One of Their Subs is Missing

[E24man]

Emergency blowing of tanks is, like everything else on Submarines, a variable feast dependant on such parameters, and not limited to, depth, water salinity, submarine speed, air pressure from the tanks, length of blow, temperature, submarine trim, submarine buoyancy etc.

It does, as you suggest, grab everyones attention when it does not do what you're expecting or hoping it will achieve.

Electric motors for a nuclear boat are limited by their size, and expectations were accordingly limited too.

Hulls, be they steel, alloy or titanium, are subject to lifetime material stresses like any any construction; as Scotty (RIP) would have it, 'Ye cannae ignore the Laws of Physics Captain'.

Edited by E24man on Sunday 3rd December 11:10

[anonymous-user]

Arnold Cunningham said:

Interesting that you say operational life has an impact on the boats depths - do the hulls actually have a fatigue life like aircraft do? I'd not considered that before, I'd always considered that under primarily compressive stress the no. cycles & stress crack propagation weren't an issue?

This is why i wondered if modern boats measure and monitor Young's modulus for the hull? I wonder if any parts of the pressure hull actually see tensile stress due the local geometry?

[anonymous-user]

KTF said:

That acoustic signal originated near 46-10S, 59-42W at 1358Z (GMT) on 15 November 2017. It was produced by the collapse (implosion) of the ARA SAN JUAN pressure-hull at a depth of 1275-feet. Sea pressure at the collapse depth was 570 PSI. The frequency of the collapse event signal (bubble-pulse) was about 4.4 Hz.

Question 2: How was the depth of the implosion estimated? Triangulation from numerous hydrophones gets your location (once you've corrected for transmission effects) but the depth? Is this perhaps a measure of the frequency of the implosion pulse? (as water density increases with depth?)


ETA: Turns out, Household lightbulbs hold the answer: Imploding_LightBulbs_UW

;-)

Edited by anonymous-user on Sunday 3rd December 13:08

[jjohnson23]

[quote=Max_Torque]

Question 2: How was the depth of the implosion estimated? Triangulation from numerous hydrophones gets your location (once you've corrected for transmission effects) but the depth? Is this perhaps a measure of the frequency of the implosion pulse? (as water density increases with depth?)


ETA: Turns out, Household lightbulbs hold the answer: Imploding_LightBulbs_UW

;-)

I thought it would be difficult to work out but after reading that its very simple really.

[Vipers]

jjohnson23 said:

Max_Torque said:

Question 2: How was the depth of the implosion estimated? Triangulation from numerous hydrophones gets your location (once you've corrected for transmission effects) but the depth? Is this perhaps a measure of the frequency of the implosion pulse? (as water density increases with depth?)


ETA: Turns out, Household lightbulbs hold the answer: Imploding_LightBulbs_UW

;-)

I thought it would be difficult to work out but after reading that its very simple really.

All I know is Barlows formula, take a piece of pipe, and calculate the bursting pressure based on diameter and wall thickness. (and tensile strength of material).

If you double the diameter you half the bursting pressure, by doubling the wall thickness and doubling the diameter, it stays the same, works on pipe, but sod all to do with subs, but just sprung to mind reading this.

I am guessing operational depth of a sub is well within the realms of bursting depth. But if you cant stop it sinking, nothing you can do, we lost one years ago due to an inlet left open I think, the Affray.

[E24man]

The pipe formula is useful but bear in mind the ends are domed, and submarines also have watertight bulkheads along them as well as circumferential ribs which will change the perspective of the basic equation.... as well as the many, many, many holes submarines have cut into them.

[Krikkit]

It would be very interesting to know exactly how it was done - I'd imagine it wasn't trivial as it took a couple of weeks to deliver the analysis to the Argentinian officials.

[Vipers]

Thought I heard on the 0630 news they have located what may be the sub, in 1000 msw, for us oldies, that's 0.62 miles down.

If it will they recover it, how on earth could you do that. Well beyond manned intervention, I would assume if confirmed would leave it. Mind you it's not confirmed yet.

[Ayahuasca]

Assuming it was crushed as described above, what would it look like now? I am picturing a long, flat version of the sub as if it has been run over by a steam roller. Is that fair? Or would it be more ball shaped?

Either way, if they raise it it will be tough to extract human remains.

[Skii]

Ayahuasca said:

Assuming it was crushed as described above, what would it look like now? I am picturing a long, flat version of the sub as if it has been run over by a steam roller. Is that fair? Or would it be more ball shaped?

Either way, if they raise it it will be tough to extract human remains.

Depends , in the case of USS Thresher it literally shattered into small fragments strewn across the sea bed.

[anonymous-user]

If it didn't flood before it imploded (which is suggested by the obvisous acoustic signature of at least a partial catastrophic hull failure, then the water hammer tends to just rip the thing apart. In effect, everything tries to get to the middle of the sub in about 250ms and then bounces back outwards another 250ms later (the pulse was described at around 4 Hz)

[E24man]

Relatively aged hull in perhaps poor material condition with perhaps dozens of potential very weak spots around; pretty much any kind of failure could have happened but at considerable a small leak can turn catastrophic in a millisecond hence the implosion.

[dukeboy749r]

Just very sad - ad regardless of the on/off situation with the Argentinian Govt and a certain set of islands - RiP and I hope the failure is not as the result of poor Govt expenditure/maintenance

[Ayahuasca]

So the analogy would be more like a balloon bursting (in reverse) than say squeezing a coke can flat.

[anonymous-user]

Ayahuasca said:

So the analogy would be more like a balloon bursting (in reverse) than say squeezing a coke can flat.

I think so yes.

You have a compressible gas, at close to atmospheric pressure surrounded by a pressure hull, holding back hundreds of pounds per square inch of hydraulic pressure generated by an in-compressible fluid. When the hull fails catastrophically, it basically concertinas inwards, until the air pressure exceeds that of the water pressure, and then the air acts as a spring about pushes the water away again. How many cycles that occurs for depends on the depth, pressure in the hull and according to those studies, numerous other factors. In all cases, it's RIP to any poor sod unlucky enough to be inside at the time ;-(

Only boats (or subs) that flood during the sinking arrive at the bottom semi intact, assuming they have't broken their back in the original plunge from the surface (a-la Titanic)

[Vipers]

Max_Torque said:

Ayahuasca said:

So the analogy would be more like a balloon bursting (in reverse) than say squeezing a coke can flat.

I think so yes.

You have a compressible gas, at close to atmospheric pressure surrounded by a pressure hull, holding back hundreds of pounds per square inch of hydraulic pressure generated by an in-compressible fluid. When the hull fails catastrophically, it basically concertinas inwards, until the air pressure exceeds that of the water pressure, and then the air acts as a spring about pushes the water away again. How many cycles that occurs for depends on the depth, pressure in the hull and according to those studies, numerous other factors. In all cases, it's RIP to any poor sod unlucky enough to be inside at the time ;-(

Only boats (or subs) that flood during the sinking arrive at the bottom semi intact, assuming they have't broken their back in the original plunge from the surface (a-la Titanic)

The internal pressure will not exceed external pressure unless the sub hull doesnt rupture, and it does. Even if it didn't it would just equalise as the sub was crushed and stop. It doesn't cycle at all, think about it. Google for box car implosion, it shows what I mean. Got to dash, off to work.

[karma mechanic]

Vipers said:

The internal pressure will not exceed external pressure unless the sub hull doesnt rupture, and it does. Even if it didn't it would just equalise as the sub was crushed and stop. It doesn't cycle at all, think about it. Google for box car implosion, it shows what I mean. Got to dash, off to work.

The squishing of tanks occurs with a pressure differential of approximately atmospheric, so is slow and does stop once the inside and outside pressures are equal.

Underwater the pressure difference is huge, the water is not compressible and it has the weight of hundreds of metres of water column behind it. When it implodes the water squashes the air bubble down to match the pressure, but it will then continue past that point due to the massive energy from that hammer of water. The original report mentioned an energy equivalent to many tons of TNT. Eventually the momentum of the inrushing water is braked to a stop by the pressure of the air bubble (water pressure plus momentum of inrushing water), and as noted by max_torque above it then gets the chance to expand to equalise the pressure back to the water depth pressure again. That's the 'spring' action, and that cycle accounts for the 4Hz event (250ms in and rebound). Obviously it doesn't continue oscillating for long due to the chaotic nature of all the metal, debris, air and bubbles damping it out, the cycle is primarily the implosion, bubble compression and rebound to static pressure.

Edited by karma mechanic on Tuesday 5th December 10:02

[MartG]

This video shows the effect quite well, albeit with explosions rather than implosions

https://www.youtube.com/watch?v=M5gHFJyMQ6o

[shouldbworking]

I was reading a thread on another forum about this and found the photos from 2014 when one of their subs (the ARA Santa Cruz) ran aground, revealing a fairly grim hull condition. It doesn't paint a good picture of their armed forces


https://sundodgers.com/2014/06/24/argentine-submar...

[ecsrobin]

shouldbworking said:

I was reading a thread on another forum about this and found the photos from 2014 when one of their subs (the ARA Santa Cruz) ran aground, revealing a fairly grim hull condition. It doesn't paint a good picture of their armed forces


https://sundodgers.com/2014/06/24/argentine-submar...

They have been in a bad way for years! https://ukdefencejournal.org.uk/argentine-military...

http://www.janes.com/article/75921/submarine-emerg...

They also don’t buy anything new.

http://www.janes.com/article/75538/argentina-finis...

http://www.janes.com/article/74967/argentine-army-...

Edited by ecsrobin on Wednesday 6th December 19:40