Re: ATM Truss tube vibrations - cloth jackets

["Kenneth Hunter" <kb7h@onemain.com>]

I would recommend that the rope be "extra long" but not fill up the tube. If it were to fill the tube and have nowhere to go, the tube would vibrate at a lower frequency. 

Secure one end and push a bit extra inside while twisting the rope so that it curls somewhat inside the tube then secure the other end. The idea is that as the tube vibrates, it comes into contact with the rope which deadens the vibrtion by absorbing the energy. As Dominic says, "exchange motion for heat" although there is not very much heat generated as the motion is minimal. 

Tom's question about what happens when the tube is vertical only applies to one tube out of the eight (assuming a typical DOB) as the tubes are not oriented in parallel planes and even then, the one tube is vertical only for the shortest of times. 

Twisting the rope so that it coils around "inside the tubing" takes care of the possible vertical tube not being damped but be careful not to "PACK" the rope inside the tube.

Ken Hunter

-----Original Message-----
From: "William Thornley" <billt051@hotmail.com>
Date: Sat, 18 Aug 2001 22:30:18 +1000
To: kb7h@onemain.com, h.kasler@worldnet.att.net, krajcit@3lefties.com
Subject: Re: ATM Truss tube vibrations - cloth jackets


> Hi Ken,
> 
> Is the rope tensioned? Is it compressed (rammed) in the tube? Is it's OD the 
> same as the tubes ID? Coir, hemp or poly?
> 
> TIA,
> 
> Bill
> 
> 
> >From: "Kenneth Hunter" <kb7h@onemain.com>
> >Reply-To: "Kenneth Hunter" <kb7h@onemain.com>
> >To: h.kasler@worldnet.att.net, "Tom & Lou Krajci" <krajcit@3lefties.com>
> >CC: <atm@shore.net>
> >Subject: Re: ATM Truss tube vibrations - cloth jackets
> >Date: Thu, 16 Aug 2001 08:10:29 +0800
> >
> >
> >The simplest way to dampen out the vibrations is to put a piece of rope 
> >INSIDE each tube that is glued at each end. I keep suggesting it but nobody 
> >seems to want a SIMPLE solution, I guess if you can't evaluate it with 
> >Calculus... it isn't worth trying.
> >
> >Ken Hunter
> >
> >-----Original Message-----
> >From: "Herb Kasler" <h.kasler@worldnet.att.net>
> >Date: Wed, 15 Aug 2001 11:30:24 -0700
> >To: "Tom & Lou Krajci" <krajcit@3lefties.com>
> >Subject: Re: ATM Truss tube vibrations - cloth jackets
> >
> >
> > >
> > > Question for the group:
> > >
> > > Tom's mention of fundamental frequencies got me thinking about a damping
> > > strategy. If the whole truss tube has to behave like a standing wave in
> > > order to vibrate problematically, then whatever frequency it has must 
> >have
> > > an integral number of wavelengths along the length of the tube. If this 
> >is
> > > the case, then the introduction of a single, "inconveniently" placed 
> >point
> > > of fixation (node) along the length of the tube would constrain the 
> >truss
> > > only to very high frequency vibrational modes.
> > >
> > >  Something as simple as a short length of wire connecting the tubes
> > > crosswise to their nighbors might work. Two tubes thus connected would 
> >only
> > > be able to vibrate in concert, either in phase or with a node at the 
> >point
> > > at which they are fixed to oneanother. In any other vibrational mode 
> >they
> > > would damp eachother out. Careful placement of the crossbridge would 
> >make it
> > > impossible for both neighboring tubes to have a node at the point of
> > > connection except at very high frequencies. As for in-phase vibration, 
> >one
> > > could deal with that by making the crossbridge diagonal, so that for a 
> >given
> > > identical vibrational mode, the two points of connection will of 
> >necessity
> > > be out of phase with eachother. It seems to me that if it's done 
> >correctly,
> > > with at least four and possibly eight such connections for an 8-member
> > > truss, you'd be able to make an essentially vibration-free truss with 
> >almost
> > > no added bulk or weight. Of course, if you do it exactly wrong, the 
> >thing
> > > will sing like a bass fiddle!
> > >
> > > OK, so has anybody out there ever tried this?
> > >
> > > Later,
> > > Herb.
> > >
> > >
> > >
> >
> >--
> >
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> >
> 
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