A question for someone clever.

[DaveGarland]

Ok so this has nothing to do with astronomy I know. But I know this forum attracts some very clever people. So what I want to know is this. Today for a bit of fresh air I walked across the old Severn bridge to Wales and back (air was VERY fresh!). Now what I noticed was that all the vertical cables had these weird knobbly things on them (see pic). They appeared to just be on a short length of thick cable and I couldn't for the life of me work out what these were. Does anyone know???

[DBushell]

They look slike droplets of water in some kind of form of metal art for the bridge.......purely decoration I reckon.

[Photosbykev]

possibly weights to adjust the resonant frequency of the cables to avoid them shaking the bridge to bits? or decorative, or both

[astrofox]

definatly anti resonator balance weights. You see the same sort of thing on Supergrid lines to stop wind induced oscillataions

[DaveGarland]

Ah that sounds reasonable. I don't think they're for decoration though as there are some really high up that you wouldn't really notice.

[JamesF]

They're called Stockbridge Dampers, and they're to dissipate vibration in the cable caused by the wind.

James

[The Sailor]

Google is the job

These objects are called Stockbridge dampers. They dampen wind-induced vibrations of the cables, reducing cable fatigue. As wind passes across the cables, they shed vortices which cause them to vibrate at low amplitudes - in the millimetre range - but at high frequency, around 60 hertz.

The oddly shaped masses are called dogbones, for an obvious reason. They are tuned so that they flap when the cable starts to vibrate. The flapping of the dogbones dissipates the energy of the vibrating cable. They are also used on high-tension power lines and for large road-sign support spans.

The dampers are tuned so that they flap and dissipate energy when the cable starts to vibrate

Copy and pasted I'm afraid

Jim

[Treeden]

... Copy and pasted I'm afraid

You were doing really well until that last line Jim. I had you down for the top prize.... a pack of Tesco's finest mince pies!

Seeing as you're so honest though, you can still have the mincers.

[The Sailor]

Mincers, I know I sail but you think I swing? lol Nice offer but rather have Jaffa Cakes, pretty please

Jim

[username]

What can happen to badly designed bridges (I think this was the one that made the engineers consider the effects wind resonance a bit more)

[DaveGarland]

They might dampen the oscillation in the cables but the up and down motion of the bridge is quite alarming. And when a large truck goes past... I don't know if anyone else has walked over a large suspension bridge but they really have a life of their own. You don't really notice it when your speeding along in a car. Quite some experience.

[username]

They might dampen the oscillation in the cables but the up and down motion of the bridge is quite alarming. And when a large trunk goes back... I don't know if anyone else has walked over a large suspension bridge but they really have a life of their own. You don't really notice it when your speeding along in a car. Quite snowman experience.

I think that is designed in to the bridge. It's disconcerting but it ensures the main supports just support the weight of the bridge and load and not the traffic induced vibrations

[DaveGarland]

I've had to edit my last post due to typos. My phone autocorrect also has a life of it's own lol.

[faulksy]

as said dampers to allow for flex e.t.c. in cables save peeps being ejaculated into the air

[The Sailor]

ejaculated into the air

Okay, I have a one track mind

Jim

[Photosbykev]

woohoo I got it right :)

[faulksy]

Okay, I have a one track mind

Jim

was going to put tossed off, but i thought it was worse, couldnt and still cant think of a better word :grin:

[The Sailor]

was going to put tossed off, but i thought it was worse, couldnt and still cant think of a better word :grin:

Chucked? lol

Jim

[DaveGarland]

Just an afterthought, but looking over the edge (scary!) you can see the mahoosive tidal water flow going under the bridge. It really flies through. Now a question for someone REALLY clever would be how to harness that energy? I know there have been loads of ideas on this over the years and for one reason or another they have all been dropped but surely there must be some economical way of doing it. Free energy all from the power of the moon! Now there's something to fire the imagination!

[JamesF]

Kind of a bit like this, you mean:

http://en.wikipedia.org/wiki/Severn_Barrage

?

James

[The Sailor]

Just an afterthought, but looking over the edge (scary!) you can see the mahoosive tidal water flow going under the bridge. It really flies through. Now a question for someone REALLY clever would be how to harness that energy? I know there have been loads of ideas on this over the years and for one reason or another they have all been dropped but surely there must be some economical way of doing it. Free energy all from the power of the moon! Now there's something to fire the imagination!

Probably one of the best places that we could generate a lot of power but theres a problem, a couples of toads, yes same old story. I am not going to bang a drum here, no sence.

Jim

[DaveGarland]

Yup. Like I said there's been loads of ideas over the years but all dropped for one reason or another. Could we not somehow incorporate some kind of toad sanctuary or something?

[JamesF]

That's kind of what the environmentalists wanted to do by using the tidal lagoon idea. Unfortunately no-one else seems to think it's an economic proposal.

If we wait a while though, the problem will go away. As sea levels rise they'll destroy all the riverside habitats anyhow

James

[DaveGarland]

We need to develop renewable energy to stop climate change. We can't do that it'll effect the local habitat. If we do nothing the local habitat will be destroyed by climate change blah blah blah! Wouldn't happen in China would it? They'd just build a dam and take the energy.

[JamesF]

Wouldn't happen in China would it? They'd just build a dam and take the energy.

Probably they'd just build another coal-fired power station

James