Humor Random Comments Thread

[GLS]

Look who also went down on that thing...

 

[jedidia]

I wonder if anybody will ever come up with a dsl that enables you to define trees in an actually convenient way in code...

 

[Thunder Chicken]

I was watching an interview of an expert online and he said that traditional hull materials like steel and titanium are more "compliant" than carbon fiber, and that the traditional materials provide certain integrity even during an implosion. What does that mean?

I don't know who this "expert" was, but if your vessel implodes it would make very little difference to you whether it was made of titanium or steel or carbon fiber. Failure is failure.

As for the material properties, metals generally are tougher than composites and have an elastic region where applied load will deform them, but when the load is removed the part will spring back to its original shape. If you take a paper clip and use it to hold a few sheets of paper together, it will spring back to its original shape when you remove them. If you load beyond that elastic region, metals will plastically deform - they don't break or fail necessarily, but if they are unloaded the part won't return to its original shape. If you take that same paper clip and pry it open to put it on too many sheets of paper it won't spring back. Many metals can take on quite a lot of plastic deformation before they fail completely, so they can give you some warning of impending failure if the parts are designed correctly.

Composites are very stiff and relatively brittle. They are strong until they suddenly aren't. Being stiff, they don't deform very much until they begin to fail, and once they begin to fail they tend to accelerate to failure exponentially fast.

 

[Thunder Chicken]

I also wonder if maybe the composite hull was actually designed appropriately for the pressure loads (it did make several dives, after all), but perhaps it took some seemingly insignificant impact while the vessel was being handled during launch or recovery that compromised it. The composite hull itself was covered by fairings, but maybe these fairings or the titanium dome took a hit during handling that transferred the impact force to the composite. It would not take much local damage to compromise the strength of that hull.

 

[MaxBuzz]

deep-submergence vehicles "Mir" receivers

Konsul-class submersible (Russia)


Jiaolong-class submersible (China)

 

[steph]

So.....this is what he'd been saying in 2020. Perhaps that anti-safety drive got to him and he thought that, since safety margins are exaggerated, it can probably go deeper anyways.

OceanGate raises $18M to build a bigger submersible fleet and set up Titanic trips

OceanGate says it has raised $18.1 million to support the expansion of its fleet of deep-sea submersibles and set the stage for dives to the wreck of the Titanic in 2021.

www.geekwire.com

But I'd sure be asking questions and doing some googling if I were to pay 250.000 for a trip to the bottom of the sea. I guess they all fell for the 'it's expensive, so it's probably safe' fallacy.

 

[Thunder Chicken]

Interesting tidbits from "inside the community"

This is horrifying. They had hull integrity sensors detecting delamination and they dumped ballast trying to get back to the surface. All that sensor system did was give them advance warning of their imminent and inescapable doom, ensuring they spent their last moments in terror. Once failure starts in composites, it will continue exponentially even if additional loading is arrested. They would have somehow needed to unload that hull in seconds to avoid complete failure, but it would take better parts of hours to rise out of the pressures destroying the hull. That sensor array is comprehensively useless as a safety warning system.

But I'd sure be asking questions and doing some googling if I were to pay 250.000 for a trip to the bottom of the sea. I guess they all fell for the 'it's expensive, so it's probably safe' fallacy.

I think a part of the confidence of the customers was that the CEO of the company and veteran divers like Paul-Henry Nargeolet were willing to take the dive as well. The fact that the Titan made several dives previously also inspired some confidence. If someone has a particular desire to undertake a certain adventure, they generally aren't going to be searching for reasons to deter them. The superficial confidence that the CEO himself was willing to take the dive and had done so previously several times was probably all they needed.

 

[Linguofreak]

The timescale can be best described as "By all means instantly".

<snip>

All the crew inside notices about it, is the sound. The frequency at which the fibers fail increases exponentially, the integrity of the hull drops fast and then, all breaks in a few milliseconds.

A millisecond is 2*10^40 Planck times, so "by all means instantly" doesn't describe the situation. A millisecond is a really long time. I wouldn't even accept "in a light crossing time for the volume in question" as "instantly" (though I don't expect anything to be moving relativistically in this scenario).

And I'm not asking what the crew experiences. By the time the real dynamics of the situation start happening, neurological timescales are much longer than the relevant dynamical timescales. That's already been established. I'm interested in the raw physics of what happens when it goes from a statics problem to a dynamics problem.

 

[Thunder Chicken]

And I'm not asking what the crew experiences. By the time the real dynamics of the situation start happening, neurological timescales are much longer than the relevant dynamical timescales. That's already been established. I'm interested in the raw physics of what happens when it goes from a statics problem to a dynamics problem.

It basically goes from a statics problem to another statics problem at a different equilibrium in an instant. It's a violent, non-linear buckling transient going between the two states.

 

[Linguofreak]

It basically goes from a statics problem to another statics problem at a different equilibrium in an instant. It's a violent, non-linear buckling transient going between the two states.

If you look at it with high enough time resolution, there's a dynamics problem sandwiched between the two statics problems. If you don't know what that looks like, it's OK to say so; if I knew, I wouldn't be asking, and I'm sure it's a difficult problem. I would be interested in an educated guess, though.

Bottom line, if you know, or can guess: what does this look like at a million frames per second?

 

[Thunder Chicken]

If you look at it with high enough time resolution, there's a dynamics problem sandwiched between the two statics problems. If you don't know what that looks like, it's OK to say so; if I knew, I wouldn't be asking, and I'm sure it's a difficult problem. I would be interested in an educated guess, though.

Bottom line, if you know, or can guess: what does this look like at a million frames per second?

Non-linear dynamics, especially with fluid/structure interaction and thermodynamic processes, is exceedingly complicated in detail.

The actual transient of structural buckling is really only of interest to niche applications such as design of pop-through diaphragms and such. In all other instances, buckling is a failure mode to be avoided. Engineers need to know where the buckling stability envelope is and design to stay within it at all costs.

Speaking in broad strokes, as the hull collapses, parts of it may move at large fractions of the speed of sound in water. Note that the speed of sound in water is approximately 1500 m/s or 3300 mph. At those speeds, the assumption that seawater is incompressible is no longer correct. Rarefaction and compression waves form, and you basically get a water hammer from hell smashing everything. Some transient cavitation may be possible if the rarefaction waves cause pressure to drop below the vapor pressure of the water. These pressure waves would propagate away from the implosion and constitute the acoustic sound of the implosion that can travel quite some distance.

The air space in the hull goes from atmospheric pressure to water pressure in an instant. At the Titanic depth the compression would reduce the volume of the air to about 1% of the original volume. This rapid compression would heat the air, and it happens faster than heat can be conducted to the water, so that remaining air could reach isentropic temperatures as high as 1400 C. (IIRC in one of the US Navy sub implosion incidents evidence of compression ignition of fuels, papers, and textiles was found in the wreckage, but I'm having trouble finding citations for this as the Titan is dominating the internet right now). This air would quickly cool and reduce in volume further, and at those pressures and temperatures it would probably go into solution in the seawater. Few if any gas bubbles would persist for long. The sub doesn't really flood in the sense of water displacing air, but the water basically compresses and absorbs the air.

 

[Urwumpe]

A millisecond is 2*10^40 Planck times, so "by all means instantly" doesn't describe the situation. A millisecond is a really long time. I wouldn't even accept "in a light crossing time for the volume in question" as "instantly" (though I don't expect anything to be moving relativistically in this scenario).

Hell no. Most sensors on Earth couldn't measure an event that is only a millisecond long. Including human senses.

Using Planck times is the LEAST reasonable way to measure time.

 

[Linguofreak]

The air space in the hull goes from atmospheric pressure to water pressure in an instant. At the Titanic depth the compression would reduce the volume of the air to about 1% of the original volume. This rapid compression would heat the air, and it happens faster than heat can be conducted to the water, so that remaining air could reach isentropic temperatures as high as 1400 C. (IIRC in one of the US Navy sub implosion incidents evidence of compression ignition of fuels, papers, and textiles was found in the wreckage, but I'm having trouble finding citations for this as the Titan is dominating the internet right now). This air would quickly cool and reduce in volume further, and at those pressures and temperatures it would probably go into solution in the seawater. Few if any gas bubbles would persist for long. The sub doesn't really flood in the sense of water displacing air, but the water basically compresses and absorbs the air.

So one thing I'm interested in here is roughly how much of the air bubble collapse can be attributed to deformation of the hull (or inward movement of fragments), and how much can be attributed to water moving ahead of solid material.

Also, how much is the water itself going to heat due to frictional, collisional, and adiabatic effects? I can well imagine we might end up with large amounts of supercritical water here (the pressure is already supercritical, and there's a large amount of energy involved).

 

[Linguofreak]

Hell no. Most sensors on Earth couldn't measure an event that is only a millisecond long. Including human senses.

Using Planck times is the LEAST reasonable way to measure time.

It's much shorter than the relevant timescales here, but the point is that we're nowhere near the time resolution limit for the universe for this kind of event. There's an actual sequence of events, not just a jump from one timestep to the next. Even if most of our sensors don't have the necessary time resolution, we certainly have sensors that do, and even if we didn't, there are events much shorter than we can directly resolve whose dynamics we know, or at least can model roughly.

 

[Urwumpe]

It's much shorter than the relevant timescales here, but the point is that we're nowhere near the time resolution limit for the universe for this kind of event. There's an actual sequence of events, not just a jump from one timestep to the next. Even if most of our sensors don't have the necessary time resolution, we certainly have sensors that do, and even if we didn't, there are events much shorter than we can directly resolve whose dynamics we know, or at least can model roughly.

Why?

 

[Linguofreak]

Why?

Why what?

Why do I want to know? Because I have enough curiosity to rip all 9 lives from a million cats.

 

[Thunder Chicken]

So one thing I'm interested in here is roughly how much of the air bubble collapse can be attributed to deformation of the hull (or inward movement of fragments), and how much can be attributed to water moving ahead of solid material.

You're really asking questions that can't be answered without more detailed knowledge of the hull geometry and detailed transient analysis of the implosion. Any answer some random person on the internet gives you for this will be extracted from their posterior. I recommend you pursue a graduate degree or three in engineering and physics and purchase some time on a supercomputer for this analysis. Please publish your results. Good luck.

Also, how much is the water itself going to heat due to frictional, collisional, and adiabatic effects? I can well imagine we might end up with large amounts of supercritical water here (the pressure is already supercritical, and there's a large amount of energy involved).

Well, the Atlantic Ocean is a rather large mass. As energetic as the effects might be locally, I'm sure the average temperature of the Atlantic Ocean did not change a whit. I doubt any meaningful amount of water exceeded the critical temperature for any period of time. The ocean water is firmly in the compressed liquid region, not supercritical.


I should charge you tuition.

 

[n72.75]

Hell no. Most sensors on Earth couldn't measure an event that is only a millisecond long. Including human senses.

Using Planck times is the LEAST reasonable way to measure time.

I used to be professionally involved with understanding failure modes in textiles. Even the stretchy ones require fast loggers for strain and load, but I did a lot of work with some very cheep (because I didn't mind much if they got smashed sometimes) 8kHz DAQs. I had a few other fun toys that could look into the 200 kHz range with some optical measurements.


I will say, w.r.t. compressive failures, there is no good reason to load fiber in compression. Very small strains in the overall structure can result in local strains many many orders of magnitude higher. Fibers are pretty much always in a permanent state of being buckled, on account of being fibers. I cannot think of a worse way to build a submarine...maybe wood, but at least we have a few more centuries of experience building boats out of wood.

 

[Linguofreak]

You're really asking questions that can't be answered without more detailed knowledge of the hull geometry and detailed transient analysis of the implosion. Any answer some random person on the internet gives you for this will be extracted from their posterior. I recommend you pursue a graduate degree or three in engineering and physics and purchase some time on a supercomputer for this analysis. Please publish your results. Good luck.

Fair enough.

Well, the Atlantic Ocean is a rather large mass. As energetic as the effects might be locally, I'm sure the average temperature of the Atlantic Ocean did not change a whit. I doubt any meaningful amount of water exceeded the critical temperature for any period of time. The ocean water is firmly in the compressed liquid region, not supercritical.

"Large amount" being enough to affect the cooling and mixing dynamics of the collapsing air bubble over the timescale of the event and its immediate aftermath.

I'll publish my results.

 

[Thunder Chicken]

I cannot think of a worse way to build a submarine...maybe wood, but at least we have a few more centuries of experience building boats out of wood.

No cardboard, no cardboard derivatives (like paper), no string, no cellotape...very rigorous maritime engineering standards are needed.