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Anonymous Poster #1

# Natural Frequency for Torsional Vibration of Fixed Fixed Beam

03/05/2017 3:33 PM

Hi All:

I am trying to calculate natural frequency for torsional vibration of fixed fixed beam using following formula in US system.

=1/2*3.142 sqrt(K*g/mr^2) hz

Where K=J*G/L

and G=Modulus of rigidity

g=acceleration due to gravity=386.4 in/se2

m=mass hanging on the beam at distance 'r' from the longitudenal axis

My question is how does the equation above (if its right) is affected if I change the beam from fixed fixed to fixed -free.

thanks

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Join Date: Jul 2005
Location: Stoke-on-Trent, UK
Posts: 3603
#1

### Re: Natural Frequency for Torsional Vibration of Fixed Fixed Beam

03/07/2017 9:04 AM

My question is how does the equation above (if its right) is affected if I change the beam from fixed fixed to fixed -free.

My guess is it's lower by a factor 2. The mass accelerated is 2x, and the restoring force for a given angular twist is 0.5x so change is √(2/0.5) = 2.

I don't understand m=mass hanging on the beam at distance 'r' from the longitudinal axis.

Just noticed you also posted this in Aerospace.

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