Why does ansys repeat natural frequencies?

- October 30, 2021 at 4:45 pm
  
  hollow4444
  Subscriber
  
  Hey was hunting for a solution for this. I have a fixed hanging bar 1m long and 500sqmm cross sec area. When I do a modal analysis I’m getting 1st and 2nd frequency as 18 and 3rd and 4th Frequency as 116.
  
  any idea how I can remove the repeats?
  
  thanks
- November 1, 2021 at 10:23 am
  
  Vigneswaran Sridharan
  Ansys Employee
  
  Hi Both effective mass and participation factor are parameters that help the user to get an answer for questions like:
  How many modes to extract?
  Which modes are contributing to the problem?
  Why do natural frequencies repeat in modal analysis?
  I will recommend you to watch the course on Modal analysis available atModal Analysis | Ansys Innovation Courses.
  This course has all the important background information for Modal analysis.
  Vigneswaran
- November 1, 2021 at 12:33 pm
  
  hollow4444
  Subscriber
  
  Hey Vigneshwar Would you be able to assist with a quick fix?
  Im doing this assessemnt due tomorrow evening and was wondering if i could fix it relatively quickly.
  
  I have taken 1) 4 Nodes and recieved the same repeats.
  2) i took 6 Nodes and still received the same repeats.
  
  I need to compare the First 4 Natural frequencies with Ansys and analytical method.
  
  Using analytical method(Roarks Formula) i get the first 4 Frequencies as :