General Mechanical

General Mechanical

NonZero Natural Frequency 4, 5, 6 for free free B.C

    • omidrastkhiz
      Subscriber

      Hi everyone,

      I have a segment which is a stator part of generator, and I want to the free free modal analysis on it, and no matter if I use nothing for boundary condition or 4 springs (Body to Ground), It gives me a large number for Natural frequency number 5 and 6, (104,130 Hz), and I also wanted to check equivalent elastic strain ( for mode No. 5), but it doesn't allow me to to do it and gives me an error "A result is invalid with the current output control settings."

      Also the Result from experiment is very different from what I get in Ansys ( Ansys 7th mode: 180Hz Experiment 7th Mode around to 51Hz), However the mode shapes seem to be right. I checked the contact region and They are all ok (Bonded in my case), and meshing is also fine I think. the weight of the segment is almost 3200 Kg.


    • Erik Kostson
      Ansys Employee
      Good MorningnnThis could possible be due to the contacts - use shared topology (to get a compatible mesh) instead of contacts.nnErikn
    • omidrastkhiz
      Subscriber
      nThank you very much Erik,nAs you said, I am trying to remove contact and use share topology, and here as you can see, I couldn't do it from share topology in workbench tab in SpaceClaim, I should also say, I have many small elements with thickness of 5 mm which in touch from both sides (Pattern elements in red in the picture), so I did from the Properties tab, Analysis window, and I selected share instead of none for all the elements, and when I do the meshing it gives me 4 errors in the last picture, nFirst I need to say is it right if I select the share topology the way I did, ( since it automatically removed most contact regions), and do you know what should I do for meshing it, for meshing it I used multi zone method and next time with no methods and no other features( automatically by program control ) but still gives me an error,nnnOmid.n
    • Erik Kostson
      Ansys Employee
      HinnYour geometry seems a bit complex and perhaps it is not easy to use shared topology - not sure, but perhaps you know if you can make it more simple and thus make it easier to use a shared top. Unfortunately I can not help much with that, but as we said the nozzero or high freq. for rigid body modes, could possible be due to the contacts, so that is my feedback overall.nnGood luckErikn
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