May/June 2024 - 18

Vehicle design
Warp, gage via Google Earth
data due to the track configuration changes related to the
metro expansion. " We collected so much data that we've been
able to extrapolate much more than that, " Croft said.
Analysis of this data has yielded information on:
* Long-term trends in vibration levels over time
* Differences between tracks
* Relative vertical and lateral vibration levels
* Repeatability of short-term vibration monitoring
* Effect of train type on vibration levels
Figure 3 shows some of the data collected in the study -
FIGURE 1. Warp and gage measurements and alerts
overlaid on a map of the system.
Image: Siemens
specifically vertical vibration data during one year. The green
line shows the 95th percentile of maximum vibration levels,
averaged more than 1,000 events (95th percentile vibration
level is a metric used for vibration standards and compliance
in Australia).
Croft noted there are three stand-out points in this data
that warrant closer examination. The first is the notable commencement
of large numbers of train passby events with
lower vibration levels in March 2021. This corresponds to the
opening of the new inbound track, which was further away
from the vibration sensor. The second is the spike in vibrations
at the start of study. This corresponds to a proliferation of
wheel flats related to issues with newly-acquired rolling stock.
Croft added the issue was resolved soon after data collection
for this study commenced, resulting in reduced maximum
vibration levels by October 2021.
The third is the drop-off of the 95th percentile between
FIGURE 2. Chart of potentially problematic combinations
of vehicle components based on track data and
multibody simulation.
Image: Siemens
120
115
105
110
100
95
90
85
95th percentile 1000 events
Passby Lmax,S
December 2020 and January 2021. This corresponds to a
period in which maintenance work on the Sydney Harbor
Bridge disrupted normal operations. During this period, the
line ran a reduced timetable service, utilizing only one train
type-the Waratah type.
The Waratah trains were introduced between 2011 and
2018 and make up 81 percent of the traffic on the North
Sydney line. Tangara trains, introduced between 1988 and
1995, make up 16 percent of the traffic and the remaining
three percent is made up of other train types.
" The Tangara are older but very similar in specification
to the Waratah trains, " Croft said. " The differences between
these trains becomes quite clear, however, when the Tangara
trains are highlighted in the vibration data. The Tangara trains,
despite making up a small percentage of the fleet, account for
nearly all of the high vibration events. On average, the Tangara
trains generated +5 dBV vertical vibrations and +6 dBV. "
Croft explained the Waratah and Tangara trains have very
FIGURE 3. Maximum vibration levels measured
over the course of one year.
Image: Briony Croft presentation
similar suspension systems and only a small difference in unsprung
mass; otherwise, the two vehicles are not substantively
different. For the Sydney case study, this left wheel flats as the
likely culprit for the cars' different performance.
To compare wheel condition between the two car types,
Croft looked at wheel impact load detector (WILD) data network-wide
during the same time period as the vibration data.
This data showed that out of 866 Waratah cars, 60 (seven
percent) generated WILD flags. Of the 447 Tangara cars, 476
(106 percent) generated WILD flags.
18 Mass Transit | MAY/JUNE 2024
Sep-20
Oct-20
Nov-20
Dec-20
Jan-21
Feb-21
Mar-21
Apr-21
May-21
Jun-21
Jul-21
Aug-21
Sep-21
Vertical vibration train passby Lmax,S
(dbV re 1e-9 m/s)
May/June 2024

Table of Contents for the Digital Edition of May/June 2024
