rigidBodyDynamics::restraints::externalForce: New restraint to apply a time-varying force

Description
    Time-dependent external force restraint using Function1.

Usage
    Example applying a constant force to the floatingObject:
    restraints
    {
        force
        {
            type        externalForce;
            body        floatingObject;
            location    (0 0 0);
            force       (100 0 0);
        }
    }

Based on code contributed by SeongMo Yeon
Resolves contribution request https://bugs.openfoam.org/view.php?id=3358

src/rigidBodyDynamics/restraints/externalForce/externalForce.C

@@ -0,0 +1,128 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2019 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 "externalForce.H"
+#include "rigidBodyModel.H"
+#include "rigidBodyModelState.H"
+#include "OneConstant.H"
+#include "addToRunTimeSelectionTable.H"
+
+// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace RBD
+{
+namespace restraints
+{
+    defineTypeNameAndDebug(externalForce, 0);
+
+    addToRunTimeSelectionTable
+    (
+        restraint,
+        externalForce,
+        dictionary
+    );
+}
+}
+}
+
+
+// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //
+
+Foam::RBD::restraints::externalForce::externalForce
+(
+    const word& name,
+    const dictionary& dict,
+    const rigidBodyModel& model
+)
+:
+    restraint(name, dict, model),
+    externalForce_(nullptr)
+{
+    read(dict);
+}
+
+
+// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //
+
+Foam::RBD::restraints::externalForce::~externalForce()
+{}
+
+
+// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //
+
+void Foam::RBD::restraints::externalForce::restrain
+(
+    scalarField& tau,
+    Field<spatialVector>& fx,
+    const rigidBodyModelState& state
+) const
+{
+    const vector force = externalForce_().value(state.t());
+    const vector moment(location_ ^ force);
+
+    if (model_.debug)
+    {
+        Info<< " location " << location_
+            << " force " << force
+            << " moment " << moment
+            << endl;
+    }
+
+    // Accumulate the force for the restrained body
+    fx[bodyIndex_] += spatialVector(moment, force);
+}
+
+
+bool Foam::RBD::restraints::externalForce::read
+(
+    const dictionary& dict
+)
+{
+    restraint::read(dict);
+
+    coeffs_.lookup("location") >> location_;
+
+    externalForce_ = Function1<vector>::New("force", coeffs_);
+
+    return true;
+}
+
+
+void Foam::RBD::restraints::externalForce::write
+(
+    Ostream& os
+) const
+{
+    restraint::write(os);
+
+    writeEntry(os, "location", location_);
+
+    writeEntry(os, externalForce_());
+}
+
+
+// ************************************************************************* //

src/rigidBodyDynamics/restraints/externalForce/externalForce.H

@@ -0,0 +1,141 @@
+/*---------------------------------------------------------------------------*\
+  =========                 |
+  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
+   \\    /   O peration     | Website:  https://openfoam.org
+    \\  /    A nd           | Copyright (C) 2019 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::RBD::restraints::externalForce
+
+Description
+    Time-dependent external force restraint using Function1.
+
+Usage
+    Example applying a constant force to the floatingObject:
+    \verbatim
+    restraints
+    {
+        force
+        {
+            type        externalForce;
+            body        floatingObject;
+            location    (0 0 0);
+            force       (100 0 0);
+        }
+    }
+    \endverbatim
+
+SourceFiles
+    externalForce.C
+
+\*---------------------------------------------------------------------------*/
+
+#ifndef RBD_restraints_externalForce_H
+#define RBD_restraints_externalForce_H
+
+#include "rigidBodyRestraint.H"
+#include "Function1.H"
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+namespace Foam
+{
+namespace RBD
+{
+namespace restraints
+{
+
+/*---------------------------------------------------------------------------*\
+                          Class externalForce Declaration
+\*---------------------------------------------------------------------------*/
+
+class externalForce
+:
+    public restraint
+{
+    // Private data
+
+        //- External force (N)
+        autoPtr<Function1<vector>> externalForce_;
+
+        //- Point of application of the force
+        vector location_;
+
+
+public:
+
+    //- Runtime type information
+    TypeName("externalForce");
+
+
+    // Constructors
+
+        //- Construct from components
+        externalForce
+        (
+            const word& name,
+            const dictionary& dict,
+            const rigidBodyModel& model
+        );
+
+        //- Construct and return a clone
+        virtual autoPtr<restraint> clone() const
+        {
+            return autoPtr<restraint>
+            (
+                new externalForce(*this)
+            );
+        }
+
+
+    //- Destructor
+    virtual ~externalForce();
+
+
+    // Member Functions
+
+        //- Accumulate the retraint internal joint forces into the tau field and
+        //  external forces into the fx field
+        virtual void restrain
+        (
+            scalarField& tau,
+            Field<spatialVector>& fx,
+            const rigidBodyModelState& state
+        ) const;
+
+        //- Update properties from given dictionary
+        virtual bool read(const dictionary& dict);
+
+        //- Write
+        virtual void write(Ostream&) const;
+};
+
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+} // End namespace restraints
+} // End namespace RBD
+} // End namespace Foam
+
+// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
+
+#endif
+
+// ************************************************************************* //