321 constrain set vs Inertia Relief

[matteoviery]

Whats is the difference bewtten 321 set constrain and Inertia Relief


for a stress and for a model analysis?


Thanks for your help

 

[Ray Ellender]

For a stress analysis, there is not much difference, as I believe that Inertia Reliefeffectively makes an internal 3-2-1 constraint system in order to run; you just can't see it or control where the fixed point is. Both need balanced loads, i.e. the reaction force as well as the action force. If you don't apply a balanced load set, with Inertia relief, Mechanica applies body loads, e.g. gravity, to get a balanced load, which may not be what you had in mind. Apart from that, they give the same result, except the zero displacement point will be at a different place.


You can't use Inertia Relief in a modal analysis - but then you aren't applying any loads in a modal analysis anyway, but you can run an unconstrained modal


So if you are not bothered about where the fixed point is, and you have a balanced load set, use Inertia relief, as it saves time setting up. Otherwise make a 3-2-1 constraint system.
Edited by: Ray Ellender

 

[Kaz Z06]

Inertia Relief provides weak springs that stabilize the body so there are no rigid body movements. I believe they are applied to the CG. Inertia Relief is an excellent option if you've conducted a MDO analysis and want to pass the loads into Mechanica for a structural run - I've used this process many times before and it works very well.