高频电磁干扰对传输线耦合全波建模方法

对于场线耦合问题,经典传输线理论不适用于求解高频电磁干扰辐照下传输线负载上的电压和电流响应。针对这一问题,首先介绍了一种基于天线理论和模拟行为建模（ABM）的时域全波建模方法。该方法利用Harrington矩量法将电流积分方程离散并推导得到宏模型时域表达式,然后利用ABM频域功能实现频变参数的傅里叶逆变换和时域卷积计算。利用电路求解器,该建模方法可直接求解任意结构传输线耦合的负载处瞬态响应;与传统全波算法相比,模型一旦建立便可应用于任意入射场和线性/非线性负载的情况,无需重复耗时地求解电流积分方程。该方法可简化全波算法求解过程,提高仿真计算效率,尤其便于在入射场和负载存在不确定参数时进行高效重复抽样计算以获得统计特性。然后以高频电磁干扰耦合有损大地上的双导体传输线为例,通过与数值电磁代码和传统传输线理论方法的求解结果对比,验证了所提宏模型的有效性以及传输线理论在解决场线耦合问题时的局限性。结果表明,基于全波方法构建的宏模型可在时域内高效准确地求解高频电磁干扰辐照下任意形状传输线负载上的瞬态响应。     

基于光学相干测振系统的微悬臂梁缺陷检测

提出了基于光学相干测振(optical coherence vibrometer,OCV)系统的微悬臂梁缺陷检测方法.自搭建的OCV系统最大振动位移量程、最大振动频率分别为2.574 mm和138.5 kHz,应用该系统对含缺陷微悬臂梁-附加质量块耦合结构进行振动测量获得其固有频率,并利用附加质量块对固有频率的影响特性...     

Multi-cracks detection of a beam-like structure based on the on-vehicle vibration signal and wavelet analysis

In this paper, a new method for detecting a multi-cracked beam-like structure subjected to a moving vehicle is presented. The crack model is adopted from fracture mechanics. The dynamic response of the bridge-vehicle system is measured directly from the moving vehicle. When moving along the structure, the moving vehicle causes small distortions in the dynamic response of the bridge-vehicle system at the crack locations. In general, these small distortions are difficult to detect visually. However, wavelet transform has recently emerged to be an effective method of detecting such small distortions. Large values (peaks) in the wavelet transform indicate the existence of the cracks. The locations of the cracks are pinpointed by positions of peaks of the wavelet transform and the velocity of the moving vehicle. Numerical results show that the method can detect cracks as small as 10% of the beam height. The proposed method is applicable for low velocity-movements while high velocity-movements are not recommended. The method presents an idea for measuring the vibration directly from the vehicle for crack detection problem in practice.     

QUASI-PERIODIC VIBRATION OF CRACKED ROTOR ON FLEXIBLE BEARINGS

A cracked rotor on flexible bearings is studied in this paper. The vibration of such a system has many complexities because of the crack and bearing flexibility. However, if the properties of the bearings are known, the system can be simplified by supposing that, the vibration due to weight is dominant. Equations of motion are derived, and a linear system in which the crack has been considered as an external disturbance described by a series of trigonometric functions is obtained. Consequently, the quasi-periodic vibrations of the rotor and bearings are established by harmonic balance method and approximate values of the vibration determined by truncating the higher order terms. It is believed that the simulated results will be useful for crack detection in the case of weight-dominant rotors.     

Damage detection of cracked thick rotating blades by a spatial wavelet based approach

This paper presents a technique for blade damage detection based on spatial wavelet analysis. The wavelet transform is used to analyze spatially distributed signals (e.g. mode shape) of cracked thick rotating blades. First, a finite element model is applied to the vibration of a thick rotating blade with a single edge crack. The effects of transverse shear deformation and rotatory inertia are taken into account. Then the mode shapes of the cracked rotating blade are analyzed by wavelet transformation. The effects of crack locations and sizes on the wavelet coefficients are studied. It is found that the distributions of the wavelet coefficients can identify the crack position of the rotating blades by showing a peak at the position of the crack. Then the signals are analyzed by wavelet transform. It is found that the distributions of the wavelet coefficients can identify the crack position. Assumed measurement errors are added to nth mode shape for evaluating the effect of measurement errors on the capability of detecting crack position. The moving average method is used to process the data with assumed measurement errors. The crack positions can also be identified when there exist assumed measurement errors.     

VIBRATION-BASED DIAGNOSTICS OF FATIGUE DAMAGE OF BEAM-LIKE STRUCTURES

The analytical investigation of vibration of damaged structures is a complicated problem. This problem may be simplified if a structure can be represented in the form of a beam with corresponding boundary and loading conditions. In this connection, free vibrations of an elastic cantilever Bernoulli-Euler beam with a closing edge transverse crack is considered in the present work as a model of a structure with a fatigue crack. The modelling of bending vibrations of a beam with a closing crack is realized based on the solutions for an intact beam and for a beam with an open crack. The algorithm of consecutive (cycle-by-cycle) calculation of beam mode shapes amplitudes is presented. It is shown that at the instant of crack opening and closing, the growth of the so-called concomitant mode shapes which differ from the initially given mode shape takes place. Moreover, each of the half-cycles is characterized by a non-recurrent set of amplitudes of concomitant modes of vibration and these amplitudes are heavily dependent on the crack depth.The vibration characteristics of damage based on the estimation of non-linear distortions of the displacement, acceleration and strain waves of a cracked beam are investigated, and the comparative evaluation of their sensitivity is carried out.     

Frequency-domain Hadamard spectroscopy

A new technique is proposed for multichannel excitation and detection of NMR signals in the frequency domain, an alternative to the widely used pulse-excited Fourier transform method. An extensive array of N radiofrequency irradiation channels covers the spectrum of interest. A selective radiofrequency pulse sequence is applied to each channel, generating a steady-state NMR response acquired one-point-at-a-time in the intervals between pulses. The excitation pattern is repeated N times, phase-encoded according to a Hadamard matrix, and the corresponding N composite responses are decoded by reference to the same matrix. This multiplex technique offers the same sensitivity advantage as conventional Fourier transform spectroscopy. The irradiation pattern may be tailored to concentrate on interesting spectral regions, to facilitate homonuclear double resonance, or to avoid exciting strong solvent peaks. As no free induction decay is involved, the new method avoids problems of pulse breakthrough or lineshape distortion by premature termination of the time-domain signal.     

Time-domain analytic solutions of two-wire transmission line excited by a plane-wave field

This paper reports that an analytic method is used to calculate the load responses of the two-wire transmission line excited by a plane-wave directly in the time domain. By the frequency-domain Baum Liu-Tesehe （BLT） equation, the time-domain analytic solutions are obtained and expressed in an infinite geometric series. Moreover, it is shown that there exist only finite nonzero terms in the infinite geometric series if the time variate is at a finite interval. In other word, the time-domain analytic solutions are expanded in a finite geometric series indeed if the time variate is at a finite interval. The computed results are subsequently compared with transient responses obtained by using the frequency-domain BLT equation via a fast Fourier transform, and the agreement is excellent.     

闭合裂纹非共线混频超声检测试验研究

针对结构中微裂纹检测难题,发展了一种闭合裂纹非共线混频超声检测方法。在对非共线混频超声检测机理分析基础上,进行了结构中疲劳裂纹混频非线性超声检测实验。对有无裂纹试件中检测信号进行了滤波和时频分析,结果表明,可根据信号滤波后时域波形中是否存在明显的混频波包或时频分析中是否存在明显的和频分量,实现有无闭合裂纹的判识;通过移动激励探头的位置,控制两列入射声波在试件中的交汇位置,实现试件中不同深度位置的混频非线性检测。并根据测得的混频非线性系数沿试件深度方向上分布,实现了闭合裂纹沿深度方向上长度的测量。研究工作为结构中微裂纹定量评价做了有益探索。     

Reduced-order modeling for mistuned centrifugal impellers with crack damages

An efficient method for nonlinear vibration analysis of mistuned centrifugal impellers with crack damages is presented. The main objective is to investigate the effects of mistuning and cracks on the vibration features of centrifugal impellers and to explore effective techniques for crack detection. Firstly, in order to reduce the input information needed for component mode synthesis (CMS), the whole model of an impeller is obtained by rotation transformation based on the finite element model of a sector model. Then, a hybrid-interface method of CMS is employed to generate a reduced-order model (ROM) for the cracked impeller. The degrees of freedom on the crack surfaces are retained in the ROM to simulate the crack breathing effects. A novel approach for computing the inversion of large sparse matrix is proposed to save memory space during model order reduction by partitioning the matrix into many smaller blocks. Moreover, to investigate the effects of mistuning and cracks on the resonant frequencies, the bilinear frequency approximation is used to estimate the resonant frequencies of the mistuned impeller with a crack. Additionally, statistical analysis is performed using the Monte Carlo simulation to study the statistical characteristics of the resonant frequencies versus crack length at different mistuning levels. The results show that the most significant effect of mistuning and cracks on the vibration response is the shift and split of the two resonant frequencies with the same nodal diameters. Finally, potential quantitative indicators for detection of crack of centrifugal impellers are discussed.     

Detecting damage in vibrating structures with a scanning LDV

It has been demonstrated, through experiments on laboratory-scale structures, that structural defects such as cracks can be detected and located using a continuously scanning laser Doppler vibrometer (LDV) if vibration sufficient to flex the defect can be induced and if the defects are such as to produce localised mode shape discontinuities. This paper describes such a method of defect detection using a short linear scan at the crack location. Through-cracks are easily detected in thin metal plates whereas narrow slots in a solid cantilever beam have no easily identifiable effect unless they extend more than half-way through the thickness. Cracks in a reinforced-concrete beam introduced marked and identifiable discontinuities in mode shapes. Speckle noise affects the measurements, sometimes seriously. A simple low-pass filter may improve the signal quality.     

Adaptive bistable stochastic resonance and its application in mechanical fault feature extraction

Stochastic resonance (SR) is an important approach to detect weak vibration signals from heavy background noise. In order to increase the calculation speed and improve the weak feature detection performance, a new bistable model has been built. With this model, an adaptive and fast SR method based on dyadic wavelet transform and least square system parameters solving is proposed in this paper. By adding the second-order differential item into the traditional bistable model, noise utilization can be increased and the quality of SR output signal can be improved. The iteration algorithm for implementing the adaptive SR is given. Compared with the traditional adaptive SR method, this algorithm does not need to set up the searching range and searching step size of the system parameters, but only requires a few iterations. The proposed method, discrete wavelet transform and the traditional adaptive SR method are applied to analyzing simulated vibration signals and extracting the fault feature of a rotor system. The contrastive results verify the superiority of the proposed method, and it can be effectively applied to weak mechanical fault feature extraction.     

应用改进的矩阵束方法加速混响室时域仿真

为了减少混响室时域全波仿真的计算量,首次对混响室时域响应的预测做出探索研究。以改良矩阵束方法为基础,提出一种计算效率更高的矩阵束方法,并验证了该方法的正确性与稳定性。用复指数幂求和式对混响室的时域波形进行拟合,利用该方法能够高效求解出拟合式中的各极点,实现了对混响室时域响应的近似外推。由电场强度的前20 000步计算结果,可快速预测得到后20 000步响应,发现束参数比例取0.62左右时,对多个采样点的电场均可得到良好的预测效果,可保证仿真与预测相结合得到的结果与真实结果的频域相对误差小于15%。这种结合预测的仿真算法可节省计算量约50%。     

应用改进的矩阵束方法加速混响室时域仿真

为了减少混响室时域全波仿真的计算量,首次对混响室时域响应的预测做出探索研究。以改良矩阵束方法为基础,提出一种计算效率更高的矩阵束方法,并验证了该方法的正确性与稳定性。用复指数幂求和式对混响室的时域波形进行拟合,利用该方法能够高效求解出拟合式中的各极点,实现了对混响室时域响应的近似外推。由电场强度的前20 000步计算结果,可快速预测得到后20 000步响应,发现束参数比例取0.62左右时,对多个采样点的电场均可得到良好的预测效果,可保证仿真与预测相结合得到的结果与真实结果的频域相对误差小于15%。这种结合预测的仿真算法可节省计算量约50%。     

Rigid finite element model of a cracked rotor

The article introduces a new mathematical model for the cracked rotating shaft. The model is based on the rigid finite element (RFE) method, which has previously been successfully applied for the dynamic analysis of many complicated, mechanical structures. In this article, the RFE method is extended and adopted for the modeling of rotating machines. An original concept of crack modeling utilizing the RFE method is developed. The crack is presented as a set of spring–damping elements of variable stiffness connecting two sections of the shaft. An alternative approach for approximating the breathing mechanism of the crack is introduced. The approach is simple and allows one to intuitively and systematically prepare and analyze the model of a cracked rotor.The proposed method is illustrated with numerical and experimental results. The experiments conducted for the uncracked free–free rotor as well as the numerical results obtained with other software confirm the accuracy of the RFE model. The numerical analysis conducted for a set of cracked rotors has shown that, depending on the eccentricity and its angular location, the breathing behavior of the crack may take different forms. In spite of this, the frequency spectra for different cracks are almost identical.Due to its simplicity and numerous advantages, the proposed approach may be useful for rotor crack detection, especially if methods utilizing the mathematical model of the rotor are applied.     

接触缺陷的振动调制超声导波检测技术研究

针对常规线性超声检测方法无法实现板结构接触类缺陷(如微裂纹、脱粘等)检测问题,将超声导波技术与振动声调制技术相结合,利用稀疏分布传感器发展了一种板结构中接触缺陷非线性超声检测方法。通过低频振动改变缺陷的接触状况,使得通过接触面的高频导波信号的相位和幅值受到调制。对受低频振动调制的超声导波二维时间序列进行时频分析,由于接触类缺陷的存在,在振动调制超声导波序列的时频分布上出现明显的低频振动频率分量。利用提取出的低频振动频率下的超声导波信号,进行了结构接触缺陷成像处理。检测试验表明,基于振动声调制的超声导波缺陷成像方法可以实现结构中的接触类缺陷检测。     

亮氨酸与异亮氨酸的低频集体振动的太赫兹光谱研究

太赫兹(THz)波是指频率在0.1～10 THz频段的电磁波。太赫兹光谱技术不同于以往的检测手段,可以用于检测氨基酸同分异构体,反映物质的分子结构和构型,对食品安全和药品药性控制有着重要的意义。亮氨酸与异亮氨酸属于同系的同分异构体,它们具有近似的分子结构,但物理化学性质有很大的差别。生物大分子的太赫兹吸收与其分子间氢键和分子内氢键的振动和转动能级相关的偶极跃迁有关,可以利用分子偶极跃迁进行生物分子的指纹识别。采用太赫兹时域光谱(THz-TDS)和傅里叶红外光谱(FTIR),对亮氨酸和异亮氨酸进行了测量。在中红外波段亮氨酸与异亮氨酸的吸收光谱几乎完全重叠,而在太赫兹频波段可以观察到它们的光谱存在明显差异,因此太赫兹光谱能够作为快速准确鉴别这两种物质的方法。采用密度泛函理论(DFT)对亮氨酸和异亮氨酸的低频集体振动模式进行理论模拟,并对其太赫兹光谱进行研究和讨论。通过比较实验和理论结果,计算得到的峰位与实验结果可以互相印证。     

金属杆内疲劳裂纹与振动/超声相互作用及其定量表征

根据同步解调的原理,考察振动声调制检测输出信号中的调制成分,对金属杆内振动/超声在裂纹面上的相互作用进行了分析.制作了含有不同尺寸裂纹的铝杆试样,以扫频激励的方式得到合适的高频激励参数,分析输出信号中的调制信息,发现工件中的高频超声可分为两部分:一部分声波通过裂纹面,受到低频振动信号的调制,另一部分则保持不变。在此基础上对非线性调制模型进行了修正,并提出了一种用于裂纹检测的定量方法。与超声C扫描检测结果对比表明,此定量方法可用于估计金属杆中疲劳裂纹尺寸。     

一种适于1维磁等离子体电磁波传输特性的FDTD分析

提出了一个新的分析各向异性磁等离子体中电磁波传输特性的时域有限差分（FDTD）方法。该方法是将电流密度矢量与电场强度矢量之间的本构方程基于拉普拉斯变换原理转到复频域,然后再逆变换到时域得到它们之间显式的方程,最后再结合指数差分,得到离散时域的显式的FDTD迭代方程,解决了本构方程中电流密度矢量的分量相互耦合而不易直接离散的困难。该方法在数学上具有简单明了和易于计算的特点,同时通过该方法计算各向异性等离子体板的电磁波反射和透射系数,与其解析解进行比较,结果表明了该方法的准确性和有效性。