基于摄动方法的受损薄板模态分析

将结构的损伤用δ函数进行表达，建立损伤条件下薄板的自由振动方程。利用一阶摄动方法给出摄动项的一般表达式，并结合δ函数的性质，求出受损薄板模态参数的解析表达式。以一个四边简支的受损薄板为数值算例，计算损伤条件下其模态参数的变化。最后分析损伤情况对模态参数的影响，为利用动力学特性对板的损伤监控和检测提供理论依据。     

受损悬臂梁的模态分析研究

基于Euler-Bernoulli梁的自由振动方程,利用一阶摄动方法,对受损悬臂梁进行了模态分析计算,并利用Pro/MECHANICA有限元结构分析软件对悬臂梁受损前后的模态进行分析,与摄动数值计算方法进行比较,验证摄动理论分析的正确性。通过具体算例,得出悬臂梁在受损前后前四阶固有频率,以及在各个固有频率下的位移、应力云图,从而验证了基于摄动法理论分析的正确性,为利用动力学特性对悬臂梁的损伤监控和检测提供了理论依据。     

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     

基于曲率模态与柔度曲率的损伤识别

以含两条裂纹的两端固定梁为例,采用曲率模态差和模态柔度曲率差来检测结构的损伤。首先将梁的裂纹模拟为无质量的等效扭转弹簧,推导了裂纹梁的特征微分方程,利用边界条件和裂纹位置的连续性条件推导得到该裂纹梁的振形函数解析表达式。然后用中心差分法分别求解裂纹梁损伤前后的曲率模态值和模态柔度曲率值,利用其差值确定梁的损伤位置,进而确定损伤程度。最后讨论了曲率模态和柔度曲率对结构损伤识别的敏感性。     

一种工作模态参数的在线时域辨识方法

根据环境激励具有随机性以及线性系统在环境激励下各输出点响应之间的相关函数与系统的脉冲响应函数具有相同的数学表达式等特点，给出了在线模态参数识别的理论，并提出了仅根据环境激励响应识别模态参数的新方法。     

基于模态参数识别的塔式起重机金属结构损伤检测有限元方法

以塔式起重机的一个标准节为研究对象,采用有限元软件对其金属结构进行了模态分析,分析了金属结构损伤位置和模态参数之间的关系,推导出了表征系统损伤位置的系统损伤矩阵表达式。并在Msc.Patran软件上进行了建模仿真,通过测量该模型系统的模态参数,利用损伤矩阵找出了结构的单一和多重损伤,验证了该方法的在该结构上的可行性。     

基于模态参数灵敏度分析的结构损伤识别研究

结构损伤通常以结构中刚度损失为特征。结构的损伤会引起结构参数的改变,结构参数变化会导致结构模态参数(固有频率、振型)的变化,因此寻求结构损伤与结构模态参数之间的关系十分重要。文中根据结构振动特征方程,推导了结构模态参数对结构参数改变的灵敏度表达式,建立了结构模态参数对以单元刚度为特征的结构损伤识别关系式,识别结构损伤的位置和损伤程度。文中制作了无损伤、有损伤3根悬臂梁钢板试件,测取试件结构固有频率与振型,根据无损伤试件结构图,建立了有限元模型,计算其结构固有频率与振型。将无损伤试件测得的模态参数作为有限元模型修正依据,并用两种损伤条件下测得的数据修正无损伤的有限元模型,将单元刚度作为修正参数,应用灵敏度方法来识别悬臂梁钢板试件损伤的位置和程度,其结果与实际基本一致,证明了方法的有效性。     

有色噪声激励下基于应变响应的频域拟合算法

提出了一种有色噪声激励下基于应变响应的工作模态参数识别方法。首先,从应变频响函数出发,将工作模态参数识别方法应用到有色激励下的应变响应信号,推导出仅利用应变响应的多自由度系统模态参数表达式;其次,对悬臂梁进行数值仿真,分析了模态识别误差并验证了该方法的有效性;最后,通过悬臂梁实验验证了在真实有色噪声环境中,该方法依然具有很高的识别精度。     

复合L形宽频压电悬臂梁的建模与仿真

为提高单频压电悬臂梁的振动能量采集转换效率,提出一种复合L形压电悬臂梁的宽频拓展技术,通过在单频压电悬臂梁水平结构中增加一个辅助垂直悬臂梁,组成L形压电悬臂梁,通过控制L形压电悬臂梁的结构和材料参数使悬臂梁的2阶模态频率为1阶模态频率的2倍,将1阶、2阶模态频率串联起来形成一个宽频的谐振带。利用拉格朗日方程和模态假设法建立了L形压电悬臂梁的频率方程和振动方程,通过数值仿真分析了L形压电悬臂梁结构和材料参数对其频率特性和振动特性的影响,并确定了系统的最佳结构和材料参数,实例验证了悬臂梁宽频拓展方法的正确性。     

失谐对叶片一轮盘结构振动特性的影响

研究了失谐对叶片一轮盘结构系统振动特性的影响。将叶片模拟为固定在轮盘上的悬臂梁模型，采用Hamilton变分原理和Galerkin方法，导出了系统的运动方程表达式。求解状态方程的特征值问题获得系统的特征向量。以一个含16个叶片的叶片一轮盘结构为例，分析了它的振动模态。结果表明，失谐会导致系统的振动模态出现局部化现象。分析了叶片的失谐量和轮盘的转速对结构振动模态局部化的影响。     

一种基于模型修改的结构多点损伤识别方法

可用于结构损伤识别的方法很多。一般来讲正向方法直接利用结构模态参数的变化，逆向方法则利用模态参数变化反演结构物理参数变化，还有些方法利用了神经网络和模式识别技术。文中利用模型修改的思想，通过逆向方法计算结构单元刚度变化系数来对结构的多点损伤进行识别。以一个七自由度弹簧阻尼质量系统作为研究对象，用数值模拟方法及特征系统实现算法计算系统的模态参数，并用这些模态参数验证所提出方法的可行性，结果表明该方法对多点损伤的识别是简单而可行的。     

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.     

运用拓扑优化的结构损伤定位

以结构共振频率和结构某点的反共振频率为基础,对拓扑优化中的渐进结构优化法应用于结构损伤定位的可行性进行了研究。基于结构共振频率和反共振频率的灵敏度分析,建立了损伤定位的数学模型,提出了利用渐进结构优化法进行损伤定位的策略。针对单一和多处损伤结构,分别给出了损伤定位的数值算例,对不同的损伤结构予以讨论,并准确识别出了损伤位置。结果表明,在已经测得结构损伤前后共振频率和反共振频率的基础上,渐进结构优化法能够在整个结构区域内寻找损伤点,有较好的搜寻效果。     

A frequency response function-based damage identification method for cylindrical shell structures

In this paper, a structural damage identification method (SDIM) is developed for cylindrical shells and the numerically simulated damage identification tests are conducted to study the feasibility of the proposed SDIM. The SDIM is derived from the frequency response function solved from the structural dynamic equations of damaged cylindrical shells. A damage distribution function is used to represent the distribution and magnitudes of the local damages within a cylindrical shell. In contrast with most existing modal parameters-based SDIMs which require the modal parameters measured in both intact and damaged states, the present SDIM requires only the FRF-data measured in the damaged state. By virtue of utilizing FRF-data, one is able to make the inverse problem of damage identification well-posed by choosing as many sets of excitation frequency and FRF measurement point as needed to obtain a sufficient number of equations.     

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.     

DAMAGE IDENTIFICATION USING CHANGES OF EIGENFREQUENCIES AND MODE SHAPES

In the present paper, we describe an approach to identify the location and the extent of the damage introduced into the steel frame, using a two-step procedure. In the first step, the measured dynamic response of the original undamaged structure was used to generate a reference finite element (FE) model of the structure. The selected parameters were identified by means of a mathematical optimisation algorithm (‘updating procedure'), minimising an objective function containing the test/analyses differences of eigenfrequencies and mode shapes. The uncertain model parameters had to be chosen with care in order to retain the physical significance of the updated model. In the next step, the experimental modal data of the damaged structure were used to identify the extent of the damages. This was based on comparing the changes of stiffness parameters identified from the undamaged and the damaged structure. With the identified parameters, the FE model was able to reproduce the experimental data as close as possible and allowed the identification of the extent of the damage.     

Damage detection in frame structures using damage locating vectors

Among the numerous vibration based damage detection methods, some are using dynamically measured flexibility matrix to detect and locate damage in the structure. One of the methods in this category is damage locating vector (DLV). It is based on extracting a set of load vectors from flexibility shifts that cause the same deformation in damaged and undamaged structures. As a result, the damaged member can be located by studying the characterizing stress of all members. In this study, the application of DLV method on damage detection of 3D frame structure was conducted. Some factors like the number of measured DOFs and the accuracy of modal data were assumed to be ideal so that other parameters could be examined. The characterizing stress for a 3D structure and the accuracy of damage index in different damage scenarios are discussed.     

损伤识别在车用储氢容器模态试验中的应用

针对车用高压储氢容器的复合纤维缠绕结构在其使用过程中的安全问题,开展了体积为0.074m3车用纤维缠绕储氢容器的模态试验研究。根据完好容器、反复充装引起的桶身轻微损伤和疲劳破裂两种疲劳损伤状态容器的模态分析,探讨了基于模态参数进行损伤识别的可行性。研究表明,无论是轻微损伤还是疲劳破裂状态,局部的疲劳裂纹对损伤前后的频响函数有一定影响但并不敏感,无法基于频率响应函数判定损伤是否发生并确定损伤位置,但基于损伤前后振型比较可以实现损伤判定并预测损伤位置。该研究为确定车用储氢结构的在线损伤识别奠定了实践基础。