岩体爆破损伤声波测试信号频谱特征的小波(包)分析

 岩体爆破损伤特性除了影响声波速度外,同时造成声波能量衰减和频谱特征的变化。为弥补单纯声波速度分析的不足,更好地利用岩体声波信号携带的丰富信息,在某地下工程围岩中开展10次小药量模拟爆破岩体损伤声波测试研究。针对傅立叶分析的缺陷,运用小波(包)变换方法,对声波测试信号的频谱特征进行分解分析。研究结果表明：(1) 经小波(包)变换得到的爆破前后岩体声波频谱特征变化规律非常明显;(2) 2–4,2–5和2–6尺度下小波分量的幅值和功率谱密度远大于其他尺度下的小波分量的幅值和功率谱密度,对岩体爆破损伤的敏感性较好;(3) 岩体爆破损伤作用导致声波测试信号的能量集中区和最大能量分布百分比对应的频段(频率)向低频方向偏移。研究成果对于揭示岩体爆破损伤与声波测试信号频谱特征之间的内在联系具有一定的指导意义。     

小波变换在结构损伤检测中的应用

小波变换具有良好的时频局部化性质,特别适合于分析和处理突变信号。在获得结构的动力学响应的基础上,应用小波变换对结构响应信号进行小波分解。根据各种响应信号对损伤的灵敏度,选择损伤特征,通过捕捉结构出现损伤的时刻,实现对结构时间监控。     

Enhanced Hilbert–Huang transform and its application to modal identification

The well‐known Hilbert–Huang transform (HHT) consists of empirical mode decomposition to extract intrinsic mode functions (IMFs) and Hilbert spectral analysis to obtain time–frequency characteristics of IMFs through the Hilbert transform. There are two mathematical requirements that limit application of the Hilbert transform. Moreover, noise effects caused by the empirical mode decomposition procedure add a scatter to derivative‐based instantaneous frequency determined by the Hilbert transform. In this paper, a new enhanced HHT is proposed in which by avoiding mathematical limitations of the Hilbert spectral analysis, an additional parameter is employed to reduce the noise effects on the instantaneous frequencies of IMFs. To demonstrate the efficacy of the proposed method, two case studies associated with structural modal identification are selected. In the first case, through identification of a typical 3‐DOF structural model subjected to a random excitation, accuracy of the enhanced method is verified. In the second case, ambient response data recorded from a real 15‐story building are analyzed, and nine modal frequencies of the building are identified. The case studies indicate that the enhanced HHT provides more accurate and physically meaningful results than HHT and is capable to be an efficient tool in structural engineering applications. Copyright © 2012 John Wiley & Sons, Ltd.     

爆破震动信号的时频分析

针对具体的爆破震动信号,基于短时Fourier变换(STFT)、连续小波变换(CWT)、离散小波变换(DWT)和Hilbert-Huang变换(HHT)进行时频分析比较研究。结果表明:STFT使用的窗函数固定,分辨率单一,其分析结果只能大致反映信号能量随时间的变化;小波变换(WT)以小波基为变换基础,具有多分辨率特点,其分析结果较详细地反映了质点震动强度随时间的衰减起伏变化,但小波谱的能量在频率范围内分布较宽;HHT自适应性强、高效,Hilbert能量谱能清晰地表明能量随时频的具体分布,并且大部分能量都集中在有限的能量谱线上。分析认为HHT是一种全新而更优越的分析与处理爆破震动信号的时频方法。     

煤岩界面弱反射波小波多分辨分析

煤层厚度探测，特别是放顶煤开采时顶煤厚度快速、准确地探测对掌握放煤力度、保证煤质以及准确计算回收率具有重要意义。声波反射法是目前顶煤厚度探测的有效方法之一。弱反射波信号识别是声波法煤层厚度探测中的一个关键问题。针对这一问题，对顶煤厚度探测信号进行了小波多分辨分析；提出了从小波的紧支性、连续性和高阶消失矩3个方面选择小波基对信号进行分解的原则；应用Db4小波对实测信号进行了4层多尺度分解，分析了煤层夹矸和煤层顶板反射波在不同尺度下的时频特征，提高了煤岩界面弱反射波的识别能力和煤层厚度探测的精度。     

用空间分布信号的小波变换识别岩石材料的损伤

以空间分布信号的小波变换技术为基础，提出了一个识别岩石材料损伤的新方法。这个方法的理论基础是：岩石材料的损伤将使得结构的测量信号在损伤部位产生扰动。尽管测量信号中包含着材料损伤的信息，但很难直接从测量信号中发现损伤的确切位置，不过可以从测量信号的小波变换中发现损伤的位置，并用实验验证了这种方法的可靠性，即用声发射实验对含有预制裂纹的圆柱形水泥砂浆试样进行检测，可以得到沿试样轴向不同位置处的初至波幅度，对初至波幅度信号进行小波变换，结果表明，损伤位置与小波系数出现较大扰动的位置相对应，这说明本方法是可行的。     

Wavelet-Based Structural Health Monitoring of Earthquake Excited Structures

Abstract:   The article presents a wavelet-based structural health monitoring technique for structures subjected to an earthquake excitation utilizing the instantaneous modal information. The instantaneous mode shape information is first extracted from the vibration response data collected during an earthquake event by using a wavelet packet sifting process. A confidence index (CI) is proposed to validate the results obtained. The identified normalized instantaneous mode shapes in conjunction with the corresponding CIs can be effectively used to monitor damage development in the structure. The effectiveness of the proposed approach is illustrated for two damage scenarios, sudden stiffness loss and progressive stiffness degradation, and different base excitations including three real earthquake signals and a random signal. Consistently good results were obtained in all cases. Issues related to robustness of the method in the presence of a measurement noise and sensitivity to damage severity are discussed.     

整体钢框架结构中连续板热振动特性试验

采用自制火灾试验炉对整体钢框架中4个钢筋混凝土连续板格和2个组合钢梁的热振动特性进行了试验研究。采集了构件受火时的加速度信号并尝试利用希尔伯特变换提取主频率,并对加速度信号进行时域分析和频域分析。时域分析结果表明:加速度信号强度与边界约束和裂缝开展密切相关,约束越强,振动信号越弱;主裂缝开展导致板格加速度信号发生突变,而组合钢梁的信号突变则受到应力重分布和主裂缝开展的影响;升温阶段加速度曲线可分为3个阶段,前期和后期振动幅值很小,中期振动幅值较大且伴随较多的信号突变。频域分析结果表明:受火时主频率变化显著并呈现下降的趋势,但频率改变只能反映裂缝开展程度,不能确定裂缝位置,且频率变化近似与挠度的变化过程相对应;通过振动特征分析可以有效监测楼板的变形、裂缝开展等受火行为。     

Decentralized damage identification using wavelet signal analysis embedded on wireless smart sensors

In this paper, a decentralized damage identification method using wavelet signal analysis tools embedded on wireless smart sensors (Imote2) has been proposed and experimentally validated. The damage identification analysis is decentralized by calculating discrete wavelet coefficients for acceleration in Imote2 sensors and transmitting the wavelet coefficients to a base station for damage identification through wavelet entropy indices. The wavelet entropy is modified to serve as a damage-sensitive signature that can be obtained both at different spatial locations and time stations to indicate existence of damage. It is known that wavelet-based approaches have clear advantages over Fourier transform-based ones for damage identification, since the wavelet transform allows for a wider choice of basis functions. This flexibility allows the wavelet transform to isolate changes in a signal that may be difficult to detect using other transform methods. To assess the reliability of the measurement signals, the wireless sensors have been compared with reference wired sensors. The proposed decentralized method for damage identification is verified via experimental tests using two laboratory structures: a three-story shear building structure and a three-dimensional truss bridge structure.     

On applicability of Hilbert–Huang transform for vibration analysis of a two-member truss

The Hilbert–Huang transform (HHT) proposed for treating the time history data of nonlinear dynamic systems comprises two parts: the empirical mode decomposition and the Hilbert transform. In this study, focus is placed on the physical interpretation of the HHT results for an elastic two-member truss, for which the nonlinear behaviour can be clearly interpreted at various stages of excitation, from nearly linear, nonlinear, period-doubling, to chaotic. The instantaneous frequency of the truss is computed using the HHT or derivative-based HHT. In each case, the result obtained by the fast Fourier transform is also presented for comparison. It is concluded that the enforcement by the HHT of the data set to be symmetric with respect to the local zero mean in extracting the intrinsic mode functions may result in frequencies that are not physically meaningful. Care needs to be taken when using HHT for interpreting the frequency contents of a nonlinear structure.     

A neuro-wavelet technique for seismic damage identification of cantilever structures

A method based on artificial neural networks and wavelet transform is proposed for identifying seismic-induced damage of cantilever structures. In the proposed method, response accelerations are measured at strategically selected locations. To extract damage-induced sharp transitions from the measured signals, they are decomposed by continuous wavelet transform. The size of the decomposed signals is reduced by principal component analysis (PCA). Principal components obtained from PCA are fed to a set of neural networks to identify damage. The proposed algorithm is applied to a tall airport traffic control tower by means of numerical simulations. The obtained results show that the proposed method effectively identifies seismic-induced damage, and the noise intensity has a negligible effect on the predicted results. Moreover, the trained neural network system is able to predict the seismic-induced damage of unseen samples well.     

基于小波能量的钢丝绳断丝损伤信号处理

提出了利用小波能量作为钢丝绳断丝损伤信号处理的1个特征量．根据Parseval能量积分等式从理论上推导了小波变换系数具有能量的量纲,将小波能量引入钢丝绳断丝信号处理中是可行的．通过对信号进行多层离散小波分解建立了小波能量求解的方程式,计算不同频带内钢丝绳断丝损伤信号的能量值,这些频带内的能量统计是在时域波形上进行的,体现了小波分析具有时频分析能力．最后针对不同的断丝损伤情况,分别求解各个频带内的小波能量值,修正了应用于钢丝绳断丝损伤信号处理的小波能量计算公式．试验结果表明小波能量表征断丝信号的1个特征量是有意义的．     

Risk-based economic assessment of mitigation strategies for power distribution poles subjected to hurricanes

This paper presents a risk-based framework to assess the hurricane damage risks to distribution poles, and investigates the risks, costs and benefit of different mitigation strategies. It is estimated that power outages due to storms cause approximately $270 million in repair/replacement costs annually in the USA. Hurricane Irene alone left approximately 6 million residents without power along the east coast of the USA in 2011, causing an estimated $5–$7 billion in damages. These high repair/replacement costs warrant an investigation of mitigation strategies that may aid in reducing replacement and damage costs. This paper describes the reliability analysis of typical timber distribution poles and probabilistic wind models to determine failure probabilities for specific locations. Furthermore, in order to more accurately portray the behaviour of distribution poles, the proposed framework includes the degradation and service-proven reliability of timber distribution poles. Four mitigation strategies are developed, and the cost effectiveness of each strategy is evaluated. In order to assess the cost effectiveness, a life cycle cost analysis is conducted for each mitigation strategy. This paper finds that appropriate mitigation strategies can reduce replacement costs of distribution poles associated with hurricane wind by 2060.     

时频联合分析方法在土木工程中的研究现状

时频联合分析方法因能同时提供信号的局部时频特征,适于分析非平稳信号而在土木工程领域得到了极大应用。线性变换、双线性变换和Hilbert-Huang变换是土木工程中常用的时频联合分析方法。根据时频分析方法的理论,将其应用于人工地震波模拟、结构动力反应分析和可靠性估计、结构参数识别及损伤检测等领域。通过对其在土木工程中的应用进行总结,提出了存在的问题,探讨了进一步研究的方向。     

小波变换理论及其在岩石声学特性研究中的应用

应用小波变换理论将岩石声波信号分解成不同频带通道的小波分量，然后对各频带信号进行分析，提出了对应力敏感的加权波谱参数；通过对岩石在单轴受荷条件下和劈裂过程中的声波数据的处理，表明加权波谱参数随应力的变化具有极强的规律性。     

基于小波变换的时域反射法对岩土体变形监测信号的多尺度分析

为更加充分、准确、高效地利用TDR法岩土体变形监测过程中实时得到的同轴电缆反射信号,提出以Haar小波变换对该信号进行多尺度分析,利用大尺度下细节信号特征识别后期岩土体变形失稳发生区域,并将其应用于两个工程实例中。结果表明:运用小波变换分析电缆反射信号不仅能从岩土体变形初期TDR测试仪接收信号中较为准确地突显后期导致岩土体失稳的剪切变形区域或位置,而且可以通过多个不同时点原始信号小波分析结果的对比,直观地获知岩土体内部相应时段内发生运动变形的区域。因此,运用该方法可充分挖掘同轴电缆反射信号中内含的岩土体变形信息,对有效实现岩土体早期变形失稳预警具有积极的意义。     

结合小波分析的金属面夹芯组合板损伤检测

夹芯板作为一种保温隔热性能良好的新型建筑材料,在建筑工程中逐渐被广泛应用.通过采用超声波法对各种在正常使用过程中可能出现的夹芯板损伤进行检测,并用小波分析技术对超声回波的信号进行去噪处理,并对处理过超声回波信号进行小波分解.结果表明:经过小波去噪和小波分解之后,能够通过识别出反射回波信号的到达时间和各级小波分解的波形较...     

岩石超声波信号的小波时频分析

岩石超声波信号是一种非平稳信号.由于传统的短时Fourier变换(STFT)使用的窗函数固定,分辨率单一,其分析结果只能大致反映信号能量随时间的变化.小波变换(WT)以小波基为变换基础,具有多分辨率特点,其分析结果较详细地反映了质点震动强度随时间的衰减起伏变化.分析认为小波变换是一种更优越的处理岩石声学信号的时频方法.     

离散小波变换在变截面梁损伤识别中的研究应用

利用离散小波变换,对一个三跨连续刚构变截面桥梁的简化模型进行了损伤识别。对该模型提取纵向位移和竖向挠度信息,利用不同小波函数分别对它们进行离散小波变换分析。通过比较,讨论了在损伤识别过程中不同小波函数的选取方法以及在损伤识别中效果较好的信号类型。     

Seismic damage detection of tall airport traffic control towers using wavelet analysis

In this study, the applicability of continuous wavelet transform (CWT) and discrete wavelet transform (DWT) for seismic damage detection of tall airport traffic control (ATC) towers was investigated. Nonlinear finite element (NFE) model of Kuala Lumpur International Airport (KLIA) ATC tower with the height of 120 m was created using discrete moment-curvature hinges. Three different strong ground motions excited the tower and three different damage scenarios were then obtained. Response accelerations at four strategically selected locations were analysed by CWT and DWT to detect the damage scenarios. It was found that CWT successfully detects seismic-induced damage even when the signals are polluted by noises. On the other hand, DWT is quite sensitive to noisy signals and successful damage detection by DWT depends on noise level and sampling interval. Moreover, it was observed that DWT is more sensitive to the change in the stiffness of the tower structural elements than CWT.