natural frequency of a radially compressed ring 3

[cspkumar]

Hi all,

I am looking at the eigen-value analysis of a ring compressed radially using nodal forces. The natural frequencies increased when I used load stiffening option in Algor when compared to a ring with no loads on it. The constraints were the same for both. Is this correct? I am not sure if this is right.

I think for a beam in tension, the natural frequencies would increase and decrease when in compression (when the load is less than the buckling load), but here, in the case of the ring, the frequencies are increasing in compression. Could someone explain this to me?

Thanks,
Kumar

 

[cspkumar]

Hi all,
It was a software glitch. Somehow it got corrupt and I had to delete and load it again. Now, the first real mode for an unloaded ring is out-of-plane flexure mode with a frequency of 11.75 Hz. The first in-plane flexure mode frequency is 12.1 Hz, which agrees with Englishmuffin's equation(3% error, I am sure like what englishmuffin said, if I use more nodes, I would converge to the theory). Even the buckling analysis worked. The code came back with 2.013, which is what I expected.
Thanks for all the replies. It was very very informative. Thanks again,
Kumar

 

[EnglishMuffin]

Interesting that GregLocock got close to the right frequency using the wrong material with an apparent additional error in his calculation. Some people just can't go wrong!