[keepfit]

Dear Foamers,

suppose I know the point cloud (point mass particles) positions in the CFD domain. I want to know the velocities at the point mass particle locations.

Obvious we need to interpolate point field value in cell where the point particle is located. In my case, the U field is known, and the mesh is uniform. I could simply code a Trilinear interpolation scheme (or inverse distance weighting), however I suppose these algorithms already exist in OpenFOAM.

The thing is in OF, it is so complicated to fine-tune some functions, as the right low-level API is hard to find (most hated), and hard to use. what I did so far:

#include "interpolationCellPoint.H"
#include "interpolationCellPointFace.H"

....


autoPtr <Foam::interpolation<vector>> U_interp;

 Uf_interp = Foam::interpolation<vector>::New("cellPoint", U);
 //Uf_interp.reset(Foam::interpolation<vector>::New("cellPoint", U).ptr());

Suppose the point at vector p(x, y, z) is inside cell_i: so the interpolated velocity at p should be like:

Foam::vector U_p = U_interp.interpolate(p, cell_i);

Nevertheless, it seems that interpolate function does not exit.

class Foam::autoPtr<Foam::interpolation<Foam::Vector<dou ble> > >’ has no member named ‘interpolate’

But the function interpolate is clearly defined in code (line 84): What is the possible reason to for this error? I alwalys had headache to deal with OF's overly-complicated low-level functions or data structure (not modern C++ built-in ones), even after years of CFD/OF experience.

Any suggestions would be appreciated!

Update 1: tried a new method:

  const objectRegistry& db = mesh_.thisDb();
  const IOdictionary& fvSchemes = db.lookupObject<IOdictionary>("fvSchemes");
  dictionary interpolationSchemes = fvSchemes.subDict("interpolationSchemes");

  Uf_interp = Foam::interpolationCellPoint<vector>::New(interpolationSchemes, coupling_world.UField());

... 
vector Up = Uf_interp().interpolate(p, cell_i);

still no success. First error says "U" is missing in interpolationSchemes, when I add "U linear", and it says "flux(U)" is missing, in this case linear is no longer suitable. I can't believe I am stuck in this simple issue. Using OF with low level functions is really struggling.

Update 2: Can't believe so much time wasted on this simple issue (complexity-wise). Will implement Trilinear interpolation scheme for point field value at given position / cell-ID (uniform mesh), this might save my day!

[einstein_zee]

Hi there, Can you try this one "U_interp().interpolate(p, cell_i)".

[s1291]

Maybe it is useful to take a look to some function objects that use the interpolation, e.g.:

$FOAM_SRC/functionObjects/field/streamlines/streamlinesParticle.H

or

$FOAM_SRC/functionObjects/field/streamlines/streamlines.C

[keepfit]

Originally Posted by einstein_zee

Hi there, Can you try this one "U_interp().interpolate(p, cell_i)".

Thanks! I added

dictionary interpolationDict = mesh.solutionDict().subDict("interpolationSchemes");
Uf_interp = Foam::interpolationCellPoint<vector>::New(interpolationDict, coupling_world.UField());

and tried your method to add "()", seems still not working

Entry 'interpolationSchemes' not found in dictionary "... mycase/system/fvSolution"

"interpolationSchemes" does exist in system/fvSchemes, why OF looking for the keyworld in fvSolution?

[keepfit]

Originally Posted by s1291

Maybe it is useful to take a look to some function objects that use the interpolation, e.g.:

$FOAM_SRC/functionObjects/field/streamlines/streamlinesParticle.H

or

$FOAM_SRC/functionObjects/field/streamlines/streamlines.C

Thanks for the hint. Again, i have to deal with the " particle::trackingData" API. Seems in OF some simplest functionalities are buried so deeply so that u have go through A LOT of digging up. . All I need is to obtain interpolated field at position p within given cell-i.

[einstein_zee]

Originally Posted by keepfit

Thanks! I added

dictionary interpolationDict = mesh.solutionDict().subDict("interpolationSchemes");
Uf_interp = Foam::interpolationCellPoint<vector>::New(interpolationDict, coupling_world.UField());

and tried your method to add "()", seems still not working

Entry 'interpolationSchemes' not found in dictionary "... mycase/system/fvSolution"

"interpolationSchemes" does exist in system/fvSchemes, why OF looking for the keyworld in fvSolution?

It looks in fvSolution because you told him to . You are using "mesh.solutionDict()" and that is the solution dictionary("fvSolution")... you may try it with mesh.schemesDict() instead.

[keepfit]

Originally Posted by einstein_zee

It looks in fvSolution because you told him to . You are using "mesh.solutionDict()" and that is the solution dictionary("fvSolution")... you may try it with mesh.schemesDict() instead.

thanks for the tip. I actually did it in Update 1. However, the error is:

Entry 'U' not found in dictionary "xxx/system/fvSchemes.interpolationSchemes"

when I change interpolationSchemes to:

interpolationSchemes
{
    default         linear;
    U               cellPoint;
}

It seems okay. I need to test whether the interpolate(pos, cell_i) function works or not.

Update 1:

Fluid velocity at point particle location seems not interpolated correctly by

Foam::vector U_p = U_interp.interpolate(p, cell_i);

cellPoint changed to cellPointFace, the interpolated field at point p seems not right as well, according to point field values on the cell_i's vertices (U_p < every cell_point field value!).

[Saeb-sahand]

How interpolate results in cell points (nodes)
For instace, how interpolate scalareField (P,T) in cell points?