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VIBRATION STUDIES

Question asked by JAMES PARE on Sep 25, 2008
Latest reply on Aug 19, 2011 by James Pare

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HELLO, TRYING TO SIMULATE VIBRATION STUDIES USING SOLIDWORKS/COSMO
THE STUDIES WE RECEIVE SHOW CHARTS WITH ACCERLATION VS FREQUENCY
ACCERLATION BEING "g" VS THE FREQUENCY
BASICALLY WHAT WE ARE TRYING TO DO IS SIMULATE A A FIXTURE BEING SUBJECTED TO A SINUSOIDAL VIBRATION AT ALL FREQUENCIES FRO 10HZ TO 200 HZ , THIS BAND OF FREQUENCIES IS LOGARITHMICALLY SWEPT OVER A DURATION OF 3 MINUTES AT A ACCERLATION OF 1 (G)
AFTER THAT IS PERFORMED I NEED TO DETERMINE IF THERE IS A RESONANT FREQUENCY ABOVE OR BELOW 200

I'VE BEEN TRYTING TO DO A DYNAMIC FREQUENCY STUDY USING MODAL, HARMONIC & / OR RANDOM VIBRATION
BUT I CANT GET EXACTLY WHAT I'M LOOKING FOR
ANY HELP OR SUGGECTIONS WOULD BE VERY MUCH APPRECIATED

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Vince Adams Sep 25, 2008 2:07 PM

Hi James, you can do this using a Harmonic analysis and simply setting the range you are looking at. If you are concerned about frequencies near 200 Hz, I'd suggest running the simulation out to 300 Hz to make sure you pick up vibration in the low 200's. Vibration analysis on real-world parts isn't an exact science. Small variations in assembly position, bolt preload or excitation orientation can produce measurable variations in resonant response. You also want to make sure you calculate frequencies up to 400 Hz to make sure higher-order effects don't get missed. Failure to include higher frequency resonance in lower frequency responses is called Modal Truncation. Better to have more frequencies than less!

Good luck!

Vince

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Vince Adams @ Vince Adams on Sep 25, 2008 2:10 PM

One more thing, the solution doesn't take into account the duration of your test sweep, 3 minutes. The solver assumes that each frequency iteration is allowed to reach steady-state before moving on to the next. Realistically, if your actual sweep was too quick to allow resonant responses to reach steady-state, your Simulation may over-predict response. At a minimum, this calculation will be conservative.

-- Vince

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James Pare @ Vince Adams on Aug 19, 2011 7:52 AM

Vince, I am getting some physical results that are not matching the simulation results

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JAMES PARE Sep 25, 2008 2:22 PM

sounds good
will try your suggestions
thanks!!!

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JAMES PARE Sep 25, 2008 2:27 PM

should i use upper bound frequency or # of frequency option?

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Jose Eduardo Fernandes de Camargo @ JAMES PARE on Mar 19, 2009 6:02 PM

James,

As Vince told above, you should have to use the "UPPER BOUND FREQUENCY" as the 300 or 400Hz Vince had mentioned!

Good luck and best regards,

Eduardo Camargo

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Vince Adams Sep 25, 2008 2:07 PM
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Hi James, you can do this using a Harmonic analysis and simply setting the range you are looking at. If you are concerned about frequencies near 200 Hz, I'd suggest running the simulation out to 300 Hz to make sure you pick up vibration in the low 200's. Vibration analysis on real-world parts isn't an exact science. Small variations in assembly position, bolt preload or excitation orientation can produce measurable variations in resonant response. You also want to make sure you calculate frequencies up to 400 Hz to make sure higher-order effects don't get missed. Failure to include higher frequency resonance in lower frequency responses is called Modal Truncation. Better to have more frequencies than less!

Good luck!

Vince
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- Vince Adams @ Vince Adams on Sep 25, 2008 2:10 PM
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  One more thing, the solution doesn't take into account the duration of your test sweep, 3 minutes. The solver assumes that each frequency iteration is allowed to reach steady-state before moving on to the next. Realistically, if your actual sweep was too quick to allow resonant responses to reach steady-state, your Simulation may over-predict response. At a minimum, this calculation will be conservative.
  
  -- Vince
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  - James Pare @ Vince Adams on Aug 19, 2011 7:52 AM
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    Vince, I am getting some physical results that are not matching the simulation results
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JAMES PARE Sep 25, 2008 2:22 PM
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sounds good
will try your suggestions
thanks!!!
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JAMES PARE Sep 25, 2008 2:27 PM
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should i use upper bound frequency or # of frequency option?
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- Jose Eduardo Fernandes de Camargo @ JAMES PARE on Mar 19, 2009 6:02 PM
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  James,
  
  As Vince told above, you should have to use the "UPPER BOUND FREQUENCY" as the 300 or 400Hz Vince had mentioned!
  
  Good luck and best regards,
  
  Eduardo Camargo
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