Wind Vibration Study of Long-span Steel Arch Structure of Beijing Capital International Airport

IntroductionThe long-span light-weight steel arch struc-tures have been widely used in the world due to itsbeautiful shape and reasonable mechanical charac-teristics. With the development of the computa-tional theory, the steel arch span becomes longerand longer. So, the wind loads become the majoror even dominant loads applied on steel arch struc-tural system[1~3]. The distress and damage willprobably occur in the structure, because of thelong term wind-induced vibration.1 Structural Wind-in…     

石龙山隧道爆破振动信号的小波分析

采用db8作为小波基函数,对石龙山隧道同一炮次下垂直向、水平切向和水平径向的原始爆破振动信号进行尺度为7的一维离散小波变化。通过MATLAB程序分别计算了原始信号、各层小波的功率谱及能量比例;详细分析了各层小波的幅值特性、频谱特性及能量分布特性。研究结果表明:垂直向、水平切向和水平径向的优势频率分别为78.125～2 500 Hz、39.062 5～312.5 Hz和39.062 5～625 Hz。该分析方法在频率及能量分析方面的优势可以更加全面地获取爆破振动信号所带来的信息。     

Research on Morlet Wavelet Based Lamb Wave Spatial Sampling Signal Optimization Method

In recent years, Lamb wave and piezoelectric transducers (PZTs) array based wavenumber filtering technique for damage estimation has been gradually studied. Compared with the time domain and frequency domain analysis of the Lamb wave signals, the wavenumber domain analysis is an effective approach to distinguish wave propagating direction and wave modes. However, the spatial resolution sampled by the PZTs is lower than that sampled by scanning laser Doppler vibrometer. As for the diameter of the PZT, it cannot be very small. In this paper, a new Lamb wave spatial sampling signal optimization method based on Morlet wavelet is proposed. Firstly, the frequency band parameter of the Morlet mother wavelet function is calculated by the Lamb wave excitation signal. Then, the sum of squared errors between the Lamb wave spatial sampling signal and the Morlet wavelet function fitting waveform at each scale factor and time factor is calculated. Finally, the scale factor and time factor corresponding to the least sum of squared errors can be judged to be the best match scale factor and time factor respectively, and the Morlet wavelet function fitting waveform in that scale factor and time factor can be seen as the optimized Lamb wave spatial sampling signal. The validation experiment performed on a glass fiber epoxy composite plate shows that the proposed method can improve the spatial resolution and length of the Lamb wave spatial sampling signal, and the sum of squared errors of this method is no more than 0.2.     

A NOVEL METHOD FOR NETWORK WORM DETECTION BASED ON WAVELET PACKET ANALYSIS

Objective To detect unknown network worm at its early propagation stage. Methods On the basis of characteristics of network worm attack, the concept of failed connection flow （FCT） was defined. Based on wavelet packet analysis of FCT time series, this method computed the energy associated with each wavelet packet of FCT time series, transformed the FCT time series into a series of energy distribution vector on frequency domain, then a trained K-nearest neighbor （KNN） classifier was applied to identify the worm. Results The experiment showed that the method could identify network worm when the worm started to scan. Compared to theoretic value, the identification error ratio was 5.69%. Conclusion The method can detect unknown network worm at its early propagation stage effectively.     

基于小波变换的混沌信号特征研究

应用小波方法将混沌信号的频谱特征和吸引子的几何结构相结合进行研究,结果表明,在不同尺度上对混沌信号进行连续小波变换时,其小波系数具有很强的相似性,但不能够完全重构原来的吸引子.对信号进行多尺度分解后发现其低频系数部分基本能够重现原吸引子的结构特征,而高频系数部分不能实现这一目标.为了定量刻画混沌信号在小波变换条件下的分形特征,计算了其在不同尺度时的关联维数,并分析了关联维数计算的影响因素.     

基于路面不平整度的车辆振动响应分析方法

为了分析路面与车辆的相互作用,提出了四自由度1/2车辆模型相对于不平整路面耦合振动分析方法。根据GB/T7031-1986建议的公路路面功率谱密度的拟合表达式,在分析了运行汽车固有振动频率和行驶速度的影响后,获得分布在一定频率范围内的离散功率谱密度数据,利用离散傅立叶逆变换得到路面不平度值,并以此作为1/2车辆垂向动力学模型的输入激励,通过数值仿真得到运行车辆系统在不同路面不平整度下的时域响应。分析结果表明:车辆动荷载系数随车速增大呈线性增加,随路面等级变差呈非线性增大,路面等级是影响车辆动力作用的最显著因素。     

高速列车随车移动点的脉动风速模拟

以修正Karman风速谱为目标谱, 基于最小信息准则确定线性滤波法自回归模型的阶数, 采用线性滤波法和谐波叠加法模拟了高速列车随车移动点的脉动风速时间历程, 并验证了模拟结果的可靠性, 对比了2种方法模拟脉动风速均值、方差、幅频、相频等特征变量以及风速分布规律的差异, 并分析了2种方法的计算效率。分析结果表明: 采用2种方法得到的脉动风速功率谱密度均围绕目标谱波动; 脉动风速均值约为0, 由于随机数的使用, 使得脉动风速峰值在个别时间点存在差异, 且在低频区域得到的仿真谱差异可能超过50%;不同风向角下计算所得脉动风速均值的差异小于2%, 且脉动风速的分布规律几乎一致; 当列车运行速度为80m·s-1, 且距地面高度10m处平均风速为25m·s-1时, 2种方法得到的脉动风速峰值均值间的差异小于1%, 表明2种方法均适用于模拟高速列车随车移动点的脉动风速; 2种方法所得脉动风速幅值均随脉动风速频率的增大而减小, 相位在-π~π内波动, 脉动风速分布在-3~3m·s-1内的差异仅为0.48%;采用2种方法所得脉动风速点数满足高斯分布, 且高斯分布拟合系数最大差异为3.15%;采用线性滤波法模拟所得脉动风速波动比谐波叠加法大7.89%, 其稳定性劣于谐波叠加法; 采用线性滤波法的计算时间约为谐波叠加法的1/9, 其计算效率远高于谐波叠加法。      

井下低压电力线多载波通信系统的小波基选择

在简要分析我国煤矿配电网的基本结构的基础上,提出基于小波变换的通信系统,该系统采用小波基取代传统的正交频分复用中的余弦函数基的多载波调制技术.通过对6种典型小波基分析比较,结合井下低压电力线的应用条件,给出OFDM通信系统中小波基的选择原则,指出正交性在OFDM系统中具有重要作用.     

小波变换在诊断奇异信号中的作用

分析了传统的Fourier变换和短时Fourier变换STFT等两种信号分析方法在时-频分析中存在的问题。阐述了小波变换在诊断奇异信号中的作用。     

大跨度悬索桥静风稳定可靠性分析

基于一次二阶矩可靠度理论和非线性静风稳定性的分析方法,把静风失稳风速、基准风速及风速随机性修正系数作为随机变量,提出了大跨度桥梁静风稳定性可靠度分析方法.以某大跨度悬索桥为工程实例,对不同初始风攻角下的静风失稳进行了可靠性分析,并进一步作了静风失稳可靠度敏感性分析.结果表明：该桥基本上不会发生静风失稳,＋3°;初始攻角工况是该桥发生静风失稳的控制工况,静风失稳可靠度对静风失稳风速最敏感.     

荆岳长江大桥附近大风特征及设计风速推算研究

利用岳阳气象站1952~2000年逐年10 min平均最大风速资料序列,对大风特征进行了分析.利用极值Ⅰ型分布曲线,推算出气象站处基本风速,结合沿江观测对比记录,通过比值法把基本风速推算到设计风速.结果表明:(1)桥位附近10 min平均年最大风速极值24.7 m/s,主导风为东北风;(2)不同重现期(100,50,30,10 a)10 m高处10 min平均年最大风速(基本风速)分别为27.6,25.4,23.8,20.2 m/s;(3)考虑5%的计算误差,桥位区不同重现期(100,50,30,10 a)10 m高处10 min平均年最大风速(设计风速)分别为29.0,26.7,25.0,21.2 m/s;(4)利用近地层风速随高度的指数变化推算出300 m以下每10 m高度层的设计基准风速.     

基于特征正交分解的桥梁风场模拟

推导出了随机过程特征正交分解计算公式.为提高原型谱表示法的计算速度,将特征正交分解的强形式,即基于功率谱矩阵的随机过程特征正交分解(SPT)引入到谱表示法中,代替原有的对功率谱矩阵的Cho lesky分解,并给出了实用的模拟公式.该算法可用FFT加速.结合模态截断技术,POD的引进可节省谱表示法模拟的计算量.通过算例,定义了风的吹动模态,说明了风场SPT的明确的物理意义,同时模拟方法的有效性亦得到验证.     

基于混沌理论的建设项目环保投资估算研究

采用混沌时间序列分析技术对我国高速公路环保投资做了较为全面的研究,分析了1997年—2006年我国部分高速公路环保投资的数据。首先对数据结构进行定性分析,通过频数分布图,发现环保投资数据与正态分布之间存在着差异。功率谱分析、主分量分析则清楚表明序列具有非线性性质,主分量分析还表明序列具有混沌迹象。在定性分析的基础上,通过计算序列的有关非线性特征值对其混沌性质进行进一步确认。采用G—P算法计算序列的相关维,采用小数据量法计算最大Lyapunov指数。计算得到的最大Lyapunov指数为正数,说明环保投资序列处于混沌状态,可以使用混沌时间序列方法对建设项目可行性研究阶段环保投资进行估算。     

Novel Adaptive Beamforming Algorithm Based on Wavelet Packet Transform

An analysis of the received signal of array antennas shows that the received signal has multi-resolution characteristics, and hence the wavelet packet theory can be used to detect the signal. By emplying wavelet packet theory to adaptive beamforming, a wavelet packet transform-based adaptive beamforming algorithm (WP-ABF) is proposed . This WP-ABF algorithm uses wavelet packet transform as the preprocessing, and the wavelet packet transformed signal uses least mean square algorithm to implement the adaptive beamfonning. White noise can be wiped off under wavelet packet transform according to the different characteristics of signal and white under the wavelet packet transform. Theoretical analysis and simulations demonstrate that the proposed WP-ABF algorithm converges faster than the conventional adaptive beamforming algorithm and the wavelet transform-based beamforming algorithm. Simulation results also reveal that the convergence of the algorithm relates closely to the wavelet base and series; that is, the algorithm convergence gets better with the increasing of series, and for the same series of wavelet base the convergence gets better with the increasing of regularity.     

大跨度钢管混凝土拱桥时域抖振分析

探讨了利用非平稳随机过程理论和少量的实际风速记录模拟自然风,并以此作为桥址处的自然风用时域抖振分析方法对某系杆拱桥进行抖振时域分析。通过将计算结果与风洞试验结果的比较,发现二者误差不大。     

内河表面实测水流流速数据处理技术研究

水流流速是河流研究、航道项目设计中的重要参数,由于测量仪器自有的噪声误差、水流运动的脉动性以及测量人员的随机测量错误,都可能导致测量误差较大,不能保证数据的准确性.针对这一问题,文章采用数学分析法,以每个施测横向断面为基本单位,依次使用小波包滤波去噪和移动平均值法过滤,很好地消除了数据噪声及波动误差,流速的横向分布的连续性有了很大提高.通过傅里叶转换方程对降噪前后进行能谱分析,降噪前后差异很小,趋势基本一致.最后,借助SMS软件将数据点离散,生成了河段地形图.其结论方法可以为同类河流的实测流速数据处理提供技术支持.     

主动来流模拟技术试验研究

随着现代大跨度桥梁不断向长大化方向发展,风荷载作用越来越突出,风洞试验作为研究的最重要手段需要精细化,以准确模拟自然风特性。本文在充分调研基础上,进行主动来流模拟技术研究,基于主动控制风洞,制作主动振动机翼,调整不同来流的能量分配,实现了多点来流风速与气动力分量等试验数据实时同步采集,提出空间同步转换法,解决了试验模型处流场真实状况准确测试问题,充分模拟多项气动力,为更加精细化分析提供有效的方法和手段。利用主来流模拟技术,通过数值分析,从理论上对窄带谱、宽带谱来流的空间相关性进行研究,分析解释了部分典型气动力现象,得到有意义结论,为深入研究提供参考资料。     

利用GNSS时序分析辨识大跨桥梁结构荷载响应研究

使用小波分析、功率谱密度等方法,对武汉市阳逻大桥GNSS监测数据进行分析,识别并分离大桥不同位置结构车辆移动荷载响应、车辆振动荷载响应和噪声,首先去除噪声,然后利用信号不同频率特性,分离静态信号和动态信号,从而得到更为清晰的大跨度桥动力响应特性。     

A Computational Model for Pedestrian Level Wind Environment Around Tall Buildings

A computational model has been developed for the simulation of pedestrian level wind environment around tall buildings by coupling the numerical simulation of the full-scale site and meteorological station materials. In the first step, the hybrid/mixed finite element method is employed to solve the two dimensional Navier-Stokes equation for the flow field around tall buildings, in view of the influence of fluctuating wind, the flow field is revised with the effective wind velocity. The velocity ratio is defined in order to relate numerical wind velocity to oncoming reference wind velocity. In the second step, the frequency occurred discomfort wind velocity as a suitable criterion is calculated by use of the coupling between the numerical wind velocity and the wind velocity at the nearest meteorological station. The prediction accuracy of the wind environment simulation by use of the computation model will be discussed. Using the available wind data at the nearest meteorological station as well as the established criteria of wind discomfort, the frequency of wind discomfort can be predicted. A numerical example is given to illustrate the application of the proposed method.     

小波分析在弧焊机器人视觉检测中的应用

针对弧焊机器人薄板对接、搭接焊缝的自动焊接问题,将小波分析应用在CCD直接获取的焊缝图像的处理中,用来提取焊缝轨迹.根据薄板的对接和搭接焊缝图像的特点,建立了斜坡型及梯形小波分析模型,通过对模型的多尺度小波变换和李氏指数的分析,可以区分焊缝的边缘类型,从而增强了焊缝轨迹提取方法的抗干扰性和适应性,也为弧焊机器人的自动化和智能化焊接提供一定的技术参考.