[MoeCFD]

Hi All,

I am working with an STL file. I used surfaceCheck to evaluate the quality of the surface. The surfaceCheck utility produced badFaces file. The file has 7 bad faces. The goal is that I want to visualize those bad faces so I can fix them therefore I used surfaceSubset to generate a new STL of those faces as shown in the code below. However, I am getting the following error after executing:

surfaceSubset badFaces edited_pore_scaled_Zflow.stl badface.stl

/*---------------------------------------------------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1706                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
Build  : v1706
Arch   :  
Date   : 
Time   : 
Host   :
PID    : 
Case   :
nProcs : 1
sigFpe : Enabling floating point exception trapping (FOAM_SIGFPE).
fileModificationChecking : Monitoring run-time modified files using timeStampMaster (fileModificationSkew 10)
allowSystemOperations : Allowing user-supplied system call operations

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
Reading dictionary "badFaces" ...


--> FOAM FATAL IO ERROR:
Expected a '(' or a '{' while reading List, found on line 5 the label 75112

file: badFaces at line 5.

    From function char Foam::Istream::readBeginList(const char*)
    in file db/IOstreams/IOstreams/Istream.C at line 134.

FOAM exiting

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  2.1.x                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      surfaceSubsetDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

// Select triangles by label
faces #include "badFaces";

// Select triangles using given points (local point numbering)
localPoints ( );

// Select triangles using given edges
edges ();

// Select triangles (with face centre) inside box
zone
(
/*    (0      -10000  -10000)
    (0   10000  10000)*/
);

// Select triangles (with face centre) inside or outside of another surface.
// (always selects triangles that are 'on' other surface)
surface
{
    name "edited_pore_scaled_Zflow.stl";
    outside     yes;
}

// Extend selection with edge neighbours
addFaceNeighbours no;

// Invert selection
invertSelection false; // when true-it will remove badfaces and write the good part only

// ************************************************************************* //

[alexeym]

Hi,

Command should be

surfaceSubset surfaceSubsetDict edited_pore_scaled_Zflow.stl bad_faces.stl

Where surfaceSubsetDict could be either as you have posted, or just

FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      surfaceSubsetDict;
}

faces #include "badFaces";

localPoints ();

edges ();

zone ();

addFaceNeighbours no;

invertSelection false;

[Owais Shabbir]

Hi,


I want to know after finding and visualizing these badFaces, how could I get rid of them?



Thanks.

[alexeym]

Hi,

It depends on available tools. For example, MeshLab is quite good at removing bad faces. If you need to just remove these badFaces, you can edit STL with Gmsh (this way it is just select and press delete). Or you can use less picky mesher to create tetrahedral mesh from the surface with badFaces and then save outer surface of generated mesh.

[Owais Shabbir]

Hi Alexey,



I have tried LabMesh. When I try the 'repair/clean' filter; there is no option for precisely badFaces. Could you guide me which faces in Labmesh represent badFaces?


I also have GMSH but again I lack the knowledge of how to select the badFaces.

[alexeym]

You visualize your badFaces with let's say ParaView and then select them in Gmsh with a mouse? Or there are thousands of such faces? IIRC there is a possibility to select faces using IDs, so you can select them using values from badFaces file.

In MeshLab you can not supply your badFaces, yet there are software's own criteria for selection of low quality faces.

Also it is not quite clear what do you mean by "get rid of them"?

[Owais Shabbir]

Hi Alexey,

To my understanding (which is basic) badFaces, illegalFaces and problemFaces lead to bad results of simulations. Or I understood it wrong?

That's why I thought of deleting or getting rid of them.

Thanks

[alexeym]

Well...

Initial question was about STL surface, which was used to generate mesh. Those badFaces lead to difficulties during mesh generation. And has (almost) nothing to do with simulation per se.

Now to the question of "getting rid". Face is just a connectivity. OK, you have deleted a face, now you have got a hole in your surface (maybe not if the face was, for example, internal extra-face, or erroneously generated face with zero area).

There are many different types of bad faces. Certain you can simply delete. For certain you need to modify points of you surface. It would be easier if you create new post with illustrations (your surface with coloured badFaces).