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本文以管网造价为优化目标,管网拓扑结构为优化参数,管网节点最低可靠度为约束条件,建立了供水管网抗震拓扑优化模型。在供水管网功能可靠性分析方法的基础上,结合单元概率重要度分析方法,利用模拟退火算法提出了供水管网的抗震拓扑优化方法,并对一典型供水管网进行了拓扑优化分析。分析表明,对于管网抗震拓扑优化这样一个组合优化问题,模拟退火算法提供了一类很好的途径,以此为基础进行供水管网抗震可靠性优化设计具有很好的效果。 相似文献
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如果管线抗震可靠性已知,关于整个管网的抗震可靠性,即各点在指定烈度水平下相对于某个震害挡次仍可得到供水的概率,前人的工作只做到对节点进行估计。由于管线内点上存在着无以数计的用户或称次级管网,因此,我们必须研究抗震可靠性场分布。这样做不仅可以对父子型管网进行解耦分析,以利于实际课题在时空双向上的分割与联系,而且也可以成为分析兄弟型管网的一种技巧。前者意义自明,对于后者本文以冕宁县城给水管网为例进行分析研究。 相似文献
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从系统全局出发,以管道单元动态抗震可靠度和震后给水管网各节点的动态自由水压为参数,以优化加固后的管网系统震后水压总降幅最小或系统加固总投入最小为优化目标,对加固方案进行优选,从而给出管网系统的抗震加固优化策略。根据管网系统的功能要求、震害特点,将优化变量转化为较少的离散变量,并利用正交枚举法进行简化计算,从而避免了大规模非线性规划求解的困难,为给水管网的抗震加固优化提供了实用有效的方法。 相似文献
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在广泛收集供水管网资料的基础上,采用ＧＩＳ技术建立了大连开发区供水管网基础据数库,实现了基础资料的动态化、可视化。在此基础上,采用Ｍｏｎｔｅ Ｃａｒｌｏ技术,对开发区供水管网进行了系统的抗震可靠性研究,为开发区防震减灾对策的实用性和可操作性提供了依据。 相似文献
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大型城市管网抗震可靠性分析与优化 总被引：3，自引：0，他引：3
本文提出了地震作用下供水系统的渗漏模型,发展了地震后带渗漏管网的流分析技术,结合一次二阶矩方法获得了地震后供水管网的功能可靠度。针对供燃气管网系统则提出了一类高效精确的大型网络抗震连通可靠度分析的概率解析算法———递推分解算法。以上述管网抗震可靠性分析理论为基础,分别发展了基于模拟退火算法的供水系统网络拓扑优化分析理论和基于遗传算法的供燃气网络系统拓扑优化理论。 相似文献
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将有限元反应及其灵敏度分析与结构可靠度分析的近似解析方法结合起来,可以进行具有隐式功能函数的大型复杂结构的可靠性分析。在基于位移的非线性纤维梁柱单元及其灵敏度直接微分表达式的基础上,通过力学变换、概率变换和反应灵敏度,将结构可靠度计算方法FORM和SORM与有限元方法有机地集成在一起。依据现行抗震设计规范,建立了钢框架结构典型构件承载能力和结构层间变形能力的抗震极限状态方程,利用地震作用的等效随机静力模型,采用非线性有限元静力可靠度方法,对一实际工程结构的抗震可靠度及其灵敏度进行了概率分析和评价,结果表明：尽管在大震作用下该结构的层间弹塑性变形可靠度较高,但是构件极限承载能力的可靠度指标较低,仍然存在失效的可能性。因此,仅验算“小震”作用下结构的承载能力可靠度和“大震”作用下结构的变形能力可靠度是不够的,还需要验算在“中震”和“大震”作用下结构的极限承载能力可靠度。 相似文献
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基于蒙特卡罗法的城市燃气管网抗震连通可靠性分析 总被引：1，自引：0，他引：1
在对燃气管道进行地震反应判别的基础上,计算管道的抗震可靠度,并结合图论将城市燃气管网简化为源点、汇点和边线,建立管网简化模型。采用蒙特卡罗法对某六节点网络模型进行抗震连通可靠性分析,结果表明:随着迭代次数的增加,近似解以更小的误差接近精确解的概率更大;迭代次数取为5 000时,能够较好地满足精度要求。通过对连通性矩阵进行分析,探讨了设定源点提高目标汇点连通可靠度的可行性。最后,以保定市区的大型燃气管网为例,计算了Ⅶ~Ⅸ度地震烈度下管网的连通可靠度,对比了设定源点对汇点连通可靠度的影响,为该市燃气管网的震害预测和抗震优化提供参考。 相似文献
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Gtz Schroth Luciana Ferreira Da Silva Marc‐Andree Wolf Wenceslau Geraldes Teixeira Wolfgang Zech 《水文研究》1999,13(10):1423-1436
The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
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M. A. Kahn 《洁净——土壤、空气、水》2000,28(2):95-101
Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate. 相似文献
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