Structural optimization in truth dimensionOptimisation structurale dans la dimension de vérité

Optimization theory has advanced considerably during the last three decades as is illustrated by a vast number of published books, surveys, and papers concerning this subject. An optimal decision under uncertainty conditions is dependent on the Engineer's objectives, which may be not known with certainty or represented by natural language. To deal with this problem, in this paper, a new approach based on coupling the existing knowledge of experts and numerical results obtained from traditional optimization techniques is presented using non-conventional logic. To cite this article: C. Tran, C. R. Mecanique 330 (2002) 609–614.     

结构动力模型修正方法研究进展

叙述了结构动力模型修正方法的一般原理及与其密切相关的模型缩聚和模态扩展方法, 并且挑选其中具有代表性的文献, 介绍和比较了3种主要的修正方法, 即传统的动力模型修 正方法, 包括矩阵型修正方法和参数型修正方法, 和最近兴起的基于神经网络的模型修正方 法, 重点分析了这些方法的优点和不足之处, 力图能使读者对于这一研究领域的发展有一个 脉络清晰的了解. 最后, 就目前研究中尚未解决的问题作了一些探讨.     

Hybrid determination of equivalent characteristics of perforated plates

In this paper, we have adopted the hybrid method, which combines experimental and numerical methods, to investigate the dynamic behavior of perforated plates. It was found that the modal assurance criterion is a useful criterion to judge the degree of similarity between experimental and numerical models. The difference between the experimental and numerical models can be reduced via sensitivity testing and by checking the correlation coefficient. The equivalent material properties of the perforated plates were also obtained by the hybrid method. In addition, the curve-fitting technique was utilized to find the relationship of the mass remnant ratio with the parameter ratio. The functions obtained from the curve fitting can be used to predict accurately the equivalent material properties and resonant frequencies of perforated plates of the diagonal array.     

Experimental Investigation on Dynamic Railway Sleeper/Ballast Interaction

In ballasted railway tracks, one of the important components that supports the rails and distributes wheel/rail loading onto the ballast supporting formation is a railway sleeper (sometimes is also called a “railway tie”). This paper presents results of an experimental modal analysis of prestressed concrete sleepers in both free-free and in-situ conditions, incorporating the dynamic influence of sleeper/ballast interaction. Dynamic interaction between concrete sleepers and ballast support is crucial for the development of a dynamic model of railway track capable of predicting its responses to impact loads due to wheel flats, wheel burns, irregularities of the rail, etc. In this study, four types of prestressed concrete sleepers were in-kind provided by the Australian manufacturers. The concrete sleepers were tested using an impact hammer excitation technique over the frequency range of interest, 0–1600 Hz. Frequency response functions (FRFs) were measured using PULSE modal testing system. The FRFs were processed using STAR modal analysis package to identify natural frequencies and the corresponding mode shapes for the sleepers. The conclusions are presented about the effect of the sleeper/ballast interaction on the dynamic properties of prestressed concrete sleepers and their use for predicting railway track dynamic responses.     

Modale Behandlung linearer periodisch zeitvarianter Bewegungsgleichungen

Übersicht Lineare, periodisch zeitvariante Bewegungsgleichungen treten im Hubschrauber- und Windturbinenbau auf. Der Getriebebau und die Rotordynamik liefern weitere Beispiele. In diesem Bericht wird ein systematischer Weg zu ihrer Lösung dargestellt. Mit dem Ansatz von Hill wird die homogene Lösung über die Lösung eines Eigenwertproblems gewonnen. Nach Anpassung an die Anfangsbedingungen liefert sie die Fundamentalmatrix des Systems.Ähnlich wie bei zeitinvarianten Systemen, existieren auch bei zeitvarianten Systemen Orthogonalitätsbedingungen, die die Eigenvektoren erfüllen. Die Eigenvektoren selbst sind allerdings zeitabhängig. Benutzt man die Eigenvektoren als Ansatzvektor zur Berechnung der erzwungenen Schwingungen (Transformation mit der zeitvarianten Modalmatrix des Systems), so gelingt es, die Bewegungsgleichungen des Systems in entkoppelte, zeitinvariante zu überführen. Sie lassen sich in bekannter Weise lösen. Dieses Vorgehen wird auf eine moderne Windkraftanlage angewandt. Sie wurde zunächst mit 372 Freiheitsgraden modelliert, die aber auf 18 vor der numerischen Weiterbehandlung kondensiert wurden. Das Stabilitätsverhalten und die Antwortspektren auf stochastische Anregung durch den Wind wurden auf dem oben beschriebenen Weg ermittelt.

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MODAL SYNTHESIS METHOD FOR NORM COMPUTATION OF H∞ DECENTRALIZED CONTROL SYSTEMS （ I ）

When using H∞ techniques to design decentralized controllers for large systems,the whole system is divided into subsystems, which are analysed using H∞ control theorybefore being recombined. An analogy was established with substructural analysis instructural mechanics, in which H∞ decentralized control theory corresponds to substructuralmodal synthesis theory so that the optimal H∞ norm of the whole system corresponds to thefundamental vibration frequency of the whole structure. Hence, modal synthesismethodology and the extended Wittrick-Williams algorithm were transplanted from structuralmechanics to compute the optimal H∞ norm of the control system. The orthogonality and theexpansion theorem of eigenfunctions of the subsystems H∞ control are presented in part(I) of the paper. The modal synthesis method for computation of the optimal H∞ norm ofdecentralized control systems and numerical examples are presented in part (Ⅱ).     

钢筋混凝土梁振动特性参数与损伤状况关系的数值仿真研究

基于分离式有限元理论,分别建立了存在钢筋混凝土局部松脱等多种形式损伤的钢筋混凝土梁横向弯曲振动力学模型,利用此模型能够计算各种损伤梁的固有频率等振动特性参数。对这些振动特性参数与各种损伤的状况之间的关系进行了数值仿真研究。提出固有频率可以作为钢筋混凝土梁损伤定性辨识的指标;针对不同的损伤形式,位移模态振型、曲率模态振型和剩余模态力向量是对局部损伤位置敏感的振动特性参数,可以利用敏感参数的绝对残差向量进行局部损伤的定位辨识;敏感参数绝对残差向量的范数与损伤程度具有良好的单调性关系,可以作为局部损伤定量辨识的指标。     

DAMAGE DETECTION IN BUILDINGS USING A TWO-STAGE SENSITIVITY-BASED METHOD FROM MODAL TEST DATA

Many multi-story or highrise buildings consisting of a number of identical stories are usually considered as periodic spring-mass systems. The general expressions of natural frequencies, mode shapes, slopes and curvatures of mode shapes of the periodic spring-mass system by utilizing the periodic structure theory are derived in this paper. The sensitivities of these mode parameters with respect to structural damages, which do not depend on the physical parameters of the original structures, are obtained. Based on the sensitivity analysis of these mode parameters, a two-stage method is proposed to localize and quantify damages of multi-story or highrise buildings. The slopes and curvatures of mode shapes, which are highly sensitive to local damages,are used to localize the damages. Subsequently, the limited measured natural frequencies, which have a better accuracy than the other mode parameters, are used to quantify the extent of damages within the potential damaged locations. The experimental results of a 3-story experimental building demonstrate that the single or multiple damages of buildings, either slight or severe,can be correctly localized by using only the slope or curvature of mode shape in one of the lower modes, in which the change of natural frequency is the largest, and can be accurately quantified by the limited measured natural frequencies with noise pollution.     

大跨径斜拉—悬索协作体系桥动力分析

斜拉-悬索协作体系桥作为一种新的超大跨径桥型，综合了悬索桥和斜拉桥的特点，国内外对这种桥型的研究尚少。本文根据空间有限元计算模型，对伶仃东航道斜拉-悬索协作体系桥设计方案进行了模态分析，分析了斜拉-悬吊协作体系桥的固有特性，讨论了不同主梁纵向约束方式和辅助墩的设置情况的影响，为此类桥型结构的动力性能分析提供了有价值的参考。     

GDR法在大型结构模态分析中的应用

有限元模态分析中，往往需要减缩矩阵阶数来减小求解规模，目前应用较多的是Guyan静力凝聚法和Kuhar动力凝聚法。本文从理论上分析一种不常用的方法一广义动力化简法(GDR法)，阐述该方法的基本原理、应用过程及其与前两种方法相比的优越性，并通过对城市客车的有限元模态计算加以验证。