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dandersonjr1-Visitor
1-Visitor
June 30, 2011
Question

How to apply a force/moment in Mechanica?

  • June 30, 2011
  • 16 replies
  • 6538 views

Good Day All,


Trying to apply a force & moment in mechanica to a surface on a part.
Do I have to apply this using Advance, Total Load, Uniform to get mechanica to apply the moment?
When I use a Simple Force/Moment Load mechanica ignors the Moment for some reason.
To close to the holiday and my brain needs a vacation.



Any help would be appreciated.
Thanks
Don Anderson

16 replies

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C
ckatsis1-Visitor
1-Visitor
July 6, 2011

A Total Load at Point will apply a linear force distribution to the referenced surface that is statically equivalent to the specified force/moment at the specified location. There is only one such force distribution.


The force distribution applied by the total load at point is unrelated to the density of the mesh on the referenced surface. And of course there will be many more degrees of freedom on the surface beyond the nodes as the solution reaches high polynomial orders.


Typically, applying moments on surfaces of shells doesn't produced the desired effect. In this example, the part will not "feel" a distributed moment from the body that has been skipped. It will feel a distributed force.


I would model this situation with a total load at point (as in the model Don attached).


Thanks,


Christos Katsis

A
Anonymous
July 6, 2011
I think it is all clear as mud now to me, since I have had some sleep. I
wasn't seeing that the distribution that Joe was talking about

was more related to the vectorial direction and magnitude of the applied
force as Randy eluded to in component form normal and tangential.

I was thinking there was some sort of issue with the applied force on the
surface not being even or not being uniformly distributed

on to the underlying mesh.



Steve






C
ckatsis1-Visitor
1-Visitor
July 6, 2011

One more thing that I forgot to mention in my previous post...


To minimize confusion and give a hint for the appropriate modeling technique, in Creo 1, the moment fields in the Load Definition dialog are inactive if the referenced geometric entity is expected to not have rotational degrees of freedom. In other words, the moment fields are availble for the application of a load on a point, curve or surface, onlyif that entity is associated with a shell, shell pair or beam. Otherwise, they will be inactive.


The same is the case for the enforced rotations in the Constraint Definition dialog.


Thanks,


Christos

I
iapanovitch1-Visitor
1-Visitor
July 7, 2011
To put Christos's explanation in a more layman's terms:

The moment loadis represented as adistributed translational force statically equivalent (i.e. exerting the same effect)to the moment load applied
That translational force distribution is similar to what one might call a "bolt pattern" distribution, i.e. the force magnitude is directly proportional to the distance from the CG of the surface (to which the moment is applied) to the given point (linear distribution). This is the assumed (by the Mechanica developers) force distribution for TLAP, and the user has no control over it (that's perhaps why the complaint about difficulty to control. To be fair, though, this is how most if not all other FEA systems do that too). Such an assumption is necessary, otherwise the force distribution would not be mathematically unique. Another assumed distribution, for instance quadratic, would result in a different "quadratic TLAP", and so on

Hope this addendum is somewhat useful.
Iouri (Yuri) Apanovitch

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iapanovitch1-Visitor
1-Visitor
July 7, 2011
Just one more thing...

Christos, given all the confusion around the TLAP (the questions seem to resurface over and over again, every year), it seems to me that having Razna guys putting together a quick whitepaper explaining how TLAP works, with some pictures/diagrams (which we all know are worth a thousand words) would be of huge benefitto the the Mechanica user community.

MSC has done a great similar explanation job with RBE3 (this is what Nastran guys use to apply moments to solid meshes). BTW, you could also add in there that Mechanica's Weighted Link feature (which, if I'm not mistaken, is "RBE3 withiut weights") could be used in place of TLAP, and perhaps obsolete TLAP althogether.

Regards,
Iouri (Yuri) Apanovitch

P
PAULKORENKIEWIC1-Visitor
1-Visitor
July 7, 2011
Hmmm... IF only there was a website we could go to where we could easily
search for "Suggested Techniques"... Yes, it's Friday for me, and yes,
I am being ironic...

Thanks...

Paul Korenkiewicz
FEV, Inc.
4554 Glenmeade
Auburn Hills, MI., 48326

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