Hyperloop

[IceWendigo]

I also think it would be worth examining a slightly larger cabin that would be a tad wider than a minivan/SUV that could accommodate an alley to a small bathroom in the back like you have on some bus and planes.

Although Ive been on School Bus trips with toddlers that took 30 min or more without a bathroom on the bus (but in a worse case it would have been possible to stop at a restaurant or gas station along the way, which is not possible in a tube), so its not an absolute must, but it is certainly a nice to have accomodation.

 

[lorih]

I think Elon might take me off his Christmas card list if he isn't a humor-receptive mood.

Brianman, you get a christmas card from Elon?!? I shall kneel in front of you at next year's TESLIVE, and not rise until I feel the gentle touch of your hand on my reverently bowed head, oh anointed one! All hail Brianman!:wink:


Disclosure: Brianman understands joking and sarcasm between friends. For everyone else, I'm not actually picking on Brianman, don't shoot me!

 

[twinklejet]

Some MIT Professor Emeritus called in to CNBC to claim that Elon stole his idea...?! Anyone knows whether there's any truth to that? I can't believe CNBC ran with that without fully verifying it... (they literally said "benefit of the doubt")

 

[Sparky]

Just want to share this article:

• The Hyperloop Is About Attitudeat TheStreet(Tue 9:24AM EDT)

I like this.
I just got through making a similar comparison about national attitudes with one of my kids at dinner last night. Musk seems intent on injecting some adrenalin into our collective dream-muscles. They seem to have atrophied over the last 40 years. We've been sitting on the cynic's couch too long.

And more interestingly, a read at the end:
Dream other dreams, and better.

I am lost after the reading.

Yeah, Twain had a long-standing God-grievance. And with this writing, near his death, he didn't want there to be any doubts that he was not about to grant "God" forgiveness. I suppose I can find some parallels with Twain's cultural depth and breadth and Musk's extensive technical chops. Like Musk, Twain was also a brilliant businessman; but appreciation for that attribute gets attenuated by his other skills as humorist, orator and writer.

 

[CapitalistOppressor]

Yes I noted the spring/damper. But a car also has a spring/damper and I don't think you will be very comfortable in your MS going over a traffic calming hump if your MS is going at a scale speed of about 70000 mph. (Not quite the same thing but just trying to emphasize the idea of 700mph at 1mm.)

I just don't see how expansion joints can be designed that would not create a substantial roughness. If expansion joint were at every pylon, the expansion joint would have to accommodate a delta length of 10.8E-6*30m*80degK= 0.026m or about 1 inch. 80deg K comes from ambient temp swing of perhaps -20 to 120 deg F and the 10.8E-6 is the linear expansion coefficient of steel. Remember, these have to hold a vacuum.

I think making the tubes out of Aluminum and using superconducting magnetic levitation might work (yes, the paper said that is too expensive.)

I don't see why you are deviating from what is already discussed in the paper. They specifically address thermal expansion, and expansion joints at every pillar is pretty far from what they are proposing. There might be real problems with the solution that they are putting forward, but their design is nothing like what you are discussing.

The key advantages of a tube vs. a railway track are that it can be built above the ground on pylons and it can be built in prefabricated sections that are dropped in place and joined with an orbital seam welder.

The steel construction allows simple welding processes to join different tube sections together. A specifically designed cleaning and boring machine will make it possible to surface finish the inside of the tube and welded joints for a better gliding surface.

The tube will be supported by pillars which constrain the tube in the vertical direction but allow longitudinal slip for thermal expansion as well as dampened lateral slip to reduce the risk posed by earthquakes. In addition, the pillar to tube connection nominal position will be adjustable vertically and laterally to ensure proper alignment despite possible ground settling. These minimally constrained pillars to tube joints will also allow a smoother ride.

Specially designed slip joints at each station will be able take any tube length variance due to thermal expansion. This is an ideal location for the thermal expansion joints as the speed is much lower nearby the stations. It thus allows the tube to be smooth and welded along the high speed gliding middle section.

The same goes with your vacuum comment. The design is a low pressure environment, not a vacuum, and they clearly anticipate leakage and discuss commercially available pumping systems that have more capacity than they believe will be required. The fact that the system embraces imperfection in the ambient environment is a strength, and the primary engineering question is whether you can in fact bail out enough atmosphere to keep up with the leaks, while maintaining ambient pressure within the margins that the pods can deal with.

However, a low pressure (vs. almost no pressure) system set to a level where standard commercial pumps could easily overcome an air leak and the transport pods could handle variable air density would be inherently robust. Unfortunately, this means that there is a non-trivial amount of air in the tube and leads us straight into another problem.

I'm not trying to pick on you, because you obviously have a lot of technical capability to contribute to the discussion, its just that I am much more interested in your thoughts on the feasibility what is actually discussed in the paper.

Specifically, Elon clearly see's the tube's interior as being effectively seamless and smooth over the vast bulk of its path, with the tube moving horizontally at the top of the pillars, and what must be quite large expansion joints at the termini. He actually mentions them being similar to the telescoping tubes at airports -

A ground based high speed rail system is susceptible to Earthquakes and needs frequent expansion joints to deal with thermal expansion/contraction and subtle, large scale land movement. By building a system on pylons, where the tube is not rigidly fixed at any point, you can dramatically mitigate Earthquake risk and avoid the need for expansion joints. Tucked away inside each pylon, you could place two adjustable lateral (XY) dampers and one vertical (Z) damper. These would absorb the small length changes between pylons due to thermal changes, as well as long form subtle height changes. As land slowly settles to a new position over time, the damper neutral position can be adjusted accordingly. 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.

So what are your thoughts on the actual design? It seems to me that this kind of mega-slip joint would also be required to pivot to accommodate the thermal expansion of a unitary megatube. How much slop is required for multi-hundred mile segments?

- - - Updated - - -

Some MIT Professor Emeritus called in to CNBC to claim that Elon stole his idea...?! Anyone knows whether there's any truth to that? I can't believe CNBC ran with that without fully verifying it... (they literally said "benefit of the doubt")

What's to steal? He's not trying to patent it. And unless this professor has patented it he doesn't really have anything to talk about except how he plans to block development of the idea until someone pays him off.

 

[deonb]

Specifically, Elon clearly see's the tube's interior as being effectively seamless and smooth over the vast bulk of its path, with the tube moving horizontally at the top of the pillars, and what must be quite large expansion joints at the termini. He actually mentions them being similar to the telescoping tubes at airports

Question: The weather in San Francisco, L.A, and on the way is quite different.

e.g. Today it's:

SF: 70
Coalinga: 100
LA: 81

It can also be much more drastic if you have coastal rain, and inline heat.

Wont the non-uniform temperature across the length be a problem if you try to use a seamless thermal expansion approach?

 

[30seconds]

what i find sad is that I can't find a decent article anywhere where actual experts (fluid dynamics, aeronautics, mech engineers, etc.) who were independent of the project were asked for their initial opinions. our media is quite a bit stupider than I thought, and I already had low low expectations.

 

[Rodolfo Paiz]

In an emergency you do what you can. I believe design precludes bathrooms and accommodating them isn't really possible without changing the design a lot. You are free to not use the hyperloop as a consequence.

I find your attitude and tone extremely negative and dismissive. I'm sorry for you if you need to feel that way, but it certainly isn't going to affect me. I'm beyond caring what know-it-all naysayers may throw at me.

This alpha design came out yesterday, for Pete's sake. It's not a final design spec. Any and all parameters may change, even dramatically so. The pax+vehicles tube certainly accommodates different design criteria than the pax-only tube, for example. JRod just rightly noted that it's going to have to be handicap-accessible, and there are lots of other considerations that will come to be included over time. Plus, the Hyperloop is postulated as being ideal for trips of "up to 1000 miles," which would take roughly 90 minutes based on this alpha doc.

Relax. None of us have all the answers, and at this point we should be focused more on raising questions.

 

[stevezzzz]

@Rodolfo: Just play soothing music, let the cabin altitude rise to 25,000'MSL, and everybody has a nice, 30 minute nap...

:biggrin:

 

[TheTalkingMule]

what i find sad is that I can't find a decent article anywhere where actual experts (fluid dynamics, aeronautics, mech engineers, etc.) who were independent of the project were asked for their initial opinions. our media is quite a bit stupider than I thought, and I already had low low expectations.

The media gives the masses what they want, period. All you have to do is look at this thread, it's 80% discussion of when you need a bathroom for 4 year-olds. I'd have like to have seen what you're talking about this morning as well, but the actual engineering doesn't have wide enough appeal. I'm sure we'll see plenty of insane analysis in the coming weeks from the more fringe sources.

 

[Norbert]

Ahem... Not to toot my own horn, but - Toot!
:biggrin:

You got very close! (Although that was just 3 weeks ago, and in fairness to some older speculation, you already had a lot of hints and discussion to build on... )

 

[Larry Hutchinson]

I don't see why you are deviating from what is already discussed in the paper. They specifically address thermal expansion, and expansion joints at every pillar is pretty far from what they are proposing. There might be real problems with the solution that they are putting forward, but their design is nothing like what you are discussing.

I was responding to RDoc who said

Why do you think the expansion joints would be a problem? With the exception of the final end points that would take up the sum of the expansion/contraction, they would be distributed along the length of the tube so each would only have to handle a fraction of a mm change.

My calculations show 25mm, not a fraction of a mm. And if the expansion joints were not distributed, you would end up with 1 inch per hundred feet at the stations. That boggles the mind (at least mine.)

The same goes with your vacuum comment. The design is a low pressure environment, not a vacuum, and they clearly anticipate leakage and discuss commercially available pumping systems that have more capacity than they believe will be required. The fact that the system embraces imperfection in the ambient environment is a strength, and the primary engineering question is whether you can in fact bail out enough atmosphere to keep up with the leaks, while maintaining ambient pressure within the margins that the pods can deal with.

The environment is 1/6 of Mars which is 1% of Earth. So as far as the forces acting on the structure, it might as well be a hard vacuum.

So what are your thoughts on the actual design? It seems to me that this kind of mega-slip joint would also be required to pivot to accommodate the thermal expansion of a unitary megatube. How much slop is required for multi-hundred mile segments?

The slop would be (1inch/100ft)*5280ft/mi*100mi= 5280in= 440ft per 100mi.

 

[RDoc]

One comment on ride smoothness vs minor imperfections in the tube. The car is supported down it's entire length with 28 pairs of air pads which are very simple structures, likely just aluminum or carbon fiber pads with the aluminum linear motor rotor, so they are going to have very low mass, much lower than a wheel, disk brake, and tire for example. This means that the ratio of unsprung to sprung mass will be very low, so the inertia of the car plus the distributed support of all the pads should minimize the disturbance to the passengers ride from tube imperfections.

 

[JRP3]

Bathroom issue solved. Next.

 

[Norbert]

Some MIT Professor Emeritus called in to CNBC to claim that Elon stole his idea...?! Anyone knows whether there's any truth to that? I can't believe CNBC ran with that without fully verifying it... (they literally said "benefit of the doubt")

I don't buy it. He talks about "too many similarities", but only mentioned 3 interesting ones (apart from coincidences such as in the cost number 6.8 million):

1. evacuated tube (well there've been a lot of those ideas around, including ET3 which Elon's paper does mention explicitly)
2. Maglev trains (this is even wrong! Elon's proposal does *not* use magnetic levitation, it uses air cushion)
3. ground? support (I'm not sure about the word "ground", and have no idea what else it could be, but that is hardly a unique idea for trains.)

So as far as I can tell that leaves only the "evacuated tube" as a real idea in common, and Elon's paper already says that his proposal is not the first with evacuated tubes. However, in an interview he mentions that he has not seen "low-pressure" tubes before (as opposed to "vacuum" or near-vacuum, as perfect vacuum is not achievable in any case).

Also, quickly googling Frankel only revealed that he has been credited with the idea to run trains in evacuated tubes, but nothing else was mentioned in common with Elon's proposal. Only some cooperation with MagLev ideas (which do not apply here). Frankel can hardly claim credit for running trains between "two cities" as a unique idea.

My impression is that Frankel hasn't even examined Elon's proposal in detail. Certainly, the CNBC report fails to identify anything which could back up his complaint in any meaningful way.

 

[jeff_adams]

USA Today article has an expert that claims it won't work. Says the high velocity will build up too much heat for the capsules. He said he didn't see how the water tank could provide enough cooling for the trip.

 

[Norbert]

My calculations show 25mm, not a fraction of a mm. And if the expansion joints were not distributed, you would end up with 1 inch per hundred feet at the stations. That boggles the mind (at least mine.)

If you have professional-level experience in making such calculations, I guess that would a good enough reason to write them down and send them to one of the hyperloop email addresses, along with a description of your concerns. To me it sounds like the proposal would involve such calculations already, even if they are not mentioned in detail, and it might be interesting (at least for you, but perhaps for both sides) to resolve the differences. I'd expect there is a solution to this.

- - - Updated - - -

USA Today article has an expert that claims it won't work. Says the high velocity will build up too much heat for the capsules. He said he didn't see how the water tank could provide enough cooling for the trip.

The water tank? Is that a joke? It would have to be the air that is flowing around the pod, and through it, I suppose.

 

[kevin99]

@JRP3, hilarious!

 

[jeff_adams]

The water tank? Is that a joke? It would have to be the air that is flowing around the pod, and through it, I suppose.

He was talking about the air flow friction of traveling that fast in a tube. Think of how hot a rifle barrel gets after a bullet is fired. That heat would have to be dealt with.

 

[AudubonB]

*It is a wonderfully remarkable platform as a starting point for The Fifth Mode, as Mr. Musk has called it.

*I am glad to see he is proposing elevating it atop extant rights-of-way. To answer the "Why not above aqueduct?" questioner - I am going to guess that California's aqueducts MIGHT have sharper turns in them than does, e.g., I-5, so atop the freeway is likely to be a better first-iteration site.

*I have some insight into fluid dynamics parameters that can be of use for the team, so I shall be sending them off to the open platform as requested.

*I LOVED that reference to Mars's atmosphere. Provides an excellent reference point to gain deeper understanding of the situation......for just about exactly one human being on this planet (EM IS human, isn't he.....?????? )

*$999999999 fine for in-seat micturation. Problem solved - take your minivan. And I'm sure that input of mine will no more stop this topic than a cork would.....

*The logistical problem of how, where and how large to make the dis/embarkation sites can be, it occurred to me right away, the single most contentious piece of the concept. Compared to that snarlygack, Hyperloop's physics is a cakewalk.

*I would love to see other paired cities/spiderwebs of NoAm Hyperloop locations presented.

*As also conjectured Kevin99, I tearfully can envisage China forging ahead and bringing to fruition this venture while California and the rest of our nation dithers.

*Expansion joints: our Trans-Alaska Pipeline is a 4' diameter tube that is 815 miles long. On any particular day, it may be encountering temperature differentials along its length of 45 degrees C. It is not a problem.