Algorithm for Automatic Detection of Topological Changes in Water Distribution Networks

Topological and pressure-driven analyses are an integral part of reliability/risk considerations for a water distribution system. For example, it is often necessary to identify which parts of the distribution network are isolated from water sources after the valves have been closed in response to a mechanical pipe failure. Pressure-driven analysis is then necessary to ascertain the consequences of pipe failures in terms of the performance of the functioning subsystem while pipe breaks are being fixed in the isolated area. Therefore, it is extremely useful to have an algorithm for the automatic identification of nodes/pipes disconnected from the water source(s). However, this is a complex problem because valves sometimes significantly modify the network topology. Furthermore, the use of isolation valves can cause a demand shortage to some customers (due to pressure reduction) during the abnormal operating conditions in the system. Thus, pressure-driven simulation of the network behavior is required. For these reasons, a novel algorithm capable of automatic detection of topological network changes is coupled with a robust pressure-driven simulation model. This algorithm is tested on two case studies involving a small artificial water distribution system and a larger, real-life network. The results obtained clearly demonstrate the robustness of the algorithm developed.     

Pipe Index Vector: A Method to Improve Genetic-Algorithm-Based Pipe Optimization

This paper proposes a methodology for the optimal design of water distribution systems based on genetic algorithms. The objective of the optimization is to minimize the capital cost, subject to ensuring adequate pressures at all nodes during peak demands. The proposed method is novel in that it involves the use of a pipe index vector to control the genetic algorithm search. The pipe index vector is a measure of the relative importance of pipes in a network in terms of their impact on the hydraulic performance of the network. By using the pipe index vector it is possible to exclude regions of the search space where impractical and infeasible solutions exist. By reducing the search space it is possible to generate feasible solutions more quickly and hence process much healthier populations than would be the case in a standard genetic algorithm. This results in optimal solutions being found in a fewer number of generations resulting in a substantial saving in terms of computational time. The method has been tested on several networks, including networks used for benchmark testing least cost design algorithms, and has been shown to be efficient and robust.     

Impulse Response Method for Pipeline Systems Equipped with Water Hammer Protection Devices

Surge protection devices, such as surge tanks and air chambers, have been modeled with the impulse response method for transient analysis of water distribution systems. The lumped inertia model and continuity equation are used to represent nonpipe hydraulic elements. Results of pressure or discharge variations obtained by using the impulse response method and the method of characteristics are in good agreement. The impulse response method provides total pressure and discharge along any pipeline segment by direct integration of the ratio of complex head or complex discharge to a complex downstream discharge, respectively. A modification is proposed so that transition between turbulent and laminar flows can be considered. The representation of hydraulic devices has been incorporated into the impedance matrix method, which was developed for heterogeneous and multilooped pipe network systems. The potential advantages of the proposed method over other conventional approaches were investigated by applying the proposed method to hypothetical pipe network systems.     

Water Distribution Network Design Using Heuristics-Based Algorithm

Water distribution network that includes supply reservoirs, overhead tanks, consumer demand nodes, interconnecting pipes, lifting pumps, and control valves is the main mode of water supply for majority of the communities especially in urban areas. Supply of required quantity of water and at right time is the primary objective of water distribution network analysis. The analysis of water distribution networks can be broadly classified into design and operation problems and both problems have been the focus of many researchers over the past three decades. In the water distribution network design problems, the target is attaining the cost effective configuration that satisfies the minimum hydraulic head requirement at the demand nodes. In this paper, a new algorithm for design of water distribution network namely “heuristics-based algorithm” which completely utilizes the implicit information associated with the water distribution network to be designed has been proposed and validated with two water distribution networks. It is found that the proposed algorithm performs well for the least-cost design of water distribution networks.     

Valve Closure in Graph-Theoretical Models for Slow Transient Network Analysis

A valve closure algorithm is presented for inclusion within a slow transient (rigid water column) pipe network model. The algorithm is specifically formulated for (but not limited to) node-based, graph-theoretical models and is both direct and accurate. It is distinguished from conventional approaches by its direct assignment of the final discharge at closure to zero and subsequent use of the head loss at the closing valve to compute the flow rate in pipes incident to the closing valve. As a result, redistribution of residual flow prior to closure to these incident pipes is not required, leading to a less computationally demanding and more robust algorithm than previously published valve closure procedures. Application of the valve closure algorithm is illustrated in a pipe network, which also nicely demonstrates again the relation between rigid water column and water hammer models.     

Force conditions of pressing light-alloy drill pipes with spiral ribbing

The equation for calculating the pressing force of drill pipes with spiral ribbing is proposed from the Perlin procedure based on the balance of active and reactive forces. The cross-section of a spiral pipe is presented in a form of a smooth pipe with a screw arrangement of metal fibers and outer spiral edges. A component taking into account the energy spent for the screw motion of metal is added to the formula. It is shown that the compacting force, which is found according to the modernized formula, is 28% larger than for a smooth pipe with the equal area. It is revealed that an increase in the angle of ascent of the rib spiral leads to an increase in force compared with that for longitudinally edged pipes.     

Analysis of PVC Pipe-Wall Viscoelasticity during Water Hammer

This research work focuses on the analysis of hydraulic transients in polyvinyl chloride (PVC) pipes, which are characterized by a viscoelastic rheological behavior. Transient pressure data were collected in a pipe rig consisting of a set of PVC pipes. The creep function of the PVC pipes was determined by using an inverse transient model based on collected transient pressure data and compared with that obtained by carrying out mechanical tensile tests of PVC pipe specimens. The numerical results obtained from the transient solver have shown that the attenuation, dispersion, and shape of transient pressures were well described. The incorporation of the viscoelastic mechanical behavior in the hydraulic transient model has provided an excellent fitting between numerical results and observed data. Calibrated creep function based on inverse analysis fit the one determined by mechanical tests well, which emphasized the importance of pipe-wall viscoelasticity in hydraulic transients in PVC pipes.     

Leaks and Water Use Representation in Water Distribution System Models: Finding a Working Equivalence

The challenge of water demand representation in water distribution systems is revisited with a brief exploration of the relationship between a pressure-dependent leak and a fixed legitimate demand. Specifically, the idea that a leak can be modeled as an increment to legitimate demand in such a way that it entails an equivalent impact on both water loss and energy consumption is explored. Conversely, the representation of demands as leaks is briefly considered. The effectiveness of pressure reduction and demand curtailment as leak management schemes are compared for a single pipe system. The influence of pipe resistance on this relationship is assessed, suggesting that such schemes are more important in rougher pipes. In general, the notion that leakage and demand analysis/management are two sides of the same coin, and that pressure/demand management is essentially conservation, is put forth.     

Hydraulic Deterioration Models for Storm-Water Drainage Pipes: Ordered Probit versus Probabilistic Neural Network

A decrease in discharge capacity of storm-water drainage pipes is the result of the so-called hydraulic deterioration which reduces the cross sectional area of pipes and increases the pipe roughness. Hydraulic deterioration is caused by tree root intrusion, sediment accumulation, and encrustation, and is affected by many influential factors such as pipe size and pipe location. Predicting hydraulic deterioration is important for effective management of drainage pipes. An ordered probit deterioration model (OPDM) and a probabilistic neural network deterioration model (PNNDM) were developed in this study using the influential factors as model inputs and the hydraulic condition as model output. Their predictive performances were compared against each other using a case study from Melbourne, Australia with a sample of 417 storm-water drainage pipes subjected to closed circuit television inspection. The results show that the PNNDM is more suitable for predicting the hydraulic deterioration and outperforms the OPDM. Several input factors such as pipe size and pipe age are found significant to the hydraulic deterioration.     

Impact of Chlorinated Water Exposure on Contaminant Transport and Surface and Bulk Properties of High-Density Polyethylene and Cross-Linked Polyethylene Potable Water Pipes

The aim of this work was to determine if the aging of polyethylene (HDPE, PEX-A and PEX-B) water pipes by exposure to chlorinated water altered polar and nonpolar contaminant diffusivity and solubility by analyzing new, laboratory-aged, and exhumed water-distribution system polyethylene (PE) pipes. After 141?days of aging in pH 6.5 water with 45??mg/L free chlorine, the surface chemistry and bulk properties of PEX-A pipe were unaffected. Carbonyl bonds (σ = 1,713??cm-1) were detected on the surfaces of HDPE and PEX-B pipe, and these oxygenated surfaces became more hydrophilic, resulting in statistically significant increases in diffusion rates. All 10 contaminant and four pipe material combinations had diffusivity increases on average of 50% for polar contaminants and 5% for nonpolar contaminants. Contaminant solubility was slightly increased for aged PEX-A and slightly decreased for PEX-B pipes. Toluene and trichloromethane diffusivity and solubility values for 7- to 25-year-old buried water utility pipes were similar to values for new and laboratory-aged HDPE-based materials. Because chlorinated water exposure alters how polar contaminants interact with aged PE pipes, results of this work should be considered in future health risk assessments, water quality modeling, pipe performance, and service-life considerations.     

Microscopic Visualization Technique to Predict the Permeation of Organic Solvents through PVC Pipes in Water Distribution Systems

Organic contaminants may permeate through plastic pipes in water distribution systems and adversely affect the quality of drinking water. In this study, we developed a microscopic visualization technique to investigate the permeation of common organic contaminants (benzene, toluene, ethylbenzene, xylene, and trichloroethene) through polyvinyl chloride (PVC) pipes. By observing the propagation of organic moving fronts in the pipe materials with a light microscope, the technique was able to predict the permeation breakthrough times through PVC pipes that were determined in the pipe-bottle test. The advance of an organic moving front was found to be linearly dependent on the square-root of time and the propagation rate increased with an increase in the external organic chemical activity. Permeation of organic mixtures into PVC pipes was found to be additive in proportion to the permeation rates and volume percents of each component. In combination with a 2-year pipe-bottle test for PVC pipes exposed to premium gasoline, mathematical extrapolations based on the microscopic visualization tests predicted that PVC pipe are likely to resist permeation by commercial gasoline for the service life of the pipe.     

Contaminant Diffusion, Solubility, and Material Property Differences between HDPE and PEX Potable Water Pipes

The objectives of this work were to identify differences between the composition, bulk properties, contaminant diffusivity and solubility for new high-density polyethylene (HDPE) pipe and crosslinked polyethylene (PEX) pipe, as well as determine which contaminant and polymer properties are useful for predicting contaminant fate in water pipe. Variations in PE pipe density (0.9371–0.9547?g/cm3), crystallinity (69–72%), crosslinking (60 and 76%), and oxidative induction time (33 to >295?min.) were detected. While numerically these differences seem minor, results show that slight material differences have a notable effect on contaminant diffusivity and solubility. Nonpolar contaminant diffusivity and solubility were best predicted by bulk density. Polar contaminants were more soluble and diffused faster through PEX than HDPE pipes because PEX pipes contained a greater amount of oxygen. For all materials, dipole moment and Log Kow were good predictors of contaminant fate and molecular volume was only useful for predicting diffusivity and solubility values for haloalkane and nonpolar aromatic contaminants.     

Field Studies of Discoloration in Water Distribution Systems: Model Verification and Practical Implications

Discoloration in water distribution systems has been studied in partnership with a number of U.K. water companies by measuring the turbidity response to changes in hydraulic conditions induced by systematic flushing. The resulting data was used to verify a predictive empirical model and hence the underlying assumptions made in its development. Model simulations, made using previously established parameters defined solely by pipe diameter and pipe material, are presented alongside measured data to demonstrate this verification. The primary cause of discoloration observed is the mobilization of material from cohesive layers bonded to pipe walls. These layers demonstrate a profile of increasing shear strength with increasing degree of discoloration. Differences are demonstrated in the layer and ultimate shear strength characteristics of the discoloration layers formed in iron and plastic pipes, with a modeled shear stress of 1.2?N/m2 shown to exhaust material layers in plastic pipes. Based on the observed data it is theorized that accumulation of material to the pipe walls is primarily dependent on two mechanisms; ubiquitous background concentrations in the bulk water, and if present corrosion by-products from iron pipes and fittings. A consequence of this is that all pipes within a water distribution system are susceptible to the development of material layers. In the formulation of operation and maintenance strategies it is suggested that iron and plastic pipes should be treated differently to obtain optimum operational effectiveness and minimize discoloration risk.     

Detection of Patterns in Water Distribution Pipe Breakage Using Spatial Scan Statistics for Point Events in a Physical Network

Infrastructure systems of many U.S. cities are in poor condition, with many assets reaching the end of their service life and requiring significant capital investments. One primary requirement to optimize the allocation of investments in such systems is an effective assessment of the physical condition of assets. This paper addresses the physical condition assessment of drinking water distribution systems by analyzing pipe breakage data as the main source of evidence about the current physical condition of water distribution pipes over space. From this spatial perspective, the primary questions are whether data sets present unexpected clustering of pipe breaks, and where those break clusters are located if they do exist. This paper presents a novel approach that aims to detect and locate clusters of break points in a water distribution network. The proposed approach extends existing spatial scan statistic approaches, which are commonly used for detection of disease outbreaks in a two-dimensional spatial framework, to data collected from networked infrastructure systems. This proposed approach is described and tested in a data set that consists of 491 breaks that occurred over six years in a 160-mi water distribution network. The results presented in this paper indicate that the adapted spatial scan statistic approach applied to points in physical networks is able to detect clusters of noncompact shapes, and that these clusters present significantly higher than expected breakage rates even after accounting for pipe age and diameter. Several possible hypotheses are explored for potential causes of these clusters.     

分簇无线传感器网络中提高网络连通性的协作算法

针对分簇无线传感器网络提出了一种基于虚拟天线阵列的协作算法.该算法通过节点间的协作来提高网络连通性,所有节点均按照泊松Voronoj网格模型进行分簇,簇首根据通信链路决定是否激活节点协作;若节点协作算法被激活,簇首从其成员中选择适合的节点作为协作节点共同组成虚拟天线阵列.通过协作,可扩展簇间的通信范围从而与远方节点直接通信以避免出现通信覆盖盲区,或者可补偿信道增益以防止由于信道深衰落所导致的传输失败.仿真结果表明,协作算法在通信过程中具有更好的连通性及能量效率,可有效降低接收端的丢包率,维持网络的连通性,从而延长网络的工作时间.     

Pressure-Driven Demand and Leakage Simulation for Water Distribution Networks

Increasingly, water loss via leakage is acknowledged as one of the main challenges facing water distribution system operations. The consideration of water loss over time, as systems age, physical networks grow, and consumption patterns mature, should form an integral part of effective asset management, rendering any simulation model capable of quantifying pressure-driven leakage indispensable. To this end, a novel steady-state network simulation model that fully integrates into a classical hydraulic representation, pressure-driven demand and leakage at the pipe level is developed and presented here. After presenting a brief literature review about leakage modeling, the importance of a more realistic simulation model allowing for leakage analysis is demonstrated. The algorithm is then tested from a numerical standpoint and subjected to a convergence analysis. These analyses are performed on a case study involving two networks derived from real systems. Experimentally observed convergence/error statistics demonstrate the high robustness of the proposed pressure-driven demand and leakage simulation model.     

翻转内衬技术在煤气管修复工程上的应用

煤气管网随着运行时间的增加，易发生煤气泄漏，引发各种事故。利用翻转内衬软管技术，修复并延长旧管网的使用寿命，经济，技术，安全等性能良好。     

Water Distribution Network Renewal Planning

This paper provides an overview of the writers' previous work in formulating a comprehensive approach to the important problem of water distribution network renewal planning, with a particular emphasis on the computing aspects involved. As pipes in a water distribution network age in service, they are characterized by increased frequency of breakage and decreased hydraulic capacity. The resulting service failures incur utility costs for the repair or rehabilitation of the pipe systems and consumer costs for degraded system performance. The challenge to the decision maker is to determine the most cost-effective plan in terms of what pipes in the network to rehabilitate, by which rehabilitation alternative and at what time in the planning horizon, subject to the constraints of service requirements (system reliability, service pressure, etc.) A dynamic programming approach, combined with partial and implicit enumeration schemes, was used to search the vast combinatorial solution space that this problem presents. A computer program was written to implement these concepts. A hydraulic network solver is used by the program to assure the network conformance to hydraulic constraints during the search for a solution. The outcome is a strategy that identifies, for each pipe in the network, the optimal rehabilitation∕renewal alternative and its optimal time of implementation. The significance of this method is in its ability to identify an optimal rehabilitation strategy while considering the deterioration of both structural integrity and hydraulic capacity of the entire network. The best current heuristic method is limited in practical studies to a network of up to 15–20 pipe links. A more efficient heuristic method is required for implementing these principles in a larger-scale water distribution system and is the subject of current research.     

球墨铸铁管在工程中的应用与分析

近几年来，球墨铸铁管在企业工程建设供水管网中已被广泛应用。分析了该管材在济钢工程中的应用情况，认为它具有强度高、韧性好、抗腐蚀能力强、寿命长、安装方便等优点，是一种比较理想的管材。     

New Computational Fluid Dynamic Procedure to Estimate Friction and Local Losses in Coextruded Drip Laterals

The design of trickle irrigation systems is crucial to optimize profitability and to warrant high values for the emission uniformity (EU) coefficient. EU depends on variation of the pressure head due to head losses along the lines and elevation changes, as well as the water temperature, and other parameters related to the emitters (manufacturer’s coefficient of variation, number of emitters per plants, emitter spacing). Trickle irrigation plants are usually designed using small diameter plastic pipes (polyethylene or polyvinyl chloride). The design problem, therefore, needs to consider head losses along the lines as well as emitter discharge variations due to the manufacturer’s variability. Variations in the hydraulic head are a consequence of both friction losses along the pipe and local losses due to the emitters’ connections, whose importance has been recently emphasized. Since each local loss depends on the emitter type (in-line or on-line) as well as on its shape and dimensions, the morphological variability of the commercially available emitter requires experimental investigations to determine local losses in drip laterals. On the other hand, local losses can be estimated by the mean of computational fluid dynamics (CFD) models, allowing analysis of velocity profiles and the turbulence caused by the emitters’ connections. FLUENT software can be considered a powerful tool to evaluate friction and local losses in drip irrigation laterals, after the necessary validation has been carried out by means of experimental data. The main objective of this study was to assess a CFD technique to evaluate friction and local losses in laterals with in-line coextruded emitters. The model was initially used to choose the turbulence model allowing the most accurate estimation of friction losses in small diameter polyethylene pipes, characterized by low Reynolds number. Second, the possibility of using CFD to predict local losses in drip irrigation laterals with a commercially available coextruded emitter was investigated. Simulated local losses were obtained as difference of the total and friction losses along a trunk of pipe, where one single emitter was installed, not considering the emitter outflow. The proposed procedure allows to evaluate local losses for other different emitter models, avoiding tedious and time-consuming experiments.