garry@batcomputer.tn.cornell.edu (Garry Wiegand) (11/05/87)
(Cross-posted to rec.railroad) In article <8710291320.AA08591@bu-cs.BU.EDU> BIOMED@CZHETH5A.BITNET writes: >Everybody talks about these 'warm superconductors'. ... > >HOW will they change the world ? The most intriguing idea I've heard so far is to apply them to cheap magnetic levitation for trains. I'd guess the trains would travel significantly faster, use less fuel, and be exceedingly smooth and quieter-riding. The fuel is probably not significant, but could the other things give trains a shot at a comeback? I'd *love* to have an alternative to airplanes! Does anyone have technical knowledge? (I admit I would *not* love to have trains travelling at 400 mph past my house.) garry wiegand (garry@oak.cadif.cornell.edu - ARPA) (garry@crnlthry - BITNET)
neanders@phoenix.Princeton.EDU (Nels Anderson) (11/06/87)
In connection with high-temperature superconductors, garry@oak.cadif.cornell.edu writes in article <2824@batcomputer.tn.cornell.edu>: >The most intriguing idea I've heard so far is to apply them to cheap magnetic >levitation for trains. > >Does anyone have technical knowledge? Well, I have a little. Just a bit of the physics. I don't know anything about the engineering problems. According to an article in the IEEE Spectrum about three years ago, there are two types of magnetic levitation: electromagnetic and electrodynamic. In the electromagnetic system both the train and the track contain electromagnets. I believe the train's magnets are actually below the track, in a monorail-type arrangement. The magnets are oriented so as to attract each other, with the result that the train is pulled up. A control system is required to maintain the proper separation between the two sets of magnets, reducing the field if they come to close and increasing it if they get too far apart. Superconducting electromagnets could be used to eliminate resistive losses. Electrodynamic suspension is somewhat more elegant. It is based on the principle that a changing magnetic field will tend to induce a current in a conductor (copper, aluminum or a superconductor, for example). The induced current will flow in such a way as to create a magnetic field counter to the original field. If, for example, the changing magnetic field is caused by a magnet moving over the surface of the conductor, the induced currents in the conductor will repel the magnet in the vertical direction while attracting it horizontally. So the magnet is levitated and at the same time held near the center of the conductor. The catch here is that in normal conductors the induced currents die out rapidly. Constant motion is required to maintain the induced magnetic field. In a superconductor, however, the currents continue to flow indefinitely. Thus, if you send a magnet skimming over a block of aluminum at sufficiently high speed, the magnet will be levitated. If it slows down, however, the levitation will disappear. If you do the same thing with a superconductor, you find that the levitation persists even when the magnet isn't moving. A New York Times article on superconductors a few months ago showed a magnet suspended over a superconductor (or it may have been a superconductor suspended over a magnet -- the principal is the same). Without superconducting technology, an electrodynamically suspended train would contain an ordinary electromagnet and might ride over an aluminum track. (The track just has to be a good conductor and must not be ferromagnetic. It would start out on wheels. After reaching sufficient speed it would lift off the track. The New York Times article mentioned the possibility of using superconducting technology for the electromagnet. If superconductors were really cheap, the track could be superconducting as well. Then the train would float as soon as its magnets were turned on -- there would be no need to get up to speed. Superconducting track would also save energy, since the induced currents in nonsuperconducting track will tend to dissipate. The energy they dissipate has to come from somewhere, and I believe it shows up as a retarding force on the train. This would be quite substantial; the induced currents holding up a fast-moving train would be comparable to currents in the train's own magnets. Magnetic trains have been demonstrated by the British, Germans and, of course, the Japanese. As I recall from the IEEE article, the British system was electromagnetic. I don't know about the other two, but I believe that either or both of the German and Japanese experiments rely on conventional cold (liquid helium) superconductors. Nothing has been said yet about propulsion, as opposed to levitation. I presume that it is done by magnetic repulsion or attraction between electromagnets in the track and the train. I could go on at greater length about these things, but I suspect that everybody is bored already. Unfortunately I know only about the physical principals involved and nothing about the practical engineering problems. (Besides, my thesis advisor would dispute my claim to understanding ANY physical principals.) neanders@phoenix.princeton.edu neanders@phoenix.UUCP 6070106@pucc.bitnet
rvk@houdi.UUCP (R.KLINE) (11/06/87)
one benefit of magnetic levitation would probably be significantly lower roadbed wear. the primary function of "tracks" would be to correct lateral excursions. fuel savings might be significant because the major source of friction would now be wind drag. -r. kline
dmc@videovax.Tek.COM (Donald M. Craig) (11/10/87)
Once upon a time the Ontario government had (maybe they still do) a `Transportation Research Centre' in Kingston, Ontario. They had a maglev track and a train that ran around on it, using technology licensed from a German company (Krauss-Maffei ?). It seemed to work fine, in the summer. But when the winter blizzards howled off the Saint Lawrence River the track was buried under ice and snow, and all the lovely hovering clearances disappeared. They might still have the train, but they never bought another. There's a lot of sophistication in old train technology. When the Canadian National Railways introduced a United Technologies turbine powered (jet fuel yet) `Turbo' train on the Toronto - Montreal run in the early seventies, it took ten years of re-engineering before the things would run reliably during the winter. I remember on several occasions having to transfer to the diesel `Rapido' when the `Turbo' failed in the thick of a blizzard. Don Craig Tektronix Television Systems
robertj@yale-zoo-suned..arpa (Rob Jellinghaus) (11/16/87)
One aspect of the new superconductors that has not been touched on yet
is their applicability to electric motors. With current technology,
electric cars are not practical, because the motors are too heavy and
too inefficient, as are the batteries.
Warm superconductors could solve both of these problems. We could
create motors half the size and many times more powerful than the
electric motors of today. The batteries could also become more
efficient by orders of magnitude. This could get us out of our current
reliance on petrochemicals, and greatly reduce humanity's destruction
of the biosphere. Not to mention you never need go to the gas station
again; just plug in your car overnight!
Of course, this leaves out questions of intense electromagnetic fields
inside the car, ability to quickly accelerate, etc. But GE recently
created a solar-powered car that crossed Australia at an average speed
of over 40 mph (if memory serves). The thing only drove during the
daylight hours, but that's still an impressive feat. And that was with
non-superconductor technology. If that can be done now, imagine what
will be done when the supercoductors come along!
Rob Jellinghaus | "Lemme graze in your veldt,
jellinghaus@yale.edu.UUCP | Lemme trample your albino,
ROBERTJ@{yalecs,yalevm}.BITNET | Lemme nibble on your buds,
!..!ihnp4!hsi!yale!jellinghaus | I'm your... Love Rhino" -- Bloom Countydjw@beta.UUCP (David Wade, Computer Confuser Group, Chaotic Section, Administrator of illogical "Do Whiles".) (11/22/87)
In article <18946@yale-celray.yale.UUCP> robertj@yale.UUCP writes: > Not to mention you never need go to the gas station >again; just plug in your car overnight! > >Rob Jellinghaus And your house will burn down as the MEGAWATTS come swiftly into the noload battery...