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Use of a laplacian mesh motion solver with the 6DoF or rigidBodyMotion libraries

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Old   September 10, 2019, 08:20
Default Use of a laplacian mesh motion solver with the 6DoF or rigidBodyMotion libraries
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Hi all,
I'm trying to simulate the motion of multiple rigid bodies in a flow. The mesh motion solvers in the 6DoF and rigidBodyDynamics libraries aren't suitable for my geometry, I need velocityLaplacian or displacementLaplacian. This is has been done in these tutorials:

http://www.tfd.chalmers.se/~hani/kur...usUrquhart.pdf
http://www.tfd.chalmers.se/~hani/kur...Minghao_Wu.pdf

What they do is set the mesh motion solver to displacementLaplacian in the dynamicMeshDict file and apply a sixDoFRigidBodyDisplacement boundary condition to the patches corresponding to the rigid bodies in the pointMotionU file. However, from OpenFOAM 5 onward, the 6DoFDisplacement boundary condition has been removed. Apparently the condition was buggy in parallel: https://bugs.openfoam.org/view.php?id=2487

The reason for the removal is given here:
https://github.com/OpenFOAM/OpenFOAM...4de84638ad6933

Quote:
These legacy boundary conditions are no longer needed and have been superseded by the more flexible sixDoFRigidBodyMotion and rigidBodyMotion solvers. See tutorials:

incompressible/pimpleDyMFoam/wingMotion/wingMotion2D_pimpleDyMFoam
multiphase/interDyMFoam/RAS/DTCHull
multiphase/interDyMFoam/RAS/floatingObject
The thing is, I can't figure out how to use the Laplacian mesh motion solvers in OpenFOAM 6 without using these boundary conditions. None of the tutorials do something like this as far as I'm aware. Is it even possible without a lot of coding?
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Old   September 10, 2019, 15:05
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Here is an example with the rigidBody 6dof solver. This is essentially the same solver, there are however differences to the 6dof solver you are using. Which might be irrelevant. Nevertheless an example for that solver:

Code:
dynamicFvMesh       dynamicMotionSolverFvMesh;
motionSolverLibs   ("librigidBodyMeshMotion.so");
motionSolver        rigidBodyMotionSolver;
meshSolver          
{

   // replace this with your solver
    solver displacementLayeredMotion;
    regions
    {
        rotorZone
        {
            interpolationScheme linear;
            boundaryField
            {
                rotor
                {
                    type            follow;
                    patch           rotor; 
                }
                stator
                {
                    type            fixedValue;
                    value           uniform (0 0 0);
                }
            }
        }
    }
}


report              on;
rho                 rhoInf;
rhoInf              1000;
g                   (0 0 0);

solver
{
    type  Newmark;
    beta  0.5;
    gamma 0.25;
}

accelerationRelaxation 0.3;
//accelerationDamping    0.0;
nIter                  1;
/*
ramp table
(
    (0   0)
    (0.1 0)
);
*/

bodies
{
    rotor
    {
        type            sphere;
        parent          root;
        mass            8.15;
        radius          0.0399; 
        centreOfMass    (0 0 0);
        transform       (1 0 0 0 1 0 0 0 1) (0 0 0);

        joint
        {
                type  composite;
                joints
                (
                    { type Px; }
                    { type Py; }
                );
        }

        patches         (rotor);
        //innerDistance   0;
        //outerDistance   0.00029526;
    }
}
    
restraints
{
    linearSpring
    {
        type            linearSpring;
        anchor          (0 0 0);
        restLength      0;
        body            rotor;
        refAttachmentPt (0 0 0);
        stiffness       125000;
        damping         404;
    }  
}
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Old   September 11, 2019, 10:07
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This works like a charm, thanks a lot.
One question, how did you learn how to do this? A tutorial? Reading the source code? Asking someone else?
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Old   September 11, 2019, 10:13
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Reading the source code of the rigid body library and most importantly many years of experience
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Old   June 26, 2020, 07:45
Default How to modify oscillatingDisplacement input values to only Displacement values
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Hello,


My case is similar to the study done by http://www.tfd.chalmers.se/~hani/kur...usUrquhart.pdf



From the above report in section 1.4.3 the author used oscillatingDisplacement for floatingObject


Code:


floatingObject
{
type            oscillatingDisplacement;
amplitude       (0.03 0 0);
omega           6;
value           uniform (0 0 0);
}


In my case I would like to provide displacement from a text file (for example earthquake time history data for base excitation).


Is there a way to do it and how to import data or txt file into pointfields file. Any suggestions will be helpful.



Thanks in advance
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Old   June 26, 2020, 08:19
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Quote:
Originally Posted by neko2650 View Post
Is there a way to do it and how to import data or txt file into pointfields file. Any suggestions will be helpful.
Sure, you can modify the oscillatingDisplacement class by adding a member of type interpolationTable. Then you can specify the address of the file you want it to read from in the same way you specify omega or amplitude.

If the member variable is called, for example, basePosition, then to lookup a value from the file at time "t", you can write:
Code:
scalar value = basePosition(t);
Look into code that makes use of the interpolationTable class for clear examples.
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Old   June 26, 2020, 09:58
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Thank you for immediate response.
I tried looking for examples in tutorials for type interpolationTable but didnt found but I found an example usage in API
URL: https://cpp.openfoam.org/v5/classFoa...tionTable.html

Code:
 
readerType      csv;     
fileName        "$FOAM_CASE/constant/p0vsTime.csv";     
hasHeaderLine   true;   // skip first line     
timeColumn      0;      // time is in column 0     
valueColumns    (1);    // value starts in column 1
I have a small doubt regarding
Quote:
Sure, you can modify the oscillatingDisplacement class by adding a member of type interpolationTable.
Here how can I modify oscillatingDisplacement class i.e should I add the above lines in

Code:
floatingObject
{
 type            oscillatingDisplacement;
...
}
or do I need to modify src file and generate a custom for example MyoscillatingDisplacement class file
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Old   June 26, 2020, 10:07
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You need to modify the original header and source files and compile them as a new boundary condition. Once that's done, the lines fileName, hasHeaderLine... are added in the pointDisplacement file under whichever patch is supposed to move.

If you can't find examples for interpolationTable, try the timeFunction1 class, it provides similar functionality.
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