/*---------------------------------------------------------------------------*\
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License
    This file is part of OpenFOAM.

    OpenFOAM is free software: you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    OpenFOAM is distributed in the hope that it will be useful, but WITHOUT
    ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
    FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
    for more details.

    You should have received a copy of the GNU General Public License
    along with OpenFOAM.  If not, see <http://www.gnu.org/licenses/>.

Class
    Foam::laminarModels::generalisedNewtonianViscosityModels::CrossPowerLaw

Description
    Cross-Power law generalised Newtonian viscosity model

    The coefficient applied to strain rate \f$\gamma\f$ can be specified either
    as the constant \c m or the critical stress level at the transition to
    shear thinning \c tauStar if \c tauStar is provided:

    Kinematic viscosity [m^2/s]

    \f[
        \nu = \nu_\infty + \frac{(\nu_0 - \nu_\infty)}{1 + (m\gamma)^n}
    \f]

    or

    \f[
        \nu = \nu_\infty
            + \frac{(\nu_0 - \nu_\infty)}
                   {1 + \left(\frac{\nu_0\gamma}{\tau^*}\right)^n}
    \f]

    Example specification:
    \verbatim
         viscosityModel CrossPowerLaw;

         nuInf      10;
         m          0.4;
         n          3;
    \endverbatim

    Note the viscosity \c nu0 at zero strain rate is a physical property,
    generally specified in the physicalProperties file.

SourceFiles
    CrossPowerLaw.C

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

#ifndef CrossPowerLaw_H
#define CrossPowerLaw_H

#include "strainRateViscosityModel.H"

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

namespace Foam
{
namespace laminarModels
{
namespace generalisedNewtonianViscosityModels
{

/*---------------------------------------------------------------------------*\
                        Class CrossPowerLaw Declaration
\*---------------------------------------------------------------------------*/

class CrossPowerLaw
:
    public strainRateViscosityModel
{
    // Private Data

        dimensionedScalar nuInf_;
        dimensionedScalar m_;
        dimensionedScalar tauStar_;
        dimensionedScalar n_;


public:

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


    // Constructors

        //- Construct from components
        CrossPowerLaw
        (
            const dictionary& viscosityProperties,
            const Foam::viscosity& viscosity,
            const volVectorField& U
        );


    //- Destructor
    virtual ~CrossPowerLaw()
    {}


    // Member Functions

        //- Read transportProperties dictionary
        virtual bool read(const dictionary& viscosityProperties);

        //- Return the laminar viscosity
        virtual tmp<volScalarField> nu
        (
            const volScalarField& nu0,
            const volScalarField& strainRate
        ) const;
};


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

} // End namespace generalisedNewtonianViscosityModels
} // End namespace laminarModels
} // End namespace Foam

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

#endif

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