1. Tuned Mass Damper for Railway Noise Control
Wilson Ho and Banting Wong
Wilson Acoustics Limited
David England
MTR Corporation 1

2. Contents Introduction Working Principle Damper Development History
Decay Rate Measurement
Trackside N&V Measurement
Saloon Noise Measurement
Summary
Wilson Acoustics Limited

3. VolkerRail (Corus) Shrey & Veit
Photo Taken from Innotrans in Berlin
Courtesy: Eric Tam from Pandrol UK Ltd.
VolkerRail (Corus)
Shrey & Veit

4. Vossloh
SEKISUI
STRAIL astic

5. Introduction Tuned Mass Rail Damper developed in Hong Kong since 2007
Shear direction oscillation
Each oscillation mass response to both lateral and vertical vibration
Multiple Frequency Tuning
Reduce rail noise radiation
Wilson Acoustics Limited

6. Working Principles Direct Damping (Hysteresis disipation)
Rail vibration displacement is very small, in the order of μm
Small strain in damping material  small energy dissipation
Effective at high frequency only (>1000Hz)
Broadband absorption
Tuned Mass Damping
Wilson Acoustics Limited

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8. Absorber movement is amplified and anti-phase.
Tuned Mass Damping
Absorber movement is amplified and anti-phase.
Energy is dissipated by hysteresis  higher amplitude, more dissipation
Effective for low frequency vibration (<1000Hz), and narrow bandwidth
Wilson Acoustics Limited 8

9. Damper Development History
↑1st Prototype (2007)
Tonal saloon noise at curve track
Tuned Mass Damper with single resonance
Absorption to rail web vibration
Attach to rail by magnets
→ 2nd Prototype (2007)
Vibration absorption for both rail foot and web
Absorption to both vertical and lateral vibration
Multiple resonance frequency
Attach to rail by magnets, 1 to 2kN adhesive force
Wilson Acoustics Limited

10. Damper Development History
← 3rd Prototype (2008)
2 clamping clips
~5kN clamping force
→ 4th Prototype (2009)
3 clamping clips
~12kN clamping force
Structural components are strengthened to sustain ~40kN force
Wilson Acoustics Limited

11. Damper Design <300Hz - The rail is not an effective noise radiator
Hz - Tuned Mass Damping Mechanism
6 oscillation masses are individually tuned to cover broadband
>1000Hz - Direct Damping (Hysteresis)
A thin layer of viscous damping material

12. Damper Frequency Tuning
800Hz
630Hz
400 & 800Hz
315Hz
where
G is dynamic shear modulus of the resilient layer
A is the surface area of resilient layer
b is the thickness of the resilient layer
M is the oscillation mass
1000Hz
Frequency
Rubber Type
Dimension
315Hz
55o Neoprene
40 x 45 x 1.25 mm
400Hz &
800Hz
50 x 55 x 1.25 mm
50 x 56 x 1 mm
630Hz
40 x 40 x 1 mm
55 x 58 x 1 mm
1000Hz
65o Neoprene
63 x 65 x 1 mm
Resilient Layers
Mechanical loss factor is chosen to be 0.1 ~ 0.5 to cover the entire vibration bandwidth.
Wilson Acoustics Limited

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15. Vibration of every mass is anti-phase and amplified.
Wilson Acoustics Limited

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17. oscillation directions
Oscillation along shear directions of resilient layers.
vibration absorption in both vertical and lateral directions,
allows greater oscillation amplitude thus better vibration absorption.

18. Laboratory Testing
For every oscillation mass, resonance frequency is checked by impact test
Wilson Acoustics Limited

21. Contents Introduction Working Principle Damper Development History
Decay Rate Measurement
Trackside N&V Measurement
Saloon Noise Measurement
Summary
Wilson Acoustics Limited

22. Track Decay Rate Track Decay Rate, dB/m
Excitation
Track Decay Rate, dB/m
~ vibration attenuation per meter of track ~ EN 15461:2008
Vibration bending wave propagate along the rail and radiate as noise
Damper increases track decay rate
 Shorter vibration propagation distance
 Shorter noise radiation length
 Reduce wayside / saloon noise
Long Noise Radiation Length
Short Noise Radiation Length
Wilson Acoustics Limited

23. Rail Pin-Pin Resonance
Vertical pin-pin
825Hz
Lateral pin-pin
385Hz
For UIC60 rail at 700mm support spacing

24. Track Decay Rate
Wilson Acoustics Limited

25. Track Decay Rate Measurement
Vertical pin-pin
Lateral pin-pin
Wilson Acoustics Limited

26. Contents Introduction Working Principle Damper Development History
Decay Rate Measurement
Trackside N&V Measurement
Saloon Noise Measurement
Summary
Wilson Acoustics Limited

27. Trackside N&V Measurement
Tunnel N&V Measurement
Saloon Noise Measurement
Before Damper
Installation
22/06/2010
1st Day After
25/06/2010
26/06/2010
~2 weeks after installation
05/07/2010
11/07/2010
6 months after installation
T.B.A
12 months after installation
Track Parameters
Rail
EN 60
Support Type
Low Vibration Trackform
(Resiliently Booted Concrete Block)
Stiffness of LVT Support Pad
26-35kN/mm
Static Stiffness of Rail Pad
75-90kN/mm
Curvature
300m
Train Speed
60-70 km/h
Wilson Acoustics Limited

28. Trackside N&V Measurement
Average Reduction ~10dB(A)
Average Reduction ~7dB(A)

29. Average Reduction ~9dB(A)
Trackside N&V Measurement
Average Reduction ~9dB(A)

30. Vibration Time History (Under Rail)

31. Vibration Time History (Rail Web)

32. Trackside N&V Measurement
Tunnel Walkway
Reverberant Field Microphone
Average Noise Reduction ~3.4dB(A)
High Rail Near Field Microphone
Average Noise Reduction ~3.5dB(A)

33. Trackside N&V Measurement
Sleeper Field Side
Sleeper Gauge Side

34. Trackside N&V Measurement
Sleeper Field Side
Average Reduction 1.0~1.4dB(A)
Sleeper Gauge Side
Average Reduction 2.3~3.3dB(A)

35. 1st Day After Damper Installation
Projected SWL from Track Components
Without Damper
1st Day After Damper Installation
Noise radiation from wheel is not included.
Radiation efficiency for rail vibration is based on TWINS model
Radiation efficiency for sleeper is approximated by pulsating sphere in half plane.
Wilson Acoustics Limited

36. Contents Introduction Working Principle Damper Development History
Decay Rate Measurement
Trackside N&V Measurement
Saloon Noise Measurement
Summary
Wilson Acoustics Limited

37. Saloon Noise Measurement
Noise measurement conducted inside trailer car.
Public announcement switched off throughout the measurement.

38. Figure 4.1 Saloon Noise Level Time History
2dB(A)
Damper Section, 50m
Tunnel Reverberation Noise

39. Average Noise Reduction 2.8dB(A)
Saloon Noise Spectrum
5dB(A)
Average Noise Reduction 2.8dB(A)

40. Contents Introduction Working Principle Damper Development History
Decay Rate Measurement
Trackside N&V Measurement
Saloon Noise Measurement
Summary
Wilson Acoustics Limited

41. Summary A new type of Tuned Mass Rail Damper is developed in HK
- shear direction oscillation
- both lateral and vertical vibration damping
- multiple frequency tuning (6 frequencies in the current design)
The damper increases the track decay rate thus reduces rail noise radiation
- vertical decay rate increased to ~9 -10 dB/m
- lateral decay rate increased to ~7 dB/m
Noise reduction with 50m damper installed for a trial test,
- tunnel noise is reduced by 3.5dB(A)
- saloon noise is reduced by 2.8dB(A)
- with longer damper section, noise reduction would be ~4dB(A)
Performance of the damper is limited by the concrete sleeper resonance vibration which radiate noise at 300Hz resonance peak. Without concrete sleeper vibration, higher noise reduction is anticipated.
Wilson Acoustics Limited

42. Q & A
Wilson Acoustics Limited