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Why is access to turbulence fields provided as const?

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Old   December 18, 2019, 06:27
Default Why is access to turbulence fields provided as const?
  #1
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Rishikesh
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Short version:
In OpenFOAM-6, I am trying to work on some mesh-to-mesh interpolation of fields (using meshToMesh.H -> imDirect). The turbulence variable return const tmp access to members, which lead to problem in interpolation. How should I go about it?


Details:

For the kEpsilon model, the turbulence variables k and epsilon, members of turbulenceModel (src/TurbulenceModels/turbulenceModels/RAS), are protected:

Code:
            volScalarField k_;
            volScalarField epsilon_;
These can be accessed through the functions:
Code:
//- Return the turbulence kinetic energy
         virtual tmp<volScalarField> k() const
        {
            return k_;
        }

        //- Return the turbulence kinetic energy dissipation rate
        virtual tmp<volScalarField> epsilon() const
        {
            return epsilon_;
        }
So, I try to access them for interpolation as so:
Code:
//source

    tmp<volScalarField> tksrc = turbulenceFluid[i].k();
    volScalarField& ksrc = tksrc.ref();
//tgt

    tmp<volScalarField> tktgt = turbulenceFluid[1-i].k();
    volScalarField& ktgt = tktgt.ref();
and similarly for epsilon.

Because of the use of tmp and const nature of access, appears to cause troubles when I try to interpolate the fields from one mesh to the other.
Code:
Attempt to acquire non-const reference to const object from a tmp<N4Foam14GeometricFieldIdNS_12fvPatchFieldENS_7volMeshEEE>tionThermoMoleFractions
sets
surfaces
)
My question is should I remove the const from the function, virtual tmp<volScalarField> const k() ? Or is their some reasoning behind putting it there that needs to be considered? Is there a correct way to implement access to these so that finally a volScalarField to volScalarField interpolation can be carried out by manipulating these datatypes correctly, without having to add additional non-const access function to the kEpsilon model? Would much appreciate feedback on this!!


PS: The idea of adding non-const access function comes, because I also did interpolation of volume fraction fields (src/transportModels/twoPhaseMixture model), but there the reference to alpha fields is returned via two methods, which allows manipulation via interpolation.


Code:
        //- Return the phase-fraction of phase 1
        const volScalarField& alpha1() const
        {
            return alpha1_;
        }

        //- Return the phase-fraction of phase 1
        volScalarField& alpha1()
        {
            return alpha1_;
        }
PS: the mapping operation is elementary, going as:
Code:
    mapF2C.mapSrcToTgt
    (
        epsilonsrc,
        plusEqOp<scalar> (),
        epsilontgt
    );
It seems to work correctly for other fields.
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Old   December 18, 2019, 08:49
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  #2
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Santiago Lopez Castano
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Quote:
Originally Posted by mrishi View Post
Short version:
In OpenFOAM-6, I am trying to work on some mesh-to-mesh interpolation of fields (using meshToMesh.H -> imDirect). The turbulence variable return const tmp access to members, which lead to problem in interpolation. How should I go about it?


Details:

For the kEpsilon model, the turbulence variables k and epsilon, members of turbulenceModel (src/TurbulenceModels/turbulenceModels/RAS), are protected:

Code:
            volScalarField k_;
            volScalarField epsilon_;
These can be accessed through the functions:
Code:
//- Return the turbulence kinetic energy
         virtual tmp<volScalarField> k() const
        {
            return k_;
        }

        //- Return the turbulence kinetic energy dissipation rate
        virtual tmp<volScalarField> epsilon() const
        {
            return epsilon_;
        }
So, I try to access them for interpolation as so:
Code:
//source

    tmp<volScalarField> tksrc = turbulenceFluid[i].k();
    volScalarField& ksrc = tksrc.ref();
//tgt

    tmp<volScalarField> tktgt = turbulenceFluid[1-i].k();
    volScalarField& ktgt = tktgt.ref();
and similarly for epsilon.

Because of the use of tmp and const nature of access, appears to cause troubles when I try to interpolate the fields from one mesh to the other.
Code:
Attempt to acquire non-const reference to const object from a tmp<N4Foam14GeometricFieldIdNS_12fvPatchFieldENS_7volMeshEEE>tionThermoMoleFractions
sets
surfaces
)
My question is should I remove the const from the function, virtual tmp<volScalarField> const k() ? Or is their some reasoning behind putting it there that needs to be considered? Is there a correct way to implement access to these so that finally a volScalarField to volScalarField interpolation can be carried out by manipulating these datatypes correctly, without having to add additional non-const access function to the kEpsilon model? Would much appreciate feedback on this!!


PS: The idea of adding non-const access function comes, because I also did interpolation of volume fraction fields (src/transportModels/twoPhaseMixture model), but there the reference to alpha fields is returned via two methods, which allows manipulation via interpolation.


Code:
        //- Return the phase-fraction of phase 1
        const volScalarField& alpha1() const
        {
            return alpha1_;
        }

        //- Return the phase-fraction of phase 1
        volScalarField& alpha1()
        {
            return alpha1_;
        }
PS: the mapping operation is elementary, going as:
Code:
    mapF2C.mapSrcToTgt
    (
        epsilonsrc,
        plusEqOp<scalar> (),
        epsilontgt
    );
It seems to work correctly for other fields.
use const_cast<> to convert to non-const reference...
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Old   December 24, 2019, 07:47
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  #3
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Rishikesh
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Thanks!!! worked like a charm
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Old   January 23, 2020, 13:51
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  #4
aot
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Andreas Otto
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How did you solve the problem. I'm facing the same issue.
Could you please post the code snippet.
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