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More services...Effect of tension on eigenfrequency
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Last post: January 30, 2013 10:36pm UTC
January 30, 2013 9:55pm UTC
Effect of tension on eigenfrequency
Hi,
I'm trying to model the effect of tension on the eigenfrequency, and I think I'm misunderstanding the use of boundary loads. I have a long and narrow bridge (fixed at both ends, free along the length). I would expect that adding a boundary load on either end of the bridge, in opposing directions, would essentially be like tensioning a string, which will cause the resonance frequency to increase. But I'm not seeing any change in resonance. Why not?
I've also tried anything else I could think of that might change the resonance - body loads, strain at either end, etc. Nothing effects the first fundamental resonance. Any ideas would be hugely appreciated!
Regards,
Jillian
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January 30, 2013 10:36pm UTC in response to Jillian Kiser
Re: Effect of tension on eigenfrequency
Jillian,
Well, your fixed constraint conditions are overriding your boundary load condition at the end points. So, even in a stationary solution you will get a zero stress solution. You will want to consider only fixing one end.
There are a couple of ways to simulate the effect of tension (stress) on the natural frequency of your system. COMSOL has a very nice model in the model library called "Vibrating String" that I would advise you work through. I think that will help you a lot.
In my opinion, the most intuitive way to set up the problem is by solving in 2 steps. First, a stationary step that solves for the pre-stressed state of your system. Then, an eigenfrequency step that solves for the natural frequencies of the tensioned member(s). This method is covered in the Vibrating String example I mentioned.
Best regards,
Josh Thomas
AltaSim Technologies
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