RE: [PSUBS-MAILIST] Re: Calculation request

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

Carsten,

Finally! I got back to this after a long abscence due 1st to work and then
to vacation.

I re-read your emails with all the details about the materials and
dimensions, and ran the calculation again. The spreadsheet gives me a
failure depth of 229 feet, quite close to your 243 feet!

When the spreadsheet refers to "bulkheads" it does so in the sense of
STRUCTURAL bulkheads. These may be actual bulkheads, or they may be simply
extra-heavy frames. In the case of the "monster" sub, the "bulkheads" are
just very light structures, they do not meet this definition. When you only
have frames, not structural bulkheads, you may consider the endcaps
themselves to be your only bulkheads, so you do always have at least 2 (your
right, the formulas don't work with none). So, the "length between
bulkheads" becomes the length of the cylinder, excluding the hemispherical
parts.

I really thank you for pursuing this and providing all the detailed info.
For me it was a way of validating the spreadsheet. However, there is also a
cautionary lesson... the data definition in the spreadsheet is easy to
mis-interpret, this is far from a fool-proof tool. If anyone is using it for
their designs, PLEASE hand-check your calculations or better yet, consult a
professional engineer.

NOTE: I do suspect there is an error with the general instability part of
the spreadsheet at this time, but it errs conservatively. Nonetheless I will
be looking into this in more detail and publishing a new version once fixed.

Alec Smyth



-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org]On Behalf Of Carsten
Standfuß
Sent: Saturday, December 18, 1999 6:52 AM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Re: Calculation request


Carsten - from Germany

Hi Alex,

I used this spreadsheet today and found maybe a mistake - or I made a
mistake.

If I print in for "lenght between bulkheads" a zero and I get in the
calculations print out = division error by O. So I print in at "lenght
between
bulkheads" a lenght longer than the sub, and longer and longer..
The collapse deeps get lower and lower. Seems there is no way to
calculate
the hull of the "monster" with this programm because their are no heavy
bulkheads,
in fact they are lighter than the frames.
(it must be a deep their were the frames only hold the shell..)
What should I print in for a submarine without bulkheads? It seems
I can use the endcaps distance for the "lenght between bulkheads" but
the
endcaps are also smaller in thickness than the frames.

Regards, Carsten


Alec Smyth schrieb:
>
> I made a spreadsheet which is downloadable from the PSUBS site in the
> section "Design Guidelines and Tools". However, please take the results
with
> a high degree of scepticism (note warning on the page). As you can see
from
> the discrepancies we are encountering, the spreadsheet may or may not be
> correct. The spreadsheet is strictly for reinforced cylinders with
> hemispherical end caps, although the endcaps are assumed stronger than the
> cylinder (which of course is not necessarily true, but should be if the
> shell thicknesses are the same).
>
> Alec Smyth