大振幅驻波的实验研究Ⅱ：驻波场谐波的饱和

Experimental investigation on finite-amplitude standing waves:Ⅱ.saturation of harmonics in standing wave field

大振幅驻波在激波形成前的过程中，谐波声压级随基波声压级（Ｌｐ１）增长而出现饱和现象。在Ｌｐ１＜１５３ｄＢ时，ｍ次谐波声压振幅ｐｍ与基波声压幅值ｐ１；呈ｐｍ～ｐｍ１关系。基波升高１ｄＢ，ｍ次谐波升高ｍｄＢ。之后，各次谐波均开始趋于饱和。次数越高，饱和越快，ｐｍ～ｐｍ１的关系逐渐变为ｐｍ～ｐ１的趋向。在频率域内，变化过程大致可划分为三个区域：Ｉ．线性区；Ⅱ．变化区；Ⅲ．激波区。三个区域对应了时域的激波形成。Ｌｐ１＞１６０ｄＢ后，即可认为激波已经形成。基波与电信号的关系也呈饱和现象，但与频率有关。上述结果有助于理论研究工作的进一步深入。

In the process of shock formation, it was found that the tendency to saturation exists for harmonics with the increasing of foundamental sound pressure level (L p1).When L p1 < 153 dB, the relation between the sound pressure amplitude of m-th harmonic pm and that of fundamental P1 is about pm￣ p.When the fundamental changes 1 dB,the m-th harmonic will increase m dB. The fundamental and all its harmonics start their transition toward saturation at about the same time during the increas of excitation.The relation of pm￣ p tends to p.￣ P1. The trend of saturation can be divided into three regions in frequency domain: Ⅰ.linear region; Ⅱ. alteration region, and Ⅲ. shock region. When L p1 > 160 dB, the shock is formed. These results are useful for further theoretical work.