Li Zhiyuan

Image Source Model of Coherent Noise in Outdoor Half - open Space

Nowadays, noise prediction of industrial enterprises are mostly based on ISO 9613-2, which requires that the influence of coherent sources be disregarded. However, outdoor noise sources in industrial enterprises are mainly distributed in a halfopen space and form several coherent sources because of multiple reflections. The image source model of coherent noise in outdoor half-open spaces has elicited much research attention. To increase the prediction accuracy of sound fields inside and outside half-open spaces, an image source model of noise in a half-open space was proposed. The model considers coherent sound fields. First, multi-level image sources were established through a geometric method, and the positions of image sources were determined. Second, the reflection coefficient of the plane wave and the effective sound source were determined through acoustic beam tracing. Third, analog computation of different boundary materials was implemented by adding the impedances of different boundaries. The sound fields in a half-open space with rigid impedance and absorption boundaries were calculated with the proposed, boundary element, and ISO 9613-2 models. Results showed that the ISO 9613-2 model can only reflect the overall attenuation trend of sound energy, whereas the proposed coherent image source model and the boundary element model can reflect the fluctuation trends of sound waves at different positions. The calculated results of the coherent image source model and the boundary element model were basically consistent; the errors were controlled within 1.5 dB. However, compared with the boundary element model, the proposed coherent image source model has approximately 100 times higher computational efficiency. This high accuracy reveals the proposed coherent image source model’s applicability and accuracy. The model is particularly suitable for remote noise prediction in outdoor half-open spaces.This study aimed to determine the influence of mining thickness on the rationality of upward mining in coal seam group. Numerical simulation and theoretical analysis were performed to investigate the influence of the mining thicknesses of initial mining seam on the destruction and pressure relief effect of the upper coal seam in a high-gas coal seam group. The mechanical model of the roof failure based on the mining thickness was established by assuming that the gob formed after adjacent panels have fully been caved is the infinite plane. On the basis of this model, an equation was derived to calculate the roof failure height of the panel. Considering the geological conditions of No. 9 and No. 12 coal seams of Zhaogezhuang Coal Mine, economic effectiveness, and proposed techniques, we concluded that the top layer (4 m) of the No. 12 coal seam should be mined first. The top layer of the No. 9 coal seam should be subsequently mined. The topcaving technique was applied to the exploitation of the lower layer of the No. 12 coal seam. Practically monitored data revealed that the deformation and failure of the No. 2699 panel roadway was small and controllable, the amount of gas emission was reduced significantly, and the effect of upward mining was active. The results of this study provide theory basics for mine designing, and it is the provision of a reference for safe and efficient coal exploitation under similar conditions.