reducing n-dof vibrating system to 1-dof equivalent

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Hmmm..if I have it right, you want to compare your modeled damper against a proven model with more parameters.

One way to go would be to collapse the various D'sOF with super stiff springs and super nominal masses except one spring and one mass. The proven model will presumable continue to provide the goods to compare with your simpler system??

Brian Whatcott Altus OK

Thanks Brian.

I need to prove that my controller will work on a real turbine. I know a postgrad who has access to the industrial program and because he is busy he wants me to make my model match his rather than change his model to match mine.

The tower he has used is tapered and so has varying bending stiffness all the way allong it. He has modelled that tapered tower with 19 masses connected in series with springs and small dampers.

We can disable the aerodynamic drag on his tower so we are effecticvely looking at the 19-dof system with only the mass element at the top pf the tower being forced by the rotor's aerodynamic thrust.

I was thinking that if I only considered the first vibrational mode of his model, I could then combine all of his masses and springs into juat one large mass and spring with the same natural frequency etc.

Im just not sure if that can be done accurately or if it would just end up representing nothing.

Adam

Hmn, in Finland we usually do the "heavier" work in dissertations than in industry. Is it enough to solve the lowest (natural) frequency? And will the 1D model be physically realistic as compared to nD (this comes down to what you changes one can model).

There is distinction between the drag (compare average force and Strouhal numbers) and variations in drag ("including" other frequencies). Hope this is more clear than in the past post.

Best of luck with real turbine.

Br,

ari

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This reminds me of the engineering history of Pratt & Witney's developmental efforts with radial engines. It can be found on line - it's fascinating. Those guys were hairy armed engineers no doubt - they would run a test engine to destruction: analyze and beef up the failed component, and run 'er again to destruction.

They were proccupied with crank modes some of which were aggravated by propeller syncing with the reduction gearbox - which led them to use prime ratio gear sets to avoid resonance. They certainly focussed on the lowest mode first, and picked off one or two higher modes along the way. They did good work with pendular resonant dampers - a kind of passive version of what I guess you may be doing.

This initiative remnds me of skyscraper sway controllers - big chunks rolling around on the top story (sounds scary?)

Is it too much to try for a trial installation on a windmill? That would be easy to instrument for results, I imagine.

But any cross check would be instructive for you I'd think. Keep us in touch with results. Dynamic stabilzation of structures is trendy.

Brian Whatcott Altus OK