Frequency response limit

- October 5, 2021 at 2:04 pm
  
  renatoaf
  Subscriber
  
  Hi, I would like to understand if it is possible to simulate the limit of frequency of certain piece or structure. I mean if I have a very flexible structure the response frequency will respond until a certain value while a rigid structure will respond until higher frequency.
  How to find until which value (limit) the structure will really respond?
  
  Thanks,
  Renato
- October 6, 2021 at 6:29 pm
  
  danielshaw
  Ansys Employee
  
  You need to run a modal analysis to identify the eigenfrequencies and mode shapes. The eigenfrequencies are a function of the stiffness/mass. The flexible portions of the structure will be excited at low frequencies and the stiffer portions at higher frequencies. You can post-process the modal results to determine the response frequencies for different portions of the model.
- October 6, 2021 at 7:17 pm
  
  renatoaf
  Subscriber
  
  Thanks Daniel,
  I understood, but my point is how to know up to frequency that portion can respond, I mean, for a very flexible structure 100 Hz does not make sense, however 20 Hz could.
  How to know up to xxx Hz is feaseble, higher not?
  
  Thanks.
- October 13, 2021 at 11:19 am
  
  jonsoln
  Subscriber
  
  If you run a harmonic simulation you can get the frequency response as output. This gives you a Bode diagram showing the amplification in the frequency range specified. You will se that up to the resonance frequency the amplification is 1 (0 dB) or larger, but when you cross the resonance frequency it rapidly declines. There is no hard limit to which frequencies the structure will respond to, you have to decide at what frequency the amplification is small enough to be negligible.
- October 13, 2021 at 2:11 pm
  
  renatoaf
  Subscriber
  
  Thank you Jon, it┬┤s clear now.
  Regards Renato