System identification of linear structures based on Hilbert–Huang spectral analysis. Part 2: Complex modes

A method, based on the Hilbert–Huang spectral analysis, has been proposed by the authors to identify linear structures in which normal modes exist (i.e., real eigenvalues and eigenvectors). Frequently, all the eigenvalues and eigenvectors of linear structures are complex. In this paper, the method is extended further to identify general linear structures with complex modes using the free vibration response data polluted by noise. Measured response signals are first decomposed into modal responses using the method of Empirical Mode Decomposition with intermittency criteria. Each modal response contains the contribution of a complex conjugate pair of modes with a unique frequency and a damping ratio. Then, each modal response is decomposed in the frequency–time domain to yield instantaneous phase angle and amplitude using the Hilbert transform. Based on a single measurement of the impulse response time history at one appropriate location, the complex eigenvalues of the linear structure can be identified using a simple analysis procedure. When the response time histories are measured at all locations, the proposed methodology is capable of identifying the complex mode shapes as well as the mass, damping and stiffness matrices of the structure. The effectiveness and accuracy of the method presented are illustrated through numerical simulations. It is demonstrated that dynamic characteristics of linear structures with complex modes can be identified effectively using the proposed method. Copyright © 2003 John Wiley & Sons, Ltd.     

Evaluation of predictors of non‐linear seismic demands using ‘fishbone’ models of SMRF buildings

Predictors (or estimates) of seismic structural demands that are less computationally time‐consuming than non‐linear dynamic analysis can be useful for structural performance assessment and for design. In this paper, we evaluate the bias and precision of predictors that make use of, at most, (i) elastic modal vibration properties of the given structure, (ii) the results of a non‐linear static pushover analysis of the structure, and (iii) elastic and inelastic single‐degree‐of‐freedom time‐history analyses for the specified ground motion record. The main predictor of interest is an extension of first‐mode elastic spectral acceleration that additionally takes into account both the second‐mode contribution to (elastic) structural response and the effects of inelasticity. This predictor is evaluated with respect to non‐linear dynamic analysis results for ‘fishbone’ models of steel moment‐resisting frame (SMRF) buildings. The relatively small number of degrees of freedom for each fishbone model allows us to consider several short‐to‐long period buildings and numerous near‐ and far‐field earthquake ground motions of interest in both Japan and the U.S. Before doing so, though, we verify that estimates of the bias and precision of the predictor obtained using fishbone models are effectively equivalent to those based on typical ‘full‐frame’ models of the same buildings. Copyright © 2003 John Wiley & Sons, Ltd.     

Continuous wavelet-like filter for a spherical surface and its application to localized admittance function on Mars

We have developed a 2D isotropic continuous wavelet-like transform for a spherical surface. The transform is simply defined as the surface convolution between the original field and a kernel, based on the zeroth-order Bessel function with a spherical correction. This spherical correction violates the geometric similarity for the various scales of the kernels, which becomes more apparent at longer wavelengths. We found numerically that this transform is practically equivalent to a Gaussian bandpass filter in the spherical harmonic domain. We have applied this wavelet-like transform on the recently acquired Martian gravity and topography fields. Using a ratio constructed locally from these two fields, we have constructed a map describing the lateral variations of the localized admittance function on Mars.     

垂线测量数据管理软件的研制及应用

介绍了基于局域网络开发的垂线测量数据管理软件的组成、原理、功能、操作及应用，该软件操作简单、使用方便、极易掌握，并能通过多方位、直观的图形表示来反映监测对象的挠度、倾斜、水平位移状态。     

采用Creator生成三维地形

介绍了Creator地形转换的四种算法，讨论了在Creator中生成地形的过程，并以福建省闽清地区水口店为研究区域，建立直观性的、真实性的三维地形。     

常用GPS载波相位差分电文格式分析与比较

介绍了差分GPS传输载波相位差分信息的常用电文格式，比较了其优缺点，提出了在低带宽的条件下更适合采用CMR格式的结论。     

基于Voronoi图的空间方向关系形式化描述模型

运用认知心理学信息加工的观点，建立了基于Voronoi图的空间方向关系形式化描述模型，并详细阐述了模型的逻辑结构、数据结构和空间方向的计算过程。为了验证模型的正确性，列举了该模型计算空间方向的几个例子，并总结了模型的优、缺点。     

遥感数据的遗传-超平面分割算法

在传统的采用超平面作为判别边界的分割方法中，使用统计学的方法确定类判别界面，当区域间的统计值大于区域内的统计值时，就会出现类判决界面难于确定的问题。遗传算法的特点是进行全局优化搜索，利用这种算法优势可以解决传统算法难以解决的超平面空间定位问题，从而解决类判决界面的确定问题。通过EOS／MODIS图像数据的分割对该方法作了详细的介绍，其分类精度明显高于统计学分类方法。     

无拓扑矢量数据快速压缩算法的研究与实现

首先论述传统矢量数据压缩算法：道格拉斯—普克法，分析将其应用于多边形边界数据压缩所造成的图形失真现象，在此基础上提出一种针对无拓扑矢量数据的快速压缩算法，并在MapInfo环境中实现该算法。     

三角钢标对GPS测量影响的试验分析

GPS测量控制网为了与地面国家控制网进行联合的平差，必须与国家坐标系进行联测，GPS接收机有时也必须安置在有三角钢标的旧有控制点上。通过对此分析研究了三角钢标对GPS测量的影响，对设计和实施GPS测量的用户具有一定的参考价值。