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Reading the 1995 Master's Thesis referenced below would lead one to believe that the Nodruob tube is impossible.
However - I'm with Brian on this one.
The Thesis analysis considers oval or elliptical cross sections of a uniform tube while the manufacturers drawing that are provided clearly show a rectangular cross-section.
If a rectangular cross-section is used and if the outer wall is sufficiently thicker (stiffer) than the inner wall then Brian's Concertina model clearly results in the desired Nodruob behavior. (or so it seems to me)
Reading the Concertina analogy took my mind back MANY years to the 'Milk Bottle with Cream in the Neck' conundrum.
(How does the pressure on the bottom change when the cream is mixed uniformly into the milk.)
On Oct 26, 2012, at 7:19 PM, John Denker wrote:
The fundamental idea can be explained using little more
than high-school-level math and physics ideas. I threw
together a few words and a diagram:
The fundamental concept is one thing; the details are
On 10/26/2012 08:56 AM, Roberto Carabajal wrote:
the foundations including Hooke`s and Young`sIf you want to understand it at that level of detail,
that involves quite a bit of mathematics, including
fourth-order Green functions, elliptic integrals, et
cetera ... rather more detail than we usually get into
on this list.
In practice, you would probably learn more from thinking
about the basic concepts and then doing a finite-element
analysis ... rather than just staring at the equations.
A detailed analysis is available (free for all):
Cynthia D. Conway,
“ANALYTICAL ANALYSIS OF TIP TRAVEL IN A BOURDON TUBE”