WAL Rail Damper for Track Noise Reduction

Wilson Acoustics Limited

Wilson Acoustics Limited www.wal.hk

Contents

• Rail Damper Working Principles

• Damper Development History

• WAL Rail Damper Characteristics

• Manufacturing and Installation

• Frequency Tuning & Rubber Selection

• Laboratory Testing

• Field Measurement

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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

rail

damper

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

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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

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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.

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4. Nylon nuts are screwed onto the top of conventional steel nuts.

The high thread friction prevents nut loosening after repeated train passage.

3. 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

1. 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.

2. 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.

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Damper Assembly• Before transportation to site for installation,

damper components are assembled into 3 parts

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Damper Installation

• 10-15 dampers can be installed per hour by 1 team comprising 2 people.

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• 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

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Saloon Noise Critical Frequency 315-1600HzSaloon Noise Critical Frequency 315-1600Hz

315-1000Hz 315-1000Hz Tuned Mass Damping Mechanism Tuned Mass Damping MechanismThe oscillation masses in each damper are tuned at specific frequencies within 300Hz to 1000Hz to absorb the vibration energy.

>1000Hz >1000Hz Viscous Damping Mechanism Viscous Damping MechanismThe 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 Limited www.wal.hk

Damper Frequency Tuning800Hz

400 & 800Hz315Hz

630Hz

1000Hz

12

2

11 eqt

bM

GAf

where G is dynamic shear modulus of the resilient layerA is the surface area of resilient layerb is the thickness of the resilient layerM is the oscillation mass

Frequency Rubber Type Dimension

315Hz 550 Neoprene 40 x 45 x 1.25 mm

400Hz &

800Hz

550 Neoprene 50 x 55 x 1.25 mm

550 Neoprene 50 x 56 x 1 mm

630Hz 550 Neoprene 40 x 40 x 1 mm

800Hz 550 Neoprene 55 x 58 x 1 mm

1000Hz 650 Neoprene 63 x 65 x 1 mm

Frequency tuning can be achieved by adjusting the shear stiffness and dimensions of resilient rubber.

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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

555500 - 65 - 6500 Neoprene was selected. Neoprene was selected. (A common material used in trackbed isolation)(A common material used in trackbed isolation)

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Laboratory Testing

• General test and detail test are conducted to check the damper resonance frequencies.

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Track Decay Rate Measurement

400Hz, Lateral

1000Hz, Lateral

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Track Decay Rate Measurement

0.1

1

10

100

31.5 63 125 250 500 1000 2000 4000

1/3 Octave Band Center Frequency, Hz

Tra

ck D

ecay

Rat

e, d

B/m

lateral decay rate measured at rail head w/o damper

lateral decay rate measured at rail head w damper

vertical decay rate measured under rail w/o damper

vertical decay rate measured under rail w damper

Estimated Rail Noise Reduction 4-8 dBWilson Acoustics Limited www.wal.hk

The End

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Oscillation Mass A

Oscillation Mass B

Oscillation Mass C

Oscillation Mass D1 & D2

Oscillation Mass E

Resilient Layers

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