Mechanical Engineering Department, The Hong Kong Polytechnic University, Hung Hom, Hong Kong, SAR China.
J Acoust Soc Am. 2013 Sep;134(3):1960-9. doi: 10.1121/1.4816542.
The performance of a sound barrier is usually degraded if a large reflecting surface is placed on the source side. A wave-trapping barrier (WTB), with its inner surface covered by wedge-shaped structures, has been proposed to confine waves within the area between the barrier and the reflecting surface, and thus improve the performance. In this paper, the deterioration in performance of a conventional sound barrier due to the reflecting surface is first explained in terms of the resonance effect of the trapped modes. At each resonance frequency, a strong and mode-controlled sound field is generated by the noise source both within and in the vicinity outside the region bounded by the sound barrier and the reflecting surface. It is found that the peak sound pressures in the barrier's shadow zone, which correspond to the minimum values in the barrier's insertion loss, are largely determined by the resonance frequencies and by the shapes and losses of the trapped modes. These peak pressures usually result in high sound intensity component impinging normal to the barrier surface near the top. The WTB can alter the sound wave diffraction at the top of the barrier if the wavelengths of the sound wave are comparable or smaller than the dimensions of the wedge. In this case, the modified barrier profile is capable of re-organizing the pressure distribution within the bounded domain and altering the acoustic properties near the top of the sound barrier.
如果在声源侧放置一个大的反射面，声屏障的性能通常会降低。已经提出了一种波陷屏障（WTB），其内表面覆盖有楔形结构，用于将波限制在屏障和反射面之间的区域内，从而提高性能。在本文中，首先根据陷波模式的共振效应来解释由于反射面而导致常规声屏障性能下降的原因。在每个共振频率下，噪声源都会在由声屏障和反射面围成的区域内及其附近产生强烈的、模式受控的声场。结果发现，在屏障的阴影区域中的峰值声压（对应于屏障插入损耗的最小值）主要由共振频率以及陷波模式的形状和损耗决定。这些峰值压力通常会导致靠近顶部的屏障表面法线方向上的高声音强度分量。如果声波的波长与楔形的尺寸相当或更小，则 WTB 可以改变屏障顶部的声波衍射。在这种情况下，经过修正的屏障轮廓能够重新组织有界域内的压力分布，并改变声屏障顶部附近的声学特性。
