Re: Spring simulation questions

scohen-2 · ‎May 21, 2014

Hi

I created a simple macpherson strut with a spring but no damper and applied gravity only.

the simulation ran fine but then I found that the system is damped (see attached graph).

Why?

I applied no damping and no friction, so why is it slowing down?

Thanks!

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ChrisKaswer · ‎May 22, 2014

Turn gravity off and compare its results to the same displacement curve you've already shared as the .jpg image.

scohen-2 · ‎May 22, 2014

ok, so I ran the simulation again.

first time for 50 sec with gravity turned off

Second time with gravity on for 500 sec

In both cases the system eventually relaxes

My question remains, why?

ChrisKaswer · ‎May 22, 2014

OK, that's unusual. With gravity and friction off, a simple spinrg-mass system should oscilate indefinitely. Can you share your model?

scohen-2 · ‎May 23, 2014

Educational version

ehaenen · ‎May 24, 2014

Shai

Unfortunately I cannot open your files, because I have a full version, this doesn't open educational.

Please check whether your analysis happens to have structural damping selected.

Then switch this off, or set to 0%

Erik

scohen-2 · ‎May 27, 2014

Where would I make that selection?

I couldn't find the option in the menues

Is it a selection that i make for each part or the whole assembly?

ehaenen · ‎May 27, 2014

You do that in the time response analysis definition, in the bottom of the form: damping coefficient

ChrisKaswer · ‎May 27, 2014

Erik,

This is an MDO analysis, not a Simulate dynamic analysis. Only rigid bodies are considered.

I'll try a simple, similar analysis and see what I get, as I've got the commercial version as well and can't open your posted files.

Chris

ehaenen · ‎May 28, 2014

Oops

Didn't see that, wasn't paying enough attention.

Thanks Chris