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

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

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

Vossloh SEKISUI STRAIL astic

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 www.wal.hk

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 www.wal.hk

Wilson Acoustics Limited www.wal.hk 7

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 www.wal.hk 8

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 www.wal.hk

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 www.wal.hk

Damper Design <300Hz - The rail is not an effective noise radiator 315-1000Hz - Tuned Mass Damping Mechanism 6 oscillation masses are individually tuned to cover broadband >1000Hz - Direct Damping (Hysteresis) A thin layer of viscous damping material

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 www.wal.hk

Wilson Acoustics Limited www.wal.hk

Wilson Acoustics Limited www.wal.hk

Vibration of every mass is anti-phase and amplified. Wilson Acoustics Limited www.wal.hk

Wilson Acoustics Limited www.wal.hk

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.

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

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

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 www.wal.hk

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

Track Decay Rate Wilson Acoustics Limited www.wal.hk

Track Decay Rate Measurement Vertical pin-pin Lateral pin-pin Wilson Acoustics Limited www.wal.hk

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

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 www.wal.hk

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

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

Vibration Time History (Under Rail)

Vibration Time History (Rail Web)

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)

Trackside N&V Measurement Sleeper Field Side Sleeper Gauge Side

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

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 www.wal.hk

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

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

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

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

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

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 www.wal.hk

Q & A Wilson Acoustics Limited www.wal.hk