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[TowerTalk] Fwd: Fwd: Tower Permitting Spec's

To: towertalk@contesting.com
Subject: [TowerTalk] Fwd: Fwd: Tower Permitting Spec's
From: Hans Hammarquist via TowerTalk <towertalk@contesting.com>
Reply-to: Hans Hammarquist <hanslg@aol.com>
Date: Tue, 1 May 2018 12:46:08 -0400
List-post: <mailto:towertalk@contesting.com>
 You can wrap it with mos tanything, ropes, wires, hoses, you name it. It 
should probably "stick out" so it really affect the wind passing by. It idea is 
that the wind is ot able to "meet" on the back side of the tube.

I bet you can find how wide the rope/wire/hose has to be effective by searching 
the i-net

Hans - N2JFS

 

 

-----Original Message-----
From: jimlux <jimlux@earthlink.net>
To: towertalk <towertalk@contesting.com>
Sent: Tue, May 1, 2018 8:46 am
Subject: Re: [TowerTalk] Fwd: Tower Permitting Spec's

On 5/1/18 12:31 AM, J Chaloupka via TowerTalk wrote:> Wondering, couldn't you 
wrap heavy gauge wire in a coarse spiral around the mast, similar to the wire 
wrapped around the proverbial automobile receiving antenna mast, in an attempt 
to dampen the vibration?  (Aluminum wire on an Aluminum mast)(look at the 2013 
Chrysler Town and Country van as example)You can - and it can be plastic, or 
rope, or almost anything.  What I don't know off hand is how big that spiral 
has to be.  Obviously, wrapping a AWG 20 wire isn't going to do it.One thing to 
think about, though, is that the vibration may be excited somewhere else 
(guys?) and the tower just happens to be the resonator.The other thing is to 
make it stiffer (raise the resonant frequency) so it's not excited, or to make 
the diameter different in different places.This is a pretty complicated 
phenomenon - you don't see aluminum flagpoles having the problem.Interestingly, 
the phenomenon is probably more severe in moderate winds, rat
 her than high winds (turbulence in the wind inhibits the effect)Here's the 
formula:f = 0.185 * V/Df in HzV in m/sD in meters1 mi/hr = 0.48 m/s1 " = 0.025 
mso a 2" mast in a 10 mi/hr wind (0.05 m, 4.8m/s) would tend to vibrate at 1.78 
Hz.On the other hand a 1/4" guy wire will be oscillating at 8 times that, 
around 14 Hz.I'd guess that the guy wires are higher Q than the mast.More info 
at:  
http://www.tdee.ulg.ac.be/userfiles/file/Vibrations_eoliennes_intro.pdfhttp://sites.ieee.org/pes-resource-center/files/2015/08/PES-TR17-Aeolian-Vibration-of-Single-Conductors-Final-08-17-2015.pdf______________________________________________________________________________________________TowerTalk
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listTowerTalk@contesting.comhttp://lists.contesting.com/mailman/listinfo/towertalk
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