Analysis And Control Of Wheel-rail Vibration And Sound Radiation Of Metro Elevated Line In Mountain City

Urban rail transit by virtue of its huge transportation volume,safe and reliable,punctual operation,no traffic jam etc advantages,has developed rapidly in our country in recent years.Viaduct line is an important line laying form in urban rail transit with short construction period,convenient maintenance and flexible line layout.Rail transit in urban areas not only relieves the strain of city traffic,but also brings about a decrease in noise pollution to the living,manufacturing,and scientific research areas along the route.To mitigate the repercussions of rail transit noise on those living close to the line,it is essential to anticipate the sound radiation of wheel-rail vibration due to rail transit vehicles.In the planning and design stage of urban rail transit,reasonable and effective vibration and noise reduction measures can be implemented.This thesis takes the Shijingpo-Shuangbei Section elevated line of Chongqing Rail Transit Line 1 as its engineering background,with a focus on the spatial distribution of noise in mountainous cities.The primary research findings and accomplishments are as follows:(1)Analysis of measured noise characteristics along elevated viaduct in mountain city.For the monitoring of noise along,including the bridge structure,wheel/rail noise and sensitive noise,obtained the 1/3 octave of each measuring point sound pressure level,as a reference of the acoustic model validation;By means of 1/3 octave sound pressure level of each measurement point,the energy analysis was carried out,and the ratio of low frequency,medium frequency and high frequency sound energy was compared.It was concluded that the high frequency noise accounted for the largest proportion,and wheel and rail noise was the main noise contribution source.Through the evaluation of the sound environment along the metro line,it is concluded that the noise of the metro elevated line in mountain city exceeds the standard limit by 10 d B.(2)Establishment of coupled vibration and noise prediction model for elevated railway in mountain city.Firstly,the vehicle submodel,track submodel and bridge submodel are established,and the vehicle-rail-bridge coupling vibration model is established using the wheel-rail relationship and the bridge-rail relationship.Secondly,the wheel-rail response data is taken as the acoustic boundary to establish the acoustic radiation model.Verification of the model’s accuracy has been achieved at last.Verification of the wheel-rail coupling acoustic radiation model is achieved through the measured noise data.The error between 1/3 octave data obtained from the acoustic radiation model and the measured data is within 4%.The model established in this paper can better predict wheel-rail noise.(3)Analysis of sound and vibration characteristics of wheel-rail system of elevated line in mountain city.Firstly,the modal,harmonic response,acoustic radiation efficiency,acoustic power,acoustic directivity and acoustic contribution rate of the wheel and rail subsystem are analyzed respectively.Secondly,the spatial sound field distribution of the wheel-rail coupling system in mountainous cities is analyzed,and the maximum sound pressure level is evenly distributed in mountainous cities.Finally,the influence of speed on the wheel-rail dynamic characteristics and acoustic radiation is analyzed.It is concluded that reducing speed can optimize dynamic characteristics and sound environment.(4)Noise control measures of elevated line in mountain city.According to the wheel-rail coupling system in mountain city established in Chapter 4,four noise control measures are proposed: elastic wheel,damped rail,fully enclosed sound barrier and building layout.An initial assessment of the acoustic radiation and dynamic properties of the elastic wheel and damping rail reveals that the two indexes have been optimized,thus decreasing noise by a factor of 2-3d B.Secondly,the noise reduction effect and its influence on the bridge are studied,and it is concluded that the measure can reduce the noise by 10 d B,but it can double the bridge deflection.Finally,the building layout is optimized.By changing the building’s orientation to 45° Angle with the line,the noise reduction can be about 3.3d B,making the building far away from the sound source,and the sound pressure level change becomes minimal after 50 m.