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I don't believe that an experimental tube is going to be somehow magically cheaper and easier to route and build than train tracks. Do you really think the spe

I don't believe that an experimental tube is going to be somehow magically cheaper and easier to route and build than train tracks. Do you really think the special interests that are making HSR so difficult and expensive would say, "Oh, do whatever you like with your tube."? These are extremely important issues that advocates seem to be glossing over. Putting the guideway on pylons doesn't magically eliminate land issues, you will still have to deal with visual impacts, along with any number of anticipated and unanticipated problems. Musk should do what the Germans did with the TR0x series of maglev vehicles, build a 10-20 mile test section someplace and demonstrate that is analysis is sound. (perhaps more in the future--why wouldn't California design with this goal [350 km/h] in mind?) There are a variety of reasons, but one important reason I have to deal with is that the speed of shear waves through soil is only on the order of a couple of hundred miles per hour. When a train exceeds the shear wave speed, ground-borne vibration waves "build up" in a manner similar to the shock wave created in air when a plane exceeds the speed of sound, causing a ground-borne vibration equivalent of a "sonic boom" that can cause problems for wayside structures. I believe the French have started to experience this with some of their higher-speed TGV experiments and we don't have a good way to handle this yet.

digikata 13y ago
> When a train exceeds the shear wave speed, ground-borne vibration waves "build up" in a manner similar to the shock wave created in air when a plane exceeds the speed of sound... Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they?
- Anechoic 13y ago
  Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they? Maybe, maybe not. Guideway supports (pylons) are typically founded into the bedrock which does reduce vibration somewhat, but the vertical motion of the pylon moving against the soil will still generate shear waves. This is why a demonstration project would be useful.
  - pxtang 13y ago
    I recall reading that the pylons had vertical and horizontal dampers to protect against earthquakes (among other minor natural changes), so wouldn't those dampers be able to cancel out the shear waves?
    - Anechoic 13y ago
      No. Well, I suppose you could design an active vibration system to (almost) completely cancel the vertical vibration motion, but know you're talking about a powered system in each pylon of incredible complexity. Passive resilient systems could help with higher frequency vibration (above say 100 Hz or so, depending on the forces and weights involved), but for lower frequency vibration (especially below 20 Hz), the resilient elements would have to be so compliant that even a gentle breeze would create very high vibrations in the guideway itself, which would be incompatible with the speeds of the cars inside. You could make the pylons so massive that the forces from the vehicles couldn't move it, but again you're talking about higher construction and material costs, as well as visual impacts.
      - 6ren 13y ago
        Ah! Note that the pods are far lighter than trains, being more like a lightweight aircraft. This would reduce the effect considerably.
        Anechoic 13y ago
        Vibration from trains is proportional to the unsprung weight of the vehicle (basically the axle, wheels and traction motors) rather than the vibration of the whole vehicle (which is isolated by the primary and secondary train suspensions). For a heavy rail transit vehicle (NYC transit, MBTA Red Line, CTA vehicle, etc), you're talking about 2,700 kg. I don't have numbers handy for HSR trainsets.
        6ren 13y ago
        The air cushion isolates the entire vehicle... perhaps making the "unsprung" weight 0?
javert 13y ago
> Musk should do what the Germans did with the TR0x series of maglev vehicles Musk has already given more than enough for the world and done more than enough. Somebody should do it, but we should not expect him to do it.
- iamjustin 13y ago
  We shouldn't expect him to demonstrate his idea?
  - danielweber 13y ago
    He says he won't do it himself for a long time. He's busy with other things.
  - anko 13y ago
    I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop. But it's nice that he is presenting the idea so the world can do their own analysis and even implement it before he has the chance.
    - enraged_camel 13y ago
      >>I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop. Specifically, an affordable Tesla car could benefit the entire world, whereas the Hyperloop would (at least initially) only benefit people living in LA and SF.
      - jarek 13y ago
        What are the benefits to the world market of an affordable Tesla compared to, say, a modernized version of the Volkswagen Lupo, or a plug-in Up! ?
        manmal 13y ago
        They both benefit the world. Fact is, there is no modernized 3-Liter-Lupo, and I've heard no rumors that there ever will be (?). Until there is, Tesla will be the one who demonstrates what is possible.
yk 13y ago
> one important reason I have to deal with is that the speed of shear waves through soil is only on the order of a couple of hundred miles per hour. Perhaps a stupid question, but the shock wave forms because the trains is moving continuously over the ground? So if you put the entire thing on stilts, there would be one wave formed at t0, x0 when the train reaches pylon 0 and the next wave would be at t1, x1 etc. So the interference pattern for the waves would look vastly different. ( This holds of course only for point like trains... )
- Anechoic 13y ago
  Yes, rather than a line-source, you have multiple incoherent point sources, but those point sources are being excited along a line at a rate faster than the shear wave speed. So yes, it somewhat different, but also similar. A test segment would go a long way to determining if/how much of a problem this might be in a hyperloop system.
6ren 13y ago
The pod is basically flying. Although its weight of course is still ultimately borne by the pythons, perhaps it's mushed out and dampened in a way that reduces the ground-boom effect? But it sounds like one of the (many) bugs that must be worked out. spaceX wasn't all smooth sailing.
deleted 13y ago
[deleted]

digikata 13y ago

> When a train exceeds the shear wave speed, ground-borne vibration waves "build up" in a manner similar to the shock wave created in air when a plane exceeds the speed of sound... Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they?

Anechoic 13y ago
Putting the railway or tubes on pylons would give you an opportunity to dampen or otherwise transform those vibrations wouldn't they? Maybe, maybe not. Guideway supports (pylons) are typically founded into the bedrock which does reduce vibration somewhat, but the vertical motion of the pylon moving against the soil will still generate shear waves. This is why a demonstration project would be useful.
- pxtang 13y ago
  I recall reading that the pylons had vertical and horizontal dampers to protect against earthquakes (among other minor natural changes), so wouldn't those dampers be able to cancel out the shear waves?
  - Anechoic 13y ago
    No. Well, I suppose you could design an active vibration system to (almost) completely cancel the vertical vibration motion, but know you're talking about a powered system in each pylon of incredible complexity. Passive resilient systems could help with higher frequency vibration (above say 100 Hz or so, depending on the forces and weights involved), but for lower frequency vibration (especially below 20 Hz), the resilient elements would have to be so compliant that even a gentle breeze would create very high vibrations in the guideway itself, which would be incompatible with the speeds of the cars inside. You could make the pylons so massive that the forces from the vehicles couldn't move it, but again you're talking about higher construction and material costs, as well as visual impacts.
    - 6ren 13y ago
      Ah! Note that the pods are far lighter than trains, being more like a lightweight aircraft. This would reduce the effect considerably.
      - Anechoic 13y ago
        Vibration from trains is proportional to the unsprung weight of the vehicle (basically the axle, wheels and traction motors) rather than the vibration of the whole vehicle (which is isolated by the primary and secondary train suspensions). For a heavy rail transit vehicle (NYC transit, MBTA Red Line, CTA vehicle, etc), you're talking about 2,700 kg. I don't have numbers handy for HSR trainsets.
        6ren 13y ago
        The air cushion isolates the entire vehicle... perhaps making the "unsprung" weight 0?

javert 13y ago

> Musk should do what the Germans did with the TR0x series of maglev vehicles Musk has already given more than enough for the world and done more than enough. Somebody should do it, but we should not expect him to do it.

iamjustin 13y ago
We shouldn't expect him to demonstrate his idea?
- danielweber 13y ago
  He says he won't do it himself for a long time. He's busy with other things.
- anko 13y ago
  I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop. But it's nice that he is presenting the idea so the world can do their own analysis and even implement it before he has the chance.
  - enraged_camel 13y ago
    >>I think tesla motors releasing an affordable car would benefit the world a lot more than the hyperloop. Specifically, an affordable Tesla car could benefit the entire world, whereas the Hyperloop would (at least initially) only benefit people living in LA and SF.
    - jarek 13y ago
      What are the benefits to the world market of an affordable Tesla compared to, say, a modernized version of the Volkswagen Lupo, or a plug-in Up! ?
      - manmal 13y ago
        They both benefit the world. Fact is, there is no modernized 3-Liter-Lupo, and I've heard no rumors that there ever will be (?). Until there is, Tesla will be the one who demonstrates what is possible.

yk 13y ago

> one important reason I have to deal with is that the speed of shear waves through soil is only on the order of a couple of hundred miles per hour. Perhaps a stupid question, but the shock wave forms because the trains is moving continuously over the ground? So if you put the entire thing on stilts, there would be one wave formed at t0, x0 when the train reaches pylon 0 and the next wave would be at t1, x1 etc. So the interference pattern for the waves would look vastly different. ( This holds of course only for point like trains... )

Anechoic 13y ago
Yes, rather than a line-source, you have multiple incoherent point sources, but those point sources are being excited along a line at a rate faster than the shear wave speed. So yes, it somewhat different, but also similar. A test segment would go a long way to determining if/how much of a problem this might be in a hyperloop system.

6ren 13y ago

The pod is basically flying. Although its weight of course is still ultimately borne by the pythons, perhaps it's mushed out and dampened in a way that reduces the ground-boom effect? But it sounds like one of the (many) bugs that must be worked out. spaceX wasn't all smooth sailing.

deleted 13y ago

[deleted]