Author Topic: The Hyperloop: BUSTED  (Read 75257 times)

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Offline Maxlor

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Re: The Hyperloop: BUSTED
« Reply #50 on: July 27, 2016, 12:39:10 pm »
So, the simulation is done, here's the result:



What you see is a section of the tube 5km in length and 2.23 diameter (the diameter is drawn 100x bigger so we can more easily see what's happening) with the left end open. The scale is orange at the very left = outside pressure, dark blue = vacuum. The turquoise at the right near the end of the animation is about 0.75 * outside pressure.

The animation should be drawn in real time, i.e. at 10 frames per second, with one frame corresponding to 0.1 seconds in simulation time.

What we can clearly see is that the pressure behind the wave front drops as the wave runs through the tube, and that the wave front itself becomes more spread out. If we take that factor of 0.75/5km, after 35km (average distance to next car) we'll have a factor of 0.13, which doesn't seem so catastrophic anymore.
 
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Offline System Error Message

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Re: The Hyperloop: BUSTED
« Reply #51 on: July 27, 2016, 02:33:47 pm »
I think one of the problems people arguing this have is that they have been using smaller models since the size of the tube matters for how severe re-pressurisation is.

If the even of pressurisation perhaps other parts of the tubes could also start repressurising but at a slower rate to reduce the severity of a tube breaking up.

However i think that this hyperloop specifically is a scam and that it is better to get investors for R&D instead of trying to show that you are building it or something like that. I know people have good intentions but it is the R&D that is needed first. Its more to do with their presentation that makes me thing it is a scam like with those many sites that try to show cool technological stuff which arent real but make it seem plausible.
 

Offline Buriedcode

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Re: The Hyperloop: BUSTED
« Reply #52 on: July 27, 2016, 04:44:54 pm »
Seems to me just another example of technology being driven by the extremely wealthy who, whilst of course educated and successful, have no real grasp of practical engineering. I think it can work, but will it be practical and make money? nope.  It's not as bad as U-beam -which isn't complete fruitloopery as you can transfer power, its just woefully impractical and dangerous if it is to transfer any useful power.  I'm sure current engineering can make a single 'hyperloop' line work, but the only point would be to have something that seems futuristic and would become a black hole for its investors.

Also, people like Elon Musk make headlines.  Remember a few months back he claimed that he thought the 'universe was a simulation'?  Why was that news? its a very old idea, floated by many philosophers, and of course made into a successful film franchise.  It was news because he said it, and the media like to think that those who have built very successful businesses must know everything about everything.
 

Online edavid

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Re: The Hyperloop: BUSTED
« Reply #53 on: July 27, 2016, 05:29:47 pm »
You Europeans are missing the context, which is the enormous boondoggle/scam called California High Speed Rail.  Hyperloop may seem implausible, but at least it has a chance, where most people think CHSR is guaranteed to fail :(
« Last Edit: July 27, 2016, 05:31:28 pm by edavid »
 

Online T3sl4co1l

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Re: The Hyperloop: BUSTED
« Reply #54 on: July 27, 2016, 05:47:30 pm »
You Europeans are missing the context, which is the enormous boondoggle/scam called California High Speed Rail.  Hyperloop may seem implausible, but at least it has a chance, where most people think CHSR is guaranteed to fail :(

Worth noting that, although SF and LA are, themselves, rather large cities / metro areas, the fact is this: the distance between them is equivalent to travelling between states in Europe.  Except, when you travel between states in Europe, you pass tens (hundreds?) of stops at large and small cities, along the way, say between Paris and Berlin for instance.

The vast majority of the US, is so large, and so low density, that you can drive the same distance without finding more than villages.

Not that the route between SF and LA is that low density (I forget which cities the planned route passes, but it'll be more than just the two endpoints), but it's still not the kind of density that makes railways so beneficial in Europe.

Here in Wisconsin, we've had the same sorts of proposals.  We waste enough money on sports stadiums for crappy teams and games (but, I'm no fan of baseball, anyway... *cough* ;) ), we don't need to spend that kind of money on a rail that connects the two largest cities and a hundred miles of farmland!

Tim
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Offline StillTrying

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Re: The Hyperloop: BUSTED
« Reply #55 on: July 28, 2016, 01:24:30 am »
You Europeans are missing the context, which is the enormous boondoggle/scam called California High Speed Rail.  Hyperloop may seem implausible, but at least it has a chance, where most people think CHSR is guaranteed to fail :(

We're trying, we've got HS2, or as we like to call it H2S.  http://stophs2.org
CML+  That took much longer than I thought it would.
 

Online Alex Eisenhut

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Re: The Hyperloop: BUSTED
« Reply #56 on: July 28, 2016, 01:34:02 am »
Bah, Solaren, now THAT's a scam!

http://www.solarenspace.com/
 

Offline rs20

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Re: The Hyperloop: BUSTED
« Reply #57 on: July 28, 2016, 01:35:06 am »
The thing I don't get about this whole thing is that the logic seems to be: if you break the seal, everyone dies --> BUSTED!.

Well, by that metric, airplanes, trains, cars are all BUSTED as well because one can contrive (and see demonstrations of) deaths due to failures of components of all these things.

It's obviously a very very ambitious idea, and I have strong doubts whether it will ever succeed. But to call it "BUSTED", frankly, dilutes the brand of the word BUSTED which should be restricted to things that are impossible, not just dangerous.
 

Online EEVblog

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Re: The Hyperloop: BUSTED
« Reply #58 on: July 28, 2016, 01:43:34 am »
I'm not saying the Hyperloop can work, and I certainly don't have the skills do design the whole system, but I also don't make absolute claims, like Thunderf00t does.

He's doing back of the envelop calcs to show how impractical and fragile the system is going to be.
You only need one of those showstoppers to be true to the entire project to be a guaranteed bust.

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If you make claims, back them up with solid evidence. I don't know why you're calling me out here

Because you said this:
Quote
Unconvincing bust. He simplifies things quite a bit, takes several cheap shots, and doesn't allow for any obvious or less obvious solutions to the fatal problems he mentions.

That implies that you think he's wrong and you have "obvious" solution to his argument.
Please present those obvious and less obvious solutions.

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, since this is exactly what you did in your various busting videos: let them have every detail that you can't 100% show isn't possible, and still show it doesn't work. Or is it just that because Thunderf00t can make a fancy video that he's more right? Hyperloop's videos are even fancier, you know...

It's about back of the envelope practicality calcs.

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Expansion of tubes, station shifting by hundreds of meters: as mentioned earlier in this thread, wouldn't rail tracks have the same problem? You don't see those shifting around all the time. Steel on this scale has quite a bit of elasticity to it, it can be compressed. Or if that's not an option, you can use sliding seals. Shock absorbers use those, and they hold up to a lot more than just 100kPa. I'm sure there are other solutions as well.

Shock absorbers are much smaller in diameter, not a good analogy.
And you need thousands of these large diameter seals to work perffectly 24/7 to keep this system working. It's a fundamentally stupid idea from a practical engineering standpoint, when you can eliminate all that problem with existing proven tech at half the speed (MagLev)

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Lot's of vacuum seals, and implication that it's impossible to get them all to seal properly: probably true

Now your getting it.

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but Hyperloop claim the distributed nature of the vacuum pumps will handle leaks, which even they acknowlege are unavoidable. So is it possible to make the seals reliable enough? I don't know, Thunderf00t certainly doesn't show any evidence that it isn't.

The argument is that it seems pretty stupid to even try to manage such a system.

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The video segments showing those interior designers: what are they doing in the video, they're supposed to show that Hyperloop consists of idea people with little background in engineering?

Solar Roadways have engineers.
UBeam have some of the finest ultrasonic PhD's in the world.
Both of these ideas will never ever work.

Quote
Massive buckling problems due to temperature differentials: Couldn't you just make the pipes strong enough to handle it? Maybe that'd make it economically unviable, but that's not what Thunderf00t says - he says it's technically impossible. But it's clearly not, otherwise gas pipelines would buckle all the time. There's really very little in the way of technical limits as to how strong you can make something, as evidenced by submarines (military ones handle thousands of kPa, research ones tens of thousands even) or, say, dams and tunnels. And if the steel pipe on it's own really is too weak, welding in some rings as shown in th picture above should do it? Or does that make it too expensive already? I don't know, but I do know that there isn't a technical problem here.

It's technically possible if you throw money at it, but any practical engineer should be able to see all the big potential showstopper issues here. Unless you have a cool job at Hyperloop and then you have blinkers on, just like those at uBeam.

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A catastrophic accident of a single car causing destruction of every other car in the system: Yeah, no. First, even if you open the pipe to its full diameter and let air rush in, that shockwave is going to die down, question is, how quickly. Now I'm not sure how to calculate this situation (but I have a COMSOL simulation running over night) but we could get a very rough idea by using the formula for calculating pressure drop from a compressor in a pneumatic system with constant flow. The numbers say, after about 66km there's about a 100kPa drop, after 37km (average car distance according to Hyperloop) there's a roughly 60kPa drop. Now clearly, that isn't the definitive answer since the actual situation isn't static, but it's enough to make me think that friction plays a role here and the pressure wave is not going to travel through the whole system at full strength, destroying everything, as Thunderf00t claims.

I agree you are likely right here. But one incident will take down the entire system and likely costs lives. It's an inherent fragile engineering system. In fact it's probably the most fragile system you could come up with. Good engineering does not base itself around an inherently fragile system.

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Second, why would the whole system have to be one open, connected tube? You could add a pressure lock every 1km that opens for cars and closes behind them, which would thus contain a catastrophe.

A door (and seals) that need to automatically open and close every 1km, at 1000kmh, do the math. This idea simply takes you further down the rabbit hole of impracticality.
You are trying to come up with a solution to fix an idea that is inherently flawed.

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The engine: actually, that turbine is not meant for propulsion. Hyperloop say that the cars are powered by external linear actuators, the turbine is there to avoid the cars pushing a column of air in front of them, which even at 0.1kPa, will add up. So it doesn't have to produce any noticeable thrust. Of course, it might still be possible that even just moving the amount of air involved is impossible, I don't know. The parts of the video are based on a misunderstanding and aren't really helpful.

Probably right.
 

Online EEVblog

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Re: The Hyperloop: BUSTED
« Reply #59 on: July 28, 2016, 01:48:23 am »
What we can clearly see is that the pressure behind the wave front drops as the wave runs through the tube, and that the wave front itself becomes more spread out. If we take that factor of 0.75/5km, after 35km (average distance to next car) we'll have a factor of 0.13, which doesn't seem so catastrophic anymore.

You can go ride it first then, good luck. I'll take the infinitely more robust and safe MagLev at half the speed thanks.
 

Online EEVblog

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Re: The Hyperloop: BUSTED
« Reply #60 on: July 28, 2016, 01:50:07 am »
It's obviously a very very ambitious idea, and I have strong doubts whether it will ever succeed. But to call it "BUSTED", frankly, dilutes the brand of the word BUSTED which should be restricted to things that are impossible, not just dangerous.

BUSTED means it isn't a practical solution.
 

Online EEVblog

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Re: The Hyperloop: BUSTED
« Reply #61 on: July 28, 2016, 01:55:10 am »
Qantas 32 had lots of error messages :P

It was crazy!
I highly recommend the book:
http://amzn.to/2a9vfSm
You didnt get my joke in relation to my name lol.

I didn't get the joke because it wasn't a joke!
If you read the QF32 book, it's all about constant endless error messages being kicked up by the ECAM system and how they spent hours working through them.
 

Offline StillTrying

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Re: The Hyperloop: BUSTED
« Reply #62 on: July 28, 2016, 02:19:57 am »
Why not leave all the air in it, but make it a very fast wind tunnel, there'd be almost no wind resistance for 'the pod' then.
CML+  That took much longer than I thought it would.
 

Online T3sl4co1l

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Re: The Hyperloop: BUSTED
« Reply #63 on: July 28, 2016, 02:24:12 am »
Why not leave all the air in it, but make it a very fast wind tunnel, there'd be almost no wind resistance for 'the pod' then.

Tremendous resistance from the pipe itself, and the 'pod' exhibits greater shear as the air is either confined to a smaller cross section (where the pod itself is), or the buildup of pressure waves (if supersonic flow, which would be necessary for comparable speed).

You'd need tens of atmospheres at one end of the pipe to maintain anywhere near subsonic flow, which you can imagine wouldn't go over well...  Otherwise, you'd need pumps along the pipe to maintain flow, which is just as bad.

Another way to think of it: you have less shear per unit length (maybe) on a maglev train car, which travels the same speed but through free air (not air in a pipe).  But that's drag only from the train's surface, not the entirety of the tracks it runs on!

Or in still other words:
The surface of a maglev train is only the train's body length.  The inner surface of a "pneumatic tube" is the entire length of the tube!

Tim
« Last Edit: July 28, 2016, 02:26:20 am by T3sl4co1l »
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Online edavid

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Re: The Hyperloop: BUSTED
« Reply #64 on: July 28, 2016, 02:25:27 am »
You can go ride it first then, good luck. I'll take the infinitely more robust and safe MagLev at half the speed thanks.

Are you sure the first ride on a 380MPH MagLev would be robust and safe  :-//
 

Offline StillTrying

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Re: The Hyperloop: BUSTED
« Reply #65 on: July 28, 2016, 02:39:36 am »
The inner surface of a "pneumatic tube" is the entire length of the tube!
I was surprised in the simulation above, that the air wavefront didn't quickly become very bullet shaped, it didn't look right to me.
CML+  That took much longer than I thought it would.
 

Offline Mark_Of_Sanity

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Re: The Hyperloop: BUSTED
« Reply #66 on: July 28, 2016, 02:53:10 am »
So, the simulation is done, here's the result:



...

Can you please share your equations and calculations?
This is the second time I've seen someone mention how the cascade scenario TF points to is a miscalculaton.
Another guy I quoted earlier on mentioned that the flow would be reduced to 5% after 2km into the pipe.
I haven't seen many try and proof read thunderf00ts claim of air rushing in at full volume at the speed of sound.

Also initially you can avoid any human danger by only using this for cargo transport.

Btw EEVblog, Hyperloop is maglev train, the turbine is there to further reduce air resistance
by shoving that air under or behind the capsule apparently.


p.s.

I am also a huge fan of the maglev train and especially love the transrapid by the Germans which is now dead unfortunately.
It would attract the train on to the rail then let go, and attract 100 000 times per second to maintain a constant gap of 10mm.
What a beauty!
« Last Edit: July 28, 2016, 02:56:37 am by Mark_Of_Sanity »
 

Online T3sl4co1l

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Re: The Hyperloop: BUSTED
« Reply #67 on: July 28, 2016, 03:07:55 am »
The inner surface of a "pneumatic tube" is the entire length of the tube!
I was surprised in the simulation above, that the air wavefront didn't quickly become very bullet shaped, it didn't look right to me.

Wave physics!  You'll see that at the entry opening, but it's a plane wave (more or less) that pushes ahead.

The ripples are from dispersion, because the pipe is an acoustic waveguide (which, unlike EM waveguide, does support low frequencies -- acoustic waves are longitudinal, so a pipe goes all the way down to DC, which requires a coax cable (supports TEM mode) for EM waves).  Wave velocity varies with frequency, so the frequency components in the wavefront spread out as they propagate.

Dispersion also has another effect:

Because the frequency components separate, the wave front is no longer a sharp rising edge, but a series of ripples (something like a sinc(t) function, although it's more of a chirp wavelet).  This manifests as a weaker overpressure, less peak acceleration when the wave hits something.

This is geometric in origin, and independent of loss.  But losses will also contribute to dispersion, and considerably reduce the amount of pressure being supplied towards the wavefront.  (Essentially, very low frequencies are significantly attenuated and delayed: hence, still more dispersion.)  Which is akin to a tsunami, where the amplitude may not be much (a few feet / 10s of kPa), but even if the wavefront doesn't cause immediate damage, the constant and maintained flow will soon overwhelm anything in the way, pushing it around like matchsticks.

A shockwave is a phenomenon where so much energy has been pushed into the wavefront, that it heats up (adiabatically), thus raising the speed of sound and allowing the wavefront to propagate faster than the cool air it moves into.  This is impossible* from atmospheric pressure alone, so we don't have to worry about shockwaves here.

*Well, maybe if the air rushes into a vacuum tube (as we're talking about here, but not so long that the wavefront disperses), then hits a rigid end wall and bounces back.  That causes the wavefront to double back on itself, raising the pressure inside the tube (from the capped end towards the mouth) to about double, which will therefore heat it, and accelerate the return wave.  The result will be a ringdown waveform (nominally a square wave, since it's a constant cross-section transmission line) with an odd duty cycle.

Tim
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Offline StillTrying

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Re: The Hyperloop: BUSTED
« Reply #68 on: July 28, 2016, 03:30:11 am »
I'm still convinced that the front should be bullet shaped.
https://www.google.com/search?hl=en-GB&gbv=2&tbm=isch&q=laminar+flow+in+pipe
CML+  That took much longer than I thought it would.
 

Offline rs20

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Re: The Hyperloop: BUSTED
« Reply #69 on: July 28, 2016, 03:51:17 am »
I'm still convinced that the front should be bullet shaped.
https://www.google.com/search?hl=en-GB&gbv=2&tbm=isch&q=laminar+flow+in+pipe

Only if friction/loss is factored in. (Not taking a position on whether it should be or not, it's just silly to have a debate on "whether the front should be bullet shaped" because the answer to that question is totally contingent on whether you want to factor in wall friction.)
 

Offline StillTrying

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Re: The Hyperloop: BUSTED
« Reply #70 on: July 28, 2016, 04:03:03 am »
Only if friction/loss is factored in. (Not taking a position on whether it should be or not, it's just silly to have a debate on "whether the front should be bullet shaped" because the answer to that question is totally contingent on whether you want to factor in wall friction.)

As T3sl4co1l said "Tremendous resistance from the pipe itself". So no need to take that into account then.  :)
CML+  That took much longer than I thought it would.
 

Online T3sl4co1l

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Re: The Hyperloop: BUSTED
« Reply #71 on: July 28, 2016, 05:14:53 am »
Only if friction/loss is factored in. (Not taking a position on whether it should be or not, it's just silly to have a debate on "whether the front should be bullet shaped" because the answer to that question is totally contingent on whether you want to factor in wall friction.)

But it's not dependent. :)

Tim
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Offline Maxlor

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Re: The Hyperloop: BUSTED
« Reply #72 on: July 28, 2016, 05:27:31 pm »
The wavefront might be bullet shaped actually, I haven't checked. If it is, it would be hard to see, since the plot is stretched 100x vertically as mentioned above.

As for equations and so on: heh, I have no idea. I just put the geometry, fluid (air in this case) and pressure parameters into COMSOL's turbulent flow models, and tweaked the params a bit until it would finish the simulation in about 18 hours instead of 10 years, and then let it do its thing. And as for how COMSOL comes up with its results... eh that'd be quite an essay, but I'm sure someone has written it already :)
 
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Offline TheAmmoniacal

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Re: The Hyperloop: BUSTED
« Reply #73 on: July 28, 2016, 05:49:15 pm »
I collect [corporate] mugs.
MTBF ~ 700.000 h
 

Offline Kilrah

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Re: The Hyperloop: BUSTED
« Reply #74 on: July 28, 2016, 06:14:49 pm »
Second, why would the whole system have to be one open, connected tube? You could add a pressure lock every 1km that opens for cars and closes behind them, which would thus contain a catastrophe.

Now one fails to open:




>1000km/h into a wall sounds awesome!
 


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