Use of springs in ProMechanica

[ptc-380107]

Dear ProM's,

This is probably a bit basic, but I feel compelled to ask the question. In
the practical use of mechanica, I am having a bit of a problem
understanding what practical uses there are for springs in analysis. Can
someone give me a practical example? Maybe a short description of the
intended use for springs?

Any help would be greatly appreciated...

Greg Saiter....

[ptc-691624]

Greg,

I am sure there are many uses, but I always use the to take out rigid
body motion. It is better than a rigid restraint, which may cause
unrealistic stress.


John

[doug.bittner]

Hi Greg,

We design multiple axis positioning systems (think X-Y stages). I use
springs to model the linear bearings. The ProM-springs are a bit flaky
in torsion, but with careful set-up, a quad set can model a linear
bearing's pitch, yaw, and roll stiffnesses, as well as the lateral Ky &
Kz.

Good luck, and happy modeling.
-Doug


Doug Bittner
Staff Mechanical Engineer
Danaher Motion - Dover

[randyspeed]

Greg,

By far, springs in FEA have been mostly used to model fasteners. However,
there are other novel uses, such as those you have already heard of from
other users.

Springs are very efficient (run time) and represent the most basic property
of the finite element method, stiffness. They do a very nice job of solving
the force and displacement components of a model. You will not have stress
output available for springs.

The caveat with springs is that since there is no area at the point of load
transfer, stresses are unreliable at the mating parts in the vicinity of the
spring attach points. If you are solving for stresses in your analysis, you
may consider excluding elements in those vicinities from convergence (MPA
convergence algorithm, of course). The run will complete much faster.


Randy Speed
President and CEO
Speed Consulting, LLC
(972) 938-0490 ph (972) 937-2319 fax
www.speedconsulting.com

[rdubr]

Randy,

Can you exclude elements in integrated mode - or only independent Mechanica?