RE: [PSUBS-MAILIST] Need formulas please

["Marten Liebster" <mliebster@tbteam.com>]

Hugo,

No offense taken. I am a programmer not an engineer, as such I have a
different outlook on this. As an example of what I mean: I've been writing
code for many years in the language of Visual Basic. For work I've had to
write programs in Java. To do so, I've been able to look through a book,
familiarize myself and quickly produce a working program. The same for goes
for C++. 

My initial mindset was listed in the simple 4 step overview: 
1)Design it so that it's round. 
2)Put on some ballast tanks
3)Fill them until you sink. 
4)Blow them to rise. 

However I am rapidly learning that if I continue with this mindset, it won't
work. By that I mean I could kill myself. 

That is the reason why I've requested the formulas. I'm trying to be able to
look at the physics of the situation - not the simplified approach I started
with. I do realize that I can't just plug the numbers into a calculator and
out comes a sub.  I am learning an immense amount about subs and what goes
in to the design. My primary goal is to build a safe device, not only the
hull. The design I wind up with will have redundant systems for propulsion,
life support, etc..

I've already established goals for the sub. I want to see what's involved in
attaining them. I am not looking to build a sub that comparable to the
mighty CSSX. The 4 steps listed above are not my stated goals.

I'm sorry if my questions are too broad for this mailing list. If I am
asking questions in the wrong place, please let me know where they should be
posed. My goal in asking is to learn not too annoy.

Marten

-----Original Message-----
From: owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of Hugo Marrero
Sent: Monday, May 03, 2004 4:45 PM
To: 'personal_submersibles@psubs.org'
Subject: RE: [PSUBS-MAILIST] Need formulas please


Marten,


There might be a certain ring of truth in what you were told. Probably what
they meant is that the total pressure exerted over the entire surface area
of the sub would be more than 6,000 lbs. instead of psi. It may have been a
simple confusion with the units of measurement. However as you will see in
the next example, ever this number was way off the ballpark.

To expand on it let's say that you have a cylinder which is 10" in diameter
and 10" long (to make it simple to calculate)... you can plug in your own
numbers.... and amaze yourself   :o)

If you know the entire surface area of the cylinder you can determine the
pressure exerted in the entire cylinder by applying the following formula:

(This formula applies only to a basic cylinder, whenever you have odd shapes
and appendages added the complexity of the calculations involved is beyond
the scope of this site. You should have a professional engineer do these
calculations for you, normally this includes Finite Element Analysis) 

P= (S)X(P)

Where S is the Surface Area of the Cylinder (This includes the curved
surface area + the surface area of both lids)

Now the Formula for the surface area of the cylinder is:

S = 2?r2 + 2?rh

Where the first part is the area of both ends and the second part is the
curved surface area.

By substituting the numbers above for the radius (5) and the height (10)we
have

[(6.28).(25)] + [(6.28).(5).(10)] = 157 + 314 = 471 SQ in

Now multiply 471 square inches by the ambient pressure at 100 ft which is
14.7 psi every 33 ft plus 14.7 psi for the atmospheric pressure (This is
called PSIA or Absolute Ambient Pressure)

(100/33)+ 1 = 4.0303 Atmospheres Absolute X 14.7 PSI = 59.24541 PSIA  (This
is the absolute ambient pressure at 100 ft.)

Now Multiply the PSIA X the surface area of the cylinder

59.24541 LBS/SQ IN X 471 SQ IN = 27,904.58811 LBS

This means that the ambient pressure is exerting a force of roughly 14 TONS
throughout the entire surface area of the cylinder walls at 100 ft deep! And
this is just a small cylinder 10 inches in diameter by 10 inches high !!!!

Marten, I took the time to explain this because I want to emphasize the
danger of relying on the information you are getting no matter how well
intended may be. If you really want to learn, you have to do your homework,
no one can do it for you. If you believe everything you hear and take it as
gospel, that's as foolish as using sewing thread to bungee jump because
someone assured you that it will work just fine. There is no substitute for
knowledge and safety. 

With this I don't want to offend anyone here. I have been diving submarines
for over 10 years, and as many know here, I am an advocate of SAFETY as the
FIRST and foremost consideration when diving a manned submersible. While
many people may be well intended or because someone maybe doing something a
certain way, it doesn't mean that they are right or that they are doing it
with safety in mind.

There is no simple formula to build a sub, as the calculations and the
formulas required will vary depending on the shape, operational depth,
external gear, and equipment on board. For example, there is a formula for
calculating the minimum size that your main ballast tank should be, and that
depends upon many other factors. And the size of your ballast tanks combined
with the maximum operating depth will determine the volume of air required
to be in the safe side, this in turn will determine the size of the
cylinders and pressures that you will use in the balast system. 

There is no magic formula to build a sub, no matter how small it is, and the
scope of this web site is to narrow to cover everything there is to know to
design a safe submersible, unless 5 or 10 people volunteer 100% of their
time to devote themselves to it, and even that may not be enough.

Marten, there is something about your way of about it that worries me... for
example here is a copy of your own email:

I always thought of it as: 

1)Design it so that it's round. 
2)Put on some ballast tanks
3)Fill them until you sink. 
4)Blow them to rise. 

Strictly from an Engineering point of view you are setting yourself up to
fail. To begin with your stated goals are too vague. Second you are defining
goals without even understanding the problem at hand. This goes against all
practical knowledge. The first goal in any engineering task should be to
study the problem at hand in order to understand it. After all how can you
state your goals to solve a problem if you do not understand it? That's like
sailing across the ocean without the knowledge about how to handle a
sailboat, navigating and without navigation aids. 

I hope that I have not offended you with this information, my purpose is to
keep people thinking on the importance of safety and knowledge to
successfuly build your own sub.

Have a great day...



Hugo




-----Original Message-----
From: Marten Liebster [mailto:mliebster@tbteam.com]
Sent: Monday, May 03, 2004 1:25
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Need formulas please



As my emails have shown, I am in the process of understanding all that goes
into designing into a PSUB. I always thought of it as: 1) Design it so that
it's round. 2)Put on some ballast tanks 3)Fill them until you sink. 4)Blow
them to rise. 

I've received much insight the past few weeks as I started to take a serious
look into it. This was achieved by posting here, reading archives and
looking through psubs.org.

Someone posted that at 100' there's more than 6,000 psi on the hull. I, as a
programmer not a engineer, would like to be able to calculate such things.
The spreadsheet that allows you to enter variables to end up with a crush
depth, is also great.

I would like to put together a website or application that would contain the
many various pertinent formulas. Formulas such as being able to calculate
the weight of the hull, how much air volume inside my pressure hull, how
much water needs to be brought in to sink the sub, etc... 

This would be publicly available to hopefully assist others. Perhaps even
include the ability to save specific info about the user's sub to save time
in the future. Including internal items that add weight and take away from
the internal air volume.

So I would appreciate it if people could send formulas (with descriptions)
and point me to the various places that contain such formulas. Also any laws
(natural/scientific) that govern the operation of a sub would wonderful.

I want to be able, with some degree of confidence, determine what a safe
operating depth a design would be capable. If I can help others to safely
design their subs, it would be my way of giving back for all the help I've
thus received.

Marten