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Utopia Talk / Politics / Hyperloop and physics
Nimatzo
iChihuaha
Sat Aug 08 06:39:43
So, isn't it a really bad idea to transport people in vacuum tubes? From a physical perspective, a lot of energy goes into pumping out the air, like tactical nuclear levels of energy for any decently sized distances. In the event of even a small rupture of the tube, all the energy is gonna get released in an uncontrolled and catastrophic manner. Failure at a single point would obliterate almost the entire structure.

Seems like an engineering nightmare?
Habebe
Member
Sat Aug 08 06:48:53
Well, couldnt the same be said about N. Power plants? Which is what makes them so expensive. The safe guarding against such damage.
Habebe
Member
Sat Aug 08 06:50:50
Afaik, the big hold up is the digging of the tunnels. Which is why the boring company has been working on it and afaik actually has the worlds fastest boring machine.

A competition is coming up soon, that should be cool.Well to me.
Nimatzo
iChihuaha
Sat Aug 08 07:33:10
I don’t think it is the same order of problem, you can shut down a reactor that is having problems, on the off chance all safety mechanisms are broken or some disaster like a tsunami or mother of all earth quakes, you can have serious problems. Even then a complete meltdown is unlikely. But with a vacuum tube, a single point rupture for whatever reason would result in catastrophic failure as air would rush in at the speed of sound.



Habebe
Member
Sat Aug 08 08:49:47
Well, considering its under ground, tunneled through rock I beleive, what would happen? A cave in?
Nimatzo
iChihuaha
Sat Aug 08 10:34:09
Everyone in the tubes would die and the entire tube would be in ruins, I would speculate.
Habebe
Member
Sat Aug 08 10:53:02
http://www...e-hyperloop-crashes-2013-8?amp

This isnt exactly what you were talking about but it discusses crashes and loss of oxygen.

I foumd an article about the top 3 ways you could die in a vaccuum tune.
Habebe
Member
Sat Aug 08 10:56:23
http://www...-riding-a-hyperloop/a-46776789

Here we go.
Nimatzo
iChihuaha
Sat Aug 08 11:25:28
Yea, that is what I also find, the most discussed disasters never involve the tubes cracking.

Keep in mind, this is a very very small vacuum chamber compared to the ones hyperloop is visualizing.

http://youtu.be/0N17tEW_WEU
Nimatzo
iChihuaha
Sat Aug 08 11:26:32
Go to the 2:40 mark
TJ
Member
Sat Aug 08 11:47:14
ouch-crush time
Im better then you
2012 UP Football Champ
Sat Aug 08 12:06:42
I think I'll be a late adapter on that.
The Children
Member
Sat Aug 08 13:50:11
hypaloop is a scam.

it will never come 2 fruition like mgs4 for xbox360.
xbots r still waitin 4 that game and turnin into skeletons waitin 4 it.

hypaloop will never be real. if u believed them frauds, it wuld have come in 2018...

even da tunnel is a joke.
Nimatzo
iChihuaha
Sat Aug 08 14:12:58
That video is actually quite fascinating when you think about it. The chamber wall ruptures and as the air rushes in the surrounding atmosphere crushes the tube. I think that physically what takes place, implosion?
Seb
Member
Sat Aug 08 14:19:06
Nim:

No, because in the event of a puncture the rate of energy release is limited to the pressure differential between vacuum and air over the volume of the hole.

The air enters the puncture at the speed of sound, but the hole is small. So the volume of air entering in a given time is proportional to the size of the hole, and the stored energy released by its expansion is therefore fixed to that.

Its not like the entire network can pop like a balloon :-)
Seb
Member
Sat Aug 08 14:24:27
Nim:

No, what is happening there is simply the pressure differential between the outside air and a vacuum physically crushing the cylindrical body of the tank like if you crushed an empty can of soda.

Note it's a tank not a vacuum chamber. It's not meant to take a vacuum.

The Children
Member
Sat Aug 08 14:30:58
hypascam.

ask the dumbass indians how far hypaloop has advanced in there country.

ask the stupid americans how much hypaloop they travellin on each day.

its a scam that will never be.

they try 2 leapfrog 3 generations when in reality they gotta follow each gen like everyone else lolololololol.

Hrothgar
Member
Sat Aug 08 16:01:47
You would think in reality the hyper loop tube would not be a near vacuum, but some level of negative pressure to reduce drag on the vehicle, yet avoid catastrophic failure situations in event of air leaks/earth quakes.
Seb
Member
Sat Aug 08 17:26:04
Hrothgar:

Rupturing the tube wouldn't cause the tube to collapse.

Any tube built to operate with that pressure differential will have a safety margin. Rupture won't cause it to collapse, air rushing in will reduce the pressure differential. All it will do is cause the the cars inside to slow down.

Hyperloops won't operate at full vacuum anyway - not for safety reasons but because as the air pressure gets lower, the marginal value of reducing it further decreases.

It becomes more efficient for the cars to simply scoop up the air in front and compress the air and root it out the back. Yes it takes energy, but less than trying to pump the entire network further down.
Seb
Member
Sat Aug 08 17:28:26
Note, I don't think there's much sense in hyperloop. I think there are likely very few scenarios where it makes sense.

But the idea they are at risk of catastrophic failure is not right.

You won't be sucked out of a hole and the tubes won't implode.

But if there was a leak in a car, you might suffocate I guess.

But then, that's true in an aeroplane. The reality is planes don't often spring leaks.
Seb
Member
Sat Aug 08 17:29:45
Two hyperloop cars colliding might be an issue. But then, the impact would kill you before you suffocate. And trains go through metro tunnels all over the world with very very few collisions.
Habebe
Member
Sat Aug 08 17:52:05
"
You won't be sucked out of a hole and the tubes won't implode."

Deb WRONG again. Next henis gonna say electricity is safe and it won't kill you to flip a light switch.

As for the need, I guess this os two part.

1. The US missed out on HSR. This is our answer to that while not contesting traffic.

2. I think Musk wants this tech on lock down for mars and realizes that current tech is too slow. If you look at most everything he does it revolves around tech that is useful for Mars colonization.
Seb
Member
Sun Aug 09 00:50:53
Habebe, as a PhD student in nuclear fusion, I spent four years operating ultra high vacuum systems (far higher than anything hyperloop). Leaks were common. Nobody got sucked into the giant vacuum chamber we operated.

It just doesn't work like that.

The pressure differential between the atmosphere and a perfect vacuum is 100,000 Pascal's (kg per meter).

That means the tube itself needs to be thick, high grade steel (or buried and encased in concrete). This just means hyperloop tunnels are going to be big, heavy and expensive to build.

The only risk of catastrophic implosion is if you try to make a vessel not designed for vacuum hold a vacuum, as in the above. This is like building an airplane out of concrete, releasing it at cruising altitude and speed, and suggesting it's immediate plummet to the floor is representative of what could happen to a 747.


For a cm sized hole, it's about a kg of force pushing air through it.

Imagine a kg (2 lb bag of sugar) weighing down a flat metal square 1cm by 1cm standing on the palm of your hand.

That's not going to pierce the skin.

Now within the tube, the cars themselves face the alternative issue: they are pressurised within a vacuum. Again, a hole will cause them to leak air out, with a risk of suffocation. But not this idea that somehow you'll be sucked out is dodgy.





The Children
Member
Sun Aug 09 01:17:17
just 1 word. wheres hypaloop now and which country is operatin hypascam now.

OWNED OWNED OWNED!!!

go get ur brains checked, u morons.

the thing was announced in 2010.
its been over 10 years and ur still waitin on the first scraps.

it will never happen.
Nimatzo
iChihuaha
Sun Aug 09 15:13:37
Thanks seb.

You are right, a small rupture wouldn’t spread along the the tubes, it wouldn’t implode as that tank did! It didn’t make intuitive sense, since I know leaks in space are not that dramatic.

But, a failure on one section (not a small hole but complete severing) would send a wall of air rushing into both ends of the tube at the speed of sound. I have no idea what that would do to the tubes themselves, but the next capsule would do so well as it is hit by the air wall. It seems, albeit not as sensitive, that the risk for complete disaster is very high?
The Children
Member
Sun Aug 09 15:20:25
theorectical discussions about nottin.

this thing is a scam. it will never be real.

discussin how this will implode or not.

the answer is, it will never implode becoz nottin will ever be built, becoz nottin will ever come.

its a frikkin scam.
Habebe
Member
Sun Aug 09 15:33:45
Seb, So are you saying that electricity won't jump out and kill us?
The Children
Member
Sun Aug 09 15:34:31
well well well, whattaya know. just as i been sayin this, another new video appears http://www.youtube.com/watch?v=2h6Cz4hwuEI

BAMMM. its like i can read minds.

frikkin hell. i told ya so, idiots. anyone with a decent workin mind culdve told ya. if it isnt there after a few years, its coz ur being scammed.



The Children
Member
Sun Aug 09 16:47:28
lmao did i just break ur tiny little bubblez?

i mean how fuckin deluded do people have 2 be 2 even believe this bullshit.

just watch the video. 2020.

its 2020 NOW. so where is it. not only is it far from done. there isnt even 1 tunnel. get the fuck outta here.

get back into da line, bitchasses. u aint leapfroggin 30 years of rail volution.

lmao
The Children
Member
Sun Aug 09 17:00:55
god damn thunderfoot completely DEMOLISHED u idiots!

fuckin hell, i like this quote:

"10 years later, not a single person even built anything, the only thats changed are the computer graphics!!!"

FUCKIN HOLY HELL, ROASTED!!!! the computer graphics. the CGI they used 2 bling bling blind ur eyes is da only thing that actually changed and built in 10 years time. LMAO suckers, u are it.
Habebe
Member
Sun Aug 09 17:17:59
Tc, You do realize China is building one as well, is that fake?
Seb
Member
Sun Aug 09 17:52:50
So, suppose a giant reached down and ripped the tube open, what would happen?

Well, yes, you'd get a shockwave heading down the tube at the speed of sound, I can work out to first orders the number, but I don't think it will be that impressive tbh. Probably not nearly as bad as a low velocity car crash.

In the end you are looking at a few meters cubed of air, which doesn't weigh very much.

Habebe:

Ummm, lost track of you analogy so I'm not sure.

Immsaying
Seb
Member
Sun Aug 09 17:58:01
I'm saying if you build hyperloop, its pretty easy to design in such a way that vacuum isn't a big risk (compared to tonnes of cars full of people zooming around at supersonic speeds).

But the cost and energy involved kin building the infrastructure seems prohibitive to me.

Especially as most high value jobs that would merit such fast travel have just been demonstrated as viable by teleconference over the last three months.

I just don't think anyone will need to move enough people at such speeds regularly point to point over long enough distance that the speed translates as enough time savings to merit the capital investment. Trains are a fuck ton easier and cheaper than huge steel and concrete tubes pumped to low pressure with magnetically levitate train inside them.



Habebe
Member
Sun Aug 09 18:03:34
Seb, No analogy, bad joke is all. I wasnt actually saying you were wrong.
Nimatzo
iChihuaha
Mon Aug 10 03:11:58
Seb
"So, suppose a giant reached down and ripped the tube open, what would happen?"

Is that the only way you can think of that could rupture the tube?

"I can work out to first orders the number, but I don't think it will be that impressive tbh. Probably not nearly as bad as a low velocity car crash."

1 atm preassure differential is about 10 tons /m2 of force, which is more like a truck than a car.

The upside of a low velocity car crash is that you have airbags, seatbelts, deformation zones and not traveling near the speed of sound in a tube.
Nimatzo
iChihuaha
Mon Aug 10 03:18:01
"In the end you are looking at a few meters cubed of air, which doesn't weigh very much."

Doesn't this depend on how far ahead the tube was broken? The column of air could be several km long, mass could be in the 10's of tons, no?
Seb
Member
Mon Aug 10 06:00:47
Nim:

No, just using a hypothetical scenario - helps sometimes to be clear on the effect. Cause is irrelevant.
Seb
Member
Mon Aug 10 06:03:49
Re pressure, the static differential between the front of the car and inside of the car is zero. Because the inside of the car is pressurised to 1atm.

I.e. in steady state the car goes from needing to withstand 1atm of pressure from inside to the outside (vacuum tube), to not needing to withstand any.

It's the dynamic pressure that matters: "how much force is required to bring the mass of inrushing air to a halt relative to the car when it slams into the front of the car".
Nimatzo
iChihuaha
Mon Aug 10 08:44:06
Seb
"how much force is required to bring the mass of inrushing air to a halt relative to the car when it slams into the front of the car"

And perhaps even more important, what will that do to the capsule and the people inside it? 1 ATM = 15 PSI.

http://www...xplosionsandRefugeChambers.pdf

It would obliterate the capsule, kill everyone inside and destroy another section of the tube. The air would continue until it hits both ends of the tube, presuambly causing great destruction.
The Children
Member
Mon Aug 10 08:59:18
http://www.youtube.com/watch?v=m1OfFHL7EIM

so 22 billion suckered out of that hole and not a single thing they build culd they point 2?

Hello darkness my old friend, i come 2 talk 2 u again...

Dakyron
Member
Mon Aug 10 10:47:37
You would just have safety points where the tube would close off, say every 5 miles. So if there is a catastrophic rupture, the damage would be contained.
Dakyron
Member
Mon Aug 10 10:48:20
A catastrophic rupture is going to be caused by bomb, earthquake, cavern collapse, etc... which would be bad and kill some people anyway.
Seb
Member
Mon Aug 10 13:10:01
Nim:

Yeah, but the capsule is already pressurised to 1 ATM.

So the net pressure on the capsule wall is zero: 1atm from the air that's got into the tube, 1atm from the air inside the capsule.
Seb
Member
Mon Aug 10 13:10:07
Nim:

Yeah, but the capsule is already pressurised to 1 ATM.

So the net pressure on the capsule wall is zero: 1atm from the air that's got into the tube, 1atm from the air inside the capsule.
Seb
Member
Mon Aug 10 13:11:30
When the capsule is in the vacuum tube before the giant rips it up, there's a net 14 psi force on the inside of the capsule wall pushing out.
Habebe
Member
Mon Aug 10 13:31:38
What is this Giants median income? Asking for a friend.
Seb
Member
Mon Aug 10 14:53:58
The same as UK and US median sallary.
Nimatzo
iChihuaha
Mon Aug 10 16:17:50
I am not sure we are talking about the same effect. It's not the 1 atm of pressure, the capsule like an airplane or a spacecraft can withstand vacuum and transition to 1 atm of pressure, no problems. I am talking about the shock wave/air wall, traveling in the tube at the speed of sound as air pours into the vacuum. It would literally be like any other shock wave from an explosion.

A blast wave of 14 PSI, according to the link I posted, would destroyed most reinforced buildings and kill almost everyone inside.
sam adams
Member
Mon Aug 10 18:50:12
The shock wave would disperse with distance as you got further away from the breach, due to friction with the wall. Additionally you could close doors, slow down the capsules.

The capsules moving towards the breach, near the breach, are dead.
sam adams
Member
Mon Aug 10 18:51:09
This applies to large breaches. Small ruptures qre survivable.
sam adams
Member
Mon Aug 10 18:55:13
But every time a capsule hits the well formed wave front a new large breach could occur, especially if it hadnt slowed down yet.

Also the right resonant tube frequency could tear it apart as the wave front advances, but that should be easily designed out these days.
The Children
Member
Tue Aug 11 01:40:34
dunt worry it wunt bust for shits.

http://www.youtube.com/watch?v=eWTD0s8i6Rw

didnt u guys get the memo. the capsule is encoated with vibraniumz that these colonialists stole from wakandaa.

it is stronger than steel, smart as it can sensor integrities and impactz.

makin the capsule the most powerfull giant bullet, it will never collapse.

wtf are u idiots debatin about implosion and explosion. didnt u know vibranium is the strongest materual in the universe, u fuckin idiots.


The Children
Member
Tue Aug 11 01:42:22
ruptures...lmao u fuckin idiots.

vibraniumz doesnt rupture. u rupture, idiot.
vibraniumz doesnt bend, doesnt break, doesnt melt, doesnt implode, shock resistant.

it is da strongest material in the universe, wtf r u even on about.
Seb
Member
Tue Aug 11 02:22:22
Nim:

That's the point, if I blew at you, that's a blast wave at 14psi (static pressure, plus the dynamic pressure - the force required to slow the air down).

The 14psi doesn't matter because there's 14psi pushing the other way. Everything's pressurised to 14psi.

Another way to think about it: at the mouth of the breach, there is 14psi pushinh a block of air, accelerating it down the tube. One the air is moving at the sound speed, it stops accelerating because the molecules on average are no longer colliding so there can be no transfer. They are all moving down the tube at sound speed. Because the air has accelerated, it becomes less dense (greater separation between molecules).

The only thing you need to worry about is the mass of air and the relative speed of the shock front with respect to the capsule front.

So the capsule front is the head of a piston and all the air rushing in piles up against the front of the capsule.

Force is equal to rate of change of momentum, so it's how much momentum does the capsule need to impart to slow the air over how much time.

I suspect it's pretty easy to handle actually, especially as the capsule front needs to be built to withstand 14psi anyway as the capsules are at 1atm sitting in a vacuum tube.


Sam:

By near, if you are talking a few tens of meters, anything that can cause a big beach in the tube, given the engineering requirements of the tube, will necessarily destroy the capsule.

The bigger issue is the capsules moving at whatever ridiculous speed it is and hits beach debris, not inrushing air.

I.e. a very very high speed derailment.




Seb
Member
Tue Aug 11 02:23:24
If it's far away with for that not to be an issue, pretty sure inrushing air and shock fronts are not going to be an issue.
Nimatzo
iChihuaha
Tue Aug 11 02:51:12
I get that. Why I mentioned at the speed of sound and size of air column. The 14 psi is just the differential between surface level atm and near vaccum, creating the movement. It would be worse (more force) at higher pressure diff and vice versa.

There are videos of vacuum breach inside a small glas tube with a metal ball. The ball smashes out the other end. The ball has higher density than the air, so comparable to a capsule, probably, but of course the capsule would have breaks.

The youtuber and scientist Phil Mason aka thunderfoot has done several busted videos on this. Which is where most of my info is comming from.

Seb
Member
Tue Aug 11 03:34:49
Nim:

If you flicked the ball hard with you finger (well below 14psi impact pressure ) - would it be able to break though the glass tube do you reckon?
Nimatzo
iChihuaha
Tue Aug 11 04:54:23
Seb
Possibly, it was lab glass tubes, not very thick. It is meant to illustrate how air/vacuum differential will rapidly accelerate something that has a higher density to catastrophic effect.

I am not sure what the difference is between a shock wave that is the product of air vacuum differential at 14 PSI and one from a bomb? Because the one from the bomb is quite bad for human health and structures.
The Children
Member
Tue Aug 11 11:10:07
with vibraniumz nottin will explode or implode. dunt u fuckin idiots get it by now.

the material is light, is 10x stronger than steel and its smartz. it can sense when theres damage and send real impulses back 2 command HQ where they monitor the pods live and can bring it back be4 rupture takes place.

its vibraniumz, didnt u get the memo. they created the materials themselves.
Seb
Member
Tue Aug 11 14:11:06
Nim:

The over pressure (i.e. over 14 PSI atm) from a bomb is many tens of PSI. I.e. to blow the glass out of a window is 1 PSI, but to buckle corrugated aluminium panels is 2psi. Loaded train cars demolished is about 9-10 psi.

The 14psi of atmospheric pressure doesn't matter, except to initially drive the shockwave. It's what flicks the ball bearing. But the shockwave won't necessarily exert a 14psi peak over-pressure on the carriage.

Indeed, I suspect that 14psi is the maximum possible peak over pressure that could be generated in the frame of reference of the vacuum tube as I can't immediately think about how the shockwave could result in compression of the air above atmospheric pressure.

Probably considerably lower, but depends on factors like the speed of the carriage and how quickly the shock wave attenuates.

I would be much more worried about the carriage getting hit by debris from whatever caused the large breach, and whatever caused the large breaches direct effect.

In short, what this boils down to is "What if an earthquake, bomb, or other catastophe hits the tube while a carriage is nearby and moving", and offers no more risk than the same question for rail: "What if an earthquake, bomb, or other catastrophe hits a high speed rail line while a train is nearby and moving".

The answer is the same: the carriage will crash, and there is a great risk that many people will die in the resulting collision.

Only, I think it is much harder to damage a hyperloop tube than a section of rail, by virtue of the specs it needs to be built to in order to hold a vacuum.

In short, this isn't really the right thing to worry about.

What is the right thing to worry about is "my god this requires how much capex per mile? How much opex? Are you insane man? How many people have a need to travel that fast that we can charge them enough to make this make money?"
The Children
Member
Tue Aug 11 16:53:53
http://www.youtube.com/watch?v=fvMXvRA03ps

China is science
america is about believin...

sam adams
Member
Tue Aug 11 17:18:04
I generally agree with seb. Due to the higher speeds and vacuum its going to be a little more dangerous but not massively so compared with normal trains.

But from an economics point of view you arent beating 787s and a320s.
Nimatzo
iChihuaha
Wed Aug 12 02:59:55
Hmmm. So, I tried to look for more info and my understanding is that, no one really knows, it is theoretical. Are there any experiments that guys know of?

Arguably, this is going to be a difficult project for other reasons as you mention seb, but I was convinced it was a much more fundamental issue.
Seb
Member
Wed Aug 12 03:17:01
Nim:

Pretty sure that it's well known - it's just difficult.

Shockwave modelling is "hard" in the sense that it's best done numerically which requires beefy computers and complicated fluid dynamic codes and/or kinetic models.

Alternatively you can use scale model experiments and/or empirical scaling laws based off of such experiments.

The scenario I set out was deliberately simple - less poetically, there is a train travelling down a depressurised tube with an end cap on the end which is suddenly removed exposing the tube to a constant source of 1atm gas, leading to a rush of air down the tube towards the train.

There may in fact be an analytical solution, but it seems so simple (essentially a 1D problem) that I imagine there is a text book solution somewhere, but probably in obscure aeronautical and vacuum engineering manuals or whatever field it is that studies explosions.


Seb
Member
Wed Aug 12 03:17:12
Or balistics.
Seb
Member
Wed Aug 12 04:32:10
Hmm. One issue might be the deceleration - if the shockwave provides enough momentum it might jolt the carriage enough to give people whiplash...

Realistically tough, I think you'd just have the equivalent of a crumple zone. The capsules have a compressor fan at the front that sucks up the low pressure (it's not actually vacuum) air in front of the carriage, compresses it, and routes it out the back.

If you mounted this assembly on say, half inch steel plate itself mounted on stiff springs / honeycomb structure, the shockwave will damage the fan assembly, and it's energy will be dissipated crushing the crumple zone. Kinda like a whiffle plate / shield for space craft.

Job done. This would also protect against debris.

Just don't think that's an issue.
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