[TenTec] Aeolian Vibration

[Neal Laugman]

> No doubt your poly rope was trying to shrink with the cold too and
> had plenty of tension.

That was exactly it.

> So you left a twig leaning on the poly to upset that resonance?

It was holding up the end of an 80m inverted vee and  I tried to bungee
the line but it just found new resonance. I finally just dropped the
line that night. I really needed to get some sleep. I used some
dacron after that. Learned a lesson in false economy, and that's what I
got for being cheap <g>.

-- 
Neal, NL7VL

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On Mon, 10 Jan 2011 23:19:42 -0600
"Dr. Gerald N. Johnson" <geraldj at weather.net> wrote:

> Power and open phone wires (not used much anymore) sound the loudest 
> with just a 2 or 3 mph wind. Any stronger wind and the wind noise
> hides the sound on the ground. Those wires are generally strung at a
> fairly high tension to minimize the need for tall poles. One way of
> checking the tension is to strike the line and measure the time it
> takes that wave to propagate the span out and back.
> 
> No doubt your poly rope was trying to shrink with the cold too and
> had plenty of tension.
> 
> So you left a twig leaning on the poly to upset that resonance?
> 
> 73, Jerry, K0CQ
> 
> 73, Jerry, K0CQ
> 
> On 1/10/2011 10:03 PM, Neal Laugman wrote:
> > Jerry and the group:
> >
> >> The wire elements in the Hex Beam and Spideream surely vibrate in
> >> the wind, on power and phone wires its called Aeolian vibrations,
> >> most prominent at light winds.
> >> http://www.uh.edu/engines/epi1653.htm describes it in more detail.
> >
> > I wondered if there was a name for that effect. Polyrope was indeed
> > my enemy one 30 below moonlit night out in the Alaskan Bush. I had a
> > 20-foot spruce pole mast attached to a cabin's perlin with a
> > polyrope halyard running the length of the mast. I thought I was
> > loosing it as I the entire cabin seemed to resonate with this
> > chilling sound. After I had been outside a couple of times checking
> > for flying saucers, I finally figured out the mystery whilst
> > reclining in my bunk. I went back outside, put the flashlight to
> > the eighth-inch line, touched it - and the sound stopped! It was
> > the temperature and an ever-so-slight breeze off the river.
> >
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