The Application of Advanced Signal Processing Techniques to Induction Motor Bearing Condition Diagnosis

Four approaches based on bispectral and wavelet analysis of vibration signals are investigated as signal processing techniques for application in the diagnosis of a number of induction motor rolling element bearing faults. The bearing conditions considered are a normal bearing and bearings with cage and inner and outer race faults. The vibration analysis methods investigated are based on the bispectrum, the bispectrum diagonal slice, the summed bispectrum and wavelets. Singular value decomposition (SVD) is used to extract the most significant features from the vibration signatures and the features are used as inputs to an artificial neural network trained to identify the bearing faults. The results obtained show that the diagnostic system using a supervised multi-layer perceptron type neural network is capable of classifying bearing condition with high success rate, particularly when applied to summed bispectrum signatures.     

Detection of rolling bearing defects using discrete wavelet analysis

In the detection of bearing faults the so much desired objective remains the extraction of the defect vibratory signature from the measured signal in which immerses the random noise and other components of the machine. In this article a denoising method of the measured signals is presented. Based on the optimization of wavelet multiresolution analysis, it uses the kurtosis as an optimization and evaluation criterion, several parameters were then selected. The experimental results show the validity of this method within the detection of several defects simulated on ball bearings. The various configurations, in which the signals were measured, allow leading to optimum conditions of its application. The application of WMRA on filtered signals allows better results than its application on wide bands signals or a simple band pass filtering.     

Planetary gearbox with localised bearings and gears faults: simulation and time/frequency analysis

Planets bearings of planetary gear sets exhibit high rate of failure; detection of these faults which may result in catastrophic breakdowns have always been challenging. The objective of this paper is to investigate the planetary gears vibration properties in healthy and faulty conditions. To seek this goal a previously proposed lumped parameter model (LPM) of planetary gear trains is integrated with a more comprehensive bearing model. This modified LPM includes time varying gear mesh and bearing stiffness and also nonlinear bearing stiffness due to the assumption of Hertzian contact between the rollers/balls and races. The proposed model is completely general and accepts any inner/outer race bearing defect location and profile in addition to its original capacity of modelling cracks and spalls of gears; therefore, various combinations of gears and bearing defects are also applicable. The model is exploited to attain the dynamic response of the system in order to identify and analyze localized faults signatures for inner and outer races as well as rolling elements of planets bearings. Moreover, bearing defect frequencies of inner/outer race and ball/roller and also their sidebands are discussed thoroughly. Finally, frequency response of the system for different sizes of planets bearing faults are compared and statistical diagnostic algorithms are tested to investigate faults presence and growth.     

Effect of localized faults on chaotic vibration of rolling element bearings

This paper investigates the effect of localized faults on the chaotic vibration of rolling element bearings. The presence of chaotic behavior is demonstrated using experimental vibration data. A nonlinear mathematical model is developed that captures bearing dynamics. The numerical simulations of the model agree with the experimental evidence and provide insight into the bearings chaotic response in a wide range of rotational speeds. The bearing chaotic behavior is quantified using the Lyapunov exponent and correlation dimension. It is further shown that these measures can be exploited in detecting bearing failure.     

高速列车轴承可靠性评估关键力学参量研究进展

轴承是高速列车牵引传动和轮轴系统的关键零部件. 受列车运行过程中电机转矩、齿轮啮合以及轮轨随机激励的影响,轴承可能发生疲劳破坏, 严重影响高速列车的行车安全.我国特有的复杂运用条件对轴承部件的疲劳性能提出了更高的要求,而轴承疲劳可靠性的基础理论和关键技术是我国轴承正向设计研发中的薄弱环节.可靠性评估方面的相关研究在解决轴承可靠性研究的瓶颈问题中起到了承上启下的关键作用.高速列车轴承可靠性评估手段与技术旨在获得使用环境中轴承可靠性评估的关键力学参量,并以此推动复杂激励下轴承疲劳可靠性理论研究. 因此,需要哪些关键力学参量并且在复杂的实际使用环境下如何去获取这些力学参量是进行高速列车轴承可靠性评估的关键所在.本文首先概述了高速列车轴承所处的复杂使用环境及运用中的主要失效模式,并据此分析了高速列车轴承可靠性评估所需的关键力学参量,强调了轴承内部滚滑行为和载荷分布在可靠性评估和轴承状态监测中的重要作用,之后从计算模型和测试技术等方面系统阐述了针对这两个关键力学参量的研究进展.最后提出了在高速列车轴承可靠性评估关键力学参量特征及测试技术研究中值得关注的若干问题.      

Determination of hydrodynamic behavior of gas–solid fluidized beds using statistical analysis of acoustic emissions

In the processes involving the movement of solid particles, acoustic emissions are caused by particle friction, collision and fluid turbulence. Particle behavior can therefore be monitored and characterized by assessing the acoustic emission signals. Herein, extensive measurements were carried out by microphone at different superficial gas velocities with different particle sizes. Acoustic emission signals were processed using statistical analysis from which the minimum fluidization velocity was determined from the variation of standard deviation, skewness and kurtosis of acoustic emission signals against superficial gas velocity. Initial minimum fluidization velocity, corresponding to onset of fluidization of finer particles in the solids mixture, at which isolated bubbles occur, was also detected by this method. It was shown that the acoustic emission measurement is highly feasible as a practical method for monitoring the hydrodynamics of gas–solid fluidized beds.     

基于荧光法的滚动轴承内部润滑油层分布研究

润滑油在轴承内的分布及其变化规律对轴承的润滑性能有显著影响. 在本文中搭建了滚动轴承模拟试验台,基于激光诱导荧光方法实现了滚动轴承内钢球-外圈接触区附近润滑油分布的观察与测量,获得了润滑油供给油层分布的三维形貌图,研究了不同供油量和转速对轴承内部供给油层分布的影响规律. 试验结果表明充分润滑条件下相邻钢球-外圈接触区供给油池之间会形成相互连接的油带;在高速情况下,钢球-外圈接触区供给油层厚度受前一个接触区尾部空穴影响而减小;供油量的增加会增大表观油池,但并不意味着入口有效供油层的增加.      

常温下16MnR板材焊接缺陷声发射特性研究

对预制的含有未焊透缺陷的16MnR焊接矩形试样,进行了室内声发射试验.分析了试验中记录的试样拉伸曲线和声发射信号,阐述了试样声发射信号的分布情况和相应的应力状况.通过缺陷的断裂力学计算,预测了产生大量声发射信号的应力值,将声发射信号的产生和试样所受的应力状况有效地联系起来,对含缺陷容器的声发射检测有一定的指导作用.选择合适的小波函数,分析了试验中声发射信号的不同参量,对比了声发射信号不同参量在小波分析中的差异,得出了声发射信号的时域内分布特征和相应的应力状况.     

Use of generalized refined composite multiscale fractional dispersion entropy to diagnose the faults of rolling bearing

Nonlinear Dynamics - A typical symptom of vibration signals collected from rolling bearings with local faults is the existence of periodic transients, which makes the intrinsic structure of...     

Evolutive and nonlinear vibrations of rotor on aerodynamic bearings

The use of air as a lubricant in aerodynamic bearings is advantageous, particularly in the food industry. Aerodynamic bearings with tilting pads have complicated stiffness and damping properties and need a very detailed theoretical and experimental research. Response curves of rigid rotor supported on aerodynamic bearings are presented for a linear but evolutive mathematical model. Due to non-monotone properties of stiffness and damping matrices at variable revolutions, a new resonance appears. The mathematical model of rotor vibrations in the whole area of bearing clearance is also developed in the consideration of strongly nonlinear properties of aerodynamic bearing.     

永磁向心轴承承载能力与刚度的计算

目前，尽管磁浮轴承技术的研究与开发应用已经受到国内外学者的广泛重视，但在永磁向心轴承承载能力的研究方面，却还存在着两个尚待解决的问题：一是将环形磁体作为无限长条形磁体处理，二是只能对轴承承载能力进行估算。针对这种情况，根据等效磁荷理论，在圆环状态下对轴向控制的永磁向心轴承的承载能力和刚度进行了研究，建立了永磁向心轴承承载能力数学模型，并对其计算结果作了试验验证，同时还提出了利用刚度系数建立的可供工程设计应用的永磁轴承承载能力和刚度的计算公式。结果表明，承载能力的计算值与实测值相当吻合；在偏心距的实际应用范围内，永磁向心轴承的径向刚度是个常量；内外磁环的轴向位移对磁轴承的承载能力和刚度都有明显的影响．因此，为了最大限度地提高这种轴承的承载能力和刚度，就要在设计其结构的过程中注意尽力保证内外磁环轴向对齐。     

油膜轴承负荷特性的数值解析

轧机油膜轴承频繁出现巴氏合金剥落、龟裂等现象，直接影响到油膜轴承的使用寿命和轧制生产的正常进行，应用三维弹性接触问题的边界元法对宝钢2050支承辊油膜轴承载荷分布进行分析研究，建立了油膜轴承的接触模型，模拟真实的约束与受力，结果轴承出现严重偏载现象，通过改善约束条件，在自位情况下轴承偏载现象大幅度降低，同时接触应力也在一定程度上减小，从而使得轴承的承载能力得到提高，由于考虑了弹性变形的影响，该方法具有计算精度高，收敛速度快等优点。     

Acoustic Emission Analysis of Nanoindentation-Induced Fracture Events

Monitoring of acoustic emission activity is employed to characterize the initiation and progression of local failure processes during nanoindentation-induced fracture. Specimens of various brittle materials are loaded with a cube-corner indenter and acoustic emission activity is monitored during the entire loading and unloading event using a transducer mounted inside the specimen holder. As observed from the nanoindentation and acoustic emission response, there are fundamental differences in the fracture behavior of the various materials. Post-failure observations are used to identify particular features in the acoustic emission signal that correspond to specific types of fracture events. Furthermore, analysis of the parametric and transient acoustic emission data is used to establish the crack-initiation threshold, crack-arrest threshold, and energy dissipation during failure. It is demonstrated that the monitoring of acoustic emission signals yields both qualitative and quantitative information regarding highly localized failure events in brittle materials.     

Q235钢细观损伤声发射源动态观测实验研究

金属材料细观损伤过程伴随有瞬态应力波的释放,利用声发射检测技术可采集到应力波的信息,但由于缺少直观可视的手段,利用声发射信息定量评价金属材料的细观损伤存在困难。本文将SEMtester1000原位拉伸试验机、MZ1000正置显微镜和PCI-2型声发射检测系统相结合,搭建了声发射源动态观测实验系统。以Q235钢可视化原位拉伸实验为例,获取了晶体的滑移和夹杂物的断裂两种典型声发射源图像及对应的声发射信号。通过对不同声发射源信号的分析可知,滑移是一个持续的过程,复杂的滑移活动会产生多类型的声发射信号。夹杂物断裂是瞬态过程,产生典型的突发型声发射信号,能量较滑移信号更高。依据声发射源动态观察结果及图像分析,建立了基于声发射机制的Q235钢细观损伤模型。     

Acoustic-emission crack monitoring in fracture-toughness tests for AISI 4340 and SA533B steels

The feasibility of using acoustic-emission techniques for the characterization of fracture resistance in AISI 4340 and SA533B steels is examined. The critical value of J-integral (J _IC ) is measured with a single small specimen (compact tension) loaded in the elastic-plastic range at room temperature. Initiation is detected during loading by acoustic emission. A new AE procedure for crack-growth monitoring in fracture-toughness specimens has been proposed. The possibility of discriminating AE signals from noncritical sources, such as void nucleation during crack-tip plastic deformation and signals from a growing crack, is discussed.     

Thermal problems of multilobe journal bearing tribosystem

Oil film temperature distribution is a key factor in the solution of thermal problems in journal bearings. It allows to find the maximum oil film temperature, thermal distortions of bearing structure and heat flow to and from bearing. The paper describes the results of theoretical investigations into the basic factors in the solution of thermal problems, i.e. the oil film temperature distribution and maximum oil film temperature. The 4-lobe journal bearing operating at laminar oil film as well as in aligned conditions of journal and bush axis was considered. The oil film temperature distribution and maximum oil film temperature have been obtained from the numerical solution of bearing geometry, Reynolds, energy and viscosity equations. The results obtained and the applied code of computation lead to the solution of thermal problems of bearing operation.     

水润滑高速动静压轴承试验研究

研究了动静压轴承在水介质润滑和高速、高压极端工况条件下,最小液膜厚度和流量等性能参数的变化情况,并将其与理论预测结果进行比较.结果表明,水润滑动静压轴承在高速时能够稳定运行,且形成完整的润滑液膜,没有出现明显的汽化及汽蚀现象,试验后轴承表面涂层基本完好.试验结果显示出轴承的承载能力和流量主要取决于供水压力,这与理论预测结果基本一致.     

滑动轴承-转子系统非线性裂纹故障特征及其实验研究

由于材料缺陷以及疲劳运转等多种因素，轴承-转子系统常出现轴上裂纹故障，进一步发展会产生断轴巨大事故。本文考虑滑动轴承支承的单盘转子系统，分析轴上裂纹对系统振动特性的影响，并采用谐波小波变换技术分析实验结果，结果表明在充分考虑支承条件的基础上，裂纹的存在不仅在频域上出现了亚频、超频的频率分量，在时域上也有明显的奇异现象。说明谐波小波变换作为时域分析的有力工具，可以用于滑动轴承-转子系统裂纹故障的早期诊断。     

Stresses in dried wood. Modelling and experimental identification

The paper presents a simple mathematical model of drying that permits evaluation of moisture content distribution in dried wood during the constant and falling drying rate periods and, in particular, estimation of stresses generated from the moment when the moisture content at the body surface reaches the fibre saturation point (FSP). The acoustic emission method (AE) is used for monitoring the state of stress in dried wood. The numerically evaluated drying induced stresses are compared with the number of acoustic signals and their energy monitored on line during drying tests. It can be stated that the enhanced emission of acoustic signals occurs at those moments when the drying induced stresses approach their maximum. Both the numerical calculus and the experimental tests were conducted on a pine-wood sample in the form of a disk.     

推力轴承瞬态启动油膜热不稳定性的线性分析

以简化推力轴承为对象 ,理论上证明了推力轴承运行时存在热不稳定性 ,采用小扰动分析法得到了油膜温度的扰动方程 ,应用简正模态分析法推导了无量纲热不稳定性准则数以及推力轴承运行的热不稳定性准则 .