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 probabilistic damage identification approach for structures with uncertainties under unknown input

To avoid the false positives of damages in the deterministic identification method induced by uncertainties in measurement noise, a probabilistic method is proposed to identify damages of the structures with uncertainties under unknown input. The proposed probabilistic method is developed from a deterministic simultaneous identification method of structural physical parameters and input based on dynamic response sensitivity. The deterministic simultaneous identification method is first derived. The effect of uncertainties caused by measurement noise on the identified parameters is then investigated. The statistical parameters of the identified structural parameters are calculated. The damage index is derived from the statistical parameters of the physical parameters of intact and damaged structure. The probability of identified damage, defined as the probability of identified structural stiffness smaller than that of intact structure, is further derived using the probability method. A twelve-story building and a nine-bay three-dimensional frame structure are, respectively, analyzed numerically and experimentally using the proposed method. The research results indicate that the probabilistic simultaneous identification method for damage and input can decrease the false positives of damages in contrast with the deterministic method under intensive measurement noise, and it can also achieve an accurate identification for structural unknown input.     

基于四电极法的CFRP结构损伤检测研究

碳纤维复合材料(CFRP)被广泛用于航空航天领域,实现其结构健康监测对提高适航审定的损伤容限探测水平、降低检测成本具有重要意义。针对飞机使用的CFRP层压结构材料,利用碳纤维的自传感特点及结构损伤的电学敏感特性,基于四电极法提出3种激励模式下的电阻抗无损检测方法,以实现非侵入、无辐射、低成本的快速无损结构健康监测。利用有限元分析软件COMSOL构建各向异性CFRP层压板模型,通过提取有效电压差与电压灵敏度参数,对比分析不同类型结构损伤检测效果,从而获取适用于CFRP层压板结构损伤检测的最优激励测量模式。综合实验结果表明,双电极激励模式整体表现较优。     

桥梁结构损伤的振动模态检测

首先介绍了桥梁结构损伤检测的振动模态方法的原理及其４ 个要素。总结了用模态参数（固有频率、阻尼比及位移振型）进行损伤检测评估的困难,进而阐述应变模态测量的原理及其用于桥梁结构损伤检测时,相对于位移模态的优势。由于应变模态方法应用于实桥检测受到传统应变测量手段的制约,本文最后提出了一种通过相邻点振动位移的测量,推估桥梁在动载作用下的应力状态,进行实桥损伤检测的途径,并推荐一种新型低频高灵敏度传感器作为位移测量用传感器。     

An experimental demonstration of tailored excitations for improved damage detection in the presence of operational variability

We have shown in previous work that the parameters governing the dynamic evolution of a system of ordinary differential equations may be modified via an evolutionary algorithm to yield excitations that improve damage detection sensitivity in a computational model of a structural health monitoring application. In this work we use the same method to develop improved excitations for an experimental system. Improvement in change detection sensitivity is shown for several generated excitations. In addition, we present an excitation that increases the robustness of the damage detection feature to the types of parameter perturbations that arise not from damage, but from environmental sources such as temperature change.     

基于自适应技术的结构参数与输入同步反演

发展一种基于遗传优化算法的自适应追踪技术,结合输入未知条件下的二次误差平方和方法,利用事件中的加速度响应数据实现结构参数与输入的同步反演,判断并追踪结构损伤,包括损伤发生的时间、位置和程度。三自由度迟滞非线性系统数值仿真结果表明,该方法能够精确有效地追踪结构参数的变化,并同步反演结构的未知输入。此外,对三自由度基础隔振结构模型进行了多工况实验研究。结果表明,所发展方法能够实时有效地追踪结构时变物理参数、反演结构未知基底激励,进而精准地获取结构的损伤信息。     

Duffing振子与响应灵敏度结合的结构损伤检测方法

阐述了Holmes型Duffing方程的混沌特性用于强噪声背景下弱信号检测的机理。针对强噪声背景下的结构损伤定位问题,提出了基于Duffing振子和响应灵敏度结合的结构损伤定位方法,仅通过一组特定的参数来实现对于噪声背景下响应信号的提取,避开了传统的Duffing振子参数选择的繁琐性,适用于更高的噪声水平,同等噪声水平下较传统的时域响应灵敏度方法计算量更小。将该方法用于强噪声背景下三维桥梁结构模型的损伤检测,结果表明,该方法在强噪声背景环境下能较好地实现损伤定位,为强噪声背景环境下的实际工程结构损伤识别提供了良好的思路。     

An hybrid real genetic algorithm to detect structural damage using modal properties

An hybrid real-coded Genetic Algorithm with damage penalization is implemented to locate and quantify structural damage. Genetic Algorithms provide a powerful tool to solved optimization problems. With an appropriate selection of their operators and parameters they can potentially explore the entire solution space and reach the global optimum. Here, the set-up of the Genetic Algorithm operators and parameters is addressed, providing guidelines to their selection in similar damage detection problems. The performance of five fundamental functions based on modal data is studied. In addition, this paper proposes the use of a damage penalization that satisfactorily avoids false damage detection due to experimental noise or numerical errors. A tridimensional space frame structure with single and multiple damages scenarios provides an experimental framework which verifies the approach. The method is tested with different levels of incompleteness in the measured degrees of freedom. The results show that this approach reaches a much more precise solution than conventional optimization methods. A scenario of three simultaneous damage locations was correctly located and quantified by measuring only a 6.3% of the total degrees of freedom.     

结构损伤诊断的改进静力方法

利用柔度分解技术,提出一种改进的静力方法用于工程结构损伤诊断中。通过在结构静力反应方程中引入柔度分解式,得到求解柔度扰动参数的线性方程组。由该线性方程组首先计算出各单元柔度扰动参数,再根据柔度扰动参数和刚度扰动参数(损伤参数)之间的关系式,即可计算出各单元损伤参数,据此即可评估结构的损伤状况。所提方法避免了已有方法中需要求解非线性方程组的缺点,无论损伤程度大小如何,均不需要进行迭代运算即可获得精度良好的计算结果。以一个桁架结构为例对所提方法进行验证。结果表明:无论损伤程度大小如何,所提方法只需经过一次计算即可获得精度较高的识别结果,避免多次迭代,显示该方法在计算上的优越性。     

Damage identification by multi-model updating in the modal and in the time domain

Computational model updating techniques are used to adjust selected parameters of finite element models in order to make the models compatible with experimental data. This is done by minimizing the differences (residuals) of analytical and experimental data, for example, natural frequencies and mode shapes by numerical optimization procedures. For a long-time updating techniques have also been investigated with regard to their ability to localize and quantify structural damage. The success of such an approach is mainly governed by the quality of the damage model and its ability to describe the structural property changes due to damage in a physical meaningful way. Our experience has shown that due to unavoidable modelling simplifications and measurement errors the changes of the corresponding damage parameters do not always indicate structural modifications introduced by damage alone but indicate also the existence of other modelling uncertainties which may be distributed all over the structure. This means that there are two types of parameters which have to be distinguished: the damage parameters and the other parameters accounting for general modelling and test data uncertainties. Although these general parameters may be physically meaningless they are necessary to achieve a good fit of the test data and it might happen that they cannot be distinguished from the damage parameters. For complex industrial structures it is seldom possible to generate unique structural models covering all possible damage scenarios so that one has to expect, that the parameters introduced for describing the damage will not be fully consistent with the physical reality. Even then the change of such parameters identified from test data taken continuously or temporarily over the time may serve as a feature for structural health monitoring. It is well known that low-frequency modal test data or static response data are not very well suited for detecting and quantifying localized small size damage. Time domain response data from impact tests carry high-frequency information which usually is lost when experimental modal data are utilized for damage identification. Even so only little literature was found addressing the utilization of experimental time histories for model updating in conjunction with damage identification.In the present paper we summarize the methodology of computational model updating and report about our experience with damage identification using two different model updating techniques. The first is based on classical modal residuals (natural frequencies and mode shapes) which is extended to allow for simultaneous updating of two models, one for the initial undamaged structure and the second for the damaged structure using the test data of both states (multi-model updating). The second technique uses residuals composed of measured and analytical time histories. Time histories have the advantage of carrying high-frequency information which is beneficial for the detection of local damage and which usually is lost when modal residuals are used. Both techniques have been applied to the same beam structure consisting of two thin face sheets which were bonded together by an adhesive layer. It was the aim of this application to study the performance of the two techniques to localize and quantify the damage which was introduced locally in the adhesive layer.     

改进的特征值灵敏度在结构损伤识别中的应用

传统的特征值灵敏度分析中忽略了振型变化的影响,导致特征值灵敏度难以准确地识别出结构损伤。为提高特征值灵敏度的准确性,利用未损伤结构的振型线性表示损伤情况下结构振型的变化,进而改进了特征值灵敏度的理论分析方法。在不同的损伤工况下,计算数值模型改进前后的特征值灵敏度,验证表明改进后的特征值灵敏度具有更高的精度。以孔洞直径和位置均未知的实际结构为研究对象,利用改进后灵敏度方法准确识别了结构损伤的位置和程度,与结构的孔洞直径和位置实测值相吻合,表明了改进后灵敏度方法具有准确实用性,从而弥补了传统特征值灵敏度法在结构损伤识别中的缺陷。     

基于材料磁特性的结构疲劳损伤磁测方法研究

结构疲劳损伤测量和评估方法的研究是一个难点。由于疲劳损伤伴随材料磁特性的变化,且磁测法测量简单方便,所以利用材料磁特性测量和评估结构的疲劳损伤具有实际意义。以Q235钢为试件,通过构建疲劳损伤磁测试验平台,研究了循环应力下,基于磁滞回线的结构疲劳损伤磁测法。结果表明,疲劳损伤不同,磁滞回线也不同。提取磁滞回线的矫顽力H_c和剩磁B_r作为特征量进行分析,结果显示,试件失效前的疲劳过程大致分为两个阶段:首先是H_c和B_r的快速增大阶段,该阶段的H_c和B_r对疲劳损伤的灵敏度较高;然后是H_c和B_r的变化缓慢阶段,该阶段的H_c和B_r对疲劳损伤的灵敏度较低。最后分析了H_c和B_r与疲劳累积损伤D的变化关系,能够为结构疲劳损伤的定量评估及在线监测技术的研究提供基础。     

Environmental effects on the identified natural frequencies of the Dowling Hall Footbridge

Continuous monitoring of structural vibrations is becoming increasingly common as sensors and data acquisition systems become more affordable, and as system and damage identification methods develop. In vibration-based structural health monitoring, the dynamic modal parameters of a structure are usually used as damage-sensitive features. The modal parameters are often sensitive to changing environmental conditions such as temperature, humidity, or excitation amplitude. Environmental conditions can have as large an effect on the modal parameters as significant structural damage, so these effects should be accounted for before applying damage identification methods. This paper presents results from a continuous monitoring system installed on the Dowling Hall Footbridge on the campus of Tufts University. Significant variability in the identified natural frequencies is observed; these changes in natural frequency are strongly correlated with temperature. Several nonlinear models are proposed to represent the relationship between the identified natural frequencies and measured temperatures. The final model is then validated using independent sets of measured data. Finally, confidence intervals are estimated for the identified natural frequencies as a function of temperature. The ratio of observed outliers to the expected rate of outliers based on the confidence level can be used as a damage detection index.     

运用波传播和子结构技术检测结构损伤

提出了一种基于波传播和子结构技术来检测大型周期结构损伤的方法,分析了存在单一扰乱单元的有限周期结构的自由波传播,讨论了单元柔度变化对结构自振频率变化的敏感性。通过求解敏感性方程,用测得的自振频率的变化检测了大型周期结构的损伤位置和程度,并通过与子结构方法的结合,进一步提高了大型周期结构损伤检测的准确性和计算效率。对周期弹簧－质量结构损伤识别的数值结果说明,该方法不仅对结构损伤的位置和大小能够作出良好地预测,而且不需要知识未损伤结构的原始信息,只需要测得结构损伤前后的少数几个自振频率的变化,这对于实际的工程运用具有一定的吸引力。     

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。     

藏式古建筑木结构损伤识别的数值模拟

为保护藏式古建筑木结构,针对实际中众多结构存在的梁、柱构件损伤问题进行了损伤识别理论的研究。基于实地勘查结果,对梁、柱构件的残损类型和残损机理进行了汇总和分析。以某典型藏式古建筑多层梁柱排架结构为损伤识别对象,在建立其有限元模型的基础上,采用振动响应灵敏度损伤识别方法对该结构梁、柱构件的3种不同损伤状态进行了数值模拟识别。为了模拟古建筑结构构件之间物理参数离散性大的特点,给每个构件的弹性模量添加了随机误差。识别时,为了减小离散的物理参数对结果收敛性和准确性的影响,采用修正的正则化方法求解识别方程。结果表明,该方法可以克服测量噪声的影响,准确识别出藏式古建筑木结构梁、柱构件的损伤,为该类型结构实际的损伤识别提供了理论依据。     

一种多目标传感器优化布置方法及其应用

为解决复杂结构损伤识别中的传感器优化布置问题,以某发射台为研究对象,提出了一种多目标传感器优化布置方法(multi-objective optimum sensor placement,简称MO-OSP)。从结构运动方程出发,推导了同时具有各自由度模态独立性信息、损伤灵敏度信息以及运动能量信息的综合信息矩阵。根据信息熵原理,以协调灵敏度矩阵条件数最小和信息矩阵最大为目标,构造了能够兼顾算法敏感性和鲁棒性的目标函数,进而实现测点优选。采用多个评价准则和损伤识别实例,将所提方法与已有的3种典型传感器优化布置方法进行了对比分析。结果表明,提出的MO-OSP方法能充分满足模态线性独立和损伤敏感性,还具有较强的抗噪声性能,是解决复杂结构损伤识别中传感器优化布置问题的有效方法。     

Creep-fatigue design studies for a sodium-cooled fast reactor with tube sheet-to-shell structure subjected to elevated temperature service

In this paper, creep-fatigue damage under elevated temperatures is investigated for a tube sheet-to-shell structure, which is one of the main structures under Gen-IV class 1 components. To do this, detailed step-by-step procedures, including the elastic structural analysis and the ASME-NH code application, are described for a defined representative load cycle. From the sensitivity studies for various design parameters, such as hold time duration, shell thickness, and operating temperature, it is found that a reduction of thickness can decrease the thermal bending stresses, but the negative effect is that it may increase the primary stress and enhance the creep damage. The normal operating temperature is the most significant parameter in the creep-fatigue design.     

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。     

基于响应面修正敏度模型的结构可靠性影响因素分析方法

针对实际工况下结构可靠性影响因素复杂多样的特点,提出一种基于响应面修正敏度模型的结构可靠性影响因素分析方法。首先,融合最优多项式响应面函数与Sobol’灵敏度算法,推导出兼顾多影响因素局部与全局灵敏度分析的响应面修正灵敏度模型。并在此基础上,结合耦合因素的试验设计与极差验证、多体动力学分析、结构静力学分析,建立一种结构可靠性影响因素的灵敏度量化分析方法。最后,以典型收割机结构为分析对象对提出方法进行实例研究,研究结果表明脱粒滚筒转速对结构可靠性的灵敏度影响最大,粮仓负载的影响最小,其平均预测精度为97.36%,提出的方法可以实现多种耦合影响因素的灵敏度精确分析,从而为结构可靠性影响因素评估提供了一种思路。