Stochastic modelling of soil moisture dynamics in a grassland of Qilian Mountain at point scale   总被引：2，自引：0，他引：2  

Liu Hu  Zhao WenZhi  He ZhiBin  Zhang LiJie 《中国科学D辑(英文版)》2007,50(12):1844-1856

Stochastic modeling of soil moisture dynamics is crucial to the quantitative understanding of plant responses to water stresses,hydrological control of nutrient cycling processes,water competition among plants,and some other ecological dynamics,and thus has become a hotspot in ecohydrology at present.In this paper,we based on the continuously monitored data of soil moisture during 2002―2005 and daily precipitation date of 1992―2006,and tried to make a probabilistic analysis of soil moisture dynamics at point scale in a grassland of Qilian Mountain by integrating the stochastic model improved by Laio and the Monte Carlo method.The results show that the inter-annual variations for the soil moisture patterns at different depths are very significant,and that the coefficient of variance(CV) of surface soil moisture(20 cm) is almost continually kept at about 0.23 whether in the rich or poor rainy years.Interestingly,it has been found that the maximal CV of soil moisture has not always appeared at the surface layer.Comparison of the analytically derived soil moisture probability density function(PDF) with the statistical distribution of the observed soil moisture data suggests that the stochastic model can reasonably describe and predict the soil moisture dynamics of the grassland in Qilian Mountain at point scale.By extracting the statistical information of the historical precipitation data in 1994―2006,and inputting them into the stochastic model,we analytically derived the long-term soil moisture PDF without considering the inter-annual climate fluctuations,and then numerically derived the one when considering the inter-annual fluctuation effects in combination with a Monte-Carlo procedure.It was found that,though the peak position of the probability density distribution significantly moved towards drought when considering the disturbance forces,and its width was narrowed,accordingly its peak value was increased,no significant bimodality was observed in the soil moisture dynamics under the given intensity of random fluctuation disturbance.  相似文献   

Application of saddlepoint approximation in reliability analysis of dynamic systems     

阮家荣  王家  区兆驹 《地震工程与工程振动(英文版)》2007,6(4):391-400

The application of the saddlepoint approximation to reliability analysis of dynamic systems is investigated. The failure event in reliability problems is formulated as the exceedance of a single performance variable over a prescribed threshold level. The saddlepoint approximation technique provides a choice to estimate the cumulative distribution function (CDF) of the performance variable. The failure probability is obtained as the value of the complement CDF at a specif ied threshold. The method requires computing the saddlepoint from a simple algebraic equation that depends on the cumulant generating function (CGF) of the performance variable. A method for calculating the saddlepoint using random samples of the performance variable is presented. The applicable region of the saddlepoint approximation is discussed in detail. A 10-story shear building model with white noise excitation illustrates the accuracy and effi ciency of the proposed methodology.  相似文献   

A derived probability distribution approach to stormwater quality modeling     

Jieyun Chen  Barry J. Adams 《Advances in water resources》2007

The closed-form analytical stormwater quality models are developed for simulating urban catchment pollutant buildup and washoff processes. By integrating the rainfall–runoff transformation with pollutant buildup and washoff functions, stormwater quality measures, such as the cumulative distribution functions (CDFs) of pollutant loads, the expected value of pollutant event mean concentrations (EMCs) and the average annual pollutant load can be derived. This paper presents methodologies and major procedures for the development of urban stormwater quality models based on derived probability distribution theory. In order to investigate the spatial variation in model parameters and its impact on stormwater pollutant buildup and washoff processes as well as pollutant loads to receiving waters, an extended form of the original rainfall–runoff transformation which is based on lumped runoff coefficient approach is proposed to differentiate runoff generation mechanisms between the impervious and pervious areas of the catchment. In addition, as a contrast to the aggregated pollutant buildup models formulated with a single lumped buildup parameter, the disaggregated form of the pollutant buildup model is proposed by introducing a number of physically-based parameters associated with pollutant buildup and washoff processes into the pollutant load models. The results from the case study indicate that analytical urban stormwater management model are capable of providing results in good agreement with the field measurements, and can be employed as alternatives to continuous simulation models in the evaluation of long-term stormwater quality measures.  相似文献   

景像匹配仿真的一种新方法   总被引：3，自引：0，他引：3  

艾浩军  胡瑞敏  丁明跃 《武汉大学学报(信息科学版)》2001,26(3):261-265

分析了影响景像相关匹配精度的各种误差因素，并给出它们的误差仿真模型，该模型可以适应飞行姿态、飞行器特性，天候等条件变化时的匹配概率估计，并可以与图像特征参数分析方法相结合。实验验证了该模型的有效性，且可以快速地给出影像图的适配性估计图，用于飞行器的航迹规划。  相似文献   

测震学多项指标综合预测概率分析     

顾瑾平  钱家栋  王琤琤 《地震》2001,21(2):46-52

通过对测震学各单项指标的预测效能调研，为进一步提取前兆信息，选择了7项测震学指标：频次、地震蠕变、6值、缺震、η值、GL值和调制比，进行综合概率分析。7项指标对关注地区的全时空扫描并考虑了空间单元异常与中强震地点对应的模糊关系，得到指标在各空间单元异常后发生中强震的条件概率。根据历史上每个单项指标的预报效能求计算综合概率时的指标权重，按贝叶斯定律得到相应不同指标在不同时间窗和不同空间单元时中强震发生的加权综合概率。计算结果（1970年以来）表明，对华北地区和川滇地区这一综合概率方法预测效能的R值评估超过0.5。  相似文献   

石河子市多层砖混结构房屋震害概率矩阵的建立     

唐丽华  宋立军  薛健  苗军 《内陆地震》2001,15(4):347-354

以概率理论为基础，采用震害指数法对石河子市重要建筑物中的多层砖混结构房屋进行抗力计算，通过抽样计算建立了石河子市砖混结构房屋按建筑年代分类的震害概率矩阵，又进一步综合这次普查得到的相关统计数据建立了修正的石河子市砖混结构房屋震害概率矩阵，从而为群体房屋的震害预测提供依据。  相似文献   

A new inverse method and application to ocean data     

魏恩泊  田纪伟  顾国庆 《中国科学D辑(英文版)》2001,44(6):490-497

A new method is proposed to inverse normalization data of hidden variables in a dynamical system by embedding a time series in multidimensional spaces and applying a normalization analysis to the conditional probability density of points in the reconstructed phase spaces. The method is robust in the application to Lorenz system and 4-dimensional R?ssler system by testing quantitatively and qualitatively the correlation coefficient between inverse data and original data in time domain and in frequency domain, respectively. By applying the method to analyzing the South China Sea data, the normalization data of wind speed is extracted from the sea surface temperature time series.  相似文献   

可靠性数学在斜坡稳定性分析中的应用   总被引：1，自引：1，他引：1  

刘焕喜  刘涌江 《西北地质》2001,34(2):37-42

本文将可靠性数学的相关理论引入斜坡稳定分析中，结合斜坡在变形破坏中的各影响因素均具有一定随机性的实际情况，提出了基于概率方法的斜坡稳定性可靠性计算公式，具有一定的现实意义。  相似文献   

A Reliability Based Expert System for Assessment and Mitigation of Landslides Hazard Under Seismic Loading     

Al-Homoud  Azm S.  Tahtamoni  Wisam W. 《Natural Hazards》2001,24(1):13-51

Different models were developed for evaluating the probabilistic three-dimensional (3-D) stability analysis of earth slopes and embankments under earthquake loading using both the safety factor and the displacement criteria of slope failure.The probabilistic models evaluate the probability of failure under seismic loading considering the different sources of uncertainties involved in the problem. The models also take into consideration the spatial variabilities and correlations of soil properties. The developed models are incorporated in a computer program PTDDSSA.These analysis/design procedures are incorporated within a code named SARETL developed in this study for stability analysis and remediation of earthquake triggered landslides. In addition to the dynamic inertia forces, the system takes into consideration local site effects.The code is capable of assessing the landslide hazard affecting major transportation routes in the event of earthquakes and preparing earthquake induced landslide hazard maps (i.e., maps showing expected displacements and probability of slope/embankments failure) for different earthquake magnitudes and environmental conditions. It can also beused for proposing a mitigation strategy against landslides.  相似文献   

耗能－隔震柔性底层钢管混凝土结构的振动台实验和损伤分析     

刘兴业  王海超  邓文樵 《地震工程与工程振动》1996,(4)

本文采用人工神经元网络理论，对城市公路网络中的单元路段和桥梁的震害预测进行了探讨。在前人研究的基础上，提出了解决这一非确定性问题的一个有效的方法，对于深入研究生命线工程系统震害的规律具有普遍的意义，从而使我们有可能避免地震造成的破坏和最大限度地减小损失，为抗震减灾提供决策依据。  相似文献