改进经验模态分解在动平衡信号提取中的应用

在变频结构干扰和强噪声背景下，传统方法从原始振动信号中提取动平衡信号的精度不高。本文采用经验模态分解可以根据实时振动信号的局部特征时间尺度，将其自适应分解为有限多个由高频到低频排列的、正交的本征模态函数；同时利用自回归预测模型延拓信号端点，以消除分解过程的边界效应对低频动平衡信号的影响；最后，根据功率谱密度可以快速、有效地判断出代表基频信号的本征模态函数。实验结果证明，该方法可以高精度提取动平衡信号，在相同测量条件下，能够获得较高的一次不平衡量降低率和较好的重复性能。     

LabVIEW在货运车箱振动自功率谱密度函数分析中的应用

在实验室内对车载物资和装备进行随机振动试验具有很大的经济意义,目前国际上普遍采用的一种试验方法是在频域内再现功率谱密度和随机波形,而功率谱密度通常是由实测振动数据经过自功率谱密度函数分析后得到.LabVIEW可以很好的完成自功率谱密度函数分析.首先介绍了LabVIEW中有关自功率谱密度函数的基本理论和算法,对待处理原始数据进行了简要介绍,然后详细叙述了自功率谱密度函数的计算步骤,最后开发出集数据输入、计算以及显示保存结果等功能于一体的虚拟仪器.经实践检验证明该虚拟仪器实用且效率高.     

Approximation and reconstruction of continuous signals using differential Chebyshev transformation

A method for physical process approximation using the differential Taylor transformation is substantiated. The power basis is transformed to bases of orthogonal Chebyshev polynomials. It is shown that the convergence of series is substantially increased by transition to expansion in Chebyshev polynomials of first kind and shifted Chebyshev polynomials. An algorithm for calculating differential spectrum discretes is formulated. It is observed that in the Chebyshev bases, the value of spectrum discretes decreases constantly as their number grows. In this case, it is possible to stop computing the discretes as they achieve the required small value, but this cannot be done in the power basis. Numerical examples illustrate the advantage of the proposed approach.     

Development and characterization of flexible heating fabric based on conductive filaments

Active heating garments will be a promising product for improving life quality of rheumatisants and old people in the future. This paper presented an improved fabrication method of flexible heating fabrics (FHFs) which were developed by weaving intermittently silver filaments (SFs) or coated silver yarns (CSYs) into plain fabrics, this method can control more easily density of conductive filaments and rated power of FHFs in terms of requirements. Resistance thermostability and utmost load current of several kinds of conductive materials were utilized to determine an appropriate conductive material of FHFs. Subsequently, performances of FHF with SFs were characterized by a temperature controlling and power measuring device that was developed in our laboratory. Experimental results show SF can load over 0.3 A current, but the CSY and coated silver knitted fabric (CSKF) can load less than 0.1 A current. However, resistance variation ratios (RVRs) of SF are less than etc. 1.66%, but the RVRs of CSY and CSKF exceed 10% and 20%, when environment temperature increases from room temperature to 80 and 100 °C. Furthermore, strong positive linear correlations are between rated power and utmost ascending temperature of FHFs and between power consumption and presetting equilibrium temperatures of FHFs. In general, measurement data and analysis results can provide help for the design and prediction of physical properties of FHFs.     

Deconvolution of Stark broadened spectra for multi-point density measurements in a flow Z-pinch

Stark broadened emission spectra, once separated from other broadening effects, provide a convenient non-perturbing means of making plasma density measurements. A deconvolution technique has been developed to measure plasma densities in the ZaP flow Z-pinch experiment. The ZaP experiment uses sheared flow to mitigate MHD instabilities. The pinches exhibit Stark broadened emission spectra, which are captured at 20 locations using a multi-chord spectroscopic system. Spectra that are time- and chord-integrated are well approximated by a Voigt function. The proposed method simultaneously resolves plasma electron density and ion temperature by deconvolving the spectral Voigt profile into constituent functions: a Gaussian function associated with instrument effects and Doppler broadening by temperature; and a Lorentzian function associated with Stark broadening by electron density. The method uses analytic Fourier transforms of the constituent functions to fit the Voigt profile in the Fourier domain. The method is discussed and compared to a basic least-squares fit. The Fourier transform fitting routine requires fewer fitting parameters and shows promise in being less susceptible to instrumental noise and to contamination from neighboring spectral lines. The method is evaluated and tested using simulated lines and is applied to experimental data for the 229.69 nm C III line from multiple chords to determine plasma density and temperature across the diameter of the pinch. These measurements are used to gain a better understanding of Z-pinch equilibria.     

基于经验模分解的陀螺信号去噪

陀螺随机漂移是影响寻北精度的重要因素,小波消噪方法对小波基和分解尺度等因素依赖性较强。提出了一种新的基于功率谱密度准则的经验模态分解(EMD)去噪方法,可有效解决传统EMD去噪自适应滤波器截止阶数难以确定的难题,该方法将经验模态分解得到的固有模态函数(IMF)分为信号分量起主导作用模态与噪声分量起主导作用模态,并对噪声分量起主导作用的模态进行类似小波软阈值去噪的方法进行滤波,然后与信号分量起主导作用的模态共同对信号重建实现去噪。将该方法应用于测试信号与陀螺信号的去噪,结果表明:新方法能有效地判断噪声与信号起主导作用的模态分界点,具有良好的去噪效果,且不受主观参数的影响,具有自适应性。     

Modified self-organising map for automated novelty detection applied to vibration signal monitoring

This paper proposes a novelty detection-based method for machine condition monitoring (MCM) using vibration signals and a new feature extraction method based on higher-order statistics of the power spectral density. This novel MCM method is based on Kohonen's self-organising map and adopts a multidimensional dissimilarity measure for dual class classification. The approach is designed to be highly modular and scale well for a multi-sensor condition monitoring environment. Experiments using real-world vibration data sets with upto eight sensors have shown high accuracy in classification and robustness across different condition monitoring applications.     

A DUAL FITTING ALGORITHM FOR MODAL PARAMETERS IDENTIFICATION

A dual fitting algorithm (DFA) for modal parameters identification is presented. The method is implemented in three steps: first, the coefficients of the Forsythe orthogonal polynomials for the rational fraction of the frequency response functions (FRFs) are obtained by fitting the experimental FRF data; then the coefficients of the orthogonal polynomials are converted into the coefficients of ordinary power polynomials by the fitting method again; and finally, the poles and residues of the rational fraction of FRFs in ordinary power polynomials are extracted to identify the modal parameters. Some notes to the definition and use of the recurrence formulation for the real half-function Forsythe orthogonal polynomials are introduced. An example is given to show the aspects of the present method.     

基于数字孪生的电网变压器故障诊断方法

为减少电网安全隐患,保障用户正常用电,提出基于数字孪生的电网变压器故障诊断方法。 利用传感器设备,结合全要素实体基本信息,模拟变压器运行状态,在虚拟空间内建立数字孪生体,包括几何、物理、规则和行为 4 个模型。 在该孪生体中,利用正交全局与局部保持嵌入算法将初始故障特征集合变换到高维核空间内,计算映射矩阵,获得映射向量最大特征值,提取低维敏感特征;结合提取的故障特征,在规则模型中采用概率神经网络算法,建立概率密度函数,使用差分进化方法,确立初始种群,经过反复的变异、交叉操作,丰富种群多样性,确定最佳平滑因子,当达到最佳迭代次数时,输出最佳诊断结果。 仿真实验表明,所提算法能够有效区分不同故障特征,减少诊断时间,可获得更加精确的诊断结果。     

多轴应力响应下结构振动疲劳寿命预估的时域方法研究

应用Von Mises应力准则将多轴应力响应等效合成为单轴应力,给出了基于功率谱输入和时域输入的多轴应力响应振动疲劳寿命预估方法,时域输入法的求解过程没有丢失应力分量相位的相互信息,较功率谱输入法更完备。针对激励载荷是以功率谱密度函数形式表达的,提出了Monte-Carlo伪随机历程模拟将激励功率谱转换到时域激励中,再通过时域输入法进行寿命预估的求解思路,保证了等效合成的Von Mises应力的相位信息具有实际的物理意义,可指导多轴应力响应下结构振动疲劳寿命的精确预估以及声疲劳试验研究。     

Reduction of system order using power spectral density function-generalization of liaw's dispersion analysis

The method of model reduction based on dispersion analysis and the continued fraction is extended to treat the system which has multiple poles or has simple or multiple poles on the imaginary axis. Using the power spectral density function and preserving the dynamic modes with large power contibutions, the denominator of the reduced model is obtained and its numerator is obtained by using the continued-fraction method. This method is proved to give better approximation to an original system through examples than other methods.     

Comparison of an Eigenvector Music Method with Classical FFT and Model Based AR Methods in the Analysis of Mitral Valve Doppler Signals

Abstract

Mitral valve stenosis is an important heart condition that develops when the mitral valve fails to open as wide as it should. In this study, we have performed Eigenvector based Music, FFT based Welch, and AR based Burg methods of Doppler signals real clinical data from patients with mitral valve stenosis and healthy volunteers. Using these methods, we have not only utilized power spectral density distribution graphs, but also facilitated Doppler sonograms and estimation of SBI to obtain medical information about mitral stenosis and determination of spectral broadening in the presence of mitral stenosis. In conclusion, this research has shown that frequency level of maximum power spectral density is distinctive and there is an advantage in using the EIG‐Music over the FFT‐Welch and AR‐Burg for the determination of SBI. Using the Music method among them, the calculation of SBI may help determine mitral valve stenosis.     

基于LabVIEW的振动噪声测试和分析系统开发

开发基于LabVIEW的振动噪声测试和分析系统。该系统具有对振动噪声进行实时数据采集，并对采集到的数据进行消噪滤波的预处理，然后通过信号分析工具对其进行相应的频谱分析、相关和功率谱密度分析，最后对分析结果进行存储管理的功能。另外，该系统还具有人机界面友好、运行速度快、开发周期短、易于维护和开发等特点。     

基于微波雷达传感器的固体流量测量系统的研究

本文使用微波多普勒雷达传感器(MRS),基于LabVIEW设计固体质量流量测量系统。首先,使用NI PCI-6251采集所测固体的多普勒回波信号,之后对回波信号进行处理分析,可计算出固体流动的平均速度,再通过对回波信号的相关性分析得到其功率谱密度,建立谱密度与质量流量之间的线性关系,依据该线性关系通过谱密度计算出所测固体流量。实验证明,该系统具有较好的实时性及可操作性,对质量流量的测量具有实际应用意义。     

High-level noise source for the calibration of Johnson noise power thermometers

A new high-level noise source was developed specifically for the calibration of Johnson noise power thermometers (JNPT), but it is useful in other applications requiring a stable, wideband, well-defined noise power spectral density. The design concept for the noise source is based on the fact that the open-circuit thermal noise voltage of a feedback resistor, connecting the output to the input of an inverting amplifier, is available at the amplifier output from an equivalent low output impedance caused by the feedback mechanism. The noise power spectral density level at the noise source output is equivalent to the density of the open-circuit thermal noise of a 100-Omega resistor at a temperature of about 64 000 K. The noise source has an output power spectral density that is flat to within 0.1% (0.0043 dB) in the frequency range 1-150 kHz which brackets typical passbands of the signal-processing channels of JNPTs. The noise source was evaluated by comparing its output noise power with the thermal noise power generated by a platinum resistor of known ohmic value at the temperature of the aluminum freezing point (933.52 K). The measured noise power was within 0.06% of the value computed from the fundamental thermal noise equation of Nyquist. The power spectral density varies less than 0.03% for ambient temperature fluctuations in the range 15 degrees -35 degrees C.     

互联悬架液压参数灵敏度分析及优化

针对液压参数对互联悬架输出响应影响程度大小的问题,建立了四自由度液压互联悬架半车侧倾耦合频域模型,通过计算系统的传递函数及施加路面激励,得到了悬架模型在垂直模态和侧倾模态下的加速度谱密度响应。采用基于模糊灰色关联的灵敏度分析方法对悬架垂直模态和侧倾模态进行分析,得到了各液压参数的灰色关联度。运用多目标优化算法NSGA-Ⅱ,以两种模态下的悬架响应为优化目标,对灵敏度大的液压参数进行了优化。优化后两种模态下加速度功率谱密度峰值及加速度均方根值均有减小,液压互联悬架平顺性得到提高。     

Flexural-torsional coupled vibration of slewing beams using various types of orthogonal polynomials

Dynamic behavior of flexural-torsional coupled vibration of rotating beams using the Rayleigh-Ritz method with orthogonal polynomials as basis functions is studied. Performance of various orthogonal polynomials is compared to each other in terms of their efficiency and accuracy in determining the required natural frequencies. Orthogonal polynomials and functions studied in the present work are : Legendre, Chebyshev, integrated Legendre, modified Duncan polynomials, the special trigonometric functions used in conjunction with Hermite cubics, and beam characteristic orthogonal polynomials. A total of 5 cases of beam boundary conditions and rotation are studied for their natural frequencies. The obtained natural frequencies and mode shapes are compared to those available in various references and the results for coupled flexural-torsional vibrations are especially compared to both previously available references and with those obtained using NASTRAN finite element package. Among all the examined orthogonal functions, Legendre orthogonal polynomials are the most efficient in overall CPU time, mainly because of ease in performing the integration required for determining the stiffness and mass matrices.     

Calculation of absolute values of the spectral energy density of polychromatic radiation

A method for calculating absolute values of the spectral distribution of the radiant energy of a polychromatic source is described for the case in which the spectral distribution of the radiant energy is recorded in relative units, and the time dependence of a current pulse of a photodetector the spectral sensitivity of which is known in absolute units is measured. The expression for the time-averaged spectral density of the radiation power for the pulse-periodic operation of a radiant source is given.     

基于ANSYS Workbench的RV减速器随机振动分析

以RV减速器为研究对象,建立了RV减速器的三维模型,导入Adams中进行运动学仿真,得到了正齿轮的加速度;利用ANSYS Workbench求解得到RV减速器的固有频率,根据概率统计学分析技术推导功率谱密度函数;最后,将功率谱密度峰值提取后导入ANSYS Workbench的Random vibration模块作随机振动分析。该方法考虑了随机振动因素对机构应力以及安全裕度的影响,为处理RV减速器工作可靠性问题提供了一种新的方法。