How can I prevent vibration of metal structure in wind?

[Round Square]

Pipe insulation on the bars?

[jrwalliker]

Try wrapping some thick cable or hosepipe around each bar in a helix - something like one turn around the bar for each 10-15cm of length. This should disrupt the vortex formation which may be driving the resonance.

John

[Sponix]

Once you find a soloution you can sell it to your neighbours!

:)

sponix

[Kate]

Speed of sound in air is circa 1100 fps, so at 50 Hz) the wavelength is 22 ft.

Is there *any* dimension on the bars that is near *any* fraction of

22, that is 22, 11, 5.5, 2.75 ft? I'm thinking possibly of the horizontal bar that tops the smaller, vertical ones, being the culprit?

I'm beginning to think that the vertical bars might not have much to do with it. The long, horizontal bar seems much more like the culprit. Are the ends sealed with no air access whatsoever?

[The3rd Earl Of Derby]

Is you're life complicated?

p.s whats "fps"?

-- Sir Benjamin Middlethwaite

[Dave Fawthrop]

| |Englishman in Adana (Turkey) wrote: | |>The wind doesn't have to be very strong to start the vibration, I guess |>the frequency is around 40-60Hz (compared to mains hum on a radio). | |Speed of sound in air is circa 1100 fps, so at 50 Hz) the wavelength |is 22 ft. | |Is there *any* dimension on the bars that is near *any* fraction of |22, that is 22, 11, 5.5, 2.75 ft? I'm thinking possibly of the |horizontal bar that tops the smaller, vertical ones, being the |culprit? | |>I tried holding the bars sometimes, but holding the one making a noise |>makes another start!! and it's difficult to determine which is the |>culprit. | |I'm beginning to think that the vertical bars might not have much to |do with it. The long, horizontal bar seems much more like the culprit. |Are the ends sealed with no air access whatsoever?

Sealing tubes with building sealant would be cheap.

[Donwill]

What has that got to do with it? she is doing a damn good job of solving the prob.

Come on Benjamin, where have you been? fps = feet per second Donwill

[Sponix]

Possibly the bars are hollow tubes with open ends. The wind blowing across the tops would be like blowing across the tops of empty milk bottles.

Check the ends of the bars, block them off if they are hollow and see what happens.

sponix

[The3rd Earl Of Derby]

Its all very well working out the speed of sound and distance measurement, but he needs a practical solution to stop the resonating.

A bit like an mathematician who complained of having constipation. Someone said he should work it out with a pencil.

-- Sir Benjamin Middlethwaite

[Donwill]

A real engineer tries to understand the problem before applying his/her mind to producing a solution.

I suppose it's easier than using a computer even in these days of minaturisation. Roll on Nano engineering you can get rid of your pencil then Benjamin.

Regards Donwill

[Mike Harrison]

And if it is the bars themselves resonating as opposed to acting like organ pipes, and they are hollow, filling them with sand ought to damp vibration sufficiently as it will absorb the vibration energy.

[The3rd Earl Of Derby]

Ok, lets look at this way.

Say she spends half hour working out where the bars are resonating and comes to the conclusion they are resonating towards the middle, great! we are back to square one we cant put stabilisers in the middle because of safety reasons so now we have to work out a solution to stop it bearing in mind this is all costing money to the poor bloke who's hired an engineer.

Practicability comes before Theory in my book.

-- Sir Benjamin Middlethwaite

[The3rd Earl Of Derby]

Perhaps a picture of the situation in this problem is called for, so we can all actaully get a better idea of coming up with a solution.

-- Sir Benjamin Middlethwaite

[john2]

this is probably the best solution. Metal chimney flues on factories nearly all have a spiral blade running up them at 45 deg. or so to prevent wind induced vibration

Google for "spiral chimney wind spoiler"

john2

[Englishman in Adana (Turkey)]

Ok heres for another update:

The vertical bars are, I guess, tubes made of stainless. They are enclosed at the bottom in a rectangular section and the top disappears into the horizontal bar. Therefore the ends are not open, either to cause 'organ pipe' resonance, or to put sand in (which is an idea I liked).

Maybe I can drill holes at various spacings down the tubes and cause them to play a nice melody with the wind!!

The idea about wrapping a wire or tube around in a spiral sounds good, this is also used on electric transmission lines -

again, thanks for all the answers! Now for an interesting weekends work ;)

PS: after asking this question, arriving home in the evening to find no wind and complete silence amazed me. First time the wind ceased in 2 months!! This group is REALLY effective!! lol

[keith_765]

Try a coat of DX grease, and tell the world .LOL

[Donwill]

Each to his own. Cheers Don

[zymurgy]

Horizontal bar with inward facing spikes ? ;)

P.

[zymurgy]

The power line people solved this easily ages ago, with the dampers shown on the left of here :

't you make a suspended weight to a similar design ?

Hmm. This would change the pitch granted, but they would be better supported, lessening the possibility of resonance.

Cheers

Paul.

[Kate]

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This reply should be ignored by "Sir Benjamin Middlethwaite" on the grounds that it is technically oriented, and his sensibilities in that area seem very delicate.

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Well, I did the Google search, thanks for the steer. I came across this web site:

cause and a couple of remedies are shown in Figure 2, although there are doubtless many other ways of making a spoiler: a spiral wrap of thick string or plastic tube, for example.

Let us know how things work out.