30-08-2014, 11:59 AM
Maglev Trains rains
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Abstract
Technical trials on a maglev train track began in Japan in the 1970s, and a speed of 500 kph/310 mph has been reached, with
a cruising altitude of 10 cm/4 in. The train is levitated by electromagnets and forward thrust is provided by linear motors
aboard the cars, propelling the train along a reaction plate
Introduction
Did you ever see a train without any wheels? Did you
ever think of using magnets to get around? Well, Robert
Goddard and a few other scientists did. I'm going to
tell you about their invention, the ‘MAGLEV
TRAINS’.
The Magnetic Levitating Train or Maglev Train was
first constructed in the 1960's. The Japanese tried to
build one in the 1960's but did not have enough
knowledge of magnets and it was a glichy experiment.
Not until recently did they pick up on their experiment
to create the maglev train. Maglev trains have come a
long way. It all started with just a few trains in Germany
and with one train in Japan. Now the idea has spread.
Principle of Maglev
Maglev is a system in which the vehicle runs levitated
from the guideway (corresponding to the rail tracks of
conventional railways) by using electromagnetic forces
between superconducting magnets on board the vehicle
and coils on the ground. The following is a general
explanation of the principle of Maglev.
Principle of magnetic levitation:
Principle of magnetic levitation: The "8" figured Principle of magnetic levitation:
levitation coils are installed on the sidewalls of the
guideway. When the on-board superconducting
magnets pass at a high speed about several centimeters
below the center of these coils, an electric current is
induced within the coils, which then act as
electromagnets temporarily. As a result, there are forces
which push the superconducting magnet upwards and
ones which pull them upwards simultaneously, thereby
levitating the Maglev vehicle.
Developing Technology
Maglev train technology is a popular topic of
transportation conversation in several countries.
Germany and Japan are both developing maglev train
technology, and both are currently testing prototypes
of their trains. (The German company "Transrapid
International" also has a train in commercial use -- more
about that in the next section.) Although based on
similar concepts, the German and Japanese trains have
distinct differences
Are Maglev Trains Safe?
Maglev trains have proven to be exceptionally safe,
quiet, and fast. Beacause there's no friction with the
ground, maglev trains are much more quiet than trucks
and automobiles. The only sound caused by the trains
is the 'whoosh' as the train goes by from the air friction.
Farmers in Germany who have trains running over
their fields, when asked about how the feel about the
trains running through their farm replied "We don't
even know it's there". Cows don't even lift their heads
when trains come through at 250mph. Maglev trains
are also almost accident free. They are above any
obstacles on the ground and are enclosed in or around
the track. Also the propulsion system caused by the
magnetic fields disallows trains to come to close to other
trains on the track.
The first official Maglev line: 2004, Shanghai opened
line between the airport and the financial district. line between the airport and the financial district.
The lenght of this line is 30km, the possible top speed
on this route: 432km / hr..
Maglev is an acronym for: Magnetic Levitated. Magnetic Levitated.
Maglev Suspension Versus Wheeled Suspension
Cited advantages of maglev trains over wheeled trains
(1, 12) include:
1. Wheels produce medium to high environmental
noise levels.
2. Wheeled systems rely on propulsion through
wheel-rail friction, and the high aerodynamic drag
forces lead to upper speed limits due to limited
wheel-rail adhesion.
3. Maglev vehicles can accelerate and decelerate
rapidly and bank steeply on curves.
4. Suspension through point contact (up to 70,000
psi or 482 MPa) leads to increased structural
requirements and increased wear/maintenance.
Frequently Asked Questions
How fast can maglev trains travel?
As long as the track is straight enough that the train
doesn't experience severe accelerations up, down, left,
or right, there is no limit to how fast it can go. In fact,
the levitation process becomes more and more energy
efficient as the speed increases. However, the moving
train does experience a pressure drag force (a type of
air resistance) that increases roughly as the square of
the train's speed. The power needed to overcome this
drag force increases as the cube of the train's speed,
making it impractical to propel the train forward above
a certain speed.
What would be a legitimate form of propulsion for
magnetic trains?
The most sensible propulsion system for a magnetically
levitated train would be a linear electric motor. This
motor would consist of electromagnets on the train and
electromagnets on the track. By turning these
electromagnets on and off at carefully chosen moments,
they can be used to pull or push the train forward for
propulsion or backward for breaking. The timing is
important because, for propulsion, the magnet on the
train must always be attracted toward the track magnet
in front of it and repelled by the track magnet behind
it. For breaking, this relationship must be reversed.
How does a magnetic train work? How can I make
an experiment with it for a school project?
There are many techniques for supporting a train on
magnetic forces, but the simplest and most promising
involves electrodynamic levitation. In this technique,
the train has a strong magnet under it and it rides on
an aluminum track. The train leaves the station on
rubber wheels and then begins to fly on a cushion of
magnetic forces when its speed is high enough. Its
moving magnet induces electric currents in the
aluminum track and these currents are themselves
magnetic. The train and track repel one another so
strongly with magnetic forces that the train hovers tens
of centimeters above the track.
To demonstration this effect, you can lower a very
strong magnet above a rapidly spinning aluminum disk.
In my class, I spin a sturdy aluminum disk with a motor
and lower a 5 cm diameter disk magnet onto its surface.
I hold the magnet firmly with a strap made of duct
tape, so that the magnet won't fly across the room or
flip over as it descends. Instead of touching the spinning
disk, the magnet floats about 2 cm above it. If you try
this experiment, don't spin the aluminum disk too fast
or it will tear itself apart. It should spin about as fast as
an electric fan on high speed. Also, be careful with the
magnet, because it will experience magnetic drag forces
as well as the magnetic lift force. If you don't hold tight,
it will be yanked out of your hand.
For a simpler experiment that anyone can do, float an
aluminum pie plate in a basin of water and circle one
pole of a strong magnet just above its surface. The pie
plate will begin to spin with the magnet. You are again
inducing currents in the aluminum, making it
magnetic. While the forces here are too weak to lift the
magnet in your hand, they are enough to cause the pie
plate to begin spinning, even though you never actually touch it. This technique is used in many electric
motors. That's physics for you--the same principles just
keep showing up in seemingly different machines.
If magnetic trains are to work, wouldn't friction on
the bottom of the train create thermal energy which
would destroy the magnetism of the train?
When a magnetically levitated train is operating
properly, it doesn't touch the track and experiences no
friction. In principle, it shouldn't get hot at all. The
magnetic drag effect will warm the track slightly, but
that won't matter to the train's magnets. Actually, the
train's magnets will almost certainly be
superconducting wire coils with currents flowing in
them. That type of magnet doesn't depend on the
magnetic order of permanent magnets. It's the magnetic
order of permanent magnets that is destroyed by heat.
An electromagnetic coil will stay magnetic as long as
current flows through it, even if it's so hot that it's ready
to melt.