Titanic tourist sub missing

[smartcooky]

Now about that Scott Manley video...

One thing that bugged me about it ever since, is that basically he treats some of it like an EXplosion instead of an implosion. E.g., water under pressure rushes in, which he thinks pops one endcap and the window outwards. Which only makes sense as long as you don't think about it long enough to realize that there's the same water pressure on the other side too.

Because that is exactly what it is! What did you think happens in an implosion... all the water rushes in a millisecond and just stops? What did you think happens to the air inside?

It's exactly like with a CRT implosion. Air coming in isn't pushing anything outwards, because there's the same pressure of air on the outside. The only pieces that fly out are those that bounced on something else going inwards. You can see that very clearly on some very high speed camera videos of one imploding.

Not always true. The water rushing in compresses the air inside, and this can cause parts of the structure not yet flooded to blow material out, in an explosion. There have been some estimates that the air pressure rose to such a degree, the temperature spiked to hundreds of degrees.

Listen to the testimony of this guy...



Listen to the whole thing (it's only 6 minutes) but pay particular attention to what he says from about 2:11. He explains what he thinks is the cause of the failure... that the forward glue seal between the carbon fibre cylinder and the titanium ring failed, and not only that, it failed all around the ring, all at once. The in-rushing water spiked the air pressure inside so quickly and to such a tremendous level that the view-port and the aft dome and service structure blew outwards, with the view-port ending up a long way from the wreckage... that's an explosion that following a catastrophic implosion.

 

[SpuriusMaximus]

Because that is exactly what it is! What did you think happens in an implosion... all the water rushes in a millisecond and just stops? What did you think happens to the air inside?

It equalizes to the pressure of the water outside?

 

[SpuriusMaximus]

Also, are we watching the same video? Because the one I watched actually doesn't go into any of the physics of that. It's mostly about the failure being near-instantaneous all around, which is not unexpected. As I was saying the shockwave would go at many kilometres per second in carbon fibre composite, so yeah, it going around that ring in a fraction of a millisecond is exactly what I'd expect.

 

[rjh01]

It equalizes to the pressure of the water outside?

It does more than that. The water rushing in does so at a fast speed. When the air inside is at the same pressure as the water the water that is rushing in is still moving at a fast speed, so it keeps on moving, increasing the pressure.


The major problem with titanium is fabrication and soldering. These are extremely hard to do. Ref: https://en.wikipedia.org/wiki/Titanium#Fabrication

 

[smartcooky]

It equalizes to the pressure of the water outside?

That would be true if it was a slow leak, or even a leak at a moderate speed where the air might have an opportunity to escape before being pressurized to any extent. This wasn't. This was the Titan filling up with water in about one millisecond, one, one thousandths of a second. To put that into some perspective in relation to all the simulations you might have watched, lets assume that the video was running at 30 fps (30 frames per second). Each frame is displayed 1/30th of a second intervals.

30 fps - Each frame is displayed at 1/30th of a second intervals - 33 milliseconds.
The implosion happens between frames. One frame everything looks OK, the next frame, the implosion has happened, the Titan is full of water at a pressure of 2½ tons per square inch, and everyone in it is pink mist.

So lets run the camera at 150 fps to give us slo-mo at 1/5th normal speed

150 fps - Each frame is displayed at 1/150th of a second intervals - 6.7 milliseconds.
The implosion happens between frames. One frame everything looks OK, the next frame, the implosion has happened, the Titan is full of water at a pressure of 2½ tons per square inch, and everyone in it is pink mist.

Now lets run the camera at 300 fps to give us slo-mo at 1/10th normal speed

300 fps - Each frame is displayed 1/300th of a second intervals - 3.3 milliseconds.
The implosion happens between frames. One frame everything looks OK, the next frame, the implosion has happened, the Titan is full of water at a pressure of 2½ tons per square inch, and everyone in it is pink mist.

Its only when we run the camera at over 1,000 fps that we might catch the implosion in a frame. THAT is how fast this happened.

The Titan's veiwport was blown OUTWARDS and ended up INTACT, over 5 metres away from the front of the wreckage, and keep in mind, it moved that far against the force of 2½ tones per square inch water pressure... let that sink in for a moment! Now I don't need an engineering degree to understand that if the veiwport was crushed inwards, it would have ended up inside the wreckage.

 

[SpuriusMaximus]

I never said it was the viewport that crushed inwards. And I've already said that the structural collapse can happen in less than even a millisecond, given that a shockwave would travel through the material at kilometres per second. I'm just not seeing how water would flow in against a HIGHER pressure than outside, which such an explosion scenario would involve. It doesn't matter if it's for a millisecond or whatever, that's not how fluid dynamics work. Water doesn't just forget pressure differentials if they're for too short. You need to get more into the quantum level for that kinda thing to happen.

There is the kinetic energy of the water already coming in, but even that's a finite amount.

More importantly, though it's not what we see with the rest of the sub. There are no bits blown outwards, it's all shoved inside and into the other dome. A scenario where pressure inside somehow ends up higher than outside, would have blown at least some of those strips of hull outwards.

Plus, it's not actually needed to explain anything, like why they ended up in different places. The front dome ended up on the seabed BETWEEN the tail part and the actual crushed sub with the other dome, even though the front end and the other two would have started going in opposite directions. Which tells you that position has nothing to do with how fast they were going in what direction. It's more like just them tumbling differently through the water on the way down.

As a similar situation, Bismarck's turrets also went in different places than the hull, distributed in roughly a straight line, even though they just slid out of the barbettes as she was going down, no inner pressure pushing them in any direction. And you'd expect them to just sink like a huge steel brick given their weight.

As for why the window popped, it seems to me like the shockwave going through the titanium or even a water hammer effect (such as an aftershock shockwave through the water, see depth charges for how that works) can be a good enough explanation. There was no groove all around to keep it in more aggressively, so to speak, like the rings had with the hull. Once pressure equalized it wouldn't take all that much shockwave to dislodge that wedge or at least get it unstuck, after which, see Bismarck's turrets for why it would end up in another place.

 

[erwinl]

I never said it was the viewport that crushed inwards. And I've already said that the structural collapse can happen in less than even a millisecond, given that a shockwave would travel through the material at kilometres per second. I'm just not seeing how water would flow in against a HIGHER pressure than outside, which such an explosion scenario would involve. It doesn't matter if it's for a millisecond or whatever, that's not how fluid dynamics work. Water doesn't just forget pressure differentials if they're for too short. You need to get more into the quantum level for that kinda thing to happen.

There is the kinetic energy of the water already coming in, but even that's a finite amount.

More importantly, though it's not what we see with the rest of the sub. There are no bits blown outwards, it's all shoved inside and into the other dome. A scenario where pressure inside somehow ends up higher than outside, would have blown at least some of those strips of hull outwards.

Plus, it's not actually needed to explain anything, like why they ended up in different places. The front dome ended up on the seabed BETWEEN the tail part and the actual crushed sub with the other dome, even though the front end and the other two would have started going in opposite directions. Which tells you that position has nothing to do with how fast they were going in what direction. It's more like just them tumbling differently through the water on the way down.

As a similar situation, Bismarck's turrets also went in different places than the hull, distributed in roughly a straight line, even though they just slid out of the barbettes as she was going down, no inner pressure pushing them in any direction. And you'd expect them to just sink like a huge steel brick given their weight.

As for why the window popped, it seems to me like the shockwave going through the titanium or even a water hammer effect (such as an aftershock shockwave through the water, see depth charges for how that works) can be a good enough explanation. There was no groove all around to keep it in more aggressively, so to speak, like the rings had with the hull. Once pressure equalized it wouldn't take all that much shockwave to dislodge that wedge or at least get it unstuck, after which, see Bismarck's turrets for why it would end up in another place.

Then what do you think that happened?
With the front hemisphere and ring cleanly separated and the hull mostly crushed into the rear hemisphere?
You must have a better idea surely.

 

[Jack by the hedge]

Several tons of water filling the sub from the rear end in a millisecond would have a lot of inertia when it (and the sub's contents) hit the inside of the window.

 

[Darat]

Several tons of water filling the sub from the rear end in a millisecond would have a lot of inertia when it (and the sub's contents) hit the inside of the window.

It would act like a piston.

 

[Myriad]

Several tons of water filling the sub from the rear end in a millisecond would have a lot of inertia when it (and the sub's contents) hit the inside of the window.

Right. That inertia, moving toward the inside of the bow hemisphere, was the unequal force remaining when the water pressure inside "equalized" with the pressure outside.

 

[SpuriusMaximus]

Then what do you think that happened?
With the front hemisphere and ring cleanly separated and the hull mostly crushed into the rear hemisphere?

I don't really have to have a better idea to see what's wrong with one. But here goes anyway:

I think that exactly that happened: the separation around the ring went around at probably something like 10 km/s (considering the angle of the fibres), and it was mostly just left behind, so to speak, as the rest of the hull just collapsed towards the rear dome. The shock of which threw off the unpressurised rear section.

You can see how violently that went, by looking at the screws in the video between the rear dome and the rear ring. Because it's now ajar. The force of that impact basically stripped one of the screws for a length of I'd say a foot or so.

Meanwhile, that wedge shaped porthole probably wasn't even that securely fixed towards the outside to start with. It only needed to be secure enough to not come out during transport. Once submerged, the pressure of the water alone would hold it closed tighter than any screw. Once that's no longer the case, give it a couple of hard water hammer hits (again, see how depth charges work) and it would probably come off like a charm.

 

[SpuriusMaximus]

Several tons of water filling the sub from the rear end in a millisecond would have a lot of inertia when it (and the sub's contents) hit the inside of the window.

The sub was filled from the FRONT end, not from the rear. If there was a place where that water could have picked up enough speed for inertia to cause an overpressure, it would have been a lot worse towards the rear. But that's not what we see at the rear. The composite hull there still went inwards, not outwards.

 

[Puppycow]

Now about that Scott Manley video...

One thing that bugged me about it ever since, is that basically he treats some of it like an EXplosion instead of an implosion. E.g., water under pressure rushes in, which he thinks pops one endcap and the window outwards. Which only makes sense as long as you don't think about it long enough to realize that there's the same water pressure on the other side too.

It's exactly like with a CRT implosion. Air coming in isn't pushing anything outwards, because there's the same pressure of air on the outside. The only pieces that fly out are those that bounced on something else going inwards. You can see that very clearly on some very high speed camera videos of one imploding.

Well the other half would be pushed away from the endcap, wouldn't it, as it filled with water. In any case as long as the end cap was separated from the rest of the sub, it would probably land on the ocean floor some distance away, as there were a few hundred more meters to fall to the bottom. And I would imagine the inrushing water would act like a wedge to separate the severed pieces.

 

[SpuriusMaximus]

The OTHER end being pushed away isn't the same as some extra pressure, way above the surrounding water, happening inside. Especially when the other end shows NO evidence of that happening.

 

[Jack by the hedge]

The sub was filled from the FRONT end, not from the rear. If there was a place where that water could have picked up enough speed for inertia to cause an overpressure, it would have been a lot worse towards the rear. But that's not what we see at the rear. The composite hull there still went inwards, not outwards.

Sorry, yes, I had that the wrong way around. I rewatched the video. With the water entering at the same end as the hemisphere with the window, it's harder to imagine the water impacting the window as a coherent slug that could have pushed it out.

The thing which strikes me is that a leak at the front joint would very rapidly have filled the sub, but what we see is not that, rather it's that the carbon fibre tube is almost completely destroyed, with the remaining debris pushed into the rear. So I think the tube failed starting at the front and the sub would have concertina-ed, with the end caps accelerating toward each other while water crashed in around the failure. Whether the window might have been pushed out by the impact when the imploding ends hit incompressible liquid, I can't quite picture.

 

[smartcooky]

I repeat.

The DOME SHAPED (not wedge shaped) veiwport was blown OUTWARDS and ended up INTACT, over 5 metres away from the front of the wreckage, against the force of 2½ tones per square inch water pressure. That could not happen by being "bounced on something else going inwards", and it didn't just fall off!

This is why Scott Manley sometimes refers to an "explosion" because in certain implosion scenarios, an extremely rapid implosion causes the air pressure inside to spike rapidly before it can escape. That air has to go somewhere in very little time - in this case, the most likely candidate for escape is the weakest point on the front titanium dome, the viewport, which would be blown outwards.

 

[SpuriusMaximus]

Yes, well, watch some videos about its shape. It's a truncated cone. Well, a truncated spkere arc, but same idea. And yes, it was kept in place by 2.5 tons of water per square inch while that sub is in one piece, but exactly 0 once the pressure equalized.

As for the rest, yeah, yeah, blah, blah, blah, come back when you actually have a physical explanation for the whole data, not just "but the window popped outwards!!!111eleventeen" and a bunch of handwaving

 

[SpuriusMaximus]

Sorry, yes, I had that the wrong way around. I rewatched the video. With the water entering at the same end as the hemisphere with the window, it's harder to imagine the water impacting the window as a coherent slug that could have pushed it out.

The thing which strikes me is that a leak at the front joint would very rapidly have filled the sub, but what we see is not that, rather it's that the carbon fibre tube is almost completely destroyed, with the remaining debris pushed into the rear. So I think the tube failed starting at the front and the sub would have concertina-ed, with the end caps accelerating toward each other while water crashed in around the failure. Whether the window might have been pushed out by the impact when the imploding ends hit incompressible liquid, I can't quite picture.

It's not entirely unexpected, if you think about it. The speed of sound in water (which is the speed that pressure propagates) is about 1.5 km/s. In air, even under cannon conditions, it's even lower. The speed of sound along the length of the sub, accounting for the direction of the fibre, is something like 6 times that. So essentially everything would start structurally failing before much water actually starting to get in. Once the crap started hitting the ventilation device, it did so at hypersonic speeds. (By the standards of above the sea level.) It in fact went (literally) Mach 30, blasted the fan to bits, and kept going.

Basically there's a reason I mentioned water hammer effects and depth charges. Yes, the water would crush the air bubble and rebound and then rebound again, but that's milliseconds later than the actual crush of the hull.

And really, even at the other end, yeah, water inertia hitting the aft dome probably had some effect, but if I had to bet, then 4-5 tons worth of carbon fibre hull crashing into it... probably also didn't help. Is all I'm saying

 

[smartcooky]

Yes, well, watch some videos about its shape. It's a truncated cone. Well, a truncated spkere arc, but same idea. And yes, it was kept in place by 2.5 tons of water per square inch while that sub is in one piece, but exactly 0 once the pressure equalized.

The INSIDE shape was a truncated cone, the OUTSIDE shape was a ******* DOME!! It would be IMPOSSIBLE for that to remain intact and be forced INWARDS unless the countersunk hole in the titanium hemisphere into which it was mounted was shattered. We can see clearly that it is completely intact, and therefore, for the veiwport to have ended up as far away as it did, it MUST have been blown outwards. If it just "fell off", it would have been sitting right next to the wreckage of the main hull on the sea floor.

As for the rest, yeah, yeah, blah, blah, blah, come back when you actually have a physical explanation for the whole data, not just "but the window popped outwards!!!111eleventeen" and a bunch of handwaving

I have given you a physical explanation, but you just handwaved it away.

If you want a "physics" explanation, that's different... we'll have to wait for that.

 

[SpuriusMaximus]

The INSIDE shape was a truncated cone, the OUTSIDE shape was a ******* DOME!! It would be IMPOSSIBLE for that to remain intact and be forced INWARDS

Well, it's just as well then that I never said it went inwards, innit?