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...     

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...     

近场子空间聚焦的碰摩故障声发射定位方法

针对宽带多源声发射信号的相干、多模态和能量衰减快问题,提出一种近场多重相干信号子空间聚焦的定位算法用于碰摩故障声发射源的定位检测。首先,为滤除干扰模态波、减小频散效应,采用基于模态声发射传播特性分析的小波分解滤波方法,从碰摩初期的声发射信号中获取零阶模态波及波速用于定位计算;其次,为实现信号解相干,提出基于双边相关变换(TCT)的近场聚焦矩阵估计方法;最后,针对声发射信号的能量衰减快问题,利用近场基于特征分解的多重信号分类(N-MUSIC)的空间谱估计方法来实现声源的精确定位。理论分析和实验结果表明:该方法定位精度高、计算复杂度低、稳定性强,能有效识别多个相干碰摩声源。相比传统相干子空间算法(CSM),该方法减少了信号初值和聚焦频点的计算量,对双声源的分辨概率较现有修正近场多重信号分类算法提高了17%,是一种有效的碰摩故障源检测方法。     

金属点蚀过程声发射源机制研究

研究了腐蚀特别是点蚀过程产生应力波,即声发射(AE)的源机制,估算了单个钝化膜破裂所产生的薄板表面位移量级,并用实验进行了论证。作者提出,利用板波声发射理论加上参数识别方法,可将腐蚀过程产生的声发射信号同背景噪声相区别。     

腐蚀声发射信号降噪方法

为了从复杂背景噪声中有效地检测出腐蚀声发射信号,采用短时分形维数和离散分数余弦变换相结合的降噪方法,利用声发射检测系统,对6% FeCl₃·6H₂O溶液中Q235钢板的全面腐蚀和局部腐蚀声发射信号进行了降噪处理。实验结果表明,腐蚀声发射信号分别加入白噪声、有色噪声和粉红噪声,在输入信噪比为0~15dB的条件下,此方法降噪效果与标准离散余弦、离散分数余弦变换方法相比,输出信噪比最高可提升8 dB。所述降噪方法对检测腐蚀声发射信号以及对金属剩余寿命的评价具有一定意义。      

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.     

钢轨裂纹伤损声发射源的建模仿真与特征分析

高速铁路的发展对钢轨的安全性提出了特殊要求,因此对钢轨内部裂纹的特征分析具有重要意义。为了研究钢轨内部裂纹声发射源特征,对钢轨中不同类型、深度和传导距离的裂纹声发射源进行了分析.采用有限元方法建立了钢轨模型并通过实验验证,然后结合小波方法和瑞利-兰姆方程分析了裂纹声发射源的特征。结果表明:钢轨中不同类型和不同频率特征的声发射源能够利用声发射模态之间的强度比率来识别;轨腰深度上的声发射源具有统一的模态特征,而轨头和轨底的声发射源则具有复杂的模态特征;同时,不同类型声发射源在钢轨中的传导特征差异明显。研究结果对利用声发射技术进行钢轨裂纹检测提供了指导,可作为实际应用的重要参考。     

钢轨裂纹伤损声发射源的建模仿真与特征分析

高速铁路的发展对钢轨的安全性提出了特殊要求,因此对钢轨内部裂纹的特征分析具有重要意义。为了研究钢轨内部裂纹声发射源特征,对钢轨中不同类型、深度和传导距离的裂纹声发射源进行了分析.采用有限元方法建立了钢轨模型并通过实验验证,然后结合小波方法和瑞利-兰姆方程分析了裂纹声发射源的特征。结果表明:钢轨中不同类型和不同频率特征的声发射源能够利用声发射模态之间的强度比率来识别;轨腰深度上的声发射源具有统一的模态特征,而轨头和轨底的声发射源则具有复杂的模态特征;同时,不同类型声发射源在钢轨中的传导特征差异明显。研究结果对利用声发射技术进行钢轨裂纹检测提供了指导,可作为实际应用的重要参考。     

A non-iterative partial discharge source location method for transformers employing acoustic emission techniques

Partial discharge (PD) causes premature insulation failure of transformers. It is essential to detect PD to avoid unwanted failure of transformers. Only detection of PD is not sufficient for a transformer of huge size, unless it is possible to locate. Acoustic partial discharge measurement is advantageous for PD source location. There are different algorithms for PD source location. These are iterative and require large number of acoustic emission (AE) sensors. This paper presents a non-iterative source location algorithm employing four AE sensors. This algorithm is applied to experimental data. Proposed algorithm is also applied to published data and compared with existing iterative methods. Main error for source location is due to arrival time calculation. In order to reduce the error in AE signal arrival time calculation, different arrival time calculation methods are discussed and a comprehensive method is proposed. By applying these methods, arrival time is calculated from measured signal.     

Toward a probabilistic acoustic emission source location algorithm: A Bayesian approach

Acoustic emissions (AE) are stress waves initiated by sudden strain releases within a solid body. These can be caused by internal mechanisms such as crack opening or propagation, crushing, or rubbing of crack surfaces. One application for the AE technique in the field of Structural Engineering is Structural Health Monitoring (SHM). With piezo-electric sensors mounted to the surface of the structure, stress waves can be detected, recorded, and stored for later analysis. An important step in quantitative AE analysis is the estimation of the stress wave source locations. Commonly, source location results are presented in a rather deterministic manner as spatial and temporal points, excluding information about uncertainties and errors. Due to variability in the material properties and uncertainty in the mathematical model, measures of uncertainty are needed beyond best-fit point solutions for source locations. This paper introduces a novel holistic framework for the development of a probabilistic source location algorithm. Bayesian analysis methods with Markov Chain Monte Carlo (MCMC) simulation are employed where all source location parameters are described with posterior probability density functions (PDFs). The proposed methodology is applied to an example employing data collected from a realistic section of a reinforced concrete bridge column. The selected approach is general and has the advantage that it can be extended and refined efficiently. Results are discussed and future steps to improve the algorithm are suggested.     

Acoustic emission source location in plates using wavelet analysis and cross time frequency spectrum

In this study, the theories of wavelet transform and cross-time frequency spectrum (CTFS) are used to locate AE source with frequency-varying wave velocity in plate-type structures. A rectangular array of four sensors is installed on the plate. When an impact is generated by an artificial AE source such as Hsu–Nielsen method of pencil lead breaking (PLB) at any position of the plate, the AE signals will be detected by four sensors at different times. By wavelet packet decomposition, a packet of signals with frequency range of 0.125–0.25 MHz is selected. The CTFS is calculated by the short-time Fourier transform of the cross-correlation between considered packets captured by AE sensors. The time delay is calculated when the CTFS reaches the maximum value and the corresponding frequency is extracted per this maximum value. The resulting frequency is used to calculate the group velocity of wave velocity in combination with dispersive curve. The resulted locating error shows the high precision of proposed algorithm.     

Sparsity constrained deconvolution approaches for acoustic source mapping

Using microphone arrays for estimating source locations and strengths has become common practice in aeroacoustic applications. The classical delay-and-sum approach suffers from low resolution and high sidelobes and the resulting beamforming maps are difficult to interpret. The deconvolution approach for the mapping of acoustic sources (DAMAS) deconvolution algorithm recovers the actual source levels from the contaminated delay-and-sum results by defining an inverse problem that can be represented as a linear system of equations. In this paper, the deconvolution problem is carried onto the sparse signal representation area and a sparsity constrained deconvolution approach (SC-DAMAS) is presented for solving the DAMAS inverse problem. A sparsity preserving covariance matrix fitting approach (CMF) is also presented to overcome the drawbacks of the DAMAS inverse problem. The proposed algorithms are convex optimization problems. Our simulations show that CMF and SC-DAMAS outperform DAMAS and as the noise in the measurements increases, CMF works better than both DAMAS and SC-DAMAS. It is observed that the proposed algorithms converge faster than DAMAS. A modification to SC-DAMAS is also provided which makes it significantly faster than DAMAS and CMF. For the correlated source case, the CMF-C algorithm is proposed and compared with DAMAS-C. Improvements in performance are obtained similar to the uncorrelated case.     

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.     

A covariance fitting approach for correlated acoustic source mapping

Microphone arrays are commonly used for noise source localization and power estimation in aeroacoustic measurements. The delay-and-sum (DAS) beamformer, which is the most widely used beamforming algorithm in practice, suffers from low resolution and high sidelobe level problems. Therefore, deconvolution approaches, such as the deconvolution approach for the mapping of acoustic sources (DAMAS), are often used for extracting the actual source powers from the contaminated DAS results. However, most deconvolution approaches assume that the sources are uncorrelated. Although deconvolution algorithms that can deal with correlated sources, such as DAMAS for correlated sources, do exist, these algorithms are computationally impractical even for small scanning grid sizes. This paper presents a covariance fitting approach for the mapping of acoustic correlated sources (MACS), which can work with uncorrelated, partially correlated or even coherent sources with a reasonably low computational complexity. MACS minimizes a quadratic cost function in a cyclic manner by making use of convex optimization and sparsity, and is guaranteed to converge at least locally. Simulations and experimental data acquired at the University of Florida Aeroacoustic Flow Facility with a 63-element logarithmic spiral microphone array in the absence of flow are used to demonstrate the performance of MACS.     

Improving accuracy of acoustic source localization in anisotropic plates

The acoustic source localization technique for anisotropic plates proposed by the authors in an earlier publication ([1] Kundu et al., 2012) is improved in this paper by adopting some modifications. The improvements are experimentally verified on anisotropic flat and curved composite plates. Difficulties associated with the original technique were first investigated before making any modification. It was noted that the accuracy of this technique depends strongly on the accuracy of the measured time difference of arrivals (TDOA) at different receiving sensors placed in close proximity in a sensor cluster. The sensor cluster is needed to obtain the direction of the acoustic source without knowing the material properties of the plate. Two modifications are proposed to obtain the accurate TDOA. The first one is to replace the recorded full time histories by only their initial parts – the first dip and peak – for the subsequent signal processing. The second modification is to place the sensors in the sensor cluster as close as possible. It is shown that the predictions are improved significantly with these modifications. These modifications are then applied to another sensor cluster based technique called the beamforming technique, to see if similar improvements are achieved for that technique also with these modifications.     

Design of a self-calibrating simulated acoustic emission source

The use of conical piezoelectric transducers as point acoustic sources has been investigated. It has been shown that transducers based on a design originally developed at the National Institute for Standards and Technology in the USA can be used as point transmitters over the frequency range of interest in acoustic emission measurements (100 kHz to around 1 MHz). They should, therefore, be suitable for use in experiments to calibrate structures so that acoustic emission source strengths can be determined. It has also been shown that measurements of the response of the transmitting transducer backing can be used to assess the coupling efficiency, and hence to remove concerns about inconsistent coupling affecting the calibration measurements. The results indicate that the variation of the backing response with coupling is due to a shift in the resonance frequencies of the transducer with the mechanical load impedance. If other transducers can be shown to behave in a similar fashion this effect could be used to measure coupling in standard acoustic emission and ultrasonic transducers.     

Estimation of the location of a farfield acoustic source

A backward integration method for estimating the location of a source of sound waves in the atmosphere is presented. This geometric acoustics method is based upon the analysis of microphone array measurements to determine the incoming ray direction in three dimensions. The equations governing the propagation of the ray are then integrated backward in time. The sound source lies somewhere along the calculated ray path. The intersection of such loci from more than one array would provide an estimate of the source location. The method appears to be very rapid to implement and, assuming the time delays to be accurately measured, limited in accuracy only by the timeliness of the input sound speed and velocity profiles in the atmosphere.