Acoustic scattering from a suspension of flocculated sediments
Acoustic scattering from a suspension of flocculated sediments
复制标题
DOI：
10.1002/jgrc.20197
复制
发表时间：
2013-05
影响因子：
--
通讯作者：
Iain T. MacDonald;Christopher E. Vincent;Peter D. Thorne;Benjamin D. Moate
中科院分区：
文献类型：
--
作者：
Iain T. MacDonald;Christopher E. Vincent;Peter D. Thorne;Benjamin D. Moate
为了研究细泥沙悬浮液在非絮凝（初级）状态和不同絮凝水平下高频声波（3-5 MHz）的后向散射，进行了一系列实验室对照实验。利用光学系统和沉降管确定絮凝体的大小和下落速度分布，从而确定絮凝体密度。实验结果表明，絮凝颗粒的声学特性不完全受原生颗粒的控制；絮体结构的某些方面影响着散射特性。总体趋势是随着絮凝程度的增加，形态函数（Ks）增加。在总散射截面（内联图像）中也观察到这种趋势，但这一结果依赖于絮凝颗粒的粘性吸收可以忽略不计的假设。将实测散射特性与弹性（ES）和流体球（FS）两种理论模型的预测值进行了比较。虽然结果表明，在目前的形式下，这两个模型都不能充分代表絮凝颗粒悬浮液的散射特性，但这两个模型确实为测量提供了上限（ES）和下限（FS）。就声学测量絮凝沉积物浓度的操作使用而言，经验关系可以与观测结果相匹配，但是，在对声音如何与絮凝颗粒相互作用有更好的理论理解之前，这种经验关系的拟合可能有些为时过早。
A series of controlled laboratory experiments have been conducted to investigate the backscatter of high frequency sound (3-5 MHz) from suspensions of fine sediment in its unflocculated (primary) state and at various levels of flocculation. The size and fall-velocity distribution of the flocs was determined using an optical system and a settling tube, thus allowing floc density to be determined. The measurements have conclusively demonstrated that the acoustic properties of the flocculated particles are not solely controlled by the primary particles; some aspect of the floc structure is influencing the scattering characteristics. The overall trend is for the form function (Ks) to increase as the degree of flocculation increase. This trend was also observed in the total scattering cross section (inline image) but this result is dependent on the assumption that viscous absorption for flocculated particles is negligible. The measured scattering properties are compared to the predicted values from two theoretical models, the elastic (ES) and fluid sphere (FS) models. While the results show that, in their current form, neither model is capable of adequately representing the scattering characteristics of a suspension of flocculated particles, the two models did provide upper (ES) and lower (FS) bounds to the measurements. In terms of the operational use of acoustics to measure the concentration of flocculated sediments, empirical relationships could be fitted to the observations but, until a better theoretical understanding of how sound interacts with flocculated particles is achieved, the fitting of such empirical relations may be somewhat premature.