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.     

水下无源导航系统仿真匹配算法研究

针对水下无源导航(地形辅助导航)系统的特点，充分利用各种海洋地理特征传感器获取信息，进行数据预处理、算法分析、性能评估，然后进行智能数据融合，进而完成水下无源导航系统模块化的仿真设计，为水下无源导航系统的进一步研究提供可行的方法和技术。仿真结果表明，采用水下地形匹配辅助导航，能够有效地修正惯导误差达到设计要求，为真实海洋环境下的精确导航提供可靠的技术依据。     

Geology and Genesis of the Ta'ergou Skarn - Quartz Vein Tungsten Deposit in the North Qilian Caledonian Orogenic Belt, Northwest China

Abstract. The Ta'ergou tungsten deposit in Gansu province, northwestern China, is located in the western part of the North Qilian Caledonian orogen, and consists of scheelite skarn bodies and wolframite quartz veins. The tungsten‐bearing skarn developed by the replacement of carbonate layers intercalated in the Precambrian schist and amphibolite whereas wolframite‐quartz ore veins developed along a group of fractures that cut through horizontal skarns. The Ta'ergou tungsten deposit is genetically related to the Caledonian Yeniutan granodiorite intrusion and occurs ca. 500 m wide in the exo‐contact zone 300 ～ 500 m apart from the intrusion. The granodiorite displays a lower grade of differentiation, low content of SiO₂ and high contents of mafic components. There are three types of fluid inclusions in the wolframite‐quartz vein systems, i. e. aqueous, CO₂‐H₂O and CO₂‐rich. The homogenization temperature of aqueous inclusion ranges from 140 to 380d?C and their salinities from 6.4 to 17.4 equivalent wt% NaCl. Laser Raman spectroscopy shows that the inclusions contain a relatively high content of CO₂. The δ³⁴S values of skarn type sulfides range from +8.1 to +12.7 per mil and those of quartz vein sulfides from +9.3 to +14.9 per mil, similar to sulfides of the granodiorite with from +6.0 to +11.7 per mil. The δ¹⁸O values of quartz are between +10.5 and +13.3 per mil and those of wolframite between +3.4 and +5.1 per mil. The δ¹⁸O water values of ore forming fluids range from +0.6 to +6.4 per mil and suggest the mixture of magmatic fluids with meteoric water formed the ore‐forming fluids. It has been proved that Precambrian strata in the west sector of North Qilian region are enriched in tungsten. We propose the strata were remelted to be tungsten‐granitoid during subduction. The polymetallic tungsten was gradually accumulated into the roof pendants of the granite intrusion by fractional crystallization and then was deposited by hydrothermal fluids during metasomatism and infilling along fractures. On the other hand, the granite intrusion also acted as “heating machine” to make hydrothermal fluids leach out the metals from Precambrian strata and these metals joined the ore‐forming hydrothermal system.     

岩体边坡工程中的位移监测及分析

边坡工程的监测取决于监测人员对岩(土)体介质的认识程度和选择相应的方法和手段。通过对江西德兴铜矿大山村选矿厂东部边坡和北部楔形地质结构体稳定状况的监测,阐述了在边坡工程中位移监测的应用及有关分析。     

打桩挤土的现场试验研究及土体位移的计算公式

打桩挤土使周围土体发生位移,对周围其他桩及附近原有建筑物和基础设施产生破坏。本文通过典型工程打桩过程中的监测数据,运用小孔扩张理论结合回归分析方法导出了计算土体位移量的经验公式。运用该公式可定量预估挤土程度,防止意外事故的发生。     

硫同位素混合总体筛分

现代矿床学研究表明，绝大多数矿床的形成具有多来源、多阶段、多成因的特点。定量研究S同位素来源可将形成一个矿床的过程看作是多个总体的混合或叠加，在数学上这种混合或叠加可以用混合总体筛分的数学模型来描述。笔者在长江中下游地区和湖南东坡矿田中成功地应用混合总体筛分的数学模型，定量研究了S同位素来源的问题，这一问题的解决对于研究成矿物质来源和成矿机理具有重要的意义。     

Deconvolving the δO seawater component from subseasonal coral δO and Sr/Ca at Rarotonga in the southwestern subtropical Pacific for the period 1726 to 1997

To reconstruct oceanographic variations in the subtropical South Pacific, 271-year long subseasonal time series of Sr/Ca and δ¹⁸O were generated from a coral growing at Rarotonga (21.5°S, 159.5°W). In this case, coral Sr/Ca appears to be an excellent proxy for sea surface temperature (SST) and coral δ¹⁸O is a function of both SST and seawater δ¹⁸O composition (δ¹⁸O_sw). Here, we focus on extracting the δ¹⁸O_sw signal from these proxy records. A method is presented assuming that coral Sr/Ca is solely a function of SST and that coral δ¹⁸O is a function of both SST and δ¹⁸O_sw. This method separates the effects of δ¹⁸O_sw from SST by breaking the instantaneous changes of coral δ¹⁸O into separate contributions by instantaneous SST and δ¹⁸O_sw changes, respectively. The results show that on average δ¹⁸O_sw at Rarotonga explains ∼39% of the variance in δ¹⁸O and that variations in SST explains the remaining ∼61% of δ¹⁸O variance. Reconstructed δ¹⁸O_sw shows systematic increases in summer months (December-February) consistent with the regional pattern of variations in precipitation and evaporation. The δ¹⁸O_sw also shows a positive linear correlation with satellite-derived estimated salinity for the period 1980 to 1997 (r = 0.72). This linear correlation between reconstructed δ¹⁸O_sw and salinity makes it possible to use the reconstructed δ¹⁸O_sw to estimate the past interannual and decadal salinity changes in this region. Comparisons of coral δ¹⁸O and δ¹⁸O_sw at Rarotonga with the Pacific decadal oscillation index suggest that the decadal and interdecadal salinity and SST variability at Rarotonga appears to be related to basin-scale decadal variability in the Pacific.     

河西走廊东部强雷暴天气分析与预报

根据1961～2000年武威站雷暴天气实况资料分析了河西走廊东部40年强雷暴天气发生的气候规律，并研究了河西走廊东部强雷暴天气发生的4种环流背景及4种主要天气条件，归纳总结出其短期预报着眼点，为雷暴天气预报业务系统的研制奠定了基础。     

泰山顶部近地层风的方差与谱分析

风在速度与方向上的不稳定性可引发结构振动并可导致损坏。山顶风较少受局地作用影响, 流场较稳定，作为典型风况对山顶风湍流脉动情形进行的观测和分析，对于研究建筑结构风载振动情形有着重要意义。在不同风况下对泰山气象站近地层风的风速和风向进行了同时、逐秒测记，所得样本经检验符合正态分布。计算表明，风向样本方差显著大于风速样本方差。绘制了各风速、风向样本自、互谱密度曲线图。谱图显示诸样本具有红噪声序列特征，不同样本自、互谱密度曲线具有相近形状，而以风速自谱曲线吻合程度最好，谱密度曲线在周期为4秒及2秒处有峰值。此后的研究应结合记录仪器的改进增加采样频率，对周期为2秒以下谱曲线作进一步分析。     

天气形势调整过程中连续暴雨的个例分析

本文在分析了天气尺度背景及形成连续暴雨的物理量条件的基础上，找出连续三天暴雨的成因：由于大范围形势调整过程中同一低压系统在不同的环流形势配置下造成的，是天气形势调整过程中产生的，而不是通常概念上由于大范围环流形势稳定、有利降雨的系统得以持续影响造成的。