水下航行器共形声基阵流噪声建模与特性研究

The background noise of an underwater acoustic array is one of the critical influences on the performance of a sonar system. Reducing the noise level effectively or knowing about the space-time characteristic of the background noise is important for improving the detection performance of a sonar system.Based on the Liepmann’s theory of vortex sound, the power spectrum from the boundary layer transition received at the stagnation point of an axisymmetric body will be analyzed and predicted. The diffraction loss around the axisymmetric body will be taken into account.A standard metal buoyant unit will be designed to measure the flow noise in a lake experiment. Then the analytic result of the flow noise will be compared with the experiment data. .In addition,the diffracted sound field on the head surface of an axisymmetric body will be calculated by the Uniform geometrical Theory of Diffraction.The ray path between the source point and the field point on the surface of an axisymmetric body will be traced by the dynamic programming method.Based on the boundary element method, the array manifold of the acoustic conformal array will be calculated. The physical properties of the diffracted sound field will be studied, which is important for improving the performance of the array signal processing.The conventional beamformer、the minimum variance distortionless response beamformer and the second-order cone programming beamformer will be dedigned for the conformal array on the head of the axisymmetric body in flow noise field.Then the optimizing beampatterns of the conformal array in flow noise field will be given.

水声基阵背景噪声是影响声呐系统探测性能的一个重要因素，有效降低声基阵的背景噪声级或准确掌握背景噪声的时空统计特性可以增强声呐系统对微弱信号的检测能力。本课题将以水下回转体流噪声为对象展开研究，基于Liepmann涡声理论，采用Josserand通过实验测得的间歇因子和湍斑猝发频率，对回转体流体动力参数进行估算，进而对回转体边界层转捩区辐射至头部驻点处的声功率谱进行计算和分析，并考虑绕射损失的影响。同时设计无动力上浮实验对回转体流噪声进行测量，对理论计算结果进行验证。.本课题将引入几何光学中的一致性几何绕射理论对回转体头部表面的绕射声场进行计算和分析。首先采用动态规划方法对回转体头部表面的绕射射线进行寻迹，然后采用边界元方法对回转体头部共形声基阵的阵列流形进行计算，最后对回转体转捩区辐射噪声的绕射声场对其头部共形声基阵波束形成器性能的影响进行研究，进而为优化阵处理性能提供技术依据。

水声基阵背景噪声是影响声呐系统探测性能的一个重要因素，有效降低声基阵的背景噪声级或准确掌握背景噪声的时空统计特性可以增强声呐系统对微弱信号的检测能力。基于涡声理论，采用解析方法对回转体流体动力参数进行了估算，进而对回转体边界层转捩区辐射至头部驻点处的声功率谱进行了计算和分析。提出了一种基于一致性几何绕射理论的回转体头部表面绕射声场计算方法。采用动态规划方法对回转体头部表面的绕射射线进行了寻迹，采用边界元方法计算了回转体头部共形声基阵的阵列流形，研究了回转体转捩区辐射噪声的绕射声场对其头部共形声基阵波束形成器性能的影响，为优化阵处理性能提供了技术依据。最后设计了无动力上浮试验，对回转体流噪声计算结果进行了验证。研究结果表明：来流速度和回转体直径是影响转捩区长度和噪声功率谱的主要因素。当回转体转捩区的长度减小时，转捩区辐射声功率的谱峰将向高频迁移；回转体头部表面的声绕射损失对转捩区辐射到头部驻点处的声功率谱有较大影响，特别是在高频段内绕射损失不可忽略。回转体头部声基阵的噪声相关性较弱；在设定的中心频率处，位于回转体顶端一侧的阵元之间的噪声相关性略高于顶端平面阵元之间的噪声相关性。当考虑障板的散射和绕射作用时，单个阵元接收来自不同方向信号时的幅度响应差异较大，信号从同一方向入射时，各个阵元对该入射信号的响应也都不相同，因而回转体头部障板对声基阵阵列流形的影响较大，不能对共形声基阵的各阵元作各向同性的假设。