[zweihuehner]

For a research project I want to simulate a Wave energy converter (WEC) in extreme waves with OpenFoam.
The WEC consists of two articulated floating bodies which is why I choose the overset Mesh method for modelling.

I was already able to set up a simulation with one body but I am failing to do so with two bodies (firstly without articulation).
Does anyone have experience with this? So far I just added a second object in the dynamicMeshDict like so:

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v2106                                 |
|   \\  /    A nd           | Website:  www.openfoam.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      dynamicMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dynamicFvMesh   dynamicOversetFvMesh;

solvers
{
     VF
     {
        motionSolverLibs (fvMotionSolvers);

        motionSolver            solidBody;
        solidBodyMotionFunction drivenLinearMotion;

        cellSet                 c0;
        cOfGdisplacement        CofG;
    }

    Obj1
    {
        motionSolverLibs   (sixDoFRigidBodyMotion);
        motionSolver        sixDoFRigidBodyMotion;

        cellSet         c1;

        patches         (WEC1);
        innerDistance   1000.0;
        outerDistance   1001.0;

        centreOfMass    (4 0.75 1);
        cOfGdisplacement    CofG;

        // Cuboid dimensions
        Lx              0.5;
        Ly              0.3;
        Lz              0.2;

        // 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 0.9;
        accelerationDamping    1;

        solver
        {
            type Newmark;
        }

        restraints
        {

            linearSpring
            {
                sixDoFRigidBodyMotionRestraint linearSpring;
                anchor            (2 0.75 0);
                refAttachmentPt   (3.75 0.75 0.9);
                stiffness         300;
                damping           0;
                restLength        1.96787;
            }

        }
    }

    Obj2
    {
        motionSolverLibs   (sixDoFRigidBodyMotion);
        motionSolver        sixDoFRigidBodyMotion;

        cellSet         c2;

        patches         (WEC2);
        innerDistance   1000.0;
        outerDistance   1001.0;

        centreOfMass    (3.4 0.75 1);
        cOfGdisplacement    CofG;

        // Cuboid dimensions
        Lx              0.5;
        Ly              0.3;
        Lz              0.2;

        // 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 0.9;
        accelerationDamping    1;

        solver
        {
            type Newmark;
        }

        restraints
        {

            linearSpring
            {
                sixDoFRigidBodyMotionRestraint linearSpring;
                anchor            (1.4 0.75 0);
                refAttachmentPt   (3.15 0.75 0.9);
                stiffness         300;
                damping           0;
                restLength        1.96787;
            }

        }
    }

}
// ************************************************************************* //

I found no other helping examples or code snippets dealing with the same problem except for this one: Multiple Floating Objects with 6DoF in OF 2.3.0
Unfortunately I think this solution is derived from the "twosimplerotors" example and does not allow 6DOF.


However, I can not imagine that it is not possible to simulate two floating bodies with openFoam with overset Mesh.


Looking forwards to help.

[mahsankhan]

Hey Faro Schäfer,


Did you find any solution for using more than 1 body in OpenFOAM with 6DoF? Let me know, please. Thank you so much.


Regards,
Ahsan

[Jim1310]

For overset meshes it mmight not be possible to simulate multiple bodies (for deformable mesh it is possible, see report from Chalmers University from Magnus Urquhart). Lately i have found that there has been made a new type of overset mesh found in https://journal.openfoam.com/index.p...rticle/view/96 . It is called dynamicOversetZoneFvMesh and inherits from oversetBase and dynamicMultimOtionSolverFvMesh, with the later one enabling the capability of having multiple zones of overset meshes. I have also made a case of 2D floating bodies (in v2306) where the functionality of the above code is demonstrated. In that case one body performs oscillating rotating motion and the other is freely moving.

[cfdphd]

Hello Dimitris Tsoumpelis,

Can you share your case of 2D floating bodies?

Thank you.

[Jim1310]

Yes of course, i think i have it attached it in the post above. In any case though here it is. (actually it takes very little space, i probably had forgotten to provide the zip application the '-r' option).