基于量子高斯混合模型的振动信号降噪方法

由于机械设备振动信号受到背景噪声的干扰,造成机械设备故障状态特征不明显,因此提出了一种基于量子高斯混合模型的振动信号降噪方法。首先,对振动信号进行双树复小波包变换,对双树复小波包系数建立高斯混合模型,根据贝叶斯最大后验估计准则,得到双树复小波包系数收缩函数;然后,利用双树复小波包系数父代和子代的空间相关性,结合量子叠加态理论计算噪声信号和有用信号小波系数出现的概率值;最后,根据量子叠加态得到的概率参数值调节高斯混合模型中的小波包系数收缩函数,使小波包系数自适应非线性收缩,提高高斯混合模型的局部自适应性,实现机械振动信号的降噪处理。仿真信号和实测行星齿轮箱振动信号实验结果表明,该方法能够有效地去除振动信号中的噪声,凸显机械设备的故障状态特征。     

基于双树复小波的重叠块阈值降噪方法

针对机械早期故障信号受到强背景噪声影响导致故障特征不明显的问题,提出一种基于双树复小波包的重叠块阈值降噪方法。利用有限冗余双树复小波包变换对信号进行具有平移不变性的稀疏分解,结合双树复小波包变换系数所具有的稀疏集簇和邻域相关性特点,建立重叠块阈值估计模型,通过最小化包含块稀疏模型的适应度函数获得估计信号,分析了重叠块阈值降噪各参数对降噪效果的影响和参数优化原则,仿真与实测信号实验结果表明,该方法在不同信号和不同噪声水平下均有效地抑制了噪声干扰,提高了信噪比。     

基于偶树复小波和改进型阈值函数的降噪方法 及其应用

为更好地保留原有用信号信息,有效恢复强噪声背景下微弱故障信号,提出了一种基于对偶树复小波和改进型阈值函数的降噪方法,将其应用于机械故障诊断,取得了较好效果。运用对偶树复小波变换滤波器设计方法和改进型阈值函数,以实施降噪的具体步骤。该法充分利用了对偶树复小波变换的平移不变的优良特性,同时,改进型阈值函数与传统软、硬阈值降噪算法相比,克服了软阈值信号失真和硬阈值信号不连续、振荡等缺点。实验表明：此法有效去除了噪声,是一种较好的提取微弱故障信号的方法。     

基于双树复小波包的发动机振动信号特征提取研究

针对柴油机缸盖振动信号的特征提取问题,提出了一种基于双树复小波包变换和自适应块阈值降噪的标准化相对能量提取方法,双树复小波包利用并行双树实小波变换分解系数达到信息互补,从而获得近似平移不变性和减少了信息的丢失.自适应分块阈值能够随所分析的信号自适应估计最优阈值,达到更好的降噪效果,同时引入消除频率混叠的算法,抑制了双树复小波包分解过程中虚假频率的产生.仿真信号和试验分析该方法能够更有效地消除噪声影响,所提取的相对能量特征具有更好的可区分度.     

基于双树复小波与非线性时间序列的降噪方法

针对双树复小波变换传统软阈值降噪方法对实、虚部树系数分别进行阈值处理时提取的强背景噪声下轴承故障特征信号效果不理想,且实、虚部分离的阈值处理方法会引起局部相位失真问题,利用故障信号小波变换系数具有周期性与双树复小波系数模震荡小等特点,提出双树复小波变换与非线性时间序列方法相结合的强背景噪声下轴承故障特征提取方法。对故障信号进行双树复小波变换,获得各层小波系数并求模,选择系数模周期性较强层系数进行非线性时间序列处理,增强系数中周期性成分,抑制随机噪声;对增强后系数进行软阈值处理消除直流成分对提取结果的影响;将处理后系数还原为复数形式进行双树复小波重构,可成功提取弱故障特征信号。仿真、试验信号处理结果表明,该方法能有效提取强背景噪声下的故障特征信号。     

双树复小波和双谱在轴承故障诊断中的应用

针对非线性、非平稳且包含强烈的噪声的轴承故障振动信号难以有效提取故障特征信息进行故障识别的问题,提出基于双树复小波变换和双谱的故障诊断方法。首先利用双树复小波变换将故障轴承振动信号分解为若干个不同频带的分量,选择出包含故障特征的分量;然后对该分量进行希尔伯特包络解调;最后对包络信号求其双谱图,从而有效地提取出故障信号的特征频率,准确地进行故障识别。滚动轴承故障实验和工程应用表明,该方法能有效地提取故障轴承的故障特征频率,并且几乎可以完全抑制噪声,验证了方法的可行性和有效性。     

小波变换域双谱分析及其在滚动轴承故障诊断中的应用

工程信号不仅会受到高斯噪声干扰，而且也会受到非高斯噪声干扰。而传统双谱分析方法从理论上仅能抑制高斯噪声，但对非高斯噪声是无能为力的。针对传统双谱存在的不足，将小波变换和双谱分析结合，提出了一种基于小波变换域非参数化双谱故障诊断方法，并应用到滚动轴承故障诊断中。考虑到滚动轴承信号幅值调制特点，在本方法中，对处理信号采用了希尔伯特变换技术，以进行解调。实验结果表明，小波域双谱优于传统双谱，特别是在非高斯噪声情况下，小波域双谱更有优势；研究为滚动轴承故障诊断提供了一种新的有效方法。     

小波域隐Markov树模型降噪算法的改进

提出了适应于更一般情况的基于小波域隐Markov树(HMT)模型信号降噪的改进算法。通常算法以数个零均值高斯函数加权之和描述信号小波系数统计分布,在有些情况下可能带来严重失真。改进算法以一般统计模型描述信号小波系数分布,以最优估计方式对其降噪,能够避免不适当统计模型可能带来的潜在失真。数据仿真表明该算法有时可以减少降噪信号的MSE(均方误差)80％以上。     

基于双树复小波包峭度图的轴承故障诊断研究

针对传统包络谱和峭度图分析技术的缺陷,提出了一种基于双树复小波包峭度图的轴承故障诊断方法。该方法综合利用了双树复小波包变换和峭度图分析技术,克服了原峭度图方法只采用FIR和短时傅立叶变换滤波器的缺点,提高了从强噪声环境中提取瞬态冲击特征的能力。首先利用双树复小波包变换,将振动信号分解成不同频带的分量,然后计算各小波分量的谱峭度,再利用谱峭度的滤波器作用,计算最大峭度值对应分量信号的包络谱,根据包络谱就可识别齿轮箱轴承的故障部位和类型。齿轮箱轴承故障振动实验信号的研究结果表明：该方法不仅提高了信噪比和频带选择的正确性,而且能有效地识别轴承的故障。     

基于双树复小波和奇异差分谱的齿轮故障诊断研究

针对故障齿轮振动信号的非平稳特征和包含强烈噪声,很难提取故障特征频率的情况,提出了基于双树复小波和奇异差分谱的故障诊断方法。首先将非平稳的故障振动信号通过双树复小波分解为几个不同频段的分量;由于噪声的影响,从各个分量的频谱中难以准确地得到故障频率。然后对包含故障特征的分量构建Hankel矩阵并进行奇异值分解,求奇异值差分谱曲线,确定奇异值个数进行SVD重构降噪,由此实现对故障特征信息的提取。最后再求希尔伯特包络谱,便能准确地得到故障频率。实验结果和工程应用表明,该方法可以有效地提取齿轮的故障特征信息,验证了方法的可行性和有效性。     

Hidden Markov tree model applied to ECG delineation

A new electrocardiogram (ECG) delineation method is proposed, which uses a hidden Markov tree model. The aim of this approach is, on the one hand, to use wavelet coefficients to characterize the different ECG waves, and, on the other hand, to link these coefficients by a tree structure enabling wave change to be detected. By associating this method with a fusion method between scales based on the concept of context, good results are obtained on a special database created for the risk analysis of atrial fibrillation, particularly in P-wave delineation.     

自适应冗余提升小波降噪分析及其在轴承故障识别中的应用

为有效识别机械设备中滚动轴承的微弱故障信息,本文提出一种自适应冗余提升小波降噪方法。根据待分解低频尺度系数所含的不同特征,应用范数准则来自适应地选取最匹配于该尺度系数特征的小波函数。同时,引入多孔算法,用以通过冗余性来保证逐层分解后各尺度系数和小波系数所含有的丰富的信息量。接下来,对各层小波系数采用变尺度阈值降噪算法,并对降噪后的系数进行重构及包络谱分析,进而提取滚动轴承的故障特征。应用上述方法分别对轴承实验台轴承混合故障信号和现场实际信号进行分析,均较好地实现了故障识别,验证了本文方法的有效性。     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

基于事故树的深孔爆破边坡稳定性分析

为了能够对爆破后形成的露天边坡稳定性进行合理的分析评价,结合大小鱼山岛露天爆破边坡失稳的情况,采用事故树分析方法,建立了工程爆破现场露天边坡失稳事故树模型。计算出事故树的最小割集96个,最小径集3个以及基本事件的结构重要度系数,并得到基本事件结构重要度排序,找出了导致边坡失稳的主要原因是边坡监测和边坡支护。然后根据基本事件结构重要度的排序,制定合理有序的预防措施。事故树分析方法可以全面阐述露天矿边坡失稳的各种因素和逻辑关系,并通过对结构重要性分析,提出合理预防措施,为爆破露天边坡的安全管理提供参考依据。     

Evaluation of seismic performance of an electric substation using event tree/fault tree technique

In this study, we use the event tree/fault tree technique to evaluate the performance of an electric substation in the event of an earthquake. The substation is considered as a combination of components (equipment and structures), and the event trees and fault trees are established to delineate the interrelationships of these components. Using the fragility data of individual components in the event trees and fault trees, the probabilities that the substation as a whole fails at various levels of ground shaking can be determined and displayed as substation fragility curves. Furthermore, using the minimum cut set technique, the most critical and vulnerable component in the substation can be identified. Substation 21, a key electric power supplier to several major hospitals in downtown Memphis, is selected to illustrate this technique.     

R-D匹配优选小波包零树图像压缩

为使R-D小波包优选算法与零树编码在量化精度上更好地匹配，对R-D小波包优选算法的寻优次序进行修改，使小波包各节点的量化精度差异不超过一位。实验结果表明，R-D匹配优选小波包零树编码可以取得与R—D优选小波包零树编码相当或比后者更好的图像压缩效果，可见R-D匹配优选算法是更适合零树编码的小波包优选算法。     

Computer-aided fault tree synthesis III: Real-time fault location

This paper is devoted to fault tree synthesis and is split up into three parts. Part I starts with the introduction of component models that show all fault propagation through the components and fault initiation by the components in both directions (upstream and downstream). Subsequently, it is shown how to create system models that interconnect a system's components and environmental variables. Then a fault tree construction algorithm is introduced which is able to generate fault trees from the given system and component models in two steps. First a causal tree is constructed showing the propagation paths for all basic events leading to any deviation in the top parameter. All control loops (feedback and feedforward loops) in this causal tree must be traced prior to any fault tree construction since they might prevent some faults from reaching the top parameter. They consequently require a special treatment. Part I ends showing how to adapt the causal trees for these loops. Part II discusses the final step of the fault tree construction algorithm, i.e. it shows how fault trees can be abstracted from the causal diagram, and ends with a comprehensive example. Finally, Part III discusses a method for real-time fault location which is based on the causal tree construction procedure introduced in Part I.     

Structured fault tree synthesis based on system decomposition

The purpose of this article is to explain how to decompose a system so that its fault trees can be synthesized more efficiently and in a structured and recursive manner. Under such a decomposition, modules such as control/trip loops will be regarded as dummy units at first so that the system size can be reduced significantly and dramatically. The fault tree of a top event can thus be constructed as follows: the one for the reduced system is synthesized first and then each of its terminal events, when these are events of a dummy unit, will be further developed. In order to carry out such a synthesis automatically, each dummy unit must be tried first, in order to be standardized, so that its unit-model can be established, and then saved in a database in advance. A suitable system input format must also be designed so that the fault tree can be synthesized automatically simply by keying-in the top event and the system.     

离散余弦变换在滚动轴承故障诊断中的应用

本文探讨了应用离散余弦变换分析滚动轴承故障的方法,采用小波基将滚动轴承振动信号变换到时间－尺度域,对高频段的小波系数用离散余弦变换进行包络分析。通过对滚动轴承具有外圈缺陷、内圈缺陷的情况下振动信号的分析,说明这种方法可以有效的用于效地用于滚动轴承的故障诊断。     

Computer-aided fault tree synthesis I (system modeling and causal trees)

This paper is devoted to fault tree synthesis and is split up into three parts. Part I starts with the introduction of component models that show all fault propagation through the components and fault initiation by the components in both directions (upstream and downstream). Subsequently, it is shown how to create system models that interconnect a system's components and environmental variables. Then a fault tree construction algorithm is introduced which is able to generate fault trees from the given system and component models in two steps. First a causal tree is constructed showing the propagation paths for all basic events leading to any deviation in the top parameter. All control loops (feedback and feedforward loops) in this causal tree must be traced prior to any fault tree construction since they might prevent some faults from reaching the top parameter. They consequently require a special treatment. Part I ends showing how to adapt the causal trees for these loops. Part II discusses the final step of the fault tree construction algorithm, i.e. it shows how fault trees can be abstracted from the causal diagram and ends with a comprehensive example. Finally, Part III discusses a method for real-time fault location which is based on the causal tree construction procedure introducted in Part I.