Experimental Examination with Elevated Structural Model Concerning Multiple Reflection of Noise Barrier in Noise Forecast of the Ordinary Railways

摘要

Model experiments were conducted to examine the multiple reflections to forecast the noise from the ordinary railway. Noise radiation characteristics were compared with clearances between the train and the barrier covered with or without the sound absorption material taken as parameters. The sound ray method was applied to study the behavior of sound with results summarized below. 1. Noise radiation characteristics exhibit horizontal directivity or less steep contours as the train/barrier clearance is widened. Covering the barrier with the sound absorption material tends to make the contours of the noise radiation characteristics steeper. 2. The influence of multiple reflections occurring between the train and the barrier should be changed in the range of 0-2 dB depending on the train/barrier clearance and the position of predicting point. 3. The reduction in level of noise is small at measuring points where the bottom of the train is visible by reason that the sound absorption material dose not participate in the noise. At hidden measuring points, the reduction level grows more greatly at more elevated heights for the same off-track distance. Although we are able to make clear that the influence of multiple reflections varies depending on the train/barrier clearance and where the expected measuring point is, we could not quantify determine the influences of multiple reflections. For further investigations, a simulation taking advantage of the boundary element method and other studies are scheduled.