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Changing velocity with time

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Old   May 19, 2021, 08:43
Default Changing velocity with time
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Richard Kelly
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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.
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Old   May 19, 2021, 10:01
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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);
        }
    }
}


// ************************************************************************* //
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Old   May 19, 2021, 11:38
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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
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Old   May 19, 2021, 11:41
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Richard Kelly
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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.
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Old   May 19, 2021, 11:54
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Quote:
Originally Posted by otaolafr View Post
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

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.
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Old   May 19, 2021, 12:37
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Quote:
Originally Posted by RichardKelly View Post
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
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Old   May 19, 2021, 12:42
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Quote:
Originally Posted by otaolafr View Post
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!
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Old   May 20, 2021, 12:40
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Have you tried tabluated6DoFMotionCoeffs? Something like this link dynamicFvMesh - tabulated motion of a solid body + mesh morphing


I haven't tested it myself, but think it can be a solution for you.
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Old   May 20, 2021, 13:12
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Quote:
Originally Posted by Marpole View Post
Have you tried tabluated6DoFMotionCoeffs? Something like this link dynamicFvMesh - tabulated motion of a solid body + mesh morphing


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.
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