Envelope order tracking for fault detection in rolling element bearings

An envelope order tracking analysis scheme is proposed in the paper for the fault detection of rolling element bearing (REB) under varying-speed running condition. The developed method takes the advantages of order tracking, envelope analysis and spectral kurtosis. The fast kurtogram algorithm is utilized to obtain both optimal center frequency and bandwidth of the band-pass filter based on the maximum spectral kurtosis. The envelope containing vibration features of the incipient REB fault can be extracted adaptively. The envelope is re-sampled by the even-angle sampling scheme, and thus the non-stationary signal in the time domain is represented as a quasi-stationary signal in the angular domain. As a result, the frequency-smear problem can be eliminated in order spectrum and the fault diagnosis of REB in the varying-speed running condition of the rotating machinery is achieved. Experiments are conducted to verify the validity of the proposed method.     

A multiscale noise tuning stochastic resonance for fault diagnosis in rolling element bearings

Condition monitoring of rotating machinery is important to extend the mechanical system's reliability and operational life. However, in many cases, useful information is often overwhelmed by strong background noise and the defect frequency is difficult to be extracted. Stochastic resonance (SR) is used as a noise-assisted tool to amplify weak signals in nonlinear systems, which can detect weak signals of interest submerged in the noise. The multiscale noise tuning SR (MSTSR), which is originally based on discrete wavelet transform (DWT), has been applied to identify the fault characteristics and has also increased the signal-to-noise ratio (SNR) improvement of SR. Therefore, a novel tri-stable SR method with multiscale noise tuning (MST) is proposed to extract fault signatures for fault diagnosis of rotating machinery. The wavelet packets transform (WPT) based MST can obtain better denoising effect and higher SNR of resonance output compared with the traditional SR method. Thus the proposed method is well-suited for enhancement of rotating machine fault identification, whose effectiveness has been verified by means of practical vibration signals carrying fault information from bearings. Finally, it can be concluded that the proposed method has practical value in engineering.     

An improved multiscale noise tuning of stochastic resonance for identifying multiple transient faults in rolling element bearings

Stochastic resonance (SR), a noise-assisted tool, has been proved to be very powerful in weak signal detection. The multiscale noise tuning SR (MSTSR), which breaks the restriction of the requirement of small parameters and white noise in classical SR, has been applied to identify the characteristic frequency of a bearing. However, the multiscale noise tuning (MST), which is originally based on discrete wavelet transform (DWT), limits the signal-to-noise ratio (SNR) improvement of SR and the performance in identifying multiple bearing faults. In this paper, the wavelet packet transform (WPT) is developed and incorporated into the MSTSR method to overcome its shortcomings and to further enhance its capability in multiple faults detection of bearings. The WPT-based MST can achieve a finer tuning of multiscale noise and aims at detecting multiple target frequencies separately. By introducing WPT into the MST of SR, this paper proposes an improved SR method particularly suited for the identification of multiple transient faults in rolling element bearings. Simulated and practical bearing signals carrying multiple characteristic frequencies are employed to validate the performance improvement of the proposed method as compared to the original DWT-based MSTSR method. The results confirm the good capability of the proposed method in multi-fault diagnosis of rolling element bearings.     

基于EMD的谱峭度方法在滚动轴承故障检测中的应用

传统谱峭度方法通常采用基于短时傅里叶变换(Short Time Fourier Transform,STFT)的峭度图方法来实现。针对STFT不能保证对瞬态脉冲这种高度非平稳信号最优的分解效果的缺点,提出一种基于经验模式分解(Empirical Mode Decomposition ,EMD)的谱峭度方法。该方法首先利用EMD和Hilbert变换得到信号的时频分布,然后将信号的时频分布按照不同层数分成若干频段,通过计算各频段的峭度值得到相应的峭度图,再根据峭度最大原则选择滤波频段进行带通滤波,最后对滤波信号采用包络分析确定故障信息。实验结果表明：相比传统基于STFT的谱峭度方法,本文方法更能准确的获得轴承加速度信号的故障特征频率信息。     

滚动轴承声信号特征提取和诊断试验研究

为解决振动检测方法不能有效识别低速旋转机械滚动轴承故障问题,利用声发射检测方法,建立了滚动轴承低速声发射信号采集试验装置,对模拟人工缺陷滚动轴承声发射信号进行了采集,进而对滚动轴承声发射信号进行总体平均经验模式分解,结合能量矩及相关系数法综合判断分解后各模态分量的真伪,据此提取出特征信号并做出其局部Hilbert边际谱,最后对滚动轴承各种故障模式进行诊断。试验结果表明该诊断方法能准确识别滚动轴承声发射信号故障频率,依据特征频率及幅值大小可对低速滚动轴承故障进行有效诊断。     

大口径平背形主镜背部支撑位置优化计算方法

针对背部支撑方式的平背形反射镜,提出了一种确定主镜最佳背部支撑位置的优化计算方法。利用AN-SYS软件中的APDL语言建立了主镜的参数化模型。利用有限元法,以主反射镜光轴垂直时自重作用下的镜面最大变形量为目标函数,以相同工况下一阶自振频率为约束条件,对背部支撑点位置的相关参数和中心镜厚进行了优化分析,得到了满足镜面面型误差要求的最佳背部支撑位置及中心镜厚。     

ITER聚变装置重力支撑有限元模态分析

运用有限元分析软件ANSYS建立了ITER装置重力支撑结构环向20°的三维有限元模型,采用子空间法对ITER重力支撑结构系统进行了有限元模态分析,求出了重力支撑系统的前10阶固有频率和振型,并对振型特点进行了分析。     

Analyses of contact forces and vibration response for a defective rolling element bearing using an explicit dynamics finite element model

This paper provides insights into the physical mechanism by which defect-related impulsive forces, and consequently, vibrations are generated in defective rolling element bearings. A dynamic nonlinear finite element model of a rolling element bearing with an outer raceway defect was numerically solved using the explicit dynamics finite element software package, LS-DYNA. A hypothesis was developed to explain the numerical noise observed in the predicted vibrations and contact forces, and the noise frequencies were analytically estimated. In-depth analyses of the numerically estimated dynamic contact forces between the rolling elements and the raceways of a bearing, which are not measured in practice, and have not been reported previously, are presented in this paper. Several events associated with the traverse of the rolling elements through the outer raceway defect are elaborated, and the impulsive force generating mechanism is explained. It was found that the re-stressing of the rolling elements that occurs near the end of a raceway defect generates a burst of multiple short-duration force impulses. The modelling results also highlight that much higher contact forces and accelerations are generated on the exit of the rolling elements out of defect compared to when they strike the defective surface. A bearing with a machined outer raceway defect was tested in a controlled experiment; the measured acceleration response compared favourably with the numerically modelled acceleration results, thereby, validating the low- and high-frequency characteristics of the de-stressing and re-stressing of the rolling elements, respectively.     

Optimum running conditions for a gas turbine cogeneration system

There are currently compact and reliable gas turbines that prove very suitable for cogeneration. The present paper deals with the basic structure of a program package that makes it possible to simulate, using manufacturers' data, four of the ways in which such installations can be configured.Furthermore, this package makes it possible to determine optimum running conditions for the system analysed. The complex algorithm is used to yield the minimum operation cost, which is the function sought. We conclude with an example of software application.     

Model for the vibration produced by a single point defect in a rolling element bearing

A model is developed to describe the vibration produced by a single point defect on the inner race of a rolling element bearing under constant radial load. The model incorporates the effects of bearing geometry, shaft speed, bearing load distribution, transfer function and the exponential decay of vibration. A comparison of predicted and measured demodulated vibration spectra confirms the satisfactory performance of the model.     

An oscillatory system with a magnetic-fluid viscoinertial element

Results of measuring the damping factor of an oscillatory system the viscoinertial element of which is represented by a magnetic fluid filling a U-shaped glass tube are considered. The role of elasticity is played by an air-filled cavity that is formed in one of the tube legs under the piezoelectric plate attached to its end and serving for oscillation reception. A method of measuring the oscillation damping factor is proposed, and the results of these measurements are used to determine the shear viscosity of magnetic fluid samples as a function of magnetic field strength.     

Optimum design of aspheric collimation lenses for optical antenna system

Three kinds of aspheric collimation lenses for optical antenna have been design by optimization. The aspheric cylinder collimation lenses with aspheric surfaces (such as elliptic, hyperbolic and parabolic marginal profiles) have been researched for the semiconductor laser beam with the characteristic of dot emitting source. Based on genetic algorithm and the optimization toolbox of MTLAB, the divergence angle has been optimized. The collimation divergence angle is less than 115 μrad has been measured by laser beam analyzer. This optimum design laser beam collimation lenses as a pre-collimation system can be used for optical antenna system. And it can be widely used in modern space laser communication.     

基于功率流方法的多个动力吸振器的优化设计

针对附加多个动力吸振器的有阻尼单自由度系统,本文利用结构导纳理论,引入附加动力吸振器后振动系统的修正结构导纳,推导了振源输入系统的总功率流、传输到主振系的净功率流及吸振器吸收的功率流表达式,揭示了动力吸振器对系统功率流传递特性的控制机理。提出了以功率流为控制量进行动力吸振器优化设计策略,给出了动力吸振器优化参数的配置关系。     

Vibration quenching in a large scale rotor-bearing system using journal bearings with variable geometry

In large scale rotating machinery the resonance amplitude during the passage through resonance is a matter of consideration because of its influence in the surrounding environment of the rotational system and foundation. In this paper, a variable geometry journal bearing (VGJB), recently patented, is applied for the mounting of a large scale rotor bearing system operating at the range of medium speed. The simulation of the rotor-bearing system incorporates a recent method for simulation of a multi-segment continuous rotor in combination with nonlinear bearing forces. The use of the current bearing gives results that encourage the use of such a bearing in rotating machinery since the vibration amplitude during the passage through the critical speed can be reduced up to 60–70%. In the presented study, the developed amplitude and the rotor stresses are severely reduced compared to those of the system with normal cylindrical journal bearings during a virtual start up of the system.     

Envelope extraction based dimension reduction for independent component analysis in fault diagnosis of rolling element bearing

A robust feature extraction scheme for the rolling element bearing (REB) fault diagnosis is proposed by combining the envelope extraction and the independent component analysis (ICA). In the present approach, the envelope extraction is not only utilized to obtain the impulsive component corresponding to the faults from the REB, but also to reduce the dimension of vibration sources included in the sensor-picked signals. Consequently, the difficulty for applying the ICA algorithm under the conditions that the sensor number is limited and the source number is unknown can be successfully eliminated. Then, the ICA algorithm is employed to separate the envelopes according to the independence of vibration sources. Finally, the vibration features related to the REB faults can be separated from disturbances and clearly exposed by the envelope spectrum. Simulations and experimental tests are conducted to validate the proposed method.     

Optimum design for maximum wavelength resolution for an edge filter-based ratiometric system

This paper provides a straightforward design method for achieving a maximum wavelength resolution for an edge filter-based ratiometric system. An analysis of the influence of a range of factors on the resolution of the ratiometric wavelength measurement system was carried out. The investigation shows that, for a given input optical signal and when the working wavelength range is known, it is relatively straightforward to select an optimum slope for the edge filter that will yield a maximum resolution for the system. An experimental verification is carried out using a tunable laser and three macrobending fibre edge filters, with a good match between experimental and simulation results.     

摆臂式三点光学镜面支撑系统的研究

提出了一种摆臂式三点光学镜面支撑系统,分析了其结构原理和工作性能,给出了实现的方法和制造工艺。该支撑系统具有结构简单、刚度恒定以及无附加温度应力等特点,可用于中小型光学镜面和光学元件的支撑,特别适用于空间仪器的光学加工领域。