[noodleluvmay]

Hello everyone,

I've been trying to build a case for simulating wave interaction with an attenuator-type wave energy converter device, and I want to set the case up as shown in Figure 1. where the 2 box bodies are allowed to freely rotate around the hinge in the middle as waves pass through, and the hinge is free to move vertically (in the future potentially considering to add mooring to the geometry and allow the hinge to move freely).

I have currently set the dynamicMeshDict as follows, where I have applied joints to move freely in Y and Z, and rotate about Y axis (I think). I've also set with the transform keyword for the centre of rotation to be at the origin initially (0 0 0).

/*--------------------------------*- C++ -*----------------------------------*\
| =========                 |                                                 |
| \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox           |
|  \\    /   O peration     | Version:  v1806                                 |
|   \\  /    A nd           | Web:      www.OpenFOAM.com                      |
|    \\/     M anipulation  |                                                 |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    object      dynamicMeshDict;
}

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

motionSolverLibs    ("librigidBodyMeshMotion.so");

dynamicFvMesh       dynamicOversetFvMesh;

dynamicOversetFvMeshCoeffs
{
}

motionSolver        rigidBodyMotion;

// rigidBodyMotionCoeffs  - not needed any more
//  {
report          on;

solver
{
	type Newmark;
//     gamma   0.1;    // Velocity integration coefficient
 //   beta    0.1;    // Position integration coefficient
}

accelerationRelaxation 0.7;

//- prescribedRotation requires some sub-iterations to converge faster
//  to desired value.
// nIter   3;

bodies
{
	box1
	{

		type            rigidBody;
		parent          root;
		patches       	(box1);
		
		innerDistance   100;
		outerDistance   101;

		centreOfMass    (-20 0 0);
		  // Cuboid dimensions
		Lx              40;
		Ly              4;
		Lz              4;

		// Density of the solid
		rhoSolid        500;

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

		inertia         (1 0 0 1 0 1);
		transform       (1 0 0 0 1 0 0 0 1) (0 0 0);

		joint
		{
			type            composite;
			joints
			(
				{
					type Px;
				}
				{
					type Pz;
				}
				{
					type Ry;
				}
			);
		}
		
		constraints
		{
			fixedAxis
			{
				sixDoFRigidBodyMotionConstraint plane;
				normal (0 1 0); // constrained in y plane?
			}
		}
	
		restraints
		{
			 AngularDamper
			 {
				 sixDoFRigidBodyMotionRestraint      sphericalAngularDamper;
				 coeff                               5000;                //angular damping coefficient in Nms/rad
			 } 
		}

	} //end box1
	
    box2
	{
		type            rigidBody;
	    parent          root;
		patches         (box2);
		
		innerDistance   100;    // With overset we want to avoid the mesh
		outerDistance   101;	// deformation so have large innerDistance

		// Cuboid mass -- very simple setup. For more complicated shapes
		// see utility surfaceInertia
		 // Cuboid dimensions
		Lx              40;
		Ly              4;
		Lz              4;

		// Density of the solid
		rhoSolid        500;

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

		inertia         (1 0 0 1 0 1);
		centreOfMass    (20 0 0); // relative to the centreOfMass
										// of parent body
										// (here root = global coord system)

		// Transformation tensor and centre of rotation
		transform       (1 0 0 0 1 0 0 0 1) (0 0 0);

		joint
		{
			type            composite;
			joints
			(
				{
					type Px;
				}
				{
					type Pz;
				}
				{
					type Ry;
				}
			);
		}
		
		constraints
		{
			fixedAxis
			{
				sixDoFRigidBodyMotionConstraint plane;
				normal (0 1 0); // constrained in y plane?
			}
		}
	
		restraints
		{
			 AngularDamper
			 {
				 sixDoFRigidBodyMotionRestraint      sphericalAngularDamper;
				 coeff                               5000;                //angular damping coefficient in Nms/rad
			 } 
		}
	} // end body_Aft
}
  
  

//  } // end of rigidBodyMotionCoeffs


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

However, I am not sure if this is the correct way/syntax for setting something like this up, and I am not sure if the 'joint', 'transform', 'constraints' and 'restraints' definitions were set up properly regarding the 2 bodies and the joint.

In an initial trial run, the results at around 4s show the Centre of Rotation shifting to -85 m in Z which seems unphysical (or maybe I've interpreted it wrongly?):

Rigid-body motion of the fwd
    Centre of rotation: (0 0 -85.1395255871)
    Orientation: (1 0 0 0 1 0 0 0 1)
    Linear velocity: (0 0 -40.8709835732)
    Angular velocity: (0 0 0)
Rigid-body motion of the aft
    Centre of rotation: (0 0 -85.1395255871)
    Orientation: (1 0 0 0 1 0 0 0 1)
    Linear velocity: (0 0 -40.8709835732)
    Angular velocity: (0 0 0)
inverseDistance : detected 2 mesh regions
    zone:0 nCells:9576000  voxels:(85 85 85) bb:(-90.0000603573 -12.0000603573 -20.0000603573) (-34.0180396427 0.147119357345 -0.987181642655)
    zone:1 nCells:5615950  voxels:(85 85 85) bb:(-40.0000076955 -4.00000769553 -4.00000769553) (-34.0998923045 7.85500095484e-06 -1.09999230447)
Overset analysis : nCells : 15191950
    calculated   : 14708262
    interpolated : 250840 (interpolated from local:236708  mixed local/remote:14126  remote:6)
    hole         : 232848

I'm very new to setting up body dynamics in OpenFOAM, so I would appreciate any thoughts and input.

Thanks, everyone!