verticalDamping.H

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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.

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    for more details.

    You should have received a copy of the GNU General Public License
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Class
    Foam::fv::verticalDamping

Description
    This fvModel applies an explicit damping force to components of the vector
    field in the direction of gravity. Its intended purpose is to damp the
    vertical motions of an interface in the region approaching an outlet so that
    no reflections are generated.

    Damping is achieved by applying a force to the momentum equation
    proportional to the momentum of the flow in the direction of gravity. The
    constant of proportionality is given by a coefficient \f$\lambda\f$ which
    has units of inverse-time. In the absence of any other forces this would
    generate an exponential decay of the vertical velocity.

        \f[
            \frac{d (m u_z)}{d t} = - \lambda m u_z
        \f]
        \f[
            u_z = u_{z0} e^{- \lambda t}
        \f]

    The coefficient \f$\lambda\f$ should be set based on the desired level of
    damping and the residence time of a perturbation through the damping zone.
    For example, if waves moving at 2 [m/s] are travelling through a damping
    zone 8 [m] in length, then the residence time is 4 [s]. If it is deemed
    necessary to damp for 5 time-scales, then \f$\lambda\f$ should be set to
    equal 5/(4 [s]) = 1.2 [1/s].

Usage
    Example usage:
    \verbatim
    verticalDamping1
    {
        type            verticalDamping;

        // Define the line along which to apply the graduation
        origin          (1200 0 0);
        direction       (1 0 0);

        // Or, define multiple lines
        // origins         ((1200 0 0) (1200 -300 0) (1200 300 0));
        // directions      ((1 0 0) (0 -1 0) (0 1 0));

        scale
        {
            type        halfCosineRamp;
            start       0;
            duration    600;
        }

        lambda          [0 0 -1 0 0 0 0] 1; // Damping coefficient

        timeStart       0;
        duration        1e6;
    }
    \endverbatim

See also
    Foam::fv::damping
    Foam::fv::isotropicDamping

SourceFiles
    verticalDamping.C

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

#ifndef verticalDamping_H
#define verticalDamping_H

#include "damping.H"

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

namespace Foam
{
namespace fv
{

/*---------------------------------------------------------------------------*\
                       Class verticalDamping Declaration
\*---------------------------------------------------------------------------*/

class verticalDamping
:
    public damping
{
    // Private Member Functions

        //- Source term to momentum equation
        void add
        (
            const volVectorField& alphaRhoU,
            fvMatrix<vector>& eqn
        ) const;


public:

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


    // Constructors

        //- Construct from components
        verticalDamping
        (
            const word& name,
            const word& modelType,
            const dictionary& dict,
            const fvMesh& mesh
        );


    //- Destructor
    virtual ~verticalDamping()
    {}


    // Member Functions

         // Add explicit and implicit contributions

            //- Source term to momentum equation
            virtual void addSup
            (
                fvMatrix<vector>& eqn,
                const word& fieldName
            ) const;

            //- Source term to compressible momentum equation
            virtual void addSup
            (
                const volScalarField& rho,
                fvMatrix<vector>& eqn,
                const word& fieldName
            ) const;

            //- Source term to phase momentum equation
            virtual void addSup
            (
                const volScalarField& alpha,
                const volScalarField& rho,
                fvMatrix<vector>& eqn,
                const word& fieldName
            ) const;
};


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

} // End namespace fv
} // End namespace Foam

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

#endif

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