高阶时频分布在滚动轴承故障诊断中的应用研究

滚动轴承故障信号是非高斯、非线性、非平稳信号,由于调制性,使用幅值谱分析方法无法找到轴承故障频率。将高阶时频分布——主要是Wigner双谱分析方法应用于滚动轴承的故障诊断,计算滚动轴承振动信号的高阶时频分布,并对其沿时间轴切片,分析了切片的幅值谱。针对不同故障轴承,对其振动信号幅值谱、高阶时频分布及其切片谱的对比分析表明,高阶时频及其切片谱性能优于幅值谱。     

基于CART决策树的柴油机故障诊断方法研究

采用一种自适应局部有效值（RMS）计算方法提取柴油机缸盖振动信号时域特征,结合分类回归树（CART）算法建立故障分类模型并进行柴油机的状态识别。通过实验获取柴油机失火和撞缸两种故障工况及正常工况下的振动数据,计算出原始信号的局部RMS后,根据自适应阈值确定点火冲击区域和非点火上止点冲击区域提取局部特征,最后将特征输入CART算法中构建分类模型来验证所提取特征的有效性。结果表明：柴油机在3种状态下的识别率均达到100%,基于CART算法和局部特征提取的方法能够有效诊断柴油机故障。     

形态分量分析在滚动轴承故障诊断中的应用

滚动轴承局部故障振动信号中的周期性冲击是识别故障的关键特征.形态分量分析在由多种形态原子组成的过完备字典基础上提取信号中的不同形态成分,基于这种思想提出了一种基于新型过完备复合字典的形态分量分析方法.依据滚动轴承故障振动信号中分量间的形态差异性,改进字典后该方法可以更具针对性地提取出包含故障特征的冲击分量,配合包络谱分析准确提取故障特征频率,诊断滚动轴承局部故障.对比基于快速谱峭度法的轴承故障诊断方法,该方法可以避免人为选择共振带产生的不准确性和非最优问题,提高了故障诊断效果.通过轴承仿真信号和故障实验信号分析验证了该方法的有效性.     

Wigner高阶谱在弹丸膛内运动分析中的应用

针对传统时频分布分析的时频分布图能量聚集性差、交叉项干扰严重且对噪声敏感的问题,提出了一种基于Wigner高阶谱的膛内运动弹丸回波信号处理方法.对仿真信号从能量聚集性、交叉项抑制、抗噪声三个方面进行比较研究,结果表明Wigner高阶谱进行高阶多项式调频信号瞬时频率估计具有优势.对某型炮弹实测数据采用基于MATLAB的Wigner三谱对角切片算法获得时频分布图.提取时频分布图的时频脊线得到瞬时频率曲线.由多普勒效应公式反演出膛内弹丸的速度、加速度曲线.与实验结果相比:炮口速度相对误差为1.34％,弹丸运动距离与炮管实长的相对误差各为0.52％.验证了在强噪声环境下,Wigner高阶谱分析是膛内运动弹丸回波信号处理的一种更准确有效的方法.     

基于高阶谱和Tamura纹理的滚动轴承故障诊断

为了提高滚动轴承的故障诊断率,提出了一种基于高阶谱(high order spectrum, HOS)和Tamura纹理特征相结合的故障诊断方法。首先,通过高阶谱方法将滚动轴承故障振动信号的冲击提取出来;然后,对高阶谱进行处理得到二维等高线图;最后依据轴承故障相同时等高线图具有相似性以及不同时具有差异性这一特性,采用基于人类视觉感知的Tamura纹理描述方法提取特征参数后输入多分类支持向量机(support vector machines, SVM)中进行分类。结果表明：高阶谱结合Tamura纹理特征的滚动轴承故障诊断方法在较少特征参数下故障识别准确率能达到较高的精度,对于故障尺寸不同的混合振动信号识别准确率稳定,诊断效果良好。     

基于Hilbert谱熵的柴油机故障诊断方法研究

从信号的特征提取出发,采用局域波时频谱分析和信息熵结合的方法--Hilbert谱熵(HSE),进行柴油机振动信号的特征提取和状态识别.首先,对信号进行局域波分解;然后,根据得到的内蕴模式分量计算Hilbert谱;最后,建立基于时频分布的Hilbert谱熵,并以此作为故障识别的特征参数.以柴油机缸套与活塞间磨损的状态识别为例,根据对时域、频域和时频域的信息熵比较分析,证明了Hilbert谱熵对柴油机的状态进行评价的有效性.此方法为柴油机预知维修提供了一个有效的手段.     

基于Morlet小波变换与SVD的故障特征提取

针对Morlet小波变换结果中的特征提取问题,对连续小波变换得到的小波系数矩阵进行奇异值分解(SVD),分析了所获得的奇异值与Morlet小波变换结果中的特征信号以及噪声的对应关系.基于这种关系,通过选择合适的奇异值进行重构,清晰地提取到Morlet小波分解结果中的有效特征信息;进一步计算得到频率-能量谱,根据峰值位置能够提取冲击特征.将该方法应用于轴承振动信号的故障特征提取,并与其他方法进行了比较.结果表明,文中方法所获得的故障波形非常清晰,在低信噪比时具有较好的故障特征提取效果.     

增强组合差分乘积形态学滤波的轴承故障特征提取方法

针对滚动轴承故障信号的非线性、非平稳、强噪声特性导致的常规时频域特征提取方法受限问题,提出一种增强组合差分乘积形态学滤波的轴承故障特征提取方法。在分析数学形态学4种基本运算的正、负冲击脉冲提取特性的基础上,运用级联、差分、乘积构造的一种新的组合差分乘积算子(combination difference multiply operator, CDMO)具备了同时提取正、负冲击脉冲的能力,并发挥梯度乘积运算对脉冲提取更敏感的优势,实现故障信息的充分提取。引入故障特征频率比指标优化CDMO结构元素参数,修正待处理信号的几何特征,提取与结构元素相匹配的信号特征信息。在CDMO滤波的基础上,借助三阶累积量切片谱技术能够抑制高斯噪声、突出二次耦合分量的优势,准确提取故障特征频率及其倍频,增强轴承故障特征提取能力并抑制噪声干扰。依托2种不同来源的工程实际信号并与经典故障特征提取方法对比分析,验证了所提方法的有效性。     

基于ReliefF-PCA和SVM的发动机故障诊断方法研究

针对柴油发动机机组振动信号非线性和非平稳性以及机组实际故障案例样本数据少的特点，提出了一种基于ReliefF、主成分分析（PCA）以及支持向量机（SVM）的柴油发动机故障诊断方法。首先提取发动机冲击信号的特征参数，运用ReliefF选择出其中的敏感特征以降低处理过程的计算难度；然后采用PCA进一步提取敏感特征，消除各特征之间的相关性，避免冗余；最后利用SVM实现机组的故障分类，诊断不同类型的故障。将本文方法应用于柴油机实际典型故障案例中，结果表明该方法能有效提取柴油机缸盖振动信号中的故障敏感特征，并实现多种典型故障的诊断。     

基于双谱分析的内燃机曲轴轴承磨损故障的诊断研究

引入高阶统计量诊断曲轴轴承磨损故障,在EQ6100汽油发动机上模拟设置四种曲轴轴承间隙,并应用双干谱、双谱对振动信号进行了分析比较,结果显示双谱有效地抑制了噪声影响,较好地对曲轴轴承四种磨损状态进行了分类和识别,并揭示了非线性相位耦合随曲轴轴承磨损状态的变化规律;而运用双谱沿频率ω1=ω2的对角切片提取了曲轴轴承磨损故障诊断的特征参数,并有效地诊断了该故障.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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Brief Introduction to “Journal of Jilin University( Science Edition) ”

<正>"Journal of Jilin University(Science Edition)"is a comprehensive academic journal in the fields of science sponsored by Jilin University and administrated by the Ministry of Education of the Peoples Republic of China.The journal started publication in 1955.The original name at starting publication was"Journal of Natural Science of Northeast People University",which was changed into"Acta Scientiarum Naturalium Universitatis Jilinensis"in 1958 owing to the name change of the university.The present journal name has