Maglev (derived from magnetic levitation) is a method of propulsion that uses magnetic levitation to propel vehicles with magnets rather than with wheels, axles and bearings. With maglev, a vehicle is levitated a short distance away from a guide way using magnets to create both lift and thrust. High-speed maglev trains promise dramatic improvements for human travel if widespread adoption occurs.[1] Maglev trains move more smoothly and somewhat more quietly than wheeled mass transit systems. Their non-reliance on traction and friction means that acceleration and deceleration can surpass that of wheeled transports, and they are unaffected by weather. The power needed for levitation is typically not a large percentage of the overall energy consumption;[2] most of the power is used to overcome air resistance (drag), as with any other high-speed form of transport. Although conventional wheeled transportation can travel very quickly, a maglev system allows routine use of higher top speeds than does conventional rail, and it is this type which holds the speed record for rail transportation. Vacuum tube train systems might hypothetically allow maglev trains to attain speeds in a different order of magnitude. While no such tracks have been built commercially yet, there are efforts being made to study and develop super-maglev trains.[3] Compared to conventional wheeled trains, differences in construction affect the economics of maglev trains. In wheeled trains at very high speeds, the wear and tear from friction along with the hammer effect from wheels on rails accelerates equipment deterioration and prevents mechanically based train systems from routinely achieving higher speeds.[4] Conversely, maglev tracks have historically been found to be much more expensive to construct, but require less maintenance and have lower ongoing costs. Despite decades-long research and development, there are presently only two commercial maglev transport systems in operation, with two others under construction.[5] In April 2004, Shanghai began commercial operations of the high-speed Transrapid system. In March 2005, Japan began operation of the relatively low-speed HSST Linimo line in time for the 2005 World Expo. In its first three months, the Linimo line carried over 10 million passengers. South Korea and the Peoples Republic of China are both building low-speed maglev lines of their own design, one in Beijing and the other at Seouls Incheon Airport. Many maglev projects are controversial, and the technological potential, adoption prospects and economics of maglev systems have often been hotly debated. Evacuated tubes Some systems (notably the Swissmetro system) propose the use of vactrains—maglev train technology used in evacuated (airless) tubes, which removes air drag. This has the potential to increase speed and efficiency greatly, as most of the energy for conventional maglev trains is lost to aerodynamic drag.[42] One potential risk for passengers of trains operating in evacuated tubes is that they could be exposed to the risk of cabin depressurization unless tunnel safety monitoring systems can repressurize the tube in the event of a train malfunction or accident. The RAND Corporation has depicted a vacuum tube train that could, in theory, cross the Atlantic or the USA in ~21 minutes. Comparison with aircraft For many systems, it is possible to define a lift-to-drag ratio. For maglev systems these ratios can exceed that of aircraft (for example Inductrack can approach 200:1 at high speed, far higher than any aircraft). This can make maglev more efficient per kilometre. However, at high cruising speeds, aerodynamic drag is much larger than lift-induced drag. Jet transport aircraft take advantage of low air density at high altitudes to significantly reduce drag during cruise, hence despite their lift-to-drag ratio disadvantage, they can travel more efficiently at high speeds than maglev trains that operate at sea level (this has been proposed to be fixed by the vactrain concept). While aircraft are theoretically more flexible, commercial air routes are not. High-speed maglevs are designed to compete on journey times with flights of 800 kilometres (500 miles) or less. Additionally, while maglevs can serve several cities in between such routes and be on time in all weather conditions, airlines cannot come close to such reliability or performance. Because maglev vehicles are powered by electricity and do not carry fuel, maglev fares are less susceptible to the volatile price swings created by oil markets. Travelling via maglev also offers a significant safety margin over air travel since maglevs are designed not to crash into other maglevs or leave their guideways.[51][52][53] Aircraft fuel is a significant danger during takeoff and landing accidents. Speed Records The highest recorded speed of a maglev train is 581 km/h (361 mph), achieved in Japan by JR Centrals MLX01 superconducting maglev in 2003,[59] 6 km/h (3.7 mph) faster than the conventional TGV wheel-rail speed record. However, the operational and performance differences between these two very different technologies is far greater than a mere 6 km/h (3.7 mph) of speed. For example, the TGV record was achieved accelerating down a 72.4 km (45.0 mi) slight incline, requiring 13 minutes. It then took another 77.25 km (48.00 mi) for the TGV to stop, requiring a total distance of 149.65 km (92.99 mi) for the test.[60] The MLX01 record, however, was achieved on the 18.4 km (11.4 mi) Yamanashi test track – 1/8 the distance needed for the TGV test.[citation needed] While it is claimed high-speed maglevs can actually operate commercially at these speeds while wheel-rail trains cannot, and do so without the burden and expense of extensive maintenance, no maglev or wheel-rail commercial operation has actually been attempted at these speeds over 500 km/h.
Posted on: Sat, 14 Jun 2014 22:56:22 +0000
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