An Analysis Of External Noise Source Contribution And Influence Factors For A High-speed Train

With the development of high-speed railways and the increase of operating speed,railway noise has attracted great attentions from governments,railway departments,research institutes and universities over various countries.The contributions of external noise sources to the noise of high-speed trains and the influencing factors have hardly been studied in literature due to its complexity and limitations of existing technics.This thesis,treating on the above mentioned problem,is composed of the following contents.First,contributions of noise sources in different train body areas to the total sound power of exterior noise were sorted based on the results of train noise source identification,and the effects of the operating speed and track type were also analysised.It was found that the wheelrail noise is still the lion's share,contributing to 39.1% of the total sound power,in bridges at 300 km/h,followed by that emitted from the lower part of carbody(25.7%.),the contributions of the surfaces of car body,the pantograph and other areas of the roof are less important,and the contributions of other areas are neglible.With the increase of train speed,the contributions of the wheel-rail area and the lower part of carbody tend to decrease,while the contributions of the surfaces of car body,the pantograph and other areas of the roof increase correspondingly.Compared with the bridge sections,the importance of the wheel-rail area and the lower part of carbody reduces on the subgrade sections,and that of the surfaces of car body,the pantograph and other areas of the roof increases.Secondly,a model was established to predict the external noise of high-speed trains on the basis of the results of train noise source identification and geometrical acoustics to further study the contributions of different train areas to external noise.Validation of the prediction model was conducted by the comparing the calculated results to those measured at standard positions defined by ISO standards.Furthermore,the contributions of different train areas to the pass-by noise and the sensitivities of pass-by noise to changes in the intensity of noise sources in key areas were calculated and analyzed by using validated model.The results show that the wheel-rail noise is also still the lion's share,contributing to 37.6% of the pass-by noise,in bridges at 300 km/h,followed by that emitted from the lower part of carbody(34.1%.),the contributions of the surfaces of car body,the pantograph and other areas of the roof are less important,and the contributions of other areas are neglible.The sensitivities of pass-by noise to the changes in the intensity of noise sources in the wheel-rail area and the lower part of carbody are 0.39 and 0.35,respectively.In other words,the pass-by noise can effectively reduce 0.39 d B if the sound power level of noise sources in wheel-rail area decreasing every 1 dB.Finally,based on the experimental data and validated prediction model,the influences of train speed,track type and structure of sound barriers etc.on the contributions of different train areas to the pass-by noise were studied.The results show that,the influences of train speed and track type on the contributions of different train areas to the pass-by noise are similar to their influences on contribution to the total sound power.When the height of sound barrier is 2.05 m,the contribution of noise sources in the car body surface area is the largest.When the sound barrier height increases from 2.05 m to 3.05 m,the contribution of noise sources in the other areas of the roof is the largest,and followed by the pantograph area.Based on the relative contribution of different train areas and the corresponding sound power level spectrum under the different working conditions given in the paper,the external noise control strategy for high-speed trains can be formulated efficiently.