Apr 6 2004
Trains that shake houses do not encourage public support for the
switch of freight from road to rail. CASCO promotes social acceptance for trains
by making them quieter using small, low-energy damping
devices.
The environmental, social and economic costs of freight transport by road are
key reasons to encourage the switch from lorries to the railways. Trains are
cleaner, often quicker, use less energy and are safer for pedestrians – but
railway companies that want to build new tracks or bring old lines back into use
meet strong resistance. Concerns about infrastructure noise and vibration
exposure raise strong objections from citizens and their
representatives.
Noise and vibration can arise from several sources: the
rough contact between wheels and track is one, but others are less obvious, such
as the interaction between wheel, track and bridge structures that can travel
through the ground and induce vibrations in neighbouring buildings. The CASCO project brings a new approach to reducing noise and vibration on the railways
using innovative semi-active control devices that make a more effective use of
materials and minimise resource consumption.
“To reduce noise and
vibration in steel structures you need to dissipate energy by damping – this is
traditionally done by passive control,” explains project coordinator Dr Helmut
Wenzel, managing director of Vienna
Consulting Engineers (VCE). “Passive controls use the structure’s system
response to achieve damping. Active controls are another current technology,
these rely on big electrically driven actuators, but for large structures they
consume a lot of energy and need regular maintenance.
“The semi-active
devices CASCO develops are stand-alone, miniature devices with low power
requirements, based on magneto-rheological fluid dampers. These contain fluids
that change viscosity dramatically in a magnetic field and can be set to
dissipate vibrations from the structures they support. Such actuators are
installed at critical locations throughout structures and underneath railway
tracks to eliminate vibration. They prevent the vibrational kinetic energy from
passing into the soil by dissipating the energy locally. A key advantage is that
because of their size and robustness they can be retro-fitted in many
cases.”
Bridging theory and experiment
Railway
tunnels and bridges are strong sources of noise, both airborne and by vibrations
through the soil. The CASCO consortium selected the Rohrbach railway bridge in
Austria for trials; this steel bridge was built in 1903 and is no longer in use.
Initially extensive measurements were carried out using sensors attached
to the sleepers and girders on the bridge. Emitted noise was measured both with
and without a train passing – and the noise of the train itself was carefully
eliminated to isolate structural noise. By matching the observed vibrational
frequencies to structural elements of the bridge, it was possible to isolate the
main contributions to noise.
The bridge was then dismantled, transported
and reassembled at the European
Laboratory for Structural Assessment (ELSA) at the European Commission’s
Joint Research Centre DG in Ispra, Italy. ELSA is a partner in the project with
state-of-the-art equipment for active structural testing. “Once we rebuilt the
bridge at Ispra, we repeated our measurements to ensure the system response of
the structure was the same in the new location,” says Dr Wenzel. “This was
important for calibration and to allow a true comparison.”
Another
partner, the University of Applied Sciences in Vienna, developed a unique
approach to modelling rheological fluids that was used in the design of the
CASCO prototypes. It also has potential for more widespread
application.
The outcome of the project is a suite of innovative
semi-active devices shown to have excellent results in damping vibrational
energy. In particular a new ‘cup-spring’ isolator was developed, the subject of
a patent and capable of using both hydraulic and magneto-rheological mechanisms.
Partners continue to develop the cup-spring isolator and are moving to
commercial development for selected prototypes. Further, full-scale devices are
being made for in-situ testing by Austrian Railways (ÖBB), which has dedicated an operational
steel bridge for this purpose.
For more railway information