周期特征的极坐标同步增强及其在轴承故障检测中的应用

提出一种信号周期瞬态特征的极坐标检测方法,该方法在小波变换的基础上,针对信号中有限种可能的周期瞬态情况,将信号的小波变换的时频特征表示为极坐标图上某一区域的显著增强的特征,实现了周期瞬态特征的检测与增强.针对轴承的3种典型故障,采用极坐标同步增强策略,将轴承故障特征以显著的形式表示在极坐标上,实现了轴承故障的检测.     

应用分数傅立叶变换方法的水下目标特征提取

针对基于传统时频分析方法的水下目标特征提取方法的缺陷,引入了一种新的时频分析方法——分数阶傅立叶变换（FRFT）方法用于处理水下目标特征提取问题。仿真信号和实际试验数据的处理结果表明,当主动声纳的发射信号为线性调频信号时,分数阶傅立叶变换方法可以使目标的回波能量在分数阶域的对应区域聚集,使目标和混响的分数阶傅立叶变换在分数阶域上不仅呈现明显不同的特征,而且较其他时频分析方法具有抗混响的优点。     

Hilbert-Huang变换在瞬态信号检测中的应用

空投物体入水时产生具有时域冲击特性的信号,一般称之为瞬态信号。Hilbert-Huang变换可通过经验模态分解和Hilbert谱分析两种方法,从时频角度对瞬态信号进行分析。介绍了Hilbert-Huang变换的基本原理,建立了瞬态信号的数学模型,提出了基于Hilbert-Huang变换的信号重构瞬态信号检测方法,并与传统能量检测器的性能进行了对比分析,最后通过软件仿真和湖试数据处理验证了该方法的可行性和有效性。     

速变信号的小波分析应用研究

遥测速变参数处理方法大多基于经典分析方法，文中采用现代时频分析方法对遥测动态环境参数进行分析，对比算法在瞬态信号成分检测方面的优势，小波变换比傅立叶变换更适合分析非平稳信号，尤其是含瞬态或突变成分的信号．     

水下瞬态信号的检测与识别

对于水下瞬态信号这种突发性很强、持续时间又非常短、且出现后一般不再重复的信号,如何才能进行全自动的快速有效的检测与识别,是近期国内外研究的热点。针对水下目标快速变速所产生的瞬态信号的自动检测与识别问题,传统信号处理方法难以适用,文中引入了图像处理的有关理念和技术,提出了"取重心处理"的方法,并提出了一种便于工程实现的快速算法。对海试数据的分析结果表明,该方法稳定可靠,有望应用于工程实践中。     

基于复小波变换和支持向量机的缺陷类型识别

 针对传统缺陷检测存在的工序繁琐、不易在线实施、准确率低、容易受人为因素影响,以及用人工神经网络对小样本事件进行缺陷类型识别时存在泛化能力差和过学习等问题,提出一种基于复小波变换和支持向量机（SVM）模式识别理论的缺陷类型识别新方法．在利用小波对超声缺陷回波信号进行消噪的基础上,采用复小波变换获得缺陷回波信号的包络并提取其特征参数,构成输入特征向量后运用支持向量机进行分类．实验结果表明,该方法具有识别准确率高、泛化能力强、容易实现在线处理等优点．     

基于小波分析的激光探潜技术

介绍了利用小波分析的方法对水下目标的回波信号进行去噪声、检测及定位，模拟结果表明，该方法的时频可变性有效地克服了传统方法的不足。     

HHT在水雷目标特征提取中的应用

Hilbert-Huang变换（HHT）是近年来发展起来的一种处理非线性非平稳的时频分析方法。水声信号具有非线性非平稳的特点，把HHT方法应用于水声信号的分析中，将典型主动声纳信号的Hilbert边际谱和Hilbert谱分别与傅里叶幅度谱和传统的时频分析进行了比较。然后对水下目标回波的亮点模型作了仿真研究，并与小波变换作比较，最后用实际目标的回波作了分类研究。仿真与实际数据都证明了HHT在水下目标特征提取中的优越性。     

一种低截获水声遥控信号的设计方法及性能分析

提出了一种基于时频扩展技术的低截获水声遥控信号设计方法,分别采用多载波技术和直序扩频技术实现水声遥控信号的扩时调制和频谱扩展。分析了信号的时宽带宽对低截获性能的影响,采用Wigner-Ville分布对时频扩展前后信号的能量分布进行了对比研究,利用可检测距离的概念定量分析了信号时频扩展前后的低截获性能。理论分析和仿真结果表明,该时频扩展信号具有低的瞬时功率及谱密度,处理增益大,可检测距离小,能够高可靠地实现信息的隐蔽传输。     

基于声信号识别的水下焊接质量检测方法研究

水下焊接的应用领域广泛，但其焊接质量难以保障。针对水下焊接处理过程中存在的非线性程度高、参数耦合性强以及检测效率低等问题，提出了一种新的基于声信号识别的水下焊接质量检测方法。该方法通过在水下构建基于声信号采集的监测系统，实时采集焊件焊接过程中的声信息，并通过对声信号进行滤波降噪处理和特征提取，构建双权值神经网络（double-weight neural network, DWNN）模型。该模型具有优秀的高维数据非线性拟合能力，可实现水下焊接多参数与声信号多特征之间的非线性映射，且在小样本情况下仍能实现高精度的模式识别。以高强度低碳合金钢——HSLA-115钢作为焊接对象，开展水下焊接质量检测实验。结果表明，DWNN模型应用于水下焊接质量检测的识别精度可达100%。研究结果可为水下焊接工艺的优化和水下焊件专家知识库的构建提供参考依据。     

基于连续小波和统计检验的瞬态成分检测与应用

将连续小波变换和统计检验结合用于检测信号中具有一定时频分布的瞬态成分，提出了一种基于连续小波变换和统计检验的瞬态成分检测方法，并用于圆锥滚子轴承振动中的瞬态成分的检测与提取，比较有效地检测出瞬态成分，并在此基础上应用连续小波变换反演得到瞬态成分的估计，表示轴承的状态特征，作为轴承故障诊断的依据。     

盲卷积分离及其在机械振动信号消噪中的应用研究

盲源分离应用于机械振动信号的预处理中，提供了一个新的处理机制，在机械状态监测和故障诊断中具有一定的价值。本文研究了盲卷积分离的理论，提出了基于限值VQM检验控制准则的盲分离算法，根据机械振动信号的特点探讨了该方法在机械振动信号瞬态成分和噪声卷积混叠信号分离中的应用，有效地提取了瞬态成分，表明了算法的有效性。     

Imaging of Zn2+ release from pancreatic beta-cells at the level of single exocytotic events

Regulated secretion of Zn2+ from isolated pancreatic beta-cells was imaged using laser-scanning confocal microscopy. In the method, beta-cells were incubated in a solution containing the novel fluorescent Zn2+ indicator FluoZin-3. Zn2+ released from the cells reacted with the dye to form a fluorescent product, which was detected by the confocal microscope. The new dye is much brighter than Zinquin, previously used for this application, allowing detection limits of 10-40 nM and temporal resolution of 16 ms/image. The high temporal resolution allowed imaging of isolated fluorescent transients that occurred at the edge of the cells following stimulation with 20 mM glucose or 40 mM K+. Fluorescent transients took 16-50 ms to reach a peak from the initial rise and returned to baseline after 170 +/- 50 ms (n = 78 transients from 15 cells). It was concluded that the transients correspond to detection of exocytotic release of Zn2+. Analysis of the temporal and spatial dispersion of the transients indicates that the release of Zn2+ is not diffusion limited but is instead kinetically controlled in agreement with previous observations of insulin release detected by amperometry.     

An implicit method for the analysis of transient flows in pipe networks

Existing methods for the analysis of transient flows in pipe networks are often geared towards certain types of flows such as gas flows vis‐à‐vis liquid flows or isothermal flows vis‐à‐vis non‐isothermal flows. Also, simplifying assumptions are often made which introduce inaccuracies when the method is applied outside the domain for which it was originally intended. This paper describes an implicit finite difference method based on the simultaneous pressure correction approach which is valid for both liquid and gas flows, for both isothermal and non‐isothermal flows and for both fast and slow transients. The problematic convective acceleration term in the momentum equation, often neglected in other methods, is retained but eliminated by casting the momentum equation in an alternative form. The accuracy and stability of the method, depending on a time‐step weighing factor α, are illustrated by analysing fast transients in a pipeline and simple branching network. The proposed method compares very well with the second‐order‐method of characteristics and the two‐step Lax–Wendroff method. The advantages of the present method is its speed over a range of problems including both fast and slow transients, its accuracy, its stability and its flexibility. Copyright © 2001 John Wiley & Sons, Ltd.     

A new surface transducer for generating and detecting magnetic field transients in ferromagnetics

A new surface transducer is described for generating and detecting magnetic field transients or magnetization discontinuities in ferromagnetic materials [8]. The sensing is based on searching for transients of the magnetic potentials which would be likely to occur on the surface of the specimen. A coil core of high-frequency ferrite is used for this. The sensor theory presented shows the coaxial geometry of the coil core to be that which is more practicable for limiting detection to a compact volume of the specimen to be analyzed. The fundamental noise and disturbance analyses performed show adequate margins for wideband noise and external stray field disturbances. The transducer electronics for generating the varying external magnetic field in the specimen and for detecting the occurring field transients are described with a view to the optimization of the electrical circuits, and the resulting specifications are discussed. The surface transducer constructed is widely applicable for studying the magnetization characteristics of different ferromagnetics nondestructively in conjunction with stochastic-ergodic analyzers such as a pulse-height analyzer or a digital correlator through a punch-tape recorder or in on-line connection with a computer [7].     

Higher order flexural transients in a beam

The propagation of higher order flexural transients in a Timoshenko beam, subjected to impulsive boundary loads is treated in this paper. The higher order transients are either generated by higher order boundary conditions or induced by homogeneous boundary conditions. The analysis is based on the concept of a wave as a carrier of discontinuities in the field variable and its derivatives. These discontinuities are determined from a set of recurrence relations which are in turn generated by the use of time-harmonic asymptotic series solutions to the equations of motion. Numerical examples are presented to illustrate the method of solution for higher order transients and the resulting velocity, bending moment and shear force distributions have been computed.     

Energy-based effective length of the impulse response of arecursive filter

A measure for the effective length of the impulse response of a stable recursive digital filter based on accumulated energy is proposed. The new measure finds applications in several fields of digital signal processing, including estimation of the extent of attack transients for filters with dynamically varying inputs, elimination of transients in variable recursive filters, and design and implementation of linear-phase IIR systems. A general definition and a simple algorithm to evaluate it are introduced, and closed-form expressions are derived for first and second-order all-pole filters. The effect of zeros on the effective length is analyzed. An upper bound for the effective length of higher-order filters is derived using results for low-order filters, which is illustrated for classical digital lowpass filters. The use of the measure is demonstrated with examples of implementation of linear-phase IIR systems and estimation of transients in variable IIR filters     

基于信号奇异性分析的轴承故障检测方法

针对轴承振动信号利用小波单奇异点检测无法克服噪声影响的不足,提出利用小波模极大值分析信号奇异性变化进而进行轴承故障检测的方法。实验中对信号的模极大分形指数,模极大分形指数熵,Lipschitz指数以及Lipschitz指数熵等奇异特征进行分析比较,实验结果表明这些特征都能有效克服噪声影响实现故障检测,但模极大曲线数最能体现故障特征且检测效果最好。将该方法同基于小波包能量谱特征和小波单奇异点检测的方法进行比较,结果表明本文建议的方法在检测时间及检测率上都有显著提高。     

一种基于频率响应曲率的损伤检测多步判定方法

在频率响应曲率指标基础上,提出了一种多步的检测方法,使用少量的传感器进行多步判定,来提高损伤定位的准确性和可靠性。通过简支梁的有限元数值算例,详细比较了改进的模态曲率方法、改进的柔度曲率方法和该文提出的方法对梁状多损伤结构的识别效果和抗噪能力。最后采用试验建模的技术,对局部减薄的多损伤管道和局部裂纹的单损伤管道进行损伤识别试验,结果验证了该方法的优越性,对解决实际工程结构的损伤检测问题具有一定的意义。