大跨空间网格结构风振响应主要贡献模态的识别及选取

首先简单介绍静荷载参与比例的概念和基于虚拟激励法的风振响应分析原理。考虑脉动风荷载的空间相关性,推导出脉动风作用下系统背景响应总应变能的计算公式,以及模态对背景响应总应变能的贡献,从而定义了各阶模态的模态贡献系数及模态组合的累积模态贡献系数计算公式,其中模态贡献系数可以准确地识别出所有能被脉动风激振的模态,而累积模态贡献系数可以作为模态组合合理性判别的量化标准。然后介绍了一种简单的补偿模态构造方法,并提出了模态组合的选取方法和步骤。算例分析验证了模态贡献系数和累积模态贡献系数的有效性,以及低阶主要贡献模态和高阶主要贡献模态的重要性,进而指出目前通过比较前若干阶模态的相对误差或仅考虑补偿模态的模态组合选取方法并不合理。合理的模态组合应包含绝大部分主要贡献模态,以满足累积模态贡献系数大于0.9的要求。     

结构应变模态获取途径的理论与仿真研究

对应变模态的试验模态理论进行了总结,并提出了不同激励下实用的应变模态获取方式,仿真分析验证了该方法在实际应变模态测试中有效性。     

基于曲率模态的钢筋混凝土梁损伤检测研究

阐明了曲率模态的基本原理。对钢筋混凝土简支梁进行逐级加荷-卸荷试验,每次卸荷后进行动态检测试验,用DASP系统对试验数据进行分析,得到位移模态。利用二阶差分法,由位移模态得到了曲率模态。结果表明,曲率模态能较为准确地识别钢筋混凝土简支梁的损伤,且对微小损伤较为敏感,高阶的曲率模态对于损伤的敏感性高于低阶曲率模态。利用曲率模态能够较好地判定损伤的位置以及损伤的相对程度。     

梁桥固有特性测试方法

固有特性（固有频率、阻尼比、振型）是桥梁检测的重要内容。文章对近几年提出的模态测试方法理论进行了阐述,包括模态综合法、复模态法、曲率模态法、应变模态法等。分析了简支梁桥固有特性的解析方法,并应用模态理论,实测了简支梁桥的固有特性。为梁桥固有特性工程实测提供了理论上的准备。     

木梁基于曲率模态技术的损伤识别

利用有限元分析软件建立了木梁的损伤模型,获取了不同损伤参数的曲率模态;基于结构动力学中梁自由振动的理论,推导了木梁基于曲率模态的损伤程度判定理论;对人工模拟的损伤木梁进行了模态试验.结果 表明:曲率模态对损伤识别非常敏感,损伤位置可通过曲率模态图的突变判定,损伤程度可以根据突变程度判定;模态分析试验结果与有限元分析结果吻合较好;有限元算例和模态试验验证了损伤程度判定理论公式的适用性,采用曲率模态技术对木梁进行损伤检测是有效可行的.     

海洋立管湿模态振动分析

针对海洋立管的湿模态振动问题,对立管固有频率以及各阶模态的相应振型展开了研究。阐述了模态概念与模态分析的意义,运用ANSYS Workbench中的Acoustic Extension分析模块对海洋立管进行了湿模态振动分析,描述了湿模态建模方法与技巧,得到12阶固有频率与振型。通过与12阶干模态分析结果进行对比,得出两者的区别,表明了湿模态分析在做水下结构振动研究中的不可替代性。通过对立管结构进行优化,计算优化后的结构振动特性,得到的优化结果,证明了优化的可行性。模态分析为研究结构的振动特性、优化结构设计提供了一定的依据,为防止结构的共振提供了一定的参考。     

基于随机子空间法的系杆拱桥模态测试分析

通过对某座采用顶推法施工的大跨径钢管混凝土系杆拱桥进行模态测试,基于随机子空间法进行模态分析,得到了桥梁结构前6阶振动模态参数;采用桥梁结构分析软件MIDAS建立有限元模型并对桥梁进行模态分析,提取了与实测前6阶模态振型相对应的模态参数。经过比较发现,桥梁实测模态振型、自振频率与理论分析结果相吻合,实测系杆拱桥的动力特性满足要求,同时验证了随机子空间法是桥梁结构模态分析的一种有效方法。     

框架结构的高阶局部模态分析与试验

介绍了规则链武结构的局部模态特性，分析了框架结构的高阶模态及局部模态试验，表明框架结构高阶局部模态具有模态密集特性，子结构和整体结构之间存在着动力耦合。     

高桩码头基桩模态参数识别方法研究

通过建立高桩码头基桩物理模型,进行了模态试验和基于ANSYS的模态分析,结果表明:高桩码头基桩模态参数有限元模拟结果与模态试验识别结果吻合较好,验证了数值模型建立方法的正确性和高桩码头基桩模态参数基于随机子空间识别方法的可行性。     

可压缩边界层稳定性问题特征值的分布

为了充分了解可压缩边界层中稳定的特征模态的信息,用Arnoldi方法研究了3种情况特征值的分布,即:亚音速边界层、超音速边界层第1模态和超音速边界层第2模态;比较上述3种情况以及不可压的情况。结果表明:亚音速的结果与不可压的结果类似,有2个离散模态分支A和C,以及1个连续模态分支B,但更多的模态出现在了稳定的离散模态分支C上;超音速边界层比亚音速边界层多出2个离散模态分支D和E,通过观察特征函数发现这2个分支中的模态代表边界层中的1个法向局部波包;而第2模态的结果与第1模态相比,C分支变短而D和E分支变得更长。     

Studies on damage and FRP strengthening of reinforced concrete beams by vibration monitoring

In this paper, modal characteristics of reinforced concrete beam specimens are identified using experimental test data. Nine concrete beam specimens were gradually damaged and the changes of dynamic parameters were monitored from initial to the failure state. Six of the specimens were strengthened with externally bonded CFRP sheets when the load reached approximately half of the predicted failure load. The identification methods based on measured modal parameters were utilized and the efficiencies of these methods were investigated. These methods include frequency changes, Modal Assurance Criterion (MAC), Coordinate Modal Assurance Criterion (COMAC) and modal curvatures. The comparison of the methods shows that the frequency changes are not fully capable of detecting damage and predicting the potency of strengthening. The MAC values can reveal the changes of overall stiffness of the beams during the load steps. The change of stiffness at each degree of freedom of beams evaluated by COMAC and modal curvatures show that the damage identification of the beam specimens is best described by modal curvature method.     

FRP加固梁模态分析的摄动解法

采用基于Ritz函数展开的直接模态摄动法,求解纤维复合材料包覆钢筋混凝土（FRP-RC）梁的模态特性.在不考虑剪切变形和转动惯量的情况下,它将FRP-RC梁的无阻尼自由振动的变系数微分方程的求解转化成一组非线性代数方程组的求解,使得求解过程得以简化.在此基础上,计算了不同加固工况下FRP-RC梁在各种约束条件下的自振频率,并与其他方法进行了对比.数值结果表明,利用直接模态摄动法不仅可以简化计算过程,而且计算结果具有较高的精度和较强的适用性.     

斜拉桥传感器布置优化方法应用研究

根据模态置信度准则,采用模拟退火算法,提取出斜拉桥有限元模型的动力分析数据,得到了主梁加速度传感器的优化布设方案,并根据此优化方案在实际桥梁上进行了现场动力特性测试实验。对比研究结果发现：由现场实验测得的自振频率、振型位移与ANSYS理论计算出的结果十分接近,从而验证了基于MAC准则的模拟退火算法在斜拉桥加速度传感器优化布设方面是有效的和可行的。     

基于模态区间分析的结构不确定性损伤评估

针对实际工程结构中难以避免的不确定性因素,如材料非均质、边界条件不清晰、测试误差、模型误差等,提出利用模态区间分析求解包含不确定性参数的梁损伤评估方法。首先建立钢箱梁和钢筋混凝土梁的计算模型,以区间形式定义梁几何、材料参数的不确定性,体现各参数的可能波动范围;然后将结构静力学方程扩展成区间方程,通过模态逻辑对区间方程进行重新释义;最后在梁上施加集中荷载,计算得到梁关键应变点的区间工作状态。分析中通过降低梁单元的弹性模量来模拟损伤,再比较确定性方法、经典区间算法和模态区间分析的计算结果。结果表明:与确定性损伤评估方法不同,区间算法允许结构包含不确定性参数,认为落在区间包络线内的应变值是合理的,而当某荷载下应变值超出包络范围时说明梁发生了损伤;模态区间分析计算得到的区间包络范围要明显小于经典区间算法,能够有效避免计算过程的参数区间扩张,而且可以及时发现梁的损伤和损伤时所对应的外荷载,避免结构损伤进一步的恶化。     

A new technique for repairing and controlling large-scale collapse in the main transportation shaft, Chengchao iron mine, China

A new technique, the ‘supporting funnel method’, is introduced in this paper for repairing and controlling large-scale collapse in the download junction of the tunnel and main transportation shaft. The key technical points include:

Construction of a box-sectioned beam across the collapsed junction floor, which serves as a supporting structure to recover the ore download function.

Construction of an inverse cone-shaped funnel shaft below the junction in the shaft space, which has multiple functions of ore storage, transportation, and control of the rock mass around the shaft.

Implementation of post-tensioned long bolts and high pressure grouting technique in construction.

Numerical analysis of the reinforced structures has been carried out using FLAC^3D. The study shows that the merits of the technique are: (i) it ensures that the system function of the transportation is fully and economically recovered and (ii) the stability of the whole system was obtained through the local reinforcement.     

Model Updating Technique Based on Modal Participation Factors for Beam Structures

This article proposes a model updating technique based on modal participation factors for a beam structure. In this model updating technique, the error functions of the dynamic characteristic differences between measurement and model are generated as the number of modes under consideration and minimized using the multiobjective optimization techniques. A modal influence factor defined by modal participation factors for each mode is presented for the selection of the best solution from among Pareto solutions. The selection rule represented in this article makes it possible to reflect the contributions of each mode on the behavior of a structure. The model is updated using natural frequencies measured in an impact hammer test of a beam structure and the validity of the updated model is confirmed by the strain responses measured from the test. It is found that the bending stiffness of the beam structure as the parameter for model updating can be identified by the proposed techniques. Furthermore, through comparing the models updated by the simple sum model updating and the technique in this research, it is verified that the proposed technique is more appropriate for the model updating.     

FRP增强钢筋混凝土梁损伤的振动监测

采用试验数据,识别钢筋混凝土梁模态。对9个混凝土梁的破坏过程和动态参数进行监测,当荷载到达预期破坏荷载一半时,对6个梁采用外贴碳纤维布进行加固。基于所测模态参数,对识别方法进行研究并对识别方法的效率进行分析。这些方法包括频率变化、模态确证准则(MAC)、坐标模态确证准则(COMAC)和模态曲率。通过比较这些方法可知,频率变化不能完全监测损伤以及预测加固的潜力;模态确证准则的值能够揭示荷载变化过程中梁的刚度变化;对梁每个自由度的刚度变化可采用坐标模态确证准则进行评估;模态曲率方法是对梁进行损伤识别的最好方法。     

模态综合法精度分析

模态综合法是研究振动问题的常用方法。本文以均匀直角梁在它本身平面内的弯曲振动问题为例,运用模态综合法,选取不同主振型,分别计算它的平面弯曲振动的前两阶固有频率,比较不同主振型下所得出的近似频率的精度。同时,将模态综合法两种不同振型下的计算结果与有限元法计算结果相比较,通过近似频率的精度比较,来分析不同振型下模态综合法的计算精度。     

Damage Identification of a Composite Beam Using Finite Element Model Updating

Abstract:   The damage identification study presented in this article leveraged a full-scale sub-component experiment conducted in the Charles Lee Powell Structural Research Laboratories at the University of California, San Diego. As a payload project attached to a quasi-static test of a full-scale composite beam, a high-quality set of low-amplitude vibration response data was acquired from the beam at various damage levels. The Eigensystem Realization Algorithm was applied to identify the modal parameters (natural frequencies, damping ratios, displacement and macro-strain mode shapes) of the composite beam based on its impulse responses recorded in its undamaged and various damaged states using accelerometers and long-gage fiber Bragg grating strain sensors. These identified modal parameters are then used to identify the damage in the beam through a finite element model updating procedure. The identified damage is consistent with the observed damage in the composite beam.     

利用数字图像边缘检测识别梁的模态参数

基于数字图像边缘检测技术,对附集中质量的某梁模型进行振动测试,以普通数码摄像头与PC机作为视频采集设备,实时获取梁的振动图像,运用三次多项式拟合实现边缘的亚像素定位,以获取梁振动的位移时程曲线,后处理采用模态分析识别梁的模态参数,试验表明采用该方法进行低频结构的模态试验是可行的。