Noise Reduction Prediction And Design Of New Type Of Noise Barrier For High-speed Train

The high-speed railway is a convenient, fast, comfort and safe transportation mode. The residents living along the track, however, have to suffer from the noise emitted by the high-speed trains. To achieve a more environment friendly, counter measures have to be created to reduce the exterior noise of the high-speed railway. The sound barrier, among the existing measures of noise reduction, seems to be the most effective one. This thesis developed a numerical prediction model of sound barriers for high-speed railway to predict their insertion loss and help to make application evaluation and design of sound barriers.Firstly, the existing methods for evaluation of sound barriers are introduced. A comparison of an empirical method, a geometrical diffraction method and the boundary element method is performed from the aspects of accuracy and applicability. It is found that the empirical method can only deal with the simple sound barriers, such as a semi-infinite barrier; the geometrical diffraction method can take into account the interference between different waves, but it is limited to certain receiving positions and frequency ranges; the boundary element method is recognized as a method with relatively high accuracy.Secondly, the characteristics of the exterior noise of the high-speed trains running between Beijing and Shanghai are studied through the site tests in typical operating conditions, in which the ISO3095-2005standards are employed. The equivalent continuous A-weighted sound pressure level, noise time history and spectral characteristics are analyzed to assess the noise level and main frequencies.Thirdly, a prediction model is developed by the boundary element method to assess the insertion loss of sound barrier in operation based on the sound source identification tests of high-speed trains. The train and track structures are taken into account. By compared to the field results, the prediction model is validated. Furthermore, the prediction model is employed to examine influences of different factors on the insertion loss of a sound barrier, including the locations of the sound source, the sound barrier geometry (sound barrier height, top structure) and acoustic absorption conditions.At last, in order to decrease the multiple reflections between sound barriers a new type of sound barrier with diffuse structure is designed based on the better understanding of the exterior noise characteristics of high-speed trains and existing sound barriers. To evaluate the new barrier’s effects, a series of numerical simulations and specimen tests on noise reduction effectiveness are conducted and compared to those of existing barriers. This work provides an important reference to optimize sound barrier structures..