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I envision a new super-broad gauge railway connecting the world's main economic centers*. This railway would have a track width of 3 m, more than twice as wide as the world standard gauge of 1.4 m.
The giant trains using this network would be able to carry about 5 times as much cargo or passengers
for the same length. There are two principal advantages compared to standard-gauge: a) lower ton-kilometer and passenger-kilometer energy consumption and cost. This is due to a lower surface area/volume ratio and other economies of scale. b) Higher speeds are economically feasible, for same reasons as above and because wear and tear is lower on more massive rails and wheels. Standard gauge high speed rail travels at 320-350 km/h (220 mph). These trains could probably cruise at 500 km/h (300 mph).
This world-spanning network would fill the market gap between ships and airplanes. Shipping a container from Shanghai to New York currently takes 2-3 weeks. By broad gauge rail it would take 24 hours. It would greatly reduce shipping costs and encourage economic growth.
The passenger version would use quadruple decker trains with very spacious accomodation. It would allow intercontinental travel slightly slower but cheaper than airliners (longest journey London-New York would take 36 hours). Since more people would be able to afford these journeys, the high capicity trains are likely to fill. And when oil prices reach $200/barrel in the next decade, it might even replace airliners as the main form of long distance travel.
It would cost a fortune, but if the US, the EU, Japan and China all chipped in it might be doable. Beats spending $500+ billion on manned space programs anyhow.
* Route:
This railway would start in the flatlands of Northern Europe, connecting the cities of Paris, Amsterdam, Hamburg, Berlin, and Warsaw (and possibly London via a a second Chunnel) from where it would continue to Moscow. From Moscow it would roughly follow the course of the Trans-Siberian Rail Road.
One branch would split off to Beijing, from where it would continue along the Chinese coast to Shanghai and Hong Kong, then heading south to Bangkok, Kuala Lumpur and Singapore.
A second branch would cross a bridge onto Sakhalin island, from where it would continue via Hokkaido to mainland Japan over two underwater tunnels, eventually reaching Tokyo and Osaka.
A third branch would cross the Bering Strait inside one last tunnel (the longest of all), and head across Alaska to Vancouver and Seattle. From Seattle, it would again branch into two lines: One to California (SF, SJ, LA, SD) and one across the United States, connecting Chicago and metro areas in the North East (Washington, Philadelphia, New York, Boston).
Small section of your idea
http://en.wikipedia.org/wiki/Betuweroute
Initial costestimation: 1,1 billion euro's, final cost:4,7 billion. 20,000 man years to build. Major political problems. [zeno, Oct 24 2007]
Outline of proposed route
http://sixpop.com/i...s/file/25292389.png
[manicdictator, Oct 24 2007]
A 47' gauge track?
http://charles_w.tripod.com/widerr.html
Another halfbaked scheme [ldischler, Oct 25 2007]
Breitspurbahn
http://en.wikipedia.../wiki/Breitspurbahn
[kinemojo, Oct 26 2007]
Plate Tectonics
http://en.wikipedia...Plates_tect2_en.svg
[manicdictator, Oct 26 2007]
Aerodynamics
http://www.grc.nasa...2/airplane/bga.html
NASA - guide to aerodynamics [MisterQED, Oct 26 2007]
Aerodynamics
http://selair.selki...cs1/Drag/Page5.html
[manicdictator, Oct 26 2007]
http://selair.selki...cs1/Drag/Page2.html
[the dog's breakfast, Oct 27 2007]
Raindrops aren't teardrop shaped.
http://ga.water.usg.../raindropshape.html
[david_scothern, Oct 29 2007]
Fineness ratio
http://stinet.dtic....dentifier=AD0603802
Missile design [david_scothern, Oct 29 2007]
Minimum drag (in water this time)
http://books.google...TaLeO_CSHA5jAcHGCDw
[david_scothern, Oct 29 2007]
Train drag coefficients
http://www.prod.san....pl/1995/951268.pdf
Page 18, second paragraph reproduced here. [david_scothern, Oct 31 2007]
[link]
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I like it...it would be like fast cruise ship travel only on land. With 3 (about 10 feet) meter guage rails, the cars could be almost 16 feet wide...perhaps 18 feet. Comfortable sleeping compartments, luxurious and spacious dining, and the sight seeing would be unbelievable except in the long undersea tunnels. I think it would pay itself off in less than fifty years, too...including cost of maintenance. One super train could probably carry five thousand people. I love the idea, as impractical as it may seem today. |
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Idea was good until the numbers started flying out from nowhere. Suggest truncating after the fifth paragraph. |
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[Texticle] I've taken the proposed route out of the main text and added it as an appendix for those who feel like keeping on reading. |
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As a general idea it's enough to undestand that it would span the Northen Hemisphere. |
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It's been suggested before. I favor a super-wide gauge, like thirty feet, so everybody's standard rail cars can be loaded onto it crossways. I also like the straight-line great-circle route across the Bering Strait--bump that northward a bit, and you've got flat ground from Louisiana to the Caspian. |
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I want a model supertrain.....[gears in head grind].......I'm just going to setup an N scale layout with N scale buildings and scenery but use HO scale trains and track for the super train. |
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seriously, + I like this idea |
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Dude, you chopped off the bit I liked and retained the bit with which I had beef. Fair enough. |
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//with which I had beef// what part d i d you like? |
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The conceptual bit. Wide railway, linking economic centres. |
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The figures detract from the idea as they appear to be the product of fantasy and conjecture rather than engineering and economic calculus. |
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I don't get it. Why does a wider gauge mean lower surface area/volume ratio? How does the geometry work? I can understand that wear-and-tear is less on more massive rails and wheels, but is this not possible with standard gauge? Is there a link to some engineering information? Will there be a lounge car? |
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// Why does a wider gauge mean lower surface area/volume ratio? // |
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A wider gauge allows wider and taller trains. If you tried to put a train that is 6 m wide and 10 m tall on a standard 1.4 m gauge it would be rather unstable and fall over when somebody sneezes. |
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These trains would have about 5 times as much volume as a standard train for a given length. |
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// I can understand that wear-and-tear is less on more massive rails and wheels, but is this not possible with standard gauge? // |
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It would be possible to make the train heavier, but not bigger. |
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// Will there be a lounge car? // |
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On four decks there should be space for a lot of amenities just like on a cruiser. Ultimately it will depend on the class you're travelling in. |
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//The figures detract from the idea as they appear to be the product of fantasy and conjecture rather than engineering and economic calculus.// |
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The figures are meant as estimates and I can explain them if you like: |
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The 320-350 km/h figure is not a fantasy. This is how fast the TGV cruises. It has a top speed of 570 km/h but it is uneconomical at that speed. It is fair to assume that a train 5 times as massive would be able to cruise at 500 km/h. |
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The journey times of 24 and 36 hours are based on distances I measured on Google Earth: Paris-Bering Strait: 12,000 km. Bering Strait-New York: 6,000 km, etc. |
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$200/barrel is predicted by many economists for the next decade. Look up "peak oil". |
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$400 billion is what Bush wanted to spend on the Manned Moon Program 2.0. China is probably spending a large amount too. |
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Marked for deletion, to expensive. Forgive my scepticism, you'll understand if you read up on this link. |
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The more pressure you have on a surface, the faster it fails. And not just linearly, but exponentially.
You could make the rails much wider, or have more of them, I suppose. |
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Quad rail train! love it! |
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More speed requires more energy input to push air out of the way. |
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// The more pressure you have on a surface, the faster it fails. And not just linearly, but exponentially.
You could make the rails much wider, or have more of them, I suppose. // |
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Wider rails AND bigger wheel diameters AND possibly more wheels, don't forget. |
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You could adjust the above parameters so that the pressure of each wheel on the rail is the same as of standard-gauge. |
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Would seriously fuck with Rubik's Earth. Like braces on a 3x3x3. |
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Wider trains mean more air resistance, so less efficient. Longer thinner trains are more efficient. Spur rails would be harder. Some gain could be made by making loading perpendicular. More than two rails would cause problems unless unrealistic efforts were made to make them all level. I think all this could be solved with intelligent leaning trains, though easing loading and unloading would be big. |
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//Wider trains mean more air resistance, so less efficient. Longer thinner trains are more efficient// |
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This is incorrect. Basic high school physics: Let's assume that rolling resistance is negligible for the time being. There are two types of drag relevant to trains. a) Form, or pressure drag and b) skin friction drag. The first is *roughly* proportional to the frontal area and the second is proportional the the total surface area of the train. |
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Now the question is, for a given amount of volume, what is the most aerodynamic shape? A sphere has very low skin friction drag but very high pressure drag. A long, thin rod has very low pressure drag but very high skin friction drag. Overall, both the sphere and the spaghetti shape have high drag. But there is a sweet spot somewhere in the middle of the two shapes where both pressure and skin drag are relatively low. This optimal shape varies a little depending on the conditions, but almost always ends up being a "cigar shape". A penguin is said to have one of the most streamlined shapes in nature. Have you ever noticed how pegiuns are cigar-shaped rather than snake-shaped? |
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Now that we've determined our ideal shape of the train, the next question is, what is more efficient, a small train or a large train? When we double the volume, we don't double the area. Therefore, both types of drag *per unit volume* become smaller and smaller as the object gets larger because the area/volume ratio decreases. This is why large container ships are infinitely more energy efficient per ton-kilometer than small delivery vans. |
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The lessons are: a) A wider, shorter train is more efficient that a long, thin train because it's closer to a cigar shape. b) Given the same shape, a train of higher total volume consumes less energy *per ton-kilometer* than a train of lower volume, even if its absolute energy consumption is higher. |
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[MisterQED] you're wrong about more rails being unfeasible. Technically, having more than three wheels in total is unfeasible for the same reason. The reason that trains with more than three wheels are possible: Suspension. Fundamentally, suspension reduces the stiffness of the system, so load sharing becomes less sensitive to small variations in displacement. |
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I don't think multiple rails would be necessary, but I wanted to make the above clear. |
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According to the link both sides of the Bering Strait are located on the North American plate. Where is this fault line you speak of? |
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And there is also a fault line going straight through Japan - a land of tunnels. How does that work? |
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I'm not convinced that air-friction in haulage trains is significant enough in terms of overall energy expenditure to warrant building a special track in order to try and optimise it. |
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If you're dragging thousands (millions) of tons of cargo - in comparison to the work required to shift those sorts of weights, air resistance is going to be negligible. |
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If there is a reason for having a wider track, then it might be to provide stability for larger loads. But this stability would also require thicker, stronger rails that are less likely to splay apart (or to otherwise shift relative to one another under strain) which in turn would be more expensive, both to build and maintain. |
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I do like the idea of a massive land-train, slowly trundling along, carrying oil-tanker style loads - though for this sort of heavy cargo, speed just wouldn't be an option - having got up to speed, you'd never be able to stop. |
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Good point. What about rolling resistance though? Wouldn't that also be a lot lower per ton-kilometer? I am not sure how much lower. |
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Also, the advantage of a larger and faster train is higher capacity. |
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Did you know that Russia has plans to use Shinkansen trains *for freight* across the trans-siberian? |
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What would be cheaper is a worldwide network of HO/OO gauge trains for very small freight. For example, if you're a Chinese cigarette lighter manufacturer and you want to ship a consignment of cigarette lighters to Chicago, what better transport option would there be than a train several miles long of HO/OO goods wagons travelling north to Siberia, across the Bering Straits (on a cheap bridge - it won't be heavily loaded), down through Canada and the northwestern USA and then east to Chicago? |
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Trains crossing the Bering Strait would be an unbelieveably bad idea, as the continents won't behave. |
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// Trains crossing the Bering Strait would be an unbelieveably bad idea, as the continents won't behave. // |
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Seikan Tunnel is a great example of some pretty awesome engineering - but, like Rayford said, going across the Bering Straight is a whole other kettle of fish, due to you having to cross the fault-line of two entirely different continents. I'm not sure how you'd deal with one half of the tunnel moving by say 2cm a year in relation to the other half of the tunnel. After say, 5 years, your tracks might have a 10cm gap between them, or worse, been rammed into one another and buckled, or sheared from one another - whatever the overall movement, it's not good for train tracks. |
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The Seikan tunnel dealt with all manner of engineering problems, but massive continental drift was not one of them. |
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Apologies. Was a little rude on reading my comment. |
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The guts of my point though was that a long narrow train will pass through the air much more easily than a shorter train with a larger cross sectional area. This is directly related to energy consumption of engines. |
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Penguins would be long and skinny if they did not have to do other things like eat and poo as well as swim. Their form follows the sum of that which is necessary for them to be penguins; only a part of that is moving easily through the water. |
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Okay, I like it because rail is great. As they're touting on TV commercials right now, rail moves a ton of freight over 400 miles on one gallon of fuel. That's darned good. And it moves a mountain of freight when it moves any, so there's your economy of scale. |
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There are certain things that must be considered. Existing tunnels and bridges were designed for standard gauge rolling stock. Widening a tunnel is no mean feat, and you can't just widen the bridges - they'll have to built completely anew, for the new, heavier trains. This represents a serious hidden cost in this project. Across much of the Plains you can begin this project immediately, constructing supergauge feeder lines that run to existing standard gauge lines that cross the Rockies, Alleghenies, Appalachians, etc. |
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The idea of running such a massive train at such very high speeds is troubling. It would be a huge savings to run the train at just 300kmh - 186mph, faster than anything in the US that doesn't have wings - and sharply reduce the expected stresses on the vehicle and tracks. It would also sharply reduce the projected energy costs: aero drag isn't linear in its progression. |
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Besides, 300kmh gets you from coast-to-coast across the US in just 24 hours; if you need it there quicker you should have sent it yesterday. |
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Skin drag and pressure drag are both significant. The slower you go, the less there is of either. The "sweet spot" you mention isn't based on shape, it's based on money. What minimizes drag and fuel consumption while maximizing volume, transit speed? Find that number and you've got a winner. |
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The presumption that a bigger, heavier train can cruise faster than the TGV is bizarre. Why would you think that? It takes energy to get up to speed, and energy to keep the mass rolling, and God's Own Brakes to come to a sudden stop if an emergency demands it. |
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Alignment is everything on rails. Get it wrong and you go over the side. Here's why: |
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Imagine a wide, short drawer, like in a cheap dresser. Get it a little cockeyed and it jams. Now imagine a long, narrow drawer. Get it a little cockeyed and it still slides in smoothly. |
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These extra-wide train cars are like that short, wide drawer. There will be much more leverage between the couplings and the wheels trying to push the wheels right off the rails if the alignment should get a little off, if a strong gust of wind should push just right, or even if the car should flex too much. And since the car is so much wider, it will flex more. How fast do you want to be going when that happens? |
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300kmh is a great speed - even 200kmh will get you completely across the country much, much faster than if you drove. And the wider cars are a great idea. But I think you've leapt a little farther than you've looked. |
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I'm bunning it anyway, because I love trains and I think they are the wave of future transportation. |
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If you scale all dimensions of the train up equally, then I think that things work in your favour - your surface area per unit volume decreases, so you have less drag per unit volume. This gets you a more efficient train. Your motors increase in size along with everything else, so your power to weight ratio is constant. Your brakes get bigger, so your braking power per unit mass is the same. |
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Of course it will use more power, it's twice as big. At a given speed, it will use less than twice as much power though. Fuel costs per kilogram transported will be lower. Alternatively, for the same fuel cost, you can go faster. |
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According to the link both sides of the Bering Strait are on the North American Plate. Where is this fault line you speak of? |
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// The presumption that a bigger, heavier train can cruise faster than the TGV is bizarre. Why would you think that? // |
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The only reason that a TGV doesn't cruise faster than it does is economics, not engineering limitations. A TGV cruising at 500 km/h uses too much energy per passenger to be competitive. That's why they have to slow it down to 320 km/h. |
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A bigger train uses less energy per passenger. Therefore it could cruise economically at a higher speed. |
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Ah - right you are, I just assumed that the plate would split at the junction between two 'continental' masses. My mistake. Carry on. |
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We're still going to have to manage the continental drift thing at other places where we cross between one continent and another - at least it's more convenient to deal with these things if they're above ground. |
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//The guts of my point though was that a long narrow train will pass through the air much more easily than a shorter train with a larger cross sectional area// |
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Can you actually show me a theory that explains this or are you just speculating? I would be glad to know for sure. I'm still pretty sure that my theory is correct. But I might be wrong of course. I wish somebody here had a degree in fluid dynamics... |
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Thought experiment: Take short cylinder of *constant volume* and keep stretching it until it gets thinner and thinner. |
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Does the total drag force on this cylinder keep getting smaller and smaller, or does it reach a minimum at some point and go up again? |
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Let's look at the limiting case: The total surface area of this cylinder is given by A=2* (pi*V*l)^0.5, where V is the constant volume and l is the length. If the length tends to infinity, then so will the area. Therefore, also the skin friction component of the drag becomes infinitely high for and infinitely long and thin cylinder (ie. a line). |
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Conclusion: There IS such a thing as an optimum shape somewhere between a sphere and a spaghetti. |
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The question is, is a train with dimensions 400m x 3m x 4m already thinner than the optimum? I think so. |
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From an university earodynamics lecture: |
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"The fuselage should also be designed with the optimum fineness ratio. This ratio (length/width) is too large on most aircraft (i.e. they are too long and skinny, which increases skin friction.) The optimum shape is much more "egg like" as on the Questair Venture." |
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I was going to write in saying that longer thinner shapes are more aerodynamic that wider shorter shapes, using such common examples as aircraft (ever seen any penguin shaped aircraft?), bullets (all the long range cartridges are long and thin), displacement hull sail boats (here it is hydrodynamic drag, but that just changes the density figure, shapes that are hydrodynamic are also aerodynamic, and longer sailboats ALWAYS win.) and ocean mammals (I’ll take your penguin and raise a bottlenose dolphin or false whale), but a quick search of the web is finding that trains are weird aerodynamic objects and skin effects really do make a lot of difference. I guess a train is aerodynamically more like a needle (length to width) than a bullet. Not enough to double the speed, as drag increases with the square of the velocity, but a bunch. |
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//ever seen any penguin shaped aircraft?// |
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The Questair Venture apparently. |
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Giant ground-effect aircraft crossing the seas would be a better solution. Less infrastructure cost and similar economies of scale. |
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If you check the other information from the link that you provided - just on a different page- you will find that they state that form, or pressure drag is the principle parasitic drag on an object moving through the air, not surface friction. Yes it plays a part, but a longer, thinner object (more pencil shaped) will always move through the air more easily than one of the same volume that is wider, a more aerodynamic shape will simply allow it to approach the long slender model's efficiency, not exceed it. |
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I disagree. Consider the near-infinite case - something with unit volume, but a length of ten kilometres or so, in free fall. That's going to see much higher drag than something with unit volume, of teardrop proportions. |
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(If not, then raindrops, whose shape is dictated primarily by gravity and drag, would be needle shaped and not teardrop shaped!) |
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Well, no David, the raindrop is also bound by surface tension and tends towards a spherical shape. It would fall as such if not affected by drag, which is what pulls it into the shape of a teardrop as it falls. A long needle shape will fall faster. It is more streamlined, but water will not retain this shape in freefall. |
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Where do you think there are no engineering limitations in your concept? The TGV is kept to its lower speed in large part due to the extreme discomfort experienced by passengers at the highest speed. The vibration and air pressure inside the cars become very uncomfortable. |
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Don't forget that those same factors exist in your concept, because there's air everywhere. Vibration is a fact of moving vehicles. I'd hate to see one of the wheels fracture at top speed. |
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You could conceivably make each car airtight and pressurized, but that adds complexity and weight. Granted, weight is a lot less of an issue on a train than an aircraft, but it's still there and it doesn't generate any revenue on its own. |
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"A big train uses less energy per passenger." Well, yes, but that advantage completely goes away - and then some, I'm guessing - if you nearly double the speed. You might be pulling power for only half the time, but you're pulling eight times as much. |
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I realise that surface tension plays a part; hence the "primarily". |
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Turns out I'm wrong about raindrops anyway (see link). |
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However, for a given set of conditions, there is an optimum "fineness ratio" i.e. ratio of length to cross-sectional area (see next link). Granted, this is only a precis of an article not available to the general public, but have a look and you might see where I'm coming from. |
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Wider, thicker, further apart rails embedded in a more massive base are less bumpy. |
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I don't think full pressurization would be necessary at 500 km/h, as long as you make the cabin airtight enough. This is already done with the TGV. The Shanghai maglev travels at 430 km/h and doesn't need pressurization either. |
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"Wider, thicker, further apart rails embedded in a more massive base are less bumpy." |
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At 500kmh what appear to be very broad, shallow dips and rises become very sharp potholes and bumps. Constructing the railway for such a high-speed line will require the most precise sort of equipment and control. |
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Not that that cannot be done - the Chunnel drillers met in the middle with a misalignment of only half an inch. But it'll add to the cost of construction. The payback is going to take a while. |
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No, full pressurization is not necessary, but pressure control certainly is. The cars will need to be sealed, the passages between cars will need to be sealed, etc. Simple scoops oriented fore and aft can add and release pressure as needed, need determined by automated systems. Again, though, that's just another thing that adds to the complexity. |
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I like the whole idea, I really do. It was Brunel, I think, who ran several supergauge lines across the UK; that's something you may enjoy reading up on. |
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//If you scale all dimensions of the train up equally, then I think that things work in your favour// - [david_scothern] You forgot the square/cube law: you have to scale up the strengths of your materials simultaneously or you're going to have problems. Particularly with brakes, wheels and axles. |
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[Lurch] You're right - your axles have to get stronger as you scale the vehicle's height, all other things being equal. With width (assuming simple scaling, as if the cross-section was stretched sideways in MS Paint) there need be no effect, as your contact patch widens proportionally. To minimise bending moments in that case, you might want more rails. But yes, with height your strength must increase. For similar reasons, large mammals can typically jump no higher than small mammals can. |
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I'm going to ask a question, it's a bit imprecise and woolly, but nonetheless here it is:
- If large vehicles are no more efficient than small ones, then why are cargo carriers typically made as big as possible? It's true of trucks, ships and aircraft. |
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I can't believe that it's purely about minimising the crew's wage costs - take a look at the Emma Maersk (massive container ship) for instance, and tell me that using one crew instead of two (one ship instead of two) was sufficiently attractive to spend the tens of millions developing and building the ship? |
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I know, it's not a knockout argument. But I'm going to suggest that it's relevant. |
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Anyhow, as I mentioned above, a google search on "optimum fineness ratio" says that there is a balance to be sought between minimal frontal area and minimal surface area, for lowest drag at a given speed, density etc. |
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Larger vehicles *are* more efficient per unit volume than small vehicles. This is easy to prove if you consider the limiting cases. |
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Volume ~ length^3;
Total drag ~ length^2 |
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Therefore if length becomes infinite drag/volume becomes zero. |
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So, if we had an infinitely long train, drag would be zero? Would a train that wrapped around the world and swallowed it's own tail be close enough? |
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"Therefore if length becomes infinite drag/volume becomes zero" |
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What? Drag is a function of surface friction, surface area, and velocity. Drag/volume does not ever become zero unless your vehicle is AT REST. And if your vehicle is infinitely long, then the value of drag, unless it can be reduced to zero - which you cannot do - must also be INFINITY. |
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Class is over. You are dismissed. |
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// So, if we had an infinitely long train, drag would be zero?// |
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No. If we had an infinitely LARGE train DRAG/VOLUME would be zero. |
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Look up the concept of "mathematical limits" before you make a fool of yourself. I guess you are still in middle school and haven't covered that topic yet, so I'll try to explain: |
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When lenght becomes infinite, both drag and volume become infinity. |
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Infinity divided by infinity is NOT always infinity. It depends on how you define infinity. |
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In this particular case infinity/infinity is defined as
length^2 / lenght^3 when length tends to infinity. This expression becomes zero. |
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Every time I see this idea, I read it as
"Intercontinental Super-Bread Guage
Railway". |
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[map] No Australian beef, coal or wheat for you! |
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Thanks for the hamburger raindrops [David] |
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The majority of drag on a train is from the frontal surface area of the train, therefore, they should be kept as small in this dimension as possible. |
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Skin friction plays a very minor part (in terms of total drag) in comparison, so total surface area, while not irrelevant, is very much a secondary consideration in train design. |
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So an increase in length (increased total surface area) has little bearing on the total amount of drag, while an increase in width and height (increased frontal surface area) increases total drag dramatically. |
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So a longer thinner train is more efficient and is more easily able to travel at higher speeds than a shorter fatter train of the same volume. |
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Please see the link, it is a different page of the site that you linked to. |
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"It depends on how you define infinity." |
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I hadn't resorted to personal attacks against you, and I won't now. I'm sorry you felt compelled to do so. |
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You seem to be forgetting certain aspects of your own idea while raising "infinity" as a supporting value in your stated formulae. I haven't bothered with the formulae, and certainly I concede that infinity will make values trend toward zero when applied correctly, and toward infinity when applied in other ways. However, infinity is not a useful value in this context, and to even mention infinity in this context while trying to support your idea is ludicrous. You shouldn't have done it. |
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Taken from link "Train Drag Coefficients" above: |
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/Train drag coefficient for different train lengths can be expected to vary approximately in direct proportion to length, with a minimum cd of about 0.3 for a train consisting of a single power car of optimum aerodynamic design. For such an optimized design each additional car will increase cd by about 0.075. For current high-speed train designs, typified by the TGV, each car will increase cd by about 0.10./ |
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In other words, the drag at the nose and tail is a lot more important on a short train (end effects dominate) than on a long one. There exists an optimum length to cross-sectional area ratio. |
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Yeah, but--in hopes of side-tracking (heh) that discussion--if you double the frontal area of the train, you are doubling the volume (for the same length). So you can halve the speed and still get the same amount of freight transported. (Or something like that.) |
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This thing will be faster than a ship door-to-door. We could run it at 5 mph from Topeka to Tashkent and still save time over many other methods of transport. |
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"Platform 17 for the Continent. Platform
12 for the incontinent." |
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//I hadn't resorted to personal attacks against you, and I won't now. I'm sorry you felt compelled to do so.// |
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Personal attack or no personal attack, you wrote your post in condescending tone. |
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Quote: "Class over. You are dismissed" |
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If you like to use insults to support your argument then expect insults in return! Hint: My response was a tongue-in-cheek jab at your schoolboy-themed language, not a personal attack. |
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// However, infinity is not a useful value in this context// |
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I never said it was a useful value. It is a useful abstraction to find out what a function does as x gets larger and larger. |
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Given constant aspect ratio, what happens to drag/volume as length tends to infinity? It tends to zero. |
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There you go. I've used the word "infinity" to support my argument. My apologies. |
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// and to even mention infinity in this context while trying to support your idea is ludicrous. You shouldn't have done done it // |
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more of that condescending tone... |
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OK, leave it there or take it to email. |
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As I said way up there, you should have left the figures out. |
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