基于灵敏度分析的机械系统损伤识别方法

提出了一种基于振动灵敏度分析的机械系统损伤识别方法。该方法同时考虑了固有频率灵敏度和固有模态灵敏度 ,既可用于损伤定位 ,也能用于确定损伤大小 ,且对单个损伤和多个损伤情况都适用。为了提高识别的精度 ,考虑了二阶灵敏度。针对工程实际的需要 ,分析了不完备模态和模态测量误差对该方法识别精度的影响。算例表明 :本方法合理可靠 ,具有足够的精度。     

Matrix of the covariance of covariance of acceleration responses for damage detection from ambient vibration measurements

A new matrix on the covariance of covariance is formed from the auto/cross-correlation function of acceleration responses of a structure under white noise ambient excitation. The components of the covariance matrix are proved to be function of the modal parameters (modal frequency, mode shape, and damping parameter) of the structure. Information from all the vibration modes of the structure limited by the sampling frequency contributes to these components. The formulated covariance matrix contains more information on the vibration modes of the structure that cannot be obtained by the general methods for extracting modal parameters. When the component of the covariance matrix is used for damage detection, it is found more sensitive to local stiffness reduction than the first few modal frequencies and mode shapes obtained from ambient excitation. A simply supported 31 bar plane truss structure is studied numerically where a multiple damage scenario with different noise levels is identified with satisfactory results.     

Dynamic identification of a reinforced concrete damaged bridge

The results of a series of harmonically forced tests carried out on a reinforced concrete single-span bridge subjected to increasing levels of damage are interpreted in this paper. The deck structure of the bridge consists of a slab and three simply supported beams. The damage is represented by a series of notches made on a lateral beam to simulate the effect of incremental concentrated damage. The variation of lower natural frequencies shows an anomalous increase in the transition from one intermediate damage configuration to the next ones. Vibration mode shapes show an appreciable asymmetry in the reference configuration, despite the nominal symmetry of the bridge. A justification of this unexpected dynamic behavior is presented in this paper. The analysis is based on progressive identification of an accurate finite element model of the reference configuration and on reconstruction of damage evolution from natural frequency and vibration mode measurements. Changes in modal curvature of the first two vibration modes evaluated along the main beams are successfully used to identify the location of the damage.     

Dynamic characteristics of a damaged plate

It is very important to well understand the dynamic characteristics of damaged structures to successfully develop or to choose a most appropriate structural damage identification method (SDIM) as the means of non-destructive testing. In this paper, the dynamic equation of motion for damaged plates is derived by introducing a damage distribution function, which may characterize the effective state of structural damages. It is found that structural damages may induce the coupling between modal coordinates. The effects of damages on the vibration characteristics of a plate depending on their locations, sizes, and magnitudes are numerically investigated in a systematic way. The numerical investigations are also given to the effects of damage-induced modal coupling on the changes in vibration characteristics and to the minimum number of natural modes required to predict sufficiently accurate vibration characteristics of damaged plates.     

An experimental study on damage detection of structures using a timber beam

Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.     

动调陀螺组合体减振器的模态分析

使用有限元软件MSC／NASTRAN对动调陀螺组合体进行了模态分析与研究，并给出了陀螺组合体的15阶模态频率和振型。分析结果表明，陀螺组合体前6阶模态频率对其整体振动有很大的影响，同时验证了陀螺组合体的固有频率将远离外界激振频率，不会因为受到外界频率的激振而发生工作失效。     

基于振动能量分布的模态振型识别及频率继承性分析

在商用车振动系统中,对乘坐舒适性影响最大的是驾驶室悬置和前后主悬架。这两个参数对整车模态频率的分布起着关键的作用。为了研究整车频率分布与两者的关系,本文在整车多体动力学振动模型的基础上,分别建立驾驶室隔振系统模型和悬上质量(驾驶室和车架)隔振系统模型,并且提出以振动能量分布来识别振型的方法,确定整车振动系统中各阶模态来源。最后提出频率继承率的概念,并以此评价识别出的对应模态间联系的密切程度。模态来源与频率继承率将为后续的优化改进提供重要参考。     

Dynamic characteristics and model updating of damaged slab from ambient vibration measurements

This paper reports a field investigation using ambient vibration testing on a damaged floor slab of a reinforced concrete frame building. Due to unexpected heavy rainfall, the hill slope at the rear of building failed triggering a major landslide and causing major damage to the perimeter beams and parts of the slab on the first floor. The modal parameters namely natural frequencies and mode shapes were acquired using output only identification technique and the results obtained from the undamaged and damaged floor slabs were compared. It was observed that there was a 25–53% drop in natural frequencies of the damaged slab compared to the undamaged slab, with a much bigger drop for the lower modes. The irregularities in mode shapes identified correlates with the location of the cracks as revealed from visual examination on the damaged slab. Two finite element models of the slab were created using a finite element software package. The damaged slab was updated manually so as to match the modal parameters obtained experimentally. The results from this study further highlight the possibility and feasibility of using non-destructive vibration testing for condition monitoring of structures over more conventional testing techniques.     

基于应变模态的模态应变能损伤识别方法

传统模态应变能计算需要完备模态振型信息,而模态振型信息中存在转角自由度难以准确获取的问题,为解决该问题,开展基于应变模态的模态应变能损伤识别研究,实现了结构损伤的定量识别。首先,通过基于应变与位移之间的联系,推导出应变模态与位移模态之间的转换矩阵;其次,利用应变模态代替位移模态计算单元模态应变能,建立基于灵敏度分析的损伤识别方程组;最后,根据奇异值截断法求解该方程组识别结构损伤。以一两端固支梁结构为对象,开展数值仿真和实验研究。结果表明,该方法可以有效识别出结构的损伤位置和损伤程度,相对于基于振型扩充的模态应变能损伤识别方法,具有更好精度和抗噪性能。     

考虑转向架影响的重载货车车厢模态特性

为深入研究转向架对重载货车动力学特性的影响,以某空车工况的40t轴重矿石车为研究对象,在实车装配模型的基础上建立了整车及车厢的力学仿真模型,并应用有限元法对二者进行了模态分析。对实际车辆进行了模态实验研究,通过计算结果及实验结果的对比,从刚体振型及弹性体振型两个方面考察了转向架对重载货车车厢模态特性的影响。研究表明,转向架的质量、刚度及边界条件均会对模态计算结果产生影响,整车模型能更精确地描述实车的模态特性。     

基于MD.Nastran的某型机载雷达机箱力学仿真分析

基于MD.Nastran有限元分析软件,提出了某型机载雷达机箱的有限元建模方法,并对其分别进行了过载、模态和随机振动仿真分析.模态分析时采用Block lanczos方法求解了机箱的前十阶固有频率和振型.随机振动分析得出了各SRU(内场可更换单元)模块对基础激励的振动响应情况.仿真结果对该机箱的后续结构优化、减重设计有...     

Numerical investigation on vibration characteristics of a micro-speaker diaphragm considering thermoforming effects

Micro-speaker diaphragms play an important role in generating desired sound responses, and are designed to have thin membrane shapes for flexibility in the axial direction. The micro-speaker diaphragms are formed from thin polymer film through the thermoforming process, in which local thickness reductions occur due to strain localization. This thickness reduction results in a change in vibration characteristics of the diaphragm and different sound responses from that of the original design. In this study, the effect of this thickness change in the diaphragm on its vibration characteristics is numerically investigated by coupling thermoforming simulation, structural analysis and modal analysis. Thus, the thickness change in the diaphragm is calculated from the thermoforming simulation, and reflected in the further structural and modal analyses in order to estimate the relevant stiffness and vibration modes. Comparing these simulation results with those from a diaphragm with the uniform thickness, it is found that a local thickness reduction results in the stiffness reduction and the relevant change in the natural frequencies and the corresponding vibration modes.     

刚柔耦合动力系统固有振动特性研究

针对柔性基础上马达的隔振设计问题,建立了刚柔耦合机械系统的动力学方程,对机器基础的模态耦合振动和固有频率偏移进行了数值计算和试验研究。研究结果表明,耦合系统的基频小于机器的安装频率;在高频段,柔性基础模态为耦合系统的主导模态。     

Effect of modal filter errors on vibration control characteristics

When designing a control system for vibration suppression of flexible structures using modal control strategy, one must know the modal displacements and velocities of the controlled modes. If the vibration control forces are designed based on inaccurate modal states, the closed-loop performance of the vibration control system will be degraded depending on the extent of the modal filter errors. In this study, the effect of modal filter errors on the vibration control characteristics of flexible structures is analyzed for IMSC (Independent Modal Space Control). A Lyapunov asymptotic stability condition that depends on the magnitude of the modal filter errors is derived. The extent of the response deviation of the closed-loop system is also derived and evaluated using operator techniques. The extent of the response deviation is found to be proportional to the magnitude of the modal filter errors.     

PolyMAX法在自升式平台模型损伤检测中的应用

对某自升式海洋平台模型进行了脉冲锤击法试验模态研究.采用移动力锤法对自升式海洋平台模型无损伤和有损伤两种工况进行振动测试,对振动数据采用PolyMAX法进行模态分析,研究了两种工况下的结构动态特性.试验分析结果表明,PolyMAX方法在自升式海洋平台模型损伤检测中,不仅能够获得清晰的稳态图,还可以有效识别结构模态频率、模态振型;根据平台模型损伤前后的模态参数可知,平台模型损伤后X,Y方向的一阶频率均有明显降低,尤其是损伤处模态振型变化更为明显.该特征为自升式海洋平台损伤检测提供了一个依据.     

几种常用损伤动力指纹的适用性研究

通过讨论几种常用动力指纹的模态灵敏度,研究了它们的适用性。采用特征灵敏度分析技术,导出了频率、振型和模态柔度对结构参数的灵敏度计算表达式,在此基础上定义了模态加权指针来定量描述各阶模态的损伤动力指纹对结构损伤的灵敏度。通过典型模态稀疏和模态密集结构模型的数值模拟研究发现：对于模态稀疏的简单结构。低阶模态柔度对结构损伤较为敏感;对于模态密集的复杂结构。低阶频率、振型和模态柔度的损伤灵敏度均较差,而且模态柔度在低阶模态条件下远没有在高阶模态条件下对结构损伤敏感。     

基于贝叶斯运行模态分析法的砂轮架动态特性分析

为了研究砂轮架的固有模态和在工作环境中的谐波模态,运用贝叶斯理论和运行模态分析相结合的模态参数识别技术--分步测试的贝叶斯运行模态分析法对环境状态下的砂轮架进行模态识别,获得了结构的动态特性,包括固有频率、振型以及阻尼特性等,并对外激励和预测误差水平以及信噪比进行了评估;将该模态识别结果与传统试验模态分析结果进行对比,验证了贝叶斯运行模态分析法的应用可行性;进一步在工作环境下对砂轮架进行了振动测试,对比开机前的模态识别结果和开机后砂轮架的功率谱密度图,成功地区分出砂轮架的固有模态和实际工作环境中由结构周期激励引起的谐波模态。     

超声电机定子模态频率的调节

Langevin振子型杆式超声电机利用两个空间正交、同频的弯曲振动模态工作.由于Langevin振子具有预紧力沿周向分布不均、加工有误差和材料不均匀等缺陷,加工好的电机定子两相弯振模态频率往往不一致.本文从理论上分析了两相模态频率不一致对电机输出性能的影响,并提出了一种调节电机模态频率的方法.通过结构摄动理论可知,当在电机定子的合适位置去除或增加一块质量时,能改变其模态频率.求解定子的动力学方程,得出了定子修改后的模态频率.通过有限元分析和模态分析,确定了定子修改的合适位置.最后制作了定子样机,对修改前后的定子模态频率进行了测试.结果表明,两相弯振模态频率之差由原来的1 860 Hz调整到了0 Hz,验证了本文方法的正确性.本文方法在定子装配好的状态下,对其两相频率进行调节,可以降低超声电机的制作成本,提高电机的输出性能.     

快速液压夯实机关键部件的模态分析

利用ANSYS Workbench软件对HHT 3进行模态分析,得到箱体前6阶固有频率和相应的主振型,并与主要振源的工作频率进行比较.结果表明:HHT 3正常工作时,箱体夯锤的冲击振动频率和发动机振动频率均小于实际情况,因此不会发生共振.