基于不完备实测模态数据的结构损伤识别方法研究

在传统的基于模型修正的损伤识别中,由于实测模态信息有限而待识别参数过多,往往导致损伤识别方程出现较大误差,从而限制了该方法在复杂结构中的应用。为解决这一问题,对结构的自由度进行了分解,将损伤结构中模态振型的未测量部分表达为已测量到的模态振型、模态频率以及结构其它参数的函数。将损伤视为结构单元刚度的减小,利用完好结构的计算模态数据以及损伤结构扩充后的实测模态数据,建立了结构的损伤识别方程。运用信赖域优化算法对具有双重约束条件的目标函数进行最小化,识别出了结构各单元的刚度损伤参数。通过两个损伤识别数值仿真算例及实验验证,结果表明,在测点数量有限及测试噪声等不利因素影响下,所提方法只需运用少量的实测模态信息,即可实现结构损伤位置及程度的准确识别,同时算法具有较好的鲁棒性。     

基于静动力凝聚及扩展卡尔曼滤波的连续梁桥损伤识别

以卡尔曼滤波算法为代表的物理参数识别方法在结构损伤识别方面得到广泛应用,但限于状态方程的复杂性,大部分应用集中在具有平动自由度的剪切型建筑结构模型,且一般需要较完备的激励和响应信息。利用静力凝聚方法消去转动自由度以建立力学模型,并提出考虑Rayleigh阻尼的动力凝聚方法,实现了较复杂连续梁桥有限元模型的等效简化。针对桥梁检测及健康监测需求,提出了利用锤击产生自由振动的激励方式进行连续梁桥扩展卡尔曼滤波在线损伤识别方法,从而克服了传统方法需要复杂激励信号的不足。以一座三跨连续梁桥为例进行了仿真分析,识别出了不同位置的刚度和阻尼物理参数,参数识别结果具有较高精度和抗噪性,收敛速度快,证明该方法有效可行。     

基于频率变化识别结构损伤的摄动有限元方法

在结构有限元计算模型中定义了单元的损伤识别参数,将摄动理论与振动理论相结合导出结构振动特征值的一、二阶摄动方程,并由此建立了结构的一、二次损伤识别方程,给出了两种方程在欠定情况下求解损伤识别参数的优化算法。该方法仅使用在役结构固有频率测量值就能识别出结构的损伤位置和损伤程度,以及结构的老化程度,避免了使用模态振型识别结构损伤,因测量精度不高或自由度不足带来的误差。通过一座连续梁桥损伤识别的数值仿真结果,证明了该方法的有效性和实用性。该方法可用于大型结构的损伤识别或健康监测。     

一种模态振型的直接扩阶方法

传统的模型缩阶及模态扩阶方法是以计算传递矩阵为手段.该文提出一种实测模态振型空间不完备问题的直接处理方法,即未测试自由度振型值的直接估计方法.通过引入一复合向量,该向量由对应于主自由度的实测振型值与对应于从自由度的待估算值组成.依靠实测模态及有限元模型信息对复合向量中未测试自由度的振型值进行重新估算,进而获得空间完备的模态振型.该文采用5 自由度的弹簧-质量体系验证方法的正确性;借助平面框架结构探讨新方法较传统方法在低阶模态振型估算精度上的优势.数值结果表明:所提出方法不需质量归一化条件以及实测模态与有限元振型的比例条件;同时,该方法较传统方法在低阶模态振型扩阶上具有更好的精度,并允许有限元模型具有一定的模型误差.     

Structural shape optimization using equivalent static loads transformed from dynamic loads

In structural optimization, static loads are generally utilized although real external forces are dynamic. Dynamic loads have been considered only in small‐scale problems. Recently, an algorithm for dynamic response optimization using transformation of dynamic loads into equivalent static loads has been proposed. The transformation is conducted to match the displacement fields from dynamic and static analyses. This algorithm can be applied to large‐scale problems. However, the application has been limited to size optimization. The present study applies the algorithm to shape optimization. Because the number of degrees of freedom of finite element models is usually very large in shape optimization, it is difficult to conduct dynamic response optimization with conventional methods that directly treat dynamic response in the time domain. The optimization process is carried out by interfacing an optimization system and an analysis system for structural dynamics. Various examples are solved to verify the algorithm. The results are compared to the results from static loads. It is found that the algorithm using static loads transformed from dynamic loads based on displacement is valid for very large‐scale shape optimization problems. Copyright © 2005 John Wiley & Sons, Ltd.     

Novel displacement function for discontinuous deformation analysis based on mean value coordinates

The rotation degree of freedom in discontinuous deformation analysis (DDA) may cause false volume expansion when a block undergoes a large rotation. We propose a block displacement function to prevent this defect. Specifically, the degrees of freedom in a block are redefined by incremental displacements at its vertices, and displacement is formulated based on the mean value coordinates. In addition, the finite element method with updated Lagrangian formulation is employed to derive the equilibrium equations, while the contact analysis and implicit time integration for dynamics is maintained from the original DDA. After each time step, the block configuration is updated by adding the new degrees of freedom to the previous coordinates of the block vertices. Results from numerical examples confirm the effectiveness of the proposed approach to prevent false volume expansion, ensure correctness of contact analysis, and provide realistic stress results when simulating large rotations.     

A New Locking Free Higher Order Finite Element Formulation for Composite Beams.

A refined 2-node, 7 DOF/node beam element formulation is presented in this paper. This formulation is based on higher order shear deformation theory with lateral contraction for axial-flexural-shear coupled deformation in asymmetrically stacked laminated composite beams. In addition to axial, transverse and rotational degrees of freedom, the formulation also incorporates the lateral contraction and its higher order counterparts as degrees of freedom. The element shape functions are derived by solving the static part of the governing equations. The element considers general ply stacking and the numerical results shows that the element exhibits super convergent property. The efficiency of the element in capturing both the static and dynamic inter-laminar stresses is demonstrated. The accuracy of the element to capture free vibration and wave propogation responses with small problem sizes is also demonstrated.     

Comparative analysis of three-dimensional frames by dynamic relaxation methods

Analysis of three-dimensional frames is a complex process. Each node of these structures has six degrees of freedom, which results in a large set of governing equations. Investigators have utilized the computer power to extend the application of numerical approaches. One of these methods is named dynamic relaxation technique. This strategy explicitly solves the simultaneous system of equations. In this scheme, the static structural equilibrium equations are converted into a dynamic one by adding fictitious mass and damping. To perform nonlinear geometric analysis of 3D frames, 12 classical DR methods are exploited. Previously, the abilities of these approaches in analyzing these structures have not been compared. In each technique, time step, mass, and damping matrices are obtained based on other researchers' works. The structural behavior is assessed with and without considering the shear deformations. For both cases, the load–displacement curves are depicted. In this article, 11 different frames are analyzed. Since a few nonlinear solutions of 3D frames are available, these structures can be used as a benchmark in the future studies. Finally, the used algorithms are graded based on their required number of iterations and analysis time. Findings prove that the Qiang, Rezaiee-Pajand and Sarafrzi techniques perform more successfully in comparison to the other schemes.     

叶片局部损伤对大型水平轴风力机静动态特性影响的仿真分析

基于参数化整机模型研究风力机的静态和动态特性,以及叶片局部损伤对单叶片和整机的静动态特性影响规律,揭示叶片局部损伤与这些特性的关系。使用ANSYS的APDL语言,实现MW级水平轴风力机复合材料叶片的参数化建模;采用公共几何元素、连接单元和自由度耦合等方法,组建包含叶片、轮毂、塔架等部件的整机有限元模型。计算分析了重力、离心力和风压力共同作用下正常整机和包含叶片局部损伤的整机在迎风位置时的静态响应。比较了正常和损伤状态下根部固定单叶片和装入整机中叶片的动态应变响应。研究表明:对根部固定的单叶片,风轮面内的动态应变响应随迎风面损伤程度的增大而减小;对整机中的叶片,垂直风轮面的动态应变响应随迎风面损伤程度的增大而增大。研究方法和结论对大型水平轴风力机叶片损伤的在线监测具有重要 意义。     

未知地震激励下结构恢复力及质量非参数化识别

地震作用过程中结构恢复力是描述结构损伤发生发展过程定量描述的基础,更有助于描述结构在地震中破坏模式的演化。该文研究地震激励下结构部分质量及动力响应信息未知时,结构非线性恢复力、质量以及未知加速度时程的非参数化识别方法。首先,根据部分已知动力响应测量和质量信息,识别地震加速度时程。随后,利用记忆衰退全局加权迭代扩展卡尔曼滤波算法,引入幂级数多项式表征结构恢复力,实现了结构质量与非线性恢复力的非参数化识别。将具有非线性恢复力的磁流变阻尼器中引入到一个剪切型多自由度结构构成非线性系统,考虑测量噪声的影响,通过数值模拟验证了在噪声及较大质量初始误差情况下该方法识别结构质量、非线性恢复力及地震动加速度时程的识别效果。     

Improved dynamic analysis of structures with mechanical uncertainties under deterministic input

This paper addresses the dynamic analysis of linear systems with uncertain parameters subjected to deterministic excitation. The conventional methods dealing with stochastic structures are based on series expansion of stochastic quantities with respect to uncertain parameters, by means of either Taylor expansion, perturbation technique or Neumann expansion and evaluate the first- and second-order moments of the response by solving deterministic equations. Unfortunately, these methods lead to significant error when the coefficients of variation of uncertainties are relatively large. Herein, an improved first-order perturbation approach is proposed, which considers the stochastic quantities as the sum of their mean and deviation. Comparisons with conventional second-order perturbation approach and Monte Carlo simulations illustrate the efficiency of the proposed method. Applications are discussed in order to investigate the influence of mass, damping and stiffness uncertainty on the dynamic response of the system.     

A transverse shear deformation theory for homogeneous monoclinic plates

Summary A general two-dimensional theory suitable for the static and/or dynamic analysis of a transverse shear deformable plate, constructed of a homogeneous, monoclinic, linearly elastic material and subjected to any type of shear tractions at its lateral planes, is presented. Developed on the basis of Hamilton's principle, in conjunction with the method of Lagrange multipliers, this new theory accounts for an unlimited number of choices of through-thickness displacement distributions, while, starting with the smallest possible number of independent displacement components (five, for a shear deformation theory), it is capable of further operating with as many degrees of freedom as desired. For the particular case of a theory operating with five degrees of freedom, special attention is given to displacement expansions producing symmetric, through thicknes, distributions of transverse shear strain. For the cylindrical bending problem of a specially orthotropic plate, the governing equations of that five-degrees-of-freedom theory are solved and for three different choices of symmetric, through tickness, transverse shear deformation, numerical results are obtained and compared with corresponding results based on the exact three-dimensional solution existing in the literature. The comparisons made show clearly, that the multiple options offered by the new theory, by either suitably altering the displacement expansions or gradually increasing the degrees of freedom involved, will be found useful in future studies dealing with the static and/or dynamic analysis of homogeneous plates.     

有限位移下张力腿平台的非线性动力响应

与一阶无限小位移情况不同,张力腿平台(TLP)发生有限位移时,所受外力与响应耦合,运动方程也必须在瞬时位置建立。建立了有限位移情况下张力腿平台非线性动力响应分析模型,其中考虑了由六自由度有限位移引起的多种非线性因素,如各自由度之间的耦合、瞬时位置、瞬时湿表面等;还包括自由表面效应、粘性力等因素引起的非线性。推导出张力腿平台六自由度有限运动非线性控制方程。对一个名为“ISSCTLP”的典型张力腿平台进行了数值计算,求得该平台在规则波作用下的六自由度运动响应。用退化到线性范围的解与已有解进行了对比,吻合良好。数值结果表明,综合考虑非线性因素后响应有明显改变。     

火炮多柔体系统动力学的自动建模技术

本文介绍了火炮多柔体系统动力学的自动建模技术,包括火炮多体系统拓扑结构的自动识别、坐标系及自由度的自动确定、运动学公式的自动推导、载荷的自动施加、运动微分方程的自动组集和自动求解等。建模过程的自动化避免了繁琐的人工推导,并且可实现模型的通用性,从而可在计算机上方便地对任意类型火炮的发射过程进行仿真,有效地用于火炮设计。     

基于动力推覆方法的储液罐抗震分析

为有效评估储液罐在弹塑性阶段的抗震性能,经凝聚流体域压力自由度,建立流固耦合系统的等效动力方程,然后合并同频振型并基于广义逆理论导出谱加速度-谱位移性能曲线的投影方程,并通过控制谐波参数实现流固耦合系统的单向动力推覆,以此确定性能曲线并作为储液罐的单自由度广义本构模型。时程分析表明:上述广义本构模型的滞回曲线及时程结果与流固耦合系统吻合良好,罐体刚度均呈渐近退化。该文方法与静力推覆分析的计算耗时大致相仿,消除了特征节点对性能曲线的影响,并可考虑弹塑性阶段内罐体抗力分布的改变。     

结构物理参数时域识别的子结构方法研究

研究了输入、输出信息皆不完备情况下的结构参数识别以及荷载反演问题。阐述了一种通用的子结构动力方程及其参数识别方程建立的基本原理和方法,并针对实际工程检测中子结构参数识别方程的输入特性,分别采用一种与之相适应的分解反演算法或统计平均算法。子结构技术与分解算法或统计平均算法的有效结合,为有限测点条件下的结构参数识别及荷载反演问题提供了一个较好的解决方案。大量的数值计算结果表明,本文提出的方法具有很好的参数识别精度及荷载反演效果。     

部分观测下基于子结构的大型结构损伤诊断法

该文提出一种适用于大型结构在激励与响应部分观测情况下进行结构损伤诊断的方法。基于有限元模型,大型结构被划分成若干个子结构。相邻子结构间的作用,视为对子结构的“附加未知激励”。依次采用扩展卡尔曼估计和最小二乘估计识别扩展状态向量和未知外部激励,在子结构界面响应未观测的情况下,对各子结构的单元动力参数分别进行识别,并以追踪子结构内单元结构参数的变化,例如单元刚度的退化,对大型结构的局部损伤进行诊断。通过一个较大型的平面桁架桥的损伤识别数值算例,证实了该方法的可行性。与其他方法相比,提出的方法减少了对结构响应观测的要求。     

结构动力分析的静态子结构法

文中把静态子结构法与 Ritz 向量直接叠加法相结合,构成了结构动力分析的静态子结构方法,这一方法对于大型结构的动力分析问题是十分有效的。     

A shell element for the prediction of residual load-carrying capacities due to delamination

This paper deals with layered plates and shells subjected to static loading. The kinematic assumptions are extended by a jump function in dependence of a damage parameter. Additionally, an intermediate layer is arranged at any position of the laminate. This allows numerical simulation of onset and growth of delaminations. The equations of the boundary value problem include besides the equilibrium in terms of stress resultants, the local equilibrium in terms of stresses, the geometric field equations, the constitutive equations, and a constraint which enforces the correct shape of a superposed displacement field through the thickness as well as boundary conditions. The weak form of the boundary value problem and the associated finite element formulation for quadrilaterals is derived. The developed shell element possesses the usual 5 or 6 degrees of freedom at the nodes. This is an essential feature since standard geometrical boundary conditions can be applied and the elements are applicable to shell intersection problems. With the developed model, residual load-carrying capacities of layered shells due to delamination failure are computed.     

Mesoscale magnetism

Magnetic interactions give rise to a surprising amount of complexity due to the fact that both static and dynamic magnetic properties are governed by competing short-range exchange interactions and long-range dipolar coupling. Even though the underlying dynamical equations are well established, the connection of magnetization dynamics to other degrees of freedom, such as optical excitations, charge and heat flow, or mechanical motion, make magnetism a mesoscale research problem that is still wide open for exploration. Synthesizing magnetic materials and heterostructures with tailored properties will allow to take advantage of magnetic interactions spanning many length-scales, which can be probed with advanced spectroscopy and microscopy and modeled with multi-scale simulations. This review highlights some of the current basic research topics in mesoscale magnetism, which beyond their fundamental science impact are also expected to influence applications ranging from information technologies to magnetism based energy conversion.