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1.
供水管网模型中,节点流量Q、管道直径D和管道粗糙系数C是带有不确定性的随机变量,为分析其对管网模型不确定性的影响,以静态模型的参数取值为基准值,通过随机抽样,重新分配管网模型的节点流量Q、管道直径D和管道粗糙系数C,利用新的模型参数值驱动水力模型,得到节点压力和管道流量,重复抽样10 000次。统计分析表明,管道直径的随机性对模型结果的影响显著,建议管网校核时应该把管道直径也作为一个校核参数。  相似文献   

2.
本文依据水力学基本原理推导了有压管网水流的最小能量损失原理,并利用网络图论及其矩阵对给水管网进行表示,借助连支、树支管段概论,提出适用于给水管网水力计算和优化设计计算的数学模型。在管网水力计算时,管段初流量分配由计算机自动完成,不需编环号,手工预处理数据量少,当所计算管网的节点或管段数需要增减时,原始输入数据调整量小。在管网优化设计中,采用建立在动态技术经济分析理论基础上的管网等额年费用现值最小作为目标函数。约束条件中还考虑了现有管段管径约束,以使该计算模型也适应于扩建、改建管网设计计算。优化计…  相似文献   

3.
供水管网的节点用水量和水损系数具有明显的不确定性,为研究节点用水量和水损系数的不确定性对供水管网水力特性的影响,提出了在假定他们的随机变化服从正态分布的条件下,采用蒙特卡罗随机抽样法,对所获的每组节点用水量和水损系数的抽样值,应用稳态的水力模型计算相应的节点测压管水头和管段流量,得出节点测压管水头和管段流量的统计值的计算方法。文中给出了该算法在两管网中的应用。  相似文献   

4.
运用图论的树形结构理论分析污水管网的拓扑结构,提出用隶属度表示街区或集中用水点与管段的对应关系,并给出隶属度矩阵的概念和求解方法。基于隶属度建立矩阵计算模型,用Matlab编程实现设计流量的自动求解。结合实例,验证了模型求解大型污水管网设计流量的可行性和快捷性。  相似文献   

5.
提出一种基于慢变流理论的给水管网泄漏诊断与定位模型,即首先对管网施加随时间缓慢变化的压力激励,如果管网中存在泄漏,随着压力的不同泄漏程度也不一样,进而影响到管网中其他节点压力和管段流量等参数的变化;依据系统辨识反问题分析方法,实时监测管网监测点处的状态参数,运用贝叶斯算法对模型的预测参数——泄漏位置和泄漏量的概率值大小进行寻优,寻找模型计算值与测量值之间吻合程度最好的预测参数,得到最可能的泄漏位置与泄漏量。通过对算例管网的计算结果表明,采用该模型能够对漏失点和漏失量进行满足概率要求的准确诊断。  相似文献   

6.
史义雄 《给水排水》2007,33(4):113-116
针对污水管网设计中设计流量计算工作量大的问题,在分析城市污水管网结构的基础上,提出了管段及节点的编号方法,建立了污水管网节点连续性方程,以求解污水管网设计流量.结合实例,采用Matlab语言编写求解程序,并验证了程序的可行性.  相似文献   

7.
多定压节点管网具有复杂的拓扑关系,可充分发挥图论的优势对其进行水力计算.通过引入虚节最和虚环的概念将多定压节点问题转化为单定压节点问题,对相关矩阵按照定压和非定压节点、虚管段和实际管段、树支和链支管段进行分块表示.推导出了采用链支流量矩阵进行管网水力计算的解析表达式,在此基础上得到了适于计算机求解的离散模型,同时将此方法应用于实际算例并与Hardy Cross法的计算结果进行了对比.  相似文献   

8.
通过对非线性映射理论及技术的研究和应用,提出了一种新的城市供水管网压力监测点布置方法。以某开发区供水管网为例,首先利用EPANET水力模拟软件对供水管网不同运行工况进行水力模拟,得到各节点压力模拟数值矩阵。然后,采用非线性映射分析方法对该压力模拟数值矩阵进行非线性映射变换,得到一系列独立的二维点群,实现压力变化特征相似节点的聚类和分组。最后,根据各节点压力变化的近似程度和特征,提出供水管网压力监测点的布置方案。应用表明,该方法实用性强,提高了节点压力分析的直观程度和可视化水平。  相似文献   

9.
辽西丘陵区饮水安全工程供水村屯比较偏远,住户少而零散,供水管网多采用枝状管网布设。以前设计部门通常采用比流量法进行管网水力计算,忽略了管段沿线用水量的差别,计算出的管段流量和管径不太符合实际。采用节点流量法,并利用Excel表格,插入公式进行试算调整。该方法管段流量是根据实际用水户数确定的,管路流量更接近实际流量。并通过试算确定合理的管径,保证管道总水头损失和自由水头值趋于最小值,既保证了用户正常用水又避免了浪费。  相似文献   

10.
建立长效的管网模型动态更新管理机制,实现管网模型动态模拟,是供水企业提高管网系统安全运行可靠性和克服由管网设施的隐蔽性而带来管理盲目性的有效手段。以绍兴市为例,详细阐述了给水管网水力模型的动态更新措施,主要包括管网拓扑结构、阀门开度数据、节点水量数据和校验数据等4方面的动态更新。工程实践表明,经过动态更新后的水力模型能够保持较高的精度,管段流量和节点压力全部都符合检验标准,达到了既定的目标。  相似文献   

11.
To analyze water distribution networks under pressure-deficient conditions, most of the available hydraulic simulators, including EPANET 2, must be either modified by embedding pressure-dependent demands in the governing network equations or run repeatedly with successive adjustments made to specific parameters until a sufficient hydraulic consistency is obtained. This paper presents and discusses a simple technique that implements the square root relationship between the nodal demand and the nodal pressure using EPANET 2 tools and allows a water distribution network with pressure-dependent demands to be solved in a single run of the unmodified snapshot hydraulic analysis engine of EPANET 2. In this technique, artificial strings made up of a flow control valve, a pipe with a check valve, and a reservoir are connected to the demand nodes before running the engine, and the pressure-dependent demands are determined as the flows in the strings. The resistance of the artificial pipes is chosen such that the demands are satisfied in full at a desired nodal pressure. The proposed technique shows reasonable convergence as evidenced by its testing on example networks.  相似文献   

12.
1 . INTRODUCTIONReliabilityofwaterdistributionsystemsisofincreasingconcerntowaterdistributionsystemdesignersandoperators.Theapplicationofreliabilityconceptstotheoptimizationmodelsfortheminimum costdesignofwaterdistributionsystemscanensureareasonabletra…  相似文献   

13.
The water distribution system (WDS) rehabilitation problem is defined here as a multi-objective optimisation problem under uncertainty. Two alternative problem formulations are considered. The first objective in both approaches is to minimise the total rehabilitation cost. The second objective is to either maximise the overall WDS robustness or to minimise the total WDS risk. The WDS robustness is defined as the probability of simultaneously satisfying minimum pressure head constraints at all nodes in the network. Total risk is defined as the sum of nodal risks, where nodal risk is defined as the product of the probability of pressure failure at that node and consequence of such failure. Decision variables are the alternative rehabilitation options for each pipe in the network. The only source of uncertainty is the future water consumption. Uncertain demands are modelled using any probability density functions (PDFs) assigned in the problem formulation phase. The corresponding PDFs of the analysed nodal heads are calculated using the Latin Hypercube sampling technique. The optimal rehabilitation problem is solved using the newly developed rNSGAII method which is a modification of the well-known NSGAII optimisation algorithm. In rNSGAII a small number of demand samples are used for each fitness evaluation leading to significant computational savings when compared to the full sampling approach. The two alternative approaches are tested, verified and their performance compared on the New York tunnels case study. The results obtained demonstrate that both new methodologies are capable of identifying the robust (near) Pareto optimal fronts while making significant computational savings.  相似文献   

14.
The analysis of the water distribution network is complicated and requires several assumptions to simplify its problem definition. Demand Driven Analysis (DDA) is typically used to analyse the network assuming that all network nodes can deliver the required demand regardless of the available pressure. In the case of analysing an existing network under deficit condition such as pipe breakage or extra demand required for firefighting, assumptions used to simulate the network with DDA is not valid. Node Head Flow Relationship (NHFR) should be considered through Pressure Driven Analysis (PDA) to analyse the network. Most PDA methods assume that the networks are airtight which means that if the pressure at any demand node is negative, delivered demand will be equal to zero and the flow is permitted in the connected pipes (Siphonic flow). This assumption is hydraulically incorrect since the air is allowed to get into the connected pipes and prevent their flow leading to node isolation. In this paper, a new Pressure Driven Analysis to Prevent Siphonic Flow (PDA-SF) approach is proposed to analyze the network under deficit conditions and consider isolating the nodes that show available head less than node elevation. The PDA-SF was tested and compared to previous methods in four case studies under steady state analysis or extended period simulation. The case studies cover also different network conditions whether node isolation is needed or not. The PDA-SF was able to solve different networks where other methods failed to achieve the required demand or service pressure. The new PDA-SF method shall enable peers and modelers to better simulate and analysis water distribution networks.  相似文献   

15.
For transient analysis of a pipe network, the unsteady flow governing equations should be solved to obtain the extreme pressure heads in the system, which may be faced with several uncertainties. To evaluate that to what extent the input uncertainties can affect the system responses, a simulation model based on the fuzzy sets theory is introduced. For this purpose, triangular fuzzy numbers are used to represent the input uncertainties. Then, to obtain the extreme pressure heads in each location of the network and at each level of uncertainty, four independent optimization problems are solved. In these problems, the nodal maximum and minimum pressure heads are the objective functions and the simulation parameters are the decision variables. Accordingly, for fuzzy analysis of a pipe network, a complicated many-objective optimization problem arises. To solve the problem efficiently a many-objective genetic algorithm is coupled to the transient simulation model. To speed up the analysis, a transient simulation model in the frequency domain is used. The proposed model is applied to a pipe network and the results are discussed. The model is found computationally fast and promising for real applications.  相似文献   

16.
Dire Dawa, the second largest city of Ethiopia, was facing about the distribution system adopted for supplying clean water. It was being observed that an intermittent type of supply with main and secondary distribution pipes. It was observed that, the current water demand has surpassed the present existing supply about 65%. Hence, in order to provide sufficient quantity and good potable water with continuous (24 X 7) water supply for various sectors of study area: Sabiyan region, Dire Dawa, Ethiopia, was selected. Also, Dire Dawa Water Supply & Sewerage Authority has taken a strong decision in order to validate and examine the existing water distribution network for improved water supply. On the other hand, the main important factor which effects the validation is that the age of pipes and other accessories in present existing network were longstanding. Therefore, to avoid the leakage losses and various problems encountered with the present system, a detailed is study is conducted and the analysis is carried out using EPANET tool to design for continuous water supply. After thorough analysis by considering future concerns, it was suggested that, two GLSRs of each with 2.7 Mm3 capacity may be provided in order to meet the future demands. The tanks are provided at required elevation to ensure that the water flows in all pipes of the network efficiently. Based on the output it was observed that the diameter of pipes from the existing system ought to be revised. Additionally, other parameters which effect the network like frictional losses, velocity of flow in the pipes, residual head and pressure at nodes were also examined thoroughly by the use of different tools like WaterGEMS and Auto CAD in addition to EPANET.  相似文献   

17.
There are three methods for analysing the flow and pressure distribution in looped water supply networks (the loop method, the node method, the pipe method), accounting for the chosen unknown hydraulic parameters. For all of these methods, the nonlinear system of equations can be solved using iterative procedures (Hardy–Cross, Newton–Raphson, linear theory). In the cases of the extension or the rehabilitation of distribution networks, the unknown parameters are the hydraulic heads at nodes, and the nodal method for network analysis is preferred. In this paper, a generalised classic model is developed for the nodal analysis of complex looped systems with non-standard network components and the solvability of new problems, along with the determination of the pressure state in the system. In addition, this paper exhibits a different approach to this problem by using the variational formulation method for the development of a new analysis model based on unconditioned optimisation techniques. This model has the advantage of using a specialised optimisation algorithm, which directly minimises an objective multivariable function without constraints, implemented in a computer program. The two proposed models are compared with the classic Hardy–Cross method, and the results indicated a good performance of these models. Finally, a study is performed regarding the implications of the long-term operation of the pipe network on energy consumption using these models. The new models can serve as guidelines to supplement existing procedures of network analysis.  相似文献   

18.

The water distribution network needs to be rehabilitated when the network is unable to perform the desired function. In this study, a methodology is developed to identify the critical pipes in the water distribution network for its rehabilitation by using four network reliability metrics: supply shortage, pressure decline, energy loss per unit length, and the hydraulic uniformity index. These metrics consider different aspects of reliability of the water distribution network using pressure-dependent analysis to calculate the overall criticality of the pipes. In contrast to the conventional reliability index, the present study uses both the normal and abnormal conditions at nodes (fire demand) and pipe (pipe failure) and thus, provides more balance reliability metrics for the network. The literature shows that the node and pipe level metrics have been used separately, whereas in this study both the node and pipe level metrics are combined to develop the present methodology. The methodology is applied to four different water distribution networks, including one typical realistic water distribution network, the data for which is adopted from literature. The results show that the methodology can identify the critical pipes successfully to prioritize the water distribution network rehabilitation and found to be simple in implementation for practicing professionals. The results further show that the critical pipes are found to be located from the source on the paths that do not have a loop or around the nodes of higher demand. The study might also be useful for the extension plan of a water distribution network along with strengthening the deficient nodes/ pipes of the network.

  相似文献   

19.
Flow distribution headers play a major role in heat exchangers. The selection of header diameter, branch pipe diameter, branch pipe spacing etc. is based on the designer's experience and general guide lines. The proper selection of the header dimensions will yield uniform flow distribution in heat exchangers, which in turn will enhance the heat exchanger efficiency. In this work, the flow distribution in branch pipes and the pressure variation across the branch pipes in laminar and low turbulence region is studied with two models of the inlet dividing headers. When the numerical analysis has been applied, its inability to predict the no flow condition through the branch pipes is revealed. The results are presented in the form of flow rate ratio through branch pipes and nondimensional coefficients across branch pipes which are useful to apply the existing mathematical models for the present experimental setup.  相似文献   

20.
In water distribution systems (WDSs), the available flow at a demand node is dependent on the pressure at that node. When a network is lacking in pressure, not all consumer demands will be met in full. In this context, the assumption that all demands are fully satisfied regardless of the pressure in the system becomes unreasonable and represents the main limitation of the conventional demand driven analysis (DDA) approach to WDS modelling. A realistic depiction of the network performance can only be attained by considering demands to be pressure dependent. This paper presents an extension of the renowned DDA based hydraulic simulator EPANET 2 to incorporate pressure-dependent demands. This extension is termed “EPANET-PDX” (pressure-dependent extension) herein. The utilization of a continuous nodal pressure-flow function coupled with a line search and backtracking procedure greatly enhance the algorithm’s convergence rate and robustness. Simulations of real life networks consisting of multiple sources, pipes, valves and pumps were successfully executed and results are presented herein. Excellent modelling performance was achieved for analysing both normal and pressure deficient conditions of the WDSs. Detailed computational efficiency results of EPANET-PDX with reference to EPANET 2 are included as well.  相似文献   

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