Linear Static vs Linear Dynamic FEA for a moving mass having deceleration

[Zande10]

A mounted set of plates, tooling, etc. are mounted to a linear actuator that is mounted parallel to the ground. The actuator will decelerate at a known rate per the parameters in the servo controller. I am most interested in comparing two different styles of designs (plates, tooling, etc.) hanging from the carriage, off this linear actuator. Specifically once this max deceleration occurs, the corresponding displacement value. This is indeed a dynamic problem but my question is if it is reasonable to apply this max deceleration rate as a horizontal negative acceleration within a 'STATIC' FEA to obtain some idea of max displacement and way to ultimately compare designs. I sort of understand the governing equation of motion but do not fully understand the short comings with this approach as compared to a more involved time dependent dynamic analysis. For reference I have access to Solidworks FEA. Thanks for any feedback!

 

[GregLocock]

Yes, as a rough check it is common to do a static analysis, rather than a true dynamic analysis. Needless to say your Factor of Ignorance will have to be much higher because you aren't modelling resonant behaviour, there again if you do dynamic you need the damping of each mode which is a stab in the dark.

Cheers

Greg Locock


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[Denial]

Your use of the term "hanging" in your problem description suggests the possibility of pendulum behaviour.[ ] If this is the case, the situation might be significantly different from what Greg envisages in his reply above.[ ] An instance of a hanging load being accelerated/decelerated horizontally came up in thread507-512296 a few weeks ago.[ ] In that thread, see my comment of 29-Sep-23@08:46.

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[Zande10]

Thanks Greg and Denial for the feedback.

I should not have stated 'hanging'. The assemblage of parts are all bolted together. The Center of Mass of all these bolted parts are however some decent distance below the carriage of actuator. So there is a pendulum (ringing/vibrating) response of tooling upon its quick deceleration (parts are in existence and you can see this ringing).

So it sounds like even if a dynamic analysis is performed, you need to assign a dampening value upon study setup for that modal shape of interest which is a best guess without further knowledge....

 

[btrueblood]

"parts are in existence and you can see this ringing" - so you could also attach a small accelerometer or strain gages, and measure the response and extract a damping value from the data.

 

[FEA way]

Solidworks Simulation offers linear and nonlinear dynamic studies too so it might be best to just carry out both static (with "gravity" load in a given direction) and dynamic (with parts’ movement controlled by a time-dependent excitation) analysis and compare the results.

I’ve seen a similar comparison of transient and equivalent static loading in Abaqus training materials where it was shown why static analysis with centrifugal load is sufficient to evaluate the stresses in a rotor.