长江口和杭州湾浮泥声参数测量

Measurements of acoustic parameters of fluid mud in Changjiang Estuary and Hangzhou Gulf

本文报导了用４种频率（１００ｋＨｚ、１５０ｋＨｚ、５００ｋＨｚ和１５００ｋＨｚ）的超声波，对长江口和杭州湾的水底浮泥在不同重度下测得的声速和重度之间、声衰减与重度之间以及在一定重度下频率与声衰减之间的变化关系曲线。实验结果表明：在相同条件下，杭州湾浮泥的声衰减比长江口浮泥的声衰减大一点（约１０％）。在重度１０．０～１６．０ｋＮ／ｍ３之间，声衰减与重度成线性关系，声衰减与频率约成一次方关系；声速随重度的增加变化不大（约±２％），在低频率（１００ｋＨｚ和１５０ｋＨｚ）上出现一个明显的极小值，例如，长江口浮泥重度１４．５ｋＮ／ｍ３时，声速最小，约为１４６０ｍ／ｓ，杭州湾浮泥重度１３．５ｋＮ／ｍ３时，声速最小，约为１４４０ｍ／ｓ。

The acoustic attenuation coefficients and velocities of fluid mud collected from Changjiang Estuary and Hangzhou Gulf respectively have been measured with ultrasonic waves of 4 frequencies (100,150,500 and 1500kHz)in a water tank. The results show that the linear variations of acoustic attenuation coefficients with bulk densities of fluid mud in the range of 10.0￣16.0kN/m 3 for a certain frequency and with frequencies for a certain bulk density are confirmed, that the attenuation coefficient of fluid mud in Hangzhou Gulf is a little more (about 10%) than that in Changjiang Estuary for a certain bulk density at the same frequency, and that the variation of acoustic velocities with bulk densities in the range of 10.0￣16.0kN/m 3 is slight (about ±2%) and a minimun of velocity can be clearly found at 100kHz and 150kHz frequencies, e.g.1460m/s vs14.5kN/m 3 in Changjiang Estuary and 1440m/s vs13.5kN/m 3 in Hangzhou Gulf.