基于振动响应的耦合弦系统损伤检测

为解决具有相近频率和相重频率特征的多跨耦合弦系统的损伤检测问题,建立了耦合弦系统在外激励作用下的有限元运动方程.利用直接积分法计算了系统强迫振动响应,将弦的局部损伤模拟为单元面积的减少,推导了振动响应对弦单元面积的灵敏度,并利用此响应灵敏度进行弦的局部损伤识别.数值算例表明:此方法能快速准确地识别出耦合弦的局部损伤,并且对模拟的人工噪声不敏感.     

Statistical detection of structural damage based on model reduction

This paper proposes a statistical method for damage detection based on the finite element （FE） model reduction technique that utilizes measured modal data with a limited number of sensors. A deterministic damage detection process is formulated based on the model reduction technique. The probabilistie process is integrated into the deterministic damage detection process using a perturbation technique, resulting in a statistical structural damage detection method. This is achieved by deriving the first- and second-order partial derivatives of uncertain parameters, such as elasticity of the damaged member, with respect to the measurement noise, which allows expectation and covariance matrix of the uncertain parameters to be calculated. Besides the theoretical development, this paper reports numerical verification of the proposed method using a portal frame example and Monte Carlo simulation.     

结构损伤诊断的改进灵敏度方法

提出一种改进的灵敏度方法用于工程结构损伤检测中.通过在迭代算法中引入一个“加速”公式来迅速获得足够精确的识别结果,避免了多次迭代,可以大大减少计算花费.用文献[8]和文献[10]中的两个数值算例对所提方法进行了验证,并把结果和原文中的计算结果进行比较.结果表明:采用改进的方法一般只需经过一次计算即可获得精度更高的识别结果,避免了多次迭代,显著减少了计算花费,显示了改进方法突出的优越性.     

基于模态参数灵敏度的损伤方程组求解正则化方法研究

基于模态参数的结构损伤识别方法是振动损伤识别领域中应用最为广泛的方法.利用模态参数灵敏度构建结构损伤方程组,对其进行求解可以识别结构损伤位置和程度.由于实际工程中模态参数不完备性和噪声的影响,结构损伤方程易出现病态问题,直接求解可能产生错误的结果.为了解决这一问题,可以引入正则化方法进行求解.然而,各类正则化方法的基本...     

AN IMPEDANCE ANALYSIS FOR CRACK DETECTION IN THE TIMOSHENKO BEAM BASED ON THE ANTI-RESONANCE TECHNIQUE

An alternative technique for crack detection in a Timoshenko beam based on the first anti-resonant frequency is presented in this paper.Unlike the natural frequency,the anti-resonant frequency is a local parameter rather than a global parameter of structures,thus the proposed technique can be used to locate the structural defects.An impedance analysis of a cracked beam stimulated by a harmonic force based on the Timoshenko beam formulation is investigated.In order to characterize the local discontinuity due to cracks,a rotational spring model based on fracture mechanics is proposed to model the crack.Subsequently,the proposed method is verified by a numerical example of a simply-supported beam with a crack.The effect of the crack size on the anti-resonant frequency is investigated.The position of the crack of the simply-supported beam is also determined by the anti-resonance technique.The proposed technique is further applied to the"contaminated"anti-resonant frequency to detect crack damage,which is obtained by adding 1-3% noise to the calculated data.It is found that the proposed technique is effective and free from the environment noise.Finally,an experimental study is performed,which further verifies the validity of the proposed crack identification technique.     

On irregularity-based damage detection method for cracked beams

A new damage detection technique using irregularity profile of a structural mode shape is proposed in this paper. The mode-shape of a cracked beam is first obtained analytically by using a general function. Its irregularity profile is then extracted from the mode shape by a numerical filter. The location and size of the crack in the beam can be determined by the peak value appearing on the irregularity profile. Two types of numerical filters, i.e., triangular and Gaussian, are examined. It has been found that the former filter is more effective in damage detection than the latter one. Numerical simulations suggest that the irregularity-based method requires a relatively low measurement resolution. Noise stress tests are carried out to demonstrate the effectiveness and robustness of this method under the influence of noise. As a validation, the proposed method is applied to detect crack damage in an E-glass/epoxy laminated composite beam. The successful detection of the crack in the composite beam demonstrates that the irregularity-based method is capable of assessing both the location and size of the crack and can be used efficiently and effectively in damage identification and health monitoring of beam-type structures.     

A Combined Static/Dynamic Technique for Damage Detection of Laminated Composite Plates

There is a growing demand to develop viable techniques for effective damage detection of composite structures, and the dynamics-based approach has been broadly used in structural health monitoring. A new combined static/dynamic technique for improved damage detection of laminated composite plates is presented. The promise of the technique is that under the sustaining static load, the abnormality of dynamic response due to damage may become more pronounced and easy to be detected. The experimental program consists of testing an E-glass/epoxy composite plate with an embedded delamination under a pre-set static compressive force, and the dynamic response of laminated composite plates is measured using two different actuator–sensor systems: (1) PZT (lead–zirconate–titanate) actuators and scanning laser vibrometer (SLV) sensing system (PZT–SLV), and (2) PZT actuators and Polyvinylidenefluoride (PVDF) sensors (PZT–PVDF). The influence of sustaining static forces to dynamic response of delaminated composite plates is evaluated. The numerical finite element (FE) analysis is also conducted to verify the effectiveness of this technique. The experimental and numerical mode shapes are used to detect the presence, location, and size of the delamination and to study the effect of static load on dynamic response. Two relatively new damage detection algorithms (i.e., Simplified Gapped Smoothing Method (GSM) and Generalized Fractal Dimension (GFD)) are employed to analyze the Uniform Load Surface (ULS) calculated from the experimental and numerical data. From the dynamic response and analysis results using the damage detection algorithms, it is observed that as the sustaining static load increases, the delamination is much easier to be identified through the enlarged damage parameters. The present combined static/dynamic technique is capable of magnifying the effect of damage, thus improving the effectiveness of damage detection.     

Modified intelligent hybrid technique reducing experimental error over the entire target area

The intelligent hybrid technique proposed by Nishioka et al. can be used to analyze stress intensity factors from displacement data obtained by experiments with high accuracy and reliability. However, the hybrid technique suffers from inevitable error and noise involved in extracting displacement fields from the boundary experimentally the boundary obtained experimentally. In this paper, a modified intelligent hybrid technique is developed to improve the shortcomings of the current technique. The proposed hybrid technique reduces the influence of experimental errors not only on/along the boundary but also inside the target area. Taking the SaintVenant principle and the results of test simulations into account, the effectiveness of the proposed hybrid technique is discussed. Then, applying the proposed hybrid technique to the plate with a hole under tensile loading, the distribution of strain, stress, and displacement over the entire target area is calculated with high accuracy and reliability.     

Structural damage localization and evaluation based on modal data via a new evolutionary algorithm

This paper is intended to present a method for the localization and evaluation of damage in plates based on the changes in natural frequencies and mode shapes of the damaged plate using an optimization approach. The colonial competitive algorithm is employed to detect damage (or damages) in plates by optimizing a damage function. The performance of the proposed method is demonstrated by implementing the technique to two examples; a shear wall and a four-fixed supported plate with and without modal data noise including one or a large number of damages. The results confirm the applicability and efficiency of the presented method in detecting damage localization and quantification in the shear walls. Furthermore, the proposed method is implemented to the four-fixed supported plate aimed at demonstrating the high sensitivity of the proposed method in quantitative estimation of damaged plate structures. Finally, the reliability of the presented method is explored through the comparison of the obtained results and those of the other methods. It is concluded that the proposed method can be viewed as a powerful and robust method for structural damage detection in plate structures.     

一种新的小波及其在结构损伤检测中的应用

结构受冲击将引起某些部位的震荡、裂纹甚至断裂,从而导致结构刚度下降.此时振动信号会出现奇异性或携带突变信息,而这些突变信息反映了结构的损伤情况.加之冲击信号测试环境一般较为复杂,环境噪声对测试存在一定的影响.然而,利用合理的小波变换技术去噪可以识别出损伤情况.本文通过对冲击振动的信号特性进行分析构造了一种新的基本小波,并论证了该小波的基本特征.最后运用小波分析的信号奇异检测理论结合实例将该小波用于冲击振动仿真分析中.计算结果表明,利用该小波进行结构损伤信号分析能清晰地识别结构损伤的时刻.采用该小波函数的构造方法,可避免通常采用Daubechies系列小波作为信号分析而要繁琐地选择不同小波函数的过程.     

A 2-D continuous wavelet transform of mode shape data for damage detection of plate structures

A two-dimensional (2-D) continuous wavelet transform (CWT)-based damage detection algorithm using “Dergauss2d” wavelet for plate-type structures is presented. The 2-D CWT considered in this study is based on the formulation by Antoine et al. (2004). A concept of isosurface of 2-D wavelet coefficients is proposed, and it is generated to indicate the location and approximate shape or area of the damage. The proposed algorithm is a response-based damage detection technique which only requires the mode shapes of the damaged plates. This algorithm is applied to the numerical vibration mode shapes of a cantilever plate with different types of damage to illustrate its effectiveness and viability. A comparative study with other two 2-D damage detection algorithms, i.e., 2-D gapped smoothing method (GSM) and 2-D strain energy method (SEM), is performed, and it demonstrates that the proposed 2-D CWT-based algorithm is superior in noise immunity and robust with limited sensor data. The algorithm is further implemented in an experimental modal test to detect impact damage in an FRP composite plate using smart piezoelectric actuators and sensors, demonstrating its applicability to the experimental mode shapes. The present 2-D CWT-based algorithm is among a few limited studies in the literature to explore the application of 2-D wavelets in damage detection, and as demonstrated in this study, it can be used as a viable and effective technique for damage identification of plate- or shell-type structures.     

基于不完备频响函数的结构损伤统计识别研究

基于不完备频响函数数据,结合概率统计方法,提出了一种能同时考虑模型参数不确定性和测试噪声影响的结构损伤统计识别方法。首先,基于频响函数某一行向量在不同频率下的幅值数据,利用矩阵拉直运算建立了关于损伤系数的确定性识别方程。其次,假设模型参数误差和测试噪声为零均值的高斯随机变量,根据摄动理论,推导了损伤后结构刚度参数的前二阶矩。随后,利用结构损伤前后的概率分布得到了结构损伤存在概率。最后,通过一个平面桁架结构模型验证了本文方法的有效性。数值算例的研究结果表明,损伤单元的损伤存在概率远大于非损伤单元;测试噪声对识别结果的影响比模型参数不确定性的影响更为显著。     

灰色相关性分析在结构静力损伤识别中的应用

基于灰色理论的相关性分析方法，首次提出了灰色曲率关联系数的概念并将其应用到结构的静力损伤识别中，提出了对局部损伤十分敏感的静态位移曲率置信因子SDCACi，通过该因子的大小对各节点所连接的单元是否会发生损伤进行精确的判断，然后运用最小二乘法对损伤区域的损伤程度进行识别．并将该方法应用于两端固支梁的损伤识别中，由识别结果可以证明：不论测量数据(用有限元仿真计算并考虑了测量误差)的多少，该方法对结构中的单损伤和多损伤都能进行准确的定位，因此该方法在大型结构及复杂结构的损伤识别中具有广阔的应用前景．     

SBFEM与非局部宏微观损伤模型相结合的准脆性材料开裂模拟

混凝土是一种被广泛应用于土木和水利工程中的准脆性材料, 在各种内外部因素的作用下, 开裂是混凝土结构最为普遍的破坏形式, 准确模拟结构的开裂过程, 对于结构的安全评估至关重要. 将比例边界有限元与非局部宏微观损伤模型相结合提出一种准脆性材料开裂模拟新方法. 以比例边界有限元子域的比例中心作为物质点, 通过两比例中心(物质点对)之间的物质键的正伸长率来定义微细观损伤, 将某点影响域内物质键的微细观损伤加权平均得到该点的宏观拓扑损伤. 再引入能量退化函数, 将宏观拓扑损伤嵌入到比例边界有限元的基本框架中. 充分利用比例边界有限元网格允许存在悬挂节点的优势, 采用四叉树网格离散技术进行快速、高质量的多级网格划分与过渡. 通过一个I型开裂与一个混合型开裂的两个典型算例, 验证了该方法可捕获结构裂纹扩展路径与荷载变形曲线. 与现有的方法相比, 本文的损伤模型可得到更准确的局部开裂损伤带, 结果更为合理, 且具有更高的计算精度和计算效率. 当损伤过程区网格尺寸小于影响域半径的1/5时, 计算结果不存在网格敏感性问题.      

Nondestructive testing method based on lamb waves for localization and extent of damage

Based on Lamb wave analysis of propagation in plate-like structures, a damage detection method is proposed that not only locates the position of the damage accurately but also estimates its size. Similar damage detection methods focus only on localization giving no quantitative estimation of extent. To improve detection, we propose two predictive circle methods for size estimation. Numerical simulations and experiments were performed for an aluminum plate with a hole. Two PZT configurations of different sizes were designed to excite and detect Lamb waves. From cross-correlation analysis, the damage location and extent can be determined. Results show that the proposed method enables a better quantitative resolution in detection, the size of the inspection area influences the accuracy of damage identification, and the closer is the inspected area to the damage, the more accurate are the results. The method proposed can be developed into a multiple-step detection method for multi-scale analysis with prospective accuracy.     

Combined neural network and reduced FRF techniques for slight damage detection using measured response data

Summary  This paper deals with structural damage detection using measured frequency response functions (FRF) as input data to artificial neural networks (ANN). A major obstacle, the impracticality of using full-size FRF data with ANNs, was circumvented by applying a data-reduction technique based on principal component analysis (PCA). The compressed FRFs, represented by their projection onto the most significant principal components, were used as the ANN input variables instead of the raw FRF data. The output is a prediction of the actual state of the specimen, i.e. healthy or damaged. A further advantage of this particular approach is its ability to deal with relatively high measurement noise, which is a common occurrence when dealing with industrial structures. The methodology was applied to detect three different states of a space antenna: reference, slight mass damage and slight stiffness damage. About 600 FRF measurements, each with 1024 spectral points, were included in the analysis. Six 2-hidden layer networks, each with an individually-optimised architecture for a specific FRF reduction level, were used for damage detection. The results showed that it was possible to distinguish between the three states of the antenna with good accuracy, subject to using an adequate number of principal components together with a suitable neural network configuration. It was also found that the quality of the raw FRF data remained a major consideration, though the method was able to filter out some of the measurement noise. The convergence and detection properties of the networks were improved significantly by removing those FRFs associated with measurement errors. Received 9 March 2000; accepted for publication 12 December 2000     

基于改进遗传算法的桥梁结构损伤识别应用研究

提出了一种基于残余力向量和改进遗传算法的桥梁结构损伤识别方法。在无噪声的情况下,使用任意一阶模态数据,残余力向量法都能够对损伤进行准确定位。但是,振动测试数据中往往包含噪声,导致运用残余力向量法进行损伤识别完全不可行。考虑到这个问题,在常规模态分析的基础上,以节点的残余力向量构造目标函数,提出了一种用于遗传搜索优化的目标函数形式。利用改进遗传算法重点进行了噪声条件下的结构损伤定位和定量研究,并对遗传算法的参数选取问题进行了深入探讨。遗传算法的主要改进包括:采用浮点编码、采用基于标准化几何分布排名的选择策略、采用最优保存策略、采用算术交叉算子、采用自适应变异算子。最后,本文用一个连续梁桥模型进行了数值模拟,验证了所提出方法的有效性,并对方法应用中存在的一些问题进行了深入探讨。     

复合材料构件损伤类型识别的一种方法

复合材料构件在使用过程中会产生脱层、内部裂纹、裂缝等损伤，这些损伤会引起构件动态特性的变化。本文提出了通过测取构件的动态特性，结合波形分析和模式识别技术进行复合材料损伤检测和损伤类型识别的方法。在比较了飞机环境噪声信号和周期脉冲信号的优缺点的基础上，提出使用周期脉冲信号作为构件的激振信号，来进行构件动态特性的测量。本文的研究中制作了多种类型的损伤试件，进行了实验，已发现显著特征，能够对构件的多种类型损伤进行识别     

结构健康监测中的损伤检测技术研究进展

对结构健康监测研究中的结构损伤检测方法及其特点进行了介绍.从基于结构模态分析的方法和基于结构动态试验信号处理的方法两方面,阐述了结构健康监测中的损伤检测方法及其最新研究进展.基于结构模态分析的结构损伤检测方法是针对整个结构的检测,使用的模态都限于低阶模态范围内,所检测的结构应容易建立有限元模型,便于进行响应预测.基于结构动态试验信号处理的损伤检测方法通常是针对结构局部构件的损伤检测,不需要对结构进行有限元建模,而直接从测试的动态响应信号中提取表征结构损伤的特征参数.文中提出了对比性损伤检测方法和非对比性损伤检测方法的概念,并对结构损伤检测中常用的信息传感与处理技术进行了论述,指出了结构损伤检测研究中应该考虑的传感器布置问题.提出了将损伤信息的主动检测与被动检测相结合进行损伤程度判断和剩余寿命估计等问题是有待进一步深入研究的课题.      

A SINGULAR VALUE DECOMPOSITION BASED TRUNCATION ALGORITHM IN SOLVING THE STRUCTURAL DAMAGE EQUATIONS

The structural damage identification through modal data often leads to solving a set of linear equations. Special numerical treatment is sometimes required for an accurate and stable solution owing to the ill conditioning of the equations. Based on the singular value decomposition (SVD) of the coefficient matrix, an error based truncation algorithm is proposed in this paper. By rejection of selected small singular values, the influence of noise can be reduced. A simply-supported beam is used as a simulation example to compare the results to other methods.Illustrative numerical examples demonstrate the good efficiency and stability of the algorithm in the nondestructive identification of structural damage through modal data.