Hurrican force winds + ribbon = ?

[publiusr]

That is a good point. It might make for a good pilot tether demonstrator, or be useful in some wise--with a shorter tether not at ground level.

As far as keeping true space elevators from doing a 'galloping gertie,' I wonder if if would be possible to induce a counter vibration--much like noise cancellation technology. I wonder if a thin film of some type of "memory" material that will dampen some of this gallop out would be too heavy as well.

[AztecBill]

That is a good point. It might make for a good pilot tether demonstrator, or be useful in some wise--with a shorter tether not at ground level.

But we don't need it since any normal orbit can to used for the same pilot. A mass in orbit can feed tethers "up" and "Down" with counterweights for both. Both tethers can be "climbed" to add delta V cheaply. An orbiting craft would likely have to "catch the ride" at the center of mass since it is at local orbiting volocities. They can then move out or in based on which tether they "climb". This would give cheap Earth return or cheap orbit increase. Every use of the Orbiting Elevator would move the whole structure unless equal mass went in opposite directions and released at the same time. Even than they would have to go at different speeds.

[Greg Broomfield]

The greater the tension, the shorter the wavelength. For short wavelengths, the edges of the ribbon were subjected to massive increases in tension/relaxation.  When these tension bursts synchronised, the resultant shockwave travelling down the cable hit the fixing point and simply hammered it to pieces.

A 500 tonne payload hanging on a 1m wide ribbon passing through the jet stream - no chance.

The Dr Bradley Edwards' proposal included using a very narrow ribbon (or even a rope?) within the atmosphere.  Therefore if this turns out to be the issue you outline, then we may have to follow Dr Edwards' proposal.

[publiusr]

The ITCZ is a zone of constant low pressure along the equator, so the weather is actually pretty stable there. That was why Ivan was quite the shock--forming so far south.

By and large, you would not have much but some thunderstorm winds near brief squalls. I don't know about a jet being in that region--so perhaps we dodge a bullet there at least.

[Brad Blazer]

Let me resurrect this thread.
As a cabling guy, I would propose that the ribbon simply cannot survive within the atmosphere if it has a flat profile. If it is under high tension and has a wide aspect ratio, a breese  will destroy it.

This thread is pretty old. Is the current design a round profile within the atmosphere that transitions to flat in space as the threat changes?
Are there plans for dampers to suppress aeolian vibration? "Aeolian" returned no results in a search of this forum.

Sorry if this has all been hashed out but the FAQ links all seem dead and this is the only thread I found that seems to raise the issue.

[neil]

Hi Brad: I'm just one of the guys who post here. Aeolian has not been discussed in these forms as far as I know. Hoy tether has been mentioned, which is like a tubular fishnet, so that might solve the Aeolian problem, but I think it is not compatible with the pinch rollers on the climbers. I've mentioned that the climber would rotate with the flat ribbon, but no one else has discussed that either. Perhaps opening this thread will get some helpful comments. It seems unlikely that the pinch rollers will find enough traction on a slippery CNT kite string which has a huge cross sectional area compared to the portion of the starter ribbon near the anchor ship in Earth's atmosphere. Micro meteorites are the other reason for thinking very thin ribbon, as small holes blasted in a meter wide ribbon would only reduce the strength by 1 or 2%. I understand CNT is as slippery as Teflon, perhaps worse. The following quote from page 1 of this thread seems to be about Aeolian~ 

A few years back I was involved in a job involving guylines.  One test was to use flat braided ribbon instead of cable.

While the cable guys would 'sing' in high winds, the moment the tension was applied to the flat braid, the tension clasps exploded.  No, it wasn't faulty clasps, it was shock waves created by the flat face oscillations induced by the wind in the tensioned cable.

The greater the tension, the shorter the wavelength. For short wavelengths, the edges of the ribbon were subjected to massive increases in tension/relaxation.  When these tension bursts synchronised, the resultant shockwave travelling down the cable hit the fixing point and simply hammered it to pieces.

A 500 tonne payload hanging on a 1m wide ribbon passing through the jet stream - no chance.

If you don't believe me, go fly a power kite with kevlar cables, then try again with the cables replaced by flat power braids.  The moment that you put the kite into the wind your hands will be pulverised by the shockwaves.

The answer to many problems is simply not to tie down the SE at all.  Let it free float.  Don't drive to it, fly to it.

No Ice, No wind, No terrorism, No land grabbing, No lightning conductor, No problem from Moon/sun tides. etc etc. ~The free flying idea seems to be shot down by another post on page 1, so the Aeolian (does it have another name?) problem remains a possible show stopper.   Neil~

[Brad Blazer]

Neil,
Thanks for the response. There are 2 general types of vibration problems common in high tension spans: high frequency aeolian (singing) and low frequency galloping (like a jump rope with multiple nodes). Non-round profiles are most susceptible to galloping. Figure-8 style cables are commonly twisted to combat galloping but that would really be a problem for a climber.

Maybe there is an airfoil shape or varying profile that would be more vibration resistant. I doubt it is a show-stopper but some modeling and wind-tunnel testing is probably warranted.

There are many styles of capstan and pinch rollers are rare. Caterpullers are common which are like pinch rollers with belts. The problem is that the normal force is concentrated on a small area. Pinch rollers also need a mechanism to allow them to float as the strand thickness changes. I like a 3-wheel inline wrap capstan. Traction follows [Tension out = Tension in ^(friction factor*wrap angle).  With the wheels arranged in an equilateral triangle the wrap angle is about 580 degrees. The bending strain on the strand equals wheel diameter / strand thickness. Wide flat rollers should be able to accomodate either round or flat strand profiles and a large diameter will reduce bending strain while distributing the traction force over a long length. An assembly machine at the base and a disassembly machine at the station can install/uninstall the capstan on the strand. I drew up a simple model: