"Double" modes in modal analysis of simple circular membrane clamped in its boundary

  • 170 Views
  • Last Post 09 February 2019
  • Topic Is Solved
kravky posted this 08 February 2019

Hello, 

i am trying to find normal modes of simple ideal circular membrane.
I chose strecutral steel as material, and geoemtry is: diamater is 0,391mm, thickness is 0,0035mm.


However, i got "double" modes: every two modes are very very similar - with the almost same value of frequency.
i got same answer with other commercial program. 
I tried to chcange mesh, i tried do model my geomtry as solid and also as a shell/surface but i got the same problem.

see pictures: mode 4 and mode 5 is only ONE mode in reality. Why i got this result?

 

mode_4

 

mode_5

Order By: Standard | Newest | Votes
peteroznewman posted this 09 February 2019

No, you just have to recognize the pairs are the same mode separated by a rotational angle.

kravky posted this 08 February 2019

Thank You for explanation.

Should i define polar coordination system in order to get mathematically correct solutions? (not to have double modes)

peteroznewman posted this 08 February 2019

To a mathematician, there is only one mode since they generalize that the orientation of the mode in the circle is arbitrary.

To ANSYS, there are two modes since it treats X and Y axes as separate and it can't recognize that these two modes are just offset by some rotation about the center.

  • Liked by
  • kravky
Close