# The Naked Scientists Forum

### Author Topic: Ok.... so am i an idiot???  (Read 2164 times)

#### UniqueObserver

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##### Ok.... so am i an idiot???
« on: 14/06/2012 17:23:26 »
I've attatched a quick sketch showing multiple pressure skins, would this work or am i missing something fundamental??.... just something thats bugged me for a while lol

#### UniqueObserver

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##### Re: Ok.... so am i an idiot???
« Reply #1 on: 15/06/2012 04:22:42 »
Anyone?.?.?. i did try find out for myself, it works in my head but i have lots of stuff bouncing rnd in here lol

#### Phractality

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##### Re: Ok.... so am i an idiot???
« Reply #2 on: 15/06/2012 05:21:22 »
What are your pressure skins made of? To hold their shape against external pressure,  they must have rigidity and compressive strength. They must be like concentric hollow balls, with lower pressure inside than outside. If that's what you are talking about, I don't see anything extraordinary about it. What is your new theory?

#### UniqueObserver

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##### Re: Ok.... so am i an idiot???
« Reply #3 on: 15/06/2012 16:29:24 »
well i was reading about the nuclear subs and how 500m is their top depth, the i saw they only use 1 pressure skin, surely if they made layers of skins, the gaps between only needing to be small, each with its own pressure regulator, then outside pressure can be completely negated, and the skins could be made of any material depending on how many layers you have and the individual pressure drops between each, if you drop the pressure by 50% each time then your going to need a material with a high compressive strength yes.. but if you had 100 layers for example it would be a pressure drop of 1% each layer, therefore meaning that the material used could be as thin as a foil balloon

like i said its more a proof of concept...
« Last Edit: 15/06/2012 16:32:43 by UniqueObserver »

#### Phractality

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##### Re: Ok.... so am i an idiot???
« Reply #4 on: 15/06/2012 19:59:37 »
Doubling the number of skins has the same effect as doubling the thickness of each skin. The depth limit is a matter of economics. It just costs too much to make a large submarine that can go deeper. Military subs also need to have numerous openings for torpedoes and missiles, each of which must withstand the pressure. Some openings have been eliminated by substituting electrical connections. Mechanical periscopes are replaced by video cameras, for example. Someday perhaps, torpedoes will be kept in unpressurized compartments, with robots instead of men operating them. For that matter, why not replace all the humans with robots which can operate at extreme pressures. Then, you won't need any thick skins.
Small subs have been to the very bottom of the deepest part of the oceans, nearly 11 km deep.
James Cameron joins the seven-mile-low club
Now, the Chinese are bragging that they're about to be the first in the world to reach a depth of seven kilometers. The Chinese apparently haven't read a western newspaper for the last 52 years.
Chinese Submersible Arrives at the Mariana Trench, Ready to Dive

#### UniqueObserver

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##### Re: Ok.... so am i an idiot???
« Reply #5 on: 15/06/2012 20:17:25 »
i dont thik ive explained it properly, doubling the number of skins is not the same as doubling the thickness due to the pressure in the gap between each layer, surely if each progressive gap between layers was at a lower pressure than the gap before then i imagine it would act like a buffer to absorb the pressure rather than like a wall holding it back

#### Phractality

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##### Re: Ok.... so am i an idiot???
« Reply #6 on: 16/06/2012 01:21:59 »
Not so! Each layer still must have the strength to hold back its share of the pressure, and the total strength of all the layers must equal the total pressure held back. It doesn't help to have a fluid gap between layers; the fluid between layers does not help to hold back the pressure. In fact, any gap between layers is just wasted space, unless you have a use for a partly pressurized space.

Consider a cross section thru the middle of a spherical shell with inside radius r1 and ouside radius r2; the inside pressure is P1 and the outside pressure is P2. The total force between the halves is
F = π(r22p2 - r12p1).  That force is distributed evenly over the cross section area,
A = π(r22 -  r12).  So the pressure between the two halves of the shell is
F/A = (r22p2 - r12p1)/(r22 -  r12).

The compressive strength of the material must be greater than the pressure between the two halves. For steel, it's about 800 Megapascal. Then, you need a margin for safety and an allowance for enemy depth charges and torpedoes.
« Last Edit: 16/06/2012 01:35:06 by Phractality »

#### Boogie

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##### Re: Ok.... so am i an idiot???
« Reply #7 on: 09/08/2012 00:36:07 »
What if the cells between each layer were pressurized? Wouldn't each cell behave like a wall and allow UniqueObservers idea to work?

#### yor_on

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##### Re: Ok.... so am i an idiot???
« Reply #8 on: 18/08/2012 00:09:18 »
To what pressure?

#### The Naked Scientists Forum

##### Re: Ok.... so am i an idiot???
« Reply #8 on: 18/08/2012 00:09:18 »