共查询到18条相似文献,搜索用时 139 毫秒
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针对含裂纹的梁,考虑由裂纹尖端应力集中产生的局部柔度,基于应变能量原理得出裂纹附近的应力集中系数,推导裂纹区域应力与应变的关系,构造梁在裂纹处的柔度矩阵。在裂纹梁的有限元法计算过程中,将此柔度矩阵导入梁的整体刚度矩阵,完成裂纹梁在受静力载荷下位移的计算。出于裂纹梁裂纹识别的考虑,利用小波变换系数定义量图得到小波脊定位裂纹的位置。裂纹的存在导致力学响应的某些频段能量发生变化,利用小波变换对信号频率划分的功能,由频段能量的大小确定裂纹的大小。反之,讨论已知裂纹梁在受静力载荷下的位移条件来识别裂纹位置和大小的动力学反问题。通过对噪声污染的信号分析,说明此方法有良好的抗噪能力。 相似文献
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《中国工程机械学报》2015,(3)
针对单梁式起重机的缺陷问题,将有限元法和小波变换应用到结构缺陷识别中.建立了单梁式起重机梁的有限元分析模型,模拟计算了移动载荷作用下,梁结构在未损伤、微小损伤和较大损伤下的动态响应,重点研究了梁结构损伤对梁跨中响应信号的影响,发现损伤裂纹会使得梁跨中的响应信号产生间断点.通过MATLAB软件对仿真模拟得到的信号进行处理,可以明显判断损伤裂纹的空间位置,模拟计算结果对起重机结构损伤的检测和识别具有重要意义. 相似文献
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以等效弹簧模拟裂纹引起的局部软化效应,应用Bernoulli-Euler梁理论建立双裂纹阶梯悬臂梁的振动特征方程.鉴于方程含有较多的未知量,提出联合小波变换和结构测量频率的裂纹参数识别两步法.首先,含裂纹悬臂梁的一阶模态作为信号用于连续小波变换,通过小波系数的局部极值可以清楚地确定结构的裂纹位置.其次,将识别得到的裂纹位置代入双裂纹阶梯悬臂梁的特征方程,最后通过绘制两个裂纹的等效柔度的等值线图,通过交点确定满足特征方程的两个裂纹的等效柔度,并进一步确定裂纹深度.最后利用数值算例验证该方法的有效性. 相似文献
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工字截面梁轨结构裂纹损伤的小波有限元定量诊断 总被引:1,自引:0,他引:1
研究工字截面梁轨结构裂纹定量识别中的正反问题,即通过裂纹位置和深度求解结构的固有频率以及利用结构的固有频率,识别裂纹位置和深度.裂纹被看作为一扭转线弹簧,利用工字梁裂纹应力强度因子推导出线弹簧刚度,构造出结构的小波有限元刚度矩阵和质量矩阵,从而获得裂纹结构的前3阶固有频率.通过行列式变换,将反问题求解简化为只含线弹簧刚度一个未知数的一元二次方程求根问题,分别做出以不同固有频率作为输入值时裂纹位置与裂纹深度之间的解曲线,曲线交点预测出裂纹的位置与深度,试验结果验证算法的有效性. 相似文献
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实际使用中的梁类结构容易萌生裂纹,影响其使用寿命及安全可靠运行,准确判定其裂纹损伤位置对于实现梁类结构的快速准确维护处理具有重要意义,为此提出基于振动信号S变换和互信息值实现梁类结构裂纹的识别与定位。首先,基于测试获得梁类结构上分布点的振动信号;其次,利用S变换将振动信号变换到时频域,计算梁结构在裂纹损伤前后各对应位置点时频域振动信号的互信息值;最后,通过检索互信息值向量中分量的最小值位置实现裂纹区域的准确定位。为了避免引入附加质量的影响,利用机器视觉测振系统采集悬臂梁和小型复合材料叶片上的分布点振动信号,设置不同裂纹位置对梁类结构裂纹定位方法进行了验证,证明了方法的有效性。 相似文献
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基于小波熵指标的结构损伤检测 总被引:1,自引:1,他引:1
对小波熵在土木工程结构损伤检测中的适用性进行分析,利用小波变换时一频局部化性能,将小波分析和信息熵结合起来,建立小波能谱熵、小波时间熵和相对小波熵等结构损伤指标.通过数值模拟和工字梁的试验数据对各指标和损伤识别方法进行了分析检验,识别出模拟梁和试验梁的损伤位置.识别结果表明,基于小波熵的指标是一个对结构局部损伤敏感的、比较好的损伤指标. 相似文献
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提出了小波变换用于早期损伤的识别的方法.对小波理论做了简介,并通过仿真实验验证小波变换对损伤识别的能力.通过观察连续小波变换(CWT)的小波系数的模极大值或者离散小波变换(DWT)中的细节信号,识别动(静)态信号中的奇异值,从而判别出损伤的位置.此方法仅需要有损伤的结构的响应信号,不需要未损伤结构的响应信号及其结构信息,所需的信号可以是静态的,也可以是动态的.将该方法应用到带裂纹的悬臂梁有限元模型,通过瞬态、静力分析采集信号,精确定位裂纹的位置和数量.与传统方法相比,该方法不仅可行性强,经济方便,而且检测结果更为精确可靠.仿真实验表明,小波变换的方法是有力可靠的结构早期损伤识别方法. 相似文献
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将小波变换直接用于含裂纹悬臂梁的不同模态,利用小波系数在空间域上的突变指示裂纹位置,通过定义集中因子标定裂纹深度。并分析和讨论了悬臂梁前四阶模态对损伤的敏感性。通过本文的实验研究,检验了sym4小波在工程应用中的适用性,并指出二阶模态是较为敏感的损伤信息,有助于提高缺陷识别的精度和可靠性。 相似文献
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针对压电柔性悬臂梁裂缝损伤检测与损伤程度识别问题,采用小波包分析和小波神经网络相结合的方法进行裂缝深度识别实验研究.利用小波包频带能量谱构造柔性悬臂梁裂缝损伤指标,即能量比相对变化量的H2范数,并建立压电柔性梁裂缝损伤实验装置.激励柔性梁的振动,记录两路压电传感器采集的振动信号,进行小波包分解并计算损伤指标.将这些损伤指标进行组合,作为小波神经网络的输入特征参数,进行裂缝深度即损伤程度的识别.实验结果表明:能量比相对变化量的H2范数对柔性梁的裂缝损伤敏感,对测试噪声不敏感;采用的小波神经网络可以精确识别柔性梁的裂缝深度. 相似文献
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Jing Liu Weidong Zhu Panos G. Charalambides Yimin Shao Yongfeng Xu Kai Wu Huifang Xiao 《机械工程学报(英文版)》2016,29(1):163-179
As one of the main failure modes, embedded cracks occur in beam structures due to periodic loads. Hence it is useful to investigate the dynamic characteristics of a beam structure with an embedded crack for early crack detection and diagnosis. A new four-beam model with local flexibilities at crack tips is developed to investigate the transverse vibration of a cantilever beam with an embedded horizontal crack; two separate beam segments are used to model the crack region to allow opening of crack surfaces. Each beam segment is considered as an Euler-Bernoulli beam. The governing equations and the matching and boundary conditions of the four-beam model are derived using Hamilton's principle. The natural frequencies and mode shapes of the four-beam model are calculated using the transfer matrix method. The effects of the crack length, depth, and location on the first three natural frequencies and mode shapes of the cracked cantilever beam are investigated. A continuous wavelet transform method is used to analyze the mode shapes of the cracked cantilever beam. It is shown that sudden changes in spatial variations of the wavelet coefficients of the mode shapes can be used to identify the length and location of an embedded horizontal crack. The first three natural frequencies and mode shapes of a cantilever beam with an embedded crack from the finite element method and an experimental investigation are used to validate the proposed model. Local deformations in the vicinity of the crack tips can be described by the proposed four-beam model, which cannot be captured by previous methods. 相似文献
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Ser-Tong Quek Quan Wang Liang Zhang Kian-Keong Ang 《International Journal of Mechanical Sciences》2001,43(12):23
This paper examines the sensitivity of wavelet technique in the detection of cracks in beam structures. Specifically, the effects of different crack characteristics, boundary conditions, and wavelet functions employed are investigated. Crack characteristics studied include the length, orientation and width of slit. The two different boundary conditions considered are simply supported and fixed end support, and the two types of wavelets compared in this study are the Haar and Gabor wavelets. The results show that the wavelet transform is a useful tool in detection of cracks in beam structures. The dimension of the crack projected along the longitudinal direction can be deduced from the analysis. The method is sensitive to the curvature of the deflection profile and is a function of the support condition. For detection of discrete cracks, Haar wavelets exhibit superior performance. 相似文献
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《Mechanical Systems and Signal Processing》2007,21(4):1853-1884
There are significant changes in the vibration responses of cracked structures when the crack depth is significant in comparison to the depth of the structure. This fact enables the identification of cracks in structures from their vibration response data. However when the crack is relatively small, it is difficult to identify the presence of the crack by a mere observation of the vibration response data. A new approach for crack detection in beam-like structures is presented and applied to cracked simply supported beams in this paper. The approach is based on finding the difference between two sets of detail coefficients obtained by the use of the stationary wavelet transform (SWT) of two sets of mode shape data of the beam-like structure. These two sets of mode shape data, which constitute two new signal series, are obtained and reconstructed from the modal displacement data of a cracked simply supported beam. They represent the left half and the modified right half of the modal data of the simply supported beam. SWT is a redundant transform that doubles the number of input samples at each iteration. It provides a more accurate estimate of the variances at each scale and facilitates the identification of salient features in a signal, especially for recognising noise or signal rupture. It is well known that the mode shape of a beam containing a small crack is apparently a single smooth curve like that of an uncracked beam. However, the mode shape of the cracked beam actually exhibits a local peak or discontinuity in the region of damage. Therefore, the mode shape ‘signal’ of a cracked beam can be approximately considered as that of the uncracked beam contaminated by ‘noise’, which consists of response noise and the additional response due to the crack. Thus, the modal data can be decomposed by SWT into a smooth curve, called the approximation coefficient, and a detail coefficient. The difference of the detail coefficients of the two new signal series includes crack information that is useful for damage detection. The modal responses of the damaged simply supported beams used are computed using the finite element method. For real cases, mode shape data are affected by experimental noise. Therefore, mode shape data with a normally distributed random noise are also studied. The results show that the proposed method has great potential in crack detection of beam-like structures as it does not require the modal parameters of an uncracked beam as a baseline for crack detection. The effects of crack size, depth and location, and the effects of sampling interval are examined. 相似文献
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基于区间B样条小波有限元的转子裂纹定量识别 总被引:4,自引:0,他引:4
研究一种基于区间B样条小波有限元的转子横向裂纹定量识别方法.构造包含转动惯量影响的区间B样条小波Rayleigh梁单元,高精度求解裂纹转子前三阶固有频率,获得裂纹相对位置和相对深度作为变量的固有频率解曲面.然后将实测的裂纹转子前三阶固有频率作为裂纹识别问题的输入,利用三条等高线的交点定量识别出裂纹存在的相对位置和相对深度.数值仿真和试验研究结果表明,该方法鲁棒性强,单元数量少,辨识精度和效率高,为转子系统裂纹定量识别提供了新方法. 相似文献
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