The document mentions standard orbital seam wlelding, plus specialized machining equipment that travels along the tube to smooth out the gliding surface.
The capsules are only 60% the diameter of the tube, or 36% it's area (68/47% for the vehicle-carrying version), it doesn't seem to require tight tolerances for operation. I got the idea that tube distortion and movement is taken into account into the system.
Well, it's true that the top and sides of the tube don't get too close to the capsule, so those parts seem relatively low-tolerance, as you say.
But the load-bearing skis ride on an air bearing of 0.5mm to 1.3mm (see page 20), moving at over 1000km/h. As rossjudson notes, the skis are on mechanical suspension, to smooth out shocks to the riders, but it's not clear (to ignorant me) how much of a bump those skis can glide over. 0.1mm, no problem. What about 1.0mm?
On a related note, Musk seems sanguine about the sag you'd get in any structure supported by pylons (see e.g. page 27). Even with inch-thick steel walls, with pylons an average of 30m apart (100'), you'll see some sag, right? Any engineers want to comment on the deviation in 30m of inch-diameter-wall steel tubing? Let's see, 1200kph, 30m, so you pass a pylon 11 times per second. So in 0.09 seconds, you have to go from the top of one pylon, to the valley between two pylons, and back to the top of the next pylon. I guess that's all absorbed by the mechanical suspension?
So thanks for whatever you did in keeping the boats safe (both in design and construction), it was certainly much-appreciated in the Fleet.
It would be cool if you could take another look and see if the tolerances are truly what you describe, or if there's actually more room for variance.
In fact you might be able to handle some thermal expansion (at least seasonal, not daily) that way - release some clamps on a telescopic section, adjust, reclamp, melt and re-smooth the wax.
13 × 10^-6 thermal expansion coefficient of steel
45 - -40 max temp difference
570k length of tube in meters
line1 × line2 × line3 = 629m (~1890') of thermal expansion over a 570 km tube.
Did I read it right that they will take out all that expansion at the ends? To get that down to say 30m between pylons you have to have about 30 expansion joints. Can they go full speed through an expansion joint?
http://stopandmove.blogspot.fr/2013/08/hyperloop-proposal-ba...
It seems that the proposal is actully much less serious than on the first glance:
Amusingly enough, the California HSR budget for the Central Valley is under $10 billion. Ie, in the same ball-park as this proposal. The reason the HSR project is going to cost $60 billion is because it has to face an uncomfortable truth; actually getting to LA and SF is expensive. Very expensive.
Moreover, would you like to be sitting in the tube on the chair from which you can't even stand up for a half an hour without the chance to do anything but remain sitting, not getting any help the next half hour on the occasion when you get sick? Would you take your kid there? Your parent?
Designing mass transportation while ignoring such aspects is like programming without handling the limit cases "it works for N between 2 and 100 but not for 0, 1 and MAX_INT, even if these are allowed inputs." It's bad, very bad for the user, only an "astronaut developer" can love such a solution.
The first time a kid dies because it got sick the first minute of a 30-minute ride, the project is dead for good. Imagine the press, imagine the public response.
I can imagine entering the capsule to reach the international space station, preparing a whole year before. I can't imagine doing the same preparations for the ride between SF and LA. Give me the real train, thank you.
The public seems to have no issue with that concept, it is a simple risk that goes with getting on the train.
As a professional mechanical engineer I have worked on high quality steel tubes (nuclear submarines) before. The immediate thing that sticks out to me in this proposal are the tight mechanical tolerances that have to be maintained. Talking about tens of thousandths of an inch tolerances on a 10' diameter tube is not to be dismissed lightly. That is going to be tough to maintain - especially with welding heat distortion. I would image the tubes will be joined with automated friction stir welding or something similiar, but that will still require a fair amount of post weld machining which has its own pitfalls. Not to mention simple thermal expansion and contraction as the temperature changes could change the circularity and inner diameter.
I would be more interested to see a tolerance stack up of those considerations than an FEA model of the concrete pylons. I can gaurentee that we can build concrete pylons capable of holding up a steel tube, that is done all over the country dozens of different uses cases. But can we build a multi-hundred mile long steel tube to the required tolerances?
I would be inclined to trade off efficiency for manufacturability. I.e. maybe a higher internal pressure or larger diameter to make it less sensitive. There should be plenty of power from the solar panels so it doesn't have to be perfectly efficient.
I'm also surprised that the I-5 plan is cheaper than buying private land. I may be naive here, but the pylons really do take away most of the objections from farmers and installing tubes over farmland has to be a lot cheaper than doing construction above a highway. I just look at boondoggle that was the SkyTrain in NYC (tram running over a highway out to JFK airport) and wonder if that is a great option.