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11.
A wavelet-based formulation has been presented in this paper for the stochastic analysis of a linear multi-degree-of-freedom (MDOF) classically damped system subjected to earthquake ground motion. The ground motion has been modelled as a non-stationary process (both in amplitude and frequency) using wavelets. Closed-form expressions of the moments of the instantaneous Power Spectral Density Function (PSDF) of the response have been derived and used to predict the statistics of the response peak of any desired order. For illustration of the formulation, an example torsionally coupled multistoried building has been considered along with the twenty synthetically generated time-histories corresponding to an example ground motion process. © 1997 John Wiley & Sons, Ltd. 相似文献
12.
Binbin Lu Martin Charlton Paul Harris A. Stewart Fotheringham 《International journal of geographical information science》2014,28(4):660-681
Geographically weighted regression (GWR) is an important local technique for exploring spatial heterogeneity in data relationships. In fitting with Tobler’s first law of geography, each local regression of GWR is estimated with data whose influence decays with distance, distances that are commonly defined as straight line or Euclidean. However, the complexity of our real world ensures that the scope of possible distance metrics is far larger than the traditional Euclidean choice. Thus in this article, the GWR model is investigated by applying it with alternative, non-Euclidean distance (non-ED) metrics. Here we use as a case study, a London house price data set coupled with hedonic independent variables, where GWR models are calibrated with Euclidean distance (ED), road network distance and travel time metrics. The results indicate that GWR calibrated with a non-Euclidean metric can not only improve model fit, but also provide additional and useful insights into the nature of varying relationships within the house price data set. 相似文献
13.
因地震动输入方向对平面不规则结构响应的影响显著,所以本文对该类的实用多维反应谱计算方法进行了研究。首先,基于多维加速度功率谱矩阵的研究成果,引入激励输入角度和相应参数,推导了能合理考虑激励输入方向的加速度功率谱和基于平稳随机振动求解响应的计算公式。然后再引入位移谱,利用其能合理考虑激励非平稳性的特点,提出了水平双向的实用反应谱法计算公式。最后,以平面为L形的空间钢结构为例,对不同输入角度时的节点位移公式计算值与多条地震波的时程响应值进行了比较,证明该计算方法是合理的,可供结构抗震设计与分析作参考。 相似文献
14.
D.A. Hughes 《水文科学杂志》2015,60(7-8):1286-1298
AbstractTemporal variability can result from shifts in climate, or from changes in the runoff response due to land- or water-use changes, and represents a potential source of uncertainty in calibrating hydrological models. Parameter values were determined using Monte Carlo parameter sampling methods for a monthly rainfall–runoff model (Pitman model) for different sub-periods on four catchments, with different types and degrees of temporal variability, in Australia and Africa. For some catchments, parameters were not dependent upon the sub-period used and fell within expected ranges given the relatively high degree of model equifinality. In other catchments, dependencies can be identified that are associated with signals contained within the sub-periods. While the Pitman model is relatively robust in the face of temporal variability, it is concluded that better simulations will always be obtained from calibration data that include signals representing the total variability in climate, land-use change and catchment responses. 相似文献
15.
AbstractThe impact of fire on daily discharges from two mountainous basins located in the permafrost region of Eastern Siberia, the Vitimkan (969 km2) and Vitim (18 200 km2) rivers, affected by fire over 78% and 49% of their areas, respectively, in 2003, was investigated. The results of hydrological and meteorological data analysis suggest that the Vitimkan River basin had a rapid and profound hydrological response to wildfire in 2003 expressed through a 41% (133 mm) increase of summer flow. Conversely, the larger Vitim River basin showed no significant changes in discharge after the fire. The parameters of the process-based hydrological model Hydrograph were estimated for pre-fire conditions. The results of runoff simulations conducted for the continuous pre-fire periods of 1966–2002 and 1970–2002 for the Vitimkan and Vitim river basins, respectively, on a daily time step, showed satisfactory agreement with the observed flow series of both basins. Significant underestimation of precipitation and its poor representativeness for mountainous watersheds was revealed as the main cause of observed and simulated flow discrepancies, especially for high flood events. The set of dynamic parameters was developed based on data analysis and post-fire landscape changes as derived from a literature review. The model was applied to investigate the processes in the soil column and their effect on runoff formation during the post-fire period. The new set of model parameters implied the intensification of soil thaw, reduction of infiltration rate and evapotranspiration, and increase of upper subsurface flow fraction in summer flood events following the fire. According to modelling results, the post-fire thaw depth exceeded the pre-fire thaw depth by 0.4–0.7 m. Total evapotranspiration reduced by 40% in summer months, while surface flow increased almost 2.5 times during maximum flood events. 相似文献
16.
Influence of weak trends on exceedance probability 总被引：1，自引：0，他引：1
Studying the hypothetical case of a trend superimposed on a random stationary variable, we highlight the strong influence
of possible non-stationarities on exceedance probability. After a general outline, the subject is analytically developed using
the Gumbel distribution, emphasizing the quick increase of the exceedance probability over time in the presence of weak rising
trends, and its sensitive underestimation where the non-stationarity goes unnoticed or is considered negligible. Finally the
work is applied to hydrological series of rainfall and river flow.
Received: March 27, 1997 相似文献
17.
中国极端降水事件时空特征及其对夏季温度响应 总被引：7，自引：0，他引：7
基于中国1951-2014年728个气象站点日降水数据,利用POT抽样、变异点分析、趋势分析、分段回归等方法全面分析中国极端降水事件（量级、频率与发生时间）非平稳性特征及其对夏季温度响应。研究结果发现中国极端降水量级有明显变异特征,但无显著趋势变化,中国极端降水频率则相反。并且中国极端降水次数在全国大部分区域有显著增加趋势。另外,研究还表明变异点对中国极端降水量级和频率趋势特征有明显的改变,对极端降水发生时间趋势特征改变较弱;中国极端降水发生时间在中南部呈显著上升趋势,其他区域趋势性不显著。中国大部分区域夏季温度呈上升或显著上升趋势,且变异特征显著。在转折点前,中国大部分区域如西部干旱区东南部、东部干旱区西南部、华北区、华中区和西南区北部夏季温度呈下降或显著下降趋势;在转折点后,上述区域夏季温度转为上升或显著上升趋势。 相似文献
18.
Transitive Geostatistics for Stepwise Modeling Across Boundaries between Rock Regions 总被引：2，自引：1，他引：1
J. A. Vargas-Guzmán 《Mathematical Geosciences》2008,40(8):861-873
A single intrinsic stationary random field may not account for transitional heterogeneity and abrupt dissimilarity of geological
properties across boundaries between rock type regions. This paper proposes the stepwise construction of transitive covariance
models for modeling continuous properties correlated across boundaries of multiple disjoint physical domains such as rock
type bodies. Modeling in geology is usually simplified by splitting the geological space into rock type geo-domains (e.g.,
strata, sedimentary facies, soil series, diagenetic regions and alteration zones). Due to the limitations of simultaneous
solutions, a simplification is to model each domain independently at the cost of losing the conditioning of properties across
domains. This paper proposes to organize the modeling process in a triangular array which follows events in the geological
time domain; for example, the younger formations are at the top of the pyramid and the older formation at the base. The estimation
may go from top to base by assuming that younger events have perturbed older formations. Geology shows the scars of events
that cumulate in rock formations before they are finally eroded. In some cases, older formations may be parent material for
younger formations. The continuous property within each geo-domain has a conditional covariance in the main diagonal of the
array which may belong to a specific event in the geological time. This sequence leads to transitive estimation and simulations
in the physical space. If a simultaneous solution is sought (i.e., the future and past are correlated both ways), the complex
covariance functions can be constructed stepwise from conditional spectra. 相似文献
19.
场地土壤污染物含量三维刻画的研究进展 总被引：1，自引：0，他引：1
污染场地精准修复与再开发利用是改善人居环境、建设美丽中国所面临的重要课题。场地土壤污染物含量三维刻画是精准修复与再开发利用的基础。然而,场地环境是一个耦合地上地下多要素的复杂三维系统,使得基于离散稀疏土壤钻井样点和空间统计推断模型的场地土壤污染物含量刻画结果存在着较大的不确定性。本文梳理了场地土壤污染物含量三维精细刻画的目的和钻井布设方式、常用的三维刻画模型和相关案例,分析了土壤钻井数据的“稀疏偏性”特征对刻画结果的影响,总结了“非平稳浓度场”条件下三维土壤污染物含量插值模型的研究现状和存在问题。在此基础上,从多情景、非平稳、非线性、多源数据融合、多类模型耦合和复合污染刻画6个方面,展望了场地地下“黑箱”环境土壤污染物含量精细刻画的研究趋势。 相似文献
20.
Facets of uncertainty: epistemic uncertainty,non-stationarity,likelihood, hypothesis testing,and communication 总被引：1，自引：1，他引：0
Keith Beven 《水文科学杂志》2016,61(9):1652-1665
ABSTRACTThis paper presents a discussion of some of the issues associated with the multiple sources of uncertainty and non-stationarity in the analysis and modelling of hydrological systems. Different forms of aleatory, epistemic, semantic, and ontological uncertainty are defined. The potential for epistemic uncertainties to induce disinformation in calibration data and arbitrary non-stationarities in model error characteristics, and surprises in predicting the future, are discussed in the context of other forms of non-stationarity. It is suggested that a condition tree is used to be explicit about the assumptions that underlie any assessment of uncertainty. This also provides an audit trail for providing evidence to decision makers.
Editor D. Koutsoyiannis; Associate editor S. Weijs 相似文献