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Blog Hyperloop One Nearly Hits 200 MPH in First Pod Tests

Discussion in 'Cars and Transportation' started by TMC Staff, Aug 2, 2017.

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  1. TMC Staff

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    [​IMG]
    A Hyperloop One test pod reached a speed of 190 mph at the company’s vacuum tube test track. It was the first time the system had been tested with a pod - intended to carry people and cargo - not simply a sled.
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  2. KarenRei

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    Maglev. Not nearly as interesting as the original Hyperloop proposal.
     
  3. BerTX

    BerTX Active Member

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    Why is the pod pointy in the front? It doesn't help. Just looks cool?
     
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  4. TheTalkingMule

    TheTalkingMule Active Member

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    Right? Am I missing something or is this nowhere near the original vision?
     
  5. RDoc

    RDoc S85D

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    Air resistance. It's not that hard a vacuum.

    As for it not being nearly as interesting as Elon's proposal: If the goal is to build something that works, you really need to do actual engineering.
     
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  6. KarenRei

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    So I assume all of the FEA work in Hyperloop Alpha wasn't "actual engineering"?

    There are other Hyperloop companies out there than Hyperloop One. Not everyone is pursuing maglev. And the reason maglev isn't as interesting is that it's expensive. Which is sort of the whole thing Hyperloop was created to avoid.
     
  7. voyager

    voyager Member

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    Never got around this:

    Perhaps it is because hyperloop is all about going straight. ;-)
     
  8. KarenRei

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    #8 KarenRei, Aug 3, 2017
    Last edited: Aug 3, 2017
    Thunderf00t (Phil Mason) is a guy who's constantly ranting about things he has no understanding of (he's a biochemist, not an engineer). Don't take anything he says seriously.
     
  9. voyager

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    Hm, I think he makes common sense, especially regarding the near-vacuum with which Hyperloop is supposed to operate...
     
  10. KarenRei

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    You're being vague; please be more specific. Contrary to Thunderf00t's portrayal, actual engineers (rather than people who pretend to be engineers on Youtube) deal with vacuums all the time, and it's not particularly difficult; just like there are formulas and rules for pressure chambers and lines for calculating how you need to build them so that they don't explode, there are formulas and rules for vacuum chambers and lines so that they don't implode. And making something that's long and thin that holds a vacuum is much easier than making something that's shorter / fatter, like a VDU:

    [​IMG]

    If you were at a refinery and were given a choice to be standing beside a VDU when an accident occurred, or standing beside a hydrocracker when an accident occurred, choose the VDU. Trust me on this one.
     
  11. Ben W

    Ben W P85 #61, Roadster #108

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    I've often wondered whether it might make sense to add slight amounts of hydrogen or helium to the near-vacuum to increase the speed of sound, thus reducing shockwaves and increasing the Kantrowitz limit (choke point). For instance, the original Hyperloop proposal has a speed of sound of 340 m/s in the tube, which limited the theoretical pod speed to about 330 m/s. However, 50pa air + 50pa hydrogen (or even 100pa air + 100pa hydrogen) would have a speed of sound closer to 650 m/s, so a 330 m/s or even 500 m/s pod would still be well below the transsonic regime. These are tiny partial pressures, so it shouldn't present much of a fire/explosion/embrittlement hazard. But even if it did, helium would serve the purpose nearly as well. Thoughts?
     
  12. KarenRei

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    Indeed, that's exactly what I've been advocating since day 1 (did you see that proposal somewhere or did you come up with it on your own? Just curious! :) ). The downside is that it does increase your pumping requirements; the reason that they assume air in there is that they assume that it's leaked, so if you want 90% hydrogen / 10% air you have to 10x pumping requirements. That said, they've chosen very pessimistic estimates on how hard it'll be to maintain the vacuum out of an abundance of caution. Another advantage to going with light gases is that it means less air resistance at high velocities.

    I'm curious as to how hot the rarified atmosphere will be. While any heat that reaches the tube will rapidly be lost to the atmosphere, gases at near vacuum are terrible conductors of heat, and the pods are imparting significant heat to them. If the average temperature of the gas in the tube is elevated, that also elevates the speed of sound (and reduces air resistance).

    In short, Hyperloop could actually be made to go much faster than the current proposed speeds.
     
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  13. Ben W

    Ben W P85 #61, Roadster #108

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    #13 Ben W, Aug 14, 2017
    Last edited: Aug 15, 2017
    I think I came up with it myself, but it's possible I saw it somewhere else and don't remember. Counterintuitively, it could be the case that 100pa air + 100pa hydrogen incurs less air resistance at high speeds than just 100pa air (the hydrogen essentially lubricates the air, as it were), and such a mixture wouldn't incur any additional pumping costs over just 100pa air. A 50/50 blend already gives most of the benefit; going to 90% hydrogen would yield diminishing returns, though it would be interesting to see the air resistance figures for e.g. 100pa air + 900pa hydrogen. It might still be better than just 100pa air for the targeted speeds (~330 m/s), and again wouldn't increase pumping costs.

    The heat of the air in the tube is a non-issue; it equalizes within seconds to the heat of the walls. A near-vacuum is a great insulator when separating two solid objects of different temperatures, but only because it can effectively transport just a tiny amount of heat at a time from one side to the other. But a tiny amount of air only holds a tiny amount of heat, and the air is convecting, so all the heat in the air itself gets transmitted to the walls very quickly. In other words, the entire Hyperloop steel pipe is a giant and very effective heat-sink. The original Hyperloop Alpha design involved cooling the bypassed air stream, which was completely unnecessary; it could be vented hot without any negative consequences. (The "ski" air stream did have to be cooled to increase the mass flow, but now it looks like the whole suspension system is moving to maglev, so even that cooling is unnecessary.)
     
  14. KarenRei

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    #14 KarenRei, Aug 15, 2017
    Last edited: Aug 15, 2017
    Changing the design pressure would involve reengineering a good bit of details, although it's certainly possible. My biggest concerns, the more hydrogen and air you have mixing, is combustion - not under ambient conditions (they're too sparse for that), but when passing through the compressors and under the air skis. Although technically if you want to prevent that you have to get the oxygen concentration way down. Also concerns about embrittlement in the compressors and skis where the gas pressure is higher. But, these are engineering issues, and as you note, helium is also a possibility (the amount required is small, so long as leaks are kept under control, and helium recovery could potentially be integrated into the vacuum pumps - the mass of the gas you're pumping out is low, so it's not a huge amount of cooling required to liquefy the leaked-in air... and the resultant separated gases could be a value-added product stream if storing them is economically justifiable).

    Concerning heat transfer, that's a good point about the tiny heat capacity of the gas offsetting its low conductivity. On the other hand, that low heat capacity makes me wonder about deliberate heating of the gas by the pod in advance (a microwave, IR, visual, etc beam on the front of the pod), using a frequency heavily absorbed by the gas (such as hydrogen) to overcome its sparse nature. Since the gas has little mass, that's little energy to impart to heat it. But I haven't done any calculations at all to support the concept to determine if it's plausible.

    Let's see... heating, say, 1km of hydrogen, ~7m diameter, 100Pa, PV=nRT, 100*(1000*7)=n * 8,314 * 300°K, n = 280,65 mol, 1g/mol = 280,65 grams. If the pod is moving at... hmm, what speed... let's go big and say mach 10 (nearly half of orbital velocity); that's ~3400 m/s, or 0,294 seconds to heat 1km of gas. Hydrogen's specific heat is temperature-dependent, but let's say 14,5J/g-°K, so to raise the temperature by... say 1500° (4,3x'ing the sonic velocity over ambient-temperature hydrogen), that's still only 6104 joules, which in 0,294 seconds is only 20,8kW. So at least in terms of power requirements, even after losses, that should be plausible (especially considering how short of a time you'd be heating it for if you were moving at mach 10! ;) ). That still doesn't of course answer the question of, at an optimally-selected frequency, what's the minimum amount of hydrogen mass you'd have to irradiate to absorb most of the beam; I can't be bothered to dig up hydrogen absorption spectrum data at the moment ;) The beam doesn't even have to be well-collimated, since you're dealing with a broad tube and the sides should be quite reflective (having been polished to Hyperloop-tolerances, and existing in a near-vacuum environment only punctuated by brief pulses of density and heat as pods pass).

    Of course, if you're talking mach 10, you're either talking "over oceans", or "Musk's Boring Company has been a huge success", because the straightness requirements at such speeds are immense. The key issue though is that there doesn't seem to be a practical limit to how fast you can run a vehicle in Hyperloop, since the speed of sound can be readily boosted either by heating or by changing gas mixtures.
     
  15. Ben W

    Ben W P85 #61, Roadster #108

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    Does the Hyperloop One implementation still have a compressor at the front of the pod? I think the compression ratios of Hyperloop Alpha were about 10:1, which still would make very low pressure hydrogen; less of a risk for embrittlement. (And much easier to periodically replace pod parts than entire tube parts.) The compressive heating may be more problematic; I'm not sure at what temperature hydrogen + oxygen spontaneously ignites, at very low pressures. And helium works too of course.

    Mach 10 (3400 m/s) is probably still not achievable, since the speed of sound even in pure hydrogen is about Mach 3.73 (1270 m/s). You'd need a very hard vacuum to exceed that speed, and again there are diminishing returns and greatly increased risks and power requirements.

    The tube is very reflective, but there is so much more tube than air that it's still not clear you could efficiently heat the air ahead of the pod. Also there will be plenty of other infrastructure inside the tube (stators, hatches, emergency lights, etc.) that would not be as reflective. Requiring the air to be heated would add quite a bit to the complexity of the design, probably not worth it at least for v1. Also, energy you put into heating can't be recaptured, whereas energy you put into propulsion can be; the regenerative braking is a big part of Hyperloop's efficiency.
     
  16. KarenRei

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    You forget, the speed of sound is (lambda*R*T/M)^0.5, where lambda is the adiabatic constant, R is the gas constant, T is the temperature and M is the molecular mass. Hence by raising the temperature, you raise the speed of sound**. Hence the calculations about how much energy it would take to raise the temperature of the gas ahead of a pod :)

    ** Although realistically since I only used a 1500° boost in my calculations, that would only be a 2,44x boost in sonic velocity over room-temperature hydrogen. ;)

    In Hyperloop Alpha you can't have that sort of thing. At least according to my reading of the document. The tube has to be perfectly smooth inside - they even use a rotary polisher to get it smooth to fine tolerances.

    Note that with a well collimated beam, you don't need to reflect off the tube at all for the (example) 1km-ahead-of-the-pod heating. But if light rays take a couple reflections, that's not that big of a deal.

    Hahaha, no no no no.... definitely not. Hydrogen isn't even worth it for V1. :) I was merely discussing upper bounds.

    It's been a while since I read the document, but I don't believe Hyperloop does much if any regenerative braking - it's primarily coastdown. Hyperloop puts into the process in a lot of energy that can't be regained - most notably, the compressor.
     
  17. Ben W

    Ben W P85 #61, Roadster #108

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    Ah, I didn't catch that you were boosting the temperature THAT high!! Hyperloop travel at Mach 10 would be interesting; you'd weigh almost 20% less when traveling west to east (along the equator)... and considering how quickly the air temperature equalizes to the tube temperature, you'd be in massive trouble if the heating beam suddenly failed! Also, the abrupt local changes in temperature might cause some problematic longitudinal shockwaves.

    My understanding was that only the contact area of the tube with the skis (accounting for banking) had to be perfectly smooth. I didn't think that having a smooth ceiling was a requirement, for instance, and the stator assembly (for acceleration, deceleration, and reboost) would physically stick up out of the floor in any case.

    Well, my point was that it might be very much worth it for v1, because it gives substantially reduced drag practically for free. I do wonder whether they've done the calculations, at least!

    From the Hyperloop Alpha doc: "Each accelerator has two 65 MVA inverters, one to accelerate the outgoing capsule, and one to capture the energy from the incoming capsule." Doing the math: the passenger Hyperloop pod has a total weight of about 15,000kg. Accelerating each pod to 330 m/s (without any friction at all) thus requires about 227kWh, which is actually about the same as the total energy needed to drive its compressors for the whole journey. If 70-80% of the kinetic energy could be recaptured through regenerative braking, that would be hugely significant to the efficiency of the overall system.
     
  18. KarenRei

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    Interesting, so they do do some regen - it's been a while since I read it. Still, there's a great amount of coastdown in the document. For the most part, journeys are boost-coast-boost-coast-boost, etc, with the boost segments right after the transitions from low bending radius (curvy) areas to high bending radius (straight) areas..

    Heh, it didn't even occur to me that at such high speeds you'd experience a small degree of weight reduction. That's rather neat, actually ;)

    The first step is to figure out how much it leaks, on LA-to-SF length runs. Run it with air for a while. If the leak rates are low enough then one can start experimenting with helium - first on a test track, and if it plays out well, deploying it live to the existing track to reduce drag (but not increase speed). Moving up the complexity chain, the test track can start experimenting with hydrogen, while longer Hyperloops designed for light gases can start being built - ultimately fed by either hydrogen or helium. And if there's a market for very long runs (say, trans-oceanic), then the test track can start experimenting with gas heating - since it doesn't take very much energy to heat the gas. There's a nice evolutionary progression that the system can take.
     
  19. RDoc

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    IMHO, Hyperloop doesn't need any more velocity. The curve radius for the current proposed speed is huge!

    If I were designing this system, I'd go for much lower speed, say around 200-250 mph. That might well allow the system to use existing highway rights of way in many cases. Land acquisition and the whole approval process for new rights of way is a gigantic problem for any kind of mass transit.

    Such a lower speed system could be used to expand urban centers out to at least 30 miles. That would be a 10 minute ride, less than most taxi trips.

    And before we start discussing 300 mile long tunnels, the current cost of tunneling alone is about $20K per foot. Then you have to build the system.
     
  20. KarenRei

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    #20 KarenRei, Aug 16, 2017
    Last edited: Aug 16, 2017
    Certainly not in mountainous areas, but on plains, and particularly across water are large curve radii quite achievable.

    As for velocity: the goal is to replace high-speed transport, like airplanes, without their environmental footprint. If you don't do that, then you're not achieving the same goal. Slower speeds also mean longer transit times, which complicates the design.

    Hence how it's unsurprising that Musk got into boring. Boring Company's goal is to reduce boring costs by a factor of 10. And for the record, highways in the US are about $1k per foot. Also, there's no single "cost of tunneling", it varies dramatically by location, geology, and particularly cross section (to which it's nearly linearly proportional; Hyperloop has a very low cross section). Hyperloop Alpha's estimates of their tunnel costs - without Boring Company, just current tech and pricing - works out to about $10k per foot.

    I've looked into the various things Boring Company plans to do to reduce costs, by the way... and even if they don't cut them 10-fold, they'll still cut them a lot. The more you read the literature from the current boring industry the more you realize how ripe it is to undergo a massive leap forward. For example, you look up things like, what's the maximum speed that you can run the cutting head? And the basic answer you get is "We really don't know but probably vastly faster than we do today." The speed is limited because today discs are uncooled, are made from cheap alloys, and are not hot-swappable, so you have to stop the machine to replace them. Improve any one of those aspects - let alone all of them, like Boring Company plans to do - and you can run the machine far faster than they're run today. Just simply switching from intermittent to continuous casing in hard rock boring would double the speed.

    Boring will never be "easy", but there's a huge amount that can be done, and I'm not surprised that Elon jumped aboard. Heck, even the pace of "incremental" change has been leading to a surge in tunneling projects over the past decade.
     

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