5 ms·

I agree with your point #1, but your point #2 makes very little sense. Yes, thermal expansion problem solution from the original Hyperloop paper [1] is yet to b

by ash 10y ago

I agree with your point #1, but your point #2 makes very little sense. Yes, thermal expansion problem solution from the original Hyperloop paper [1] is yet to be proven to work in practice. For one, nobody has built long enough straight tube for the thermal expansion problem to matter. However, I don't see how the difference in thermal swings between California and Dubai matters. The proposed solution probability of success or failure should be the same no matter what are the thermal swings. We are talking about (maybe?) 300 meters vs 500 meters per day of expansion for the same tube length. And Dubai - Abu Dhabi route length is much shorter than SF - LA, as you've correctly noticed. [1]: "The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion <…> Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion."(http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf, page 28, section 4.2.3)

lisper 10y ago
> I don't see how the difference in thermal swings between California and Dubai matters. It doesn't really. But whatever thermal expansion problems you have in California you will have them worse in Dubai. > Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion See: http://www.leancrew.com/all-this/2013/08/hyperloop/ http://www.leancrew.com/all-this/2013/08/hyperloop/ for a detailed explanation of why this is not an adequate solution.
- ash 10y ago
  Yes, I'm aware of this post. Unfortunately, its author failed to discuss the solution from the Hyperloop paper. The author incorrectly assumed the tube is attached rigidly to the pillars and then proceeded to criticise this wrong assumption.
  - lisper 10y ago
    You need to go back and re-read this paper more carefully. The author does discuss exactly the proposal in the paper. He even quotes it: "But the real problem isn’t with the slip joints at the ends; it’s with the pillar supports along the way. Musk thinks the dampers, “tucked away inside each pylon,” need to accommodate only “the small length changes between pylons.” Wrong." In other words, the original hyperloop white paper assumes that the movement at each pylon is small, and that the only large-scale movement is at the ends. But this is wrong. There is large-scale movement throughout the system. The thermal expansion motion reaches a maximum at the ends, but it doesn't magically go away as soon as you leave the station. If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon.
    - ash 10y ago
      This quote is from the first part of the paper for which Musk "apologize[s] in advance for my loose use of language and imperfect analogies". It's just an intro. The later parts of Hyperloop paper are more precise. I've already quoted "longitudinal slip for thermal expansion" from section 4.2.3. And, unfortunately, leancrew.com article author missed the proposed solution for the problem they spent many words talking about. > If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon. Yes, of course. I agree that the problem of 100m thermal expansion is real and needs to be solved. And I'd like some arguments about why won't Hyperloop "longitudinal slip" solution work (where tube could freely move past the pillars).
      - lisper 10y ago
        Would you please post a copy of the text that you consider to be "the proposed solution for the problem" that you think leancrew missed? Because I just re-read all of 4.2.3 and I don't see it.
        ash 10y ago
        I've already quoted it in my very first comment in this thread. You could argue that writing "pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion" and "slip joints at stations…" is not detailed enough. I've concluded this "longitudinal slip" means some kind of linear bearing on top of each pillar, where straight tube could slowly move without constraints in the direction of the cumulative thermal expansion, while being constrained vertically. v v ------------- tube ------------- ^ ^ | | | | After thermal expansion: v v ------------- tube ------------- ^ ^ | | | | (Note how "tube" sign written on the tube has moved past two pillars.) Leancrew author missed the "longitudinal slip" part, because most of the article proves that thermal expansion accumulates. Of course it does! Thus the "longitudinal slip" solution. Yes, Hyperloop paper could be more detailed and more clear. Indeed, it confused leancrew author. Do you anyone knowledgable (in mechanical engineering?) who could comment on "longitudinal slip" solution? How feasible is it?

by ash 10y ago

lisper 10y ago

> I don't see how the difference in thermal swings between California and Dubai matters. It doesn't really. But whatever thermal expansion problems you have in California you will have them worse in Dubai. > Specially designed slip joints at stations will be able to take any tube length variance due to thermal expansion See: http://www.leancrew.com/all-this/2013/08/hyperloop/ http://www.leancrew.com/all-this/2013/08/hyperloop/ for a detailed explanation of why this is not an adequate solution.

ash 10y ago
Yes, I'm aware of this post. Unfortunately, its author failed to discuss the solution from the Hyperloop paper. The author incorrectly assumed the tube is attached rigidly to the pillars and then proceeded to criticise this wrong assumption.
- lisper 10y ago
  You need to go back and re-read this paper more carefully. The author does discuss exactly the proposal in the paper. He even quotes it: "But the real problem isn’t with the slip joints at the ends; it’s with the pillar supports along the way. Musk thinks the dampers, “tucked away inside each pylon,” need to accommodate only “the small length changes between pylons.” Wrong." In other words, the original hyperloop white paper assumes that the movement at each pylon is small, and that the only large-scale movement is at the ends. But this is wrong. There is large-scale movement throughout the system. The thermal expansion motion reaches a maximum at the ends, but it doesn't magically go away as soon as you leave the station. If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon.
  - ash 10y ago
    This quote is from the first part of the paper for which Musk "apologize[s] in advance for my loose use of language and imperfect analogies". It's just an intro. The later parts of Hyperloop paper are more precise. I've already quoted "longitudinal slip for thermal expansion" from section 4.2.3. And, unfortunately, leancrew.com article author missed the proposed solution for the problem they spent many words talking about. > If the tube at the station is moving 100m then the tube near the station is moving 100 meters minus epsilon. Yes, of course. I agree that the problem of 100m thermal expansion is real and needs to be solved. And I'd like some arguments about why won't Hyperloop "longitudinal slip" solution work (where tube could freely move past the pillars).
    - lisper 10y ago
      Would you please post a copy of the text that you consider to be "the proposed solution for the problem" that you think leancrew missed? Because I just re-read all of 4.2.3 and I don't see it.
      - ash 10y ago
        I've already quoted it in my very first comment in this thread. You could argue that writing "pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion" and "slip joints at stations…" is not detailed enough. I've concluded this "longitudinal slip" means some kind of linear bearing on top of each pillar, where straight tube could slowly move without constraints in the direction of the cumulative thermal expansion, while being constrained vertically. v v ------------- tube ------------- ^ ^ | | | | After thermal expansion: v v ------------- tube ------------- ^ ^ | | | | (Note how "tube" sign written on the tube has moved past two pillars.) Leancrew author missed the "longitudinal slip" part, because most of the article proves that thermal expansion accumulates. Of course it does! Thus the "longitudinal slip" solution. Yes, Hyperloop paper could be more detailed and more clear. Indeed, it confused leancrew author. Do you anyone knowledgable (in mechanical engineering?) who could comment on "longitudinal slip" solution? How feasible is it?