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-   OpenFOAM Native Meshers: snappyHexMesh and Others (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/)
-   -   eMesh file meaning in SnappyHexMesh (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/119263-emesh-file-meaning-snappyhexmesh.html)

woodwick June 13, 2013 02:08

eMesh file meaning in SnappyHexMesh
 
I was running the motorBike tutorial and I noticed that in the directory:
/tutorials/incompressible/simpleFoam/motorBike/constant/triSurface
there is a file: motorBike.eMesh
What is the role and content of an eMesh file?
I understood (correct me if I'am wrong) that the motorBike.obj.gz gives the STL geometry, the triangular surface mesh that Snappy uses to put and cut his hexa elements around. But eMesh what does it do? What is its content? I am not even able to open it with gedit :(

woodwick June 13, 2013 03:15

additional observation:
opening snappyHexMeshDict you can find :

Code:

    // Explicit feature edge refinement
    // ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

    // Specifies a level for any cell intersected by its edges.
    // This is a featureEdgeMesh, read from constant/triSurface for now.
    features
    (
        {
            file "motorBike.eMesh";
            level 0;
        }
    );

so explicit feature edge refinement...
does it mean eMesh = edgeMesh , that is: motorBike.eMesh is the file containing the list of edges of the geometry? maybe coming from surfaceFeatureExtract? mumble mumble

Eloise June 13, 2013 03:36

Hi,

you are right :) It is the file that contains the feature edges of your geometry and that is created by the surfaceFeatureExtract utility. In the snappyHexMeshDict, you specify the level of refinement needed on those edges.

Regards,
Elo´se

elvis July 2, 2013 12:32

Hi,

i tried to visulize which values would make sense via slider
http://www.cfd-online.com/Forums/ope...reextract.html

Artur July 10, 2013 04:53

You can also visualise it in paraview by using:

Code:

surfaceFeatureExtract
 surfaceFeatureConvert constant/triSurface/file_name.eMesh other_file_name.obj

and then simply opening it paraview.

s.m August 19, 2013 09:24

includedAngle ?
 
Quote:

Originally Posted by Artur (Post 438861)
You can also visualise it in paraview by using:

Code:

surfaceFeatureExtract
 surfaceFeatureConvert constant/triSurface/file_name.eMesh other_file_name.obj

and then simply opening it paraview.

Dear Artur,
when we want convert the *.stl file to *.eMesh one, we execute
"surfaceFeatureExtract -includedAngle 150 -writeObj constant/triSurface/foil2D.stl airfoil"
my question is about "includedAngle 150" ?
what is it? and what is the difference between the *eMesh file that is gained from "includedAngle 150" and the one that is gained by "includedAngle 180" ?

Thank you very much:)

Artur August 19, 2013 09:32

Depends on the version you run, I think from 2.0 or something like that it is governed by a dictionary instead of being passed options from the command line.

Include angle tells the function what angle between the faces has to be in order to constitute an edge, so 0 would mean there are no edges at all and 180 would be that a flat surface is an edge as far as I understand it.

s.m August 19, 2013 09:46

3 Attachment(s)
i excute the surfaceFeatureExtract with includedAngle 180 & includeAngle 150 & includedAngle 50
here is the results.

Artur August 19, 2013 10:12

Yup, that's what I get for airfoil sections as well. You can see that in the first case it picks up pretty much every edge of the .stl triangles and the smaller the include angle gets the more defined the edge has to be in order to be picked up by the algorithm.

s.m August 19, 2013 11:56

Quote:

Originally Posted by Artur (Post 446652)
Yup, that's what I get for airfoil sections as well. You can see that in the first case it picks up pretty much every edge of the .stl triangles and the smaller the include angle gets the more defined the edge has to be in order to be picked up by the algorithm.

As i understand the includedAngle 180 is better for this case,because it involve more edge that the other includedAngle e.g 150
do i get it right?

Artur August 19, 2013 12:06

I think there is no definite answer to your question. It's not certain that including all the possible features will yield a "good" mesh in the end.

Looking at your screenshots I'd probably go with the intermediate value because it represents the trailing edge and the section profiles at either end well but will not mess around with your mesh anywhere else. However, this is just my personal opinion and may not be correct.

s.m August 19, 2013 12:09

Quote:

Originally Posted by Artur (Post 446697)
I think there is no definite answer to your question. It's not certain that including all the possible features will yield a "good" mesh in the end.

Looking at your screenshots I'd probably go with the intermediate value because it represents the trailing edge and the section profiles at either end well but will not mess around with your mesh anywhere else. However, this is just my personal opinion and may not be correct.

"intermediate value" mean includedAngle 150?

l_r_mcglashan August 19, 2013 12:32

FYI, you can also use the "FeatureEdge" filter in paraview to help you choose an appropriate includedAngle.

Artur August 20, 2013 04:01

Quote:

Originally Posted by l_r_mcglashan (Post 446712)
FYI, you can also use the "FeatureEdge" filter in paraview to help you choose an appropriate includedAngle.

Good to know that, thanks for sharing!

@ s.m. : Yes, by intermediate I mean the middle one from the 3 you've shown, i.e. 150.

s.m August 20, 2013 06:35

Quote:

Originally Posted by l_r_mcglashan (Post 446712)
FYI, you can also use the "FeatureEdge" filter in paraview to help you choose an appropriate includedAngle.

Dear Laurence,Thank you for your suggestion:)

i don't know how to use this filter, and how should we know the proper includedAngle by using it.
could you please explain it more,
Thank you again.


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