共查询到20条相似文献，搜索用时 15 毫秒
1.
Paul H. Whitfield 《水文研究》2013,27(18):2691-2698
The centre of volume (COV), or the hydrograph centroid, is a measure of streamflow timing that is a widely used indicator of the effects of warmer temperatures on the hydrology of snowmelt streams. The COV was originally developed as a measure of land‐use effects, and its response is affected by several factors other than temperature, particularly total run‐off. A ‘toy’ model is used to demonstrate some of these effects, and these effects are also shown for streamflow data from Canada's Reference Hydrologic Basin Network. These deficiencies indicate that COV is neither specific nor robust as an indicator. Although these effects might be overcome by streamflow decomposition, the use of COV as an indicator of snowmelt timing should be avoided. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
2.
Complex site effects and building codes: Making the leap 总被引：1，自引：0，他引：1
The engineering community is aware of the importance of site effects, but it lags behind seismological studies when it comes to incorporating site effect considerations in design spectra for seismic norms. This lag is reflected in the conspicuous fact that current building codes make allowance for 1D site effects but ignore complex site effects. The purpose of this paper is to explore a way for including complex site effects in a building code environment. We take as example Eurocode 8, which is a modern code that exemplifies the current approach to site effect consideration. We examine the restrictions that we have imposed to make the problem of a feasible size and discuss the approach we have taken. We propose a strategy to incorporate a class of complex site effects in a design elastic spectrum. 相似文献
3.
高墩梁桥的地震冲撞效应及其应对策略初探 总被引：1，自引：0，他引：1
国内外多次地震表明了高墩桥梁的地震冲撞破坏现象,针对目前国内大量兴建的高墩梁桥,有必要研究高墩梁桥地震冲撞效应和减轻桥梁地震冲撞破坏的应对策略。本文根据高烈度震区的1座高墩梁桥建立全桥的空间有限元模型,并在墩-梁结合部伸缩缝处采用非线性接触单元模拟相邻梁间的冲撞行为,同时考虑了下部支座的影响;考虑不同的强震动输入,采用非线性时程分析方法,研究了高墩梁桥的地震冲撞效应及减轻冲撞的有效措施。研究结果表明:本文采用的冲撞力学模型能够合理地模拟地震作用下结构的冲撞现象;冲撞行为对结构的地震反应影响复杂;地震动特性对冲撞效应影响显著;调整伸缩逢宽度或设置弹簧-阻尼限位装置可有效缓解结构间的冲撞效应。 相似文献
4.
《Journal of Atmospheric and Solar》2007,69(12):1344-1356
It is well known that interferometric synthetic aperture radar (InSAR) measurements are affected by the atmosphere especially the troposphere. We use Shanghai as an example to analyze the properties of the effects based on a number of SAR interferograms over the region. First, Radon transform is used to examine the isotropic property of the effects. The results show that the effects in all the interferograms are anisotropic although they exhibit different patterns. Two different methods, the Jarque-Bera and the Hinich tests, are then applied to test the Gaussianity of atmospheric effects. Both of the tests reveal that the atmospheric effects are non-Gaussian. Finally, spectral analysis of the atmospheric effects is carried out and the results show that the power spectra of the atmospheric signatures in all the interferograms studied follow approximately the power law distribution. The scaling exponents estimated show that the atmospheric signatures in all the interferograms are non-stationary but with stationary increments. It is estimated based on the estimated scaling exponents that external data with spatial resolutions as high as about 0.3 km, are required to determine and correct for over 90% of the atmospheric effects in the SAR interferograms. 相似文献
5.
J. Enrique Luco 《地震工程与结构动力学》1998,27(3):225-242
A simple model for the seismic response of a one-storey structure subjected to active control in the presence of soil–structure interaction effects is presented. The approach is based on the successive use of equivalent 1-DOF oscillators which account for the effects of control and soil–structure interaction. Simple expressions for these oscillators based on exact analytical solutions of the control equations and approximate solutions of the interaction equations are presented. The study includes an evaluation of the effects of soil–structure interaction on the seismic response of actively controlled structures in which the control gains have been determined with and without inclusion of soil–structure interaction effects. A simple procedure to include the interaction effects on the control gains is also presented. © 1998 John Wiley & Sons, Ltd. 相似文献
6.
本文对大地电磁感应的场源效应进行了较详细的研究.用线电流为场源,均匀大地和三层结构为构造模型进行了计算,其结果与均匀场源的感应作了对比.场源效应受场源高度、信号周期、电阻率、测点距离等的影响.为了能更深入的了解和控制这影响,本文提出了“阻抗平均法”,该方法对消减场源效应有一定作用,使平面波的解释继续有效. 相似文献
7.
《地震工程与工程振动(英文版)》2015,(3)
This paper addresses the analytical evaluation of soil lateral heterogeneity effects,especially the random fluctuations of the soil layer's predominant frequency,on the spatial coherency of ground motion and the seismic response of multi-support structures.A coherency probabilistic model is proposed.In this model,the spatial variation of motion is attributed to wave passage effects,effects of loss of coherence in the bedrock motion and particularly site response effects(based on the assumption of vertically propagating shear-waves through a horizontal layer with random characteristics).The results indicate that soil lateral heterogeneity effects tend to cause diminution of the values of the total coherency function.This diminution is not limited to the vicinity of the mean resonant frequency of the layer,but reaches considerably high frequencies even for relatively low values of coefficient of variation(CV of 5 to 15%).Therefore,the trend of the total coherency function(exponential decay) can be influenced significantly by site effects.Finally,the proposed coherency model is applied for two different support seismic excitations.Study results indicate that the greater the soil heterogeneity,the larger are the dynamic displacements and shear forces in the columns of the oscillator(i.e.,support structure).Furthermore,these two components of the response are influenced differently by soil heterogeneity effects. 相似文献
8.
The modern transportation facilities demand that the bridges are to be constructed across the gorges that are located in seismically active areas and at the same time the site conditions compel the engineers to rest the pier foundation on soil. The purpose of this study is to assess the effects of soil–structure interaction (SSI) on the peak responses of three-span continuous deck bridge seismically isolated by the elastomeric bearings. The emphasis has been placed on gauging the significance of physical parameters that affect the response of the system and identify the circumstances under which it is necessary to include the SSI effects in the design of seismically isolated bridges. The soil surrounding the foundation of pier is modelled by frequency independent coefficients and the complete dynamic analysis is carried out in time domain using complex modal analysis method. In order to quantify the effects of SSI, the peak responses of isolated and non-isolated bridge (i.e. bridge without isolation device) are compared with the corresponding bridge ignoring these effects. A parametric study is also conducted to investigate the effects of soil flexibility and bearing parameters (such as stiffness and damping) on the response of isolated bridge system. It is observed that the soil surrounding the pier has significant effects on the response of the isolated bridges and under certain circumstances the bearing displacements at abutment locations may be underestimated if the SSI effects are not considered in the response analysis of the system. 相似文献
9.
An efficient procedure is presented for dynamic response analysis of horizontal tube array in partially filled calandria including hydrodynamic interaction effects. The procedure is general enough to consider the transfer of energy between the fluid-coupled tubes, and effects of moderator sloshing on the magnitude and the distribution of hydrodynamic forces. It has been demonstrated that the conventional added mass approach fails to represent behaviour of the tube array correctly, and it is therefore necessary to consider the flexibility of all the tubes along two directions simultaneously. The procedure presented can simulate the added damping effects due to hydrodynamic interaction. The possible use of a tuned damper tube is suggested for controlling sloshing effects for tube array in a calandria where tube frequencies and sloshing frequencies are closely spaced. The presence of surface damping in the tuned tube further brings down the response, and the suggested procedure can be effectively used to control unwarranted sloshing effects. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
10.
本文以一海洋深水环境桩柱为例,考虑到海洋地基为两相饱和土介质,基于Biot两相饱和多孔介质理论,通过数值算例分析了饱和介质中瑞利波加速度、位移分布规律并与单相弹性介质地基条件下进行了对比,结果表明,瑞利波主要作用于地表附近且振动幅度随深度衰减很快,饱和地基下的瑞利波影响深度要大于单相弹性地基,在瑞利波地震作用下,考虑两相饱和介质下的桩柱位移响应大于单相弹性介质地基。并且由于桩柱处海洋深水环境,本文对环境水体对桩柱振动响应的影响进行了研究,结果表明,流固耦合效应可明显降低桩柱运动响应,在海洋深水环境地震响应分析时,有必要考虑饱和地基以及流固耦合效应对桩柱运动响应的影响。 相似文献
11.
An account of possible anomalous effects in reflection and refraction of elastic waves at an interface between anisotropic media is presented. These effects are due to anisotropy and they cannot occur at an interface between isotropic media. The shape of the slowness surface (its local deviations from spherical symmetry) is the decisive factor for appearance of these effects. A numerical example of such anomalous behaviour of elastic waves at a free boundary of the crystal of spinel is presented. 相似文献
12.
Summary An account of possible anomalous effects in reflection and refraction of elastic waves at an interface between anisotropic media is presented. These effects are due to anisotropy and they cannot occur at an interface between isotropic media. The shape of the slowness surface (its local deviations from spherical symmetry) is the decisive factor for appearance of these effects. A numerical example of such anomalous behaviour of elastic waves at a free boundary of the crystal of spinel is presented. 相似文献
13.
For almost 80 years, deformation-induced head changes caused by poroelastic effects have been observed during pumping tests in multilayered aquifer-aquitard systems. As water in the aquifer is released from compressive storage during pumping, the aquifer is deformed both in the horizontal and vertical directions. This deformation in the pumped aquifer causes deformation in the adjacent layers, resulting in changes in pore pressure that may produce drawdown curves that differ significantly from those predicted by traditional groundwater theory. Although these deformation-induced head changes have been analyzed in several studies by poroelasticity theory, there are at present no practical guidelines for the interpretation of pumping test data influenced by these effects. To investigate the impact that poroelastic effects during pumping tests have on the estimation of hydraulic parameters, we generate synthetic data for three different aquifer-aquitard settings using a poroelasticity model, and then analyze the synthetic data using type curves and parameter estimation techniques, both of which are based on traditional groundwater theory and do not account for poroelastic effects. Results show that even when poroelastic effects result in significant deformation-induced head changes, it is possible to obtain reasonable estimates of hydraulic parameters using methods based on traditional groundwater theory, as long as pumping is sufficiently long so that deformation-induced effects have largely dissipated. 相似文献
14.
捏拢效应与P-Δ效应对地震延性需求和损伤指标的影响 总被引：1，自引：0，他引：1
文中定量地分析了捏拢效应和P-Δ效应对非弹性单自由度体系的地震延性需求和Park-Ang地震损伤指标的概率统计特征的影响。采用Bouc-W en模型描述具有P-Δ效应、捏拢效应、强度退化、刚度退化等典型特性的恢复力-位移滞回曲线;根据非弹性单自由度体系在69条强震记录作用下的动力响应,定量地分析了捏拢效应和P-Δ效应对地震延性需求和Park-Ang地震损伤指标的均值和变异系数的影响,并建立了地震延性需求的概率预测模型。计算结果表明,捏拢效应和由重力引起的P-Δ效应对地震延性需求的影响较大,而由竖向地震激励引起的P-Δ效应对地震延性需求的影响很小;对于短周期体系,建议采用对数正态或Frechet分布来描述地震延性需求的概率分布;对于长周期体系,采用Frechet分布则更为合理。 相似文献
15.
16.
A numerical coupling scheme for nonlinear time history analysis of buildings on a regional scale considering site‐city interaction effects 
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下载免费PDF全文 Seismic damage simulation of buildings on a regional scale is important for loss estimation and disaster mitigation of cities. However, the interaction among densely distributed buildings in a city and the site, ie, the “site‐city interaction (SCI) effects,” is often neglected in most regional simulations. Yet, many studies have found that the SCI effects are very important in regional simulations containing a large number of tall buildings and underground structures. Therefore, this work proposed a numerical coupling scheme for nonlinear time history analysis of buildings on a regional scale considering the SCI effects. In this study, multiple‐degree‐of‐freedom models are used to represent different buildings above the ground, while an open source spectral element program, SPEED, is used for simulating wave propagation in underlying soil layers. The proposed numerical scheme is firstly validated through a shaking table test. Then, a detailed discussion on the SCI effects in a 3D basin is performed. Finally, a nonlinear time history analysis of buildings on a regional scale is performed using the Tsinghua University campus in Beijing as a case study. The Tsinghua University campus case results show that the SCI effects will reduce the seismic responses of most buildings. However, some buildings will suffer much more severe damage when the SCI effects are considered, which may depend on the input motions, site characteristics, and building configurations. 相似文献
17.
新疆平原沙漠区湖泊干缩生态效应初探 总被引：1，自引：1，他引：0
50年代至80年代初,新疆平原沙漠区湖泊普遍处于退缩状态,一些湖泊干涸或基本干涸,这是湖泊所在流域上、中游地区灌溉事业发展的必然结果。到目前为止,湖泊干缩所引起生态环境的变化,其范围主要限于湖周有限区域;变化的幅度尚未达到对人类生活和生湖泊及湖周有限区域生态环境的恶化中,人类不正确的活动方式占了很大比重。 相似文献
18.
This paper deals with the evaluation of seismic site effects due to the local topographical and geotechnical characteristics. The amplification of surface motions is calculated by a numerical method combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The numerical technique is improved by time truncation. In the first part of this article, the accuracy and the relevance of this optimized method are presented. Moreover, parametric studies are done on slopes, ridges and canyons to characterize topographical site effects. The second part deals with sedimentary valleys. The complexity of the combination of geometrical and sedimentary effects is underlined. Extensive parametrical studies are done to discriminate the topographical and geotechnical effects on seismic ground movement amplifications in two-dimensional irregular configurations. Characteristic coefficients are defined to predict the amplifications of horizontal displacements. The accuracy of this quantitative evaluation technique is tested and discussed. 相似文献
19.
This paper deals with the evaluation of seismic site effects due to the local topographical and geotechnical characteristics. The amplification of surface motions is calculated by a numerical method combining finite elements in the near field and boundary elements in the far field (FEM/BEM). The numerical technique is improved by time truncation. In the first part of this article, the accuracy and the relevance of this optimized method are presented. Moreover, parametric studies are done on slopes, ridges and canyons to characterize topographical site effects. The second part deals with sedimentary valleys. The complexity of the combination of geometrical and sedimentary effects is underlined. Extensive parametrical studies are done to discriminate the topographical and geotechnical effects on seismic ground movement amplifications in two-dimensional irregular configurations. Characteristic coefficients are defined to predict the amplifications of horizontal displacements. The accuracy of this quantitative evaluation technique is tested and discussed. 相似文献
20.
结构-设备体系动力相互作用研究 总被引：1，自引：0，他引：1
通过结构－设备等价体系频域传递函数的比较分析，讨论了结构－设备动力相互作用对结构绝对动力反应与相对动力反应的影响。着重指出，这种影响是增大还是减小结构的动力反应取决于地震动频谱特性与结构、设备固有频率及质量比的关系。提出了利用场地土卓越周期判定上述影响的简便方法。 相似文献