| publications-4281 |
article |
1996 |
Dandy, Graeme C. and Simpson, Angus R. and Murphy, Laurence J. and Murphy, L. |
An Improved Genetic Algorithm for Pipe Network Optimization |
Water Resources Research |
10.1029/95wr02917 |
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An improved genetic algorithm (GA) formulation for pipe network optimization has been developed. The new GA uses variable power scaling of the fitness function. The exponent introduced into the fitness function is increased in magnitude as the GA computer run proceeds. In addition to the more commonly used bitwise mutation operator, an adjacency or creeping mutation operator is introduced. Finally, Gray codes rather than binary codes are used to represent the set of decision variables which make up i the pipe network design. Results are presented comparing the performance of the traditional or simple GA formulation and the improved GA formulation for the New York City tunnels problem. The case study results indicate the improved GA performs significantly better than the simple GA. In addition, the improved GA performs better than previously used traditional optimization methods such as linear, dynamic, and nonlinear programming methods and an enumerative search method. The improved GA found a solution for the New York tunriels problem which is the lowest-cost feasible discrete size solution yet presented in the literature. |
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| publications-4282 |
article |
1997 |
Islam, Mohammad Ashraful and Islam, M. Rashidul and Chaudhry, M. Hanif and Chaudhry, M. Hanif and Clark, Robert M. and Clark, Robert M. |
Inverse Modeling of Chlorine Concentration in Pipe Networks under Dynamic Condition |
Journal of Environmental Engineering |
10.1061/(asce)0733-9372(1997)123:10(1033) |
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The Surface Water Treatment Rule under the Safe Drinking Water Act and its amendments require that the water utilities maintain a detectable disinfectant residual throughout the distribution system at all times. A new computer model is presented to directly calculate the chlorine concentrations needed at the source(s) to have specified residuals at given locations in a pipe network in unsteady flow conditions by using an inverse method. Unlike the forward solution method, which calculates the source chlorine concentration by a trial-and-error procedure, the inverse solution technique presented in this paper directly calculates the source concentration required to meet a specified value at a particular point in the network. The dynamic flows and pressures are first calculated by solving the governing equations by an implicit finite-difference scheme subject to appropriate boundary conditions. For chlorine concentrations at various pipe sections and at each node, the one-dimensional transport equation is mo... |
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| publications-4283 |
article |
1998 |
Fukuyama, Francis and Axelrod, Robert and Axelrod, Robert and Jervis, Robert |
The Complexity of Cooperation: Agent-Based Models of Competition and Collaboration |
Foreign Affairs |
10.2307/20048800 |
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A collection of seven essays that serves as an introductory text on complexity theory and computer modelling in the social sciences, and as an overview of the current state of the art in this field. The articles move beyond the basic paradigm of the "Prisoner's Dilemma" to study a rich set of issues, including how to cope with errors in perception or implementation, how norms emerge, and how political actors and regions of shared culture can develop. They use the shared methodology of agent-based modelling, a technique that specifies the rules of interaction between individuals and uses computer simulation to discover emergent properties of the social system. |
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| publications-4284 |
article |
1999 |
Tillman, Donald E. and Tillman, D. and Larsen, Tove A. and Larsen, Tove A. and Pahlβ€Wostl, Claudia and Pahl-Wostl, C. and Gujer, Willi and Gujer, Willi |
Modeling the actors in water supply systems |
Water Science and Technology |
10.1016/s0273-1223(99)00055-4 |
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| publications-4285 |
article |
2000 |
Ezell, Barry and Ezell, Barry and Farr, John V. and Farr, John V. and Wiese, Ian and Wiese, Ian |
Infrastructure Risk Analysis of Municipal Water Distribution System |
Journal of Infrastructure Systems |
10.1061/(asce)1076-0342(2000)6:3(118) |
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The purpose of this paper is to present an application of the infrastructure risk analysis model to a small municipality. The paper begins by decomposing the water system along the dimensions of function, component, structure, state, and vulnerability, while considering other perspectives such as political, temporal, threat, and economic. Component vulnerability is subjectively assessed in terms of exposure and access. Based on vulnerability analysis and expert opinion, a willfull water contamination attack scenario is developed and then modeled using an event tree. Expected and extreme risk are then measured using exceedence probability. Lastly, alternatives are generated and the results are presented in a multiobjective framework. The methodological framework presented can easily be applied to other critical infrastructure elements and networks. |
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| publications-4286 |
article |
2003 |
Alvisi, Stefano and Alvisi, Stefano and Franchini, Marco and Franchini, Marco and Marinelli, Andrea and Marinelli, Alberto |
A stochastic model for representing drinking water demand at residential level |
Water Resources Management |
10.1023/a:1024100518186 |
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In this study, attention is initially focussed on modelling finely sampled (1 min) residential water demand time series. Subsequently, the possibility of simulating the water demand time series relevant to different time intervals and many users is analysed by using an aggregation approach. A cluster Neyman-Scott stochastic process (NSRP) is proposed to represent the residential water demand and a parameterisation procedureis implemented to respect the cyclical behaviour usually observed in any working day. A validation is performed on the basis of the one-minute datacollected on the water distribution system of Castelfranco Emilia located in the province of Modena (I). The elaborations performed show the validity both of the NSRP model and the parameterisation procedure proposedto represent the residential demand with fine time intervals (up to 5–10 min). On the other hand, when a procedure of aggregation is applied to represent the water demand of a high number of users, the results are nolonger satisfactory since only the mean is preserved while the other statistics, and in particular the variance, are underestimated. Copyright Kluwer Academic Publishers 2003 |
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| publications-4287 |
article |
2004 |
Berry, Jonathan W. and Hart, William E. and Phillips, Cynthia A. and Uber, James G. |
A General Integer-Programming-Based Framework for Sensor Placement in Municipal Water Networks |
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10.1061/40737(2004)455 |
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| publications-4288 |
article |
2004 |
Bousquet, François and Bousquet, François and Page, Christophe Le and Page, C. Le |
Multi-agent simulations and ecosystem management: a review |
Ecological Modelling |
10.1016/j.ecolmodel.2004.01.011 |
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| publications-4289 |
article |
2006 |
Gleick, Peter H. and Gleick, Peter H. |
Water and terrorism |
Water Policy |
10.2166/wp.2006.035 |
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The importance of freshwater and water infrastructure to human and ecosystem health and to the smooth functioning of a commercial and industrial economy makes water and water systems targets for terrorism. The chance that terrorists will strike at water systems is real; indeed, there is a long history of such attacks. Water infrastructure can be targeted directly or water can be contaminated through the introduction of poison or diseasecausing agents. The damage is done by hurting people, rendering water unusable, or destroying purification and supply infrastructure. More uncertain, however, is how significant such threats are today, compared with other targets that may be subject to terrorist attack, or how effective such attacks would actually be. Analysis and historical evidence suggest that massive casualties from attacking water systems are difficult to produce, although there may be some significant exceptions. At the same time, the risk of societal disruptions, disarray, and even overreaction on the part of governments and the public from any attack, may be high. This paper reviews the history of past attacks on water systems and the most pressing vulnerabilities and risks facing modern water systems. Suggestions of ways to reduce those risks are also presented. |
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| publications-4290 |
article |
2006 |
Klise, Katherine A. and McKenna, Sean A. |
Water quality change detection: multivariate algorithms |
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10.1117/12.665019 |
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In light of growing concern over the safety and security of our nation's drinking water, increased attention has been focused on advanced monitoring of water distribution systems. The key to these advanced monitoring systems lies in the combination of real time data and robust statistical analysis. Currently available data streams from sensors provide near real time information on water quality. Combining these data streams with change detection algorithms, this project aims to develop automated monitoring techniques that will classify real time data and denote anomalous water types. Here, water quality data in 1 hour increments over 3000 hours at 4 locations are used to test multivariate algorithms to detect anomalous water quality events. The algorithms use all available water quality sensors to measure deviation from expected water quality. Simulated anomalous water quality events are added to the measured data to test three approaches to measure this deviation. These approaches include multivariate distance measures to 1) the previous observation, 2) the closest observation in multivariate space, and 3) the closest cluster of previous water quality observations. Clusters are established using kmeans classification. Each approach uses a moving window of previous water quality measurements to classify the current measurement as normal or anomalous. Receiver Operating Characteristic (ROC) curves test the ability of each approach to discriminate between normal and anomalous water quality using a variety of thresholds and simulated anomalous events. These analyses result in a better understanding of the deviation from normal water quality that is necessary to sound an alarm. |
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