一种用于管道泄漏声定位的可调Q因子小波变换分析方法

针对泄漏声发射信号的非平稳随机特性,进行了泄漏声信号可调Q因子小波变换(Tunable Q-Factor Wavelet Transform,TQWT)的理论分析和实验研究。首先通过对典型泄漏声信号的TQWT分析,研究品质因子和分解尺度对泄漏声特征提取的影响。然后根据峭度最大原则,优选出适合泄漏声信号分析的TQWT参数。在此基础上,提出了一种基于TQWT提取管道泄漏声特征分量的方法,并将提取的特征分量进行互相关分析用于管道泄漏定位。实验结果表明,利用该方法可以有效提取出泄漏声信号中的特征分量,从而更好实现泄漏定位,定位误差较小。该项研究工作为实际工程管道泄漏检测提供了可行的解决方案。      

炉内管道泄漏声检测与定位系统的研究现状

电站锅炉管道泄漏的声检测与定位系统,已经越来越广泛地应用于电站锅炉。该系统主要利用声学技术检测炉内管道的泄漏状态,并利用多传声器定位机理对泄漏点进行定位,有效地减少了由管道泄漏引起的非计划停炉,这对电站锅炉来说意义尤为重要。本文分析了炉内管道泄漏声检测与定位系统的关键技术,介绍了该系统的发展概况及应用现状,并提出了改进方向。     

输气管道泄漏的波达时差交叉定位方法*

为了实现对管道泄漏位置的三维定位,该文提出一种基于波达时差法的交叉定位方法。将传感器阵列布放在不同位置,通过波达时差法获取远场泄漏声源的两组空间方位信息,对两组方位交叉求取空间伪交点从而完成定位。建立泄漏定位实验平台,分析了多种互相关方法以及阵列孔径、布放间距、泄漏位置等因素对延时估计和定位精度的影响。实验结果表明:选取基本互相关法对泄漏信号的10 500 Hz分量进行互相关分析,能够获取稳定的延时估计结果;在有效信号检测范围内,增大阵列孔径和布放间距能有效减少误差;该文方法相较于现有波达时差法能有效提高距离原点4 m以上泄漏位置的定位精度。     

基于时延估计的光栅阵列管道泄漏检测与定位方法研究

城市燃气在管道运输过程中存在很大的安全隐患，一旦发生危险，后果不堪设想，燃气管道泄漏的监测与定位意义重大。为解决目前大部分管道泄漏检测与定位方法存在的易受环境干扰、精度低、适用范围窄、计算难度较高等问题，提出了一种基于时延估计的光栅阵列（wFBG）管道泄漏检测与定位方法，该方法通过光栅阵列技术采集振动信号，根据采集到的泄漏振动信号时域、频域上的特征，首先通过基于短时能量分析的方法检测管道是否泄漏，然后对满足要求的信号片段进行峰值间多项式拟合获取泄漏信息到达的时刻，最后根据时间差定位泄漏点。实验结果表明，该方法能有效检测泄漏，并且在测量距离为40 m的情况下，定位误差在1 m左右。     

固定干扰源存在下的管道泄漏检测和准确定位

为了解决固定位置的声/振动干扰源引起的管道泄漏声检测的虚警或者漏点定位错误问题,利用泄漏信号源和固定干扰源之间的独立性,通过盲卷源分离算法得到泄漏信号在一定代价函数下的最优估计,并将该估计作为输入信号从检测信号中自适应预测得到泄漏信号,这样就可以保留泄漏信号中的时延信息。对实际检测信号的处理表明,应用提出来的方法可以有效的去除检测信号中来自固定干扰源的噪声,同时不损失泄漏信号中的时延信息,可在固定干扰源存在时实现管道泄漏有效检测和准确定位。      

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...     

偏振态对分布式光纤泄漏检测系统的影响研究

研制了一种基于Sagnac干涉仪的直线型分布式光纤传感器,可实时进行管道泄漏检测与定位。分析和研究了该干涉仪的泄漏检测原理、泄漏源定位方法以及光偏振态对传感器性能的影响。当两束光偏振态相同时,系统具有最佳的性能;当两束光正交时,无法实现信号检测。管道泄漏的实验结果表明,该系统能较准确地确定泄漏源位置,且定位误差为0.69%。     

多频带期望值最大声信号时延估计EI北大核心CSCD

通过分析复杂环境中不同频带声信号时延估计的差异,提出多频带期望值最大时延估计方法。为了使各频带之间无重叠,该方法采用独立分带划分声信号不同频带,然后计算各频带广义互相关函数,并对子带广义互相关函数建立最大似然模型,最后利用期望值最大算法将多维优化转为一维优化的迭代式,获得最优子带广义互相关函数,在此基础上估计声信号的时延信息。数据仿真和实际实验结果表明,多频带期望值最大化时延估计相较常规时延估计有效估计值的百分比提升了10%,并将最优频带互相关函数应用到该定位算法中,在网格间距为0.3 m时,得到的峰值区域汇聚更明显,定位效果更好。     

基于分布式光纤的埋地自来水管多点泄漏定位方法分析

基于拉曼散射测温原理，利用分布式光纤对UPVC（硬脂聚氯乙烯）和铸铁自来水管道进行模拟泄漏点定位实验。首先对采集到的原始Anti-Stokes光信号进行滤波平滑处理，再利用相关系数法对温度检测信号进行分类分析，识别自来水管有无泄漏发生，最后通过选择性阈值法识别出UVPC管以及铸铁管中的泄漏点位置。实验结果表明，该系统运行稳定且能够准确识别自来水管泄漏情况。选择性平均阈值法的使用，能够对200 m的埋地自来水管道准确地进行泄漏点的定位，定位误差为0.25 m～0.65 m。     

基于Rayleigh-Bloch模式的单层结构弯曲声波导

基于一维声栅中的Rayleigh-Bloch(RB)模式基本特点,设计了一种单层结构弯曲声波导.利用有限元方法从时域和频域两方面验证了弯曲声波导的有效性,RB模式波可以沿着波导的弯曲界面传播.研究发现,由于采用了环形结构基本单元,在该波导中存在两种传播模式,分别对应能量局域在单元间(模式-1)和单元内部(模式-2)两种情况.其中,模式-2声传输效果更佳,几乎可实现无损传输.时域研究中分别采用了调制脉冲和高斯脉冲两种信号形式,分析了它们在弯曲声波导中的传输过程.由于波导中只允许RB模式波传播,因此对于宽频信号来说,可起到滤波的效果.并且,不同模式(频率)的信号会出现在声波导的不同位置,所得结果对于声波定向传输、声探测与识别等研究具有理论与应用价值.     

噪声交叉关联强度的时间周期调制对线性过阻尼系统的随机共振的影响

针对由加性、乘性噪声和周期信号共同作用的线性过阻尼系统, 在噪声交叉关联强度受到时间周期调制的情况下,利用随机平均法推导了系统响应的信噪比的解析表达式. 研究发现这类系统比噪声间互不相关或噪声交叉关联强度为常数的线性系统具有更丰富的动力学特性, 系统响应的信噪比随交叉关联调制频率的变化出现周期振荡型随机共振, 噪声的交叉关联参数导致随机共振现象的多样化.噪声交叉关联强度的时间周期调制的引入有利于提高对微弱周期信号检测的灵敏度和实现对周期信号的频率估计. 关键词： 随机共振 周期振荡型共振 噪声交叉关联强度 信噪比     

Acoustic monitoring of background internal waves with the use of the correlation method for measuring the frequency shifts of interference maxima

A numerical experiment is carried out to demonstrate the reconstruction of the frequency spectrum of background internal waves with the use of the correlation method for measuring the frequency shifts of interference maxima. The method is based on monitoring the behavior of the frequency shift for the maximum of the cross-correlation function of signal spectra received at different instants of time. The noise immunity of the correlation method is analyzed in comparison with the direct method based on monitoring the frequency shift of a chosen maximum of the interference pattern.     

Correlation method of measuring the frequency shifts of the sound field maxima caused by perturbations of the oceanic medium

The correlation method of measuring the frequency shifts of the sound field maxima caused by the nonstationary oceanic medium is considered. The method is based on tracing the frequency shift of the maximum that is observed in the cross-correlation function of signal spectra received at different instants of time. The relation between the correlation method and the method based on measuring the frequency shifts of the maxima observed in the interference pattern of the source is analyzed. The sensitivity of the correlation method is estimated.     

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.     

On the effects of reflections on time delay estimation for leak detection in buried plastic water pipes

This paper is concerned with the way in which wave reflections in a fluid-filled pipe affect the cross-correlation function of two leak noise signals used to detect and locate leaks in buried water pipes. Propagating waves generated by leak noise reverberate in a pipe network system, as they encounter features such as changes in section, and resistance such as valves, and pipe junctions. A theoretical model of a straight pipe with discontinuities, which cause reflections, is developed and incorporated into a model of the cross-correlation function. The reasons why the reflections and the low-pass filtering properties of the pipe can be largely removed by the generalised cross-correlation (GCC) phase transform (PHAT) are determined. Using the analytical model, theoretical predictions of the basic cross-correlation function (BCC) and the GCC PHAT are compared with experimental data from a specially constructed test site in Canada.     

Leak location in gas pipelines using cross-time–frequency spectrum of leakage-induced acoustic vibrations

The correlation-based location methods are widely used in leak detection of the pipelines assuming that the acoustic speed has been known and constant. In practice, the acoustic speed is frequency-varying due to the dispersions of gas-leak-induced acoustic waves, and thus the assumption is not supported. In this work, a location scheme based on cross-time–frequency spectrum (CTFS) is intended for the gas-leak-induced acoustic waves with frequency-varying acoustic speed. In the scheme, the CTFS is obtained by the one-dimensional Fourier transform of the time domain convolution between the kernel function in correlation domain and the instantaneous cross-correlation of the two spatially separately collected acoustic signals on either sides of a leakage. Then, the time difference of arrival (TDOA) and the corresponding frequency information are extracted simultaneously when the CTFS reaches the maximum value. The resulting peak frequency is used to online determine the frequency-dependant acoustic speed in combination with the known dispersive curve of gas-leak-induced dominated mode. Finally, the gas leakage is located by the TDOA and the frequency-dependant acoustic speed of real-time determination instead of constant acoustic speed. Consequently, for the proposed scheme, the constant acoustic speed is no longer a prerequisite. The proposed scheme has been experimentally validated in leak detection of gas pipelines and results demonstrate that the average relative location errors are reduced by six times compared with the commonly used correlation-based location method.     

Methods of measuring frequency shifts in the interference structure of the sound field in oceanic waveguides

The efficiency of the correlation method is considered as applied to measuring frequency shifts of maxima in the interference structure of the sound speed under the influence of distortions of the sound-speed profile. The method is based on tracing the position of the maximum of the cross-correlation function corresponding to the spectrum of the transmitted signal in the frequency domain. The distortion is modeled by seasonal variations of the hydrological environment. The noise immunity of the method is analyzed. The correlation method is compared with other known methods of tracing frequency shifts of the interference maxima.     

Analyses of Valid Range for the Linear Approximation in a Single-Mode Laser

Using the linear approximation method, we calculated the steady-state mean normalized intensity fluctu-ation for a loss-noise model of a single-mode laser driven by a pump noise and a quantum noise, whose real part andimaginary part are cross-correlated. We analyzed the valid range for thelinear approximation method by studying theinfluences on the steady-state mean normalized intensity fluctuation by the cross-correlation coefficient, the intensities ofthe quantum and pump noise, the net gain, and the amplitude and frequency of the input signal, and we found that thevalid range becomes wider when the cross-correlation between the real and imaginary part of quantum noise is weaker,the noise intensities of quantum and pump are weaker, the laser system is far from the threshold and the signal hassmaller amplitude and higher frequency.     

Measurement of acoustic particle velocities in enclosed sound field: Assessment of two Laser Doppler Velocimetry measuring systems

The performances of two Laser Doppler Velocimetry (LDV) systems adapted for measuring the acoustic particle velocities are assessed in enclosed sound field. This assessment is performed by comparing the acoustic velocities measured by means of LDV to reference acoustic velocities estimated from sound pressure measurements. The two LDV systems are based on a single optical bench which delivers an optical signal called Doppler signal. The Doppler signal, which is frequency modulated, is analyzed by means of two signal processing systems, the BSA (Burst Spectrum Analyser from Dantec) on the one hand, and a system specifically developed for the estimation of the acoustic velocity on the other hand. Once the experimental setup has been optimized for minimizing the errors made on the reference velocities, the assessment is performed and shows that both systems can measure the acoustic velocity in enclosed field in two the frequency ranges [0-4 kHz] and [0-2 kHz] respectively for acoustic velocity amplitudes of 10 mm/s and 1 mm/s.