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Hyperloop One Becomes ‘Virgin Hyperloop One’

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Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#31

Post by ErikVandeWater »

lisper wrote: post #10

All of the Hyperloop development efforts are ignoring the elephant in the room: thermal expansion. If you do the math, the ends of a viable hyperloop track will have to move hundreds of meters [1]. No one has yet advanced even a viable idea for how to deal with that, let alone an actual design. Until that happens, the Hyperloop is vaporware. [1] It's a trivial calculation. The thermal expansion coefficient of steel i…

Just to clarify - is the thermal expansion issue both in terms of the length of the hyperloop and the inside diameter of the tube, or just the length?

Relevant discussion of thermal expansion with high speed tracks: http://boards.straightdope.com/sdmb/showthread.php?t=471152

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#32

Post by madamelic »

lisper wrote: post #17
iamgopal wrote: post #13

Earlier quoted context omitted.

Expansion joints are available since decades.

Not ones that will hold a vacuum.

I am not an engineer. Is it impossible to create one? If a tube is a vacuum, then the tube moves, I don't think that negates the vacuum or does expansion and contraction make a vacuum impossible? I wouldn't believe so.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#33

Post by pasta »

lisper wrote: post #10

All of the Hyperloop development efforts are ignoring the elephant in the room: thermal expansion. If you do the math, the ends of a viable hyperloop track will have to move hundreds of meters [1]. No one has yet advanced even a viable idea for how to deal with that, let alone an actual design. Until that happens, the Hyperloop is vaporware. [1] It's a trivial calculation. The thermal expansion coefficient of steel i…

Yeah, Elon Musk never thought about that because he was busy landing rockets.

Come on.. why do you think he did not think about that?

By the way, curves in the track can eliminate this when they can slide a little. And I can imagine there are more and better solutions.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#35

Post by drzaiusapelord »

lisper wrote: post #10

All of the Hyperloop development efforts are ignoring the elephant in the room: thermal expansion. If you do the math, the ends of a viable hyperloop track will have to move hundreds of meters [1]. No one has yet advanced even a viable idea for how to deal with that, let alone an actual design. Until that happens, the Hyperloop is vaporware. [1] It's a trivial calculation. The thermal expansion coefficient of steel i…

Musk has addressed this:

Similarly, the proposal briefly discusses thermal expansion: as the steel of the tubes heats in the hot California sun, the metal expands. That expansion needs somewhere to go. In high-speed railways, rails are allowed to overlap at the ends, but that’s not possible in the Hyperloop, and so Musk has a different solution:

“Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion,” he explained. “This is an ideal location for the thermal expansion joints as the speed is much lower nearby the stations. It thus allows the tube to be smooth and welded along the high speed gliding middle section.”

https://www.theguardian.com/technology/2016/may/12/hyperloop...

I think the hand-wringing over expansion is a bit over the top right now. Seems like its a relatively solved problem and one the Hyperloop team is taking seriously. I imagine the cost of engineering and building giant slip joints is just part of the overall cost package and probably a non-trivial part. I find it hard to believe someone as relatively trustworthy and technical as Musk is selling this concept knowing full well its impossible.

Most likely, this is a solvable problem the same way many difficult problems were solved for cars, planes, and rails during their inception. I read an analysis somewhere that the Wright brothers solved 4 or 5 'hard' problems with their first plane. Their competitors at the time weren't able to solve even one. I'm not saying Hyperloop is guaranteed to work, but declaring it 100% impossible seems overly pessimistic.

My worry is a bit more prosaic, if we gain progressive leadership in congress, we may be looking at Euro-style high speed rail in many US regions, which would invalidate the hyperloop concept. This seems less likely, imo, but by far the saner move.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#36

Post by cjsuk »

lisper wrote: post #10

All of the Hyperloop development efforts are ignoring the elephant in the room: thermal expansion. If you do the math, the ends of a viable hyperloop track will have to move hundreds of meters [1]. No one has yet advanced even a viable idea for how to deal with that, let alone an actual design. Until that happens, the Hyperloop is vaporware. [1] It's a trivial calculation. The thermal expansion coefficient of steel i…

Is there any material available with a negative expansion coefficient that can be used to offset this?

I ask because that’s how you tend to work around thermal effects in electronics.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#37

Post by pavel_lishin »

TremendousJudge wrote: post #30
rco8786 wrote: post #23

Earlier quoted context omitted.

Right. Could you imagine what people thought/said around the advent of commercial airliners or heck, even automobiles?

Or turbojet trains[1] [1] https://en.wikipedia.org/wiki/Turbojet_train

Or Ekranoplans[2]

[2] https://en.wikipedia.org/wiki/Ekranoplan

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#38

Post by clavalle »

lisper wrote: post #10

All of the Hyperloop development efforts are ignoring the elephant in the room: thermal expansion. If you do the math, the ends of a viable hyperloop track will have to move hundreds of meters [1]. No one has yet advanced even a viable idea for how to deal with that, let alone an actual design. Until that happens, the Hyperloop is vaporware. [1] It's a trivial calculation. The thermal expansion coefficient of steel i…

Compressable joints between each section?

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#39

Post by sschueller »

batrat wrote: post #16

I see so many negative comments about this, but in my opinion everything has to start somewhere. It doesn't matter how crazy and impossible it looks, it will be done eventually (and we have plenty of examples). Maybe we will not teleport in 2 seconds across the globe or this project will die, who knows if we don't try. A little bit of optimism doesn't hurt. Just saying. And for Virgin, it's not my money, if they want…

I'm not saying it can't work and we shouldn't try our best.

However from what I have seen so far I am quite disappointed as even known issues aren't addressed at all. As if the people involved are blindly going at it instead of working with people who know something about pressure vessels etc.

Sure sometimes you need an outside perspective but not like this.

Re: Hyperloop One Becomes ‘Virgin Hyperloop One’

#40

Post by alexozer »

Keeping a plain miles-long tube at at least 90% vacuum seems pretty hard to me, especially when needing to deal with evacuations and possible breakages. Why not divide the tubes into discrete sections gated by movable airtight caps that side away while passing through? If one section repressurizes due to evacuation or some other fault, so be it.
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