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RE: [PSUBS-MAILIST] circumferential lobes
The
way I think of it failures with 3, 4, 5, etc lobes are all possible on
the same hull, but one of those numbers will simply be associated with a lower
pressure, so that's the one that would occur first. The failure pressure
associated with these different numbers of lobes is a function of all sorts of
things, such as plating thickness, diameter of the hull, unsupported length
of the cylinder, etc., etc. I do not know of any one variable that has a clear
correlation, allowing you to know how many lobes a hull will collapse into. So
its a matter of plugging in several whole numbers and examining the
results.
As far as longitudinal stringers they are very
important to surface craft, which are analyzed as a beam (e.g., if you
load a tanker unevenly, you can split it in half). But in a deep diving sub, the
radial forces are so much larger than the beam loads, that any sub built to
withstand the radial force of pressure is likely to have enough longitudinal
strength just in the unsupported shell. In other words, longitudinal stringers
are not needed and their contribution to a pressure rating would probably be
negligible. I wouldn't do longitudinal stringers, they just add weight
inefficiently.
rgds,
Alec
Thanks for the help on using the Hull Calculation
Spread Sheet. But: I asked the
wrong question.
From your web site I understand the physical
properties of a lobe.
What I don't understand is what is changing in
the sub to change the number of lobes involved? Is it the addition of
horizontal stringers?
Thanks Dave