IDENTIFICATION OF TIME-VARYING MODAL PARAMETERS USING LINEAR TIME-FREQUENCY REPRESENTATION

A new method of parameter identification based on linear time-frequency representation andHilbert transform is proposed to identify modal parameters of linear time-varying systems frommeasured vibration responses. Using Gabor expansion and synthesis theory measured responses arerepresented in the time-frequency domain and modal components are reconstructed by time-frequencyfiltering. The Hilbert transform is applied to obtain time histories of the amplitude and phase angle ofeach modal component, from which time-varying frequencies and damping ratios are identified. The     

一种新型自由界面子结构模态综合法的研究

将键合图用于动态子结构分析和研究，获得其相应的特征谱矩阵和振型矩阵，提出一种新的求解自由界面模态综合法的基本原理，推导出两个子结构自由界面模态综合法的计算方法。文中给出的算例表明，基于键合图方法的自由界面模态综合法方便、有效、结果准确，并确保了整体结构分割前和综合后的键合图模型的统一。     

CONTRIBUTION TO THE EXTENSION OF MODAL ANALYSIS TO NON-LINEAR STRUCTURE USING VOLTERRA FUNCTIONAL SERIES

Modal analysis is extensively used to study dynamic behaviour of linear mechanical structures. The extension of this tool to non-linear structures is examined here, using Volterra functional series which generalises the superposition principle and permits to obtain impulse responses and transfer functions of various orders. These functions will be presented in close-form expressions which allow going from one class of functions to another one.     

子结构间联结动力学参数的实验识别

提出了两个利用实测传递函数识别子结构间联结刚度，阻尼参数的方法，它分别适用于子结构在自由状态下的有限元模型已建立和没有建立两种情况，给出了识别的数学原理，由于该方法不需对实测传递函矩阵求逆，因而有效地防止了不可避免的实测误差给参数识别造成的不利影响，提出了辨别精度。     

利用ARV模型识别水轮机轴系模态参数

针对一类输入激振力不可测的工程结构,论述了基于向量自回归（ＡＲＶ）时间序列模型的结构模态参数识别的基本原理。为考察ＡＲ系数估计的精度,利用中心要限定量建立了估计的自回归系数矩阵协方差的表达式。分别和用水轮机的随机响应信号和自由响应信号识别了模态参数。数值仿真结果表明本文给出的识别方法是鲁棒的。此外,给出了试验结果。     

USING CROSS—CORRELATION THEORY TO EXTRACT MODAL PARAMETERS IN FREQUENCY—DOMAIN

Conventional modal parameter identifications are usually based on frequency response functions, which require measurements of both the input force and the resulting response. However, in many cases, only response data are available while the actual excitations (such as wind/wave load) are not measurable. Modal parameters estimation must base itself on response-only data. Over the past years, many time-domain modal parameter identification techniques from output-only are proposed. A poly-reference frequency-domain modal identification scheme on response-only is presented. It is based on coupling the cross-correlation theory with conventional frequency-domain modal parameter extraction. An experiment using an airplane model is performed to verify the proposed method.     

不完整测量条件下检测桁架结构损伤的一种方法

提出一种利用不完整测量的模态数据检测桁架结构损伤的方法。首先采用改进的残余力向量法预先评估可能的损伤区域,在此基础上再利用特征值灵敏度法精确判断损伤位置和求解损伤程度。以一个平面桁架结构为算例验证该方法。结果表明,文中所提方法能在测量数据不完整的条件下成功识别出桁架结构的损伤情况。     

NON-LINEAR MECHANICAL SYSTEMS IDENTIFICATION USING LINEAR SYSTEMS WITH RANDOM PARAMETERS

A method to identify the parameters involved in the non-linear terms of randomly excited mechanical systems is presented. It is based on the minimisation of an index function which reflects the difference between an analytical approximation of the power-spectral density function response and the measured one. Using the concept of non-linear modes, an equivalent linear system with random parameters is used to approximate the power-spectral density. The method is applied to the ECL benchmark.     

结构损伤的一种两阶段诊断方法

提出一种结构损伤诊断的两阶段方法.利用不完整的模态测量数据,首先采用最佳逼近特征向量法, 预先评估可能的损伤区域,然后使用频率灵敏度法求解损伤程度.以平面桁架结构为例验证该方法,结果表明,文中所提方法是可行的.     

THE CONSTRUCTION OF PHYSICAL PARAMETERS FROM MODAL DATA

Some analytical models of vibrating systems may be expressed as a linear combination of known connectivity matrices. The connectivity matrices depend on the modelling method and the order of the approximation chosen, while the combination factors are determined by the physical parameters of the system. The physical parameters of such models can be identified from a single natural frequency, two mode shapes and a static deflection due to a unit load. It is shown that the identification process is determined by the solution of a certain generalised eigenvalue problem, where the physical parameter vector is proportional to one of its eigenvectors. It thus follows that generally for an n -degree-of-freedom (dof) system there are n possible solutions. Realisable solutions, however, correspond only to eigenvectors with no sign change in their entries and no vanishing elements, which limits the number of possible physical solutions. The results are demonstrated by an analytical example of an axially vibrating rod and a numerical solution for a Bernoulli–Euler beam.     

EVALUATION OF DAMPING NON-PROPORTIONALITY USING IDENTIFIED MODAL INFORMATION

This paper focuses on quantification of damping non-proportionality present in a discrete vibratory system. The study assumes that the information available is a set of identified system eigenvalues and eigenvectors and that the system parameters such as mass, stiffness, and damping matrices are unknown a priori. This set of modal parameters may be incomplete. The investigation is concentrated on how two existing analytical indices can be utilised when the modal damping matrix is not available. The quantification procedure starts with extraction of normal modes using a known algorithm. It is shown that two matrices, by-products of the normal model extraction, can be used to study damping non-proportionality. The first matrix is a scaled modal damping matrix. The paper shows that the indices developed from the scaled modal damping matrix preserves the properties of the indices based on the analytical modal damping matrix. The second matrix is a complex matrix which is obtained by expanding complex modes into the subspace of real modes. The off-diagonal elements of the complex matrix indicate coupling between modes due to damping non-proportionality. Based on this characteristic, three new indices are proposed. Numerical examples are presented to illustrate the use of the new indices and to compare them with the indices that are described in literature.     

用于结构共振疲劳寿命估计的应变模态分析

论述了共振疲劳与强迫振动疲劳的差异，强调了共振疲劳与结构的动态特性的关系。从位移模态推导了应变模态的表达式；讨论了利用应变模态分析的结果确定共振疲劳危险点位置原理和利用已知点应变时间历程确定危险点应变时间历程的方法。并讨论了利用动力修改技术避免共振疲劳的原理，最后以悬臂梁为模型进行了试验应变模态分析及疲劳试验，将悬臂梁的实际疲劳寿命与估计寿命进行了对比，说明了上述方法和原理的可行性     

STUDY OF NON-LINEAR STRUCTURE USING AN ELECTRONIC SLAVE HAMMER

Special electrical and mechanical devices are used to obtain an electronic many-head slave hammer which can produce successive force impulses with adjustable delays. We show how to use this hammer to decompose the structure response into components of various orders. The scientific framework is the Volterra series. Evaluation of impulse responses of different orders is presented as well as corresponding transfer functions. Eigenvalues of various orders are then evaluated and interpreted.     

电磁耦合无级变速传动系统

分析现有级联式电传动的优缺点,对其进行结构改进,形成一种电磁耦合无级变速传动系统。该系统主要由具有铁心绕组的转子和定子、附加调磁线圈、具有特殊磁极结构的杯形转子、感应式集流器和功率电子控制器等组成。该系统的特点是将级联式电传动与电磁滑差耦合式机械传动结合为一体,并加上非接触旋转输电,形成原动机的功率分汇流,配以变频与调磁相结合的调速手段,构成拓扑布局紧凑、调控性能优良、运转可靠的无级变速系统。经理论分析可知,系统在保持与常规电传动相当的宽广无级变速范围的同时,总体效率得到提高。系统在内燃机式汽车上使用时,可省去主离合器及发动机起动机等部件,配以储能电池组后,可以作为多能源动力总成直接应用于混合动力电动汽车上。     

模态应变能在复合材料机翼结构损伤检测中的应用

以复合材料机翼结构为研究对象，采用单元模态应变能改变率作为结构损伤标识量，对损伤结构进行损伤识别仿真。应用NASTRAN有限元程序对模型进行模态分析，模态分析的结果表明，单元模态应变能改变率对不同位置和不同程度损伤都具有较强的敏感性。应用神经网络成功识别了损伤的位置和程度，指出其可行性。     

一种基于神经网络的模态参数识别方法

提出一种利用神经网络结合自回归滑动平均时间序列分析来提取结构或系统模态参数的方法。这种方法首先运用神经网络计算出自回归滑动平均时间序列分析中的未知系数,然后提取出系统的模态参数。数值仿真及实验结果表明,该方法具有很高的识别精度、对噪声不敏感和具有很强的抗噪性的特性,这几点是传统时域辨识方法不具备的。文中提出的方法适合提取出实际系统的模态参数,对实际测量信号分析具有较好的参考价值。     

利用模态声发射技术监测飞机主结构件的日历损伤

研究了腐蚀特别是点腐蚀过程产生声发射(AE)的源机制及AE信号特点,推导了AE信号幅度与腐蚀深度及频率的关系,并说明该关系对利用AE技术监测腐蚀损伤的意义。论述了利用模态声发射(MAE)技术识别腐蚀AE信号的理论根据,介绍了利用MAE技术对飞机主结构件日历损伤进行评估的方法。基于试验获得的航空用铝合金材料在加速腐蚀过程中的声发射信号与腐蚀损伤的关系对研究材料损伤程度与声发射强度之间的内在联系有重要意义。试验表明,腐蚀能远在被肉眼发现之前即可很方便地用AE仪器检测,利用AE技术探测早期腐蚀、研究腐蚀发展规律、监测和评估腐蚀损伤具有极其良好的应用前景。     

汽车盘式刹车机构的模态与热力耦合分析

汽车盘式刹车机构在刹车片与刹车盘表面接触摩擦制动时导致刹车片发生振动,当刹车片振动频率与材料固有频率接近时,易导致片体结构暗裂崩溃。不同材料的刹车片的固有频率、与刹车盘摩擦作用产生的温度场、热力场各不相同。通过对不同的材料参数下刹车片的模态分析研究,使用Abaqus对刹车机构做显式动力学热力耦合分析;对输出的刹车片固有频率和刹车盘节点温度、位移、热应力等结果值进行对比,数据显示在刹车制动过程中复合材料的刹车片在避免共振、提高制动性能方面均要优于半金属材料。综合分析求解的结果在提高刹车制动机构的安全性与制动效能上有较大参考价值。     

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.     

基于固有频率变化的两焊点接头的疲劳损伤参量

使用有限元软件ABAQUS分析两焊点拉剪试样在疲劳裂纹扩展过程中的动态响应,研究固有频率随裂纹面积的变化.将裂纹截面积作为损伤面积,确定损伤与固有频率变化率的关系.利用损伤力学中损伤随寿命的演化规律,对疲劳损伤达到一定程度的试样进行疲劳寿命预测.结果表明,此损伤参量能较好地描述双焊点结构的疲劳破坏过程.