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Water Loss Detection via Genetic Algorithm Optimization-Based Model Calibration
Date: 8/27/2006
Authors: Zheng Yi Wu, Paul Sage
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Identifying how much water is being lost from water networks and where the losses are occurring is of great importance to water utilities both for operational and planning reasons as well as for reputation. In this paper, an optimization-based approach is presented for simultaneously quantifying and locating water losses via the process of hydraulic model calibration. The model calibration is formulated as a nonlinear optimization problem that is solved by using a genetic algorithm. The method is developed as an integrated framework of hydraulic simulation and optimization modeling. Case studies are presented to demonstrate how the integrated approach is applied to water loss detection. The results obtained show that the method is effective at detecting water loss as part of the hydraulic calibration of the network model. The accuracy of water loss detection is dependent on the quality of the field observed data and model granularity. However, it has been shown that the approach can be used for reducing the uncertainty of the water loss identification by locating water loss hotspots, which could lead to improved operating revenues at water utilities.

Multi Objective Optimization of Sensor Placement in Water Distribution Systems
Date: 8/27/2006
Authors: Zheng Yi Wu, Tom Walski
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Placement of water quality sensor has received an increasing concern for timely providing the warning of possible contamination in a water system. Due to the large dimension of water distribution network and the difficulty for predicting where a contamination event occurs, it is a great challenge for engineers to come up with good sensor locations with any confidence to effectively detect possible contamination events. The problem is complicated by the fact that sensor location is evaluated against a number of objective criteria that may include the detection likelihood, the expected detection time, affected population and contaminated water consumption. A design that improves one objective may deteriorate another. In this paper, sensor placement is formulated as a multi objective optimization problem that is solved by using a competent genetic algorithm while the contamination events are simulated by the latest development of Monte Carlo method.

Integrated Hydraulic Model and Genetic Algorithm Optimization for Informed Analysis of a Real Water System
Date: 8/27/2006
Authors: Chris Clark, Zheng Yi Wu
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: A hydraulic network model was constructed for the City of Sidney, Ohio water distribution system. It consists of 104 miles of water mains, some of which are well over a hundred year old and serve the original part of the system. The City intends to use the model for available fire flow analysis and a variety of many other applications. It is essential that the hydraulic model be able to accurately simulate the real system conditions. Model calibration is the critical step to achieve this goal. To calibrate the model, Sidney’s Public Utility Department collected the pressure data at twenty locations, along with the boundary conditions of the observed tank levels and pump operating status. The calibration proceeds by applying a well-integrated hydraulic simulation and genetic algorithm optimization modeling platform in two phases including the systemic demand calibration to establish an extended period flow balance model and hydraulic grade calibration under multiple loading conditions. The model calibration performed for the Sidney water distribution model improves the confidence in the modeling results. It assists the engineers to better understand the insight into the system hydraulics and enhances modeling quality for evaluating the available fire flow and system improvement design. This paper illustrates the critical steps of the calibration process and the applications of the calibrated model for the City of Sidney.

Efficient Pressure Dependent Demand Model for Large Water Distribution System Analysis
Date: 8/27/2006
Authors: Zheng Yi Wu, Rong He Wang, Thomas M. Walski, Shao Yu Yang, Daniel Bowdler, Christopher C. Baggett
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Conventional water distribution models are formulated under the assumption that water consumption or demand defined at nodes is a known value so that nodal hydraulic head and pipe flows can be determined by solving a set of quasi-linear equations. This formulation is well developed and valid for the scenarios that the hydraulic pressures throughout a system are adequate for delivery the required nodal demand. However, there are some scenarios where nodal pressure is not sufficient for supplying the required demand. These cases may include the planned system maintenances, unplanned pipe outages, power failure at pump stations, and insufficient water supply from water sources. In addition, some water consumptions like leakages are pressure dependent. In this paper, a robust and efficient approach for pressure dependent demand analysis is developed for simulating a variety of low pressure scenarios. A set of element criticality evaluation criteria is also proposed for quantifying the relative importance of the elements that may be out of service. The results are presented for the applications of the approach to the trivial systems and also to a large water system. It is demonstrated that great modeling performance and convergence rates are achieved for modeling pressure dependent demand conditions and evaluating the element criticality of the large water distribution systems.

Using Criticality Analysis to Identify Impact of Valve Location
Date: 8/27/2006
Authors: Thomas M. Walski, Justin Sterling Weiler, Teresa Culver
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Identifying and quantifying the critical elements in a water distribution system has traditionally involved a great deal of judgment. With the coming of computerized hydraulic analysis, it became easier to “fail” a pipe in a distribution system to assess its impact on service. However, when a failure occurs in a real system, it does not remove a single pipe from a distribution system but rather a “segment” which can be isolated using valving. A segment will often include several nodes, portions of pipes, and other elements.

In this paper, the critical segments in a real system are identified based on existing valving. Then different rules for valve installation (e.g. N valves per junction, N-1 valves per junction) are used to add or remove isolating valves from the system and determine the performance of the system as a function of the density of valving.

Determining the Accuracy of Automated Calibration of Pipe Network Models
Date: 8/27/2006
Authors: Thomas M. Walski, Nicholas DeFrank, Thomas Voglino, Rick Wood, Brian E. Whitman
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Methods to automatically calibrate water distribution system models have been available for some time but it is very difficult to prove that any method is correct. Since at any one time the ability to know all the usage and flow conditions in a real system is impossible, obtaining all of the data needed in a real water distribution system to obtain an accurate and complete data set for model calibration is unrealistic. To test the ability of automated calibration methods to predict the actual conditions in a water system a laboratory scale physical model of a water distribution system was constructed and an automated water distribution model calibration program, employing genetic algorithms, was used to calibrate the model of that system.

The results indicated that the automated calibration methods worked well in estimating pipe roughness, demands and locating closed valves. More specifically, the automated calibration model exactly matched the measured flows and pressures in the system. It was able to identify whether a valve was closed and where the demands were located. If given sufficient data, it was able to identify pipe roughness. The only problems occurred when the number of unknowns greatly exceeded the number of measurements. The model worked equally well regardless of whether the head loss equation used was the Hazen-Williams, Darcy-Weisbach or Manning equation. In all, automated calibration was successful.

The paper describes how the lab data were collected, and how the calibration program matched the lab data and provides some suggestions for users of an automated water distribution calibration model.

Water Distribution System Analysis Before Digital Computers
Date: 8/27/2006
Authors: Thomas M. Walski
Source: ASCE 8th Annual International Symposium on Water Distribution System Ananlysis
Abstract: Water distribution system analysis did not begin with the development of digital computer programs. Engineers were successfully designing, constructing and operating water distribution systems long before the coming of the computer age. This paper traces the development of analysis from Archimedes and the Roman aqueducts, through the development of principles of fluid flow by Newton, Bernoulli and Euler to the development of head loss equations by Chezy, Darcy, Weisbach, Hazen, Williams and Moody. It then looks at how principles developed for individual elements where combined to solve network problems by Cross and the subsequent development of analog computer methods. The paper will show how our understanding of hydraulics did not come about quickly but through an unraveling of one problem after another by some brilliant individuals.