全桥气弹模型颤振导数识别

将节段模型颤振导数识别方法用于全桥气弹模型,对其可行性和便利性进行详细论述;给出气弹模型模态质量的确定方法;采用随机子空间方法和随机搜索方法识别均匀流场和紊流场中苏通大桥气弹模型的18颤振导数,并和特征系统实现算法识别结果进行对比分析。研究结果表明:节段模型颤振导数识别方法是识别气弹模型颤振导数的有效和实用方法;模型模态质量可以方便地根据几何缩尺比由实桥对应值直接推算得到,且比通过模型试验实测精度更高;不同方法识别得到的均匀流场中苏通大桥气弹模型大部分颤振导数基本吻合;相对于紊流场中的气弹模型而言,均匀流场中的节段模型颤振导数识别精度更高。     

苏通大桥气弹模型气动失稳分析

大跨柔性桥梁气弹模型在风荷载作用下会产生明显的竖向、侧向位移和附加攻角。推导气弹模型实测位移修正表达式,对苏通大桥气弹模型高风速时实测位移进行修正,对比分析修正前后差异。绘制了苏通大桥主跨跨中断面、1/4断面和边跨跨中3个典型断面扭转中心的运动轨迹,分析其特点,对苏通大桥气弹模型气动失稳现象进行解释。基于随机搜索方法和随机子空间方法识别得到的模态参数,对苏通大桥气弹模型进行复模态颤振分析。分析结果表明:苏通大桥气弹模型可视为一种非常规索网复合系统,其气动失稳振动表现为保持平衡状态的竖向、侧向和扭转耦合滚动,扭转频率成分在竖弯和侧弯振动中参与很多,而竖弯和侧弯频率成分在其他两种振动中参与很少。     

基于随机振动试验的结构模态参数识别方法

文章介绍了利用随机振动的试验数据进行模态参数识别的方法。先从理论上对模态参数识别的原理进行推导,并给出通过随机振动试验进行结构模态参数识别的前提条件和理论基础公式,以及进行随机振动试验的主要步骤;然后以简支梁结构为例,通过随机振动试验求得模态参数并与有限元理论计算的结果相比较证明该方法的可行性。     

缆索承重桥梁全桥气动弹性模型模态测试分析

本文详细介绍了大跨缆索承重桥梁全桥气弹模型模态测试分析方法，结合这类桥粱全桥模型的结构及模态特征探讨了影响模态测试分析结果的各种因素。并将这些方法应用于主跨为1490m的润扬长江公路大桥南汊悬索桥全桥气弹模型模态测试分析，得到了较为理想可信的模态测试分析结果。     

高层建筑多自由度气弹模型的设计

设计了1个可重复利用的多自由度气弹模型,对该气弹模型的设计原理和调试方法进行了说明,并采用有限元方法对该模型进行模态分析,得到模型在不同刚度和质量条件下的模态参数。此模型能覆盖高层建筑的频率和振型指数变化范围,且只要两主轴方向柱子中心到原点的距离不相等,模型各主轴的前二阶平动振型均沿主轴方向。     

薄膜结构与风环境的流固耦合作用

薄膜结构与风环境之间存在着较强的流固耦合使用，并且这种耦合作用往往对薄膜结构的振动起控制作用。本将两的耦合作用分为静力耦合作用和动力耦合作用，分别建立了静力耦合模型和简化气弹模型，并对所涉及的几个因素进行了初步分析，为了下一步的风洞试验研究奠定了理论基础。     

曹妃甸煤堆防风网架气弹模型风洞试验

目前复杂网架结构风荷载通常采用刚性模型风洞试验确定,但由于忽略了结构与流体之间的耦合效应,其结果与实际结构存在偏差。气弹模型则可真实反映结构在自然边界层中的响应,但由于网架结构非常复杂,需要适当简化相似准则和选择结构主要响应振型进行设计。基于曹妃甸煤堆防风网架结构,设计1颐50气弹模型。通过应变片测试支架根部内力,得到了B类风场不同风速下网架内力风振系数;通过激光位移计测得顺风向位移响应,求得结构顺风向位移风振系数。最后比较分析了两类风振系数,为同类结构气弹模型设计制作和风振系数计算提供参考。     

大跨度挑蓬气弹模型风振系数风洞试验

气弹模型试验能够全面考虑结构和气流间相互作用,真实地反映结构在大气边界层中的受力特性和响应形式,是结构风振研究的一种重要手段。探讨适用于复杂外形建筑结构模型设计相似准则,通过一体育场大跨度挑蓬缩尺比1:200气弹模型,在模拟大气边界层风场及场址地形地物的条件下,测量体育场罩棚表面的位移响应,进而得到罩棚结构设计需要的风振系数。     

大跨越输电塔-线耦联体系风洞试验气弹模型设计研究

以榆横-潍坊1 000 k V特高压交流输变电工程线路工程为实际工程背景,研究大跨越输电塔-线耦联体系风洞试验气弹模型设计。采用离散刚度法设计输电塔气弹模型,并用自由振动法测得单塔气弹模型的自振频率。通过引入导线缩聚系数解决缩尺模型跨度过大问题,调整输电线垂度满足频率比要求。     

环境随机振动法测索力

介绍环境随机振动法在涪江四桥静载试验中的应用。     

青马悬索桥的时域模态识别

文章研究了青马悬索桥模态参数时域识别.青马桥脉动测试信号弱、干扰因素多,模拟滤波器的滤波效果又不好,而Chebyshev数字滤波器却能精确地确定通带和阻带的边缘频率,故本文采用它对脉动加速度进行预处理.然后用RD函数将脉动信号转变为自由衰减信号.为了提高时域法模态参数识别精度,本文采用了改进的特征系统实现算法.由于青马桥加劲梁长达2160m,加速度计和仪器通道数有限、测试只能分组在不同时间进行,而目前的时域模态技术只能处理同时记录的数据.本文先分组时域识别、然后通过参考点拼装全桥的模态,共识别出青马桥的79个模态,包括五个复模态.后者与青马桥典型复阻尼特性相一致.本文还把上述结果与频域法及有限元计算结果进行了比较.     

Random imperfection fields to model the size effect in laboratory wood specimens

The composite nature of a wood continuum prevents one from extrapolating the results of laboratory tests on standard wood specimens to structural elements of significant size. Therefore, these elements are usually tested under standardized loading conditions in order to detect a sort of average material behaviour.

In this paper, the initial step consists, instead, of testing the material specimens. The extension of the results to structural elements is then pursued by introducing a random field, or, in a discretized model, a random array of imperfections.

The calibration of the suitable spatial distribution of the imperfections is then investigated by a mixed experimental–numerical approach, for a reference beam. The analyses on the relative finite elements model are iterated to match the response of the full scale laboratory tests.     

Overload failure of structural components under random crack propagation and loading – a random process approach

In this paper, the problem of overload failure of a structural component under random loading and under random crack propagation is addressed. The problem is formulated by combining the first passage failure model with stochastic models of crack propagation. Disadvantages of the standard random variable approach to the problem are discussed, and an alternative random process approach is developed. The developed solution addresses both overload and critical crack growth failure modes, requires a single mean crack growth computation, allows the consideration of non-destructive inspections and significantly speeds life-time analysis. The random process approach leads to a first passage problem involving crossings of a random barrier level, which is solved by means of the ensemble up-crossing rate approximation. Limitations of this approximation are addressed and related to typical problem parameters. The concept of barrier failure dominance is discussed, and extended to the case of a barrier-defined failure. Sensitivity studies involving different problem variables are performed, helping to identify the appropriate solution method for specific problems.     

Sequential parametric identification and response of hysteretic oscillators with random excitation

Sequential methods are developed for estimating the parameters in a differential model of a curvilinear class of hysteretic force characteristics. In the case where the hysteretic force is directly observable it is shown that the hysteretic “loop” parameters may be identified by using either a two-stage linear estimation method or a one-stage method, based on a sequential non-linear filter. For oscillators with a non-observable hysteretic force it is demonstrated that the non-linear filtering approach can be extended to allow estimation of all the relevant system parameters, including the oscillator mass. The proposed methods are validated y application to both simulated and real experimental data. The latter was acquired during dynamic tests on a stranded steel cable, undergoing both sinusoidal and random flexural vibrations. Using identified parameters, good agreement between theoretical and experimental response statistics is obtained, in the case of random excitation.     

Along-wind gust effect on elevated structures

The interest in the evaluation of the dynamic response of elevated structures to wind force has increased considerably in recent years. This paper introduces a random process approach and its application to these special structures. As an example, a skylight structure is analysed by random approach in regard to the gust effect. For comparison, the same effects are also evaluated by using some of the current available building codes.Results show that the effect due to the gust is greater than that due to the steady wind. Wind pressure obtained through the random approach are quite comparable with those obtained by using the building codes. However, the random approach presented in this paper provides more detailed procedure than the building code approach for evaluating gust effect on elevuated structures.     

模拟随机过程在阻尼器力学性能试验中的应用

通过对单调循环加载方式的分析,提出了随机过程加载的概念。对一定功率谱和位移情况,在液压伺服试验系统中实现了人工模拟的随机过程的加载试验。同时,也对功率谱、位移发生变化的情况进行了分析。对随机过程加载的试验结果进行处理,提出了基于概率统计的等效刚度、等效阻尼及耗散功率谱等方法。随机过程加载解决了加载中速度、频率耦合的问题,也简化了加载工况的分类,实现了阻尼器瞬时动力性能的测试。对于其他阻尼构件如橡胶隔振支座等也具有应用意义。     

带TMD的建筑结构非平稳随机地震响应计算

通过直接积分和模态叠加两种方法研究了带TMD结构均方非平稳随机地震响应的数值计算方法。应用非平稳随机响应问题的统一解法理论,并引入常用的微分方程数值积分Runge Kutta方法,解决了复杂的非平稳随机响应问题,计算实例说明了该方法的有效性。探讨了设计非平稳地震激励TMD结构参数的方法。     

The Specification of Filtering Materials for Rapid-Gravity Filtration

A UK standard for the specification, approval and testing of filtering materials has recently been published by British Water (formed by the merger of the British Effluent and Water Association and the British Water Industries Group) in response to an identified need. This paper reviews the considerations during the preparation of the standard and provides a technical background. The approach has been to base the standard on parameters which affect the behaviour of the material during filtration, rather than to specify material composition and appearance, which are unimportant. Standards and specifications are a basis for testing, and the inclusion of irrelevant parameters can lead to unnecessary work.     

Orthogonal expansion of Gaussian wind velocity field and PDEM-based vibration analysis of wind-excited structures

An effective procedure for simulation of random wind velocity field by the orthogonal expansion method is proposed in this paper. The procedure starts with decomposing the fluctuating wind velocity field into a product of a stochastic process and a random field, which represent the time property and the spatial correlation property of wind velocity fluctuations, respectively. By an innovative orthogonal expansion technology, the stochastic process for wind velocity fluctuations may be represented as a finite sum of deterministic time functions with corresponding uncorrelated random coefficients. Similarly, the random field can be expressed as a combination form with only a few random variables by the Karhunen-Loeve decomposition. This approach actually simulates the wind velocity field with stochastic functions other than methods such as spectral representation and proper orthogonal decomposition. In the second part of the paper, the probability density evolution method (PDEM) is employed to predict the stochastic dynamic response of structures subjected to wind excitations. In the PDEM, a completely uncoupled one-dimensional partial differential equation, the generalized density evolution equation, plays a central role in governing the stochastic responses of structures. The solution of this equation will give rise to instantaneous probability density function of the responses. Finally, the accuracy and effectiveness of the approach in representing the random wind velocity field and PDEM-based dynamic response of wind-excited building are investigated.     

Recognizing Patterns in Seasonal Variation of Pavement Roughness Using Minimum Message Length Inference

Abstract: Pavement roughness is a common measure of pavement condition regularly measured by road authorities. An approach to recognize patterns of seasonal variation in rural sealed granular pavement roughness by minimum message length (MML) inference is demonstrated in this article. MML solves two fundamental questions: First, is the seasonal variation a systematic pattern or merely the result of random scatter? Second, given evidence of seasonal variation to what level of complexity should the seasonal trend be modeled? The MML technique developed does not require user input rather will identify in a quantitative and consistent manner any patterns evident in the data. The patterns identified with MML can be used to remove seasonal variation effects. The analysis utilized 104,188 roughness values obtained from a particular region in Australia over 15 years. MML inference recognized patterns of seasonal variation and demonstrated that these are not merely due to random scatter. The optimum model selected by MML inference has four separate segments of variation. These segments correspond to changes in climatic conditions that support the inference.