Rigid Body Mesh Motion + 6DoF
 

I've been reading through tutorials and web pages for a couple weeks now and can't figure out how to get this working. It seems that all the tutorials with DoF (e.g. wingMotion [flutter]) are made for small displacements and use the laplacianDisplacement solvers.

Basically, I am looking to do something like:
http://www.youtube.com/watch?v=jZwUA_xnces

I have seen many many tutorials and examples where the domain motion is a specified rotational velocity, but I'd really like it solved for (with moment of inertia, etc).

Preferably in 2.2.x, but at this point I'd be willing to install whatever necessary. If anyone can point me in the right direction (or hell, provide a gzipped case :)) of that case I'd be super grateful.

I've been working off of the mixerVesselAMI2D and wingMotion case. Basically, I'm trying to mix the multi-domain AMI capability of the mixerVessel case with the 6DoF solver from the wingMotion (flutter) case. So, my goal is to change the mixerVessel change from a specified rotor motion to a 6DoF solver (I will find a way to test with initial conditions or through an initial condition)

So, I've changed the dynamicMeshDict
In the mixer tutorial, this is where the cellZone rotation is specified. I've changed it to the dynamicFvMesh solver from the airfoil case.

So, I then copied over the pointDisplacement from the Airfoil case and basically just changed the "center point" and removed the restraints (springs).

I'm currently struggling to rotate just the rotor cellZone. My current pointDisplacement file looks like:
So I thought I was being clever by defining one side of the AMI as zeroGradient and then the other as simply fixed 0. However, the displacement is still "bleeding" across the AMI.

Any suggestions?

So I was able to fix my problem with the outside rotating. You need to create a pointZoneSet (I used the setSet utility to do it interactively rather than topoSet). Then you simply specify a "frozenPointZone"

However, the issue now is that the AMI is "breaking apart". The fvMeshSolver is still solving the displacement at each point as a function of the closest rotor point.

I feel that I'm going about this the wrong way. Can I simply specify the entire rotor cellZoneSet in the pointDisplacement library? or something like that ...

Goodness, it appears 1 day after I posted my original message they released OF 2.3 which allows solid body motion. (face palm) See below from release notes:
I will install 2.3 and see if I can get this thing working.

Hello minger,

can you tell us if you finally managed to move your mixer with the solid body motion? I am also interesting in the rotating motion without the AMI method.

Regards Cyril

OK, so I may have something working. Cyril, to address something you said, there is still AMI interfaces. We still need to communicate between the rotating and stationary zones, and the AMI handles that.

The main difference is that they rolled in a few dynamicFvMesh solver which allows the rigidbodymotion. Here is an image 0.3 s into my simulation which appears to be chugging along (mesh displacement shown first, and velocity shown second)
Attachment 29772
Attachment 29773
Attachment 29774

Here are the highlights for getting it working

• pointDisplacement point vector field. I set all my outer walls to fixed 0, the symmetry plane and the moving rotor to calculated. I fixed the stationary side of the interface to 0 and the rotating side to calculated.
• dynamicMeshDict is where everything happens. You set sixDoFRigidBodyMotionC as the solver, and then set your coefficients just like you normally would (presumably, I don't think I have) if you were defining it in pointDisplacement.
  • I set the rotor as the patch
  • I had to use LARGE distances. It seems like it interpolates all points to the nearest point in the patch listing. So, I was still getting the mesh to come apart at the interface when I had realistic values set (I was using 2 for inner and 2.1 for outer. I am now using 1e5 for inner and 1.1e5 for outer
• You do not need the fvOptions set (not sure why I was playing with it)
• I am not using the frozenPointsZone in the 6DoFCoeffs dictionary. I have it in my mesh ... but am not using it and it seems to be working. So how the solver know? I'm guessing that it knows that my patch "rotor" is inside of a certain cell zone, so it's only deforming that. But that is purely speculative and perhaps this success message is premature (although if I show only the stationary cellZone the displacement is zero everywhere)

I have uploaded my current case if anyone wants to play. There is likely a lot of garbage in there, so I apologize in advance

https://drive.google.com/file/d/0B2c...it?usp=sharing

Hi minger,

Thank you very much for you detailed information about your case and your sharing. It was all wonderful.

I want to ask you one more favor. If it is possible please tell me about the commands you have ran step by step to achieve this.

Thank you,
Mojtaba.

I mean, there weren't any specific commands. I meshed the geometry in ICEM, so needed to run fluent3DMeshToFoam to convert the .msh file into an OpenFOAM polymesh. After that, I'm simply running pimplyDyMFoam. The case set up does all the work. If you download the case and simply run that solver, it should iterate!

Thank you minger,
Yea that's right. Can you please have a look at this thread:

http://www.cfd-online.com/Forums/ope...free-body.html

Beside the problem I have mentioned above, I have some serious problem in converging the solution.

Dear minger,

many thanks for all that valuable information. Could I apply what you posted for vortex induced vibration for circular cylinder? Is it helpful for my cylinder case?

Dear Maimouna,

I think for VIV of a flow past a circular cylinder is more simple. First, define the moving patch (i.e., circular) at the dynamicMeshDict and at pointDisplacement defines the moving patch as 'calculated' type boundary condition. But Minger may have better suggestion.

Cheers
-mali-

Dear Mali'

many thanks for you post. I'm applying VIV in OF-2.2.2, so if you could please check dynamicMeshDict file and pointDisplacement file, it would be really grateful. In my case, dynamicMeshDict and pointDisplacement files are below respectively

With million of thanks.

Maimouna

Dear Maimouna,

I don't have the chance to try the file that you posted yet. But, below is the file that I'm using to simulate the VIV problem. I'm also using OpenFOAM 2.2.

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

dimensions [0 1 0 0 0 0 0];

internalField uniform (0 0 0);

boundaryField
{
square
{
type sixDoFRigidBodyDisplacement;
mass 584.6;
centreOfMass (0 0 0.5);
momentOfInertia (97.7 97.7 97.7);
orientation //22.5degree
(
1 0 0
0 1 0
0 0 1
);
velocity (0 0 0);
acceleration (0 0 0);
angularMomentum (0 0 0);
torque (0 0 0);
rhoName rhoInf;
rhoInf 1;
g (0 0 0);
report on;
constraints
{
maxIterations 500;

fixedLine1
{
sixDoFRigidBodyMotionConstraint fixedLine;
tolerance 1e-9;
relaxationFactor 0.1;
fixedLineCoeffs
{
refPoint (0 0 0);
direction (0 1 0);
}
}

fixedAxis1
{
sixDoFRigidBodyMotionConstraint fixedAxis;
tolerance 1e-06;
relaxationFactor 0.7;
fixedAxisCoeffs
{
axis ( 0 0 1);
}
}
}
restraints
{
verticalSpring
{
sixDoFRigidBodyMotionRestraint linearSpring;

linearSpringCoeffs
{
anchor (0 0 0.5);
refAttachmentPt (0 0 0.5);
stiffness 23079.1;
damping 34.89;
restLength 0;
}
}
axialSpring
{
sixDoFRigidBodyMotionRestraint linearAxialAngularSpring;

linearAxialAngularSpringCoeffs
{
axis (0 0 1);
stiffness 100000;
damping 100;
referenceOrientation $orientation;
}
}
}
value uniform (0 0 0);
}

inlet
{
type fixedValue;
value uniform (0 0 0);
}

outlet
{
type fixedValue;
value uniform (0 0 0);
}

front
{
type empty;
}
back
{
type empty;
}


}


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

Dear Mali,

many thanks for your previous post. When I applied what you posted in my case, I couldn't figure out any motion on the cylinder. Why? Could you figure out any motion in your case?

Many thanks in advanced.

Maimouna

Dear Minger,

I'm working with a system like your test case: a rotating device in water.
I have a problem. If I try to define a torque at the shaft of the device, It seems that the value imposed is only an initial condition value. If I extract a report of moment applied to the device the torque imposed don't have effect.
Do you have tested a similar case with a constant resistance to the motion?

Many thanks in advanced.

I am struggling with a similar thing as well, i.e. defining a constant resistant torque over a turbine's axis to introduce the resistance from the generator, which is connected to turbine.

It seems not possible in 'dynamicMeshDict'?? I tried 'torque (x x x)' entry but it didn't work. I know it is possible to use a spring or a damper but they seem not ok to provide a constant value.

Cheers

Mass property
 

Hey,

I am trying to simulate a ship flow. I have few questions regarding dynamic mesh. Hope someone can help. Its urgent:(


1: why is the rhoInf in the dynamic mesh 1. should it not be the density of the ship (mass/volume). I have the weight for my geometry (77 kg) and I got the volume using the Solidwork.

2. The moment of inerta. there are 3 moment of inertia
a. Principal axes of inertia and principal moments of inertia: ( kilograms *
square meters ) Taken at the center of mass.
b.Moments of inertia: ( kilograms * square meters )Taken at the center of
mass and aligned with the output coordinate system
c. Moments of inertia: ( kilograms * square meters )
Taken at the output coordinate system.


My guess for the moment of inertia was about the center of mass since that is what asked in the dynamic mesh. Bot I try to clarify it using Solidwork, I am not getting the same moment of inertia nor mass using the rhoInf as 1
so I tried to find the density using the mass in the dynamicMeah and the volume I got from the software. But I still don't have answers


Please please help. I am lost and out of ideas

Kind regards
vava10