Get the area of each wall using to source term only in boundary cell

qi.yang@polimi.it · September 2, 2020, 07:36

Hi guys,

I defined a Uw which has the same size of the total cell numbers to save the velocity only in the boundary cell. Due to the fact that the source term I need to use is Uw times the area of corresponding wall. Thus, I defined a patchArea (patchArea[faceI] = mesh.magSf().boundaryField()[patchID][faceI]

used to save that area. Note that the size of patchArea is also same as Uw, however the index is not corresponding to each other. Is there a way to rearrange the order of patchArea, to make the index consistent with Uw? I uploaded a output log file here, as you can see, the index with a non-zero value in Uw means the wall cell index. But the order in patchArea needs to be modified.
Thanks for your attention.

qi.yang@polimi.it · September 2, 2020, 08:02

This is the mesh (blockMesh and extrudeMesh) I used to make a simple calculation.

Wenyuan · September 2, 2020, 10:47

Hi,

In order to assign values to patchArea, you need to use the index for the cell adjacent to faceI, not faceI.

qi.yang@polimi.it · September 2, 2020, 11:23

Thanks for reply. I understood your point. the problem is that when I use mesh.magSf().boundaryField()[patchID][faceI] to get the area, the index is not consistent with that of cell.

Quote:

Originally Posted by Wenyuan

Hi,

In order to assign values to patchArea, you need to use the index for the cell adjacent to faceI, not faceI.

Wenyuan · September 2, 2020, 11:31

Assume cellI is a near-wall cell, faceI is the corresponding face on the wall patch. patchArea[faceI] will assign the surface area to a cell with faceI being its index. What you want is patchArea[cellI].

qi.yang@polimi.it · September 2, 2020, 11:52

I used the following code however the patchArea is wrong.
forAll(myPatch,cellI)
{
forAll(myPatch, faceI)
{

patchArea[cellI] = mesh.magSf().boundaryField()[patchID][faceI];

}
}

Code:

patchArea=dimensions      [0 2 0 0 0 0 0];

internalField   nonuniform List<scalar> 
120
(
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0.00382683433
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
)
;

boundaryField
{
    wall
    {
        type            calculated;
        value           uniform 0;
    }
    inlet
    {
        type            calculated;
        value           uniform 0;
    }
    outlet
    {
        type            calculated;
        value           uniform 0;
    }
}


Uw=dimensions      [0 1 -1 0 0 0 0];

internalField   uniform (0 0 0);

boundaryField
{
    wall
    {
        type            calculated;
        value           uniform (0 0 0);
    }
    inlet
    {
        type            calculated;
        value           uniform (0 0 0);
    }
    outlet
    {
        type            calculated;
        value           uniform (0 0 0);
    }
}

Note that the size of left matrix and right is not the same.

Quote:

Originally Posted by Wenyuan

Assume cellI is a near-wall cell, faceI is the corresponding face on the wall patch. patchArea[faceI] will assign the surface area to a cell with faceI being its index. What you want is patchArea[cellI].

Wenyuan · September 2, 2020, 12:12

There is a method called faceCells() that gives you a list of indices of patch-adjacent cells. You call this on the wall patch and get a list, say, cellList. Then cellList[faceI] is the index for the cell adjacent to faceI.

By the way, how did you calculate the Uw field?

qi.yang@polimi.it · September 2, 2020, 12:17

Code:

const fvPatchList& patches = mesh.boundary();
labelList wallList;
wallList.clear();

    forAll(patches, patchi)
    {
        const fvPatch& curPatch = patches[patchi];
        if (isType<wallFvPatch>(curPatch))
        {
            forAll(curPatch, facei)
            {
                label faceCelli = curPatch.faceCells()[facei];
                wallList.resize(wallList.size()+1);
                wallList[wallList.size()-1]=faceCelli;
            }
        }
    }
    
    forAll(wallList,i)  
    {
    Uw[wallList[i]] = U1[wallList[i]];
    }

Quote:

Originally Posted by Wenyuan

There is a method called faceCells() that gives you a list of indices of patch-adjacent cells. You call this on the wall patch and get a list, say, cellList. Then cellList[faceI] is the index for the cell adjacent to faceI.

By the way, how did you calculate the Uw field?

Wenyuan · September 2, 2020, 12:32

First, your code can be simplified to

Code:

const fvPatchList& patches = mesh.boundary();

    forAll(patches, patchi)
    {
        const fvPatch& curPatch = patches[patchi];
        if (isType<wallFvPatch>(curPatch))
        {
            forAll(curPatch, facei)
            {
                label faceCelli = curPatch.faceCells()[facei];
                Uw[faceCelli] = U1[faceCelli];
            }
        }
    }

The following line assigns the U1 value at faceCelli to Uw at the same cell.

Code:

                Uw[faceCelli] = U1[faceCelli];

So you can do similar things to patchArea by substituting Uw with patchArea and using the face area on the right hand side.

qi.yang@polimi.it · September 2, 2020, 12:41

I already tried this code but it was not right.
myArea[wallList[i]]=mesh.magSf().boundaryField()[wallList[i]];
I think the point is the size of left and right.
Assign the value of velocity at wall without problem due to Uw and U1 has same size.

Quote:

Originally Posted by Wenyuan

First, your code can be simplified to

Code:

const fvPatchList& patches = mesh.boundary();

    forAll(patches, patchi)
    {
        const fvPatch& curPatch = patches[patchi];
        if (isType<wallFvPatch>(curPatch))
        {
            forAll(curPatch, facei)
            {
                label faceCelli = curPatch.faceCells()[facei];
                Uw[faceCelli] = U1[faceCelli];
            }
        }
    }

The following line assigns the U1 value at faceCelli to Uw at the same cell.

Code:

                Uw[faceCelli] = U1[faceCelli];

So you can do similar things to patchArea by substituting Uw with patchArea and using the face area on the right hand side.

Wenyuan · September 2, 2020, 12:47

Please forget wallList.
Use facei to get face area.

qi.yang@polimi.it · September 2, 2020, 13:12

I solved the problem. Thanks a lot.

Quote:

Originally Posted by Wenyuan

Please forget wallList.
Use facei to get face area.

September 2, 2020, 12:32		#9
Wenyuan New Member Wenyuan Fan Join Date: Mar 2017 Posts: 27 Rep Power: 9	First, your code can be simplified to Code: const fvPatchList& patches = mesh.boundary(); forAll(patches, patchi) { const fvPatch& curPatch = patches[patchi]; if (isType<wallFvPatch>(curPatch)) { forAll(curPatch, facei) { label faceCelli = curPatch.faceCells()[facei]; Uw[faceCelli] = U1[faceCelli]; } } } The following line assigns the U1 value at faceCelli to Uw at the same cell. Code: Uw[faceCelli] = U1[faceCelli]; So you can do similar things to patchArea by substituting Uw with patchArea and using the face area on the right hand side.

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September 2, 2020, 10:47		#3
Wenyuan New Member Wenyuan Fan Join Date: Mar 2017 Posts: 27 Rep Power: 9	Hi, In order to assign values to patchArea, you need to use the index for the cell adjacent to faceI, not faceI.

September 2, 2020, 11:31		#5
Wenyuan New Member Wenyuan Fan Join Date: Mar 2017 Posts: 27 Rep Power: 9	Assume cellI is a near-wall cell, faceI is the corresponding face on the wall patch. patchArea[faceI] will assign the surface area to a cell with faceI being its index. What you want is patchArea[cellI].

September 2, 2020, 12:12		#7
Wenyuan New Member Wenyuan Fan Join Date: Mar 2017 Posts: 27 Rep Power: 9	There is a method called faceCells() that gives you a list of indices of patch-adjacent cells. You call this on the wall patch and get a list, say, cellList. Then cellList[faceI] is the index for the cell adjacent to faceI. By the way, how did you calculate the Uw field?

September 2, 2020, 12:47		#11
Wenyuan New Member Wenyuan Fan Join Date: Mar 2017 Posts: 27 Rep Power: 9	Please forget wallList. Use facei to get face area.