[jiadongw]

Hey Foamers,

I have worked on the motion solver rigidBodyMotion for a while, but still be struct in the linearAxialAngularSpring restraint.

Basically, I want to apply a linearAxialAngularSpring restraint to an airfoil, just like what wingMotion tutorial did using sixDoFRigidBodyMotion.
My final goal is to simulate two bodies with linearAxialAngularSpring restraint, so I guess the rigidBodyMotion solver is only choice because the sixDoFRigidBodyDisplacement has been deleted in new versions of OpenFoam.

The three official tutorials with rigidBodyMotion solver do not include linearAxialAngularSpring restraint, and the instructions about rigidBodyMotion solver seem to be quite few until now.

I try to modify the tutorial wingMotion using rigidBodyMotion solver, but is blows up after a period of time. Here is my modified dynamicMeshDict.

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  6
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      dynamicMeshDict;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dynamicFvMesh      dynamicMotionSolverFvMesh;

motionSolverLibs ("librigidBodyMeshMotion.so");

motionSolver    rigidBodyMotion;

rigidBodyMotionCoeffs
{

    report          on;

    solver
    {
        type symplectic;
    }

    g               (0 -9.81 0);
    rho             rhoInf;
    rhoInf          1;

    bodies
    {
       wing
       {
          type            rigidBody;
          parent          root;
          centreOfMass    (0.4974612746 -0.01671895744 0.125);
          mass            22.9;
          inertia         (1.958864357 0 0 3.920839234 0 2.057121362);
          transform       (1 0 0 0 1 0 0 0 1) (0.25 0.007 0.125);
   
          joint
          {
              type    composite;
              joints
              (
                   {
                       type Py;
                   }
                   {
                       type Rz;
                   }
              );
          }

          patches         (wing);
          innerDistance   0.3;
          outerDistance   1;

        }
    }

    restraints
    {
        linearSpring
        {
            type            linearSpring;
            body            wing;
            anchor          (0.25 0.007 0.125);
            refAttachmentPt (0.25 0.007 0.125);
            stiffness       4000;
            damping         2;
            restLength      0;
        } 
   
        axialSpring
        {
            type            linearAxialAngularSpring;
            body            wing;
            axis            (0 0 1);
            referenceOrientation
            (
                1 0 0
                0 1 0
                0 0 1
            );
            stiffness       700;
            damping         0.5;
        }
    }
}


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

My question is:
1) Does anyone know is there any available tutorial about the rigidBodyMotion solver with linearAxialAngularSpring restraint?
2) How to define the centre of mass, centre of rotation, transform and referenceOrientation in rigidBodyMotion solver?

Any advice is appreciated, thanks.

[Santiago]

Why dont you go to an earlier version of OF that does have what you need?

[jiadongw]

Originally Posted by Santiago

Why dont you go to an earlier version of OF that does have what you need?

Thanks for your reply, Santiago.

Yes, I have tested earlier version (OF4.0) which employs the sixDoFRigidBodyDisplacement and is able to handle multiple bodies. But its mesh solver is displacementLaplacian, which has a poor performance on rotation motion.

The new version OpenFoam treats the mesh motion using Slerp interpolation that has a amazing performance when work on the rotation motion of body. That's definitely what I need.

Anyway, thank you very much.

[Santiago]

Originally Posted by jiadongw

But its mesh solver is displacementLaplacian, which has a poor performance on rotation motion.

Is that true for your case? Does the mesh degrade so badly? Have you tried to use non conformal gridding (AMI, composite?)

[jiadongw]

Originally Posted by Santiago

Is that true for your case? Does the mesh degrade so badly? Have you tried to use non conformal gridding (AMI, composite?)

Yes, it seem to be true. My case needs a pitch angle of about 40 degrees. But the sixDoFRigidBodyDisplacement only can handle about 20 degrees rotation.

Because I want to simulate two foils which are very close to each other, I'm not sure AMI is suitable for my case.