5 ms·

A 5-mile test track won't be big enough to examine the biggest concerns: thermal and seismic. The alpha brochure linked to in the OP barely touches on the two.

by rmxt 11y ago

A 5-mile test track won't be big enough to examine the biggest concerns: thermal and seismic. The alpha brochure linked to in the OP barely touches on the two. Here [1] is a better analysis/take-down of what thermal issues such a long structure will encounter. (TL;DR: A 400-mile long continuous structure will need to accommodate 1000 feet of thermal movement over it's length and lifetime.) Seismic is another beast: it requires a much more thorough examination than the cursory glance it was given in the alpha paper. [1] http://www.leancrew.com/all-this/2013/08/hyperloop/ http://www.leancrew.com/all-this/2013/08/hyperloop/ Thermal effects on Maglev research: https://www.lib.utexas.edu/etd/d/2007/kimh10315/kimh10315.pdf https://www.lib.utexas.edu/etd/d/2007/kimh10315/kimh10315.pd... EDIT: Apologies for the negativity... I hope this reads as more of thoughtful criticism, rather than as being hypercritical.

Retric 11y ago
Thermal expansion is not really an issue that gets worse with distance, as the track can simply be made from independent segments connected with expansion joints. The issue is being able to cross from segment A to segment B not the number of such segments. In other words if it works on a test track it scales just fine, but getting that first connector to work is the hard part. Earthquakes require active dampening which defiantly increases costs, but a larger issue is how to cross fault lines as you need a very large turning radius so very long segments of track need to be able to move. AKA you can't do this: http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html Unless you’re willing to really slow down. PS: Also of note, you are going to need safety exits on a fairly regular basis and some way to quickly add air to the pipe as people are not going to be able to walk hundreds of miles in case of an issue.
- stcredzero 11y ago
  But don't we have a window of minutes to shut down the system in case of an earthquake? I thought we could get advance warning from P waves. (This doesn't work if you're in the epicenter, unfortunately.) If the car gets badly damaged, but the passenger stays alive, and the system can be fixed in a reasonable amount of time, then this is fine performance for a major earthquake event. High speed trains have similar performance in the same situation.
  - dragonwriter 11y ago
    > But don't we have a window of minutes to shut down the system in case of an earthquake? No. > I thought we could get advance warning from P waves. (This doesn't work if you're in the epicenter, unfortunately.) Yes, but the advance warning is on the order of seconds, not minutes (per Wikipedia, for deep, distant, large earthquakes, 60-90 seconds is possible, but that's still at most a minute and a half.)
    - stcredzero 11y ago
      Even so, I thought that the failure mode for tube misalignment of hundredths or even tenths of an inch would result in stoppage, and perhaps damaged "track" and cars, with trapped passengers. This isn't so different from the performance of high speed rail during natural disasters.
  - deleted 11y ago
    [deleted]
- rmxt 11y ago
  Thermal is an issue that gets worse with distance. Did you look at the article that I posted above? If you are proposing expansion/slip joints at every pier, that runs directly counter to the proposal which states that expansion joints will only be needed near the stations. [1, pg. 27] If we go according to the proposal, the slip joint at the stations on the test track will only need to accommodate ~9 feet of movement (5280x5x6.5x10^-6x100)/2 compared to something an order of magnitude higher for a full-scale track. Successfully designing for earthquakes does not necessarily mean active damping. (That is, it is not "required" as you state.) Yes, many large structures use specially designed mass or viscous dampers for dynamic loading (Citigroup Building, NYC; Taipei 101; Millennium Bridge, London), but others are designed to fail safely such that life and structure are preserved to the greatest extent possible. Specifically for bridge structures, there is the notion of plastic hinging in visible locations. [2] This way, the failures can be identified and repaired before normal use resumes. Here are some relevant state DOT guidelines. [3] [1] http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201... [2] https://en.wikipedia.org/wiki/Plastic_hinge https://en.wikipedia.org/wiki/Plastic_hinge [3] http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-memo-to-designer/page/Section%2020/20-6m.pdf http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/b...
  - msandford 11y ago
    > Thermal is an issue that gets worse with distance. I would respectfully disagree. The rail industry has figured out how to do Continuous Welded Rail (CWR) quite well, using the elasticity of steel. http://blogs.agu.org/landslideblog/2011/03/08/distorted-railway-lines-in-the-christchurch-earthquake/ http://blogs.agu.org/landslideblog/2011/03/08/distorted-rail... Similarly the tube for the Hyperloop doesn't HAVE to free-float against its foundations. It might be easier or harder depending on various factors to work on expansion joints or doing the tube equivalent of CWR. You'd probably work on both to figure out which is easier in the long run. Considering that it's a 9-11ft diameter tube with about 1" wall thickness, it's going to be pretty stiff, especially relative to traditional rails. The moment of inertia means that it should be very resistance to bending or buckling under compression and under tension steel is usually very good. Given that there are going to be plenty of turns that the track has to make, I would look at doing a combination of two things: 1. Working towards a CWR style solution 2. Allow some movement so that the corners can take up the slack as the tube expands The turns are very gradual and sweeping. But you could imagine that there's a virtual intersection between two straight portions that you determine by drawing lines from the straight portions until they meet. The actual turn will take place far from here, but it's instructive. So as the tube expands, the actual curve is going to move ever so slightly from the neutral position towards the virtual intersection. So long as there is enough room on the pylons to accommodate this, things will be pretty good. The tube will go from being curved 0.1 degrees per 100 feet to 0.105 degrees per 100 feet (or something like this) but this can be designed for and ensured that it doesn't cause the tube to buckle or collapse. It's engineering, not the utter unknown.
brenschluss 11y ago
I'd imagine that there's a great deal of prior work, research, and implementation detail on Maglev trains in Japan on this very issue. Not to say that you're not right, but that this test track is probably precisely what's needed for an initial test, since the other issues (commonly solved with expansion joints) are being actively tackled/solved by many different industries.
- rmxt 11y ago
  According to Wikipedia [1], the only 3 passenger service operational Maglev lines have lengths of 18.95 miles, 5.5 miles, and 3.8 miles, which are in China, Japan and South Korea respectively. That would make it seem like it is far from a "solved" issue. [1] https://en.wikipedia.org/wiki/Maglev#Operational_systems https://en.wikipedia.org/wiki/Maglev#Operational_systems
digikata 11y ago
It should be a pretty good step towards getting measurements on thermal issues to then spec the needed tolerances with better basis on reality... You could also build segments with the intent of inducing displacements to study what's needed for seismic inputs.

by rmxt 11y ago

Retric 11y ago

Thermal expansion is not really an issue that gets worse with distance, as the track can simply be made from independent segments connected with expansion joints. The issue is being able to cross from segment A to segment B not the number of such segments. In other words if it works on a test track it scales just fine, but getting that first connector to work is the hard part. Earthquakes require active dampening which defiantly increases costs, but a larger issue is how to cross fault lines as you need a very large turning radius so very long segments of track need to be able to move. AKA you can't do this: http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html http://pubs.usgs.gov/fs/2003/fs014-03/pipeline.html Unless you’re willing to really slow down. PS: Also of note, you are going to need safety exits on a fairly regular basis and some way to quickly add air to the pipe as people are not going to be able to walk hundreds of miles in case of an issue.

stcredzero 11y ago
But don't we have a window of minutes to shut down the system in case of an earthquake? I thought we could get advance warning from P waves. (This doesn't work if you're in the epicenter, unfortunately.) If the car gets badly damaged, but the passenger stays alive, and the system can be fixed in a reasonable amount of time, then this is fine performance for a major earthquake event. High speed trains have similar performance in the same situation.
- dragonwriter 11y ago
  > But don't we have a window of minutes to shut down the system in case of an earthquake? No. > I thought we could get advance warning from P waves. (This doesn't work if you're in the epicenter, unfortunately.) Yes, but the advance warning is on the order of seconds, not minutes (per Wikipedia, for deep, distant, large earthquakes, 60-90 seconds is possible, but that's still at most a minute and a half.)
  - stcredzero 11y ago
    Even so, I thought that the failure mode for tube misalignment of hundredths or even tenths of an inch would result in stoppage, and perhaps damaged "track" and cars, with trapped passengers. This isn't so different from the performance of high speed rail during natural disasters.
- deleted 11y ago
  [deleted]
rmxt 11y ago
Thermal is an issue that gets worse with distance. Did you look at the article that I posted above? If you are proposing expansion/slip joints at every pier, that runs directly counter to the proposal which states that expansion joints will only be needed near the stations. [1, pg. 27] If we go according to the proposal, the slip joint at the stations on the test track will only need to accommodate ~9 feet of movement (5280x5x6.5x10^-6x100)/2 compared to something an order of magnitude higher for a full-scale track. Successfully designing for earthquakes does not necessarily mean active damping. (That is, it is not "required" as you state.) Yes, many large structures use specially designed mass or viscous dampers for dynamic loading (Citigroup Building, NYC; Taipei 101; Millennium Bridge, London), but others are designed to fail safely such that life and structure are preserved to the greatest extent possible. Specifically for bridge structures, there is the notion of plastic hinging in visible locations. [2] This way, the failures can be identified and repaired before normal use resumes. Here are some relevant state DOT guidelines. [3] [1] http://www.spacex.com/sites/spacex/files/hyperloop_alpha-20130812.pdf http://www.spacex.com/sites/spacex/files/hyperloop_alpha-201... [2] https://en.wikipedia.org/wiki/Plastic_hinge https://en.wikipedia.org/wiki/Plastic_hinge [3] http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/bridge-memo-to-designer/page/Section%2020/20-6m.pdf http://www.dot.ca.gov/hq/esc/techpubs/manual/bridgemanuals/b...
- msandford 11y ago
  > Thermal is an issue that gets worse with distance. I would respectfully disagree. The rail industry has figured out how to do Continuous Welded Rail (CWR) quite well, using the elasticity of steel. http://blogs.agu.org/landslideblog/2011/03/08/distorted-railway-lines-in-the-christchurch-earthquake/ http://blogs.agu.org/landslideblog/2011/03/08/distorted-rail... Similarly the tube for the Hyperloop doesn't HAVE to free-float against its foundations. It might be easier or harder depending on various factors to work on expansion joints or doing the tube equivalent of CWR. You'd probably work on both to figure out which is easier in the long run. Considering that it's a 9-11ft diameter tube with about 1" wall thickness, it's going to be pretty stiff, especially relative to traditional rails. The moment of inertia means that it should be very resistance to bending or buckling under compression and under tension steel is usually very good. Given that there are going to be plenty of turns that the track has to make, I would look at doing a combination of two things: 1. Working towards a CWR style solution 2. Allow some movement so that the corners can take up the slack as the tube expands The turns are very gradual and sweeping. But you could imagine that there's a virtual intersection between two straight portions that you determine by drawing lines from the straight portions until they meet. The actual turn will take place far from here, but it's instructive. So as the tube expands, the actual curve is going to move ever so slightly from the neutral position towards the virtual intersection. So long as there is enough room on the pylons to accommodate this, things will be pretty good. The tube will go from being curved 0.1 degrees per 100 feet to 0.105 degrees per 100 feet (or something like this) but this can be designed for and ensured that it doesn't cause the tube to buckle or collapse. It's engineering, not the utter unknown.

brenschluss 11y ago

I'd imagine that there's a great deal of prior work, research, and implementation detail on Maglev trains in Japan on this very issue. Not to say that you're not right, but that this test track is probably precisely what's needed for an initial test, since the other issues (commonly solved with expansion joints) are being actively tackled/solved by many different industries.

rmxt 11y ago
According to Wikipedia [1], the only 3 passenger service operational Maglev lines have lengths of 18.95 miles, 5.5 miles, and 3.8 miles, which are in China, Japan and South Korea respectively. That would make it seem like it is far from a "solved" issue. [1] https://en.wikipedia.org/wiki/Maglev#Operational_systems https://en.wikipedia.org/wiki/Maglev#Operational_systems

digikata 11y ago

It should be a pretty good step towards getting measurements on thermal issues to then spec the needed tolerances with better basis on reality... You could also build segments with the intent of inducing displacements to study what's needed for seismic inputs.