/*---------------------------------------------------------------------------*\
  ==  == ====== ====   ====    |
                    \\     ||  | Multiphase Code Repository by HZDR
  ======   //   ||  || ===//   | Website: https://doi.org/10.14278/rodare.767
  ||  ||  //    ||  // || \\   | License: GPL-3.0-or-later
  ==  == ====== ====   ==  ==  |
-------------------------------------------------------------------------------
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

    Multiphase Code Repository by HZDR is based on the free software for
    computational fluid dynamics (CFD) from the OpenFOAM Foundation.
    Copyright (C) 2025 by OpenFOAM Foundation, Website: https://openfoam.org

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    files, which OpenFOAM Foundation files were modified, and which files were
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Class
    Foam::interfaceIndicatorMethods::gradAlpha

Description
    Determine the interface indicator field for a pair of continuous phases,
    i and j:

    \f[
        \mathrm{RI}_{ij} =
            \mathrm{max}(\mathrm{mag}((\nabla\alpha)_{ij}\Delta x), 1),
    \f]

    where

    \f[
        (\nabla\alpha)_{ij} = \alpha_j\nabla\alpha_i - \alpha_i\nabla\alpha_j,
    \f]

    and \f$\Delta x\f$ is the typical grid size calculated using
    a SGSdelta model.

Usage
    \verbatim
    interfaceIndicatorMethod
    {
        type    gradAlpha;
        delta   cubeRootVol;
    }
    \endverbatim

See also
    Foam::SGSdelta

SourceFiles
    gradAlpha.C

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

#ifndef gradAlpha_H
#define gradAlpha_H

#include "interfaceIndicatorMethod.H"
#include "SGSdelta.H"

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

namespace Foam
{
namespace interfaceIndicatorMethods
{

/*---------------------------------------------------------------------------*\
                          Class gradAlpha Declaration
\*---------------------------------------------------------------------------*/

class gradAlpha
:
    public interfaceIndicatorMethod
{
    // Private Data

        // Local grid size approximation model
        autoPtr<SGSdelta> delta_;


protected:

    // Protected Member Functions

        //- Indicator field between a phase interface
        virtual tmp<volScalarField> interfaceIndicator
        (
            const phaseModel& phase1,
            const phaseModel& phase2
        ) const;


public:

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


    // Constructors

        //- Construct from resolvedInterfaceSystem
        gradAlpha
        (
            const resolvedInterfaceSystem& resolvedInterface,
            const bool registerObject
        );


    //- Destructor
    virtual ~gradAlpha();
};


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

} // End namespace interfaceIndicatorMethods
} // End namespace Foam

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

#endif

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