Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Titanic tourist submersible goes missing with search under way

bbc.com

Post reply on HN
Print view View original

491–500 of 649 posts

Re: Titanic tourist submersible goes missing with search under way

#491

Post by midoridensha »

JumpCrisscross wrote: post #245
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…

> Composite properties can be fairly accurately measured and tested, just like any other material including plate steel or aluminium Metals are uniform and broadly predictable. Composites vary cure to cure. We simply don’t have the deep engineering tables that let you know how a material will behave without destructive testing.

>Metals are uniform and broadly predictable.

That's not true at all: metals have a grain structure, and how those grains are oriented can change the metal's properties in different directions.

>Composites vary cure to cure.

Metal castings can vary from cast to cast.

Re: Titanic tourist submersible goes missing with search under way

#492

Post by pjc50 »

Exuma wrote: post #280
mechhacker wrote: post #254

Earlier quoted context omitted.

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 yie…

That’s sounds crazy complicated. In engineering is it like software design where you can get very far just being bad? Like do companies hire just crap engineers who don’t know all this stuff and call it a day? (Kind of like hiring offshore to build mvp for cheapiest crappiest quality possible)

Software failures don't usually visibly lose money, make a mess, or kill people. (Sometimes they do, see RISKS). So it's possible to have the usual sort of software project failure where something is 200% over budget and time, without anyone really waking up. But if a pressure vessel goes bang people tend to notice.

Re: Titanic tourist submersible goes missing with search under way

#494

Post by wnkrshm »

numpad0 wrote: post #485
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.

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.

Re: Titanic tourist submersible goes missing with search under way

#495

Post by midoridensha »

Scoundreller wrote: post #404
readams wrote: post #68

Earlier quoted context omitted.

Also space pressure difference is much less. A fuel tank might have just a few atmospheres inside, and of course a human pressure vessel will have a bit under 1 atmosphere inside, compared to the outside which is at ~0 atm. At 4000m, the outside pressure is _400_ atmospheres compared to just one inside. It's way, way harder.

TIL my bicycle tires are at 4 atm, and higher-end ones 8, and racing ones will do 11.

>and racing ones will do 11.

No, they don't, not any more. That was decades ago.

High-end and racing road bike tires now are in the 40-75 psi range, and they're much wider than they used to be. They finally figured out that skinny, high-pressure tires are not only very uncomfortable, they're slower too.

Re: Titanic tourist submersible goes missing with search under way

#496

Post by varjag »

bagels wrote: post #356
varjag wrote: post #235

Earlier quoted context omitted.

It's traditional in deep submersibles design, dating back to bathysphere. You probably weren't hanging around when they were designing them

Tradition itself is probably the worst rationale for an engineering solution. Maybe it's the right way for other reasons?

You know what's the worst? Someone barging in into an established engineering domain and making spot judgements. This is simply incredible hubris that often is the hallmark of stupid but educated people.

If some brilliant improvement occurred to you in the first 5 seconds of hearing about some technical solution chances are this thought visited others in the past 100 years working on the problem for a living.

And if you hang around the problem just a wee longer and start actually thinking you quickly begin start to see the rationale why it was discarded. Like here, when there's a problem with air supply and the inhabitants are incapacitated, how do you open the bloody thing? But no, our hero never gets as far, he's already in a sister thread explaining how dumb it is seat belts get stuck when you pull them too fast or something.

Re: Titanic tourist submersible goes missing with search under way

#497

Post by midoridensha »

voxadam wrote: post #489
jonathankoren wrote: post #180

Earlier quoted context omitted.

And then JJ Abrams put Enterprise underwater, ostensibly to hide it from a stone age civilization. Such a hack. Ruined both of the biggest and beloved scifi franchisee. smh

At risk of defending JJ Abrams, hadn't Leonard Nimoy already submerged the Enterprise (NCC-1701-A) back in 1986 when he directed Star Trek IV? That said, I've long agreed with others here who take issue with the idea of landing star ships that are supposedly so large and structurally precarious they more or less must be built in space. On reentry the dynamic stresses on the hulls of those ships would be insane to the…

>At risk of defending JJ Abrams, hadn't Leonard Nimoy already submerged the Enterprise (NCC-1701-A) back in 1986 when he directed Star Trek IV?

Huh? No, where did you get that crazy idea?

There was no Enterprise in the movie, because it was destroyed in the previous movie. The crew used a Klingon bird of prey to go back in time, and they didn't go underwater, they built a tank inside the ship and beamed some whales (and water) into it.

>On reentry the dynamic stresses on the hulls of those ships would be insane to the point of absurdity.

And how does that compare to the stresses on ships that can (in most sci-fi) accelerate to a significant fraction of lightspeed very quickly, or perform extreme maneuvers during space battles?

Even in Star Trek, they recognized that inertia and structural forces would be a big problem with the plot, so they "invented" the "inertial dampers" and the "SIF": structural integrity field, which somehow manages to make the ship strong enough to handle crazy forces well beyond the strengths of the materials it's made from.

Re: Titanic tourist submersible goes missing with search under way

#499

Post by erik_seaberg »

mariuolo wrote: post #478
varjag wrote: post #235

Earlier quoted context omitted.

It's traditional in deep submersibles design, dating back to bathysphere. You probably weren't hanging around when they were designing them

Do passengers also need to undergo decompression before exiting the craft?

No, the crew remains at 1 atm and the hull bears the pressure difference. Ocean pressure at the Titanic’s depth is over 400 atm (6000 psi!) but the oxygen level in normal air becomes toxic even at lower pressures. Technical divers use nitrox mixes, and the hyperbaric chamber record is 70 atm for a couple hours by breathing 0.5% oxygen and 99.5% hydrogen. (This mix can’t even explode, not enough oxidizer.)

Re: Titanic tourist submersible goes missing with search under way

#500

Post by voxadam »

midoridensha wrote: post #497
voxadam wrote: post #489

Earlier quoted context omitted.

At risk of defending JJ Abrams, hadn't Leonard Nimoy already submerged the Enterprise (NCC-1701-A) back in 1986 when he directed Star Trek IV? That said, I've long agreed with others here who take issue with the idea of landing star ships that are supposedly so large and structurally precarious they more or less must be built in space. On reentry the dynamic stresses on the hulls of those ships would be insane to the…

>At risk of defending JJ Abrams, hadn't Leonard Nimoy already submerged the Enterprise (NCC-1701-A) back in 1986 when he directed Star Trek IV? Huh? No, where did you get that crazy idea? There was no Enterprise in the movie, because it was destroyed in the previous movie. The crew used a Klingon bird of prey to go back in time, and they didn't go underwater, they built a tank inside the ship and beamed some whales (…

It would seem that I'm in desperate need of a rewatch of the Star Trek movies, it has been more than a few years, my father would be ashamed.
Post reply on HN