Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Vibration damping help

  1. Sep 29, 2016 #1
    Hello i was looking at the damper CR3-100 as seen in the pic. Howver from the tech sheet given i cudnt make out whats the cutoff freq of this damper....i mean which is the frequency beyond which it doesnt let the frequency pass.....what to make of this KN/m value???? 1475173389238.png
     
  2. jcsd
  3. Sep 29, 2016 #2

    berkeman

    User Avatar

    Staff: Mentor

    Can you provide a link to that datasheet?
     
  4. Sep 29, 2016 #3
    I googled it. There is an application guide in the catalogue.

    Its a mass spring system. The cut off frequency will depend on the modal frequency of interest (ie what mass is on the spring). Isolation usually starts 1.4x the natural frequency.

    So it really depends on how much attenuation of vibraion you want. The catalogue suggests a natural frequency 1/3 the excitation frequency for 80% attenuation.
     
  5. Sep 29, 2016 #4
    The total mass of the system is 4 kgs resting on two dampers
     
  6. Sep 29, 2016 #5
    Last edited: Sep 29, 2016
  7. Sep 30, 2016 #6
    All you need to do is work through page 38 of the catalogue. What aspect are you struggling with?
     
  8. Sep 30, 2016 #7
    The system i have needs to be isolated from 30 hz freq........which means anything above 30 hz shud be damped......so how wud i know which freq this under discussion damper wud cut?
     
  9. Sep 30, 2016 #8
    You know the mass value - 4kg. So you can use part 1 on page 38 to calculate the static load per isolator W.

    You stated that it must attenuate above 30Hz. So this is your 'input excitation frequency'. You can use part 2 on page 38 to work out the required natural frequency of the system to provide 80% attenuation.

    From that you can then calculate the maximum stiffness to allow this Kv.

    Have a go at calculating these figures.
     
  10. Sep 30, 2016 #9
    1475225620237.jpg
     
  11. Sep 30, 2016 #10
    By the way how the units in the last Kv equation are cancelling out??.......i mean there is newton and hertz^2 in the numerator and m/s^2 in the denominator
     
  12. Sep 30, 2016 #11
    They look about right to me. So to provide the desired attentuation from 30Hz
    W = 20N
    Kv = 7.8 KN/m

    From the catalogue it states that:
    W < Static Max
    Kv < Kv of isolator

    So from the there are 4 tunes of isolator you posted in the OP. Which one works?
    The reason why this works is that once you go past the natural frequency, the vibration is out of phase with the input. So you start to get attenuation. I suggest you read up on vibration transmissibility.
     
  13. Sep 30, 2016 #12
    The fourth one works.......i still don't get how the units in Kv equation cancel out....Chris thankyou so much for the help...Appreciate it
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted