【作者】 胥保春；

【导师】 袁慎芳；

【作者基本信息】 南京航空航天大学 ， 测试计量技术及仪器， 2012， 博士

【摘要】 信号处理是结构健康监测方法中的一个重要环节。基于Lamb波的损伤监测方法是结构健康监测中一个研究热点，而Lamb波是典型的非平稳信号。常规傅里叶分析理论在时频联合分析方面存在局限。希尔伯特-黄变换（Hilbert-Huang transform,HHT）是目前公认的适用于分析非平稳、非线性信号的一种信号分析理论。它通过经验模式分解（Empirical Mode Decomposition,EMD）自适应特点，在时域上将信号分解为有限个特征模式函数（Intrisical Mode Function, IMF），再对每个IMF进行Hilbert变换，得到频率变化的精确表达。HHT方法在Lamb波分析中具有很好的应用前景。本文对HHT信号处理方法开展系统研究，并将结果应用于结构健康监测中。本文主要研究内容如下：1.对比了广义延拓插值与传统插值、直接均值线生成与传统均值线生成的效果，分析了边端效应原因及其选用原则，深入研究了三种常用IMF筛选停止条件原理。在此基础上，引入分解面概念，评估了这些EMD实现技术对EMD分解效果的影响，提出了基于剔除余量的IMF筛选停止条件，验证了基于该方案的EMD分解效果。2.利用实验分析了信号幅值、频率、相位的变化对极值点的影响，研究了极值点变化趋势对EMD分解效果影响。将幅值、频率、相位变化与EMD分解效果之间联系起来，通过实验归纳与数学公式推导，发现了信号影响EMD分解效果的关系式，最后利用实验对该关系式进行了验证。3.在EMD实现技术及信号自身条件对EMD分解效果影响的研究基础上，分析了模式混叠原因，提出了模式混叠可分为三种基本类型，深入研究了三种典型模式混叠解决方案原理，分析了它们的局限性，提出了基于频段EMD提取法的模式混叠处理方案，利用实验验证了该方案的模式混叠处理效果。4.研究了直达波叠加损伤散射信号后的瞬时相位变化，并利用实验对研究结果进行了验证；分析了主动Lamb波信号EMD分解非稳定的原因，引入了基于频段EMD提取法以提高分解的稳定性，并用实验进行了验证；在此基础上，利用边际谱研究了损伤散射信号对直达波的瞬时频率影响，并与信号的频谱进行了比较。5.从理论上分析了板结构冲击损伤Lamb波模式特点，利用断铅实验验证了分析结论；利用Lamb波A0模态波速计算验证了频段EMD提取法的窄带信号提取功能，在冲击实验引入该方法以实现冲击源定位；在冲击损伤诊断，利用EMD自适应分解信号的特点，得到了结构损伤激发的IMF，并用频段EMD提取法对损伤进行定位。更多还原

【Abstract】 Signal processing is important in helping the development of Structural Health Monitoring (SHM)techniques. Lamb wave based Structural Health Monitoring method is one of the most interesting hotspots for SHM. Lamb wave is a typical non-stationary signal. However, the traditional FFT analysistheory is limited for time-frequency combined analysis. Hilbert-Huang transform(HHT) is known as atheory used for non-stationary and nonlinear signal. In HHT, a signal is first decomposed into finiteIMFs by EMD, and then, with the Hilbert transform, the meaning instantaneous frequency of everyIMF that gives precise description of the varying frequency is obtained. Hence HHT shows apromising application in Lamb wave analysis. In this paper the HHT signal processing is researchedsystematically, and the research result is applied in SHM. The main research contents of this paper areas follows:Firstly, this paper compared generalized extended interpolation to Cubic Spline Interpolation andthe mean from the local maxima and the local minima to the mean of the upper and lower envelopes,then analyzed the reason of the end effects and choosing principles and researched deeply the criterionfor stoppage of three common IMF filtering. Based on the above research, the concept of thedecomposition plane was introduced and EMD realization techniques’ influence on EMDdecomposition effect was assessed. Then an IMF criterion for sifting stoppage based on excludingmargin was put forward, which verified the EMD decomposition effect based on this method.Secondly, the influence on the extreme value point by signal amplitude, frequency and phasevariation was analyzed by experiments, and then the influence on EMD decomposition effect byextreme value variation trend was researched. Combining the variation of signal amplitude, frequencyand phase with EMD decomposition, signals’ influence on EMD decomposition effect was discoveredby both experimental induction and theoretical deduction. The relationship was validated byexperiments.Thirdly, based on the research about EMD realization technique and the influence on EMDdecomposition effect by signal, the reason of mode mixing is analyzed. Three basic types of modemixing are proposed. The solution principles to the three typical mode mixing were researched deeply,and their limitations were also analyzed. EMD based on frequency bands was proposed to solve modemixing, whose mode mixing solution effect was validated by experiments.Fourthly, the instantaneous phase variation when the direct arrival wave was superimposed by damage scattering signal was researched and its result was validated by experiments. The reason whyEMD decomposition of the active Lamb wave signal is unstable is analyzed and BF-EMD wasintroduced to improve the decomposition stability. The experimental validation was followed. Basedon that, the marginal spectrum was applied to research damage’s influence on the instantaneousfrequency of direct arrival wave and the research result was compared to signal’s frequency spectrum.Fifthly, the mode feature of Lamb wave generated by impact damage was analyzed theoreticallyand validated by lead cutting experiment. The propagation velocity calculation of A0mode wasutilized to validate the extraction ability of BF-EMD about signals of narrow frequency. This methodwas introduced to realize impact source localization. During the prognosis of impact damage, IMFprovoked by structural damage was obtained by EMD self-adaptive signal decomposition and damagelocalization was realized by BF-EMD extraction method.更多还原