圆形活塞声源的有限振幅反射波

本文研究了圆形活塞声源的有限振幅声波的反射。应用像源法计算已产生的谐波本身在边界上的反射,将它们看成是反射边界上振动的新声源所产生的辐射场,再应用弱冲击理论来计算这部分场自己产生的谐波场。在水池中作了二阶谐波的反射实验,反射界面是水池壁。结果表明,谐波声压随距离的平均衰减规律与理论符合得很好。实验还表明,反射谐波场沿纵向距离以及与它相垂直的横断面上有强烈的干涉现象,而纵向相干长度比横向相干长度大一个数量级。通过理论估计,认为这种现象是由于反射壁的有限厚度、它的两个平面之间有一个很小的角度以及发射波束有一定的宽度所造成的。这样估算出来的两个相干长度与实验符合。 关键词：

FINITE-AMPLITUDE REFLECTION WAVE OF CIRCULAR PISTON SOUND SOURCES

In this paper, an experimental and theoretical investigation on finite-amplitude reflection sound wave of circular piston sources is presented. The reflected field of harmonic waves from the boundary surface have been calculated. Thinking of them as the waves which radiate from the image of the piston source and treating them as the waves that seem to be generated by a new source on the vibrating boundary surface, by means of weak-shock theory, the reflection of the finite-amplitude waves can be predicated.By making use of the boundary wall of a pool, some experiments on second harmonic reflection have been done. It is shown that the average attenuation of the harmonic pressure with distance is consistent with the theory. However, along the longitudinal distance and in the cross sections perpendicular to it there are obvious interference of the harmonic waves, and longitudinal interference lengths have an order of magnitude greater than the traverse ones. According to the theoretical evaluation, it seems to be that the reflection results from the pool wall that has a thickness, a small angle between its two boundary surfaces and a fixed beam width of the primary wave. The theoretical evaluation and the experiments are in agreement with each other.