[liviaadi]

Dear Foamers,

I would like to calculate the shear stresses in a laminar simulation of an open channel flow. I am using the interFoam solver with OF 4.1
I was trying to postProcess and calculate grad(U). But I have this error:

Executing functionObjects
--> FOAM Warning :
From function bool Foam::functionObjects::regionFunctionObject::store (Foam::word&, const Foam::tmp<T>&, bool) [with ObjectType = Foam::GeometricField<Foam::Tensor<double>, Foam::fvPatchField, Foam::volMesh>]
in file /home/ubuntu/OpenFOAM/OpenFOAM-4.1/src/OpenFOAM/lnInclude/regionFunctionObjectTemplates.C at line 61
Cannot store cache-able field with the named used in the cache.
Either choose a different name or cache the field and use the 'writeObjects' functionObject.
--> FOAM Warning : functionObject grad: Cannot find required field U

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I know that there are many threads on this topic and I have read something, but still I did not solve this problem.

Can anyone help me ?
Thanks in advance.

[floquation]

Which command exactly did you type?

Did you include something like "-field U" or "-fields (U)" in the argument list, such that the utility knows that it should read U from file?

[liviaadi]

Hi,

after the simulation:

interFoam -postProcess -func "grad(U)".

I tried also to do it in runtime by typing in the ControlDict file:

functions
{

grad
{
type grad(U);
libs ("libFVFunctionObjects.so");
fieldName "U";
resultName "gU";
}

}

but I have always the same error.
What would you suggest ?

Thanks a lot!

[uckmhnds]

this is too late answer. though it would be helpful for others. the function should be like;

functions
{

gradient /could be anything you name
{
type grad;
libs ("libfieldFunctionObjects.so");
field U;
writeControl writeTime;
}

}

[ms.hashempour]

just type:

postProcess -func "grad(U)"