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I realize I'm probably an idiot, but I do try to learn from my idiocy. Thanks for helping me learn. But I'm having trouble understanding how your reply takes

I realize I'm probably an idiot, but I do try to learn from my idiocy. Thanks for helping me learn. But I'm having trouble understanding how your reply takes everything into account, such as the fact that the hyperloop moves pods, not liquid. Pipelines for liquid are certainly a solved problem, but a pipeline of pods is new. Btw, in railroads (that other long distance transportation method) the expansion is dealt with by putting a small gap between two adjacent rails. That's obviously not possible with the hyper loop as it is currently envisioned but I think that the answer is in there: don't allow the differences to accumulate over long stretches. If that's the case, then why does the plan assume each station on the endpoints is going to absorb most of the thermal expansion? Or am I misreading? They specifically say "the stations are the ideal points to absorb thermal expansion," and the stations are on the end, so it sounds like they're aiming for a long sleeveless steel tube. Also, I was basing my criticism on Hyperloop Alpha. Obviously, their design can change in the future. But, as presented, what gives you the impression that sleeves could be incorporated into their design without causing problems for the pods? I can visualize sleeves which expand into each other, and if they overlap into the direction of travel, so that the edges are pointing away from the pods rather than toward the pods, maybe that wouldn't cause any problems. Still, the interior margin from pod to wall is very small: http://i.imgur.com/YsLDXBe.png http://i.imgur.com/YsLDXBe.png Also, consider this paragraph: The Hyperloop travel journey will feel very smooth since the capsule will be guided directly on the inner surface of the tube via the use of air bearings and suspension; this also prevents the need for costly tracks. The capsule will bank off the walls and include a control system for smooth returns to nominal capsule location from banking as well. Some specific sections of the tube will incorporate the stationary motor element (stator) which will locally guide and accelerate (or decelerate) the capsule. More details are available for the propulsion system in section 4.3. Between linear motor stations, the capsule will glide with little drag via air bearings. Sleeves would cause an edge to sort of "protrude outwards" into the path of the pod, wouldn't they? So it'd basically be a small speedbump. Again, the edge is pointed in the direction of travel, so that would basically be like the second half of a speedbump, basically a small "drop". Except since the pod is moving at 760mph, even a small drop can result in quite a lot of force, and can cause wear on the pod itself, couldn't it? And it might feel a little jarring to the passenger. If the interior needs to remain smooth, what sort of design could fulfill that requirement? (Maybe that's a big "if", but if the pod is going to bank off the walls, then it sounds like that's the case.) EDIT: Also, as someone else pointed out, pipelines that need to be straight might be a new concept. Many pipelines seem to use "U" bends, which can't be incorporated into hyperloop for obvious reasons: http://demonstrations.wolfram.com/PipelineExpansionLoop/ http://demonstrations.wolfram.com/PipelineExpansionLoop/

jacquesm 12y ago
You could simply slide one tube into the next and leave the 'gap' between the tubes sit inside the sliding portion. That way you could have ridiculously close clearance to the tube except for that tiny bit (a few cm) every hundred meters or so. Just anchor one end of each tube and let the other slide freely.
- sillysaurus3 12y ago
  Each pod weighs 7,700 lb and is traveling at 760 mph. Are you sure a few-centimeter speedbump isn't a big deal? I don't know how to calculate whether or not it would be, but I'm interested in knowing why you feel it won't cause problems. Remember, the pod comes into direct contact with the wall while banking, so it's going to take the full force of any few-centimeter bump.
  - jacquesm 12y ago
    > Are you sure a few-centimeter speedbump isn't a big deal? Depends on lots of things, such as the angle of incidence of the pod relative to the direction of the wall of the tube. > I don't know how to calculate whether or not it would be, but I'm interested in knowing why you feel it won't cause problems. I don't know how to calculate rockets landing on barges either, but SpaceX seems to be able to pull it off. There is nothing in the realm of engineering that says you can't make a bunch of tubes sliding over each other relative to the direction of travel for some vehicle to travel within that tube as long as you respect a couple of basics. One simply solution would be something like this: seg2----- --seg1 ----- ---------- 0000000 Where the '0' are the elements of the pod in contact with the wall (I would assume they're using rollers there, anything solid would wear out the wall in no time at all). That way there is no speedbump at all... It's not as if you're going to do right angle turns at the joint of two segments. Anyway, I really think you're chasing a ghost here, the problems with hyperloop are not basic engineering.
    - sillysaurus3 12y ago
      That solution is interesting, but does it account for the fact that the tube curves all throughout its route? Some parts need to be curvy, some need to be straight. Are you sure that expansion can be coaxed into a curve shape rather than linear? How? Also, curves still result in a speedbump with that solution. The pod will be traveling directly toward the gap just below "seg2" if it's banking against the wall. You could make the edge a sharp edge, like a sword's edge, but that doesn't help because due to expansion that edge will still protrude out into the path of the pod. I know it seems like it shouldn't be a hard problem, but it's looking like one. Remember, 300 meters of expansion over 350 miles is 0.85m of expansion per mile. Hold out your arms to the length of a meter and picture how much steel that is. That's what your proposed joints need to deal with: 0.05cm of expansion per meter. So if you have your joints every 20 meters, that's still a 1cm gap, which means a speedbump around curves. Wouldn't that make curves very unpleasant for the passenger and the pod? And you can't have them every meter without increasing the engineering complexity and weakening the structural integrity, right? Yet whatever solution they come up with would need to be placed less than every 20 meters, otherwise they'll get a 1cm gap.

jacquesm 12y ago

You could simply slide one tube into the next and leave the 'gap' between the tubes sit inside the sliding portion. That way you could have ridiculously close clearance to the tube except for that tiny bit (a few cm) every hundred meters or so. Just anchor one end of each tube and let the other slide freely.

sillysaurus3 12y ago
Each pod weighs 7,700 lb and is traveling at 760 mph. Are you sure a few-centimeter speedbump isn't a big deal? I don't know how to calculate whether or not it would be, but I'm interested in knowing why you feel it won't cause problems. Remember, the pod comes into direct contact with the wall while banking, so it's going to take the full force of any few-centimeter bump.
- jacquesm 12y ago
  > Are you sure a few-centimeter speedbump isn't a big deal? Depends on lots of things, such as the angle of incidence of the pod relative to the direction of the wall of the tube. > I don't know how to calculate whether or not it would be, but I'm interested in knowing why you feel it won't cause problems. I don't know how to calculate rockets landing on barges either, but SpaceX seems to be able to pull it off. There is nothing in the realm of engineering that says you can't make a bunch of tubes sliding over each other relative to the direction of travel for some vehicle to travel within that tube as long as you respect a couple of basics. One simply solution would be something like this: seg2----- --seg1 ----- ---------- 0000000 Where the '0' are the elements of the pod in contact with the wall (I would assume they're using rollers there, anything solid would wear out the wall in no time at all). That way there is no speedbump at all... It's not as if you're going to do right angle turns at the joint of two segments. Anyway, I really think you're chasing a ghost here, the problems with hyperloop are not basic engineering.
  - sillysaurus3 12y ago
    That solution is interesting, but does it account for the fact that the tube curves all throughout its route? Some parts need to be curvy, some need to be straight. Are you sure that expansion can be coaxed into a curve shape rather than linear? How? Also, curves still result in a speedbump with that solution. The pod will be traveling directly toward the gap just below "seg2" if it's banking against the wall. You could make the edge a sharp edge, like a sword's edge, but that doesn't help because due to expansion that edge will still protrude out into the path of the pod. I know it seems like it shouldn't be a hard problem, but it's looking like one. Remember, 300 meters of expansion over 350 miles is 0.85m of expansion per mile. Hold out your arms to the length of a meter and picture how much steel that is. That's what your proposed joints need to deal with: 0.05cm of expansion per meter. So if you have your joints every 20 meters, that's still a 1cm gap, which means a speedbump around curves. Wouldn't that make curves very unpleasant for the passenger and the pod? And you can't have them every meter without increasing the engineering complexity and weakening the structural integrity, right? Yet whatever solution they come up with would need to be placed less than every 20 meters, otherwise they'll get a 1cm gap.