Surface Polishing Load - Nastran
Surface Polishing Load - Nastran
(OP)
In nastran what is the best way to apply a torque along Z axis over a set of shell elements lying in the X-Y. In a simplified example the torsion test will consist of a hollow box. The top of the box (lying in X-Y plane) is essentially glued to a rotating pad. The bottom of the box is constrained in translation.
I assume the best way to apply the torque over the surface is to use a RBE2 and applying a Z moment at the independent node. Is this correct, or do you have competing suggestions? Thanks in advance.
I assume the best way to apply the torque over the surface is to use a RBE2 and applying a Z moment at the independent node. Is this correct, or do you have competing suggestions? Thanks in advance.





RE: Surface Polishing Load - Nastran
I'd model the interface to the pad using compliant elements to represent the glue, and then make some disgusting approximations on the far side of the compliant layer. Otherwise your load distribution is going to be completely wrong.
Are you interested in local stresses, or general displacements?
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Surface Polishing Load - Nastran
RE: Surface Polishing Load - Nastran
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Surface Polishing Load - Nastran
RE: Surface Polishing Load - Nastran
The manner in which the forces are distributed is analogous to the classical bolt pattern analysis. Forces and moments at the reference grid are distributed to a set of points or nodes based on geometry. A torque is distributed as forces which are proportional to their distance from the center of rotation.
As for the comment "rigid body elements have no place in real world analysis" I beg to differ. First, we are talking about rigid elements and interpolation elements which are used in the majority of aerospace and automotive models built using Nastran. Most of the major automotive and aerospace manufacturers use Nastran directly or indirectly.
RE: Surface Polishing Load - Nastran
Thank you!
RE: Surface Polishing Load - Nastran
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Surface Polishing Load - Nastran
RE: Surface Polishing Load - Nastran
In unskilled hands RBE's are very dangerous animals ! and unfortunately 4loren doesn't know that FEMAP is most likely the best known PC based FE pre and post processor in the world and thus probably falls into this category !
RE: Surface Polishing Load - Nastran
However.
In this case imagine we have a grid of 16 equal spaced nodes that represent a square surface, through which a torque is being applied normal to the surface.
You are proposing that the analyst set up a set of rbe's in order to apply the torque.
Where would you put the rbes?
What torque or force do you apply to each of the rbes?
I'm sorry, I don't think the rbes have simplified anything.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Surface Polishing Load - Nastran
I would like Johnhors to simply tell me what an RBE3 does. I know that many in my field do not know and therefore never use it. It is however a very powerful tool. Do either of you use Nastran and if so how do you get around using rigid elements then?
RE: Surface Polishing Load - Nastran
Given that 90% of the models I see have frequencies that are high compared with the real structure, I am sure that other people don't put as much time into this sort of thing as I do.
Your proposed usage of RBEs would not put the force into the model in a representatitve fashion, locally. You have welded a thick steel plate to the structure and applied a torque to that. That may be acceptable. I'd try not to do it.
Cheers
Greg Locock
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.
RE: Surface Polishing Load - Nastran