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License
    This file is part of the Multiphase Code Repository by HZDR.

    Copyright (C) 2025 by Helmholtz-Zentrum Dresden-Rossendorf e.V. (HZDR),
    Website: https://hzdr.de

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Class
    Foam::dragModels::resolutionAdaptiveInterfaceDrag

Description
    A wrapper class around two underlying drag models, which is intended for
    simulations involving large interfaces. The latter are adaptively described
    in either a resolving (R) or in an under-resolving manner (UR) or as a
    mixture of both. Both basic drag model formulations need to be selected
    separately. The degree of under-resolution is controlled via the under-
    resolution indicator function \f$f_\mathrm{UR}\f$.

    The resulting drag coefficient is calculated as follows (similarly to a
    parallel electric circuit with two resistors):
    \f[
        K = \frac{K_\mathrm{UR} K_\mathrm{R}}
                 {K_\mathrm{UR} + f_\mathrm{UR} K_\mathrm{R}}.
    \f]

SourceFiles
    resolutionAdaptiveInterfaceDrag.C

\*---------------------------------------------------------------------------*/

#ifndef resolutionAdaptiveInterfaceDrag_H
#define resolutionAdaptiveInterfaceDrag_H

#include "dragModel.H"
#include "segregatedPhaseInterface.H"

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

namespace Foam
{
namespace dragModels
{

/*---------------------------------------------------------------------------*\
               Class resolutionAdaptiveInterfaceDrag Declaration
\*---------------------------------------------------------------------------*/

class resolutionAdaptiveInterfaceDrag
:
    public dragModel
{
    // Private Data

        //- Interface
        const segregatedPhaseInterface interface_;

        //- Pointer to the underlying resolving drag model
        autoPtr<dragModel> resolvingDragModel_;

        //- Pointer to the underlying under-resolving drag model
        autoPtr<dragModel> underResolvingDragModel_;


public:

    //- Runtime type information
    TypeName("resolutionAdaptiveInterface");


    // Constructors

        //- Construct from a dictionary and an interface
        resolutionAdaptiveInterfaceDrag
        (
            const dictionary& dict,
            const phaseInterface& interface,
            const bool registerObject
        );


    //- Destructor
    virtual ~resolutionAdaptiveInterfaceDrag();


    // Member Functions

        //- Return the drag coefficient K
        //  used in the momentum equations
        //    ddt(alpha1*rho1*U1) + ... = ... K*(U1-U2)
        //    ddt(alpha2*rho2*U2) + ... = ... K*(U2-U1)
        virtual tmp<volScalarField> K() const;

        //- Return the drag coefficient Kf
        //  used in the face-momentum equations
        virtual tmp<surfaceScalarField> Kf() const;
};


// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

} // End namespace dragModels
} // End namespace Foam

// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

#endif

// ************************************************************************* //
