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

Jann N. Yang  Ying Lei  Shuwen Pan  Norden Huang 《地震工程与结构动力学》2003,32(10):1533-1554

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.  相似文献   

渭干河流域"2002·7"特大洪水分析   总被引：6，自引：0，他引：6  

黄健  毛炜峄  李燕  王顺德 《冰川冻土》2003,25(2):204-210

渭干河是塔里木河流域第六大源流, 位于天山西部南麓, 渭干河干流起点有新疆最大的流域性控制工程--克孜尔水库. 2002年7月下旬天山中西部山区出现大暴雨(雪)过程, 渭干河流域山区降水持续时间长达30 h以上, 山区降水量50 mm左右, 导致5条支流和渭干河干流出现有水文记录以来的最大洪峰, 流量超过警戒流量和危险流量的2～3.5倍, 暴雨(雪)过程结束之后, 融雪型洪峰长时间居高不下. 洪水过程中, 各支流以及暴雨与融雪等多种洪峰遭遇现象很明显. 克孜尔水库入库洪峰流量达3 660 m3*s-1, 经水库调洪错峰, 出库峰值流量为1 000 m3*s-1, 削峰率72.7%.  相似文献   

Landslide susceptibility analysis using GIS and artificial neural network     

Saro Lee  Joo‐Hyung Ryu  Kyungduck Min  Joong‐Sun Won 《地球表面变化过程与地形》2003,28(12):1361-1376

The purpose of this study is to develop landslide susceptibility analysis techniques using an arti?cial neural network and to apply the newly developed techniques to the study area of Yongin in Korea. Landslide locations were identi?ed in the study area from interpretation of aerial photographs, ?eld survey data, and a spatial database of the topography, soil type and timber cover. The landslide‐related factors (slope, curvature, soil texture, soil drainage, soil effective thickness, timber age, and timber diameter) were extracted from the spatial database. Using those factors, landslide susceptibility was analysed by arti?cial neural network methods. The landslide susceptibility index was calculated by the back‐propagation method, which is a type of arti?cial neural network method, and the susceptibility map was made with a geographic information system (GIS) program. The results of the landslide susceptibility analysis were veri?ed using landslide location data. The validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide location. A GIS was used to ef?ciently analyse the vast amount of data, and an arti?cial neural network to be an effective tool to maintain precision and accuracy. The results can be used to reduce hazards associated with landslides and to plan land use and construction. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

A procedure for evaluating seismic energy demand of framed structures     

Chung‐Che Chou  Chia‐Ming Uang 《地震工程与结构动力学》2003,32(2):229-244

Energy serves as an alternative index to response quantities like force or displacement to include the duration‐related seismic damage effect. A procedure to evaluate the absorbed energy in a multistorey frame from energy spectra was developed. For low‐ to medium‐rise frames, it required a static pushover analysis of the structure to determine the modal yield force and ductility factor of an equivalent single‐degree‐of‐freedom system for the first two modes. The energy spectra were then used to determine the energy contribution of each mode. A procedure was also developed to distribute the energy along the frame height based on energy shapes. This study showed that the second‐mode response in some cases needs to be considered to reflect the energy (or damage) concentration in the upper floors. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

System identification of the Vincent Thomas suspension bridge using earthquake records     

Andrew W. Smyth  Jin‐Song Pei  Sami F. Masri 《地震工程与结构动力学》2003,32(3):339-367

The Vincent Thomas Bridge in the Los Angeles metropolitan area, is a critical artery for commercial traffic flow in and out of the Los Angeles Harbor, and is at risk in the seismically active Southern California region, particularly because it straddles the Palos Verdes fault zone. A combination of linear and non‐linear system identification techniques is employed to obtain a complete reduced‐order, multi‐input–multi‐output (MIMO) dynamic model of the Vincent Thomas Bridge based on the dynamic response of the structure to the 1987 Whittier and 1994 Northridge earthquakes. Starting with the available acceleration measurements (which consists of 15 accelerometers on the bridge structure and 10 accelerometers at various locations on its base), an efficient least‐squares‐based time‐domain identification procedure is applied to the data set to develop a reduced‐order, equivalent linear, multi‐degree‐of‐freedom model. Although not the main focus of this study, the linear system identification method is also combined with a non‐parametric identification technique, to generate a reduced‐order non‐linear mathematical model suitable for use in subsequent studies to predict, with good fidelity, the total response of the bridge under arbitrary dynamic environments. Results of this study yield measurements of the equivalent linear modal properties (frequencies, mode shapes and non‐proportional damping) as well as quantitative measures of the extent and nature of non‐linear interaction forces arising from strong ground shaking. It is shown that, for the particular subset of observations used in the identification procedure, the apparent non‐linearities in the system restoring forces are quite significant, and they contribute substantially to the improved fidelity of the model. Also shown is the potential of the identification technique under discussion to detect slight changes in the structure's influence coefficients, which may be indicators of damage and degradation in the structure being monitored. Difficulties associated with accurately estimating damping for lightly damped long‐span structures from their earthquake response are discussed. The technical issues raised in this paper indicate the need for added spatial resolution in sensor instrumentation to obtain identified mathematical models of structural systems with the broadest range of validity. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

利用卫星测高空间技术建立数字化海洋     

彭富清  张瑞华  石磐  夏哲仁  程芦颖 《测绘工程》2003,12(1):37-40

论述了卫星测高空间技术的主要特征、科学意义及其在军事和经济建设领域的重要价值，阐明了国内外测高卫星系统的发展现状及利用卫星测高空间技术建立数字化海洋所取得的成果，分析卫星测高目前的研究方向，提出了发展我国卫星测高空间技术以及利用该技术建立数字化海洋的一些建议。  相似文献   

2001年11月14日昆仑山口西8.1级地震前地震活动性异常及其思考s   总被引：7，自引：0，他引：7       下载免费PDF全文

刘蒲雄  郑大林  车时  潘怀文  刘桂萍  杨立明 《地震学报》2003,25(2):205-210

2001年11月14日在昆仑山口西发生了8.1级地震，震中位置为90.9E、36.2N．分析表明，8.1级地震前一些主要地震活动性异常都出现了，例如空区、条带、增强、平静和震群等，且与7级大震比较，这些前兆图象的演变具有类似的过程，所不同的是8.1级地震的前兆地震活动图象涉及的区域范围更大、地震震级更高，这为特大地震的前兆识别和预报提供了依据．最后回顾了对这次大震的粗略预测，并讨论了有关大震预测的某些问题．   相似文献   

长白山天池火山区长白-敦化剖面结晶基底的探测和研究     

潘素珍  张先康  杨卓欣  张成科  赵金仁  潘纪顺  任青芳  张建狮 《地震研究》2003,26(3):271-274

时间项分析法中，应用广义最小二乘法进行反演，对长白山天池火山区岩浆系统的长白—敦化(L1)剖面的Pg波到时进行了计算处理，得到了Pg波时间项及基底速度值；取上部地壳的介质平均速度为4．5km/s，经反演求得了各点的深度值，给出了长白山天池火山区结晶基底的厚度分布。结晶基底厚度一般在2．0km左右，而在长白山天池下方结晶基底最厚处接近4．0km；在万宝和敦化附近各有一不太明显的凹陷，其原因可能与在这两个位置处有几条断裂穿过有关。  相似文献   

北京正负电子对撞机注入器复测分析     

花向红  潘正风 《测绘工程》1997,6(3):50-55

介绍北京正负电子对撞机注和器复测的精度要求，阐述采用波带板激光准直系统与精密水准测量相结合的方法，进行注入器复测的观测、数据处理与调整。根据复测数据分析了隧道地基变形与加速管位置变形及其规律，提出了一些有益的结论与建议。  相似文献   

大布苏湖沉积剖面碳酸盐含量氧同位素特征的古气候意义   总被引：10，自引：3，他引：10  

沈吉  吴瑞金  羊向东  潘红玺  安芷生 《湖泊科学》1997,9(3):217-222

对大布苏湖沉积剖面碳酸盐含量和氧同位素特征研究表明，湖区15000年以来经历了多期冷湿与暖干气候旋回，大约距今6700年左右，气候变干并进入稳定的温暖时期，湖水逐渐高度浓缩，形成了现今的盐碱湖。  相似文献