The TGV (Train a Grande Vitesse) is the French high speed train. Of
course, there is no such thing as the TGV; there are many significant differences
among the 350-odd trainsets in service today, and the name TGV refers to much
more than just the trains. Indeed, the TGV is a system which comprises train,
track, and signalling technologies that when combined make high speeds (typically
300 km/h, or 186 mph) possible. The TGV system is owned and operated by SNCF,
the French national railways, and is an integral part of French rail travel. e8u3ud
The TGV program was launched in the late 1960s. In its early stages, the program
was considered a technological dead end. Conventional wisdom at the time held
that steel wheel on steel rail technology had been explored and understood to
its fullest, and it was time to move on to more innovative technologies like
magnetic levitation and jet-powered hovertrains. As a result, the project did
not originally receive any government funding.
SNCF's idea for the TGV was to develop a high speed rail system that remained
compatible with the existing railway infrastructure. This had the important
benefit of allowing high speed trains to use existing facilities in the heart
of many cities, where building any new tracks or stations would have been prohibitively
expensive. Another advantage was the possibility of running TGV trains to many
destinations over existing trackage, after a high speed dash on a dedicated
trunk line. Clark Kent on conventional track, and Superman on special dedicated
track. Finally, having a high speed rail system that fully integrates into the
existing rail network makes it possible to build new high speed lines gradually,
opening them section by section.
The first prototype train, the TGV 001, started an extensive testing program
in the early 70's. images/proto/tgv001vsg.jpg
images/proto/tgv001vsg.jpgThe TGV 001 (photo by Jean-Paul Lescat) was powered
by a gas turbine, and on 8 December 1972, it set the world speed record for
a train in autonomous traction, at 318 km/h (198 mph). This record still stands,
23 years later. (The world's fastest diesel train is a Russian TEP80 locomotive,
with 273 km/h (147 mph). The TGV 001 made more than 175 runs at speeds in excess
of 300 km/h (186 mph) and along with other prototype trains provided valuable
engineering data for the development of the production TGV. A more detailed
history can be found elsewhere in these pages.
A completely new line was built beginning in the late seventies, running from
Paris most of the way to Lyon. On 27 September 1981, the first section of the
line was opened to revenue service by president François Mitterrand,
and the streamlined, bright orange trains became instant celebrities. It helped
that just a few months before, one of the new trainsets had smashed the world
speed record (held since 1955 by a pair of French electric locomotives) with
a run at 380 km/h (236 mph).
The new TGV was incredibly successful, and gutted the Paris-Lyon airline business.
It became one of the few parts of SNCF that turned a significant profit, and
completely payed for itself (including construction costs) in only a decade.
The French government, faced with this success, hailed the new system and offered
its backing for further development of the nascent high speed rail network.
The TGV had become a technological symbol associated with France.
Since then, new TGV lines and trains have been built, and improvements made
with each generation. In 1989, the TGV Atlantique made its debut, serving points
west of Paris. The trains incorporated many improvements over the earlier Sud-Est
generation, a sign of the continuing research and development being conducted
by SNCF and its contractors. Most notably, the 1981 record was pushed to 515.3
km/h (320.3 mph) on 18 May 1990, using the newer generation equipment. This
is also the subject of other documents in these pages.
Today, there are three major trunk lines radiating out of Paris, the most recent
one being the Nord-Europe line, opened in 1993 and connects Paris to Lille,
Belgium, the Netherlands, Germany, and Britain through the Channel tunnel. Extensions
continue to be built, although budgetary constraints have slowed the momentum
of the TGV expansion.
TGV technology has been a contender in many export ventures, to Spain (operating),
South Korea (under construction), the United States (awarded), Taiwan (awarded),
China, etc. TGV trains now visit many parts of Europe, including Germany, Britain,
Italy, Belgium, the Netherlands, and Switzerland.
What Makes the Train Special?
Looking at the train itself, the most striking aspect, to the newcomer, is the
aerodynamic styling of the nose. But that is not where the innovation lies.
Perhaps the most interesting feature of a TGV trainset is its articulation.
The cars are not merely coupled together; instead, they are semi-permanently
attached to each other, with the ends of two adjacent cars resting on a common
two-axle truck. It is thus more appropriate to speak of 'trailers' than of 'cars'.
There are several good reasons for this design. Perhaps the most obvious is
that the TGV was designed from the beginning to be a very lightweight train;
even with an axle load limit of only 17 metric tons, it made sense to reduce
the number of axles. Placing the wheels between the trailers also reduces interior
noise levels, provides more space and a higher plane for the suspension, and
improves aerodynamics (due to the lower height and small inter-trailer gaps).
Articulation of the train also allows adjacent trailers to be dynamically coupled
by dampers, and makes possible a clean, quiet passage from one trailer to the
next. Articulation has also proved to be an important safety feature, preventing
TGV trains from jack-knifing in a collision as a conventional train might.
TGV trainsets are essentially symmetric and reversible, with a locomotive, also
called power unit or power car, coupled at each end. the trailing power unit
collects power from the overhead electric catenary, and feeds power to the leading
power unit through a cable running along the roof of the train. This single-pantograph
arrangement prevents one pantograph from disturbing the wire and thus disrupting
the contact for the following pantographs. The pantographs themselves are among
the most sophisticated, some featuring active damping.
The brakes are suited for running at high speed. They are capable of dissipating
a very large amount of energy. The locomotives each have dynamic brakes, in
addition to brake shoes for emergency stops. The trailers are equipped with
four disks per axle, and in some cases backup brake shoes. Future models might
include magnetic induction track brakes.
Another innovation in the TGV system is the exclusive use of in-cab signalling
for high speed running. TGV lines do not have lineside signals; they are too
difficult to read at speed. All signalling information is transmitted to the
train through the rails, and appears to the engineer in the cab. In general,
TGV trainsets are heavily computerized, and many important functions are controlled
What Makes the Tracks Special?
Dedicated TGV lines use no special technology-- just welded rails laid on hybrid
steel and concrete ties, over a thicker than usual bed of ballast. The greatest
difference lies in the combination of curve radii and superelevation that make
high speed possible; a 5 km (3 mi) radius would be considered tight. The track
centers are spaced further apart than usual, to reduce the blast of two crossing
trains. Signalling blocks measure 1500 m (5000 ft) and certain lines allow one
train every three minutes. The catenary is of completely standard design, essentially
identical to 25 kV equipment on other French lines. The track and catenary are
aligned and tuned specially for high speed.
Safety, as usual in railways, is a top concern. High speed lines are completely
fenced off, and grade separated. Rolling stock is maintained in top condition.
The TGV safety record speaks for itself; there have been no casualties in 17
years of daily operation at speeds up to 300 km/h (186 mph). That is not to
say there have not been incidents... The most spectacular of which was the December
1993 derailment of a TGV-Réseau trainset, at a speed of 294 km/h (183
mph). This, and all other major incidents, are detailed elsewhere in these pages.
More background about the TGV and its context in railway history can be found
in the Encyclopedia Britannica.
What's in These Pages
For more specific information regarding the various aspects of the TGV program
as described above, go back to the table of contents and select the topic you
wish to explore in more depth.
Last modified: Sat Mar 28 11:36:54 PST 1998
EARLY TGV HISTORY
THE IDEA of a high speed train in France was born about 20 years before the
first TGVs entered service. At that time, about 1960, a radical new concept
was thought up; combining very high speeds and steep grades would allow a railway
to follow the contours of existing terrain, like a gentle roller-coaster. Instead
of 1 or 2 percent grades which would be considered steep in normal applications,
up to 4 percent would be feasible, thus allowing more flexible (and cheaper)
routing of new lines. Over the next several years, this very general idea gave
rise to a variety of high speed transportation concepts, which tended to move
away from conventional wheel on rail vehicles. Indeed, the French government
at the time favored more "modern" air-cushioned or maglev trains,
such as Bertin's AeroTrain. Steel wheel on rail was (wrongly) considered a dead-end
technology, the ugly duckling of the quest for higher speeds.
Simultaneously, SNCF (the French national railways) was trying to raise the
speeds of conventional trains into the range 180 to 200 km/h (110 to 125 mph)
for non-electrified sections, by using gas turbines for propulsion. Energy was
reasonably cheap in those years, and gas turbines (originally designed for helicopters)
were a compact and efficient way to fulfill requirements for more power. Following
on the TGS prototype in 1967, SNCF introduced gas turbine propulsion with the
ETG (Elément a Turbine a Gaz, or Gas Turbine Unit) turbotrains
in Paris - Cherbourg service, in March 1970.
The desire for higher speeds and the successful development of the turbotrain
program are two ideas that came together in the late 1960s, further spurred
on by the 1964 start of the Japanese Shinkansen high speed train. They were
embodied in a joint program between SNCF and industry to explore the possibility
of a high speed gas turbine unit. The project, initiated in 1967, was entitled
"Rail Possibilities on New Infrastructures" and was code-named C03.
The experimental X4300 TGS railcar, predecessor of the ETG, had been tested
at speeds up to 252 km/h (157 mph) in October of 1971, and gave promising results.
Since the very high speed lines envisioned by SNCF called for speeds of 250
km/h to 300 km/h (186 mph), SNCF had Alsthom-Atlantique build a special high
speed turbotrain prototype to test out some concepts in high speed rail. Thus
was born the turbotrain TGV (Très Grande Vitesse, or Very High Speed)
The TGV 001 Turbotrain images/proto/tgv001vsg.jpg
The TGV 001 turbotrain was a test train for a vast research program encompassing
traction, vehicle dynamics, braking, aerodynamics, signalling, and other technologies
that needed to be developed to allow higher speeds. Only one was ever built,
although it was originally planned to build a second version equipped with an
active tilt system. The studies for the tilting version were completed, but
it never reached construction because of technical difficulties with fitting
the tilt system.
The TGV 001 consisted of two power cars with three trailers in between, the
whole trainset permanently coupled together. All axles were powered by electric
motors, with the advantage of low axle loads and a high power to weight ratio.
Electric traction also made possible dynamic braking, especially effective at
high speeds. Each power car had a pair of turbines (the TURMO IIIG and then
the TURMO X, used in Sud Aviation's Super Frelon helicopter) which ran at constant
speed. They were connected to a reductor stage, whose output shaft drove an
alternator. Besides the turbine drive, the power cars had control gear for the
traction motors, dynamic brake grids, signalling and braking equipment, etc.
The TGV001 was articulated, with adjacent vehicles riding on a common truck.
This afforded a greater stability (by coupling the dynamics of carbodies) and
made space for a pneumatic secondary suspension placed level with the center
of gravity, thus reducing roll in curves.
SOME TECHNICAL SPECIFICATIONS OF THE TGV 001
Consist: Turbine + 1st class + lab car + 2nd class + turbine
Length: 92.90 m
Width: 2.81 m
Height: 3.40 m
Truck wheelbase: 2.60 m
Truck centers: 14.00 m (power car) and 18.30 m (trailers)
Weight: 192,000 kg
Power: 3760 kW (TURMO III) and 4400 kW (TURMO X)
Top Speed: 280 km/h (TURMO III) and 300 km/h (TURMO X)
Range: 1100 km
Fuel capacity: 8000 l
PLAN AND ELEVATION VIEWS (1000 x 1500 pixels)
In 5227 test runs covering almost half a million kilometers, the TGV 001 turbotrain
exceeded 300 km/h (186 mph) on 175 runs and reached a top speed of 318 km/h
(198 mph) on 08 December 1972. This was (and still is) the world speed record
for a non-electric train. The TGV 001 test campaign was an invaluable part of
project C03, proving new concepts in a realistic environment and giving extensive
engineering data on high speed operation.
Electric Power images/proto/z7001.jpg
With the oil crisis of 1974, it no longer seemed economically viable to power
the future high speed train with fossil fuels. The requirements were changed
to fully electric operation, which resulted in an extensive redesign and test
program. In April of 1974, the Z7001 experimental electric railcar, nicknamed
"Zébulon", began trials. Zébulon was rebuilt from the
Z7115, aImagesi which had been wrecked. Using this vehicle, the new Y226 long-wheelbase
power truck (precursor of the Y230 aImagei of the production TGV) was developed
and tested, with its body-mounted traction motors and tripod cardan transmission.
Body mounting of the traction motors was a major innovation; it allowed a considerable
(3300 kg) reduction in the mass of the power truck, giving it a very high critical
speed and exceptional tracking stability. Zébulon also served to develop
a two-stage high speed pantograph, which later became the AM-PSE pantograph
of the TGV Sud-Est, as well as a new type of eddy current rail brake. The eddy
current rail brake exerts a magnetic retention effort, without ever making contact
with the rail. The promise of high efficiency and low wear was however outweighed
by problems with overheating in the rail, and the design was dropped. Zébulon's
suspension, of a non-pneumatic design, gave full satisfaction so it was adopted
for the new high speed train, instead of the TGV 001's pneumatic suspension.
Over a period of 20 months, Zébulon racked up almost a million kilometers,
25000 of which were run at speeds over 300 km/h (186 mph). The highest speed
reached by Zébulon was 309 km/h (192 mph). Prospects were good for project
C03, which was fully funded by the French government in 1976. Construction of
an electric high speed line from Paris to Lyon began soon after.
Styling: Something New and Different
The styling of the original TGV, inside and out, is due to industrial designer
Jack Cooper. He was born in Britain in 1931, before moving to France. In the
mid 1950s, he spent several years working under American designer Raymond Loewy,
whose most famous designs included the Pennsylvania Railroad's GG-1 electric
locomotive aImagesi. As early as 1968, when he began working for Alsthom, Jack
Cooper was asked to draw up a "train that didn't look like a train".
He designed the TGV 001 turbotrain's look, inside and out, and soon thereafter
the TGV design was born. As early as 1975, Cooper was drawing trains that looked
surprisingly like the TGV Duplex of twenty years later! While Cooper's design
for the train's exterior was immediately accepted, he was sent back to the drawing
board numerous times while trying to come up with the interior design, which
included everything from seats to door handles.
The many design requirements were sometimes in conflict, and Cooper had to find
an optimal solution. The interior spaces had to be welcoming and comfortable,
restful, quiet, easy to clean and fix, and smoothly integrated together to create
a uniform atmosphere. Comfort was to be made accessible to all passengers while
retaining a certain status and flair. The overarching aim was to design an interior
space that was both relaxing and enjoyable.
By the late seventies, the design of the first TGV was complete. The first batch
of production trainsets was ordered on 4 November 1976. Over the next twenty
years, over 600 copies of Cooper's world-famous TGV nose would be built.
Last Minute Problems
On 28 July 1978, two pre-production TGV trainsets left the Alsthom factory in
Belfort. These would later become TGV Sud-Est trainsets 01 and 02, but for testing
purposes they had been nicknamed "Patrick" and "Sophie",
after their radio callsigns. In the following months of testing, over 15,000
modifications were made to these trainsets, which were far from trouble-free.
High speed vibration was a particularly difficult problem to root out: the new
trains were not at all comfortable at cruising speed! The solution was slow
in coming, and slightly delayed the schedule. Eventually it was found that inserting
rubber blocks under the primary suspension springs took care of the problem.
Other difficulties with high speed stability of the trucks were overcome by
1980, when the first segment of the new line from Paris to Lyon was originally
supposed to open. The first production trainset, number 03, was delivered on
25 April 1980. jpg/TGV29.JPG
Delivery of an order for 87 TGV trainsets was well underway in 1981, when trainset
16 was used for a very publicized world record run, code-named operation TGV
100 (for a target speed of 100 meters per second, or 360 km/h). The target was
exceeded on 26 February 1981, when trainset 16 reached a speed of 380 km/h (236
mph) in perfect safety. This was quite in contrast with the previous record,
set on 28 March 1955 by a pair of French electric locomotives, the CC 7107 aImagei
and the BB 9004 aImagei. In those record attempts, which some would call suicidal,
the track was severely damaged and the trains came dangerously close to derailing.
(See image collection for track damage.)
On 27 September 1981, to great fanfare, the first TGV with paying passengers
left Paris after the inauguration by French president François Mitterrand.
Thus began the long tradition of high speed ground transportation in France.
...of TGV test vehicles can be had here in the TGV pages or in the Mercurio
Thanks to Yann Nottara (email@example.com) and Mark Williams (firstname.lastname@example.org)
for providing some of this information; TGV001 photo by Jean-Paul Lescat (email@example.com).
Last modified: Sat Mar 28 09:34:26 PST 1998
TGV PSE (Paris Sud-Est)
Build dates: 1978-1985Territory: LGV Sud-Est, LGV Rhône-Alpes, LGV MediterrannéeTop
Speed: 300/270 km/h (186/168 mph) Number in Service: 107 (see roster for numbering)Supply
Voltages: 25kV 50Hz AC, 1.5kV DC (15kV 16.7Hz for some)Traction: 12 DC motors,
total continuous power 6450 kW (8650 hp) under 25kV supply, 3100 kW (4160 hp)
under 1.5kV supply, 2800 kW (3750 hp) under 15kV supply. Almost twice these
figures for 7 minutes.Length and Weight: 200 m / 385 tonnesConfiguration: 1
power car + 8 trailers + 1 power car, 350 seats (see formations)Performance
Metrics: 17 kW/tonne / 1.10 tonnes/seat / 18.34 kW/seatSpotting Features: Orange
livery (not for long), roof fairing of locomotive does not extend over cab.
Don't confuse with Atlantique or Réseau.Images: aTGV Pagesi aERS Picture
GalleryiSpecial Notes: Trainset 16 set 1981 speed record of 380 km/h (236 mph).
TGV La Poste
Build Dates: 1981-1984Territory: LGV Sud-EstTop Speed: 270 km/h (168 mph)Number
in Service: 7 (see roster for numbering)Supply Voltages: 25kV 50Hz AC, 1.5kV
DCTraction: Same as TGV Sud-EstLength and Weight: 200 m / 345 tonnesConfiguration:
1 power car + 4 trailers, 0 seats (see formations)Performance Metrics: 19 kW/tonneSpotting
Features: Yellow livery and "La Poste" letteringImages: aTGV PagesiSpecial
Notes: Always operated in pairs. Carries mail only.
Build Dates: 1989-1992Territory: LGV AtlantiqueTop Speed: 300 km/h (186 mph)
Number in Service: 105 (see roster for numbering)Supply Voltages: 25kV 50Hz
AC, 1.5kV DCTraction: 8 3-phase AC synchronous motors, total power 8800 kW (12000
hp) under 25kV supplyLength and Weight: 238 m / 484 tonnesConfiguration: 1 power
car + 10 trailers + 1 power car, 485 seats (see formations)Performance Metrics:
18 kW/tonne / 1.00 tonnes/seat / 18.14 kW/seatSpotting Features: 10 trailers
and silver/blue livery, numbering 301 to 405. Don't confuse with PSE or Réseau.Images:
aTGV Pagesi aERS Picture GalleryiSpecial Notes: Trainset 325 holds world speed
record of 515.3 km/h (320.3 mph).
AVE (Alta Velocidad Española)
Build Dates: 1991-1992Territory: Madrid-Sevilla high speed line, SpainTop Speed:
300 km/h (186 mph)Number in Service: 16Supply Voltages: 25kV 50Hz AC, 3kV DCTraction:
Same as TGV AtlantiqueLength and Weight: 200 m / 392 tonnesConfiguration: 1
power car + 8 trailers + 1 power car (329 seats)Performance Metrics: 22 kW/tonne
/ 1.19 tonnes/seat / 26.75 kW/seatSpotting Features: Rounded nose fairing, white
livery. Don't confuse with Euromed broad-gauge version.Images: aERS Picture
GalleryiSpecial Notes: The AVE is an exported Spanish TGV, closely derived from
the TGV Atlantique. It runs on German-designed high speed tracks, and is gauged
at the standard 1.435 m (4' 8.5") unlike the Spanish broad gauge of 1.668
m (5' 5.5").
Build Dates:1992-1996Territory: Mostly LGV Nord-Europe, entire TGV networkTop
Speed: 300 km/h Number in Service: 80 (see roster for numbering)Supply Voltages:
25kV 50Hz AC, 1.5kV DC (3kV DC for some)Traction: Same as TGV AtlantiqueLength
and Weight: 200 m / 386 tonnesConfiguration: 1 power car + 8 trailers + 1 power
car, 377 seats (see formations)Performance Metrics: 23 kW/tonne / 1.02 tonnes/seat
/ 23.34 kW/seatSpotting Features: 8 trailers and silver/blue livery, numbering
in 500 or 4500 series. Don't confuse with PSE or Atlantique.Images: aTGV Pagesi
aERS Picture GalleryiMore Information: See article.Special Notes: Some trainsets
are equipped with 3kV DC for service to Belgium or Italy.
Build Dates: 1993-1995Territory: LGV Nord-Europe and points northTop Speed:
300 km/h (186 mph)Number in Service: 31 (see roster for numbering)Supply Voltages:
25kV 50Hz AC, 3kV DC, 750V DC third rail (1.5kV DC for some)Traction:12 3-phase
AC asynchronous motors, total power 12200 kW (16300 hp) under 25kV supplyLength
and Weight: 394 m / 752 tonnesConfiguration: 1 power car + 18 trailers + 1 power
car, 794 seats (see formations)Performance Metrics: 16 kW/tonne / 0.98 tonnes/seat
/ 15.90 kW/seatSpotting Features: yellow duckbill nose, low profile.Images:
aERS Picture GalleryiMore Information: See article.Special Notes: International
(40/40/20) cooperation between France, Britain and Belgium.
Build Dates: 1995-1997Territory: LGV Sud-EstTop Speed: 300 km/h (186 mph)Number
in Service: 30Supply Voltages: 25kV 50Hz AC, 1.5kV DCTraction: Same as TGV AtlantiqueLength
and Weight: 200 m / 380 tonnesConfiguration: 1 power car + 8 trailers + 1 power
car, 545 seats (see formations)Performance Metrics: 23 kW/tonne / 0.70 tonnes/seat
/ 16.15 kW/seatSpotting Features: Bilevel seating, single windshield, rounder
noseImages: aTGV Pagesi aERS Picture GalleryiMore Information: See article.Special
Notes: Developed to relieve congestion on LGV Sud-Est.
Some Sources Used:
La Vie du Rail
French weekly rail magazine. Great for keeping up with the latest developments.
Good historical and international coverage. Good special editions on topics
such as the world speed record. Their photography is solid and the writing good,
despite the occasional over-patriotic bias. No wonder, since this is a publication
widely read by the employees of SNCF. Subscriptions: call (+33) 1 49 70 12 63.
Chemins de Fer
The magazine of the Association des Amis des Chemins de Fer (AFAC), with some
well-researched articles on various TGV topics. This publication is of far higher
quality than LVDR, but it is only bimonthly and very expensive. See their web
page for more info.
Railway Gazette International, Rail Passion, etc.
Of help to me was the Stanford University Engineering library, which should
have an equivalent at any large university with an engineering school. Research
papers and conference proceedings abound. A treasure trove of old primary source
documents can be found in Paris at the Bibliothèque Publique d'Informations
L'histoire du record du monde de vitesse sur rail, battu par la rame 325 du
TGV Atlantique le 18 mai 1990 avec une marche a 515,3 km/h. Tout ceci
vous provient du numéro hors-série de La Vie du Rail (voir bibliographie),
publié a cette occasion.
ACOUSTIC IMAGING OF TGV TRAINS
Measurement of the sound produced by a TGV train (or any type of high speed
train) passing at high speed is an important area of research and development.
The power dissipated as noise goes up roughly with the cube of speed, with the
result that high speed trains are rather louder than normal trains. Acoustic
measurement techniques can pinpoint exactly where the noise is coming from.
This has several important applications:
· Environmental Impact Evaluation. Data is used to develop governmental
noise prediction schemes for evaluating noise emission levels along high speed
· Sound Barrier Design. Source strengths can be used to evaluate the
efficiency of sound barriers of various designs, which are intended to reduce
the noise reaching surrounding inhabited areas.
· Train Design. Data identifies the principal sources of noise, where
improved aerodynamic design or sound shielding might reduce the amount of sound
radiated into the environment.
How is the Sound Measured? images/research/thalysmicro.jpg
The acoustic images were obtained with the SYNTACAN acoustic antenna array of
the TNO Institute for Applied Physics (TNO-TPD) in Delft, The Netherlands.
The SYNTACAN is designed for highly directional sound measurements. The complete
system uses 36 microphones, forming a sparse array with a length of nearly 80
meters. In the vertical position 24 microphones are used and the height is 10
meters. In the picture, the SYNTACAN array is shown near a high speed line in
Belgium, measuring the sound made by a Thalys trainset passing at 330 km/h,
during a measurement campaign in 1996. The SYNTACAN boom is held at a slight
angle from vertical by a crane, to correct for the cant of the track. A measurement
van contains computer equipment to log the data. In the foreground, two other
instruments are visible: a radar velocimeter, used to accurately measure the
speed of the train, and an artifical noise source used to calibrate and align
the acoustic antenna.
Using a two-dimensional Fourier analysis technique, the sound field is decomposed
into the frequency dependent contributions from different directions, which
can be associated with (partial) sound sources. The SYNTACAN system allows measurements
in the 1/1 octave bands of 125 up to 2000 Hz with a resolution of 1/12 octave.
(An octave is defined exactly the same way as in music, with 1/12 octave equal
to one half tone; middle A is 440 Hz.) Its spatial resolution in radians approximately
equals the ratio of wavelength to antenna length.
Acoustic Images of a TGV Atlantique
After being processed as described above, the data collected using the microphone
array can be displayed as an image of the train as it would look if your eyes
could "see" sound sources. The images don't look very much like a
TGV Atlantique trainset, but if you observe closely, several interesting features
can be picked out.
What you see is essentially several 2-dimensional side views of the train,
taken in different octave bands. The center frequency of each picture is labelled
above it. The images represent the measured sound pressure levels at the position
of the antenna, as a function of height and lateral position along the train.
Red is highest pressure (loudest), while dark blue is lowest. The images are
different for the various octave bands, due to the varying importance and radiation
characteristics of the noise sources and physical phenomena that generate the
High-pitched rolling noise clearly emanates from the wheels; look at the picture
in the 2000 Hz band. Most of the emission is concentrated at track level (0
meters on the vertical axis), and you can distincly see the individual bogies
of the trailers. These show up as light blue spots at the center of the image,
at a spacing of 18.7 meters (the length of a TGV trailer).
Aerodynamic noise sources are in general found all along the train. The power
units (one at each end of the trainset) are clearly the loudest; this results
in the red areas on the left and right sides of each image. You can also discern
that the pantograph is raised on the right side power unit (at the rear of the
train, which is travelling from right to left.)
Using this kind of data, it is possible to design quieter trains, better sound
barriers, and to better estimate the noise impact of high speed lines.