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1.
激光激励的Lamb波信号具有较宽的频带,且包含多个模态信息。本文采用二维傅里叶变换和时频分析等信号分析技术用于检测信号中的模态成分及缺陷信息识别。首先,对200组激光Lamb波信号进行二维傅里叶变换,得到信号的频率-波数图,可识别出激光Lamb波信号中的低阶A0、S0和高阶模态,并且A0模态能量高,可用于缺陷检测。随后对有、无缺陷状态下Lamb波信号进行连续小波变换,从时频图中识别出缺陷信号的频率成分,进一步提取特定频率下的小波系数幅值信号,实现了缺陷信息的识别。结果表明,二维傅里叶变换能较好地识别激光Lamb波的模态成分,而提取出的连续小波变换系数图,能准确实现缺陷定位。 相似文献
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小波分析技术在陀螺故障诊断中的应用研究 总被引:4,自引:0,他引:4
小波分析是一种全新的时一频两维分析技术,其对高频突变信号和低频缓变信号的分析有其独特的优点。本文分析了小波分析技术的原理,提出了将其引入机械设备故障诊断中的方法。通过对有故障陀螺振动信号的多尺度分析,研究故障信号小波变换轴心轨迹分量图,建立典型故障特征模型,从而对单故障及多故障问题进行分析与诊断。 相似文献
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We investigate damage detection in a simply-supported pre-stressed beam. A crack was propagated by fatigue loads, which were
applied up to two million cycles. Both fast Fourier transform (FFT) and continuous wavelet transform (CWT) are used in the
analysis of the structural response to impulse loads. The acceleration response of the full-scale beam was measured each time
a certain number of cycles of fatigue loads were applied. The results of this study show that both methods can clearly identify
the crack growth induced by fatigue loads. The natural frequencies found by FFT are sensitive to the crack progression. The
results from the CWT analysis show a clear difference in structural responses between the initial and damaged states of the
structure. The response accelerations are de-noised by a soft-thresholding method before they are analyzed by CWT. In addition
to the frequency components, the CWT shows the moment in time when particular frequencies occur. Therefore, wavelet analysis
has the potential of becoming an effective tool for damage detection and health monitoring of structures for which the natural
frequencies are irregularly changing. As the crack grows, the magnitude of ridges obtained by CWT analysis decreases significantly,
which indicates the reduction in structural stiffness. 相似文献
4.
连续小波变换离散化的爆炸振动特征分析 总被引:1,自引:0,他引:1
应用连续小波变换的离散化关系,针对一个改进的L-P(littlewood-paley)小波基函数,给出了一种实现频率完全分割的时频特征分析方法,并对爆炸振动时频特征进行了研究。80 kg TNT地面爆炸时地面垂向振动速度的时间能量密度分布情况表明,在质点振动峰值速度到达时刻爆炸振动的频率范围比较宽,而其他时刻的振动频率相对较为集中,时频能量分布的峰值正好对应于爆炸振动速度的峰值到达时间。基于小波变换的爆炸振动频谱特征与Fourier变换的结果具有良好的一致性。此外,还给出了利用小波变换结果建立爆炸振动随机演变理论模型的基本方法。 相似文献
5.
建立了一套对图像融合质量进行定量评价的方法和准则。其中,对于相同传感器源的图像,利用标准参考图像,选取均方误差、峰值信噪比、参考图像,以及融合图像的信息熵差、互信息作为客观评价指标;对于不同传感器源图像,选取融合图像的标准差、空间频率、信息熵以及融合图像与两源图像的互信息之和作为客观评价指标。应用此方法和准则对基于离散小波框架、基于可操纵方向金字塔变换和基于双树复小波变换三种平移不变性的图像融合方法进行了客观定量评价。实验结果表明,基于可操纵方向金字塔变换的融合方法效果最好,然后是基于离散小波框架的融合方法;基于双树复小波变换的融合方法其性能与前两种接近,且其冗余性最小。 相似文献
6.
Influence of boundary conditions relaxation on panel flutter with compressive in-plane loads 总被引:2,自引:1,他引:2
The influence of boundary conditions relaxation on two-dimensional panel flutter is studied in the presence of in-plane loading. The boundary value problem of the panel involves time-dependent boundary conditions that are converted into autonomous form using a special coordinate transformation. Galerkin's method is used to discretize the panel partial differential equation of motion into six nonlinear ordinary differential equations. The influence of boundary conditions relaxation on the panel modal frequencies and LCO amplitudes in the time and frequency domains is examined using the windowed short time Fourier transform and wavelet transform. The relaxation and system nonlinearity are found to have opposite effects on the time evolution of the panel frequency. Depending on the system damping and dynamic pressure, the panel frequency can increase or decrease with time as the boundary conditions approach the state of simple supports. Bifurcation diagrams are generated by taking the relaxation parameter, dynamic pressure, and in-plane load as control parameters. The corresponding largest Lyapunov exponent is also determined. They reveal complex dynamic characteristics of the panel, including regions of periodic, quasi-periodic, and chaotic motions. 相似文献
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Real time digital recording and numerical reconstruction of a temporal digital hologram sequence have become feasible in recent years. They provide a new measurement method which enjoys the valuable advantages of being full-field, noncontact and high precision. In this paper, a combined method of temporal digital hologram sequence and windowed Fourier transform is proposed to measure the kinematic parameters of random vibration. A series of holograms are recorded by CCD camera and the original phase can be reconstructed by Fresnel reconstruction algorithm. The three-dimensional windowed Fourier transform is used to filter noise in phase and extract the instantaneous kinematic parameters of the specimen, such as the displacement, velocity and acceleration. An experiment is conducted on a chloroprene rubber latex membrane. Results demonstrate that the proposed method determines the vibration parameters precisely and enjoys many merits. 相似文献
10.
爆破振动信号的HHT时频能量谱分析 总被引:2,自引:0,他引:2
采用希尔伯特-黄变换对爆破振动信号进行时频能量谱分析。经验模态分解中采用了极值点对称
延拓消除端点效应,采用分段三次Hemite保形插值算法插值拟合消除欠包络现象以及筛分终止局部准则;
对于传统HHT 计算瞬时频率的负峰问题采用了标准化和直接正交法解决。采用了LabView 平台实现,提
高了计算效率和实用性。 相似文献
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《力学快报》2020,10(2):98-115
This paper first reviews the application research works of wavelet transform on the fluid mechanics. Then the theories of continuous wavelet transform and multi-dimensional orthogonal(discrete) wavelet transform, including wavelet multiresolution analysis, are introduced. At last the applications of wavelet transform on 2 D and 3 D turbulent wakes and turbulent boundary layer flows are described based on the hot-wire, 2 D particle image velocimetry(PIV) and 3 D tomographic PIV. 相似文献
13.
Giuseppe Failla Massimiliano PappaticoGiuseppe Alfredo Cundari 《Mechanics Research Communications》2011,38(5):361-367
This paper introduces a wavelet-based time-dependent spectrum for arbitrary non-stationary processes, for which no exact spectrum is defined. In analogy to the spectrum already built by one of the authors (Spanos and Failla, 2004) for oscillatory processes (Priestley, 1981), the proposed spectrum is cast as a series expansion involving the square moduli of the Fourier transforms of the wavelets at a number of scales, to be chosen according to the frequency content of the process. The coefficients of the series are computed by a set of integral equations, each involving the mean square value of the wavelet transform at one of the selected scales. Simple manipulations show that the proposed wavelet-based spectrum represents indeed an approximate value for time-dependent Fourier power spectral densities, defined over scale-dependent time intervals.Numerical results, assessed in terms of statistics depending on the spectral moments, prove satisfactory for typical earthquake processes. 相似文献
14.
Some properties of the wavelet transform of trigonometric function, periodic function and nonstationary periodic function have been investigated. The results show that the peak height and width in wavelet energy spectrum of a periodic function are in proportion to its period. At the same time, a new equation, which can truly reconstruct a trigonometric function with only one scale wavelet coefficient, is presented. The reconstructed wave shape of a periodic function with the equation is better than any term of its Fourier series. And the reconstructed wave shape of a class of nonstationary periodic function with this equation agrees well with the function. 相似文献
15.
In this paper, we introduce the two-dimensional continuous wavelet transform for the automated strain analysis of the moiré
interference fringe pattern. The Fourier transform method has been widely used for automated analysis of an optical interference
fringe pattern. However, this method is hardly applicable to the analysis of the fringe pattern, which includes large displacement
range or discontinuities. We show the advantages of the wavelet transform method by applying it to experimental results on
composite laminates. 相似文献
16.
Many natural time series and signals collected from engineered systems are continuous dynamical signals. In practice, it is necessary to study nonlinearities in such continuous dynamic systems under different sampling conditions. In this paper, nonlinearity tests based on the delay vector variance (DVV) and iterative amplitude adjusted Fourier transform (IAAFT) based surrogates are first applied to Lorenz time series under various sampling rates. Traditional nonlinearity measures, such as third-order autocovariance and asymmetry due to time reversal, are shown to be sensitive to different sampling conditions whereas the relative insensitivity of the DVV proves promising. This insensitivity makes DVV a desirable nonlinearity measure for describing continuous dynamic signals and herein it is shown to be a suitable nonlinear fault diagnostic method for use in the gearbox condition monitoring. Moreover, by applying the DVV rank test, faults in gears can be identified effectively. 相似文献
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一种基于小波变换的信号突变征兆提取方法及其应用 总被引:3,自引:3,他引:0
获取故障征兆是诊断系统必须解决的首要问题。应用小波变换理论提出了一种信号突变征兆提取方法,并将它应用于转台故障诊断中。实验结果表明,这种方法在信号突变征兆提取上具有明显效果。 相似文献
19.
《International Journal of Solids and Structures》2002,39(7):1803-1816
Damage detection by the wavelet transform of the fundamental vibration mode receives much attention recently. Many investigations report successful applications of the wavelet transform in damage detection, but most of them appear to lack theoretical justifications. The objective of this contribution is to show the effectiveness of the wavelet transform by means of its capability to estimate the Lipschitz exponent. It is also addressed that the magnitude of the Lipschitz exponent can be used as a useful indicator of the damage extent. As a specific example, damaged beams are investigated both numerically and experimentally. The continuous wavelet transform (CWT) by a Mexican hat wavelet having two vanishing moments is utilized for the estimation of the Lipschitz exponent. The analysis by the CWT also gives a guideline to choose appropriate discrete wavelet transforms. 相似文献
20.
基于小波变换的重力变化信号处理技术研究 总被引:1,自引:2,他引:1
针对重力敏感器中所测信号的特点,提出了小波变换的多分辨率分析方法。采用了强制去噪和阈值去噪两种方法,利用Daubechies小波函数,分别针对三种典型情况进行了分析。结果表明,对于信噪比非常小的重力变化信号,阈值去噪法相对于强制去噪法来说效果并没有明显提高,第9层下重建信号的逼近误差满足性能指标。文中还讨论了加入确定性干扰的情况下微弱信号的提取情况,结果表明,加入大的确定性干扰后,为了满足设计要求,小波分解的尺度有所增加,整体的滤波效果与未加入确定性干扰的情况基本相同。 相似文献