Influence of stress on natural frequencies

[JeroenDevos]

Hi,

I was wondering: what's the influence of stress on the natural frequencies of a structure. I tried it for my model and I only notice a very small difference in results (0.1 Hz). This seams a bit low in my opinion.
Can anybody help me out here?

Jeroen

 

[cbrn]

Hi,
for the influence of stress, think about a guitar string: if you increse or decrease its tension, wouldn't the sound become more or less acute, respectively?
As regards the effect on a structure, 0.1 Hz difference can be a very big difference or a negligible one, depending on the structure itself and on the constraint / load pattern (and also, to what "free" frequency is it compared? Is the fundamental 0.5 Hz? or 2000 Hz? Or what?)

Regards

 

[meshparts]

Hi,

I agree with cbrn. I would add that, the effect of stress on the natural frequencies depends on how much one dmension of the structure differs from the other ones. A guitar string is much longer then thick, so effect of stress is big. If the structure has approximative equal length, height and depth, the the effect will be very small.

Regards,
Alex

 

[Hup]

Hi,

some time ago I was deriving analytically what really happens in the guitar string. It is also important the direction of prestress and the nature of examined modeshape.

By tuning the gitar string you change the frequency of the perpendicular modeshape but not the freqency of the longitudial one (hard to imagine on a guitar), considering linear material.

You can see it on the simple model; 2 springs in serie, a mass between them, both free ends constrained. The longitudial omega=sqrt((k1+k2)/m) doesn't change when stiffs are constant.

Ciao, H-up

 

[meshparts]

To Hup,

For a prestressed guitar string the longitudinal eigenfrequencies can allso change, since the cross section change and in the end also the stiffness.

Regards,
Alex