[openfoammaofnepo]

Dear All,

Due to some reason, I need to output the boundary face centroid coordinates. The output code is as follows:

#include <fstream>
#include <iostream>
#include "fvMesh.H"
#include "Time.H"
//#include "primitiveMesh.H"
#include "argList.H"
#include "polyMesh.H"
using namespace std;
int main(int argc, char *argv[])
{
    # include "setRootCase.H"
    # include "createTime.H"
    # include "createPolyMesh.H"
    using namespace Foam;

    Info<< "Output face centres of given patch\n" << endl;
    //change the patch name to your boundary name
    label patchI = mesh.boundaryMesh().findPatchID("outlet");
    label iFace = 3600;

    scalar x[iFace];
    scalar y[iFace];
    scalar z[iFace];
    forAll(mesh.boundaryMesh()[patchI].faceCentres(), faceI)
    {
        x[faceI] = mesh.boundaryMesh()[patchI].faceCentres()[faceI].x();
        y[faceI] = mesh.boundaryMesh()[patchI].faceCentres()[faceI].y();
        z[faceI] = mesh.boundaryMesh()[patchI].faceCentres()[faceI].z();
//      Info<<faceI<<" "<<x[faceI]<<" "<<y[faceI]<<" "<<z[faceI]<<" "<<endl;
    }

    //output the file
    Info<<"Output the coordinates of face centers..."<<endl;
    ofstream o_file;
    o_file.open("OUTLET.txt");


    if(o_file.is_open())
    {
        for(label i=1;i<=iFace;i++)
        {
           o_file<<x[i]<<" "<<y[i]<<" "<<z[i]<<" "<<endl;
        }
    }
    o_file.close();

}

For other one to do the tests, I also present the file and option here:

file:

PatchFaceCenter.C

EXE = $(FOAM_USER_APPBIN)/PatchFaceCenter

options:

EXE_INC = \
    -I$(LIB_SRC)/finiteVolume/lnInclude

EXE_LIBS = \
    -lfiniteVolume \
    -lgenericPatchFields

Let's take the case in the following path as an example:

/home/user/OpenFOAM/OpenFOAM-2.1.1/tutorials/combustion/fireFoam/les/smallPoolFire3D

Using the above code, I got the list of centroid coordinate of each face. For example, for the boundary face base in it, they are:

.........
0.491667 0 0.391667
0.491667 0 0.408333
0.491667 0 0.425
0.491667 0 0.441667
0.491667 0 0.458333
0.491667 0 0.475
0.491667 0 0.491667
0.00289776 0 0

It is very strange that in the last row of the above list, the coordinate (0.00289776 0 0) is in it. Obviously this point is not on that face.

Then I use the above code to extract the face centroids of another boundary face outlet, the results are as follows:

......
0.491667 1 0.391667
0.491667 1 0.408333
0.491667 1 0.425
0.491667 1 0.441667
0.491667 1 0.458333
0.491667 1 0.475
0.491667 1 0.491667
0.00289776 0 0

Again the point (0.00289776 0 0) appears in the last and in the last row. Actually it is not on that face.

I checked the boundary face centroid coordinate of my other meshes and found that the point (0.00289776 0 0) is always there in the last row of the face centroid list.

Could anyone tell me what happen to the face centroid coordinates?

Thank you so much.

OFFO

[wyldckat]

Greetings OFFO,

It seems to me that you need to study more about C/C++.
The reason why I say this, for example, is because of this piece of code:

    label iFace = 3600;

    scalar x[iFace];
    scalar y[iFace];
    scalar z[iFace];

This means that you're allocating a fixed size for the arrays x,y and z of 3600 entries only. If your patch has more than 3600 faces, then it's only natural that your program will not work as intended.

In addition, your "for" loop for saving to the file is starting at 1 when it should start at 0, namely it should be like this:

for(label i=0;i<iFace;i++)

If this wasn't enough, for example, the following code is very risky:

x[faceI] = mesh.boundaryMesh()[patchI].faceCentres()[faceI].x();

You're assuming that "faceI" will start at 0 or 1.

When programming, never assume anything. You should always try to diagnose, assess and confirm if things are working as intended, not as you hope they should.

Best regards,
Bruno

[openfoammaofnepo]

Dear Bruno,

After changing to the following, it works now:

for(label i=0;i<iFace-1;i++)

So the (0.00289776 0 0) are the numbers generated randomly by the code?

Thank you so much for your suggestion.

[wyldckat]

Originally Posted by openfoammaofnepo

After changing to the following, it works now:

for(label i=0;i<iFace-1;i++)

Not reading/studying a good manual can get you into trouble
C/C++ arrays are 0 indexed. Which means that an array of size 3600, will start in 0 and end in 3599.
Your "for" loop is ordered to run only while "i<iFace-1" is true. In other words, only while "i<3599", which means that you are not accessing the position "3599", because the last valid iteration is "3598<3599".

Originally Posted by openfoammaofnepo

So the (0.00289776 0 0) are the numbers generated randomly by the code?

You were accessing the position "3600" in the arrays, when "3599" was the last valid position. What probably happened is that the last iteration was in fact accessing the first value on the next array, and was actually outputting the same values as if you were using this code:

y[0] z[0] garbage

I believe that most Linux Distributions will provide RAM all set to "0" for an application to use, which is why the garbage entry is 0.
If you were using a more restrictive Operating System or security measure, the application should have crashed when it tried to access outside of the array size.

[openfoammaofnepo]

Thank you.

About your first comment, I double check my code, it is like the following (i<=iFace-1):

for(label i=0;i<=iFace-1;i++)

So it give me complete 3600 face centeriod coordinates now.

Thank you very much for your help.

[openfoammaofnepo]

Dear Bruno,

In openfoam, is there any defined class to write out the data into a txt file or other kind of external files? In the code I posted here, I use:

ofstream o_file;
    o_file.open("OUTLET.txt");

I was wondering if there is any better appraoches. Thank you.

OFFO

[wyldckat]

Hi OFFO,

There are many ways to solve a problem. But most of the times, what matters is that the problem is solved and not how it is solved... but then again, the "end doesn't justify the means", but still... if it works for you, why spend more time searching for another solution?

This to say that at this moment I can't remember any better way to do this. To do so I would have to look at OpenFOAM's source code and find examples on this could be done.
Therefore, I'll delegate that task to you and suggest that you study the source code examples that are located at the path given by this command:

echo $FOAM_APP/test

If you prefer to use your browser and search online: https://github.com/OpenFOAM/OpenFOAM...lications/test

Happy studying! Best regards,
Bruno