RE: Circumferential lobes ? (Fwd)

["asmyth" <asmyth@hsomail.com>]

Since I posted that spreadsheet, I guess I should attempt this explanation.
Its one of those things that is clear in a picture but hard in words.

One of the failure modes of a strengthened cylinder is called "yielding" of
the shell. The shell tucks in evenly in between two stiffeners, all the way
around the cylinder. In "buckling" the shell also tucks in between the
stiffeners, but it does not do so evenly all around. Instead, it folds into
a series of oval-shaped areas spaced equally around its diameter between a
pair of stiffeners. The "number of circumferential lobes" is the number of
such dished-in oval shaped areas.

Now, depending on all sorts of parameters, you will find the shell buckles
at a different  number of lobes. Using the spreadsheet, I just test
different numbers of lobes and zero in on the one that produces the lowest
buckling pressure. The spreadsheet could certainly be improved by making it
calculate buckling pressures for a whole range of lobe numbers, and then
automatically adopting the lowest value.

-Alec Smyth

> -----Original Message-----
> From: owner-personal_submersibles@psubs.org
> [mailto:owner-personal_submersibles@psubs.org]On Behalf Of Ray Keefer
> Sent: Monday, August 30, 1999 11:54 AM
> To: Personal_Submersibles@psubs.org
> Subject: Circumferential lobes ? (Fwd)
>
>
> >----------------Begin Forwarded Message----------------<
>
> Date: Mon, 30 Aug 1999 22:03:54 -0000
> From: "Karl & Shirin Fuller" <fullerk@voyager.co.nz>
> Subject: Circumferential lobes ?
> To: "Personal Submersibles" <Members@psubs.org>
>
> Hi friends , I have been searching the net for a while now and as
> a novice '
> surfer ' and very keen submersible builder to be , I was very
> happy to find
> this site and wouldn't let it be until 2 : 30 a.m. ! New Zealand
> is a long way
> from the sources of materials and information . If there is
> another  ' Kiwi '
> with interests in submersibles I would  certainly like to get in
> contact with
> you.
>
> Now for my question . What are CIRCUMFERENTIAL LOBES. I was playing around
> with the demo hull calculation guide from the web page , and the
> only thing I
> couldn't understand was the above.
>
> I live on a 60 ft. steel yacht which I designed and built , my
> trade , is to
> work with steel and engineering. My interest is to build about a
> 30 - 40 ft.
> diesel / electric submersible.
>
> Congrats. on such  a great web site !
>
> Karl Fuller.
>
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> >----------------End Forwarded Message----------------<
>