Abstract
Porous materials have recently been used in absorptive treatments around railway tracks to reduce noise emissions. To investigate the effect of porous materials, a finite element model has been developed. 2D models for porous materials have been considered either as an equivalent fluid or as a poroelastic material based on the Biot theory. The two models have been validated and compared with each other to check the effect of the skeleton vibration. The poroelastic FE model has been coupled with a 2D acoustic boundary element model for use in railway applications. The results show that it may be necessary to include the frame vibration, especially at low frequencies where a frame resonance occurs. A method for the characterization of porous materials is also discussed. From this it is shown that the elastic properties of the material determine the resonance frequency and the magnitude.
Highlights
The dominant source of noise from railways is rolling noise, which is generated by the surface roughness of the rail and the wheel
Porous materials are usually used in such absorptive treatments
The black line in the first graph shows the result from the rigid model, which cannot predict the effect of frame resonance around 900 Hz
Summary
The dominant source of noise from railways is rolling noise, which is generated by the surface roughness of the rail and the wheel. When analysing the performance of an absorptive treatment around the track the boundary element method is usually used as a numerical method [2, 3]. In this approach porous materials can be effectively treated as an impedance boundary. When they are mounted close to the rail or become parts of the railway track, it could be important to consider the elasticity of the material in the analysis, as the frame vibration could radiate noise, rather than just absorb it.
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