3 ms·

I think there is an inconsistency in the proposal, because he clearly mentioned cumulative expansion (page 5 of the pdf https://docs.google.com/viewer?url=http:

by 6ren 13y ago

I think there is an inconsistency in the proposal, because he clearly mentioned cumulative expansion (page 5 of the pdf https://docs.google.com/viewer?url=http://www.spacex.com/sites/spacex/files/hyperloop_alpha.pdf https://docs.google.com/viewer?url=http://www.spacex.com/sit...): A telescoping tube, similar to the boxy ones used to access airplanes at airports would be needed at the end stations to address the cumulative length change of the tube. If you're absorbing all the changes in length at the pylons, you don't need to absorb cumulative changes. Another reading is that the welded joints don't need to coincide with the pylons - that's just how it was constructed, not how it's supported. The tube ends up being continuous, with nothing special about the part of resting on the pylons, and move freely on rollers or similar. However, this reading also doesn't work, because he says of the dampers (also page 5): These would absorb the small length changes between pylons due to thermal changes... So, there's an inconsistency. But it doesn't seem like a big one to me, and not hard to overcome. And finding these bugs is one of the intended benefits of open-sourcing it. I haven't looked into the second finite analysis one, but though I looked for material consequences, it seems to be mainly a criticism of presentation. It amuses me that after spending his talent, time and money (he mentions at the start that he's paying for his blog) helping Musk's proposal, this fellow vents: I wouldn’t put my money, time, or talent in the hands of someone who takes me for a fool. Musk caught him monologuing.

Gravityloss 13y ago
A Falcon rocket is started from flat aluminium plates, which you weld into hoops. Then you weld the hoops together into a barrel. Similarly with hyperloop, you have to weld the tubes from much shorter barrel sections anyway, there's no way you're going to have 100 m x 12 m plate sections that you could then roll into a pipe. And you couldn't really bend any of that anyway at once. So there certainly are weld seams between pylons. A spiral weld might be interesting if a continuous sheet could be created at some steel mill. Some big pipes are created by welding a sheet spirally. Armadillo bought such tubes from Europe for their rockets. Though for hyperloop, bends in the pipe would require a really funny shape for the sheet. Both width and orientation of the sheet would have to change, and it would require very accurate welding ).
delinka 13y ago
Thanks! I think my memory is totally wonked. I remembered after reading your response that Musk mentioned the orbital seam welder. But yeah, I think there are some, uh, gaps in the plan. ;-)
rossjudson 13y ago
The tube does not run in a straight line. Every curved element is an opportunity to absorb thermal expansion. Imagine bending a metal rod into a curve in your hands, which remain at fixed point, while it sits on a table. Then it gets very hot, and the metal rod has expanded. If your hands have remained at the same points, the arc of the rod has gotten slightly bigger. The pipe itself has moved laterally from its prior path. This is why the lateral and vertical dampeners assist in absorbing thermal expansion.

by 6ren 13y ago

Gravityloss 13y ago

A Falcon rocket is started from flat aluminium plates, which you weld into hoops. Then you weld the hoops together into a barrel. Similarly with hyperloop, you have to weld the tubes from much shorter barrel sections anyway, there's no way you're going to have 100 m x 12 m plate sections that you could then roll into a pipe. And you couldn't really bend any of that anyway at once. So there certainly are weld seams between pylons. A spiral weld might be interesting if a continuous sheet could be created at some steel mill. Some big pipes are created by welding a sheet spirally. Armadillo bought such tubes from Europe for their rockets. Though for hyperloop, bends in the pipe would require a really funny shape for the sheet. Both width and orientation of the sheet would have to change, and it would require very accurate welding ).

delinka 13y ago

Thanks! I think my memory is totally wonked. I remembered after reading your response that Musk mentioned the orbital seam welder. But yeah, I think there are some, uh, gaps in the plan. ;-)

rossjudson 13y ago

The tube does not run in a straight line. Every curved element is an opportunity to absorb thermal expansion. Imagine bending a metal rod into a curve in your hands, which remain at fixed point, while it sits on a table. Then it gets very hot, and the metal rod has expanded. If your hands have remained at the same points, the arc of the rod has gotten slightly bigger. The pipe itself has moved laterally from its prior path. This is why the lateral and vertical dampeners assist in absorbing thermal expansion.