RE: [PSUBS-MAILIST] Need formulas please

["Mark Steed" <plutomark@mail.astate.edu>]

I have been away for a little while and I'm not really up to speed on everything but I do know that this is one of the best postings I have ever seen on the site. BRAVO ZULU Hugo- Regards, Mark

Mark E. Steed
Arkansas State University Museum
110 Cooley Drive,PO Box#490
State University, AR 72467-0490 
USA
Tel#(870)972-2074 Fax#(870)972-2793
Email: plutomark@mail.astate.edu



---------- Original Message ----------------------------------
From: Hugo Marrero <HMarrero@hboi.edu>
Reply-To: personal_submersibles@psubs.org
Date:  Mon, 3 May 2004 16:44:56 -0400 

>
>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
>
> 
>