A wind tunnel investigation on the transverse motion of aeolian sand   总被引：1，自引：0，他引：1  

ZhenTing Wang  QianHua Zhang  ZhiBao Dong 《寒旱区科学》2011,3(1):0013-0016

A wind tunnel experiment was performed to investigate aeolian grain motions in the transverse direction, which is perpendicular to the incoming flow and parallels the sand bed. The trajectories in the horizontal plane were recorded by high-speed camera. Statistical analysis of 630 trajectories shows that both the motion orientation and the time-averaged speed follow Gaussian distributions. An exclusive method was used to analyze the driving mechanism. It was concluded that the three-dimensional turbulent air flow, rather than the spin of grain or grain–bed collisions, controls the transverse motion.  相似文献   

A generalized conditional intensity measure approach and holistic ground‐motion selection     

Brendon A. Bradley 《地震工程与结构动力学》2010,39(12):1321-1342

A generalized conditional intensity measure (GCIM) approach is proposed for use in the holistic selection of ground motions for any form of seismic response analysis. The essence of the method is the construction of the multivariate distribution of any set of ground‐motion intensity measures conditioned on the occurrence of a specific ground‐motion intensity measure (commonly obtained from probabilistic seismic hazard analysis). The approach therefore allows any number of ground‐motion intensity measures identified as important in a particular seismic response problem to be considered. A holistic method of ground‐motion selection is also proposed based on the statistical comparison, for each intensity measure, of the empirical distribution of the ground‐motion suite with the ‘target’ GCIM distribution. A simple procedure to estimate the magnitude of potential bias in the results of seismic response analyses when the ground‐motion suite does not conform to the GCIM distribution is also demonstrated. The combination of these three features of the approach make it entirely holistic in that: any level of complexity in ground‐motion selection for any seismic response analysis can be exercised; users explicitly understand the simplifications made in the selected suite of ground motions; and an approximate estimate of any bias associated with such simplifications is obtained. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

桐柏老湾金矿带成矿构造体系演化研究及其地质意义          下载免费PDF全文

陈建立 《地质找矿论丛》2019,34(1):36-46

通过对老湾成矿带各期构造作用、区域变质作用、岩浆作用、矿化富集作用研究,将老湾成矿带成矿构造体系演化分为三个阶段:加里东-华力西期深层次韧性剪切作用,形成的NNW向构造控矿因素深远,起初始富集作用;从印支晚期(236～214 Ma)开始,在燕山期或期前(132.5Ma)为脆-韧性剪切-右行走滑体系,矿液再次充填控矿形成现在的富矿体;燕山末期后发生了浅层次脆、韧性构造和构造推覆。并建立了老湾金矿带"早期老湾韧性剪切成矿构造系统"与"中期高角度右型走滑脆韧性断裂构造系统叠加"和"晚期构造掩盖或破坏"三期成矿构造演化体系。三期成矿构造演化体系的建立和"晚期老湾岩体推覆于龟山岩组上"的认识,极大地拓展了赋矿地层空间,为取得找矿突破提供重要理论依据。  相似文献   

Extended consecutive modal pushover procedure for estimating seismic responses of one-way asymmetric plan tall buildings considering soil-structure interaction     

Mohammad Hadikhan Tehrani  Faramarz Khoshnoudian 《地震工程与工程振动(英文版)》2014,13(3):487-507

Performance based design becomes an effective method for estimating seismic demands of buildings. In asymmetric plan tall building the effects of higher modes and torsion are crucial. The consecutive modal pushover (CMP) procedure is one of the procedures that consider these effects. Also in previous studies the influence of soil-structure interaction (SSI) in pushover analysis is ignored. In this paper the CMP procedure is modified for one-way asymmetric plan mid and high-rise buildings considering SSI. The extended CMP (ECMP) procedure is proposed in order to overcome some limitations of the CMP procedure. In this regard, 10, 15 and 20 story buildings with asymmetric plan are studied considering SSI assuming three different soil conditions. Using nonlinear response history analysis under a set of bidirectional ground motion; the exact responses of these buildings are calculated. Then the ECMP procedure is evaluated by comparing the results of this procedure with nonlinear time history results as an exact solution as well as the modal pushover analysis procedure and FEMA 356 load patterns. The results demonstrate the accuracy of the ECMP procedure.  相似文献   

高层建筑时程分析中地震动时程选择和修改方法研究   总被引：2，自引：1，他引：1  

肖遥  张郁山  靳超宇 《震灾防御技术》2014,9(3):400-410

合理的地震动时程选择与修改方法对于高层结构的抗震设计具有重要意义,有着广泛的工程应用.本文回顾了建筑抗震设计规范对于输入地震动时程的规定,通过对现有的地震动时程选择与修改方法进行分类和定性分析,挑选了两种与规范要求衔接较好的方法.结合具体算例对两种方法进行了定量分析,结果表明以安评设计谱作为选择指标,利用最小二乘法对选择的地震动时程进行修改,可以得到离散较小且符合规范要求的地震动时程,该成果能够在现行规范要求下为结构的抗震设计提供合理可靠的依据.同时,本文也对未来地震动时程选择与修改方法的研究和发展方向进行了展望,指出条件均值谱和非弹性反应谱将是该领域未来主要的研究方向.  相似文献   

汶川地震山脚震害特征及机理分析1   总被引：1，自引：0，他引：1  

王伟  刘必灯  刘欣  沈超  周正华 《震灾防御技术》2014,9(4):863-871

汶川地震和以往地震现场震害调查表明,局部场地地形对震害的影响明显,其中,山脚房屋震害程度明显低于山顶和水平地表土层场地.针对这一震害特征,本文以汶川主震的地形效应观测强震动记录和人工爆破山体地形地震动观测记录为基础,通过数据分析,结合动力集中质量中心差分有限元法进行数值模拟分析,进一步揭示了山脚房屋震害轻微的特征不仅与其所在场地条件良好有关,更与山脚所处山体底部的几何位置直接相关.  相似文献   

Air-sea carbon-dioxide flux estimated by eddy covariance method from a buoy observation   总被引：1，自引：0，他引：1  

HUANG Yansong  SONG Jinbao  WANG Juanjuan  FAN Conghui 《海洋学报(英文版)》2012,31(6):66-71

Precise measurements of the CO2 gas transfer across the air-sea interface provide a better understanding of the global carbon cycle.The air-sea CO2 fluxes are obtained by the eddy covariance method and the bulk method from a buoy observation in the northern Huanghai sea.The effects of buoy motion on flux calculated by the eddy covariance method are demonstrated.The research shows that a motion correction can improve the correlation coefficient between the CO2 fluxes estimated from two different levels.Without the CO2-H2 O cross-correlation correction which is termed as PKT correction,the air-sea CO2 fluxes estimated by eddy covariance method using the motion corrected data are nearly an order of magnitude larger than those estimated by the bulk method.After the CO2-H2 O cross-correlation correction,some eddy covariance CO2 fluxes indeed become closer to the bulk CO2 flux,whereas some are overcorrected which are in response to small water vapor flux.  相似文献   

Study of tide prediction method influenced by nonperiodic factors based on support vector machines   总被引：1，自引：1，他引：0  

HE Shijun  ZHOU Wenjun  ZHOU Ruyan  HUANG Dongmei 《海洋学报(英文版)》2012,31(5):160-164

Harmonic analysis, the traditional tidal forecasting method, cannot take into account the impact of noncyclical factors, and is also based on the BP neural network tidal prediction model which is easily limited by the amount of data. According to the movement of celestial bodies, and considering the insufficient tidal characteristics of historical data which are impacted by the nonperiodic weather, a tidal prediction method is designed based on support vector machine (SVM) to carry out the simulation experiment by using tidal data from Xiamen Tide Gauge, Luchaogang Tide Gauge and Weifang Tide Gauge individually. And the results show that the model satisfactorily carries out the tide prediction which is influenced by noncyclical factors. At the same time, it also proves that the proposed prediction method, which when compared with harmonic analysis method and the BP neural network method, has faster modeling speed, higher prediction precision and stronger generalization ability.  相似文献   

曲率半径对大温差地区小半径曲线梁桥地震响应影响分析          下载免费PDF全文

丁万鹏  虞庐松  李子奇  王力 《地震工程学报》2022,44(1):93-99

为研究曲率半径和近断层脉冲效应对大温差地区小半径曲线梁桥在地震作用下的动力响应和碰撞效应的影响规律,以某大温差地区曲线梁桥为研究对象,建立不同曲率半径的全桥非线性有限元模型,考虑温度变化对支座性能和伸缩缝间距的影响,开展桥梁地震响应分析.结果表明:随着主梁曲率半径增大,墩底内力响应逐渐增加,邻梁间碰撞效应逐渐增强;温度...  相似文献   

隐伏金属矿床上升气流微粒特征、形成及迁移   总被引：3，自引：0，他引：3  

曹建劲 《地学前缘》2012,19(3):113-119

结合地球化学和纳米科学技术的理论和研究方法,研究隐伏金属矿床有关微粒的形成、迁移和特征。对十多个金属矿床的研究表明,隐伏金属矿体地表沉积物中上升气流微粒样品有单个微粒和微粒聚合体,单个微粒形态有球状、近球状、不规则状、规则多边形、长柱状,微粒有晶质、非晶质和部分晶质。聚合体形态一般是不规则状、球状和近球状。它们的矿物成分主要有自然Au、自然Cu、氯化物、氧化物、硫酸盐、氢氧化物等。成矿元素Au、Cu可以自然金属或自然合金形式存在,Cu、Pb、Zn等成矿元素可以氧化物或硫酸盐等形式存在,也可以存在于氧化物、氢氧化物、氯化物、硫酸盐等微粒中作为杂质元素,这些是隐伏金属矿体的指示微粒。成矿期后,与隐伏金属矿体有关微粒主要形成于断层作用、氧化作用和生物作用。在上升气流中,微粒呈“布朗运动”。  相似文献