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The Hyperloop: BUSTED
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edavid:

--- Quote from: EEVblog on July 25, 2016, 09:31:28 am ---Can someone please explain to me the requirement for the Hyperloop (apart from being cool), with all it's inherent engineering problems, over a MegLev train?

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It's to save money.  The idea is that air suspension is cheaper than MagLev.

I don't see why you couldn't put a MagLev in a low pressure tube though.


--- Quote from: hayatepilot on July 26, 2016, 05:58:12 am ---The california high speed rail from los angeles to san francisco will cost $68billion to construct. That is for a conventional train.
How on earth is Hyperloop going to build the whole thing for 1/10th the price of a conventional rail??

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The idea was that they would save a huge amount of money by not having to purchase dedicated right of way.  A lot of people have objected to that since the initial proposal.

Maxlor:

--- Quote from: EEVblog on July 26, 2016, 01:36:06 am ---
--- Quote from: Maxlor on July 25, 2016, 03:24:52 pm ---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.

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Perhaps you like to explain those solutions in detail then?

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

But hey, if you like I can go into the details.

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.

Lot's of vacuum seals, and implication that it's impossible to get them all to seal properly: probably true, 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 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? I'm pretty sure they have engineers too. This is a cheap shot at ridiculing Hyperloop, an ad hominem attack (well, ad company), when otherwise the video is meant to show that the engineering is impossible. It seems out of place.

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.

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.

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.

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.
T3sl4co1l:
More thoughts -- underlying reasons.

Space gun (EM launch)?

It's a vacuum barrel, long enough to reach high into the atmosphere (if suitably supported).  It's not advertised for escape velocity (perhaps that would be a little too ambitious of an introduction?), but could presumably be used as such, given enough power.

That's a *much* better connection to SpaceX, and gives them reason to invest.  (Still, not excluding the executive-circle-jerk possibility.  Which itself should have a bit more of an underlying reason.  Which this maybe helps with, maybe not.)

Why not promote it as such?  Well, travel is a more practical application.  People balk at "useless" pie-in-the-sky space research.  There's nothing up there.  (Yet.)

Tim
Maxlor:
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.
System Error Message:
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.
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