[Samuel Twain]

Dear all:
I am wondering how openfoam calculates y (not yPlus) which is (maybe) the shorstest distance from the cell center to the wall. And I find a function nearestPoint() which maybe is to calculate y as following:
Foam::scalar Foam::cellDistFuncs::smallestDist
(
...
) const
{
...
for (label wallFacei = 0; wallFacei < nWallFaces; wallFacei++)
{
label patchFacei = wallFaces[wallFacei];

pointHit curHit = patch[patchFacei].nearestPoint(p, points);

if (curHit.distance() < minDist)
{
minDist = curHit.distance();
minFacei = patch.start() + patchFacei;
}
}

return minDist;
}
But the source code of nearestPoint() is difficult for me to find out how nearestPoint() calculates. Could anyone please explain how nearstPoint() works or share the materials related to it?
Each reply will be appreciated.
Thanks
Samuel

[einstein_zee]

Originally Posted by Samuel Twain

Dear all:
I am wondering how openfoam calculates y (not yPlus) which is (maybe) the shorstest distance from the cell center to the wall. And I find a function nearestPoint() which maybe is to calculate y as following:
Foam::scalar Foam::cellDistFuncs::smallestDist
(
...
) const
{
...
for (label wallFacei = 0; wallFacei < nWallFaces; wallFacei++)
{
label patchFacei = wallFaces[wallFacei];

pointHit curHit = patch[patchFacei].nearestPoint(p, points);

if (curHit.distance() < minDist)
{
minDist = curHit.distance();
minFacei = patch.start() + patchFacei;
}
}

return minDist;
}
But the source code of nearestPoint() is difficult for me to find out how nearestPoint() calculates. Could anyone please explain how nearstPoint() works or share the materials related to it?
Each reply will be appreciated.
Thanks
Samuel

Hii there,

I just looked at the code and it seems to be messy to track stuff. However, I may give you at least what I understood at first glance . The version of function nearestPoint with 2 arguments of point and pointField can be found here (https://github.com/OpenFOAM/OpenFOAM...Intersection.C). You should follow the code from line 198. From what I understood, the aim here is to do the calculations with an arbitrary point and a triangulated face. So, if your face is already a triangle it will do the calculations immediately, and if not it will try to triangulate the face first and then do the calculations. Note that here face means each of single faces which constructs the whole wallFace.

And the piece of code I think you are interested to see is this one (https://github.com/OpenFOAM/OpenFOAM...le/triangleI.H). You may follow the code from line 516 to see how this calculation is done with an arbitrary point and a triangulated face. This ref. is also given there (Real-time collision detection, Christer Ericson, 2005, p136-142)
Hope this helps...

[Samuel Twain]

Originally Posted by einstein_zee

Hii there,

I just looked at the code and it seems to be messy to track stuff. However, I may give you at least what I understood at first glance . The version of function nearestPoint with 2 arguments of point and pointField can be found here (https://github.com/OpenFOAM/OpenFOAM...Intersection.C). You should follow the code from line 198. From what I understood, the aim here is to do the calculations with an arbitrary point and a triangulated face. So, if your face is already a triangle it will do the calculations immediately, and if not it will try to triangulate the face first and then do the calculations. Note that here face means each of single faces which constructs the whole wallFace.

And the piece of code I think you are interested to see is this one (https://github.com/OpenFOAM/OpenFOAM...le/triangleI.H). You may follow the code from line 516 to see how this calculation is done with an arbitrary point and a triangulated face. This ref. is also given there (Real-time collision detection, Christer Ericson, 2005, p136-142)
Hope this helps...

Thanks a lot!!! Following your suggestion, I looked at the code and looked up to "Real-time collision detection". I think I have understood what nearestPoint() does. nearestPoint() return the point on the triangulated face which is nearest to a given point( that used to be the cell center). The nearest point might be the vertex, lie on the edge or lie in the face( this algorithm can be found in "Real-time collision detection" ). If this face isn't triangulated. It will be decomposed to some triangulated faces.
Thank you again!