WAL Rail Damper for Track Noise Reduction

1. WAL Rail Damper for Track Noise Reduction Wilson Acoustics Limited Wilson Acoustics Limitedwww.wal.hk

2. Contents • Rail Damper Working Principles • Damper Development History • WAL Rail Damper Characteristics • Manufacturing and Installation • Frequency Tuning & Rubber Selection • Laboratory Testing • Field Measurement Wilson Acoustics Limitedwww.wal.hk

3. Working Principles • Vibration bending wave propagate along the rail and radiate as noise • Track Decay Rate, dB/m ~ vibration attenuation per meter track (EN 15461:2008) • Lower track decay rate  Longer vibration propagation distance  Larger effective radiation surface  Louder wayside / saloon noise • Tuned mass damper used to increase decay rate • Fn of the damper is tuned to rail vibration frequencies  rail vibration is transfer to the damper  dissipated by hysteresis rail damper Wilson Acoustics Limitedwww.wal.hk

4. Development History ↑1st Prototype (2006) • Developed after observing tonal saloon noise in MOL • Tuned Mass Damper by shear oscillation • Attach to rail by magnets → 2nd Prototype (2007) • Vibration absorption for both rail foot and rail web • Multiple resonance frequency Wilson Acoustics Limitedwww.wal.hk

5. Development History • ← 3rd Prototype (2008) • Try to conduct test on operational rail. • Magnetic mounting is not endorsed by MTR due to signaling concerns • 2 clamping clips + Wax adhesion • → 4th Prototype (2009) • Vibration measured at operational rail indicates vibration level up to 80 g • Structural components are strengthened • Mounting mechanism is improved to provide higher and persistent mounting force. Wilson Acoustics Limitedwww.wal.hk

6. The mass is oscillating along the shear directions of the resilient layers. • provides effective vibration absorption in both vertical and lateral directions, • the noise radiating surfaces of the oscillation mass is significantly reduced, • the ratio of oscillation mass to mounting mass is maximized. • allows greater oscillation amplitude thus better vibration absorption. • Gap filling material with high viscosity and low compressibility is placed at the mounting interfaces. • Under static compressive mounting force, it behaves as flexible solid and deformed to fill up the movement gaps at the mounting interfaces. • Under high frequency dynamic train excitation force, it behaves as stiff solid which provide high adhesion force and allow vibration energy to be effectively transferred to the dampers. • Resilient buffer layers are inserted at the mounting components to provide persistent mounting forces. • prevents structural damage of mounting components for exceptional high vibration >100g • Nylon nuts are screwed onto the top of conventional steel nuts. • The high thread friction prevents nut loosening after repeated train passage. Wilson Acoustics Limitedwww.wal.hk

7. Damper Assembly • Before transportation to site for installation, damper components are assembled into 3 parts Wilson Acoustics Limitedwww.wal.hk

8. Damper Installation • 10-15 dampers can be installed per hour by 1 team comprising 2 people. Wilson Acoustics Limitedwww.wal.hk

9. Each rail section has its own noise frequency • Rail damper design frequency shall be specifically tuned • Tuned for KTL curve and down-slope track section Wilson Acoustics Limitedwww.wal.hk

10. Saloon Noise Critical Frequency 315-1600Hz • 315-1000Hz  Tuned Mass Damping Mechanism • The oscillation masses in each damper are tuned at specific frequencies within 300Hz to 1000Hz to absorb the vibration energy. • >1000Hz  Viscous Damping Mechanism • The damper employs a thin layer (~0.2mm) of viscous damping material applied at the rail foot bottom face to provide effective energy dissipation by viscous damping. Wilson Acoustics Limitedwww.wal.hk

11. 800Hz 630Hz 400 & 800Hz 315Hz 1000Hz Damper Frequency Tuning 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 Frequency tuning can be achieved by adjusting the shear stiffness and dimensions of resilient rubber. Wilson Acoustics Limitedwww.wal.hk

12. Rubber Selection • Appropriate Dynamic Shear Modulus  Affects vibration absorption frequency • Appropriate Mechanical Loss Factor  Affects vibration absorption bandwidth • Durability to repeated dynamic stress • Aging resistance under operation conditions 550 - 650 Neoprene was selected. (A common material used in trackbed isolation) Wilson Acoustics Limitedwww.wal.hk

13. Laboratory Testing • General test and detail test are conducted to check the damper resonance frequencies. Wilson Acoustics Limitedwww.wal.hk

14. Track Decay Rate Measurement 400Hz, Lateral 1000Hz, Lateral Wilson Acoustics Limitedwww.wal.hk

15. Track Decay Rate Measurement Estimated Rail Noise Reduction 4-8 dB Wilson Acoustics Limitedwww.wal.hk

16. The End Wilson Acoustics Limitedwww.wal.hk

17. Oscillation Mass D1 & D2 Oscillation Mass C Oscillation Mass E Oscillation Mass B Oscillation Mass A Resilient Layers Wilson Acoustics Limitedwww.wal.hk