Why can not two modes coincide perfectly for some cases in Flutter phenomena?

[Patkin]

Hi dear friends,

I have a question about flutter phenomena. As you know, flutter occurs when two modes ( for example first mode and second mode ) coincide ( I mean after a specific velocity, the frequencies of two modes, will be the same and equal) and the damping term will change into positive which causes failure.

However, for some cases, frequencies of two modes do not coincide perfectly ( I mean they are not equal ) and damping parameter negative sign will change into positive, which mean flutter is happening.

Why this is happening ?! Why the frequencies of two modes can not coincide perfectly ?!

 

[GregLocock]

I suggest you try it with a coupled spring mass 2 dof system (ie ground-spring=-mass-spring-mass-F. You /always/ get 2 modes, at different frequencies. There is a good reason for that.

Cheers

Greg Locock


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