Noise generated from high-speed trains has been a critical environmental issue. Accuracy in the assessment of noise can affect not only the industrial development but also administration policies. Useful information can be obtained from noise source maps using directional microphone systems such as microphone array; therefore, many noise source models have been proposed on the basis of such noise source maps. However, in most of the previous studies, noise source models, such as steady monopoles and dipoles, are so simplified that the accuracy of the noise level estimation is insufficient. In this study, we propose a method for improving the accuracy of noise level estimation by considering the directivity and unsteadiness of noise sources, which are based on experimentally measured data obtained from a 2-D microphone array. In the proposed model, the noise source distribution was calculated for analysis grids around a train body at every time step. The directivity and unsteadiness of the sound sources on each grid were obtained by shifting the focal point of the microphone array along the direction of the train's motion. The time history of the wayside noise level was calculated assuming that the discrete directive noise sources being distributed on the grids were moving at a constant train speed while changing their amplitudes. This enables us to consider both the effects of directivity and the unsteadiness of the sound sources. To validate this method, noise measurements were conducted beside a Shinkansen track. By comparing the estimated time history of the noise level with the one actually measured by an omnidirectional microphone positioned at the center of the microphone array, we discuss the effect of emission characteristics of the noise sources and the accuracy of the proposed method.
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