DMD.H

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    Copyright (C) 2020-2021 OpenCFD Ltd.
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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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    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::functionObjects::DMD
 
Group
    grpFieldFunctionObjects
 
Description
    Computes a dynamic mode decomposition model on a specified field.
 
    Dynamic mode decomposition (i.e. DMD) is a data-driven
    dimensionality reduction method. DMD is being used as a mathematical
    processing tool to reveal dominant modes out of a given field (or dataset)
    each of which is associated with a constant frequency and decay rate,
    so that dynamic features of a given flow may become interpretable,
    tractable, and even reproducible without computing simulations.
    DMD only relies on input data, therefore it is an equation-free approach.
 
    References:
    \verbatim
        DMD characteristics:
            Brunton S. L. (2018).
            Dynamic mode decomposition overview.
            Seattle, Washington: University of Washington.
            youtu.be/sQvrK8AGCAo (Retrieved:24-04-20)
    \endverbatim
 
    Operands:
    \table
      Operand      | Type                 | Location
      input        | {vol,surface}<Type>Field(s)  | <time>/inputField(s)
      output file  | dat                  | postProcessing/<FO>/<time>/files
      output field | volVectorField(s)    | <time>/outputField(s)
    \endtable
 
    where \c Type can be one of:
        \c Scalar, \c Vector, \c SphericalTensor, \c SymmTensor, or \c Tensor.
 
    Output fields:
    \verbatim
      modeRe_<modeIndex>_<field>_<FO> | Real part of a mode field
      modeIm_<modeIndex>_<field>_<FO> | Imaginary part of a mode field
    \endverbatim
 
    Output files:
    \verbatim
      dynamics_<field>.dat            | Dynamics data for each mode
      filtered_dynamics_<field>.dat   | Filtered dynamics data for each mode
    \endverbatim
 
    wherein for each mode, the following quantities are output into files:
    \vartable
      freq        | Frequency
      mag         | Magnitude
      ampRe       | Amplitude coefficients (real part)
      ampIm       | Amplitude coefficients (imaginary part)
      evalRe      | Eigenvalue (real part)
      evalIm      | Eigenvalue (imaginary part)
    \endvartable
 
Usage
    Minimal example by using \c system/controlDict.functions:
    \verbatim
    DMDFO
    {
        // Mandatory entries
        type                DMD;
        libs                (fieldFunctionObjects);
        DMDModel            <DMDModel>;
        field               <word>;
 
        // Optional entries
 
            // Option-1
            patch               <word>;
 
            // Option-2
            patches             (<wordRes>);
 
        // Inherited entries
        ...
    }
    \endverbatim
 
    where the entries mean:
    \table
      Property     | Description                        | Type | Reqd | Deflt
      type         | Type name: DMD                     | word | yes  | -
      libs         | Library name: fieldFunctionObjects | word | yes  | -
      DMDModel     | Name of specified DMD model        | word | yes  | -
      field        | Name of operand field              | word | yes  | -
      patch        | Name of operand patch              | word | no   | null
      patches      | Names of operand patches        | wordRes | no   | null
    \endtable
 
    Options for the \c DMDModel entry:
    \verbatim
      STDMD    | Streaming total dynamic mode decomposition
    \endverbatim
 
    The inherited entries are elaborated in:
      - \link functionObject.H \endlink
      - \link writeFile.H \endlink
 
Note
  - Warning: DMD is an active research area at the time of writing;
    therefore, there could be cases whereat oddities can be seen.
 
SourceFiles
    DMD.C
    DMDTemplates.C
 
\*---------------------------------------------------------------------------*/
 
#ifndef Foam_functionObjects_DMD_H
#define Foam_functionObjects_DMD_H
 
#include "fvMeshFunctionObject.H"
#include "RectangularMatrix.H"
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
namespace Foam
{
 
// Forward Declarations
class DMDModel;
 
namespace functionObjects
{
 
/*---------------------------------------------------------------------------*\
                              Class DMD Declaration
\*---------------------------------------------------------------------------*/
 
class DMD
:
    public fvMeshFunctionObject
{
    typedef RectangularMatrix<scalar> RMatrix;
 
    // Private Data
 
        //- Dynamic mode decomposition model
        autoPtr<DMDModel> DMDModelPtr_;
 
        //- Augmented snapshot matrix (effectively a column vector)
        //  Upper half = current-time snapshot slot
        //  Lower half = previous-time snapshot slot
        //  A snapshot is an input dataset to be processed per execution step
        //  A single snapshot is usually referred to as the snapshot of a single
        //  time step, an augmented snapshot is constructed of two snapshots
        RMatrix z_;
 
        //- Names of operand patches
        const wordRes patches_;
 
        //- Name of operand field
        const word fieldName_;
 
        //- Number of elements in a snapshot
        label nSnap_;
 
        //- Current execution-step index of DMD,
        //- not necessarily that of the simulation
        label step_;
 
 
    // Private Member Functions
 
        // Evaluation
 
            //- Initialise snapshot at the first-execution step
            //  Initialisation at the ctor or read level is not possible
            //  since the operand field is not available in the database
            void initialise();
 
            //- Create operand snapshot by using
            //- current-time and previous-time operand fields
            void snapshot();
 
            //- Get operand field based on its base type
            template<class Type>
            bool getSnapshot();
 
            //- Store operand field based on its geometric
            //- field type after few manipulations
            //  Move previous-time field into previous-time slot in snapshot
            //  copy new current-time field into current-time slot in snapshot
            template<class GeoFieldType>
            bool storeSnapshot();
 
 
        // Access
 
            //- Return number of components of the base type of a given field
            label nComponents(const word& fieldName) const;
 
            //- Get the number of components of the base type of a given field
            template<class Type>
            bool nComponents(const word& fieldName, label& nComps) const;
 
 
public:
 
    //- Runtime type information
    TypeName("DMD");
 
 
    // Constructors
 
        //- Construct from name, Time and dictionary
        DMD
        (
            const word& name,
            const Time& runTime,
            const dictionary& dict
        );
 
        //- No copy construct
        DMD(const DMD&) = delete;
 
        //- No copy assignment
        void operator=(const DMD&) = delete;
 
 
    //- Destructor
    virtual ~DMD() = default;
 
 
    // Member Functions
 
        //- Read the function-object dictionary
        virtual bool read(const dictionary& dict);
 
        //- Execute the function-object operations
        virtual bool execute();
 
        //- Write the function-object results
        virtual bool write();
 
        //- Write DMD results
        virtual bool end();
};
 
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
} // End namespace functionObjects
} // End namespace Foam
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
#ifdef NoRepository
    #include "DMDTemplates.C"
#endif
 
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
 
#endif
 
// ************************************************************************* //