[FloB]

Hello,

I want to simulate a floating object with interDyMFoam. For that, I based my files on the tutorial floatingObject (https://github.com/OpenFOAM/OpenFOAM...floatingObject)


I wanted to change the dimensions of the mesh and the floater, so I changed blockMeshDict, dynamicMeshDict, topoSetDict and setFieldsDict files only :

blockMeshDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      blockMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

scale 1;

X0    0;
X1     300;
Y0     0;
Y1     100;
Z0  0;
Z1     20;

nx  300;
ny  100;
nz  40;

vertices
(
    ($X0 $Y0 $Z0)
    ($X1 $Y0 $Z0)
    ($X1 $Y1 $Z0)
    ($X0 $Y1 $Z0)
    ($X0 $Y0 $Z1)
    ($X1 $Y0 $Z1)
    ($X1 $Y1 $Z1)
    ($X0 $Y1 $Z1)
);

blocks
(
    hex (0 1 2 3 4 5 6 7) ($nx $ny $nz) simpleGrading (1 1 1)
);

edges
(
);

boundary
(
    inlet
    {
        type patch;
        faces
        (
            (0 4 7 3)
        );
    }
    outlet
    {
        type patch;
        faces
        (
            (2 6 5 1)
        );
    }
    stationaryWalls
    {
        type wall;
        faces
        (
            (0 3 2 1)
            (1 5 4 0)
            (3 7 6 2)
        );
    }
    atmosphere
    {
        type patch;
        faces
        (
            (4 5 6 7)
        );
    }
    floatingObject
    {
        type wall;
        faces ();
    }
);

mergePatchPairs
(
);

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

dynamicMeshDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      motionProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dynamicFvMesh       dynamicMotionSolverFvMesh;

motionSolverLibs    ("libsixDoFRigidBodyMotion.so");

motionSolver        sixDoFRigidBodyMotion;

sixDoFRigidBodyMotionCoeffs
{
    patches         (floatingObject);
    innerDistance   0;
    outerDistance   4;

    centreOfMass    (150 50 10);

    // Cuboid dimensions
    Lx              80;
    Ly              30;
    Lz              6;

    // Density of the solid
    rhoSolid        500;

    // Cuboid mass
    mass            #calc "$rhoSolid*$Lx*$Ly*$Lz";

    // Cuboid moment of inertia about the centre of mass
    momentOfInertia #codeStream
    {
        codeInclude
        #{
            #include "diagTensor.H"
        #};

        code
        #{
            scalar sqrLx = $Lx*$Lx;
            scalar sqrLy = $Ly*$Ly;
            scalar sqrLz = $Lz*$Lz;
            os  <<
                $mass
               *diagTensor(sqrLy + sqrLz, sqrLx + sqrLz, sqrLx + sqrLy)/12.0;
        #};
    };

    rho	rhoInf;
    rhoInf	1000;
    report          on;
    accelerationRelaxation 0.95;
    accelerationDamping 0.95;
    solver
    {
        type Newmark;
//	type	symplectic;
//	type	CrankNicolson;
    }

    constraints
    {
        // fixedPoint
        // {
        //     sixDoFRigidBodyMotionConstraint point;
        //     centreOfRotation (0.5 0.45 0.1);
        // }

        fixedLine
        {
            sixDoFRigidBodyMotionConstraint line;
            centreOfRotation (150 50 10);
            direction (0 1 0);
        }

        fixedAxis
        {
            sixDoFRigidBodyMotionConstraint axis;
            axis (0 1 1);
        }

    }


}


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

topoSetDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      topoSetDict;
}

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

actions
(
    {
        name    c0;
        type    cellSet;
        action  new;
        source  boxToCell;
        box (110 35 7) (190 65 13);
    }

    {
        name    c0;
        type    cellSet;
        action  invert;
    }
);


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

setFieldsDict:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  5                                     |
|   \\  /    A nd           | Web:      www.OpenFOAM.org                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "system";
    object      setFieldsDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

defaultFieldValues
(
    volScalarFieldValue alpha.water 0
    volVectorFieldValue U (0 0 0)
//    volScalarFieldValue p_rgh 0
);

regions
(
    boxToCell
    {
        box (-100 -100 -100) (500 500 10);
        fieldValues ( volScalarFieldValue alpha.water 1 );
    }
);


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

Note that I chose rhoSolid and submerged volume so that buyancy and weight forces are equal : as in my case there is not other forces, floater is supposed to be at equilibrium.


Unfortunately, with these new dimensions my simulation crashed after less than 1 s. I reduced time step to observe variables evolutions the first 1e-3/1e-2 s : I realized there was a pressure divergence. Indeed, pressure was oscillating between positive and negative value under the floater, and after a certain time values were so huge that simulation stoped.


I observed that there was no problem anymore when I reduced the X dimension of the floater (to have a shape closer to a square) and I absolutly don't know why.


However, I really wanted to simulate the shape I planed (80*30*6 m^3)
So I tried to change mesh dimension, mesh discretization, nCorrectors, nOuterCorrectors but it didn't work.

One thing helps me to solve my problem : change some fvScheme solvers :
I put Euler instead of CrankNicolson for ddtScheme and Gauss limitedLinearV 1 instead of Gauss vanLeerV for div(rhoPhi,U).
I do not know why it worked so if someone has an explanation I would be glade to read it.




Now, I'm facing again the same problem : I just wanted to suppress the constraints fixedLine and fixedAxis in dynamicMeshDict file and again, I get pressure oscillations and then divergence.
I tried to vary some parameters, without success... You'll find attached some screenshots just before the crash.


I also implemented the same model with potentialFreeSurfaceDyMFoam which is a bit similar to interDyMFoam, except there is only one phase (air is not represented). I get exactly the same problem of pressure divergence...


I would really appreciate to get some help from someone.

Thanks in advance,

Florian

[Giannis_Kaz]

Dear Florian


I have exactly the same Problem. Any suggestions?


Regards