对模态参数识别的整体正交多项式分段拟合的处理方法

在整体正交多项式识别法的基础上，介绍了在分段拟合中消除段外模态影响的方法。通过对拟合频段外的低阶和高阶模态的分析和处理，提出了用邻近拟合段前后两个频段中的模态来修正频响数据，并建立了曲线拟合模型，将本文的方法识别结果与不考虑段外模态影响的方法以及局部识别法识别结果进行了比较，结果表明本文的方法具有较好的计算精度。     

基于超声波反射法的油田注水井管柱腐蚀识别

为了延长油田注水井管柱使用寿命,提高油田采收率,提出基于超声波反射法的油田注水井管柱腐蚀的识别方法。首先,采用超声波反射法采集油田注水井管柱的超声波检测信号;然后,利用小波分析消除信号噪声,并从时域和频域提取信号特征;最后将信号特征输入SVM(支持向量机)分类器中,根据分类器输出的信号特征分类结果,实现油田注水井管柱腐蚀识别。试验结果表明,所提方法识别性能强、识别准确率高。     

基于MED-FWEO的滚动轴承故障检测

频率加权能量算子(FWEO)能够通过对信号瞬时能量的追踪消除信号中的噪声分量,突出故障冲击分量,对于轴承信号的处理具有较强的抗干扰性,然而对强噪声干扰下的信号则效果不够理想。针对该问题,提出将最小熵解卷积(MED)用于信号的预处理,以此消除信号采样过程中的传递噪声干扰,增强信噪比;而后以FWEO对处理后信号的瞬时能量进行追踪,从能量的角度进行故障特征的二次增强;最后通过包络谱分析获得诊断结果。仿真数据、实验室数据均表明所提方法能够在受强噪声干扰下的轴承故障信号中大幅消除噪声,准确提取出故障分量。     

脉冲相位光热辐射测量中的数据拟合处理方法

针对脉冲相位辐射测量中相位分析对时间信号噪声比较敏感的问题,对实验得到的温度-时间数据进行拟合处理.计算结果表明,对数据进行分段拟合(分别采用线性拟合和指数曲线拟合)能得到比较理想的近似函数.傅里叶变换后得到的相频曲线噪声小,相位图像较清晰.并且数据可用拟合函数的系数来表示,从而大大减少数据存储量.另外,通过曲线扩展和插值的方法,从理论上分析了采样频率与窗口长度对相频特性曲线的影响.     

电化学噪声分析方法的研究进展

初步回顾了近年来电化学噪声分析方法的若干研究工作,举例介绍了电化学噪声数据直流漂移、电化学噪声时-频分析、非线性分析和模式识别等分析方法的优缺点,并对电化学噪声分析方法的发展方向进行了展望。     

电化学噪声分析方法的研究进展简

初步回顾了近年来电化学噪声分析方法的若干研究工作,举例介绍了电化学噪声数据直流漂移、电化学噪声时-频分析、非线性分析和模式识别等分析方法的优缺点,并对电化学噪声分析方法的发展方向进行了展望。     

小波阈值去噪在超声测压回波处理中的应用

超声管外测压中回波信号易受到噪声的干扰,针对循环法时间测量中存在门限电压高、触发点漂移问题,提出用小波阈值去噪法对回波信号进行预处理.仿真结果表明:选用Sym8小波、"heursure"阈值准则,采用软阈值法,分解尺度为9时,去噪效果最好.去噪后,门限电压降低,消除了触发点的漂移.     

X70钢及其焊缝在含Cl-高pH值溶液中电化学噪声行为研究

研究了不同外加电位下X70钢母材及其焊缝在含Cl-的高pH溶液中电化学噪声行为,并针对电化学噪声数据进行统计分析,得到表征点蚀萌生和发展的特征图谱.结果 表明,电化学噪声技术可以有效监测X70钢的腐蚀过程,电流噪声幅值大小一定程度上反映了局部腐蚀萌生和发展过程.当X70钢处于阳极极化时,电化学噪声的能量密度谱(EDP)...     

静水压力对超纯Fe腐蚀行为的影响

采用失重测试、动电位极化和电化学噪声研究了静水压力对超纯Fe在3.5%NaCl中腐蚀行为的影响。利用离散小波分析方法去除噪声信号的直流漂移,然后进行散粒噪声和随机分析;利用Hilbert-Huang变换对噪声信号进行时频分析;用SEM观察腐蚀试样的表面形貌。失重测试和动电位极化的研究结果表明,增大静水压力提高了超纯Fe在3.5%NaCl中的腐蚀速率。电化学噪声分析结果表明,在整个浸泡期间,增大静水压力促进了点蚀的发展,提高了局部腐蚀的倾向。在浸泡初期,超纯Fe以发生局部腐蚀(如点蚀形核、亚稳态点蚀、点蚀)的模式为主,增大静水压力对点蚀形核过程有一定的抑制作用,降低了点蚀孕育速率,但对亚稳态点蚀和稳态点蚀的发展过程有促进作用,提高了点蚀生长概率;随着浸泡时间的延长,其逐渐转为以均匀腐蚀的模式为主,增大静水压力仍然促进亚稳态点蚀和稳态点蚀的发展,提高点蚀生长概率,但是却相对地抑制了均匀腐蚀过程。     

静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响

采用动电位极化和电化学噪声方法在3.5%NaCl中研究了静水压力对超纯Al/超纯Fe电偶中超纯Al腐蚀行为的影响。利用离散小波变换去除噪声信号的直流漂移,然后进行散粒噪声和随机分析;利用HilbertHuang变换对噪声信号做时频分析;用SEM观察腐蚀试样的表面形貌;用有限元方法模拟压力分布。结果表明,不同静水压力下超纯Al在3.5%NaCl溶液中皆自钝化,与超纯Fe偶合后发生点蚀。随静水压力的升高,超纯Al/超纯Fe的电偶电位逐渐降低,电偶电流逐渐增大。静水压力越高,经电偶腐蚀后超纯Al表面形成的点蚀坑尺寸越小且分布更加均匀。静水压力的提高加速了电偶腐蚀中超纯Al的点蚀孕育速率,但抑制了点蚀生长概率,降低了局部腐蚀倾向。静水压力为常压时,点蚀可沿水平、竖直方向扩展;在静水压力存在的条件下,点蚀更易于沿水平方向扩展。     

Alternating current-gas metal arc welding for application to thin sheets

The metal transfer in alternating current-gas metal arc welding (AC-GMAW) was analyzed in order to predict the drop size. The effects of complex waveforms of the process, involving both the electrode positive (EP) and the electrode negative (EN) pulse regions, were investigated analytically. The force-displacement model was modified to predict the drop size in AC-GMAW. Experiments were conducted using different types of wires for validating the predicted results. The effect of EN pulse parameters on the drop size was modeled, eliminating the need for experimental trial and error. The drop size information can be used to predict the range of the joint gap that can be bridged effectively. The proposed technique was found to be equally applicable to both direct current-gas metal arc welding and P-GMAW.     

A novel experimental arrangement for corrosion study of X60 pipeline steel weldments at turbulent flow conditions

Electrochemical noise (EN) measurements were carried out to study the effect of turbulent flow conditions on corrosion kinetic of API X60 pipeline steel weld immersed in synthetic seawater. In order to control the hydrodynamic conditions, two rotating cylinder electrodes were used. The EN data were analysed by three different statistical methods: currents transients, noise resistance and localisation index (LI). On the other hand, the spectral method was used in order to get the noise impedance. The superficial analysis using a scanning electron microscopy was carried out. According to EN analyses, the current transients indicate that the aggressiveness of the corrosion increased as the rotation speed also increased. The highest corrosion rate values were obtained at turbulent flow conditions. In the superficial analysis, a localised corrosion form was found in all corrosion processes; these results are agreed with the results obtained by LI.     

ELECTROCHEMICAL NOISE ANALYSIS OF PURE ALUMINUM IN SODIUM CHLORIDE SOLUTION WITH WAVELET TRANSFORM TECHNIQUE

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Analysis of corrosion behavior of LY12 in sodium chloride solution with wavelet transform technique

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Electrochemical noise during non‐stationary corrosion processes

In the present work, electrochemical noise (EN) was measured in three different types of experimental set‐ups in order to obtain and compare various types of corrosion. Simultaneously with EN measurements, a parallel technique was used, regarding the type of experimental set‐up: a computer visualization system combined with optical microscopy, or measurements of mechanical changes. In order to distinguish between these corrosion types and to assess corrosion rate, the measured EN signals were analysed by two different techniques: spectral and statistical. On the basis of estimated significant spectral parameters (power spectral densities of current and voltage noise, spectral noise resistance) and statistical parameters (standard deviation, localisation index and noise resistance), the passive state, localized corrosion types and uniform corrosion can be recognized. However, by these parameters it is not possible to distinguish between certain localized corrosion processes: metastable pitting, initiation and growth of stable pits, stress‐corrosion cracking. It was ascertained that these corrosion processes exhibit unstable nature, and consequently generated EN signals are usually non‐stationary. Since stationarity is required for spectral and statistical analysis, the unstable nature of these processes was recognized as the main reason for unreliable results. It is believed that these types of signal analysis give poor information about corrosion processes which can be easily identified from EN signal itself: transient corrosion processes and transitions between different corrosion processes.     

The effect of electrolyte stirring and laminar flow on measured electrochemical noise

In the present paper the influence of various types of electrolyte movement on the characteristics of measured electrochemical noise (EN) has been investigated. For this reason the measurements were performed during different phases: in a still solution, during stirring, as well as in laminar flow. In order to relate the measured EN to the development of corrosion processes, digitized images of the electrodes were recorded continuously during these measurements. After the tests were finished, the corroded electrode surfaces were examined also by the scanning electron microscope (SEM). It was established that the characteristics of EN, in general, change significantly with the movement of the solution. On the other hand, no clear difference was observed between the EN signals measured during stirring and those obtained during laminar flow. This observation, combined with the results obtained in a passive environment and in a very aggressive still solution, confirmed that the main source for the change of EN characteristics during electrolyte movement is the transformation of corrosion processes. The direct effect of the electrolyte movement on the measured EN (modulation of signals due to spatio‐temporal flow disturbances) was found to be insignificant compared to the influence of the corrosion processes themselves.     

Electrochemical noise analysis of localized corrosion by wavelet transform

Electrochemical noise (EN) was measured during pitting and stress corrosion tests in NaCl solutions for type 403 stainless steel tempered at 390 °C for 2 h. The EN data were analyzed mainly by wavelet transform in terms of the energy contribution of smooth crystal and detail crystals in three frequency regions. In the early stage of the pitting tests, general corrosion occurs, and contribution of smooth crystal to the total energy was greater than that of low frequency detail crystal, but less with the development of meta-stable pitting. A similar trend was observed in the early stage of stress corrosion cracking (SCC) tests. The contribution of low frequency detail crystals to the total energy decreased as stable pits were formed, and it was less than the energy contribution of smooth crystal when crack propagation occurred in the later stage of SCC. In addition, the contribution of energy of high frequency detail crystal is shown to be indicative of the occurrence of plastic deformation. These results demonstrate that the onset of detailed processes in pitting and SCC can be sensitively detected by wavelet analysis in terms of the energy contribution of smooth crystal and low and high frequency detail crystals, but not with that based on the change in position of peak in energy contribution of detail crystals.     

红外热波检测中热像信号重建引起的伪缺陷现象

在脉冲热激励红外热波检测中,热像信号重建技术（TSR）常用来分析和处理试验结果。该方法的特色是可以增加热像序列的空间和时间分辨率,提高信噪比,减少数据量。同时,该方法还能消除某些伪缺陷的干扰,比如脉冲闪光灯和热像仪镜头的反射所带来的伪缺陷。但是TSR是基于对温度变化曲线进行多项式曲线拟合的,而多项式曲线拟合中,拟合阶数和数据长度对拟合结果影响较大,在某些情况下可能会产生伪缺陷。阐述了热波数据重建技术原理,并以试件表面处于热不平衡状态和表面不均匀进行试验的结果来分析由于数据重建技术所产生的伪缺陷。     

Effect of microcrystallization on pitting corrosion of pure aluminium

A microcrystalline aluminium film with grain size of about 400 nm was prepared by magnetron sputtering technique. Its corrosion behaviour was investigated in NaCl containing acidic solution by means of potentiodynamic polarization curves and electrochemical noise (EN). The polarization results indicated that the corrosion potential of the sample shifted towards more positive direction, while its corrosion current density decreased compared with that of pure coarse-grain Al. The EN analysis based on stochastic model demonstrated that there existed two kinds of effect of microcrystallization on the pitting behaviour of pure aluminium: (1) the rate of pit initiation is accelerated, (2) the pit growth process was impeded. This leads to the enhancement of pitting resistance for the microcrystallized aluminium.     

NaCl溶液中LC4,LY12及纯铝腐蚀过程的电化学噪声特征

应用电化噪声（electrochemical noise)技术对航空铝合金结构材料LC4，LY12及纯铝在质量分数为2．0％的NaCl溶液中的腐蚀过程进行了研究，发现不同材料在发生点蚀时其电化学噪声的时域谱波形特征各不相同，电化学噪声的频域谱SPD（spectra power density)曲线的三个特征参数：白噪声水平W，截止频率fc和高频线性部分的斜率K均随浸泡时间的延长而变化，在发点蚀时三者均趋于极值，但三者都不能单独正确地表征点蚀的强度和趋势，实验结果时表明：点蚀时，从不同材料的SPD曲线获得的点蚀参数SE和SG的数值具有一致性，且与未点蚀时的参数值存在着明显的区别，一般在而，点蚀发生时，SE＞5且SG＜1；非点蚀时，二者的取值正好相反，因此，二者可以很好地表征点蚀的发生。