Deguchi Shinji, Hyakutake Toru
Graduate School of Biomedical Engineering, Tohoku University, 6-6-11-1306-2 Aramaki-Aoba, Sendai 980-8579, Japan.
J Biomech. 2009 May 11;42(7):824-9. doi: 10.1016/j.jbiomech.2009.01.027. Epub 2009 Mar 9.
Self-excited oscillation of the vocal folds produces a source sound of the human voiced speech. The mechanism of the self-excitation remains elusive partly because characteristics of the flow in rapidly oscillating vocal folds are unclear. This paper deals with theoretical considerations of the flow behavior in oscillating constriction based on general flow equations. The cause-and-effect relationships between time-varying glottal width and physical variables such as glottal pressure, velocity, and volume flow are analytically derived as functions of oscillatory frequency through perturbation analysis. The result shows that the unsteady effect due to convective acceleration of vocal fold wall-induced flow becomes comparable in magnitude to the Bernoulli effect at a high but physiological frequency of phonation. Consequently, a phase difference between the vocal fold motion and glottal pressure appears, enabling self-excited oscillation. The phase-lead of the pressure compared to wall motion is described as a monotonically increasing function of the Strouhal number. The above two effects essentially play the dominant role in the glottal flow. These explicit descriptions containing flow-related variables are useful for understanding of the glottal aerodynamics particularly at high frequency range of the falsetto voice register.
声带的自激振荡产生了人类语音的声源。自激机制仍然难以捉摸，部分原因是快速振荡的声带中的流动特性尚不清楚。本文基于一般流动方程对振荡收缩中的流动行为进行了理论探讨。通过微扰分析，作为振荡频率的函数，解析推导了随时间变化的声门宽度与诸如声门压力、速度和体积流量等物理变量之间的因果关系。结果表明，在高但生理发声频率下，声带壁诱导流动的对流加速度引起的非定常效应在量级上与伯努利效应相当。因此，声带运动和声门压力之间出现相位差，从而实现自激振荡。压力相对于壁运动的相位超前被描述为斯特劳哈尔数的单调递增函数。上述两种效应在声门流动中基本上起主导作用。这些包含与流动相关变量的明确描述有助于理解声门空气动力学，特别是在假声区的高频范围内。
