A note on asymptotic approximations of distributions for maxima of wave crests   总被引：1，自引：0，他引：1  

J. Rydén 《Stochastic Environmental Research and Risk Assessment (SERRA)》2006,20(4):238-242

The distribution of maxima during a given time interval is of interest in many applications in risk analysis. Within the framework of stationary Gaussian processes, several theoretical results considering asymptotics from different aspects have been derived for this distribution. In this note, we review results from the theory and study the accuracy of these approximations by exemplifying with a model for wave heights from oceanography. It turns out that for high values and the time periods normally encountered for buoy measurements, care should be taken in use of approximation based on the Gumbel distribution.  相似文献   

Sampling-based flood risk analysis for fluvial dike systems     

Richard Dawson  Jim Hall  Paul Sayers  Paul Bates  Corina Rosu 《Stochastic Environmental Research and Risk Assessment (SERRA)》2005,19(6):388-402

A dike system of moderate size has a large number of potential system states, and the loading imposed on the system is inherently random. If the system should fail, in one of its many potential failure modes, the topography of UK floodplains is usually such that hydrodynamic modelling of flood inundation is required to generate realistic estimates of flood depth and hence damage. To do so for all possible failure states may require 1,000s of computationally expensive inundation simulations. A risk-based sampling technique is proposed in order to reduce the computational resources required to estimate flood risk. The approach is novel in that the loading and dike system states (obtained using a simplified reliability analysis) are sampled according to the contribution that a given region of the space of basic variables makes to risk. The methodology is demonstrated in a strategic flood risk assessment for the city of Burton-upon-Trent in the UK. 5,000 inundation model simulations were run although it was shown that the flood risk estimate converged adequately after approximately half this number. The case study demonstrates that, amongst other factors, risk is a complex function of loadings, dike resistance, floodplain topography and the spatial distribution of floodplain assets. The application of this approach allows flood risk managers to obtain an improved understanding of the flooding system, its vulnerabilities and the most efficient means of allocating resource to improve performance. It may also be used to test how the system may respond to future external perturbations.  相似文献   

双多普勒天气雷达风场探测的可靠性研究   总被引：13，自引：7，他引：13       下载免费PDF全文

张沛源  周海光等 《应用气象学报》2002,13(4):485-496

从双多普勒天气雷达风场探测原理和多普勒天气雷达数据处理技术出发，分析了影响双勒天气雷达风场反演可靠性的内在因素。即两部雷达观测同一点的非一致性 (空间和时间上的非一致性) 和空间各测量点观测时间及照射体积的非统一性，以及微波在大气中的非直线传播和地球表面的非几何平面引起的坐标、定位等问题都严重影响了双多普勒天气雷达风场反演可靠性。该文提出一些解决办法，但在应用双多普勒天气雷达风场反演数据时，还必须进行可靠性分析。  相似文献   

城市供水系统抗震可靠性分析及对策研究   总被引：1，自引：3，他引：1  

郭恩栋  王亚东 《地震工程与工程振动》1996,16(3):104-113

本文首先详细地论述了供水网络系统的可靠性分析方法，然后选取不同的供水系统模型进行了可靠和抗震对策分析，得到了有意义的结论。  相似文献   

高边坡结构可靠度的二次处理有限元分析   总被引：1，自引：1，他引：0  

宋云连  汲敏  李树军 《工程地质学报》2008,16(4):522-527

本文依据强度折减理论,利用MIDAS/GTS有限元软件,分析计算了高边坡结构的安全系数K,找到边坡滑裂带的位置。在此基础上,对有限元输入数据和输出结果进行二次处理,建立基本随机变量c,f与滑裂带中单元的最大(和最小)主应力1(和3)的拟合关系f1(和f3),将其代入高边坡结构的功能函数Z中,使Z由隐式形式变为显式。基于该显式表示的Z,利用Monte Carlo法计算滑裂带中所有失效单元的可靠指标1,并将其单元面积A1作为权重系数,经过加权平均得到边坡结构的整体可靠指标。上述方法使得结合有限元软件计算边坡结构的整体可靠度得以简化。经实例分析可知,本文提出的方法是合理可行的,可使边坡结构整体可靠性分析得以简化,也可为高边坡结构整体可靠性分析提供理论参考。  相似文献   

应用蒙特卡罗免疫遗传算法分析土坡的稳定可靠 性   总被引：1，自引：0，他引：1  

冯利军  李竞生 《工程地质学报》2008,16(1):76-83

本文借鉴疫苗提取、疫苗接种、免疫记忆、基因亲和突变、基因重组等思想提出了一种改进的免疫遗传算法。在此基础上研究了基于本文免疫遗传算法的土坡最危险滑动面搜索方法,并将该方法与蒙特卡罗随机模拟技术相结合,用于土坡稳定可靠性分析。工程实例计算结果与实际情况相符,验证了算法的有效性和分析方法的正确性。  相似文献   

Probabilistic mapping of flood-induced backscatter changes in SAR time series     

《International Journal of Applied Earth Observation and Geoinformation》2017

The information content of flood extent maps can be increased considerably by including information on the uncertainty of the flood area delineation. This additional information can be of benefit in flood forecasting and monitoring. Furthermore, flood probability maps can be converted to binary maps showing flooded and non-flooded areas by applying a threshold probability value p_F = 0.5. In this study, a probabilistic change detection approach for flood mapping based on synthetic aperture radar (SAR) time series is proposed. For this purpose, conditional probability density functions (PDFs) for land and open water surfaces were estimated from ENVISAT ASAR Wide Swath (WS) time series containing >600 images using a reference mask of permanent water bodies. A pixel-wise harmonic model was used to account for seasonality in backscatter from land areas caused by soil moisture and vegetation dynamics. The approach was evaluated for a large-scale flood event along the River Severn, United Kingdom. The retrieved flood probability maps were compared to a reference flood mask derived from high-resolution aerial imagery by means of reliability diagrams. The obtained performance measures indicate both high reliability and confidence although there was a slight under-estimation of the flood extent, which may in part be attributed to topographically induced radar shadows along the edges of the floodplain. Furthermore, the results highlight the importance of local incidence angle for the separability between flooded and non-flooded areas as specular reflection properties of open water surfaces increase with a more oblique viewing geometry.  相似文献   

提高无定向导线精度与可靠性的方法   总被引：1，自引：1，他引：0  

裴亮  李秀坤 《测绘工程》1998,7(4):59-63

提出在无定向导线上加测方向与边长的方法提高其精度与可靠性;按间接平差设计出无定向导线的计算程序,该程序除给出平差结果和精度评定数据外,还给出各种观测值的多余观测分量,进而以数据探测法进行粗差定位。用计算实例说明本程序的应用。  相似文献   

一个以遗传算法为基础的结构可靠性分析方法   总被引：5，自引：0，他引：5  

赵衍刚  江近仁 《地震工程与工程振动》1995,15(3):47-58

本文首先总结了一次二阶矩法在结构可靠性分析时的五个弱点。针对其在寻求验算点时需要求极限状态函数的导数以及在处理多峰性极限状态函数时存在的不收敛或收敛于局部验算点等弱点，探讨了将遗传算法应用于结构可靠性分析的可能性，并在分析其应用时存在的具体问题的基础上提出了一个以智能生物为基础的遗传算法。本文的分析计算表明：遗传算法在结构可靠性分析中是适用的，它可以克服一次二阶矩法在求解验算点时存在的几个弱点。本  相似文献   

生命线工程网络结构可靠性分析     

蔡新群  黄昭庆 《华南地震》1995,15(3):61-67

生命线工程网络是一种复杂的网络结构。采用具叶斯因式分解法和布尔代数中加法形展开定理，计算了生命线工程发生震害时网络结构的可靠度。利用这两种方法进行网络结构可靠性分析，可以使计算工作量大大减少，本文还采用Ｔｒｕｅ ＢＡＳＩＣ语言开发了一套功能完善的生命线工程网络可靠性分析软件。  相似文献