| China’s high-speed railway has shown an explosive growth in the last 15 years,but as the high-speed railway network becomes more dense,and as small and medium-sized cities are able to communicate more quickly with nearby central cities due to the huge time advantage of high-speed railway,these small and medium-sized cities are also planning to build dense public transport-oriented property developments(TOD)near their high-speed rail stations;these development conditions are bound to make the noise pollution from high speed railway cover the population increased sharply.In addition,the research and development of high-speed railway with higher speed is also on the agenda.Higher speed means more violent wheel-rail interaction and greater rail traffic noise,so the control of wheel rail noise is also one of the research and development priorities for the 400 km/h high-speed railway.Against these backdrop,the environmental noise problem caused by high-speed railway is being paid more and more attention and needs to be further studied.The current outside sound source identification measurements from slab high-speed railway shows that basically the bogie area noise is the largest contribution in the process of the train through.Therefore,to control the environmental noise from high-speed railway,the noise from bogie area must be controlled firstly.Noise from bogie area mainly consists of two parts: one is the wheel-rail rolling noise from wheelset and track structure,the second is the aerodynamic noise,which is generated by the high-speed movement of the bogie in the air.Studies have shown that under low speed conditions,the wheel-rail rolling noise is the most important,however,at 350 km/h or higher,it is not clear which of the two is more important,which makes the control of high-speed railway noise very difficult.In order to get the quantitative value of the two contributions,one idea is to build a prediction model for the wheel-rail rolling noise,and the contribution of both can be obtained by subtracting the predicted value of the wheel-rail rolling noise from the test value.This idea puts high demands on the accuracy of the prediction model of wheel-rail noise.Therefore,it is necessary to develop a set of accurate rolling noise prediction models for high-speed railways that can take into account some model assumptions that have been simplified to improve their prediction accuracy.In this thesis,modeling work is carried out for the following subsystem models respectively for the characteristics of the slab high-speed railway.(1)Combining the finite element method,the principle of virtual work and the second type of Lagrangian method,the differential equation of vibration of a rotating body subjected to a fixed load is obtained in the columnar coordinate system,which contains the six degrees of freedom of the rotating body as a rigid body(including vertical,horizontal and longitudinal translation,and side roll,rocking head and rotation)and the unknown variables of the elastic vibration response of the finite element nodes.While based on the momentum and angular momentum theorems and the Fourier series method(for axisymmetric bodies such as wheelset),the vibration of the wheelset can be finally discretized and decoupled in the annulus direction,and a set of positive definite algebraic equations can be formed to solve for the vibration response of the rotating wheelset.Then the axisymmetric boundary element method is used to establish the acoustic radiation model of the wheelset,and finally the structure-acoustic coupling model of the high-speed rotating wheelset is constructed.(2)For the characteristics of the discrete support of the track,the Fourier series method is used to derive the vibration of the track structure in the frequency domain,and on the basis of the vibration response,the 2.5-dimensional boundary element method is used to derive the acoustic radiation contribution of the rail and the track slab,the prediction model contains two discrete support structures of fasteners and the slabs.The model considers the vibration response of the rail in the lateral and vertical directions and in the fixed coordinate system(fixed field points outside the vehicle)and moving coordinate system(field points moving with the vehicle),and finally constructs the high-speed track vibration model for the environmental noise outside the vehicle and the noise with the vehicle.(3)Using "moving roughness" method and "moving mass" method to get wheel-rail interaction solution,The receptance of wheelset and track at the wheel-rail contact point obtained from the vibration model of high-speed rotating wheelset and high-speed railway is taken as the input,and the high-frequency wheel-rail interaction prediction model is constructed by considering the coupling between wheel-rail in vertical and lateral directions,the non-coherence of left and right wheel-rail roughness,and the non-coherence of front and rear wheel-rail roughness.On the basis of verifying the subsystem model,the wheel-rail force obtained from the wheel-rail interaction prediction model are input into the established acoustic vibration model of wheelset and track,and the high-speed movement of the wheel-rail rolling noise sound source relative to the observe points of the environment outside the vehicle is considered to finally construct a complete high-speed railway wheel-rail noise prediction model.Based on these models,the following studies are carried out on the noise generation mechanism and influencing factors.(1)Based on the acoustic vibration model of the rotating wheelset,study the effect of rotation on the natural frequency and resonance frequency of the wheelset and the physical mechanism in it,compare the differences in acoustic radiation characteristics of the free wheelset,constrained wheel and free wheel,and discuss the influence of the upper suspension components of the wheelset and the left and right wheel track excitation methods on the vibration-acoustic characteristics of the wheelset.(2)Based on the vibration-acoustic model of high-speed track,the characteristics of receptance,vibration propagation wave and attenuation rate of high-speed rail are studied,the influence of rail slab flexibility and fastener stiffness on rail vibration characteristics are discussed,the traditional simplified formula of rail radiated sound power is compared,the reasons for the differences are analyzed and the influence of distance between rail and slab on rail acoustic radiation characteristics is discussed.(3)Based on the wheel-rail interaction prediction model and wheel-rail noise prediction model,the effects of some model assumptions(such as high-speed rotation of wheelset,vertical and lateral coupling between wheel rails and coupling of multiple wheelsets on the rail)and complex working conditions(wheel wear,rail gauge,distance between rail and rail slab,environmental temperature)are investigated.In addition,a comprehensive test on the external environmental noise of high-speed railroads in China is carried out,and the measured results are compared and discussed with the prediction results of wheel-rail rolling noise obtained from the model built in this thesis to verify the reasonableness of the calculation results on the one hand,and to determine the main characteristics of the contribution of wheel-rail rolling noise to the external environmental noise on the other hand. |
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