CFD Online Discussion Forums - How to apply an external forces on a moving body in interDyMFoam?

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- - How to apply an external forces on a moving body in interDyMFoam? (https://www.cfd-online.com/Forums/openfoam-solving/154918-how-apply-external-forces-moving-body-interdymfoam.html)

How to apply an external forces on a moving body in interDyMFoam?

Hi, is is possible to apply an explicit point force to a moving object in interDyMFoam? I imagine this could be useful when modelling a marine craft with small wings/flaps attach. If the lift force of the appendege is known, one could just apply the force without explicitly mesh and model the details.

I cannot figure out how to specify this force or if it is even possible? Does anyone have an idea?

Regards
Lars

Hi Lars,

not possible at the moment. You must somehow change the sixDoFRigidBodyMotion library. One possibility would may be to modify the memberfunction "solve()" in sixDoFRigidBodyMotionSolver.C, where motion_.updateAcceleration(...) is called, similar how the mass forces are accounted for.

Good luck!
Jan

Hi Jan, thank you for clarifying this and thanks for you suggestions.

Have a nice day!
Lars

Hi Lars, hi Jan

I'm very interested in this argument, did you find a way to add an external force in interDyMFoam solver? any suggestion?

Best regards

Federica

Hi Frederica,

I think the easiest way is to create your own restraint. Have a look at the existing restraints, e.g. the linearSpring. There a force porportional to the velocity is computed and applied to the sixDoF Body. Copy an existing, rename and modify should be straight forward.

Best regards,
Jan

Hi Jan, thank you very much for your answer :)

Federica

Quote:

Originally Posted by JNSN (Post 599731)

Hi!
I'm stuck on this problem, because I'm new in programming in openFOAM. I took a look at the .H and .c files of linearSpring restraint and I need to modify the restraintForce term with a time varying force composed like this: (Fx,0,Fx*tan(alpha)).

void Foam::sixDoFRigidBodyMotionRestraints::linearSprin g::restrain
(
const sixDoFRigidBodyMotion& motion,
vector& restraintPosition,
vector& restraintForce,
vector& restraintMoment
) const
{
restraintPosition = motion.transform(refAttachmentPt_);

vector r = restraintPosition - anchor_;

scalar magR = mag(r);
r /= (magR + VSMALL);

vector v = motion.velocity(restraintPosition);

restraintForce =

restraintMoment = vector::zero;

if (motion.report())
{
Info<< " attachmentPt - anchor " << r*magR
<< " spring length " << magR
<< " force " << restraintForce
<< endl;
}
}

Fx is the sum of Fx pressure and Fx viscous and it needs to be extract each time step from the forces.dat file. alpha is the angle between the initial position of the x-axis of the system and the new position, I think it can be extract from the motion.orientation() tensor each time step. The problem is that I don't know how to extract these data to put them into the linearSpring library.

Do you know how can I do that?
Your help would be very appreciated.

Regards

Federica

Quote:

Originally Posted by federicabi (Post 600963)

Dear Federica,

Did you get success in adding the external force in linearSpring.C file ?
I need a similar modification in linearSpring.C file, but I am still wondering how to do it. If you have already managed to do, it will be great if you could share the idea.

Apparently, in OpenFOAM 4 release, they have made a provision to add external forces, in rigid body Dynamics/rigidBodyMeshMotion

http://openfoam.org/release/4-0/

However, I don't know how to use it.

Thanks and regards,
Sachin

Quote:

Originally Posted by sachinthakre (Post 616586)

Hello Sachin,

I compiled without errors this customized linearSpring, but I haven't tried it yet because I'm still stuck on the convergence of 0DoF cases.
However here is my solution

variableLinearSpring.C

Code:

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

  =========                 |

  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox

   \\    /   O peration     |

    \\  /    A nd           | Copyright (C) 2011-2015 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 "variableLinearSpring.H"

#include "addToRunTimeSelectionTable.H"

#include "sixDoFRigidBodyMotion.H"



#include "forces.H"

#include "IOobject.H"

#include "dictionary.H"

#include "Time.H"

#include "IOmanip.H"

#include "Pstream.H"



// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //



namespace Foam

{

namespace sixDoFRigidBodyMotionRestraints

{

    defineTypeNameAndDebug(variableLinearSpring, 0);



    addToRunTimeSelectionTable

    (

        sixDoFRigidBodyMotionRestraint,

        variableLinearSpring,

        dictionary

    );

}

}





// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //



Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::variableLinearSpring

(

    const word& name,

    const dictionary& sDoFRBMRDict   

)

:

    sixDoFRigidBodyMotionRestraint(name, sDoFRBMRDict),

    refAttachmentPt_(),

    alfaini_(),

    forzaxini_()

    

{

    read(sDoFRBMRDict);

}





// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //



Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::~variableLinearSpring()

{}





// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //



void Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::restrain

(

    const sixDoFRigidBodyMotion& motion,

    vector& restraintPosition,

    vector& restraintForce,

    vector& restraintMoment

   

) const

{

    static bool firstIt_ = true;

    scalar alfa;

    scalar forzax;

    scalar forzaxPrevIter;

    scalar alfaPrevIter;

    

  

    if (firstIt_)

    {

    alfa = alfaini_;

    forzax = forzaxini_;

    }

    else

    {

      FILE *forze;

      scalar timestep;

      scalar fxp;

      scalar fyp;

      scalar fzp;

      scalar fxv;

      scalar fyv;

      scalar fzv;

      scalar fxpo;

      scalar fypo;

      scalar fzpo;

      scalar mxp;

      scalar myp;

      scalar mzp;

      scalar mxv;

      scalar myv;

      scalar mzv;

      scalar mxpo;

      scalar mypo;

      scalar mzpo;

      forze = fopen("postProcessing/forces/0.3/forces.dat", "r");



      scanf("%*[^\n]");   /* Skip to the End of the Line */

    

      for (int i = 1; i <= 3; i++)

      {

      scanf("%*1[\n]");   /* Skip Three Newline */

      }



      fscanf(forze, "%le    ((%le %le %le) (%le %le %le) (%le %le %le)) ((%le %le %le) (%le %le %le) (%le %le %le))", &timestep, &fxp, &fyp, &fzp, &fxv, &fyv, &fzv, &fxpo, &fypo, &fzpo, &mxp, &myp, &mzp, &mxv, &myv, &mzv, &mxpo, &mypo, &mzpo);



      fclose(forze);

      

      forzaxPrevIter = fxp + fxv + fxpo;

      

      alfaPrevIter = asin(motion.orientation()[7]);

      

      alfa = alfaPrevIter;

      forzax = forzaxPrevIter;

    }

    

    restraintPosition = motion.transform(refAttachmentPt_);



    vector v = motion.velocity(restraintPosition);



    restraintForce = vector(forzax,0,forzax*tan(alfa));



    restraintMoment = vector::zero;



    if (motion.report())

    {

        Info<< " attachmentPt" << restraintPosition

            << " force " << restraintForce

            << endl;

    }

        

    firstIt_ = false;

}



      

bool Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::read

(

    const dictionary& sDoFRBMRDict

)

{

    sixDoFRigidBodyMotionRestraint::read(sDoFRBMRDict);



    sDoFRBMRCoeffs_.lookup("refAttachmentPt") >> refAttachmentPt_;

    sDoFRBMRCoeffs_.lookup("alfaini") >> alfaini_;

    sDoFRBMRCoeffs_.lookup("forzaxini") >> forzaxini_;

    



    return true;

}





void Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::write

(

    Ostream& os

) const

{

    os.writeKeyword("refAttachmentPt")

        << refAttachmentPt_ << token::END_STATEMENT << nl;



    os.writeKeyword("alfaini")

        << alfaini_ << token::END_STATEMENT << nl;



    os.writeKeyword("forzaxini")

        << forzaxini_ << token::END_STATEMENT << nl;

    

    

}

variableLinearSpring.H

Code:

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

  =========                 |

  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox

   \\    /   O peration     |

    \\  /    A nd           | Copyright (C) 2011-2013 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::sixDoFRigidBodyMotionRestraints::variableLinearSpring



Description

    sixDoFRigidBodyMotionRestraints model. Variable Linear spring.



SourceFiles

    variableLinearSpring.C



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



#ifndef variableLinearSpring_H

#define variableLinearSpring_H



#include "sixDoFRigidBodyMotionRestraint.H"

#include "point.H"





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



namespace Foam

{



namespace sixDoFRigidBodyMotionRestraints

{



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

                          Class variableLinearSpring Declaration

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



class variableLinearSpring

:

    public sixDoFRigidBodyMotionRestraint

{

    // Private data



        //- Punto di applicazione del traino (punto elica)

        point refAttachmentPt_;



        //- Angolo di inclinazione della linea d'assi

    scalar alfaini_;

    

    //- Forza di resistenza iniziale

    scalar forzaxini_;

    

    

public:



    //- Runtime type information

    TypeName("variableLinearSpring");





    // Constructors



        //- Construct from components

        variableLinearSpring

        (

            const word& name,

            const dictionary& sDoFRBMRDict

        );



        //- Construct and return a clone

        virtual autoPtr<sixDoFRigidBodyMotionRestraint> clone() const

        {

            return autoPtr<sixDoFRigidBodyMotionRestraint>

            (

                new variableLinearSpring(*this)

            );

        }





    //- Destructor

    virtual ~variableLinearSpring();





    // Member Functions



        //- Calculate the restraint position, force and moment.

        //  Global reference frame vectors.

        virtual void restrain

        (

            const sixDoFRigidBodyMotion& motion,

            vector& restraintPosition,

            vector& restraintForce,

            vector& restraintMoment

        

        ) const;

    

        

        //- Update properties from given dictionary

        virtual bool read(const dictionary& sDoFRBMRCoeff);



        //- Write

        virtual void write(Ostream&) const;

};





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



} // End namespace solidBodyMotionFunctions

} // End namespace Foam



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



#endif



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

If you try it, please let me know your results.

Best regards

Federica

Dear Federica,

Thank you very much for your modified file! I had a look at it. It is interesting. I will try if I could do some Changes according to my need.

Actually, in my case, I want to modify the restraintForce equation by adding the external force term in the following way.

restraintForce = -stiffness_*(magR - restLength_)*r - damping_*(r & v)*r + F;

where, F = F0*sin(Omega*time)

I want to put in the "time" there, which I couldn't when I tried. Do you think, it can be done easily?

Best regards,
Sachin

Quote:

Originally Posted by sachinthakre (Post 617705)

Hi Sachin,

I understand your issue, I'm not good at programming in OpenFOAM but I found in the forum this post http://www.cfd-online.com/Forums/ope...vity-time.html where Alberto suggests to use runTime.timeName() as time variable, check it out!

Best regards

Federica

Dear Federica,

Thank you very much for this input! It certainly gave me some room to think about time implementation in linearSpring.C.

I actually, tried the runTime.timeName() and also, runTime.value(), but it didn't work in my case. :(

It seems, I need to find some other way:confused:

Best,
Sachin

Actually runTime.value() worked very well in OF 2. But the same code is giving problems in OF 4. Did you figure it out?:confused:

explicit point force

Quote:

Originally Posted by Larsa (Post 551528)

hi Lars
Has your problem been solved? Do you solve your problem by using new version V1706 ? I have a question ask you ，Whether this external force can make an object in the water along a uniform linear motion？
Do not use this LingeSpring, you know what better way or simple method achieve a sphere in the water uniform linear motion it?
thanks

Quote:

Originally Posted by federicabi (Post 617591)

Code:

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

  =========                 |

  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox

   \\    /   O peration     |

    \\  /    A nd           | Copyright (C) 2011-2015 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 "variableLinearSpring.H"

#include "addToRunTimeSelectionTable.H"

#include "sixDoFRigidBodyMotion.H"



#include "forces.H"

#include "IOobject.H"

#include "dictionary.H"

#include "Time.H"

#include "IOmanip.H"

#include "Pstream.H"



// * * * * * * * * * * * * * * Static Data Members * * * * * * * * * * * * * //



namespace Foam

{

namespace sixDoFRigidBodyMotionRestraints

{

    defineTypeNameAndDebug(variableLinearSpring, 0);



    addToRunTimeSelectionTable

    (

        sixDoFRigidBodyMotionRestraint,

        variableLinearSpring,

        dictionary

    );

}

}





// * * * * * * * * * * * * * * * * Constructors  * * * * * * * * * * * * * * //



Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::variableLinearSpring

(

    const word& name,

    const dictionary& sDoFRBMRDict   

)

:

    sixDoFRigidBodyMotionRestraint(name, sDoFRBMRDict),

    refAttachmentPt_(),

    alfaini_(),

    forzaxini_()

    

{

    read(sDoFRBMRDict);

}





// * * * * * * * * * * * * * * * * Destructor  * * * * * * * * * * * * * * * //



Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::~variableLinearSpring()

{}





// * * * * * * * * * * * * * * Member Functions  * * * * * * * * * * * * * * //



void Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::restrain

(

    const sixDoFRigidBodyMotion& motion,

    vector& restraintPosition,

    vector& restraintForce,

    vector& restraintMoment

   

) const

{

    static bool firstIt_ = true;

    scalar alfa;

    scalar forzax;

    scalar forzaxPrevIter;

    scalar alfaPrevIter;

    

  

    if (firstIt_)

    {

    alfa = alfaini_;

    forzax = forzaxini_;

    }

    else

    {

      FILE *forze;

      scalar timestep;

      scalar fxp;

      scalar fyp;

      scalar fzp;

      scalar fxv;

      scalar fyv;

      scalar fzv;

      scalar fxpo;

      scalar fypo;

      scalar fzpo;

      scalar mxp;

      scalar myp;

      scalar mzp;

      scalar mxv;

      scalar myv;

      scalar mzv;

      scalar mxpo;

      scalar mypo;

      scalar mzpo;

      forze = fopen("postProcessing/forces/0.3/forces.dat", "r");



      scanf("%*[^\n]");   /* Skip to the End of the Line */

    

      for (int i = 1; i <= 3; i++)

      {

      scanf("%*1[\n]");   /* Skip Three Newline */

      }



      fscanf(forze, "%le    ((%le %le %le) (%le %le %le) (%le %le %le)) ((%le %le %le) (%le %le %le) (%le %le %le))", &timestep, &fxp, &fyp, &fzp, &fxv, &fyv, &fzv, &fxpo, &fypo, &fzpo, &mxp, &myp, &mzp, &mxv, &myv, &mzv, &mxpo, &mypo, &mzpo);



      fclose(forze);

      

      forzaxPrevIter = fxp + fxv + fxpo;

      

      alfaPrevIter = asin(motion.orientation()[7]);

      

      alfa = alfaPrevIter;

      forzax = forzaxPrevIter;

    }

    

    restraintPosition = motion.transform(refAttachmentPt_);



    vector v = motion.velocity(restraintPosition);



    restraintForce = vector(forzax,0,forzax*tan(alfa));



    restraintMoment = vector::zero;



    if (motion.report())

    {

        Info<< " attachmentPt" << restraintPosition

            << " force " << restraintForce

            << endl;

    }

        

    firstIt_ = false;

}



      

bool Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::read

(

    const dictionary& sDoFRBMRDict

)

{

    sixDoFRigidBodyMotionRestraint::read(sDoFRBMRDict);



    sDoFRBMRCoeffs_.lookup("refAttachmentPt") >> refAttachmentPt_;

    sDoFRBMRCoeffs_.lookup("alfaini") >> alfaini_;

    sDoFRBMRCoeffs_.lookup("forzaxini") >> forzaxini_;

    



    return true;

}





void Foam::sixDoFRigidBodyMotionRestraints::variableLinearSpring::write

(

    Ostream& os

) const

{

    os.writeKeyword("refAttachmentPt")

        << refAttachmentPt_ << token::END_STATEMENT << nl;



    os.writeKeyword("alfaini")

        << alfaini_ << token::END_STATEMENT << nl;



    os.writeKeyword("forzaxini")

        << forzaxini_ << token::END_STATEMENT << nl;

    

    

}

variableLinearSpring.H

Code:

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

  =========                 |

  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox

   \\    /   O peration     |

    \\  /    A nd           | Copyright (C) 2011-2013 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::sixDoFRigidBodyMotionRestraints::variableLinearSpring



Description

    sixDoFRigidBodyMotionRestraints model. Variable Linear spring.



SourceFiles

    variableLinearSpring.C



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



#ifndef variableLinearSpring_H

#define variableLinearSpring_H



#include "sixDoFRigidBodyMotionRestraint.H"

#include "point.H"





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



namespace Foam

{



namespace sixDoFRigidBodyMotionRestraints

{



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

                          Class variableLinearSpring Declaration

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



class variableLinearSpring

:

    public sixDoFRigidBodyMotionRestraint

{

    // Private data



        //- Punto di applicazione del traino (punto elica)

        point refAttachmentPt_;



        //- Angolo di inclinazione della linea d'assi

    scalar alfaini_;

    

    //- Forza di resistenza iniziale

    scalar forzaxini_;

    

    

public:



    //- Runtime type information

    TypeName("variableLinearSpring");





    // Constructors



        //- Construct from components

        variableLinearSpring

        (

            const word& name,

            const dictionary& sDoFRBMRDict

        );



        //- Construct and return a clone

        virtual autoPtr<sixDoFRigidBodyMotionRestraint> clone() const

        {

            return autoPtr<sixDoFRigidBodyMotionRestraint>

            (

                new variableLinearSpring(*this)

            );

        }





    //- Destructor

    virtual ~variableLinearSpring();





    // Member Functions



        //- Calculate the restraint position, force and moment.

        //  Global reference frame vectors.

        virtual void restrain

        (

            const sixDoFRigidBodyMotion& motion,

            vector& restraintPosition,

            vector& restraintForce,

            vector& restraintMoment

        

        ) const;

    

        

        //- Update properties from given dictionary

        virtual bool read(const dictionary& sDoFRBMRCoeff);



        //- Write

        virtual void write(Ostream&) const;

};





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



} // End namespace solidBodyMotionFunctions

} // End namespace Foam



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



#endif



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

If you try it, please let me know your results.

Best regards

Federica

Hi Federica,

I tried modifying the linearSpring based on your variableLinearSpring.C and .H files. It does not show any error during compilation. But when I test it, the force shows 0 value at every timestep. Have you tried it yourself and does it work?

Regards,
Mohamad