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Hyperloop - essentially new transport

  1. Aug 2, 2013 #1
    One of these days on the TV I have seen news which has shaken me: Elon Musk has decided to intrigue the world - has declared that will soon open the project of essentially new personal transport. Which will move with speed of a sound, but will be cheaper than the plane . The construction cost of a line will be much lower, than for a high-speed train (something - here: http://en.wikipedia.org/wiki/Hyperloop <http://slon.ru/fast/future/elon-mask-obeshchaet-transport-budushchego-966070.xhtml) /

    As has told Musk it Will turn out average between "Concord", a rail gun and aerohockey. But more has told nothing: holds an intrigue.

    I, think, have understood in what here a secret and have decided this intrigue to break:)
    In my opinion - it is very simple. I am surprised that anybody has not guessed before earlier it.

    The line represents a pipe in which will be constantly supported high vacuum. That will provide low friction, and, hence, and high speed. But on such high speed of a wheel - will not sustain. And magnetic pillows - are expensive. It would be possible to fly, if vacuum is not so high. But to fly - always it is less energetically favourable, than to be floating on an air pillow. Therefore the "line" works so, that as soon as capsule "on" - the apertures under capsule will open and atmospheric air directs under capsule, creating effect of an air pillow. And as soon as capsule will leave from this place - the valve are there and then closed.
    The aero-input of air will be not big. About 0,1 atmospheres.So, friction will be in tens times less, than in an atmosphere. And powerful the aero pumps will extort constantly of air from a pipe .
    And speed will give magnets. Small friction about unloaded air will brake capsule nevertheless. Therefore the electromagnets will push it through everyone of ~30 kilometers.

    The mechanism of work of this system:
    I assume, that possible to improve it.
     
  2. jcsd
  3. Aug 2, 2013 #2

    mfb

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    Evacuation of the tube - even partially - needs a lot of energy. Why would you waste that by letting more air flow in?

    In a tube with well-defined track-like structures, something like a hovercraft looks possible, using the existing air in the tube and the walls.

    We'll see in 9 days.
     
  4. Aug 3, 2013 #3

    256bits

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    It could be that he would like to propose a scaled up version of those air tube systems used in banks for small packages.
     
  5. Aug 4, 2013 #4

    AlephZero

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    Unless Elon Musk is now living in an parallel universe, I call BS.

    Being rich and famous makes it easier to get people to listen to crackpot ideas, but it doesn't change the laws of physics.
     
  6. Aug 12, 2013 #5

    mheslep

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    Last edited: Aug 12, 2013
  7. Aug 16, 2013 #6

    mheslep

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    381 mile tube, 1 meter radius: 193 GJ to pump down, or 2MW over 24 hours.
     
  8. Aug 16, 2013 #7

    mfb

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    Or 100MW over 30 minutes, if you have to repeat it frequently (as Alexey suggested).
    And that assumes 100% efficiency.
     
  9. Aug 16, 2013 #8

    etudiant

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    The key idea is of a much lower weight vehicle, because the stresses of high speed travel are carried by the entire structure rather than concentrated on the tiny contact patch between the steel wheel and the rail.
    The tube and partial vacuum are essential refinements, the tube to keep the roadway clear and the partial vacuum to keep down the energy cost of pushing away the air.
    While it might take a while for people to get comfortable with a long high speed ride inside a glorified sewer pipe, cargo would have no such problems. Provided the service can find routes that generate enough volume,
    it might well be viable. Whether the truckers or the railways would welcome it is another question.
     
  10. Aug 16, 2013 #9

    mfb

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    I think the concept will need significant improvements before it gets widely used for cargo. In terms of stations, it looks even less flexible than regular rails (as junctions are tricky), and you cannot transport standard container sizes with the proposed tube. So how do you get cargo to the hyperloop station, in the tube, out of the tube, and from a different hyperloop station to its destination?
     
  11. Aug 16, 2013 #10

    etudiant

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    Entirely agree that junctions are a real issue, they were a bear even for monorails and here vacuum seals are involved.
    Cargo transport with containers is less of an issue imho. Airplanes have long used smaller containers, both igloos and containers with cut off corners. An 8x10 ft container would need more than a 3 meter diameter tube to fit. It does raise a gauge question for this concept, a bigger tube would have advantages, but the size picked initially would determine all future design parameters, much as Stephenson's choice of the carriage gauge for his train tracks. A bigger gauge would have been much better for train development, but even Brunel's effort to introduce it failed because too much was already invested in the incompatible small gauge tracks.
     
  12. Aug 19, 2013 #11
    I think somone's taking Futurama too literally ( watch 0.08-0.11)
     
    Last edited by a moderator: Sep 25, 2014
  13. Aug 20, 2013 #12

    mheslep

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    Cargo throws away the advantage of light weight. Traditional high speed rail doesn't handle cargo for the same reason -- too much lateral force in turns.
     
  14. Aug 21, 2013 #13

    mheslep

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    Regarding the low cost, $6B or about 6% of the (much slower) high speed rail proposal, the primary rationale appears to be the adoption of a utility pole line cost model versus one of ground level track.

    The argument appears valid to me. The criticism based on based on political impediments in California for large right of ways seems ill founded.

    Can anyone offer typical cost per mile for pole elevated utility lines? The cost of the material and even labor is irrelevant, but the right of way cost is of interest.

    Edit: Ah, AEP posts their installed costs (surprisingly) for high voltage transmission. They have $4 million per mile worst case, which includes "siting and ROW", or no more than $1.5 billion for ROW and siting, LA to SF. Musk gives $1B for "permits and land." (pg 56).
     
    Last edited: Aug 21, 2013
  15. Aug 25, 2013 #14
    There are other challenges for the Hyperloop design such as the problem of dissipating heat from the LIM (which is only 50%-75% efficient). The waste will turn up as heat and most of this would go the rotor on the vechicle.

    One the cost side I have seen an estimate for the costs of a pair of gas pipeline the same diameter as Hyperloop at $ 2.5 billion. (priced at $25,000 per inch (diameter) per kilometer from Gas Pipelines, In-Field Transport, Transmission Pipelines, LNG tanker, Natural Gas–powered Vehicles ) Given the precision required in fabrication and installation of a raised pylon this alone would be substantial. There seems to be no reason to quote such a unreasonably low cost figure EXCEPT to make the CHSR seem unreasonably expensive. (Probably the point, as has been pointed out elsewhere.)

    Any money Musk has spent on the project so far could be written off as "publicity".
     
  16. Aug 25, 2013 #15

    mheslep

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    The rotary induction motor used the Tesla vehicles, to which the proposal compares the LIM, is more than 90% efficient. But even in the case of a much lower efficiency for a linear version, how is heat dissipation an issue with the 1000 kph air flow seen by the passenger vehicle? Recall that sufficient air is collected already to supply air bearings.

    That is the cost given for offshore pipeline installation in that reference, surely not comparable.

    Musk's price for land and right of way ($1 billion LA-SF) is very comparable with the costs given by elevated transmission line companies. The costs of underground systems (e.g. gas pipelines) would seem to require more right of way and interference with structures and properties crossing the pipe path.
     
  17. Aug 25, 2013 #16

    AlephZero

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    I don't understand the basis for that claim.

    Elevated transmission lines have relatively small weight, small wind resistance, and are flexible. There is no big problem in changing direction through any required angle at any support pylon.

    On the other hand Musk's system seems to require a structurally rigid large diameter pipe aligned with relatively close tolerances, and certainly with no sharp curves either in its track along the ground or changes of vertical gradient.

    IMO a more relevant comparison would be with constructing a continuous overhead footbridge or cycle track, not a transmission line. (And a footbridge would be a much less demanding structural design than Musk's system).
     
  18. Aug 25, 2013 #17
    Im surprised nobody on the design team has considered using ground effect vehicles in the tube to eliminate the need to compress the air all together.
     
  19. Aug 25, 2013 #18

    mheslep

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    Take a look at the proposal. The one billion dollar figure refers *only* to land and right of way. The balance of the system, i.e. construction of pylons, tubes, capsules, etc is five to six billion more per the proposal.
     
  20. Aug 25, 2013 #19

    mheslep

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    At 0.001 atm (pg 12)?
     
  21. Aug 25, 2013 #20
    The efficiency is likely to be closer to the normal 50% given the air gap will be wider to allow for the fact that the vehicle will have to dynamically align itself down the channel. Given the speed, that is lot of energy and so means a lot of heat. If the heat is dissipated in the remaining air in the tube it will accumulate quickly given there are launches every 2 minutes.

    Despite the obvious difference with undersea gas pipe lines, this does not negate the comparison. Hyperloop's tube must be made to a much higher precision than ordinary gas pipe and it is laid on elevated pylons. IMHO the complexity and cost of both makes it a worthy benchmark.
     
  22. Aug 26, 2013 #21

    mfb

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    Hovering on the air is basically an application of the ground effect. The active compression reduces air resistance.
     
  23. Aug 26, 2013 #22

    mheslep

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    Perhaps pipeline costs are useful for benchmarking the tube costs, but such would not be the primary cost driver: land and right of way is.

    The unbounded costs observed in other projects like the California High Speed Rail come largely from land and right of way costs running the project up to $100B, not the rolling stock and rail. The Hyperloop proposal claims to reduce the land/ROW costs by use of an elevated path. If such a less intrusive approach is successful, then the remaining cost of construction is likely bounded to less than 10% that of ground level HSR.
     
  24. Aug 29, 2013 #23

    mheslep

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    By far the single largest line item cost in the Hyperloop proposal is the pylons: $2.6B, reinforced concrete, with the actual tube cost far behind at $650 million. The pylons are specifed as one every 30m or 25,000 in total, 6m tall typically.

    It may be that a method for reducing the pylon cost is to use another lighter weight material for the tubes. The tube material is steel (22 mm wall, 2.3 m ID). Carbon fiber reinforced polymer, for example, would be more expensive than steel, but it has a specific strength ten times that of steel. A CFRP tube would likely allow increased pylon spacing, and reduced pylon size.

    I can't readily find information to bound the cost of a CFRP tube. The steel tube works out to 1.3 metric tons per linear meter of tube, with steel currently at $650/ton.
     
  25. Feb 11, 2015 #24

    mheslep

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    Apparently the Hyperloop concept has become serious in terms of financial support and technical staff. Forbes says there are now three companies at work, and Musk has said he will finance a 5 mile test track in Texas. They are still reporting impressive $20 million/mile cost figures, or ~ten times less than the proposed California High Speed Rail project which runs ~5x slower.

    That said, I don't see a viable approach to the thermal expansion of the vacuum tube. Existing gas/fluid pipelines are deployed with room to flex; even underground pipelines are designed so as to displace soil or compressible surroundings (e.g. foam) and allow for expansion. The hyperloop with its high speed capsules mean the flex budget has to be in the sub mm range per span. This leaves only i) pressurized slip joints, or ii) axial expansion along the entire length of the pressurized route. Pylon tube mounts that allow axial slip are possible, but the expansion at the terminals seems extreme: a 500 km steel tube has axial expansion 117 m over 30 deg F. I don't know of any parallels in other infrastructure.

    Edit: carbon fiber composites offer a substantial improvement in CTE, a factor of ~7 less, or 16 m/30degF at the the terminals.
     
    Last edited: Feb 11, 2015
  26. Feb 12, 2015 #25

    mfb

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    Airtight joints with some space to expand don't look so problematic I think. You can build something like bridge expansion joints (in vacuum) for the track and make them airtight outside.

    Moving around 500km of steel tube looks too complicated.
     
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