北京市二环内供水管网DMA分区方法及安全性分析

分区计量区域(District Metering Area,DMA)作为一种有效控制管网漏失的方法,越来越受到国内外供水企业的关注。根据我国城市环状供水管网的特点并结合国外DMA划分经验,对北京市二环内供水管网进行了DMA分区规划,共划分成120个DMA。在探讨北京市DMA划分方法的基础上,建立了两个DMA示范区进行应用实践,检验了DMA分区方法的安全性与合理性,为DMA的深入研究做准备。DMA安全性研究是检验分区后DMA内部的供水水压和水质变化。通过对示范区内水压和水质的监测,发现只要DMA规划合理,控制好DMA的用户数和管线长度,正确选择进水口,就完全可以保证DMA区域内的水压与水质满足用户需求和供水安全。     

基于双参数监测的供水管网漏损实验研究

针对管网的漏损问题进行了实验研究,通过模拟不同工况下的漏水情况,对干管和支管发生漏水前后的压力和流量进行了在线监测,并分析了双参数的变化情况。结果表明,当供水管网的某一管段发生漏水时,漏点上游的流量会增大,下游的流量会减小,而上下游管段的压力均变小。调节阀门导致的流量与压力变化与漏水点引起的变化对管网的影响不同,且不同位置的漏水对干管、支管流量的影响也不同。研究结果可为判断实际供水管网漏水,以及定位漏损点提供参考。     

北京市供水管网的老化漏失规律模型研究

供水管网漏失的监测难度大,维护费用高.为了有效减少管网漏失率,需要研发管网漏失模型,从而制定合理的监测模式和维护方案.针对管网老化过程,分析了其与管网漏失率的关系,应用决策树方法开发了包含管龄和管径两个因素在内的漏失规律模型.以北京市为例,对主城区19年间(1987年-2005年)由供水管网老化造成的漏失数据进行分析.结果表明,老化漏失管道的管龄服从Weibull分布,管龄为20年左右的管道更易产生漏失.利用建立的漏失规律模型,通过ArcGIS预测了2008年北京市区供水管网的老化漏失分布情况,其结果将用于漏失监测仪的优化布置.     

供水管网漏失监测预警系统开发及应用模式

围绕城市供水管网漏失监测与控制的工程需求,以建立大规模开展漏失监测控制工作的科学管理平台为目标,设计开发了供水管网漏失监测预警系统。介绍了系统功能模块、总体逻辑关系、业务处理逻辑关系、业务流程等,并结合供水企业现场工作特点,初步建立了基于供水管网漏失监测系统的工作模式。     

供水管道漏水点的勘探

通过对管网漏水点的勘探进行探索和分析，准确找出漏水点，组织人员进行修复，并有针对性采用对策，从而达到控制漏失的目的；同时找出管线走向，阀门位置现场状况，及时补充准确资料入图可确保安全供水及防止私接等，并取得显著的社会和经济效益。     

结合模型校核和贝叶斯决策理论的管网漏失定位

管网中发生漏失事故时必然会引起其他节点的水压波动,波动程度随漏失位置和漏失流量而变化。基于这一思想,采用模型校核和贝叶斯决策理论分别建立漏失定位模型,分析了两个模型的原理及优缺点,并在此基础上提出一种改进漏失定位模型,该模型对水力模型误差和测量误差有一定的免疫力,而且具有时效性。以CP市供水管网为例,通过消火栓放水模拟漏失,求解改进的漏失定位模型得到漏失概率,从而能确定出漏失节点所在区域,达到较高的检测精度。     

基于遗传编程的供水管网漏失模型

城市供水管网漏失的探测与定位极其耗费人力和物力,为了有效减少管网漏失,需要研究管网的漏失规律,开发漏失预测模型,从而为制定合理的监测模式和维护方案提供技术支持.收集了1987年-2005年北京市主城区供水管网漏失数据,并对其进行了统计分析.利用遗传编程建立了管网总漏失次数与管龄、管径、管长之间的函数关系,发现漏失次数与管龄、管长呈正相关,与管径呈负相关.同时分析了管网漏失发生时的管龄分布情况,发现其服从Weibull分布,并据此将遗传编程计算得到的总漏失次数分配到单一管段.利用建立的漏失模型,通过ArcGIS对北京市城区供水管网漏失概率进行了计算,其结果可以作为漏失监测点优化布设的依据.     

供水管网渗漏分析与漏失检测技术

由于当前供水管网漏失检测主要依靠仪器且缺乏系统的方法,本文通过分析渗漏原因研究供水管网漏失检测技术。以某市住宅小区为例,利用孔口流出量和指数经验确定水流规律,并分析供水管网漏失成因;通过节点流量连续性方程和降压计算方程,建立供水管网水力模型;调整水量系数完成模型参数优化,再利用水力模型完成漏失检测。测试结果表明：对漏失检测技术优化后,小区内供水管网平均漏失率降低到4.446%,有效解决供水管网渗漏问题。     

鞍山市经济开发区供水管网漏失模型研究

以鞍山市经济开发区供水管网为主要研究对象,在独立划分居民、非居民区域计量基础上,以日为单位分别测试了居民、非居民的用水规律并分析其特点,借鉴时变化系数概念及居民、非居民曲线的分解与合成,提出了曲线峰值比概念.同时在测试区域内安装模拟漏水设施,在已知漏失水量的情况下得到大量峰值比与管网漏失率数据,以此为依据进行相关性计算,建立了管网漏失数学模型,并根据该区管网漏失管理要求设定了管网漏失报警系数.     

区块化供水管网系统进水点的优化设计研究

相较于区域计量分区(DMA),管网区块化(DBS)供水分区管理系统不但可以实现用水量的分区计量,而且能实现均衡水压和水龄、优化水质和降漏节能等作用,并且不会降低管网在事故状态下供水的可靠性。进水点数量和位置的确定是DBS分区管理的关键步骤,以重庆市巴南区鹿角—界石组团的界石供水区域管网为例,根据DBS分区方法,利用EPANET 2. 0软件模拟区块化供水管网系统的进水点数量和位置,对比不同供水条件下管网水压、水龄及建设运行费用,分析进水点数量和位置的确定方法。     

公路工程变更与索赔

介绍了公路工程施工中引起的各种索赔问题，阐述了索赔的方法与技巧，指出只有掌握和运用索赔理由和方法，才能有效地控制成本，提高经济效益。     

Resistance variation of low-quality aggregates

With an ever-decreasing source of aggregate, this study reports laboratory tests on geologically young material, some of which is unconsolidated, in order to determine whether they can be used as aggregates. Los Angeles abrasion and aggregate impact values were compared and correlations made between these parameters and the petrographic composition of the material, as well as some other common properties (particle shape, water absorption). The drift deposits tested consisted mainly of limestone gravels although clasts of sandstone with some deleterious chert and fine material were also present. Whilst the laboratory test results did not always conform to the requirements of the common Standards for aggregates, it was considered that, with appropriate processing, many of the materials could be used.      

Diel variation of in-stream nitrification

The diel variation of in-stream nitrification is explained as a function of observed fluctuations in temperature and pH. A simultaneous nitrogen and dissolved oxygen mass balance model was used to calculate hourly nitrification rate coefficient values. These calculated rate coefficients were based upon observed spatial and temporal changes in nitrogen species and dissolved oxygen concentrations. A non-linear regression analysis was performed to determine the functional relationship between calculated in-stream nitrification variation and observed changes in bulk fluid temperature and pH.     

Local variation in background water quality

Recent United Kingdom government surveys have provided data and maps illustrating the spatial variation in the degree of pollution of British rivers. Attention can also be focused upon water quality variation in unpolluted streams and the term background water quality has been coined to cover certain aspects of this topic.A sampling survey has been carried out in the catchment of the River Exe in Devon (1462 km²) to demonstrate the considerable extent of local variation in specific conductance, one index of background water quality. The spatial pattern revealed has been tentatively accounted for in terms of a number of environmental factors of which geology was found to be the most important, although landuse, topography and climate also exerted an influence.Further work has involved studying other indices of background water quality, specifically magnesium and chloride concentrations, in a limited portion of the Exe Basin (613 km²) and more detailed local variations have been demonstrated.     

参数变化对透视图的影响

阐述了透视图的分类及特点,介绍了用AutoCAD软件中dview命令绘制透视图的步骤,并深入分析了参数变化对透视图的影响,进而选择比较理想的选项与参数,以达到满意的透视效果。     

Sources of variation in regional economies

This paper employs a vector autoregressive (VAR) methodology to examine the role of oil price shocks, defense shocks, national, and local shocks in explaining fluctuations in non-farm employment in a sample of ten states/MSAs in the US in the period 1969–2000. These include a sample of energy rich states and a sample of presumed beneficiaries of defense spending. Existing literature provides mixed evidence on the effects of defense shocks and oil shocks or does not focus on individual states. Results of this paper indicate that oil shocks and defense shocks have more pronounced effects at the local level than they do at the national level. An increase in the price of oil has a fairly large and for the most part statistically significant positive impact on the energy rich states and has a negative and statistically significant impact in the case of the Detroit-Flint MSA. When defense shocks occur they have a sizable impact on local economies that are beneficiaries of defense spending, even though their importance over the whole sample is not always significant. A key policy implication that emerges is that macroeconomic policy at the aggregate level may not be sufficient to uniformly stabilize regional economies that face oil, defense, and local shocks. Furthermore, to the extent that some of these states are linked more to their own local economies rather than to the US economy, they would have to rely more on local stabilization policies when faced with adverse local shocks. Received: November 2001/Accepted: August 2002     

Sources of regional variation in youth employment

This paper uses state data for the late 1970's in a regression model to assess the relative importance of several hypotheses that have been advanced to explain the significant relative deterioration in youth employment opportunities. The paper also attempts to evaluate the nature and importance of regional differences with respect to the variables that are associated with youth employment opportunities. In particular the paper focuses on the effects of minimum wages and efforts to alter wages by unions, the expanded youth population and the changing labor force participation of females, differences in labor market tightness, expenditures on job training, schooling decisions on the part of young people and the general influence of poverty. Drawing on the empirical evidence, the authors conclude that a policy of regional minimum wages might result in a ten to twenty percent expansion in youth employment and achieving full employment for adult males might have an approximately equal effect.     

Temperature variation of concrete box girder bridge

On the basis of theoretical analysis and measurement on site, the temperature gradients and its variation on concrete box girder bridges resulting from ambient temperature, solar radiation, and structural temperature fields were discussed. With the help of the heat transfer theory and finite element method (FEM), the heat flux of the surface of concrete box girder was carried out, and all the heat fluxes were described as the convection. The results were compared with that from field measurements, and a good correlation was found. It was revealed that the methods, the parameters, the boundary condition used in this paper were reasonable. Last, some conclusions were obtained, which could provide the basis for box girder design under solar radiation.     

混凝土早期强度变异性分析

通过对不同强度等级的混凝土在不同龄期时的强度统计分析,初步获得了混凝土早期强度的变异性随混凝土等级的提高而降低,同一等级混凝土强度的变异性随龄期的增长而降低的规律。并对钢筋混凝土的施工管理提出了一些建议以确保建筑结构的安全。     

Temperature variation of concrete box girder bridge

On the basis of theoretical analysis and measurement on site, the temperature gradients and its variation on concrete box girder bridges resulting from ambient temperature, solar radiation, and structural temperature fields were discussed. With the help of the heat transfer theory and finite element method (FEM), the heat flux of the surface of concrete box girder was carried out, and all the heat fluxes were described as the convection. The results were compared with that from field measurements, and a good correlation was found. It was revealed that the methods, the parameters, the boundary condition used in this paper were reasonable. Last, some conclusions were obtained, which could provide the basis for box girder design under solar radiation.