【作者】 徐禹擎；

【导师】 彭临慧；

【作者基本信息】 中国海洋大学 ， 声学， 2008， 硕士

【摘要】 声纳是利用水下声波对目标进行探测和定位的设备,在军事应用和海洋探测工程方面有重要的作用,其检测阈和探测距离被认为是最重要的性能指标。对于大陆边缘及近岸水域来说,由于海底和海面的反射、潮汐、湍流、环境噪声、气泡、悬浮小颗粒的影响,浅海声传播变得非常复杂的,进而影响声纳的探测性能。所以研究悬浮体小颗粒对浅海声纳探测性能的作用是非常必要的。海洋中声传播损失包括由于几何扩展损失、介质声吸收,海底海面反射衰减,非均匀体散射。我国地势西高东低,东部近岸水域有大量泥沙流入,沉积物含量较高。除此之外风浪、潮汐等动力因素的作用也是该区域悬浮颗粒物浓度增大的主要原因。当主动声纳系统在高浓度混浊海水中对目标进行探测、定位、识别时,大量颗粒物的粘滞吸收作用和体积散射改变了海水中的声衰减,引起声纳检测阈和探测距离的相应变化。本文以Urick的粘滞吸收理论为基础,应用Pekris浅海波导模型,通过与无悬浮颗粒物海水中的声传播进行比较分析,得到近岸混浊海水中声纳检测阈和探测距离的变化关系;通过对中国近岸混浊海水数据搜集分析,整理出黄河口和东海杭州湾附近海域与声传播相关的悬浮颗粒物信息,包括悬浮颗粒物的浓度、密度、粒径和颗粒物组份信息;最后,论文了研究悬浮颗粒物引起的体积混响增量,为确定混浊海水中主动声纳工作背景干扰提供依据。论文对悬浮体小颗粒影响的声纳探测性能变化进行了数值计算,具有一定的应用价值。在对中国近岸混浊海水数据整理分析的基础上进行了数值计算,得到结论如下:(1)声纳的检测阈和探测距离都随着频率的增大而增大,且检测阈的变化ΔDT与颗粒物的粘滞吸收系数αs成正比。(2)对于某一特定频率,当悬浮颗粒物的半径和浓度不变时,粘滞吸收系数和检测阈、探测距离的变化随着密度的增大而增大。当半径和密度不变时,粘滞吸收系数、声纳检测阈和探测距离的变化与浓度成正比。相同条件下,浓度对检测阈和探测距离的影响比密度大。(3)当声纳频率在10 3Hz量级时,半径为10?5 m量级的颗粒物对粘滞吸收系数和声纳探测性能影响最大,半径为10?6 m量级的颗粒物对其影响次之;当声纳频率在10 4Hz量级时,半径为10?6 m量级的颗粒物对其影响最大,半径为10?5 m量级的颗粒物对其影响次之。(4)在上述频率范围内,对数坐标系下的体积散射强度是频率的线性增函数,斜率为40dB/十倍频程,与小颗粒物的瑞利散射规律一致。体积散射强度随着浓度、密度、粒径的增大而增大。在本文的研究范围内,体积散射强度从? 20dB变化到? 250dB。本文从理论上分析了悬浮颗粒物对声纳探测性能的作用,更进一步的工作还需要实验数据的有力支持。更多还原

【Abstract】 Sonar is used by detecting and orienting target with sound wave underwater, it plays an important part both on military use and ocean engineering. Signal-to-noise ratio and detection range are two significant sonar performance criterions. Because of sound wave’s reflection from sea surface and seabed, tide, current, ambient noise, bubble, sound wave propagation under shallow sea gets so complex that performance of sonar is influenced. So the research on sonar performance prediction by suspended particles is very necessary.In seawater sound transmission loss includes geometry spread loss, medium sound absorption, interface reflection attenuation, and nonuniform object scattering. The physiognomy of our country shows the western is higher than the eastern, a large amount of mud and sand carried with river flow into the eastern littoral water area, thus this area contains more sediments. Besides, stormy wave and tidy are also main reasons which cause accretion of suspended particles. When the active sonar system detects, orients, identifies target under high concentration suspension, viscous absorption and volume reverberation inflect the sound propagation in seawater, which cause the sonar signal-to-noise ratio and detection range expression changed.The paper based on Urick’s visco-inertial absorption theory, applies Pekeris wave-guide model, compares and analyzes sound propagation between suspension and clear seawater, thus gets the transform about sonar signal-to-noise ratio and detection range. According to collecting and analyzing the data of suspended particle along Chinese littoral sea, the paper tidies up suspended particles’concentration, density, radius, and components in Yellow River and Hangzhou Gulf, which are four aspects related to acoustics. At last, the paper researches the increment of volume reverberation by suspended particles, these can provide arguments to determine the background disturb where active sonar perform. The paper does numerical calculation about sonar detection performance caused by suspended particles.After analysis, we can conclude that:(1) Sonar signal-to-noise ratio and detection range increase as the frequency increases. The difference of signal-to-noise ratio and detection range between clear seawater and suspension is relative to visco-absorption coefficient.(2) Sonar signal-to-noise ratio and detection range increase as the concentration of suspension or density of suspended particle. Further more the effect from concentration is more obvious than density.(3) Different sonar performing frequency magnitude related to certain unique particle radius magnitude plays most significant influence on sonar performance.(4) Volume scattering-strength increases as the frequency, which is a linearity function. And it is also relative to the concentration, density, and radius. Within the study parameter area, volume scattering-strength changes from -20dB to -250dB.The paper analyzes the influence on sonar performance by suspended particles alongshore in theory, large mount of continuous data should be supported.更多还原