浅海中声源诱发海底地震波的机理及特性研究

The improvement of vibration and noise reduction technology makes the radiation source level caused by navigating ship decrease continuously, which poses a serious challenge to traditional underwater acoustic detection equipment. However, the existing noise reduction processing is still difficult to eliminate the very low frequency (VLF) radiation noise within several to dozens of Hertz. The ability to utilize VLF signal is a way to the detection of ship target. However, shallow-wave waveguide cut-off effect may make VLF acoustic signal unable to propagate remotely, which causes most of energy to be transmitted to seabed. In this way, seabed seismic wave propagating along seabed is excited. If seabed seismic wave signal can be used as an effective complement to acoustic wave, it will make up for the detection of sonar at VLF in shallow sea. This project focuses on the formation mechanism and propagation characteristics of seabed seismic wave in shallow sea. Firstly, a theoretical model of seabed seismic wave in shallow sea is established, and its wave form and characteristics are analyzed. Secondly, high-order staggered grid finite difference method is parallel processed to improve the computational efficiency, simulation study of seabed seismic wave propagation under different marine environments and sound sources is carried out, and propagation rules are summarized. Finally, combining theory and simulation results, experiment on lake is carried out to test the results. Adding up all the above works, it is expected to bring a new technical mean for shore-based remote warning detection.

减震降噪技术的提高使得舰船航行引起的辐射声源级不断降低，给传统的水声探测设备带来了严峻挑战。然而现有的降噪处理对几到几十赫兹内的甚低频辐射噪声仍很难消除，利用舰船辐射的甚低频信号是对舰船目标远程探测的一条途径。然而，浅海波导截止效应可能使得甚低频声波无法有效地远距离传播，导致大部分能量透射到海底，进而诱发出沿海底界面传播的海底地震波。这种地震波有望作为声波的有效补充，弥补声纳在浅海甚低频段上的探测空白。本项目围绕揭示浅海中声源诱发此类海底地震波的机理及特性开展研究，首先建立浅海中海底地震波的理论模型，分析其波动形式及特性；其次并行化处理高阶交错网格有限差分法，提高计算效率，开展不同海洋环境和声源条件下海底地震波传播过程的仿真研究，总结其传播规律；然后结合理论和仿真结果开展湖上试验，检验研究成果。有望为岸基远程预警探测带来新的技术手段。

航行舰船自身的振动以及辐射噪声经海水介质传播到海底，会诱发出沿海底界面传播的海底地震波，其同样携带着目标位置信息，可为舰船目标的定位、跟踪和识别提供一种新的技术手段，弥补声纳设备在浅海甚低频频段上的探测空白。. 本项目围绕理清浅海中声源诱发海底地震波的机理及特性从理论、仿真和试验三方面展开工作，主要研究成果包括：①建立了浅海中声源诱发海底地震波的理论模型，推导出了点声源在海底界面处诱发出的地震波场复积分式，系统地分析出了海底地震波的所有组成部分以及给出了各组成部分的波场解；并结合海底地震波波场的数学求解过程对其各组成部分进行了物理解释。②开发了海底地震波数值模拟的高效算法，并对浅海中单频声源诱发的海底地震波进行了数值模拟，首次展现出了浅海中各种不同类型波的时空结构，呈现出了不同海底介质、海水深度、声源频率、声源深度条件下海底地震波的波场结构和能量分布，并总结了海底地震波的传播特性。③结合理论分析和和声场数值计算的结果，利用项目组自研的地震波传感器，开展了海底地震波试验研究。气枪脉冲声源试验显示：在浅水域，利用气枪脉冲声源可以激发出不同类型的地震波信号，并可被布放在水底面上的垂向振动传感器所接收，与理论研究和数值模拟结果互相验证。该项研究为后续海底地震波在水下预警探测中的应用提供理论依据和指导，国防应用前景大。