Author Topic: Instability of the twisted rope  (Read 3397 times)

struktor

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Instability of the twisted rope
« on: September 18, 2011, 10:18:13 AM »
Helices have a maximum number of rotations that can be added to them?and it is shown that this is a geometrical feature, not a material property.
This geometrical insight explains why nearly identically appearing ropes can be made from very different materials and it is also the reason behind the unyielding nature of ropes.
Maximally rotated strands behave as zero-twist structures. Hence, under strain they neither rotate in one direction nor in the other.
The necessity for the rope to be stretched while being laid, known from Egyptian tomb scenes, follows straightforwardly, as does the function of the top, an old tool for laying ropes.
http://iopscience.iop.org/0295-5075/93/6/60004/fulltext

The problem of the ideal twisted pair:
http://etacar.put.poznan.pl/piotr.pieranski/IdealTwistedPair.html

Optimal packing of a uniform tube:
http://people.sissa.it/~michelet/prot/opt_helix/index.html
http://etacar.put.poznan.pl/piotr.pieranski/Pitch-vs-Radius.gif
http://etacar.put.poznan.pl/piotr.pieranski/CPHelices.htm

Elastic rings become unstable when sufficiently twisted.
This fundamentalinstability plays an important role
in the modeling of DNA mechanics and in cableengineering.
http://math.arizona.edu/~goriely/Papers/2006-JElast(michell).pdf
http://etacar.put.poznan.pl/piotr.pieranski/SymmetryBreaking.html


The twining of climbing plants
http://math.arizona.edu/~goriely/res-twining.html
http://etacar.put.poznan.pl/piotr.pieranski/Tendrils.html


Proving mathematically that heaps of string or hair or almost anything else
will inevitably tangle themselves up in knots."
http://physics.ucsd.edu/~des/DSmithKnotting.pdf
http://www.youtube.com/watch?v=lNWEuMJCMEk


Struktor

xarax

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Re: Instability of the twisted rope
« Reply #1 on: September 18, 2011, 06:34:01 PM »
   Struktor, you are hired !  :) 
   Is this author of the Danish article, a grand X son of the sacred physicist ?
   
(P.S. I hope that the last video will help some people here, that claim so easily I am publishing  "random knots", finally understand what really is this thing they insist talking about... :))
 
This is not a knot.

struktor

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Re: Instability of the twisted rope
« Reply #2 on: September 20, 2011, 06:45:20 PM »
American Wire Rope Catalogue and Hand Book (1913)
http://www.archive.org/details/americanwirerope00amer

The Wire Rope and Its Applications (1896)
http://www.archive.org/details/wireropeanditsa00hipkgoog
"The accompanying drawing is a photograph of a piece of our Cold-Drawn Steel Rods
half inch diametr which had knotted cold thus proving its quality and general ductlity."  :)


P.S.
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      Is this author of the Danish article, a grand X son of the sacred physicist ?

The Bohr sons:
Hans Henrick (M.D.), Eric (Chemical Engineer),
Aage (Ph.D, theoretical physicist), Ernest (Lawyer)
http://www.cord.edu/faculty/ulnessd/legacy/fall2000/pfeifer/nielsbohr.htm

The second author is called Olsen.
Whose may be a son?   ;)
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Struktor



struktor

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Re: Instability of the twisted rope
« Reply #3 on: September 21, 2011, 04:02:19 PM »
Making Cordage By Hand:
http://www.primitiveways.com/cordage.html

"Bring your hands closer together and keep twisting.
The kink should rotate on its own in a counterclockwise direction (Fig. la & b).
Twist until two or three rotations occur (Fig. 2a & b).
This is the start of a two ply cord.
At this time you can attach the end to something (or someone)
which can rotate (free-end) and keep twisting with both hands turning
clockwise OR you can attach the end to something solid (fixed-end)
and begin twisting and counter-rotating (see below)."

Cordage1 (Figure 1a & b) - While twisting of fibres creates instability that leads to a stable state.