|January 29, 2015, 14:34||
"centerOfRotation" handling in sixDoFRigidBodyMotion
Join Date: May 2014
Location: Genova, Italy
Posts: 2Rep Power: 0
I am a bit confused having an issue with the sixDoFRigidBodyMotion solver.
First of all, what is exactly, from a physical point of view, the object called "centreOfRotation"?
I presume it represents the point for which the equation that rules the rotation (i.e. Newton's second law for angular momentum) is written. In fact, all the moment arms are calculated as it was.
If I'm right, the theory says that one can choose any arbitrary point to be the center of rotation, having the same result (the moments and the moment of inertia will vary accordingly).
Of course, this point moves with the body, i.e. the distance between centreOfRotation and centreOfMass is a constant vector in the body local reference, while in the fixed reference only the magnitude of the vector is constant.
In the problem that I am studying, I need to choose "smartly" this point, so that the contribution of certain forces is zero, and the point does not coincide with the center of mass.
Now, I'm not being able to set the case successfully. I tried with setting in the constant/dynamicMeshDict an additional centreOfRotation entry, for example:
... centreOfRotation (-5 0 0); centreOfMass (0 0 0); ...
Looking at the source code at src/sixDoFRigidBodyMotion/sixDoFRigidBodyMotion/sixDoFRigidBodyMotion.C (lines 103-111), I found strange the following:
... initialCentreOfMass_ ( dict.lookupOrDefault ( "initialCentreOfMass", vector(dict.lookup("centreOfMass")) ) ), initialCentreOfRotation_(initialCentreOfMass_), ...
Did anyone have a similar problem before?
Any help is appreciated!
P.S.: the solver application I use is pimpleDyMFoam.
Last edited by ste_ge; January 30, 2015 at 04:40.
|August 4, 2016, 09:49||
Join Date: Jul 2015
Posts: 21Rep Power: 3
if you check dynamicMeshDict from pimpleDyMFoam's wingMotion case,
you will notice that centreOfRotation is set in the constraints.
If you built your case on a specific example, it would have been nice to know which one.
|centerofrotation, pimpledyfoam, sixdofrigidbodymotion|
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