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Titanic tourist submersible goes missing with search under way

bbc.com

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Re: Titanic tourist submersible goes missing with search under way

#251

Post by sokoloff »

rodgerd wrote: post #221
bell-cot wrote: post #59

Not an expert...but my impression is that the implosion , at depth, of even the very small submarine in question here would generate an extremely loud "noise". Probably obvious to any hydrophone on the support vessel, and near-certainly recorded in detail by military monitoring systems.

I would rather die in an implosion that running out of air at 3,000 metres over the course of several days.

You will never “run out of air” at 3000 meters. That’s under 10K feet.

Even pilots only have to wear oxygen for sustained flight about 12.5K feet (and that’s for cognition, not survival).

Re: Titanic tourist submersible goes missing with search under way

#252

Post by remus »

JKCalhoun wrote: post #175
carbine wrote: post #111

I'm hesitant to speculate but just sharing -- an earlier version of this submersible was scrapped: "OceanGate will take advantage of lessons learned during the construction of its carbon-hulled Titan submersible, which was originally built for Titanic journeys. Rush said tests that were conducted at the Deep Ocean Test Facility in Annapolis, Md., revealed that the Titan’s hull “showed signs of cyclic fatigue.” As a r…

Carbon seems to be the go-to material these days. It often seems to fail catastrophically in ways that, for example, steel does not. I wonder if future engineers will look back at these carbon decades and shake their heads.

> Carbon seems to be the go-to material these days. It often seems to fail catastrophically in ways that, for example, steel does not.

Carbon fibre composites are also significantly lighter and more rigid than equivalent steel structures. As with all engineering it is about choosing materials with properties that suit your application.

Re: Titanic tourist submersible goes missing with search under way

#253

Post by epgui »

carabiner wrote: post #228
londons_explore wrote: post #193

Earlier quoted context omitted.

The fact they took it to some testing facility to test for cyclic fatigue shows that they understood that it was an unknown in the design, decided to test it at a facility designed for exactly that, it failed so they redesigned presumably with a design to mitigate the failures of design one. They probably took design two through the same testing process, and presumably it passed or they wouldn't have paying guests in…

No coincidence the company is in Everett. LinkedIn shows lots of people overlap with Boeing. Also the CEO built his own composite airplane while an undergrad at Princeton.

It's completely unclear how that is "no coincidence" or how that is at all relevant.

Re: Titanic tourist submersible goes missing with search under way

#254

Post by mechhacker »

scarnz wrote: post #30

This appears to be the vessel in question: https://oceangate.com/our-subs/titan-submersible.html Pressure hull made from titanium and carbon fiber, capable of diving to 4000m (13,000 ft). I recall that one reason SpaceX switched from carbon fiber to stainless steel pressure vessels (fuel tanks) was the difficulty of detecting structural flaws. Can any engineers comment on whether that task is easier for a vessel expo…

I've had some work in designing vessels to take external pressure.

It's fundamentally a nonlinear problem. A lot of new(and some not so new) engineers don't understand the process of solving it properly

For instance, euler buckling is the simple eigenvalue problem of solving a column in compression. But, it misses: initial defect because nothing is truly straight, material nonlinear effects if the part approaches yield strength, etc. I've seen it overestimate compressive capacity as much as 3-10 times depending on how geometry and material. You have to use more advanced techniques than just force over area.

Metallic vessels are difficult enough. You have to set up the problem properly and run nonlinear solves in the right way, and account for the right (or at least bound it conservatively) initial imperfections and analyze. And provide margin. Lots of compute time for a realistic analysis. And you probably still want to test. And you want to know your material very well, as the higher it's loaded, the more nonlinear that behavior could be too.

And that's with the simplicity of metal.

Composites are different. And that's not accounting for complexities of this problem. A lot of things get brittle at lower temperatures. Steel does, and I'm not sure about this particular material but at depth I would want to know specifics of temperatures and material behavior and select the right material for the job. Matrix and fibers themselves. Either failing would be fatal. I don't know enough here to say anything other than there are a lot of variables and I'm far enough away from the problem that it would take a lot of data to convince myself that I understood what could possibly happen.

Re: Titanic tourist submersible goes missing with search under way

#255

Post by p0pcult »

vkou wrote: post #240
jacquesm wrote: post #164

Earlier quoted context omitted.

Indeed. Which is why space is easier than the deep ocean, a fact that whoever was on that sub may not have fully appreciated.

If space is easier than the deep ocean, how is it that the Trieste (the submersible that explored the Challenger Deep) was built in a year on a budget of millions by a single shipyard, while it took massive, multi-year, multi-billion dollar, national efforts to go to space?

[dead]

Re: Titanic tourist submersible goes missing with search under way

#256

Post by spokeroni »

ralphhughes wrote: post #40

Skimming the website, I assume this submersible is using electromagnetically attached drop-weights so that if anything goes wrong and power is lost, the weights drop off and the submersible floats up to the surface again? And 96 hours of life support sounds good, but unless there is another submersible nearby that can dive down, find them AND attach a line, the number of hours of life support will be irrelevant. Of c…

> I assume this submersible is using electromagnetically attached drop-weights so that if anything goes wrong and power is lost

I don't think they have any "drop-weights" which would make them positively buoyant. If I'm reading the spec-sheet correctly, the submersible itself weights ~1500lbs. Subs have ballast tanks which they pump with air and force out water to make themselves positively buoyant. But if something goes wrong with the mechanism to fill the ballast tanks, I'm guessing they'd just be stuck at depth. (disclaimer, I am far from an expert at this - I just have a cursory understanding of Boyle's law)

edit: upon viewing this video https://www.youtube.com/watch?v=29co_Hksk6o&t=157s they seem to have construction pipes as ballasts that they can drop :| God help the poor souls on that sub

Re: Titanic tourist submersible goes missing with search under way

#257

Post by crabmusket »

opwieurposiu wrote: post #197
carbine wrote: post #111

I'm hesitant to speculate but just sharing -- an earlier version of this submersible was scrapped: "OceanGate will take advantage of lessons learned during the construction of its carbon-hulled Titan submersible, which was originally built for Titanic journeys. Rush said tests that were conducted at the Deep Ocean Test Facility in Annapolis, Md., revealed that the Titan’s hull “showed signs of cyclic fatigue.” As a r…

The hatch is bolted shut from the outside. When you make it back to the surface, there is no way to get out without external support. If the mother ship can not find the sub the occupants could be trapped bobbing just below the surface until their air runs out.

That's the most horrifying detail of the whole affair, to me.

Re: Titanic tourist submersible goes missing with search under way

#258

Post by justrealist »

gmiller123456 wrote: post #229
jliptzin wrote: post #225

Earlier quoted context omitted.

Seems like a pretty stupid design if you ask me

That's what Gus Grissom said.

Lot of people probably won't get the subtext on this one.

(although he was recently-probably-exonerated in that case).

Re: Titanic tourist submersible goes missing with search under way

#259

Post by dheera »

opwieurposiu wrote: post #197
carbine wrote: post #111

I'm hesitant to speculate but just sharing -- an earlier version of this submersible was scrapped: "OceanGate will take advantage of lessons learned during the construction of its carbon-hulled Titan submersible, which was originally built for Titanic journeys. Rush said tests that were conducted at the Deep Ocean Test Facility in Annapolis, Md., revealed that the Titan’s hull “showed signs of cyclic fatigue.” As a r…

The hatch is bolted shut from the outside. When you make it back to the surface, there is no way to get out without external support. If the mother ship can not find the sub the occupants could be trapped bobbing just below the surface until their air runs out.

Could they just have some drills with diamond-tipped bits stored inside for emergency use? If needed, drill through the whole shell, stick an arm out and unbolt from the outside.

Or maybe a jackhammer to just hammer through whatever glass is there for observation purposes.

Re: Titanic tourist submersible goes missing with search under way

#260

Post by ceejayoz »

sokoloff wrote: post #251
rodgerd wrote: post #221

Earlier quoted context omitted.

I would rather die in an implosion that running out of air at 3,000 metres over the course of several days.

You will never “run out of air” at 3000 meters. That’s under 10K feet. Even pilots only have to wear oxygen for sustained flight about 12.5K feet (and that’s for cognition, not survival).

You will absolutely run out of air 3000 meters underwater, as being discussed here.
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