CFD Online Discussion Forums - Changing velocity with time

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Changing velocity with time

Hi All,

I have a case setup with a moving boat in water. I am trying to create a case to see how the boat will interact with other objects in the water. Right now I can set the velocity of the boat, but am not able to change the velocity at each timestep. I am using the dymanicMeshDict to achieve this. Below is my dict:

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

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

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

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

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    location    "constant";

    object      dynamicMeshDict;

}

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



dynamicFvMesh   dynamicMotionSolverFvMesh;



motionSolverLibs (fvMotionSolvers);



motionSolver    solidBody;



cellZone        rotatingZone;



solidBodyMotionFunction  linearMotion;



velocity (.5 0 0);



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

How do I go about changing the velocity in each time step? Will I need to get under the hood to do this? So far I have just been modifying the case dictionary files.

Found this example in tutorials/multiphase/interfoam/ras/floatingobject.

I guess code stream is being used to calculate some values.. wondering if I can do something to calculate the velocity...

Code:

/*--------------------------------*- C++ -*----------------------------------*\

| =========                 |                                                 |

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

|  \\    /   O peration     | Version:  v2012                                 |

|   \\  /    A nd           | Website:  www.openfoam.com                      |

|    \\/     M anipulation  |                                                 |

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

FoamFile

{

    version     2.0;

    format      ascii;

    class       dictionary;

    object      dynamicMeshDict;

}

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



dynamicFvMesh       dynamicMotionSolverFvMesh;



motionSolverLibs    (sixDoFRigidBodyMotion);



motionSolver        sixDoFRigidBodyMotion;



sixDoFRigidBodyMotionCoeffs

{

    patches         (floatingObject);

    innerDistance   0.05;

    outerDistance   0.35;



    centreOfMass    (0.5 0.45 0.35);



    // Cuboid dimensions

    Lx              0.3;

    Ly              0.2;

    Lz              0.5;



    // Density of the solid

    rhoSolid        500;



    // Cuboid mass

    mass            #eval{ $rhoSolid*$Lx*$Ly*$Lz };



    // Cuboid moment of inertia about the centre of mass

    momentOfInertia #codeStream

    {

        codeInclude

        #{

            #include "diagTensor.H"

        #};



        code

        #{

            scalar sqrLx = sqr($Lx);

            scalar sqrLy = sqr($Ly);

            scalar sqrLz = sqr($Lz);

            os  <<

                $mass

               *diagTensor(sqrLy + sqrLz, sqrLx + sqrLz, sqrLx + sqrLy)/12.0;

        #};

    };



    report          on;

    accelerationRelaxation 0.7;

    //accelerationDamping 0;



    solver

    {

        type Newmark;

    }



    constraints

    {

        // fixedPoint

        // {

        //     sixDoFRigidBodyMotionConstraint point;

        //     centreOfRotation (0.5 0.45 0.1);

        // }



        fixedLine

        {

            sixDoFRigidBodyMotionConstraint line;

            centreOfRotation (0.5 0.45 0.1);

            direction (0 1 0);

        }



        fixedAxis

        {

            sixDoFRigidBodyMotionConstraint axis;

            axis (0 1 0);

        }

    }

}





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

have a look at the tutorial from tobias, can not be better explained and he does a velocity that changes over time if i remember correctly (or a pressure)
https://www.youtube.com/watch?v=cvWaXBnEz1U&t=8s

Thank you for the response! It is very much appreciated. I will watch the vid and post if I have any further questions or solutions.

Quote:

Originally Posted by otaolafr (Post 804186)

Hey otaolafr, interesting vid, though not exactly what I am looking for... I am looking to change the velocity of the moving mesh, not the velocity of the fluid at a boundary.

Quote:

Originally Posted by RichardKelly (Post 804190)

Hey otaolafr, interesting vid, though not exactly what I am looking for... I am looking to change the velocity of the moving mesh, not the velocity of the fluid at a boundary.

sorry I miss read! eventhought it might help you for the programing look at part 13 I think... that is about that

Quote:

Originally Posted by otaolafr (Post 804193)

sorry I miss read! eventhought it might help you for the programing look at part 13 I think... that is about that

Thanks,

Will continue vids you suggested. Also came across this:

https://www.youtube.com/watch?v=3pfCP769C_U

The author also has a paper which I will review to see if they give any information on how they are handling the moving meshes. There is a lot going on in the vid!

Have you tried tabluated6DoFMotionCoeffs? Something like this link https://www.cfd-online.com/Forums/op...tml#post669711

I haven't tested it myself, but think it can be a solution for you.

Quote:

Originally Posted by Marpole (Post 804286)

Have you tried tabluated6DoFMotionCoeffs? Something like this link https://www.cfd-online.com/Forums/op...tml#post669711

I haven't tested it myself, but think it can be a solution for you.

Thanks Marpole,

I agree this might be better to use tabluated6DoFMotionCoeffs. I am going to play around with that solidBodyMotion solver. I will need to be able to input changes to the vessel at runtime. Still do not know if I can handle this with codestream or if I will have to change the source code. Will play around with that and perhaps upload my case if I can any headway.