Waterbed effect / direct velocity feedback

Hi there, I set up a simulation using direct velocity feedback to reduce vibrations of a mechanical 2-dof system (2 masses interconnected by a
spring and the second mass is connectet to the fixed ground). The result looks fine: vibration reduction works. But as I had a closer look to the sensitivity function "S" I found that "S" never gets bigger then "1" - how can this be explained with the "waterbed effect" from the bode integrals? Refering to the "waterbed effect" I expected the sensitivity function being smaller "1" in the vicinity of the resonance peeks and bigger than "1" in other areas - but it never goes beyond "1"!? Why? Thanks. Bye, Marcus
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Hi Marcus,
the so-called waterbed formula is only valid for systems with relative degree at least two. Is this your case?
Another idea that I have is that perhaps there is some peak, by very small. The trick is that the integral goes from zero to infinity, so i you stretch your area where the sensitivity function is "above one" to infinity, you can have very small rezonance peak. Note however, that this is just a textbook exercise. In reality, you do not have an infinity bandwidth!!!!!!!
Zdenek Hurak
marcus snipped-for-privacy@directbox.com wrote:

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