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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

#591

Post by FreshStart »

technofiend wrote: post #450
systemtest wrote: post #241

Earlier quoted context omitted.

Is there some sort of underwater "GPS" tracker they can use to track the sub?

Because there is active search and rescue happening, a much lower tech solution is to use dye. But even that presumes a canister on the outside that can be activated from the inside and which will survive the depths of the dive. In retrospect perhaps something that does that automatically if not disarmed after a certain amount of time.

Hydrophone listening for large air bubbles penetrating water boundary layers as death triangation?

Re: Titanic tourist submersible goes missing with search under way

#592

Post by jacquesm »

varjag wrote: post #578
jliptzin wrote: post #567

Earlier quoted context omitted.

It sounds like they could use some improvements, 5 people are probably dead now. Out of how many trips in that submersible? I don’t know, just wondering, but it can’t be that many. Certainly not comparable to commercial airlines. So that’s a pretty high failure rate. Being able to open the vessel from the inside in an emergency probably wouldn’t have saved them, it’s just the first thing that is too much of a red fla…

There is no hint that its probable demise had anything to do with hatch design so far. This is a recreational dive, there's absolutely no need for it as for most recreational activities.

There are quite a few other manned submersibles designed for extreme depth that do allow for the hatch to be opened from the inside, in fact that's most of them. Alvin's design would be a nice starting point. It can be opened both from the outside and from the inside.

As for what the probable cause is: we don't know, we may never know. But with a device that was apparently designed by another party who declared it unfit for purpose anything goes.

Re: Titanic tourist submersible goes missing with search under way

#593

Post by jacquesm »

varjag wrote: post #558
gizmo wrote: post #503

Earlier quoted context omitted.

Two hatches? One opens from the inside one opens from the outside? I'm sure there are other solutions. But as somebody else already pointed out: even if you get out in the middle of the ocean you're in real trouble, which makes the hatch issue kind of moot.

And that's twice the sealing surface to potentially fail.

It could be the same hatch. Very common on submarines.

Re: Titanic tourist submersible goes missing with search under way

#594

Post by jacquesm »

wnkrshm wrote: post #494
numpad0 wrote: post #485

Earlier quoted context omitted.

I was imagining a round door in the middle of the hull, like a submarine hatch, but it looks like the entire front dome comes off and that’s the “hatch”. If so, can’t they just make the front a giant screw and add handles to both sides?

The dome shape is a structural necessity to withstand the pressure, like in a soda can. Else you would need more material, more material means more weight, more weight means more bouyancy required which again means more weight etc. It's like designing a spacecraft but with different constraints.

It's pretty much the exact opposite of designing a spacecraft.

Re: Titanic tourist submersible goes missing with search under way

#595

Post by jacquesm »

Miraste wrote: post #590
stickfigure wrote: post #454

Earlier quoted context omitted.

It needs to remain perfectly watertight at over 5000psi or everyone dies. That design constraint probably eliminates most clever latch designs.

This is usually done with a plug hatch and it's not that complex. The Alvin submersible has one and it's from 1964.

Exactly. There are so many lessons learned already when designing a device like this there is no point in re-learning them the hard way, just adopt a tried and true design.

Re: Titanic tourist submersible goes missing with search under way

#596

Post by jacquesm »

durundal wrote: post #586
omniglottal wrote: post #570

Earlier quoted context omitted.

Forging and heat treatment are processes to introduce uniformity of metallic grain structures. These have been perfected over hundreds of years. I challenge you to find a single structural component in a safety-critical context which is made of cast metal.

https://www.investacast.com/industries/safety-critical/ These folks, among others, make a lot of them. You are also incorrect about forging being used to introduce uniformity into the grain, it is typically (though not always, as some forging operations may just be for establishing shape) to stretch the grains such that they are oriented along the load path, resulting in higher allowable stresses. Look up highly load…

As well as chemical treatments.

Re: Titanic tourist submersible goes missing with search under way

#597

Post by jacquesm »

mardifoufs wrote: post #349
ra wrote: post #185

Earlier quoted context omitted.

I'm no expert, but I do know there's anything fundamentally flawed about polymer composites (including carbon fibre composites) in place of metals. Composite properties can be fairly accurately measured and tested, just like any other material including plate steel or aluminium. If a structural failure has occurred, it's related to a design, manufacture or maintenance issue. For example, not enough layers, or a weakn…

Composites can be tested. Not as easily as metals can be, and it involves a lot more software analysis and even AI, but it's still possible. I work on flaw detection/segmentation with ultrasounds -and I have not directly worked with metal scans so I can't exactly compare- but we can already get some pretty good results with the right probes and scanners. The other major issue is that NDT on composites needs more care…

How does that work? Shouldn't the device be certified for such an application?

Re: Titanic tourist submersible goes missing with search under way

#598

Post by jacquesm »

yetanotherloser wrote: post #531
tim333 wrote: post #511

Earlier quoted context omitted.

People deal with potential gas cylinder failure by occasionally testing them at higher than their usual pressure. You fill them with water and pressure to say 350 bar rather than 300. At least that's what they do with scuba tanks. Even if designed well they can be dropped, corroded etc. Not sure it's practical to do that with subs.

The advantage of testing pressure vessels with water is that the failure mode is usually less bad than gas (because it doesn't expand through any breach like gas does). Unfortunately a sub is the opposite of a pressure tank (the pressure is on the outside) so you need a pressure bottle bigger than the sub to test it in. I don't think these are common or easy to come by.

I've been in the reverse, an autoclave large enough to hold an entire spacecraft. That was already engineering on a scale that defied my imagination considerably, doing the same at the level where an entire sub could be pressurized to 400 atmospheres is engineering on a different plane. I don't think you could do this any cheaper/easier than just strapping it to a tether and dropping it overboard in a very deep part of the ocean, then winch it back in to see if it survived.

Re: Titanic tourist submersible goes missing with search under way

#599

Post by jacquesm »

pfdietz wrote: post #335
kortex wrote: post #47

Earlier quoted context omitted.

I'm not really an engineer (general hobbyist, former chemist) but I have built and worked with pressure and vacuum vessels. Positive pressure (tank vs exterior) is much easier to deal with than negative pressure (vacuum vessel at 1 atm, or bathyscape with 1 atm inside and high pressure exterior). In positive pressure, your stress is mostly in the hoop mode, which is stable. This is why aluminum cans can be so thin. I…

> a buckling mode, which is inherently unstable. As soon as it goes, it goes all at once. Example of implosion of a railroad tank car: https://www.youtube.com/watch?v=Zz95_VvTxZM

Holy crap. The speed is so high you can't even catch the intermediary phases on that video. And the casual distortion of the carrying frame is such that the rear wheels of the car no longer contact the rails.

Re: Titanic tourist submersible goes missing with search under way

#600

Post by jacquesm »

profsummergig wrote: post #415
spoonfeeder006 wrote: post #344

Earlier quoted context omitted.

Just like this persian who was given a lot of money to go on the Titanic's maiden voyage, but gave the money to charity instead. He came to the USA in 1912 and spoke out against the racism here https://www.huffpost.com/entry/abdul-baha_b_1419099 > Throughout his U.S. visit he swept aside the social protocol of segregation by insisting that everywhere he spoke be open to people of all races. Not the biggest crowd plea…

The Baha'i religion is pure free thought. Truly admirable. Pity it didn't catch on (and probably never will).

This man subscribed to it:

https://en.wikipedia.org/wiki/David_Kelly_(weapons_expert)

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