河底流体-硬质多孔媒质界面的声波传播特性研究

Formed from silt and clay after long-term precipitation, hard sediments of porous medium exist in the bottom of rivers, widely. River sediments are different from that of sea. The measurements of parameters such as density, grain size and porosity are significant to silt-clearing. This proposal investigates a nondestructive method to measure sediment parameters by using relationship between acoustic reflectivity and incident angle and Scholte wave propagation characteristics. Measuring and analyzing fieldwork sampling, acoustic wave equation will be established for river sediment porous medium. To solve the fluid-porous medium interface reflectivity and Scholte wave dispersion and attenuation, the relationship between acoustic propagation characterization and porous medium will be discussed. Schlieren image technique will be implemented to visualize acoustic field dynamics in the fluid area nearby the interface. Physical mechanism of Scholte wave propagation characterization will be studied according to acoustic field Schlieren images. Acoustic nondestructive measurement method of river sediments parameters can be obtained which is based on analysis of acoustic measurements and the inversion of sediment parameters.

由粉砂、黏土长期沉淀形成的硬质多孔媒质沉积物，广泛存在于河流底部，其孔隙度等特性区别于海底沉积物，对该类沉积物密度、颗粒尺寸、孔隙率等参数的测量，在河道清淤等方面有重要意义。本项目研究利用流体-多孔媒质界面声波反射率随入射角的变化，以及Scholte波的传播特性无损测量媒质参数。对工程现场的样品进行测量和计算分析，参考海底沉积物声学研究方法，建立适用于河底沉积物的多孔媒质声学理论模型，求解流体-多孔媒质界面声反射率、Scholte波频散和衰减，讨论其与多孔媒质参数的关系。采用Schlieren高速动态成像技术直观观察界面上流体域的入射声波、反射声波和Scholte波传播的动态变化情况，探讨Scholte波传播特性的物理机理。分析声学测量结果，反演沉积物的相关参数，形成采用声学手段获取河底硬质沉积物参数的测量方法。

我国是一个多河流湖泊的国家，清除河、湖底部沉积物对于水体治理、水下建筑施工很有意义，需要快速、准确测量沉积物的物理性质。沉积物清除分为清淤和疏浚两种，疏浚的沉积物颗粒胶结好，骨架模量大，而清淤的颗粒物小，颗粒松散。.本项目研究清淤和疏浚两种情况下沉积泥沙的多孔介质模型，探讨了沉积砂岩类硬质多孔介质不同频率下声速的传播规律、针对清淤中沉积物松散、胶结差的情形，研究高频时声速与频率的关系，得到用声速求颗粒粒径和孔隙率的关系，确立的通过声速测量水饱和松散颗粒介质粒径和孔隙率的方法。为进行多孔媒质声学特性测量，研究衰减介质中声场的分布规律以及声场的纹影成像方法。.项目研究陈果中关于疏松沉积物中声速和孔隙率、平均粒径间的经验关系，建立采用超声波的方法无损测量沉积泥沙声速进而计算粒径和孔隙率对可以用于清淤现场，对推动超声在河流湖泊清淤、疏浚中的应用有重要作用。