海底沉积物压缩波声速比与物理特性的关系

海底沉积物因组成结构复杂导致声学特性复杂多样,多种理论解释模型存在参数较多且各具适用性现象·通过运用体积平均和等效参数的方法对海底沉积物声波传播机理进行研究,提出一种少参数的海底沉积物与底层海水的压缩波声速比通用模型(General Model of Sound Speed Ratio,GMSSR).GMSSR模型包含弹性结构分布因子、孔隙度、等效密度比、等效弹性模量比4个物理特性参数。分析海底沉积物两相介质结构的串联和并联两种极限情况分析,基于弹性结构分布因子和串并联结构的体积平均分布建立一般情况下海底沉积物的等效弹性模量表达式·应用GMSSR合理地分析各海域测量的海底沉积物声速比经验模型的共性和解释南海实测数据分散的范围,表明:(1)表层海底沉积物主要是以串联结构为主,接近于悬浮液状态或者体积分量很少的并联堆积状态;(2)等效弹性模量比的影响因素大于等效密度比,结构变化往往通过影响弹性结构分布因子而影响等效弹性模量比,从而引起声速比的变化;(3)不同研究海域的声速比-孔隙度经验关系具有相似性,可以通过GMSSR模型分析得出;(4)基于弹性结构分布因子的差异,可以合理解释南海海域测量表层海底沉积物声速比较大的分散性。

Relationship between the sound speed ratio of the compressional wave and the physical characteristics of seafloor sediments

The acoustic characteristics of seafloor sediments are complicated and diverse, due to their complex components and structures. A variety of theoretical interpretation model has many parameters and each has its own applicability. By using volume averaging method and equivalent parameter method, we researched the acoustic propagation mechanism of seafloor sediment, and proposed a general model of sound speed ratio of compressional wave of sediment against bottom seawater(GMSSR) with less parameter. The GMSSR contained four physical parameters including elastic structure distribution factor, porosity, equivalent density ratio and equivalent elastic modulus ratio. With the analysis of two limit states of the structures of two-phase medium of seafloor sediment: series structure and parallel structure, an equivalent elastic modulus expression of seafloor sediments under normal circumstances was established with the introduction of elastic structure distribution factor and series-parallel structure of volume averaging distribution.The GMSSR was applied to analyze the generality of empirical models and the scattering of measurement datasets of surficial seafloor sediment in different sea reasonably. The analysis showed that:(1) the surface sediment is mainly with series structure, being close to the suspension state or with little accumulation condition of parallel volume components;(2) the influence of equivalent elastic modulus ratio factor is greater than the equivalent density ratio. The structure change is often affecting the distribution of elastic structure to change the equivalent elastic modulus ratio, resulting in the change of sound velocity;(3) the different empirical equations in different study sea areas between sound speed ratio and porosity are similar and can be explained by the GMSSR;(4) the large dispersion of measurement sound speed ratio of surficial seafloor sediments in South China Sea can be reasonably interpreted by the difference of elastic structure distribution factor.