海底沉积物颗粒非均匀性对声学特性的影响研究

The seafloor sediments are usually taken as isotropic porous media in the theories of sound wave propagation. However, the heterogeneities of natural seafloor sediments can influence the sound propagation properties and cause the bulk scattering of high frequency sound wave. The effects of the heterogeneities on the acoustic properties of sediments were still described used in qualitative or random methods, which can not support the practical relationships between acoustic and physical properties and the effective theories of sound wave propagation.This project will study on the quantitative espression of the affect of the granule heterogeneities on the acoustic properties of sediments, and the granule homogeneous sediments will be sampled in seafloor and inhomogeneous sediments will be made in plexiglass tubes. This project will conduct the high frequency acoustic measurement between 25 kHz to 1 MHz, the physical and geotechnical measurement and the microstructure observation. Bsed on the probability statistical of the granule and pore structure, the reliable relationships between acoustic and granule heterogeneities can be established. Based on the frequency dependence of acoustic properties, the project will verify the application of acoustic modeling for the inhomogeneous sediments. The aim of this project is to improve the validity of the relationships between acoustic and physical properties and the theories of sound wave propagation, and has great significance in theory and application.

声波传播理论通常把海底沉积物视作均匀介质，然而自然状态下海底沉积物的非均匀性对高频声波的传播特征有重要影响。由于缺乏沉积物非均匀性对声学特性影响的有效定量表征，导致声学经验方程的预报精度较低和传播理论模型的失配，限制了经验方程和理论模型的有效应用。本课题聚焦颗粒分选性、孔隙结构、物理性质空间波动特征等颗粒非均匀性，定量表征颗粒非均匀性对海底沉积物声学特性影响。拟采集海底多类型的颗粒非均匀沉积物，并在有机玻璃管中重塑制作单一粒级的颗粒均匀沉积物模型，开展25 kHz- 1 MHz的高频声学测试、物理力学测试和微结构观测，量化沉积物的颗粒非均匀性和孔隙特征，建立沉积物声学特性与颗粒和孔隙结构参量的相关关系；基于声学特性对频率的依赖关系，探讨声波传播理论模型对非均匀沉积物的适用性。该研究可以提高预报方程的预测精度，促进海底沉积物的声学建模，具有重要的理论研究和实际应用价值。

本项目围绕着颗粒非均匀性对沉积物声学特性的影响这一主题，系统研究了多海域、多类型和宽频域的海底沉积物声学特性，开展了一系列分析测试和数值模拟工作，取得了积极进展。通过本项目研究，率先建立了不同类型海底沉积物声学特性对频率的依赖关系，构建了多类型、宽频域的海底沉积物声学频散模型；率先获取了南海珊瑚岛礁区的钙质沉积物声学特性数据，丰富了海底沉积声学的研究类型；分析了颗粒不均匀性对沉积物声学特性的影响，提出了将颗粒不均匀系数作为因子引入沉积物声传播模型的方案。上述模型和数据实现了对多类型海底沉积物目标频率下声学特性的预测，对推动海底沉积声学学科发展具有重要作用，也将在海洋声场建模、水下目标探测等领域具有广阔的应用前景。