakumar
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