Evaluation of seismic ground motion induced by topographic irregularity   总被引：1，自引：0，他引：1  

Khoa-Van Nguyen  Behrouz Gatmiri   《Soil Dynamics and Earthquake Engineering》2007,27(2):183-188

Results of an extensive numerical study on the 2D scattering of seismic waves by local topography are presented. The investigation has been conducted using the direct boundary element method. Several types of topography (slopes, canyons and ridges) are considered. The influences of some key parameters, such as exciting frequency and geometry of the irregular feature, on surface ground motion are studied in detail. It is found that local topographic conditions play an important role in the modification of seismic ground motion at the irregular feature itself and its neighbourhood. The present results can be considered to be useful from the viewpoint of earthquake engineering and seismology.  相似文献   

Nonlinear seismic response analysis of arch dam-foundation systems- part II opening and closing contact joints     

Xiuli Du  Jin Tu 《Bulletin of Earthquake Engineering》2007,5(1):121-133

A time-domain method for the analysis of arch dam-foundation rock dynamic interaction during earthquake was proposed, and the dynamic relaxation technique was adopted to obtain the initial static response for dynamic analysis by [Du et al. (2005). The paper has been contributed to Bulletin of earthquake engineering]. In this paper, a nonlinear explicit method in time domain considering the opening and closing effect of contact joints on arch dam during earthquake is further proposed by introducing the dynamic contact force model into the method. The simulation accuracy of dynamic contact force model is verified by comparing its calculation result and test result of scale model on shaking table. Finally, the influence of joints on the seismic response of Xiaowan arch dam is studied by the proposed method and some conclusions are given.  相似文献   

多窗谱分析方法及其在全球变暖研究中的应用   总被引：12，自引：0，他引：12  

江志红  屠其璞  施能 《气象学报》2001,59(4):480-490

多窗谱分析方法是一种低方差、高分辨的谱分析方法 ,尤其适合于非线性气候系统中高噪声背景下弱信号、时频演变信号的诊断分析。文中简要地介绍了多窗谱分析方法的基本原理 ,并将其用于近 1 5 0 a来全球及南、北半球温度变化的研究。结果表明 :(1 )在温度呈线性变暖的背景趋势下 ,北半球、全球年平均温度还具有显著的 40～ 70 a的准周期低频振荡 ,它们与变暖过程中的波动性密切相关 ;(2 )年代际振荡信号在北半球温度序列中也相当明显 ,南半球则存在多种低于 5 a尺度的显著振荡周期 ,半球或全球 ENSO振荡分量、QBO周期信号的振幅都具有缓变包络的特性 ;(3 )与传统功率谱估计、最大熵谱估计结果的对比表明 ,多窗谱分析方法方法得到的谱估计分辨力高 ,稳定性强。  相似文献   

冲积型金刚石砂矿与其成矿模式的讨论     

涂怀奎 《化工矿产地质》2001,23(4):239-244

中国金刚石砂矿主要分布在华北与扬子地台郯庐断裂区与沅水流域区 ,在大别山区及新疆、西藏超基性岩附近也有分布。不同时代的含金刚石金伯利岩或超基性岩带 ,经风化、剥蚀、搬运 ,形成含金刚石砂矿中间储存体 ,在水系中下游形成不同类型 (阶地、河谷、河床 )砂矿。金刚石砂矿找矿方向应是模式找矿主要有三方面 :一是矿源 ,二是中间储存体 ,三金刚石砂矿组合矿物。  相似文献   

陕西凤县金矿类型与金的预富集及找矿方向   总被引：1，自引：0，他引：1  

涂怀奎 《黄金地质》2001,7(1):73-78

陕西凤县地区金矿主要有蚀变岩与石英脉型。地层预富集是金矿形成的物质基础；岩体为金矿形成提供了Au源，而且沿构造蚀变带提供了热源，是Au活化成矿的一个重要条件；多期次热液沿构造破碎带进行交代改造形成蚀变预富集，是金矿成矿的关键。庞家河成矿模式为层预富集＋蚀变预富集＋后期多次热液交代富集成矿；佐家庄成矿模式为岩体（脉）预富集＋构造蚀变预富集＋多种热液叠加成矿。NNW向断裂带是寻找蚀变岩型金矿的主要标志；印支期与华力西期花岗岩－闪长岩带的内外接触带是寻找石英脉型及蚀变岩型金矿的主要构造带；金的预富集带是金矿成矿的有利部位，紧靠商丹大断裂南侧续分布的残余存小岩块旁侧都发现金矿床。  相似文献   

Probabilistic Seismic Hazard Assessment Along the Southeastern Coast of Vietnam     

Hong Phuong  Nguyen 《Natural Hazards》2001,24(1):53-74

On the basis of the analysis of geological, tectonic characteristics and earthquake manifestation features, a causative relation between geodynamic regime and seismicity has been established for the southeastern coastal zone and continental shelf of Vietnam. The probabilistic methods have been used to evaluate ground shaking effects at Nha Trang city aswell as for the entire study area. Short, intermediate and long term predictions of ground shaking (in the form of peak ground accelerationmaps) show high risks in the coastal zone of central Vietnam and in the southeastern continental shelf of the country.  相似文献   

考虑湿度影响的城市气溶胶夜晚温度效应   总被引：10，自引：0，他引：10  

李子华  涂晓萍 《大气科学》1996,20(3):359-366

本文利用一维非定常模式，研究了城市上空干、湿气溶胶粒子对夜间边界层温度的影响。结果表明，湿气溶胶粒子对低层大气有明显的升温作用，而对中上层大气则起降温作用，同时改变了贴地逆温层结构和边界层稳定度。  相似文献   

Simulation of acid water movement in canals   总被引：1，自引：0，他引：1  

To Van Truong  Nguyen Tat Dac  Huynh Ngoc Phienc   《Journal of Hydrology》1996,180(1-4):361-371

An attempt to tackle the problem of the propagation of acid water in canals is described, and a mathematical model to simulate the acid water movement is developed, in which the jurbanite equilibrium is found to prevail. The processes of settling owing to sedimentation, precipitation and redissolution have been considered in the modelling. Data available from Tan Thanh, in the Plain of Reeds of the Mekong Delta in Viet Nam, are used as a case study.  相似文献   

Multifractal scaling of the kinetic energy flux in solar wind turbulence     

E. Marsch  C.-Y. Tu  H. Rosenbauer 《Annales Geophysicae》1996,14(3):259-269

The geometrical and scaling properties of the energy flux of the turbulent kinetic energy in the solar wind have been studied. Using present experimental technology in solar wind measurements we cannot directly measure the real volumetric dissipation rate, <varepsilon>(t), but are constrained to represent it by its surrogate the energy flux near the dissipation range at the proton gyro scale. There is evidence for the multifractal nature of the so defined dissipation field <varepsilon>(t), a result derived from the scaling exponents of its statistical moments. The generalized dimension D _q has been determined and reveals that the dissipation field has a multifractal structure, which is not compatible with a scale-invariant cascade. The related multifractal spectrum f(<alpha>) has been estimated for the first time for MHD turbulence in the solar wind. Its features resemble those obtained for turbulent fluids and other nonlinear multifractal systems. The generalized dimension D _q can for turbulence in high-speed streams be fitted well by the functional dependence of the p-model with a comparatively large parameter p ₁=0.87, indicating a strongly intermittent multifractal energy cascade. The experimental value for D _p/3 used in the scaling exponent s(p) of the velocity structure function gives an exponent that can describe some of the observations. The scaling exponent <mu> of the autocorrelation function of <varepsilon>(t) has also been directly evaluated, being 0.37. Finally, the mean dissipation rate was determined, which could be used in solar wind heating models.  相似文献   

An extended structure-function model and its application to the analysis of solar wind intermittency properties     

C.-Y. Tu  E. Marsch  H. Rosenbauer 《Annales Geophysicae》1996,14(3):270-285

An extended structure-function model is developed by including the new effect in the p-model of Meneveau and Sreenivasan which shows that the averaged energy cascade rate changes with scale, a situation which has been found to prevail in nonfullydeveloped turbulence in the inner solar wind. This model is useful for the small-scale fluctuations in the inner heliosphere, where the turbulence is not fully developed and cannot be explained quantitatively by any of the previous intermittency turbulence models. With two model parameters, the intrinsic index of the energy spectrum <alpha>, and the fragmentation fraction P ₁, the model can fit, for the first time, all the observed scaling exponents of the structure functions, which are calculated for time lags ranging from 81 s to 0.7 h from the Helios solar wind data. From the cases we studied we cannot establish for P ₁ either a clear radial evolution trend, or a solar-wind-speed or stream-structure dependence or a systematic anisotropy for both the flow velocity and magnetic field component fluctuations. Generally, P ₁ has values between 0.7 and 0.8. However, in some cases in low-speed wind P ₁ has somewhat higher values for the magnetic components, especially for the radial component. In high-speed wind, the inferred intrinsic spectral indices (<alpha>) of the velocity and magnetic field components are about equal, while the experimental spectral indices derived from the observed power spectra differ. The magnetic index is somewhat larger than the index of the velocity spectrum. For magnetic fluctuations in both high- and low-speed winds, the intrinsic exponent <alpha> has values which are near 1.5, while the observed spectral exponent has much higher values. In the solar wind with considerable density fluctuations near the interplanetary current sheet near 1 AU, it is found that P ₁ has a comparatively high value of 0.89 for V _x . The impact of these results on the understanding of the nature of solar wind fluctuations is discussed, and the limitations in using structure functions to study intermittency are also described.  相似文献