RE: [PSUBS-MAILIST] Spreadsheet questions

[Alec Smyth <Asmyth@changepoint.com>]

Chris,

I posted the hull spreadsheet. By the way, I am still owing a correction to
it, because the general instability formula has a slight mistake. But it
errs on the side of caution as far as I can tell (in other words, the
calculated collapse pressure for general instability is lower than it should
be). I tried to describe the geometry in the spreadsheet, but let me try
again. Sorry, I have no diagram, but you will find them in the book
"Principles of Naval Architecture". I realize the rest of this message will
not be worth reading for anyone who doesn't have the spreadsheet open in
front of them, so please accept my apologies if its as much fun as sucking
on rusty nails.

-Alec


-----------------


The spreadsheet assumes a cilindrical hull with spherical endcaps,
stiffeners, and bulkheads. Let me just put down some observations about each
of these elements:

shell: By "shell" I am refering to the "skin" of the cylinder. Its diameter
is defined from the midplane of the plating. In other words, if you use
plating 0.5 inches thick and your ID is 30 inches, the diameter for the
spreadsheet would be 30.5". The endcaps are assumed to be the same thickness
of the cylindrical shell, and they have no stiffeners. The cylinder length
is the length WITHOUT the endcaps (that is calculated in the "length
overall" column.

frames: These are the stiffeners. They are assumed to be like a T, with the
"-" part of the T away from the plating. The "b" dimension is the thickness
of the plate from which the stiffeners are cut. The "c" dimension is the
depth, or in other words the difference between the inside and outside
diameter of each stiffener EXCLUDING the flange. The flange is of course the
"-" part of the "T", and is defined by dimensions "d" and "e". Most
important is understanding what I mean by a bulkhead, since you need to
enter the distance between those. 

bulkheads: A bulkhead in this spreadsheet is NOT just a little tin wall to
keep water from flowing between compartments. In fact, it does not need to
be closed at all. Instead, it is simply a frame that is grossly stronger
than the rest... so much so that I don't need to capture its specific
dimensions. If you have no such super-strong stiffeners, then consider the
endcaps themselves to be bulkheads. The "number of frames" in the
spreadsheet includes the bulkheads. So, at the very least (the case of a
bare cylinder with endcaps but without any stiffeners at all) you would
have:

	- number of frames = 2
	- frame separation = cylinder length (from shell definition)
	- length between bulkheads = ditto

...but you would quickly see that frames are definitely worth it when you
see how little pressure an un-reinforced cylinder provides.




-----Original Message-----
From: Chris Horne [mailto:chris@chrishorne.com]
Sent: Tuesday, August 01, 2000 7:44 PM
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Spreadsheet questions


Hey all:

I've recently regained interest in my own sub project, and went to
re-download
the spreadsheets for hull and prop calculations, but have a couple of
questions:

1) Is there a diagram of what all the variables are on the hull calculation?
Some
are obvious, but some aren't so clear. Or at least a better description of
what
exactly the frames, flanges, and bulkheads are referring to; I've got a good
idea, but would hate to design the sub wrong...

2) The link for the propcalc software is broken. Can someone email it to me
or
give a correct link?

Thanks-
-chris