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is it posible give prescribed motion in rigid body motion(dynamic mesh)

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Old   August 10, 2022, 02:49
Default is it posible give prescribed motion in rigid body motion(dynamic mesh)
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eunchong
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Hello Foamers


i'm newbie in openfoam and i am struggling doing my project

what i want to do is free decay test


Rotate the object(barge shape) until a certain time (i.e., rotate it to a certain angle)
pause for a certain time, and let go



t0 > t1 rotate object
t1 > t2 Hold it in that state
t2 > t3 let go and see free decay



i try give angular momentum but it seems initial value so it is hard to give certain angle
or i try to combine solid body motion and rigid body motion but it fail



i use OF2106 version and referred interFoam/RAS/movingDTChull and interFoam/RAS/floatingObject


i try so many time and out of idea
if someone know the answer I'd appreciate it if you gave me a hint

Code:
dynamicFvMesh   dynamicMotionSolverFvMesh;

motionSolverLibs (sixDoFRigidBodyMotion);

motionSolver    sixDoFRigidBodyMotion;

patches         (hull);
innerDistance   0.3;
outerDistance   1.0;

centreOfMass    (0 0 0);
mass            1000;
momentOfInertia (166.667 416.667 416.667);
angularmomentum (0 400 0)
orientation
(
1 0 0
0 1 0
0 0 1
);

rhoInf          1;
report          on;

value           uniform (0 0 0);

accelerationRelaxation 0.4;

solver
{
    type Newmark;
}

constraints
{
    zAxis
    {
        sixDoFRigidBodyMotionConstraint line;
        direction     (0 0 1);
    }
    yPlane
    {
        sixDoFRigidBodyMotionConstraint axis;
        axis          (0 1 0);
    }
}
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Old   August 22, 2022, 03:14
Default think i found the way
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eunchong
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hi former
It doesn't give a priscribed motion as I initially thought.
I found way to give initial angle of body

Here's how

first run the case in a short time

which Create a directory of time(t1) according to the write interval
in that directory of time has file which name is sixDoFrigidBodyMotionState
in t1/uniform/
Code:
centreOfRotation ( 0 0 0 );

orientation     ( 1 0 0 0 0.996194698 -0.087155742 0 0.087155742 0.996194698 );

velocity        ( 0 0 0 );

acceleration    ( 0 0 0 );

angularMomentum ( 0 0 0 );

torque          ( 0 0 0 );
You can simply change the orientation value of this value to give the corresponding initial angle which you want.


Because my case is to give a roll angle

orientation ( 1 0 0 0 0.996194698 -0.087155742 0 0.087155742 0.996194698 );


Change it to the following value


Because the angle was given while fixed on the x-axis


(0.996194698 is cos(5) , 0.087157742 is sin(5) )


if you want initial pitch you can give orientation value like this

orientation ( 0.996194698 0 -0.087155742 0 1 0 0.087155742 0 0.996194698 );
but beware if use decomposepar to calculate you need to change every sixdof file in proceesor directory

after that you can run the case as you want

I'm not an English speaker, so my explanation may be strange, I apologize for my bad English

I hope this helps who struggle with

now my problem is Allowing only two rotations: pitch and roll
But I can't find a way

If anyone knows please tell me the answer
thank
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