help me win a bet regarding subs/water pressure physics

d@rk51d3 · 09-13-07, 11:54 PM

Water (like most people

) will take the path of least resistance. In this case, that is the pinhole. The leak may be slow, but flooding is inevitable.

Sorry.

Anyway, it's not too late for a second opinion. Im sure somebody around here can come up with an opposing theory.

JALU3 · 09-14-07, 12:08 AM

It's not so much that the water in the second chamber becomes an independent body of water . . . thus asserting its own pressure . . . its that due to depth, and the weight of the water above it at that depth . . . that causes the pressure . . . therefore the weight of the water, if the structure was horizontal . . . since the water is one large body . . . will continue to exert the same amount of pressure at that constant depth . . . furthermore what is exerting the 999 lbs of pressure for the seal . . . the seal itself . . . or the air pressure behind it? If it's the airpressure behind it . . . then with no air in the first pressure the seal looses its strength and will eventually open to the out water with time and the flow of the water.

I think.

panthercules · 09-14-07, 12:18 AM

Been a (really) long time since I studied fluid mechanics, but I'm afraid I believe you lose this one. I don't believe that the size of the hole in the seal makes any difference at all to the end result, though it may well affect the amount of the flow and time to flood.

I believe that the idea that the broken seal will somehow "retain 999 psi of strength" is where you're getting led astray here. The compromised seal in effect will not retain any of its strength at all (or, perhaps more accurately, whatever "strength" that seal may retain will not matter, any more than it matters that the walls of the chamber still retain their greater-than-999-psi strength even if the whole seal is opened) - once the water starts penetrating to the first compartment, the pressure in that compartment is going to equalize with that outside (1,000 psi) no matter what, and when that happens the water (and any air that might still be trapped inside, which will be highly compressed by then) in the first chamber will indeed be exerting an equal, 1,000 psi pressure on all of the interior surfaces of the first chamber - including, unfortunately, the seal into the 2nd chamber, which will then fail in just the same manner as did the first seal. Once the 2nd chamber fills and equalizes, the third seal will fail just as the others did.

Sorry - I hope for your sake I've got this wrong, but I don't think so

billko · 09-14-07, 01:50 AM

Unfortunately I have to agree with panthercules. The water pressure in the first chamber will eventually equalize with the water on the outside, therefore breaching the second seal in the same way it did the first. As for the third chamber - lather, rinse, repeat...

Hakahura · 09-14-07, 07:10 AM

All three chambers will flood.

Godalmighty83 · 09-14-07, 07:32 AM

itl take a while but yep all chambers will fllod and eventually match outside pressure.

doesnt matter if the seal can stand 999.99999lbs, your just slowing the inevitable.

Penelope_Grey · 09-15-07, 08:13 AM

OOhhh a physics problem.

Well in reality as the guys have stated all three levels are going to be buggered in effect.

Water is just simply weight, the weight of the water is what creates pressure, a submarine or underwater structure creates a gap which water wants to fill, that is what causes pressure.

You won't get a constant slow leak... no, at first you will, yes, but as the seal on chamber 1 degrades under the pressure of the water forcing its way in, so the severity of the leak will increase. Pressure inside chamber 1 will actually increase further because the air will have nowhere to go as it fills up... except... the source of the leak, air will look to escape through there thus causing more strain, as the water level rises 2 things are happening.

1) the weight of the water will be slowly but surely forcing the seal to allow more and more through.

2) the air in chamber 1 will be compressing increasing strain on your seal weakening it further.

Eventually the seal will burst as it cannot handle the strain and a rapid flood will take place. the fact its 1lb is irrelevant... the end result is the same the only thing is the time it takes to happen.

Once chamber 1 floods the exact same things will happen to chamber 2 but quicker because it is lower down and thus water is heavier and thus more pressure on a seal. The seal on chamber 2 will give out the second quickest and then chamber 3 will give out the fastest.

The entire structure is as good as junk the second you lower it into the sea.

TarJak · 09-15-07, 05:46 PM

Quote:

Originally Posted by Penelope_Grey

OOhhh a physics problem.

Well in reality as the guys have stated all three levels are going to be buggered in effect.

Water is just simply weight, the weight of the water is what creates pressure, a submarine or underwater structure creates a gap which water wants to fill, that is what causes pressure.

You won't get a constant slow leak... no, at first you will, yes, but as the seal on chamber 1 degrades under the pressure of the water forcing its way in, so the severity of the leak will increase. Pressure inside chamber 1 will actually increase further because the air will have nowhere to go as it fills up... except... the source of the leak, air will look to escape through there thus causing more strain, as the water level rises 2 things are happening.

1) the weight of the water will be slowly but surely forcing the seal to allow more and more through.

2) the air in chamber 1 will be compressing increasing strain on your seal weakening it further.

Eventually the seal will burst as it cannot handle the strain and a rapid flood will take place. the fact its 1lb is irrelevant... the end result is the same the only thing is the time it takes to happen.

Once chamber 1 floods the exact same things will happen to chamber 2 but quicker because it is lower down and thus water is heavier and thus more pressure on a seal. The seal on chamber 2 will give out the second quickest and then chamber 3 will give out the fastest.

The entire structure is as good as junk the second you lower it into the sea.

Nice one Pen

I had a chat to a guy that manufactures hyperbaric chambers and therefore knows just about all there is to know about pressure seals and he said almost exactly the same thing.

His only caveat was what pressure the "gas" was in the chambers. Even a small amount of air pressure (say at sea level pressure), will increase the amount of pressure needed by the water to make the next seal fail. So (hope I get this right), if the air pressure inside chambers 2 and 3 is ~14psi, then the pressure needs to be 999psi+14psi to make the seal fail.

He said though given that this wasn't specified in the problem description that it may not apply to the problem at hand. He also said that different gas mixtures can also have different effects but that the "gas" pressure is the key. If it was a vacuum then failure would occur.

View Poll Results: Will chambers 2 and 3 flood?
Chambers 2 and 3 will flood	23	88.46%
Chambers 2 and 3 will not flood	3	11.54%
Voters: 26. You may not vote on this poll

09-14-07, 12:08 AM	#2
JALU3 Grey Wolf Join Date: May 2007 Location: 11SMS 98896 10565 Posts: 756 Downloads: 0 Uploads: 0	It's not so much that the water in the second chamber becomes an independent body of water . . . thus asserting its own pressure . . . its that due to depth, and the weight of the water above it at that depth . . . that causes the pressure . . . therefore the weight of the water, if the structure was horizontal . . . since the water is one large body . . . will continue to exert the same amount of pressure at that constant depth . . . furthermore what is exerting the 999 lbs of pressure for the seal . . . the seal itself . . . or the air pressure behind it? If it's the airpressure behind it . . . then with no air in the first pressure the seal looses its strength and will eventually open to the out water with time and the flow of the water. I think. __________________ "The Federation needs men like you, doctor. Men of conscience. Men of principle. Men who can sleep at night... You're also the reason Section Thirty-one exists -- someone has to protect men like you from a universe that doesn't share your sense of right and wrong." -Sloan, Section Thirty-One

09-14-07, 12:18 AM	#3
panthercules The Old Man Join Date: Apr 2005 Posts: 1,336 Downloads: 6 Uploads: 0	Been a (really) long time since I studied fluid mechanics, but I'm afraid I believe you lose this one. I don't believe that the size of the hole in the seal makes any difference at all to the end result, though it may well affect the amount of the flow and time to flood. I believe that the idea that the broken seal will somehow "retain 999 psi of strength" is where you're getting led astray here. The compromised seal in effect will not retain any of its strength at all (or, perhaps more accurately, whatever "strength" that seal may retain will not matter, any more than it matters that the walls of the chamber still retain their greater-than-999-psi strength even if the whole seal is opened) - once the water starts penetrating to the first compartment, the pressure in that compartment is going to equalize with that outside (1,000 psi) no matter what, and when that happens the water (and any air that might still be trapped inside, which will be highly compressed by then) in the first chamber will indeed be exerting an equal, 1,000 psi pressure on all of the interior surfaces of the first chamber - including, unfortunately, the seal into the 2nd chamber, which will then fail in just the same manner as did the first seal. Once the 2nd chamber fills and equalizes, the third seal will fail just as the others did. Sorry - I hope for your sake I've got this wrong, but I don't think so __________________

09-14-07, 07:10 AM	#5
Hakahura Grey Wolf Join Date: Aug 2006 Location: The United Kingdom of Great Britain and Northern Ireland Posts: 785 Downloads: 0 Uploads: 0	All three chambers will flood. __________________ Sir Humphey Appleby, GCB, KBE, MVO and MA. Britain's Greatest Orator, well bar that Churchill fellow.

09-14-07, 07:32 AM	#6
Godalmighty83 Sonar Guy Join Date: May 2005 Posts: 398 Downloads: 0 Uploads: 0	itl take a while but yep all chambers will fllod and eventually match outside pressure. doesnt matter if the seal can stand 999.99999lbs, your just slowing the inevitable. __________________ Were there monkeys? Some terrifying space monkeys maybe got loose?

09-13-07, 11:54 PM	#1
d@rk51d3 Sea Lord Join Date: Sep 2006 Location: Adelaide, South Australia Posts: 1,953 Downloads: 207 Uploads: 0	Water (like most people ) will take the path of least resistance. In this case, that is the pinhole. The leak may be slow, but flooding is inevitable. Sorry. Anyway, it's not too late for a second opinion. Im sure somebody around here can come up with an opposing theory.

09-14-07, 01:50 AM	#4
billko 中国水兵 Join Date: Jul 2007 Posts: 275 Downloads: 21 Uploads: 2	Unfortunately I have to agree with panthercules. The water pressure in the first chamber will eventually equalize with the water on the outside, therefore breaching the second seal in the same way it did the first. As for the third chamber - lather, rinse, repeat...

09-15-07, 08:13 AM	#7
Penelope_Grey Sea Lord Join Date: Feb 2007 Location: UK Posts: 1,893 Downloads: 0 Uploads: 0	OOhhh a physics problem. Well in reality as the guys have stated all three levels are going to be buggered in effect. Water is just simply weight, the weight of the water is what creates pressure, a submarine or underwater structure creates a gap which water wants to fill, that is what causes pressure. You won't get a constant slow leak... no, at first you will, yes, but as the seal on chamber 1 degrades under the pressure of the water forcing its way in, so the severity of the leak will increase. Pressure inside chamber 1 will actually increase further because the air will have nowhere to go as it fills up... except... the source of the leak, air will look to escape through there thus causing more strain, as the water level rises 2 things are happening. 1) the weight of the water will be slowly but surely forcing the seal to allow more and more through. 2) the air in chamber 1 will be compressing increasing strain on your seal weakening it further. Eventually the seal will burst as it cannot handle the strain and a rapid flood will take place. the fact its 1lb is irrelevant... the end result is the same the only thing is the time it takes to happen. Once chamber 1 floods the exact same things will happen to chamber 2 but quicker because it is lower down and thus water is heavier and thus more pressure on a seal. The seal on chamber 2 will give out the second quickest and then chamber 3 will give out the fastest. The entire structure is as good as junk the second you lower it into the sea. __________________ I SURVIVED THE FIRST EVER SUBSIM WEREWOLF HUNT - and... I actually won the game for the humans too!