Dynamic analysis of train–bridge system subjected to non‐uniform seismic excitations     

He Xia  Yan Han  Nan Zhang  Weiwei Guo 《地震工程与结构动力学》2006,35(12):1563-1579

Based on the theory of dynamic wheel–rail interactions, a dynamic model of coupled train–bridge system subjected to earthquakes is established, in which the non‐uniform characteristics of the seismic wave input from different foundations are considered. The bridge model is based on the modal comprehension analysis technique. Each vehicle is modelled with 31 degrees of freedom. The seismic loads are imposed on the bridge by using the influence matrix and exerted on the vehicles through the dynamic wheel–rail interaction relationships. The normal wheel–rail interaction is tackled by using the Hertzian contact theory, and the tangent wheel–rail interaction by the Kalker linear theory and the Shen–Hedrick–Elkins theory. A computer code is developed. A case study is performed to a continuous bridge on the planned Beijing–Shanghai high‐speed railway in China. Through input of typical seismic waves with different propagation velocities to the train–bridge system, the histories of the train running through the bridge are simulated and the dynamic responses of the bridge and the vehicles are calculated. The influences of train speed and seismic wave propagation velocity on the dynamic responses of the bridge–vehicle system are studied. The critical train speeds are proposed for running safety on high‐speed railway bridges under earthquakes of various intensities. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

利用ASAR图像监测土壤含水量和小麦覆盖度   总被引：8，自引：0，他引：8  

鲍艳松  刘良云  王纪华  李小文  李翔  宋小宇  竞霞 《遥感学报》2006,10(2):263-271

以高级合成孔径雷达（ASAR）影像数据和地面实测数据为基础，分析了裸土、低覆盖（覆盖度为0．2左右）冬小麦麦地的后向散射与土壤含水量、地表粗糙度及小麦覆盖度之间的关系，探讨了裸土和冬小麦麦地土壤含水量及小麦覆盖度的反演方法。分析结果表明：①裸土后向散射系数受地表粗糙度和土壤质地的综合影响较大，裸土的后向散射和土壤含水量正相关关系未达显著，反演裸土土壤含水量必须考虑这两个因素的影响。②冬小麦麦地两种极化后向散射对土壤含水量和小麦覆盖度的敏感性差异明显。由于小麦植株与土壤的水平同极化后向散射差异较大，水平极化后向散射系数和小麦覆盖度及土壤含水量相关性达到显著；冬小麦麦地的垂直同极化后向散射对土壤含水量较敏感，垂直极化后向散射系数和土壤含水量的相关性达到显著，但与小麦覆盖度的相关性相对较低。据此，利用冬小麦麦地的两个同极化后向散射系数，建立了后向散射系数与土壤含水量和小麦覆盖度之间的关系模型，实现了小麦覆盖度和冬小麦覆盖下的土壤含水量反演。验证结果表明：土壤含水量和小麦覆盖度反演结果与地面调查和测量结果一致。  相似文献   

甘肃北山大石山A型花岗岩体的地球化学特征及构造意义   总被引：10，自引：0，他引：10  

齐瑞荣  黄增保  金霞 《岩石矿物学杂志》2006,25(2):90-96

甘肃北山大石山岩体主要由角闪花岗岩和二长花岗岩组成,岩石的化学成分特点为过铝质(Al_2O_3含量为 12.18%～13.37%)、富硅(SiO_2含量为74.22%～78.38%)、偏碱(Na_2O+K_2O 为7.60%～8.50%),FeO~T/MgO 值高,CaO 和 MgO 含量低(分别为0.01%～0.99%和0.05%～1.15%),富含 Y、Nb 等高场强元素(HFSE)以及 F、Sr、 Ba 和 REE(∑REE=102.3×10~(-6)～120.02×10~(-6))低。这些特点与本区的 I 型和 S 型花岗岩有明显差别,是一种典型的 A_2型花岗岩。大石山岩体 Rb-Sr 等时线年龄为273 Ma,表明北山地区在海西晚期即进入造山后拉张裂解环境。  相似文献   

金堆城钼矿固体废物对水环境的污染     

李侠  张益谦 《地下水》2006,28(5):64-66

本文通过对陕西华县金堆城钼矿区西川河流经废石堆的入口处和出口处采取的水样进行了常量组分、微量组分的测定,分析其污染特征,确定出金堆城钼矿废石堆对水环境的污染指标.  相似文献   

利用GRACE轨道和加速度数据恢复地球重力场     

肖云夏哲仁  王兴涛 《测绘科学与工程》2006,26(2):8-10

本文基于高低卫卫跟踪的模式，用积分方法研究了不同重力场模型对于轨道的影响，并用3个月的GRACE轨道数据计算了新的60阶地球重力场模型，为了分析其精度，与EGM96和EIGENIS作了比较．结果表明新模型在40阶前更接近GGM02C模型。  相似文献   

Long-range Automaton Models of Earthquakes: Power-law Accelerations,Correlation Evolution,and Mode-switching     

D. Weatherley  P. Mora  M. F. Xia 《Pure and Applied Geophysics》2002,159(10):2469-2490

—?We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r ^?p dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.  相似文献   

The uplifting and environmental change of Qinghai-Xizang (Tibetan) Plateau in the past 0.9 Ma inferred from core RM of Zoige Basin   总被引：1，自引：0，他引：1  

Bin Xue  Sumin Wang  Weilan Xia  Jinglu Wu  Yunfei Wang  Junlong Qian  Shouyun Hu  Yanhong Wu  Pingzhong Zhang 《中国科学D辑(英文版)》1998,41(2):165-170

According to the synthetic multi-disciplinary study on the lake sediments from core RM of Zoige Basin, i.e. the deepest wholly-collected core in Tibetan Plateau, the palaeoclimate and palaeoenvironment for the basin in the past 0.9 Ma have been reconstructed. The analytical results suggest that there distinctively exist 3 accelerated uplifting periods for the east Plateau in the past 0.9 Ma, i.e. 800, 360 and 160 kaB.P., with the study on the sedimentary characteristics, the texture of sedimentary cycles and variations of depositional rates, in conjunction with the environment features of cold/warm to dry/wet combination. The paper also probes into the environmental effect under the 3 accelerated tectonic-upliftings on the background of global change.  相似文献   

The water-bearing numerical model and its operational forecasting experiments part I: the water-bearing numerical model     

Xia Daqing  Xu Youping 《大气科学进展》1998,15(2):221-232

ＴｈｅＷａｔｅｒ－ＢｅａｒｉｎｇＮｕｍｅｒｉｃａｌＭｏｄｅｌａｎｄＩｔｓＯｐｅｒａｔｉｏｎａｌＦｏｒｅｃａｓｔｉｎｇＥｘｐｅｒｉｍｅｎｔｓＰａｒｔＩ：ＴｈｅＷａｔｅｒ－ＢｅａｒｉｎｇＮｕｍｅｒｉｃａｌＭｏｄｅｌＸｉａＤａｑｉｎｇ（夏大庆）ａｎｄＸｕＹ...  相似文献   

沽源—多伦盆地火山岩类和花岗岩类同位素地质年代学及铀成矿条件研究   总被引：4，自引：1，他引：3  

夏毓亮  林锦荣 《铀矿地质》1998,14(5):274-281

本文对沽源-多伦盆地火山岩类和花岗岩类进行了同位素地质年代学和铀成矿条件的系统研究。确定了该区张家口组、花吉营组火山岩类均属早白至世产物,其形成年龄为125—135Ma。指出本区花岗岩浆活动有前海西期、海西期、印支期和燕山期,不存在文献中提到的自北而南分布的3条东西向海酉期花岗岩浆活动带。本文还指出该区区域铀成矿作用具有多期次的特点,同一矿床铀成矿作用的叠加是形成富铀矿体的前提。该区火山岩类钠含量较低,对铀成矿不利。然而,在不利的地质背景中局部存在利于铀成矿的地段和岩性,应作为今后重点的找矿对象。  相似文献   

永泰李农业地质背景与李叶片营养诊断   总被引：1，自引：0，他引：1  

夏春金 《福建地质》1998,17(2):85-93

通过对永泰县不同地质背景区李叶片的采集和测试矿质元素含量,分析了各区李叶营养状况。认为,要根据不同李园、不同季节的叶片营养状况,以及各地质背景区土壤矿质元素丰缺和有效态元素含量多少,进行对症施肥,以提高李果产量和品质。  相似文献