基于频率的叠层橡胶隔震支座损伤识别研究

提出一种基于自振频率的叠层橡胶隔震支座的损伤识别方法.通过叠层橡胶隔震支座的周期结构特性,利用周期结构特征波导纳法,推导自振频率与基本周期单元整体剪切模量变化之间的关系,建立自振频率变化率对单元损伤的敏感性识别方程组,并采用约束优化方法求解该识别方程组,实现基于自振频率变化的叠层橡胶隔震支座的损伤识别.算例模型考虑了上部结构对底层橡胶支座的影响,使计算模型更加符合工程实际.通过三维有限元数值仿真分析验证了本文所提损伤识别方法的有效性和精确性.     

基于特征波导纳法和敏感性分析的大型周期支撑结构损伤识别EI北大核心CSCD

提出了一种基于特征波导纳法和敏感性分析的大型周期支撑结构损伤识别方法。通过分析存在单一损伤单元有限周期支撑结构的自由波传播规律,建立了周期结构无量纲自振频率变化对基本周期单元刚度变化的敏感性分析矩阵;求解敏感性识别方程组,实现基于测量自振频率变化的大型周期支撑结构损伤检测;同时,分析表明所提出无量纲自振频率的敏感性与结构参数无关,即无需知道原始结构的准确几何物理参数就能确定敏感性系数。分别以一周期支撑梁与周期支撑法兰接头管道为例进行研究,表明该方法仅用量测损伤前后的前几阶自振频率变化就能较准确地进行周期支撑结构多损伤识别。     

基于脉动法的上海市RC剪力墙结构基本自振周期测试与分析

针对我国现行规范中剪力墙结构的基本自振周期经验公式是基于高度在50 m以下的建筑实测数据拟合而成的现状,基于脉动法对上海市已建成的总高度在45～90 m之间的62栋RC剪力墙结构进行了现场动力性能测试,识别了结构在水平纵向与横向的基本自振周期.采用其中60栋结构的数据进行了回归分析,分别给出了基于结构高宽比和幂次高度...     

基于分形的结构损伤检测方法

将分形维数用于结构损伤检测。研究结果表明,结构不同状态下的振动信号的分形维数有明显的不同,可以将分形维数作为结构损伤检测的特征量,为结构的损伤检测技术提供了一个新的分析方法。     

基于小波分析的结构损伤检测

损伤结构的动力特性具有局部时变的特征，小波变换在时域和频域都具有表征信号局部特征的能力，小波包分析利用可以伸缩和平移的可变视窗能够聚焦到信号的任意细节，因此可以对损伤结构的非线性动力特性能进行有效的分析。提出运用小波分析提取结构损伤特征向量的方法和基本原理，并进一步用神经网络进行损伤位置和程度的检测。文章通过一个两层框架的模型对小波神经网络和传统的BP网络的损伤识别精度作了对比。研究表明，小波神经网络的抗噪声能力较强，损伤识别的效果更好，运用小波神经网络进行结构损伤识别精度要优于传统的BP网络。     

基于有限元仿真的简支梁结构损伤分析

分析了简支梁结构的振动特性,建立了该结构损伤前后的有限元分析模型,模拟计算了简支梁结构在未损伤、一个损伤、两个损伤和三个损伤状况下的固有频率和振型,重点研究了不同损伤状况对它们的影响.发现损伤裂纹可使简支梁结构的固有频率降低,且其降低幅度随裂纹深度增大而增大,但不同位置的裂纹所产生的影响并不相同.模拟计算结果对简支梁结...     

某复杂高层建筑结构时程分析

运用有限元程序ANSYS 对某复杂高层建筑结构进行了模态分析及地震载荷作用下的时程分析,通过计算得出了结构的前20 阶频率、振型,并进一步计算了在地震作用下时程分析的位移及内力,结果表明该结构具有很大的抗侧刚度,且沿高度分布均匀,自振频率满足结构使用要求,为结构设计提供了可靠的参考数据.     

高层建筑结构动力稳定分析中自振周期的简化计算

对复杂的高层建筑结构非线性动力稳定分析中结构自振周期的计算和确定，提出了一种实用的简化方法，工程算例表明，本方法实用简便，又满足工程计算精度要求。     

基于动柔度变化的结构损伤检测

采用一个四自由度的弹簧－质量系统。通过数据计算表明以动柔度作为损伤识别参数比单独用固有频率或振型时的灵敏度高。本文提出了以动柔变化矢量为损伤识别参数,采用神经网络方法建立了动柔度变化矢量与损伤位置和损伤量的关系,解决了结构的损伤定位和定量识别问题,用一个混凝土简支梁模型对该方法进行了验证,说明该方法是切实可行的。     

复合支护结构自振特性的不确定性分析

本文主要研究复合支护结构自振特性的计算方法及其变异性问题，对结构自振频率采用修正系数的方法进行分析，即先计算等厚度整半砌结构的自振频率，然后按照两次衬砌厚度比，衬砌之间和周围土体的约束刚度两个修正系数进行修正得到复合支护结构的自振频率，并对所得到频率的不确定性中心点一次二阶距进行分析，由各影响因素及计算方法本身的确定必到了自振频率的变异系数。     

基于频率灵敏度方法的宏微运动平台连接架结构优化

连接架与驱动设备频率相近而发生共振,将影响宏微运动平台的稳定工作和超精密定位的实现.为避免共振,本文以连接架为研究对象,搭建连接架固有频率有限元分析模型,并对有限元模型进行实验验证.然后,基于频率灵敏度方法对有限元模型结构参数进行摄动,通过分析刚度和第1阶固有频率对结构参数的灵敏度,进行设计变量选择,再以连接架质量为约束条件,将连接架第1阶固有频率倒数作为目标函数,对连接架优化模型进行优化并进行实验验证.通过优化,连接架第1阶固有频率得到了有效的提高,避免了连接架与音圈电机发生共振,从而为宏微运动平台稳定工作和超精密定位提供可靠依据.     

Modification of dynamic characteristics of FGM plates with integrated piezoelectric layers using first‐ and second‐order approximations

This paper proposes a method for calculating the required changes in the physical properties of plates made of functionally graded materials (FGM) in order to achieve the desired eigenfrequency shifts in the structure. A finite element formulation based on the classical laminated plate theory (CLPT) is presented for an FGM plate with integrated piezoelectric layers. Using this formulation, an efficient method based on the first‐order and second‐order approximations in Taylor expansion is expressed to calculate the corresponding changes in the plate modal properties due to changes in parameters which characterize the structure's dynamic behaviour. An initial sensitivity analysis is carried out to identify the regions within the structure where modifications are most effective on the structure's dynamic characteristics. The proposed algorithm is applied to a case study with two different boundary conditions and the results are validated against exact solutions. The influence of structural modifications on dynamic response of the plate is also studied using the Newmark‐β method. Copyright © 2006 John Wiley & Sons, Ltd.     

Determining the Progression of Damage in Materials Subjected to Sustained Random Loads Using an Adaptive Finite Impulse Response Approach

It is often important to establish the ability of materials to withstand dynamic loads. This ability is best determined by subjecting the elements to sustained random loads under controlled conditions. It is during these fatigue endurance tests that the loss of structural integrity of a material or an element needs to be quantified. The research presented herein uses a recently developed continuous structural integrity assessment technique to evaluate variations in the mechanical properties (namely stiffness) of materials. The effectiveness of the technique was evaluated by undertaking controlled experiments, during which damage was simulated by varying the stiffness (in this case the length of a cantilever beam) of a physical single degree‐of‐freedom vibratory system subjected to random base excitation. Additional experiments where materials were allowed to naturally decay (structurally) under sustained random loads were also performed. Overall, the results presented in this study indicate that the technique can be a practical and effective tool for detecting small variations in the structural integrity of materials subjected to sustained random loads.     

基于有限元的手套包装机检测机构分析

手套漏气检测装置是手套漏气检测设备的核心所在,其稳定性对手套漏气检测精度有着重要的影响。为了降低手套漏气检测装置的变形和振动对手套漏气检测精度的影响,以手套漏气检测装置的支架为研究对象,运用SolidWorks对检测支架进行三维模型绘制且保存为parasolid格式导入到ANSYS Workbench中进行分析,得到检测支架形变量为0.009mm,变形量非常小,对检测精度造成的影响可以由PLC内部程序设置的修正值予以消除。再对检测支架进行模态分析和谐响应分析,得到前六阶固有频率、振型以及振幅与频率的关系,通过对比模态分析与谐响应分析结果,发现三阶固有频率186.43Hz对检测支架影响较大,容易引起共振现象。     

应用移动质量法与分形维数实现梁损伤检测

以简支裂纹梁为例,利用移动质量法结合分形维数方法实现结构损伤检测。由于质量块在振动梁不同位置时对梁固有频率的影响不同,所以当质量块沿着梁长度方向移动时可以得到一组梁－质量块系统的固有频率曲线,通过分析这组固有频率的分形维数曲线确定梁的损伤位置及其损伤程度。随后讨论附加质量块大小和分形方法参数选择对损伤检测精确性的影响。数值计算结果表明,该方法能准确的识别裂纹位置和损伤程度。该方法的主要优点在于不需要结构的模态信息,并可以在随机激励下实现。     

基于时间序列模型自回归系数灵敏度分析的结构损伤识别方法

该文在分析了时间序列模型的自回归系数对结构单元刚度灵敏度的基础上,提出了一种采用随机载荷作用下结构的时域响应数据进行损伤识别的新方法。该方法首先根据随机载荷作用下的结构响应拟合适用的时序模型;然后建立基于自回归系数的损伤灵敏度矩阵,通过该矩阵可以建立由单元损伤导致的自回归系数的变化与损伤系数变化之间的关系;最后通过求解损伤系数向量来识别损伤位置和损伤程度。对一悬臂梁结构损伤识别的数值结果表明:在计入1%和2%测量噪声的情况下,该方法仅利用单个传感器的时域测量数据,就能够较好地识别单个单元和多个单元损伤;如果对基于多个传感器的识别结果进行综合,识别结果则更加准确、可靠。     

On Crack Detection in Tuned and Mistuned Repeating Structures Using the Modal Assurance Criterion

Repeating structures in the form of multiple‐bladed rotors are used widely in turbomachinery. Mistuning in turbomachinery is caused by small differences in individual blade properties because of inevitable material and manufacturing variations, resulting in the splitting of vibration modes of the tuned system. Modal characteristics of the blades are quite sensitive to the level of mistuning present inside the structure. In addition, the existence of damage also results in changed dynamics of the complete system. This paper introduces a modal assurance criterion (MAC)‐based approach for the investigation of small defects such as cracks in a repeating structure. In order to understand the key issues involved, initial work involved a numerical study of a simple comb‐like repeating structure, followed by a detailed numerical and experimental investigation of a tuned and mistuned bladed disc. Changes to the system mode shapes and mode order arising from damage are related to the location and severity of damage. Damage, in the form of small, open cracks, is modelled using different techniques such as follows: material removal, monotonic reduction in the modulus of elasticity of selected elements at the required location and mass modification. Damage indices based on differences in the MAC that give a measure of the change in the mode shapes are introduced. MAC matrices are obtained using a reduced number of data points. The damage index is obtained from the Frobenius norm of the MAC matrix subtracted from the AutoMAC of a reference tuned model without crack. A clear correlation between the damage indices and the crack depth/location is shown. Application of this approach to the limited data obtainable from developing techniques such as blade tip timing is also explained.