搜索策略改进的波束形成定位方法研究

针对传统时差方法定位精度低和波束形成方法定位效率低的问题,提出了一种基于遗传算法和波束形成算法的海洋平台损伤定位方法。通过遗传算法对待搜索区域坐标进行编码、选择、交叉、变异等操作,对波束形成算法的搜索策略进行改进,快速搜索损伤位置坐标。实验证明,与时差定位算法相比,本文方法的定位误差降低了50%;与波束形成算法相比,本文方法的运算时间减少了53%。因此,本文方法在保证定位精度的前提下,提高了算法的执行效率,对海洋平台损伤的实时监测和定位具有一定的实用价值。     

采用分级聚焦波束形成的快速声成像算法

为了减小常规波束形成所需的庞大计算量以实现快速成像,本文提出了一种新的波束形成算法——分级聚焦波束形成。将基阵划分成各级子阵分级进行处理,对较短的子阵进行远场近似处理,逐级合并子阵进行子阵间的近场聚焦波束形成,并逐级进行波束插值。MAT- LAB仿真计算结果表明,分级聚焦法与常规波束形成相比,计算量和数据存储量大幅下降。该方法尤其适用于多焦点近场聚焦的场合。     

三维声发射源定位实验简易实现方法

本文针对声发射技术中的三维定位问题提出一种新的简易实验方案.通过传感器接收的时差信息和空间坐标实现三维立体结构中的声发射源定位,操作和计算简单,降低了实验成本.该实验方法不仅可以直观地实现三维声发射源定位过程,还可以实现声速的测量.本设计加深了学生对物理问题的理解,提高了学生对声发射技术和声源定位技术的兴趣,适合普及.     

声发射衰减特性管道泄漏定位方法

声发射技术具有灵敏度高、实时性强、覆盖范围大等优点.泄漏产生的声发射波沿管壁传播会发生衰减,通过研究衰减系数与金属晶粒散射和热流损失的关系,建立准确的声发射能量衰减模型.在此基础上,针对声发射频带宽的特点对传统衰减定位模型进行改进,提出宽频带声发射源定位模型,该方法先通过实验确定泄漏信号频带,再将滤波后的信号经过小波包...     

基于光纤光栅的冲击激励声发射响应机理与定位方法研究

在对冲击激励声发射应力波在铝合金板上的传播机理进行分析的基础上,利用ABAQUS软件构建了钢球冲击铝合金板几何模型,仿真分析了冲击应力波传播过程.理论分析了冲击应力波与FBG传感器的作用机理,基于边缘滤波原理构建了声发射传感系统,采集冲击激励声发射应力波,建立了声发射区域定位模型,提出了基于扩散映射与支持向量机(SVM)的声发射区域定位方法并进行了实验验证.在300 mm×300 mm×2 mm的铝合金板上对36个测试区域进行了多次声发射区域定位实验,实验结果表明,扩散映射结合SVM的定位结果较优,区域定位精度为30 mm×30 mm,定位正确率为97.5%,耗时0.781 s.研究结果为声发射区域定位检测提供了一种有效方法.     

混凝土中的声发射波速特性及其在源定位中的应用

利用声发射技术监测受载混凝土裂缝发展特征的首要任务是对声发射源的准确定位.为了解混凝土中声发射波速特性,提高声发射源定位精度,该文开展了一系列室内试验,构建了考虑衰减现象的声发射波速修正模型,优化建立了基于修正波速的区域穷举定位法.结果表明:水灰比越小,基准波速越大,波速随距离的衰减越大.骨料粒径越大,基准波速越大,波...     

二维板声发射源定位实验的一种简易实现方法

对声发射技术中的二维平面定位问题提出一种新的简易实验方案.采用新三角时差算法实现二维板的声源定位和GPS模拟,同时利用简易实验方法,仅用两个超声波传感器完成实验,简化实验器材,降低实验成本,适合普及,计算过程简单,同时也利于物理问题深入地理解.     

三通管路的管壁声传递损失测试方法

针对汽车进气系统三通管路的特点,提出了多通管路的管壁传递损失测试方法.并以某车型的双涡轮增压发动机进气三通管道为例,采用该方法评价其用塑料代替铝后的声学性能,主要以声传递损失来评价涡轮增压器噪声通过三通连接管路管壁的辐射和透射特性.测试过程中,三通管道的两个连接涡轮增压器端口分别用声源两次发声,靠近进气歧管端口采用两种...     

以MCS—8098单片机为核心的声发射实验系统的研制

一、引言声发射是指材料或结构受外力或内力的作用发生变形或断裂，以弹性波的形式释放出应变能的现象”‘．声发射是一种常见的物理现象，大多数金属和非金属材料在一定条件下都有声发射发生，如在温度诱发的马氏体相变中就伴有声发射现象”‘．声发射检测是声学无损检测中的重要方法，它是使构件或材料的内部结构、缺陷或潜在缺陷处于运动变化的过程中进行无损检测，即动态无损检测”‘．所以，声发射检测系统在材料研究中具有重要作用．已有的声发射检测系统体积庞大，造价又高．本系统小巧轻便，造价低廉，为高校中的实验室或其他小单位…     

三通管路管壁声传递损失测试方法

针对汽车进气系统三通管路的特点,提出了多通管路的管壁传递损失测试方法。并以某车型的双涡轮增压发动机进气三通管道为例,采用该方法评价其用塑料代替铝后的声学性能,主要以声传递损失来评价涡轮增压器噪声通过三通连接管路管壁的辐射和透射特性。测试过程中,三通管道的两个连接涡轮增压器端口分别用声源两次发声,靠近进气歧管端口采用两种不同反射末端,然后在每段管路布置两个压力场扬声器进行测试,并基于平面波分离入射波和反射波,同时在三通管道外用声功率半球面十点分布法自由场扬声器测试,经过3次测量来计算管道管壁的声传递损失。由于声传递损失是管道本身特性决定,所以该测试方法能够准确找出塑料件和金属件在不同频率的声学特性差异。而后,在声传递损失测试结果的基础上,结合近场声全息方法和波束形成原理进行声源识别,可知该三通管路材质改为塑料后主要噪声来自焊缝薄弱处的中高频透射声和管壁结构的低频辐射声。     

Near-field beamforming analysis for acoustic emission source localization

This paper attempts to introduce a near-field acoustic emission (AE) beamforming method to estimate the AE source locations by using a small array of sensors closely placed in a local region. The propagation characteristics of AE signals are investigated based on guided wave theory to discuss the feasibility of using beamforming techniques in AE signal processing. To validate the effectiveness of the AE beamforming method, a series of pencil lead break tests at various regions of a thin steel plate are conducted. The potential of this method for engineering applications are explored through rotor-stator rubbing tests. The experimental results demonstrate that the proposed method can effectively determine the region where rubbing occurs. It is expected that the work of this paper may provide a helpful analysis tool for near-field AE source localization.     

Nonlinear Kalman Filtering for acoustic emission source localization in anisotropic panels

Nonlinear Kalman Filtering is an established field in applied probability and control systems, which plays an important role in many practical applications from target tracking to weather and climate prediction. However, its application for acoustic emission (AE) source localization has been very limited. In this paper, two well-known nonlinear Kalman Filtering algorithms are presented to estimate the location of AE sources in anisotropic panels: the Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF). These algorithms are applied to two cases: velocity profile known (CASE I) and velocity profile unknown (CASE II). The algorithms are compared with a more traditional nonlinear least squares method. Experimental tests are carried out on a carbon-fiber reinforced polymer (CFRP) composite panel instrumented with a sparse array of piezoelectric transducers to validate the proposed approaches. AE sources are simulated using an instrumented miniature impulse hammer. In order to evaluate the performance of the algorithms, two metrics are used: (1) accuracy of the AE source localization and (2) computational cost. Furthermore, it is shown that both EKF and UKF can provide a confidence interval of the estimated AE source location and can account for uncertainty in time of flight measurements.     

Low speed bearing fault diagnosis using acoustic emission sensors

In this paper, a new methodology for low speed bearing fault diagnosis is presented. This acoustic emission (AE) based technique starts with a heterodyne frequency reduction approach that samples AE signals at a rate comparable to vibration centered methodologies. Then, the sampled AE signal is time synchronously resampled to account for possible fluctuations in shaft speed and bearing slippage. The resampling approach is able to segment the AE signal according to shaft crossing times such that an even number of data points are available to compute a single spectral average which is used to extract features and evaluate numerous condition indicators (CIs) for bearing fault diagnosis. Unlike existing averaging based noise reduction approaches that require the computation of multiple averages for each bearing fault type, the presented approach computes only one average for all bearing fault types. The presented technique is validated using the AE signals of seeded fault steel bearings on a bearing test rig. The results in this paper have shown that the low sampled AE signals in combination with the presented approach can be utilized to effectively extract condition indicators to diagnose all four bearing fault types at multiple low shaft speeds below 10 Hz.     

循环平稳声场的声源定位研究

旋转机械产生的辐射声场具有循环平稳特性,传统的平面近场声全息技术无法准确反映其调制特性,往往在边频带上出现虚假的能量的分布.采用循环谱密度取代功率谱密度作为重建物理量,则可准确提取循环平稳声场的调制和载波信息.考虑到循环谱密度的计算量以及特征提取的准确性,提出了循环谱密度组合切片分析法,并分析了加性白噪声对重建的影响.仿真分析及实验结果表明,此方法有较强的噪声抑制能力,全息重建的结果可准确反映声源的位置.     

Shaft angular misalignment detection using acoustic emission

Shaft angular misalignment (SAM) is a common and crucial problem in rotating machinery. Misalignment can produce several shortcomings such as premature bearing failure, increase in energy consumption, excessive seal lubricant leakage and coupling failure. Vibration analysis has been traditionally used to detect SAM; however, it presents some drawbacks i.e. high influence of machine operational conditions and strong impact of the coupling type and stiffness on vibration spectra. This paper presents an extensive experimental investigation in order to evaluate the possibility of detecting SAM, using acoustic emission (AE) technique. The test rig was operated at under different operational conditions of load and speed in order to evaluate the impact on the AE and vibration signature under normal operating conditions. To the best of the author’s knowledge, this is the first attempt to use AE for the detection of SAM under varying operational conditions. A comparative study of vibration and AE was carried out to demonstrate the potentially better performance of AE. The experimental results show that AE technique can be used as a reliable technique for SAM detection, providing enhancements over vibration analysis.     

针对周期偏移声信标的二阶高精度水声定位模型

针对传统长基线水声定位模型在以飞机黑匣子等周期偏移声信标为目标时定位精度显著下降的问题,提出了一种不依赖于信号周期信息的新型长基线定位模型。该模型将传统时延差定位模型拓展至二阶,通过求取到达时间的二阶导数,消去未知声信标周期。为避免由阶数提高引起的解算非收敛问题,引入了改进牛顿迭代算法,有效提高了新模型的收敛概率。所提出新模型的仿真试验及湖上试验的定位误差分别为3.14m和1.19m,试验结果表明,该模型实现了周期偏移声信标的高精度定位解算。     

近场声压法在定位柴油机故障中的应用

在柴油机的故障诊断中，常采用多个传感器测取柴油机的多个信号，如：振动信号，油压信号等进行分析判断各缸工作状况，所需设备复杂，数据处理繁杂。而本文提出了只用一个声压传感器就可定位并分析各缸的工况，较之以往的方法简单易行。     

分布式矢量传感器对宽带源被动定位的方法研究

本文给出了两种基于矢量传感器的被动定位方法。一般来说，对目标进行被动定位可以通过方位信息或时延信息来实现。单个矢量传感器就可以实现目标方位估计，而对多个矢量传感器接收的信号进行互相关运算即可得到目标对各矢量传感器的时延信息。本文先给出了利用方位信息进行被动定位的方法，然后给出了利用分布式矢量传感器进行方位一时延信息联合被动定位的新方法，并通过仿真分析对这两种方法的定位性能进行了比较。     

水声无源材料插入损失虚拟聚焦测量方法

提出了一种适合在有限尺寸水池中测量水声材料插入损失的方法,称为\     

Rate effect on mechanical properties of hydraulic concrete flexural-tensile specimens under low loading rates using acoustic emission technique

Acoustic emission (AE) waveform is generated by dislocation, microcracking and other irreversible changes in a concrete material. Based on the AE technique (AET), this paper focuses on strain rate effect on physical mechanisms of hydraulic concrete specimens during the entire fracture process of three point bending (TPB) flexural tests at quasi-static levels. More emphasis is placed on the influence of strain rate on AE hit rate and AE source location around peak stress. Under low strain rates, namely 0.77 × 10⁻⁷ s⁻¹, 1 × 10⁻⁷ s⁻¹ to 1 × 10⁻⁶ s⁻¹ respectively, the results show that the tensile strength increases as the strain rate increases while the peak AE hit rate decreases. Meanwhile, the specimen under a relatively higher strain rate shows a relatively wider intrinsic process zone in a more diffuser manner, lots of distributed microcracks relatively decrease stress intensity, thus delay both microcracking localization and macrocrack propagation. These phenomena can be attributed to Stéfan effect. In addition, further tests, namely the combination of AE monitoring and strain measuring systems was designed to understand the correlation between AE event activity and microfracture (i.e., microcracking and microcracking localization). The relative variation trend of cumulative AE events accords well with that of the load-deformation curve.