functionObjects::log: New functionObject to calculate the natural logarithm of a scalar field

Description
    Calculates the natural logarithm of the specified scalar field.

    Performs \f$ln(max(x, a))\f$ where \f$x\f$ is the field and \f$a\f$ an
    optional clip to handle 0 or negative \f$x\f$.

The etc/caseDicts/postProcessing/fields/log configuration file is provided so
that the simple #includeFunc can be used to execute this functionObject during
the run, e.g. for some dimensionless field x

functions
{
    #includeFunc log(x)
}

or if x might be 0 or negative in some regions the optional clip may be applied:

functions
{
    #includeFunc log(p,clip=1e-6)
}

src/functionObjects/field/Make/files

@@ -36,6 +36,7 @@ ddt/ddt.C
 mag/mag.C
 magSqr/magSqr.C
 scale/scale.C
+log/log.C
 vorticity/vorticity.C
 enstrophy/enstrophy.C
 Q/Q.C

src/functionObjects/field/log/log.C

@@ -0,0 +1,109 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2018 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+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/>.
+
+\*---------------------------------------------------------------------------*/
+
+#include "log.H"
+#include "volFields.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+    defineTypeNameAndDebug(log, 0);
+
+    addToRunTimeSelectionTable
+    (
+        functionObject,
+        log,
+        dictionary
+    );
+}
+}
+
+
+// * * * * * * * * * * * * * Private Member Functions  * * * * * * * * * * * //
+
+bool Foam::functionObjects::log::calc()
+{
+    if (foundObject<volScalarField>(fieldName_))
+    {
+        const volScalarField& x = lookupObject<volScalarField>(fieldName_);
+
+        return store
+        (
+            resultName_,
+            Foam::log(max(x, clip_))
+        );
+    }
+    else
+    {
+        return false;
+    }
+
+    return true;
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::functionObjects::log::log
+(
+    const word& name,
+    const Time& runTime,
+    const dictionary& dict
+)
+:
+    fieldExpression(name, runTime, dict)
+{
+    read(dict);
+}
+
+
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+Foam::functionObjects::log::~log()
+{}
+
+
+// * * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * //
+
+bool Foam::functionObjects::log::read(const dictionary& dict)
+{
+    fieldExpression::read(dict);
+
+    if (resultName_.empty())
+    {
+        resultName_ = "log(" + fieldName_ + ")";
+    }
+
+    clip_ = dict.lookupOrDefault<scalar>("clip", 0);
+
+    return true;
+}
+
+
+// ************************************************************************* //

src/functionObjects/field/log/log.H

@@ -0,0 +1,111 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2018 OpenFOAM Foundation
+     \\/     M anipulation  |
+-------------------------------------------------------------------------------
+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::functionObjects::log
+
+Description
+    Calculates the natural logarithm of the specified scalar field.
+
+    Performs \f$ln(max(x, a))\f$ where \f$x\f$ is the field and \f$a\f$ an
+    optional clip to handle 0 or negative \f$x\f$.
+
+See also
+    Foam::functionObjects::fieldExpression
+    Foam::functionObjects::fvMeshFunctionObject
+
+SourceFiles
+    log.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef functionObjects_log_H
+#define functionObjects_log_H
+
+#include "fieldExpression.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace functionObjects
+{
+
+/*---------------------------------------------------------------------------*\
+                          Class log Declaration
+\*---------------------------------------------------------------------------*/
+
+class log
+:
+    public fieldExpression
+{
+    // Private data
+
+        //- Optional clip (default is 0)
+        scalar clip_;
+
+
+    // Private Member Functions
+
+        //- Calculate the log field and return true if successful
+        virtual bool calc();
+
+
+public:
+
+    //- Runtime type information
+    TypeName("log");
+
+
+    // Constructors
+
+        //- Construct from Time and dictionary
+        log
+        (
+            const word& name,
+            const Time& runTime,
+            const dictionary& dict
+        );
+
+
+    //- Destructor
+    virtual ~log();
+
+
+    // Member Functions
+
+        //- Read the randomise data
+        virtual bool read(const dictionary&);
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace functionObjects
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //