May/June 2024 - 17

R
In Part 1 of this
article, a group of
experts, including
a transit operator,
three vehicle
manufacturers,
and a noise
and vibration
consultant,
examined how to
mitigate wheel/
rail-generated
noise at the
source. The
discussion
took place at
the Wheel/
Rail Interaction
'23 Rail Transit
conference, of
which Mass Transit
is the Presenting
Sponsor. Part
2 looks further
into vehicle
design efforts to
mitigate noise and
vibration and the
resulting effects on
transit/passenger
applications.
ail transit vehicle design doesn't occur in a vacuum. In addition
to optimizing individual components of a vehicle, car builders
also optimize the vehicle for the rail and track conditions it
will encounter. This means that precise track condition data is
an important component of the vehicle design process despite
not being part of the vehicle.
During the design phase of a new vehicle, car builders
use track condition data in concert with their own analyses
and simulations to quantify the systemic effects of vehicle/
track interaction on:
* Vehicle kinemtatics, including articulation angles, coupler
and carbody clearances and carbody-to-truck clearance.
* Vehicle dynamics based on wheel/rail profile interaction,
the ability to navigate special trackwork, derailment risk
and ride comfort.
* Propulsion and braking requirements, including gradients,
station stops, acceleration and deceleration requirements.
* Structural loads/forces-these are subject to customer
specification, car builder internal standards and regulatory
requirements.
" Structural load assumptions in the design phase are very
important: Are you following only the technical specification
or only the regulatory requirements? And, what do you do
when these come into conflict? " asked Kevin McClain, director
of mechanical systems engineering at Siemens Mobility Inc.
Reconciling this conflict requires good data and good
communication with the customer.
Siemens recently fulfilled a new vehicle procurement contract
that highlights the importance of having and using track
and site data in the vehicle design process. This procurement
was for an existing network that included historic trackwork
and bridges requiring a lightweight vehicle. Sections of the
network were also near historic buildings and particularly
sensitive to ground-borne vibrations. The network was in a
high-gradient landscape, which McClain explained included
many steep grades back-to-back, as well as sharp curves and
compound curves at grade.
A vehicle optimized for these conditions had to be lightweight,
with low unsprung mass and exceptionally fatigue-resistant
due to large predicted torsional loads - and it had
to be service-proven. Siemens' approach to the project was
to first define trackwork criteria based on a combination of
track drawings, track measurements and measurements of
existing vehicle dynamics. McClain said the aim was to use
the worst-case scenario out of these data sources to determine
the true operational envelope of a new car.
Siemens instrumented existing cars with a suite of measurement
devices to create its own map of the network overlaid
with truck and carbody dynamics and loads, correlated by
precise location. Among the many parameters Siemens measured,
certain track conditions appeared to be particularly
consequential in their influence on vehicle performance. These
were warp 31 feet, warp 62 feet and narrow gage.
" These are combinations of conditions and forces that can't
be found in technical drawings, " McClain said.
Siemens also collected rail profile
data and used it to inform multibody
simulation (MBS) models-essentially
enabling them to run simulated cars over
simulated tracks reflecting actual track
conditions. Notably, the as-measured
track simulated structural loads were,
on average, 20 percent higher than the
track drawing simulation, McClain added,
meaning that a car designed to the
track drawing spec would effectively be
under-built.
Using this profile data, Siemens developed
MBS models to test the individual
components of the new car on the
as-measured track and identify potentially
problematic combinations of components,
vehicle dynamics, kinematics,
structural loads and locations. Siemens
found that the vehicle/track characteristics
measured (relating to kinematics,
dynamics, propulsion, structural load)
more accurately reflected the actual operating
conditions than the technical
specifications or standards. These were
the characteristics that drove the new
car design. According to McClain, the
lesson here is simple: Accurate track data
plays a critical role in the design phase
of new car procurement.
Noise and vibration
at the source
A recent case study in Sydney, Australia,
illustrates the impact of vehicle design
and selection on ground-borne vibration
and noise. The initial focus of the study
was a rail corridor for Sydney's heavy rail
passenger line (North Sydney) that was
undergoing modification for a light-rail
extension of the Sydney Metro. At the
commencement of the study, only the
heavy rail line was in operation. During
the months that followed, the inbound
track was moved to accommodate construction
of two metro tracks between
the existing tracks, said Briony Croft,
an acoustic engineer and director at Sahaya
Consulting (Canada) and Acoustic
Studio (Australia).
The study measured vibration at the
rail corridor boundary for more than a
year (and is ongoing), collecting data on
roughly 250 trains per day. The original
goal was to measure changes in vibration
MAY/JUNE 2024 | MassTransitmag.com 17
http://www.MassTransitmag.com
May/June 2024

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