| In most situations the dominant source of noise from the railway system for conventional speeds is wheel/rail noise.Because the metro lines always in the tunnel,it is important to research on sound fields of wheel/rail noise in the tunnel.In this thesis,models are established to calculate the dynamics and sound radiation of track and wheel.Also models of wheel/rail noise in metro tunnel and on ground are established to predict sound response near wheel and rail and to study the characterization of the sound fields of wheel/rail noise in tunnel and on ground.(1)A prediction model of track dynamics is introduced to calculate the response of the rail excited by a harmonic force in frequency domain.The frequency responses of the wheel are predicted by using a modal summation and verified by a hammer impact measurement.The response of the wheelail are predicted excited by the wheelail interaction force which is obtained through the combined wheel/rail roughness divided by combined wheel,rail and contact zone receptances.(2)Two models of the direct BEM formulation in both two dimensions and three dimensions are established and the Matlab program is wrote.The effects of different numbers of CHIEF points and the Gauss points in the modelling on the numerical results are demonstrated,followed by the influence of different element size and type.The sound radiation from a pulsating cylinder is presented for the verification of the 2D BEM program.The 3D BEM program has been verified by comparing with the results which are calculated by a commercial software.(3)The sound radiation efficiency for the rail is calculated using the 2D BEM program.The sound power for the rail is calculated by combining predicted vibration spectra with radiation efficiency.The sound power for the wheel is calculated using the 3D BEM.It is clear that the rail is the dominant source in 0-1.6 kHz,while the contribution of the wheel is the dominant source above 2 kHz.(4)Two prediction models of wheel/rail noise in metro tunnel and on ground are established based on ray tracing method.The models have been verified by comparing with measured sound pressure near wheel and rail.The sound fields of wheel/rail noise in tunnel and on ground are calculated and compared with each other.It implies that sound pressure near wheel and rail in tunnel is 6.0 dBA higher than on ground.Based on the validated model,the effects of cross-section,absorption martial and the boundary of the vehicle on the numerical results are demonstrated.It is found that the sound fields in the circular tunnel and the rectangular tunnel have little difference,and the areas with obvious difference are close to the side wall and the roof of the car body.The noise reduction effect of the sound absorbing materials in the tunnel boundary is not obvious near wheel and rail,but the noise reduction effect on the side wall and the area around the car roof is remarkable.When there is no vehicle boundary,the sound pressure in the tunnel is increased by 2.5 dBA,and the sound pressure close to the side wall and the roof reduced.The research on the BEM provides a reference for the numerical calculation.The study of the sound field in the tunnel can provide the basis and reference for the study on the prediction and control of the interior noise in the tunnel. |
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