PhD Project: Development of models for rail vibration and noise radiation including the effects of rail dampers

1
PhD Project Development of models for rail
vibration and noise radiation including the
effects of rail dampers

• Rebecca Broadbent
• Supervised by
• David Thompson
• Chris Jones

2
Aims and Motivations

• Rolling Noise
• Dominant source for conventional train speeds
• Decay rate along the rail known to be important
  factor.
• Decay rate influences
• Railpad
• Rail Dampers
• Sound radiation influences
• Ballast

Improve the understanding of the effect that
interaction between different track components
has on sound radiation from the track
AND develop an improved model of rolling noise
which can be used to predict noise spectra
emitted from sections of track during a train
pass-by.
3
Railpad
Aim To investigate the dependence on frequency
and temperature of material properties of a
range of railpad samples

• Railpad is an elastomeric material beneath the
  rail foot
• Stiffness and damping affect rail decay rates
• Dynamic properties of an elastomer are dependent
  on frequency and temperature

4
Railpad Measurements

• Rig
• Four samples (20x15x5 mm).
• Excited in shear.
• Accelerometer on source side.
• Force transducer at base.
• Frequency 0-5000 Hz.
• Temperature -20oC to 40oC in 5oC steps.
• Decay rates measured on 30m test track near
  Southampton for comparison

5
Railpad - Results
Natural Rubber
Cork Rubber

• Significant difference in sound power level of
  the track when railpad temperature changes

6
Rail Damper Method
Aim To investigate the efficiency of MDOF
dampers and optimise system performance
7
Rail Damper Noise Reduction
Attenuation contours of rail dampers with a
variety of mass and stiffness ratios showing the
line of maximum attenuation

• Current rail damper designs are efficient.

8
Ballast absorption Tests in reverberation
chamber
Aim To investigate the acoustical
characteristics, and produce an acoustic model,
of railway ballast
9
Ballast - Results
170mm depth
330mm depth
10
Ballast Free Field Measurements
11
Ballast - Results

• Excess attenuation measured above concrete and
  ballast.
• Good fit seen up to approximately 3kHz where the
  model is known to be deficient.

• Ballast behaves as a multi layered porous
  absorber.

12
Future Work

• Rail damper efficiency to be quantified using
  Boundary Element model of rail
• Ballast absorption to be quantified using
  Boundary Element model of rail
• Scale model track to investigate ballast
  absorption and the sound radiated from the rail
• Track measurements to validate the railpad
  dependence predicted
• Combine railpad and rail damper dependence to
  investigate further the rail damper efficiency