@article{salomons_skulovich_ostfeld_2017, title={Battle of Water Networks DMAs: Multistage Design Approach}, volume={143}, ISSN={["1943-5452"]}, DOI={10.1061/(asce)wr.1943-5452.0000830}, abstractNote={Looped water distribution system (WDS) repartitioning to district metering areas (DMAs) gained popularity as an effective technique to manage the system and detect and reduce system leakages. However, to apply this method to real WDS, various system properties should be taken into account to ensure efficient water supply. The battle of water networks district meter areas (BWNDMA) is a challenging problem that requires the redesign of the E-Town city network in Colombia. The water utility is looking to repartition the network into manageable DMAs while supplying future demands, keeping minimum and maximum pressures, improving water quality, operating the network at uniform low pressures, balancing water sources, and meeting their seasonal production capabilities. The problem is stated as a multiobjective optimization problem with DMA partitioning being one of eight equal-weighted objectives. They may be reached by (1) closing, opening, or replacing existing pipes, (2) adding parallel pipes, (3) managing storage tanks, pressure valves, and flow-control valves, and (4) utilizing pumps in the dry season. With no known analytical methodology to optimize such a large mixed-integer nonlinear problem, a major difficulty is to find a feasible solution; therefore, a multistage classic engineering approach was taken. First, source allocation and general design were carried out for the operational zones. Then, tank volumes were adjusted to meet their constraints. At this stage, DMAs were introduced to meet pressure regulations. Finally, detailed design and fine-tuning of the operations were carried out. This paper describes the taken procedures and obtained results for the redesign of the E-Town network.}, number={10}, journal={JOURNAL OF WATER RESOURCES PLANNING AND MANAGEMENT}, author={Salomons, Elad and Skulovich, Olya and Ostfeld, Avi}, year={2017}, month={Oct} }
 @article{berglund_areti_brill_mahinthakumar_2017, title={Successive linear approximation methods for leak detection in water distribution systems}, volume={143}, DOI={10.1061/(asce)wr.1943-5452.0000784}, abstractNote={In many modern water networks, an emerging trend is to measure pressure at various points in the network for operational reasons. Because leaks typically induce a signature on pressure, these routine measurements can be used to develop nonintrusive leak detection approaches. This research employs successive linear approximation methods, based on linear programming and mixed integer linear programming, in a simulation-optimization framework to explore an alternative leak detection methodology for urban water distribution networks based on pressure measurements. The methods attempt to minimize the absolute differences between observed and simulated pressure values at the sensors to determine a linear combination of leaks that most closely approximates the observed pressure pattern. Steady-state and time-varying models of differing complexity (from small published networks to a 27,000-node network for a U.S. utility) were used to test the method. Results are presented to illustrate the method’s effectiveness under different conditions. The methods are shown to work well when pervasive pressure data and hydraulic models representing true operational conditions are available. The methods developed in this work are not intended to replace traditional leak detection methods; rather, they are meant to work in concert with available methods to more accurately and efficiently isolate leak locations and reduce water loss.}, number={8}, journal={Journal of Water Resources Planning and Management}, author={Berglund, A. and Areti, V. S. and Brill, D. and Mahinthakumar, G.}, year={2017} }
 @article{shafiee_berglund_berglund_brill_mahinthakumar_2016, title={Parallel Evolutionary Algorithm for Designing Water Distribution Networks to Minimize Background Leakage}, volume={142}, ISSN={0733-9496 1943-5452}, url={http://dx.doi.org/10.1061/(ASCE)WR.1943-5452.0000601}, DOI={10.1061/(asce)wr.1943-5452.0000601}, abstractNote={Leaks in water distribution systems waste energy and water resources, increase damage to infrastructure, and may allow contamination of potable water. This research develops an evolutionary algorithm-based approach to minimize the cost of water loss, new infrastructure, and operations that reduce background leakage. A new design approach is introduced that minimizes capital and operational costs, including energy and water loss costs. Design decisions identify a combination of infrastructure improvements, including pipe replacement and valve installment, and operation rules for tanks and pumps. Solution approaches are developed to solve both a single-objective and multiobjective problem formulation. A genetic algorithm and a nondominated sorting genetic algorithm are implemented within a high-performance computing platform to select tank sizes, pump placement and operations, placement of pressure-reducing valves, and pipe diameters for replacing pipes. The evolutionary algorithm approaches identify solutions that minimize water loss due to leakage, operational costs, and capital costs, while maintaining pressure at nodes and operational feasibility for tanks and pumps. Solutions are compared to identify a recommended design. The framework is demonstrated to redesign a water distribution system for an illustrative case study, C-Town.}, number={5}, journal={Journal of Water Resources Planning and Management}, publisher={American Society of Civil Engineers (ASCE)}, author={Shafiee, M. Ehsan and Berglund, Andrew and Berglund, Emily Zechman and Brill, E. Downey, Jr. and Mahinthakumar, G.}, year={2016}, month={May} }
 @article{wang_brill_ranjithan_sankarasubramanian_2015, title={A framework for incorporating ecological releases in single reservoir operation}, volume={78}, ISSN={0309-1708}, url={http://dx.doi.org/10.1016/j.advwatres.2015.01.006}, DOI={10.1016/j.advwatres.2015.01.006}, abstractNote={Most reservoir operation practices consider downstream environmental flow as a constraint to meet a minimum release. The resulting flow regime may not necessarily provide downstream aquatic conditions to support healthy ecosystems. These effects can be quantified in terms of changes in values of parameters that represent the flow regimes. Numerous studies have focused on determining the ecological response to hydrological alteration caused by reservoir operation. To mitigate hydrological alteration and restore the natural flow regime as much as possible, a reservoir operation framework is proposed to explicitly incorporate ecological flow requirements. A general optimization-based decision model is presented to consider simultaneously the multiple anthropogenic uses of the reservoir and desirable ecological releases represented by parameters that capture the flow regime. Multiple uses of the reservoir, including water supply, hydropower generation, etc., are modeled as a mixed integer programming problem. Hydropower generation, which is represented by a nonlinear function that usually depends on head and water flow, is linearized using a two-dimensional function. Investigations using a reservoir in Virginia, located in the southeastern United States, demonstrate that compared to standard releases based on current operation practice, releases simulated using this framework perform better in mimicking pre-development flows. The tradeoff between anthropogenic use and ecological releases is investigated. The framework is first demonstrated for instances with perfect stream flow information. To examine the flexibility of this framework in reservoir release management, monthly flow forecasts and disaggregated daily flow conditions are incorporated. Retrospective monthly flow forecasts are obtained through regression models that use gridded precipitation forecasts and gridded soil moisture estimates as predictors. A nonparametric method is chosen to disaggregate monthly flow forecasts to daily flow conditions. Compared with daily flow climatology, forecasted monthly and daily flow better preserves flow variability and result in lower changes of flow parameters under the proposed framework.}, journal={Advances in Water Resources}, publisher={Elsevier BV}, author={Wang, Hui and Brill, Earl D. and Ranjithan, Ranji S. and Sankarasubramanian, A.}, year={2015}, month={Apr}, pages={9–21} }
 @article{marchi_salomons_ostfeld_kapelan_simpson_zecchin_maier_wu_elsayed_song_et al._2014, edition={+59 co-authors}, title={Battle of the Water Networks II}, volume={140}, ISSN={0733-9496 1943-5452}, url={http://dx.doi.org/10.1061/(ASCE)WR.1943-5452.0000378}, DOI={10.1061/(ASCE)WR.1943-5452.0000378}, abstractNote={The Battle of the Water Networks II (BWN-II) is the latest of a series of competitions related to the design and operation of water distribution systems (WDSs) undertaken within the Water Distribution Systems Analysis (WDSA) Symposium series. The BWN-II problem specification involved a broadly defined design and operation problem for an existing network that has to be upgraded for increased future demands, and the addition of a new development area. The design decisions involved addition of new and parallel pipes, storage, operational controls for pumps and valves, and sizing of backup power supply. Design criteria involved hydraulic, water quality, reliability, and environmental performance measures. Fourteen teams participated in the Battle and presented their results at the 14th Water Distribution Systems Analysis conference in Adelaide, Australia, September 2012. This paper summarizes the approaches used by the participants and the results they obtained. Given the complexity of the BWN-II problem and the innovative methods required to deal with the multiobjective, high dimensional and computationally demanding nature of the problem, this paper represents a snap-shot of state of the art methods for the design and operation of water distribution systems. A general finding of this paper is that there is benefit in using a combination of heuristic engineering experience and sophisticated optimization algorithms when tackling complex real-world water distribution system design problems.}, number={7}, journal={Journal of Water Resources Planning and Management}, publisher={American Society of Civil Engineers (ASCE)}, author={Marchi, Angela and Salomons, Elad and Ostfeld, Avi and Kapelan, Zoran and Simpson, Angus R. and Zecchin, Aaron C. and Maier, Holger R. and Wu, Zheng Yi and Elsayed, Samir M. and Song, Yuan and et al.}, year={2014}, month={Jul}, pages={04014009} }
 @article{shafiee_berglund_berglund_brill_mahinthakumar_2014, title={Evolutionary Computation-based Decision-making Framework for Designing Water Networks to Minimize Background Leakage}, volume={89}, ISSN={1877-7058}, url={http://dx.doi.org/10.1016/J.PROENG.2014.11.167}, DOI={10.1016/J.PROENG.2014.11.167}, abstractNote={Abstract This research minimizes the impact of leaks on the operation of the system to reduce lost water while meeting typical management goals. A genetic algorithm approach is implemented within a high-performance computing platform to select tank sizes, pump placement and operations, placement of pressure control valves, and pipe diameters for replacing pipes. It identifies solutions that minimize water loss, operational costs, and capital costs, while maintaining pressure at nodes and operational feasibility for tanks. Multiple problem formulations are solved that use alternative objective functions and allow varying degrees of freedom in the decision space. The methodology is demonstrated to identify a water distribution system re-design for the C-Town case study.}, journal={Procedia Engineering}, publisher={Elsevier BV}, author={Shafiee, M.E. and Berglund, A. and Berglund, E. Zechman and Brill, E. Downey, Jr. and Mahinthakumar, G.}, year={2014}, pages={118–125} }
 @article{li_sankarasubramanian_ranjithan_brill_2014, title={Improved regional water management utilizing climate forecasts: An interbasin transfer model with a risk management framework}, volume={50}, ISSN={0043-1397}, url={http://dx.doi.org/10.1002/2013WR015248}, DOI={10.1002/2013wr015248}, abstractNote={Regional water supply systems undergo surplus and deficit conditions due to differences in inflow characteristics as well as due to their seasonal demand patterns. This study proposes a framework for regional water management by proposing an interbasin transfer (IBT) model that uses climate-information-based inflow forecast for minimizing the deviations from the end-of-season target storage across the participating pools. Using the ensemble streamflow forecast, the IBT water allocation model was applied for two reservoir systems in the North Carolina Triangle Area. Results show that interbasin transfers initiated by the ensemble streamflow forecast could potentially improve the overall water supply reliability as the demand continues to grow in the Triangle Area. To further understand the utility of climate forecasts in facilitating IBT under different spatial correlation structures between inflows and between the initial storages of the two systems, a synthetic experiment was designed to evaluate the framework under inflow forecast having different skills. Findings from the synthetic study can be summarized as follows: (a) inflow forecasts combined with the proposed IBT optimization model provide improved allocation in comparison to the allocations obtained under the no-transfer scenario as well as under transfers obtained with climatology; (b) spatial correlations between inflows and between initial storages among participating reservoirs could also influence the potential benefits that could be achieved through IBT; (c) IBT is particularly beneficial for systems that experience low correlations between inflows or between initial storages or on both attributes of the regional water supply system. Thus, if both infrastructure and permitting structures exist for promoting interbasin transfers, season-ahead inflow forecasts could provide added benefits in forecasting surplus/deficit conditions among the participating pools in the regional water supply system.}, number={8}, journal={Water Resources Research}, publisher={American Geophysical Union (AGU)}, author={Li, Weihua and Sankarasubramanian, A. and Ranjithan, R. S. and Brill, E. D.}, year={2014}, month={Aug}, pages={6810–6827} }
 @inproceedings{jasper_mahinthakumar_ranjithan_brill_2013, title={A Sensitivity Analysis of Data Measurement Types for Leak Detection in Water Distribution Systems}, ISBN={9780784412947}, url={http://dx.doi.org/10.1061/9780784412947.059}, DOI={10.1061/9780784412947.059}, abstractNote={It is estimated that 15-40% of water is unaccounted for in urban water systems. This is mostly caused by small leaks, which are difficult to locate. Routinely measured pressure, flow, and water quality data can be used to locate leaks in the water network using an inverse modeling approach. For a known sensor configuration, the leak locations can be found by minimizing the difference between real and simulated measurements. However, when comparing measurement types (pressure, flow, or quality), some may be more sensitive to leak location than others. Furthermore, some measurement types may be more or less sensitive depending on the leak magnitude or the proximity of the leak to the sensors. The measurements types that are more sensitive to location will have a stronger signature and would need to be weighted more in an inverse modeling approach, especially in the presence of noise. Preliminary research suggests that water quality measurements are more sensitive to leak location when a leak is small, and that flow measurements are more sensitive when a leak is large. In this research, a series of sensitivity analyses are conducted on different networks to investigate the sensitivity of these measurements with respect to leak location, magnitude, and proximity of sensors to the leak location.}, booktitle={World Environmental and Water Resources Congress 2013}, publisher={American Society of Civil Engineers}, author={Jasper, Micah N. and Mahinthakumar, Gnanamanikam (Kumar) and Ranjithan, Sanmugavadivel (Ranji) and Brill, Earl Downey}, year={2013}, month={May} }
 @inproceedings{jasper_mahinthakumar_ranjithan_brill_2013, title={Leak Detection in Water Distribution Systems Using the Dividing Rectangles (DIRECT) Search}, ISBN={9780784412947}, url={http://dx.doi.org/10.1061/9780784412947.078}, DOI={10.1061/9780784412947.078}, abstractNote={Leak detection and management is an important problem in water distribution systems because it has been documented that up to 40% of the water may be lost to leaks in many aging systems. Small gradual leaks, which represent more than half of all leaks, are difficult to locate. Routinely measured pressure, flow, and water quality data in combination with a simulation-optimization inverse modeling approach could be used to characterize leakage. In this approach, the leak locations are found by minimizing the difference between real and simulated measurements for a known sensor configuration. Simulation-optimization approaches are computationally demanding because millions of simulations of a network simulator (e.g., EPANET) may be required to achieve a satisfactory solution. This problem is alleviated using a high-performance computing (HPC) framework that enables many parallel simulations of the water system using EPANET. This research is modifying an existing global search algorithm, called the Dividing Rectangles (DIRECT) Search that is traditionally used for continuous functions to enable parallel simulations and a mix of discrete variables (for leak locations) and continuous variables (for leak magnitudes). The modified algorithm is being tested with traditional continuous test functions, discrete test functions, and test water distribution networks.}, booktitle={World Environmental and Water Resources Congress 2013}, publisher={American Society of Civil Engineers}, author={Jasper, Micah N. and Mahinthakumar, Gnanamanikam (Kumar) and Ranjithan, Sanmugavadivel (Ranji) and Brill, Earl Downey}, year={2013}, month={May} }
 @article{kumar_brill_mahinthakumar_ranjithan_2012, title={Contaminant source characterization in water distribution systems using binary signals}, volume={14}, ISSN={1464-7141 1465-1734}, url={http://dx.doi.org/10.2166/hydro.2012.073}, DOI={10.2166/hydro.2012.073}, abstractNote={This paper presents a simulation–optimization-based method for identification of contamination source characteristics in a water distribution system using filtered data from threshold-based binary water quality signals. The effects of quality and quantity of the data on the accuracy of the source identification methodology are investigated. This study also addresses the issue of non-uniqueness in contaminant source identification under various data availability conditions. To establish the robustness and applicability of the methodology, numerous scenarios are investigated for a wide range of contamination incidents associated with two different networks. Results indicate that, even though use of lower resolution sensors lead to more non-unique solutions, the true source location is always included among these solutions.}, number={3}, journal={Journal of Hydroinformatics}, publisher={IWA Publishing}, author={Kumar, Jitendra and Brill, E. Downey and Mahinthakumar, G. and Ranjithan, S. Ranji}, year={2012}, month={Jul}, pages={585–602} }
 @inproceedings{sreepathi_brill_ranjithan_mahinthakumar_2012, title={Parallel Multi-Swarm Optimization Framework for Search Problems in Water Distribution Systems}, ISBN={9780784412312}, url={http://dx.doi.org/10.1061/9780784412312.323}, DOI={10.1061/9780784412312.323}, abstractNote={Population based heuristic search methods such as evolutionary algorithms (EA) and particle swarm optimization (PSO) methods are widely used for solving optimization problems especially when classical techniques are inadequate. A parallel optimization framework using multiple concurrent particle swarms is developed and applied to water distribution problems. Details of the enabling framework that couples the optimization methods with a parallel simulator built around EPANET will be discussed. In addition, algorithmic and computational performance results using ORNL’s and ANL’s leadership class parallel architectures will be presented for leakage detection and contaminant source characterization problems for two water distribution networks with 1,834 and 12,457 nodes respectively.}, booktitle={World Environmental and Water Resources Congress 2012}, publisher={American Society of Civil Engineers}, author={Sreepathi, Sarat and Brill, Downey and Ranjithan, Ranji and Mahinthakumar, Gnanamanikam (Kumar)}, year={2012}, month={May} }
 @inproceedings{barandouzi_mahinthakumar_ranjithan_brill_2012, title={Probabilistic Mapping of Water Leakage Characterizations Using a Bayesian Approach}, ISBN={9780784412312}, url={http://dx.doi.org/10.1061/9780784412312.326}, DOI={10.1061/9780784412312.326}, abstractNote={Water Distribution Systems are one of the most substantial and vulnerable part of civil infrastructure systems. For the reason that many large water distribution systems are old, which results in more leakage and expenses (e.g., increasing pump head, pipe burst, constituents' replacement), a significant portion of water produced by the utilities never passes through the consumers' meters. Due to the complex nature and vast spatial extent of a water distribution system it may be difficult for the utility personnel to identify and fix the leaks, therefore it is imperative to develop software frameworks for modeling and analyzing leakage in water distribution system during ordinary operational conditions as well as unexpected events. In this paper a Bayesian approach with Markov chain Monte Carlo method is implemented to map probabilistic characterizations of water leakage. If for this purpose physical parameters such as pipe vintage, material, and loading are available, they can be are used to develop prior information; otherwise, a uniform prior may be assumed. Routinely measured water quality, pressure, and flow measurements together with the uncertainty in demand are used to develop the likelihood function. The analyses are facilitated through the EPANET water distribution simulation tool. The efficiency and versatility of the proposed methodology is examined using water distribution network.}, booktitle={World Environmental and Water Resources Congress 2012}, publisher={American Society of Civil Engineers}, author={Barandouzi, M. A. and Mahinthakumar, G. and Ranjithan, R. and Brill, E. D.}, year={2012}, month={May} }
 @inproceedings{kumar_sreepathi_brill_ranjithan_mahinthakumar_2010, title={Detection of Leaks in Water Distribution System Using Routine Water Quality Measurements}, ISBN={9780784411148}, url={http://dx.doi.org/10.1061/41114(371)426}, DOI={10.1061/41114(371)426}, booktitle={World Environmental and Water Resources Congress 2010}, publisher={American Society of Civil Engineers}, author={Kumar, Jitendra and Sreepathi, Sarat and Brill, E. Downey and Ranjithan, Ranji and Mahinthakumar, G.}, year={2010}, month={May} }
 @inproceedings{kumar_brill_mahinthakumar_ranjithan_2010, title={Identification of Reactive Contaminant Sources in a Water Distribution System under the Conditions of Data Uncertainties}, ISBN={9780784411148}, url={http://dx.doi.org/10.1061/41114(371)442}, DOI={10.1061/41114(371)442}, booktitle={World Environmental and Water Resources Congress 2010}, publisher={American Society of Civil Engineers}, author={Kumar, Jitendra and Brill, E. Downey and Mahinthakumar, G. and Ranjithan, Ranji}, year={2010}, month={May} }
 @article{reichold_zechman_brill_holmes_2010, title={Simulation-Optimization Framework to Support Sustainable Watershed Development by Mimicking the Predevelopment Flow Regime}, volume={136}, ISSN={0733-9496 1943-5452}, url={http://dx.doi.org/10.1061/(asce)wr.1943-5452.0000040}, DOI={10.1061/(asce)wr.1943-5452.0000040}, abstractNote={The modification of land and water resources for human use alters the natural hydrologic flow regime of a downstream receiving body of water. The natural flow regime is essential for sustaining biotic structure and equilibrium within the ecosystem. Best management practices mitigate the increased storm water runoff due to increased imperviousness and are typically designed and located within a watershed to match peak and minimum flows for a small set of targeted design storms. Ecosystems are, however, affected by all the characteristics of a long-term flow regime, including the magnitude, duration, frequency, and timing of flows. A more environmentally sustainable approach for watershed development is presented based on the minimization of differences in the characteristics of the flow regime between predevelopment and postdevelopment conditions. The indicator of hydrologic alteration (IHA) is a set of 33 hydrologic indices that characterize a flow regime and, coupled with the range of variability approach (RVA), can be used to evaluate a development strategy for its alteration of the long-term hydrologic flow regime. This paper presents a methodology to identify watershed management strategies that will have a minimal impact on the flow regime and downstream ecosystems. This methodology utilizes a metric that evaluates development strategies based on an IHA/RVA analysis implemented within a simulation-optimization framework. Continuous simulation of urban runoff for different land use strategies is enabled through the use of the storm water management model, and the resulting long-term hydrograph is analyzed using IHA/RVA. Development is allocated within subcatchments to maintain a predefined minimum level of total development while minimizing the hydrologic alteration. A hybrid optimization approach based on genetic algorithm and Nelder-Meade approaches is used to identify optimal land use allocation. Further analysis is conducted to identify alternative development patterns that allocate impervious development maximally differently among subcatchments while achieving similarly low alteration in the hydrologic flow regime.}, number={3}, journal={Journal of Water Resources Planning and Management}, publisher={American Society of Civil Engineers (ASCE)}, author={Reichold, Laurel and Zechman, Emily M. and Brill, E. Downey and Holmes, Hillary}, year={2010}, month={May}, pages={366–375} }
 @inproceedings{liu_brill_mahinthakumar_ranjithan_2009, title={A Hybrid Heuristic Search Approach for Contaminant Source Characterization}, ISBN={9780784410363}, url={http://dx.doi.org/10.1061/41036(342)63}, DOI={10.1061/41036(342)63}, abstractNote={The rapid discovery of the contaminant source and its mass loading characteristics in a water distribution system (WDS) is vital for generating an efficient control strategy during a contamination event. Previous work on the Adaptive Dynamic Optimization Technique (ADOPT), which was developed as an Evolution Strategy (ES) based procedure, presents an approach to estimate the source characteristics adaptively, given dynamically updated observation data. Although this simulation-optimization approach is promising, it is computationally expensive, which poses challenges in the context of real-time solutions. This paper reports the findings of an investigation that builds upon the prior work by introducing a hybrid heuristic search method for the real-time characterization of a contaminant source. This new method integrates the ES-based ADOPT with a logistic regression (LR) analysis and a local improvement method to expedite the convergence and possibly solve the problem quickly. As a prescreening technique, a LR analysis step is performed prior to ADOPT; this step reduces the search space by eliminating unnecessary source nodes as potential source locations. Then, a local search (LS) approach is embedded into some of the algorithmic steps in ADOPT to serve as a postscreening step that potentially speeds up the convergence in localized regions in the solution space. Numerical experiments for the proposed hybrid approach are performed on an example water distribution network, and the results are compared with those of the standard implementation of ADOPT.}, booktitle={World Environmental and Water Resources Congress 2009}, publisher={American Society of Civil Engineers}, author={Liu, Li and Brill, E. Downey and Mahinthakumar, G. (Kumar) and Ranjithan, S. Ranji}, year={2009}, month={May} }
 @inproceedings{kumar_brill_mahinthakumar_ranjithan_2009, title={Characterizing Reactive Contaminant Sources in a Water Distribution System}, ISBN={9780784410363}, url={http://dx.doi.org/10.1061/41036(342)65}, DOI={10.1061/41036(342)65}, abstractNote={Accurate knowledge of the characteristics of the contamination source during a contamination event is necessary for development of any mitigation and control strategy. Contaminant injected in a system is most likely to be reactive with chlorine; however, it is impractical for water quality monitoring systems to be able to monitor for the presence of all possible contaminants. In any distribution system, chlorine levels and other water quality parameters (pH, conductance, etc.) are routinely monitored to maintain the prescribed disinfection capacity. Any reactive contaminant would affect the chlorine levels resulting in deviations in the expected chlorine levels from those expected under normal operating conditions. Anomalies in the chlorine concentration from that of the expected value can be used as a surrogate to characterize the contaminant source in the system. In the absence of knowing the reactive characteristics of the contaminants, the location of injection, and injection pattern, source identification becomes a difficult problem to solve. Source identification can be posed as an inverse problem. In earlier work authors investigated the effect of the order of reaction kinetics of the contaminant with chlorine and its impact on source identification problem assuming the reaction kinetics to be known. That work is extended to investigate a methodology to address the source identification problem based on chlorine measurements, and the effects of different uncertain contamination conditions. Findings from a range of scenarios will be presented and discussed.}, booktitle={World Environmental and Water Resources Congress 2009}, publisher={American Society of Civil Engineers}, author={Kumar, Jitendra and Brill, E. Downey and Mahinthakumar, G and Ranjithan, Ranji}, year={2009}, month={May} }
 @inproceedings{liu_zechman_brill, jr._mahinthakumar_ranjithan_uber_2008, title={Adaptive Contamination Source Identification in Water Distribution Systems Using an Evolutionary Algorithm-based Dynamic Optimization Procedure}, ISBN={9780784409411}, url={http://dx.doi.org/10.1061/40941(247)123}, DOI={10.1061/40941(247)123}, abstractNote={Accidental drinking water contamination has long been and remains a major threat to water security throughout the world. Consequently, contamination source identification is an important and difficult problem in the managing safety in water distribution systems. This problem involves the characterization of the contaminant source based on observations that are streaming from a set of sensors in the distribution network. Since contamination spread in a water distribution network is relatively quick and unpredictable, rapid identification of the source location and related characteristics is important to take contaminant control and containment actions. As the contaminant event unfolds, the streaming data could be processed over time to adaptively estimate the source characteristics. This provides an estimate of the source characteristics at any time after a contamination event is detected, and this estimate is continually updated as new observations become available. We pose and solve this problem using a dynamic optimization procedure that could potentially provide a real-time response. As time progresses, additional data is observed at a set of sensors, changing the vector of observations that should be predicted. Thus, the prediction error function is updated dynamically, changing the objective function in the optimization model. We investigate a new multi population-based search using an evolutionary algorithm (EA) that at any time represents the solution state that best matches the available observations. The set of populations migrates to represent updated solution states as new observations are added over time. At the initial detection period, non-uniqueness is inherent in the source-identification due to inadequate information, and, consequently, several solutions may predict similarly well. To address nonuniqueness at the initial stages of the search and prevent premature convergence of the EA to an incorrect solution, the multiple populations in the proposed methodology are designed to maintain a set of alternative solutions representing different non-unique solutions. As more observations are added, the EA solutions not only migrate to better solution states, but also reduce the number of solutions as the degree of non-uniqueness diminishes. This new dynamic optimization algorithm adaptively converges to the best solution(s) to match the observations available at any time. The new method will be demonstrated for a contamination source identification problem in an illustrative water distribution network.}, booktitle={Water Distribution Systems Analysis Symposium 2006}, publisher={American Society of Civil Engineers}, author={Liu, Li and Zechman, Emily M. and Brill, Jr., E. Downey and Mahinthakumar, G. and Ranjithan, S. and Uber, James}, year={2008}, month={Mar} }
 @inproceedings{zechman_brill, jr._mahinthakumar_ranjithan_uber_2008, title={Addressing Non-uniqueness in a Water Distribution Contaminant Source Identification Problem}, ISBN={9780784409411}, url={http://dx.doi.org/10.1061/40941(247)126}, DOI={10.1061/40941(247)126}, abstractNote={The source of contamination in a water distribution system may be identified through a simulation-optimization approach. The optimization method searches for the contaminant source characteristics by iteratively estimating the contaminant plume concentrations until they match observations at sensors. The amount of information available for characterizing the source depends on the number and spatial locations of the sensors, as well as on the temporally varying stream of sensed data. The accuracy of the source characterization depends on the amount of observations available. A major factor affecting this accuracy is the degree of non-uniqueness present in the problem, which may cause misidentification of the source characteristics. As more sensors are added to the network, the non-uniqueness may be reduced and a unique solution may be identified. Thus, a key consideration when solving these problems is to assess whether the solution identified is unique, and if not, what other possible solutions are present. A systematic search for a set of alternatives that are maximally different in solution characteristics can be used to address and quantify non-uniqueness. For example, if the most different set of solutions that are identified by a search procedure are very similar, then that solution will be considered as the unique solution with a higher degree of certainty. Alternatively, identification of a set of maximally different solutions that vary widely in solution characteristics will indicate that nonuniqueness is present in the problem, and the range of solutions can be used as a general representation of the amount of non-uniqueness. This paper investigates the use of evolutionary algorithm (EA)-based alternatives generation procedures to quantify and address non-uniqueness present in a contaminant source identification problem for a water distribution network. As additional sensors may decrease the amount of non-uniqueness, several sensor configurations will be tested to investigate and quantify the improvement in uniqueness as more information is used in the source characterization.}, booktitle={Water Distribution Systems Analysis Symposium 2006}, publisher={American Society of Civil Engineers}, author={Zechman, Emily M. and Brill, Jr., E. Downey and Mahinthakumar, G. and Ranjithan, S. and Uber, James}, year={2008}, month={Mar} }
 @inproceedings{liu_brill, jr._mahinthakumar_ranjithan_2008, title={Contaminant Source Characterization Using Logistic Regression and Local Search Methods}, ISBN={9780784409763}, url={http://dx.doi.org/10.1061/40976(316)503}, DOI={10.1061/40976(316)503}, abstractNote={Given a set of contaminant concentration observations at sensors in a water distribution network, an inverse problem can be constructed to identify the contaminant source characteristics (including location, strength and release history) by coupling a water distribution simulation model with an optimization method. This approach, however, requires a large number of time-consuming simulation runs to evaluate potential solutions, and it may be difficult to converge on the best solution or set of possible solutions within a reasonable computational time. For this reason, it is desirable to appropriately reduce the decision space over which the optimization procedure must search to reduce the computational burden and to potentially produce faster convergence. We propose a method to reduce the decision space by efficiently identifying the probability of each point or demand node being a contaminant source location using mostly off-line computations. Then, the most likely source locations are used as a good starting point for local search methods to obtain the optimal injection profile(s) to match the observed concentration profile(s) over time. The proposed approach is demonstrated for a contamination source identification problem using an illustrative water distribution network.}, booktitle={World Environmental and Water Resources Congress 2008}, publisher={American Society of Civil Engineers}, author={Liu, Li and Brill, Jr., E. Downey and Mahinthakumar, G. and Ranjithan, S.}, year={2008}, month={May} }
 @inproceedings{kumar_brill_ranjithan_mahinthakumar_uber_2008, title={Source Identification for Contamination Events Involving Reactive Contaminants}, ISBN={9780784409763}, url={http://dx.doi.org/10.1061/40976(316)504}, DOI={10.1061/40976(316)504}, abstractNote={The problem of contaminant source identification in a water distribution system can be solved as an inverse problem using a simulation-optimization approach. The optimization method searches for contaminant source characteristics which lead to matching observations at the sensors. Accuracy of identification depends on the quantity and quality of data available at the sensors. The present state of the art in water quality monitoring sensors does not always allow for the detection of different kinds of contaminants in the system and they do not provide continuous contaminant concentration measurements. Some sensors provide an event detection trigger based on a specific concentration threshold yielding a binary detection/no-detection signal. Sensors also routinely monitor water quality parameters such as chlorine and pH. For example, a contaminant present in the system may react with chlorine leading to changes in chlorine-based water quality indicators. These anomalies (or deviations) in the observed water quality in the distribution system can be used as indicators of presence of contaminants in the system. A methodology for identifying the source characteristics using sensors outputting binary signals was presented by the authors recently. In the present study we investigate the interaction of reactive contaminants with chlorine in the system and its effect on water quality indicators. These anomalies indicating the presence or absence of contaminants will be used for determination of source characteristics using an evolutionary algorithm-based simulation-optimization approach.}, booktitle={World Environmental and Water Resources Congress 2008}, publisher={American Society of Civil Engineers}, author={Kumar, Jitendra and Brill, E. Downey and Ranjithan, S. Ranji and Mahinthakumar, G. and Uber, J.}, year={2008}, month={May} }
 @article{kumar_doby_baugh_brill_ranjithan_2007, title={Closure to "optimal design of redundant water distribution networks using a cluster of workstations" by Sujay V. Kumar, Troy A. Doby, John W. Baugh Jr., E. Downey Brill, and S. Ranji Ranjithan}, volume={133}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-36349011269&partnerID=MN8TOARS}, DOI={10.1061/(asce)0733-9496(2007)133:6(580)}, number={6}, journal={Journal of Water Resources Planning and Management}, author={Kumar, S. V. and Doby, T. A. and Baugh, J. W. and Brill, E. D. and Ranjithan, S. R.}, year={2007}, pages={580–581} }
 @inproceedings{liu_brill, jr._mahinthakumar_uber_zechman_ranjithan_2007, title={Considering Demand Variability and Measurement Uncertainties in Adaptive Source Characterization in Water Distribution Networks}, ISBN={9780784409275}, url={http://dx.doi.org/10.1061/40927(243)502}, DOI={10.1061/40927(243)502}, booktitle={World Environmental and Water Resources Congress 2007}, publisher={American Society of Civil Engineers}, author={Liu, Li and Brill, Jr., E. Downey and Mahinthakumar, G. and Uber, James and Zechman, Emily M. and Ranjithan, S.}, year={2007}, month={May} }
 @inbook{sreepathi_mahinthakumar_zechman_ranjithan_brill_ma_von laszewski_2007, place={Berlin Heidelberg}, series={Lecture Notes in Computer Science}, title={Cyberinfrastructure for Contamination Source Characterization in Water Distribution Systems}, ISBN={9783540725831 9783540725848}, ISSN={0302-9743 1611-3349}, url={http://dx.doi.org/10.1007/978-3-540-72584-8_139}, DOI={10.1007/978-3-540-72584-8_139}, abstractNote={This paper describes a preliminary cyberinfrastructure for contaminant characterization in water distribution systems and its deployment on the grid. The cyberinfrastructure consists of the application, middleware and hardware resources. The application core consists of various optimization modules and a simulation module. This paper focuses on the development of specific middleware components of the cyberinfrastructure that enables efficient seamless execution of the application core in a grid environment. The components developed in this research include: (i) a coarse-grained parallel wrapper for the simulation module that includes additional features for persistent execution, (ii) a seamless job submission interface, and (iii) a graphical real time application monitoring tool. The performance of the cyberinfrastructure is evaluated on a local cluster and the TeraGrid.}, booktitle={Computational Science – ICCS 2007}, publisher={Springer Berlin Heidelberg}, author={Sreepathi, Sarat and Mahinthakumar, Kumar and Zechman, Emily and Ranjithan, Ranji and Brill, Downey and Ma, Xiaosong and von Laszewski, Gregor}, editor={Shi, Y. and van Albada, G.D. and Dongarra, J. and Sloot, P.M.A.Editors}, year={2007}, pages={1058–1065}, collection={Lecture Notes in Computer Science} }
 @inproceedings{kumar_zechman_brill_mahinthakumar_ranjithan_uber_2007, title={Evaluation of Non-Uniqueness in Contaminant Source Characterization Based on Sensors with Event Detection Methods}, ISBN={9780784409275}, url={http://dx.doi.org/10.1061/40927(243)513}, DOI={10.1061/40927(243)513}, abstractNote={Due to the present state of sensor technology, during a water distribution contamination event, sensors may be able to detect only the presence of a contaminant and not necessarily the complete concentration profile. Some sensors trigger a detection based on a specified threshold concentration of observation, yielding a binary detection/no-detection signal. Event detection can also be based on observed concentrations of water quality parameters, such as pH and chlorine, which are routinely measured. These concentration observations are then processed through event detection algorithms to yield a detection/no-detection signal. These event detection techniques filter the measured concentrations at sensors to produce a discrete signal. When using this filtered information to characterize the contamination source, the certainty of identifying a unique solution is likely reduced, i.e., a set of widely different source characteristics may provide a match for the sensor observations. The authors previously presented an evolutionary algorithm-based procedure for source characterization and for assessing non-uniqueness by generating a set of maximally different alternatives. The procedure is extended here to characterize a contaminant source and any non-uniqueness arising by using sensor information processed through different event detection methods.}, booktitle={World Environmental and Water Resources Congress 2007}, publisher={American Society of Civil Engineers}, author={Kumar, Jitendra and Zechman, E. M. and Brill, E. D. and Mahinthakumar, G. and Ranjithan, S. and Uber, J.}, year={2007}, month={May} }
 @inbook{mahinthakumar_von laszewski_ranjithan_brill_uber_harrison_sreepathi_zechman_2006, place={Berlin Heidelberg}, series={Lecture Notes in Computer Science}, title={An Adaptive Cyberinfrastructure for Threat Management in Urban Water Distribution Systems}, volume={3993}, ISBN={9783540343837 9783540343844}, ISSN={0302-9743 1611-3349}, url={http://dx.doi.org/10.1007/11758532_54}, DOI={10.1007/11758532_54}, abstractNote={Threat management in drinking water distribution systems involves real-time characterization of any contaminant source and plume, design of control strategies, and design of incremental data sampling schedules. This requires dynamic integration of time-varying measurements along with analytical modules that include simulation models, adaptive sampling procedures, and optimization methods. These modules are compute-intensive, requiring multi-level parallel processing via computer clusters. Since real-time responses are critical, the computational needs must also be adaptively matched with available resources. This requires a software system to facilitate this integration via a high-performance computing architecture such that the measurement system, the analytical modules and the computing resources can mutually adapt and steer each other. This paper describes the development of such an adaptive cyberinfrastructure system facilitated by a dynamic workflow design.}, booktitle={Computational Science – ICCS 2006}, publisher={Springer}, author={Mahinthakumar, Kumar and von Laszewski, Gregor and Ranjithan, Ranji and Brill, Downey and Uber, Jim and Harrison, Ken and Sreepathi, Sarat and Zechman, Emily}, editor={Alexandrov, V.N. and Albada, G.D. and Sloot, P.M.A. and Dongarra, J.Editors}, year={2006}, pages={401–408}, collection={Lecture Notes in Computer Science} }
 @article{fu_brill_ranjithan_2006, title={Conjunctive use of models to design cost-effective ozone control strategies}, volume={56}, ISSN={["2162-2906"]}, DOI={10.1080/10473289.2006.10464492}, abstractNote={The management of tropospheric ozone (O3) is particularly difficult. The formulation of emission control strategies requires considerable information including: (1) emission inventories, (2) available control technologies, (3) meteorological data for critical design episodes, and (4) computer models that simulate atmospheric transport and chemistry. The simultaneous consideration of this information during control strategy design can be exceedingly difficult for a decision-maker. Traditional management approaches do not explicitly address cost minimization. This study presents a new approach for designing air quality management strategies; a simple air quality model is used conjunctively with a complex air quality model to obtain low-cost management strategies. A simple air quality model is used to identify potentially good solutions, and two heuristic methods are used to identify cost-effective control strategies using only a small number of simple air quality model simulations. Subsequently, the resulting strategies are verified and refined using a complex air quality model. The use of this approach may greatly reduce the number of complex air quality model runs that are required. An important component of this heuristic design framework is the use of the simple air quality model as a screening and exploratory tool. To achieve similar results with the simple and complex air}, number={6}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Fu, Joshua S. and Brill, E. Downey, III and Ranjithan, S. Ranji}, year={2006}, month={Jun}, pages={800–809} }
 @article{kumar_doby_baugh_brill_ranjithan_2006, title={Optimal design of redundant water distribution networks using a cluster of workstations}, volume={132}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-33747304468&partnerID=MN8TOARS}, DOI={10.1061/(ASCE)0733-9496(2006)132:5(374)}, abstractNote={A genetic algorithm (GA)-based method for the least-cost design of looped pipe networks for various levels of redundancy is presented in this paper. Redundancy constraints are introduced in the optimization model by considering the number of pipes assumed to be out of service at any one time. Using this approach, trade-off relationships between cost and redundancy are developed. The GA-based approach is computationally intensive, and implementations on a custom fault-tolerant distributed computing framework, called Vitri, are used to satisfy the computational requirements. The design methodology is applied to two water distribution networks of different sizes, and a comparison of the performance of the distributed GAs for the design problems is also presented. We conclude that a GA-based approach to obtaining cost-effective, redundant solutions for the least-cost design of looped pipe networks can be effectively used on a heterogeneous network of nondedicated workstations.}, number={5}, journal={Journal of Water Resources Planning and Management}, author={Kumar, S. V. and Doby, T. A. and Baugh, J. W. and Brill, E. D. and Ranjithan, S. R.}, year={2006}, pages={374–384} }
 @article{solano_dumas_harrison_ranjithan_barlaz_downey brill_2002, title={Life-Cycle-based Solid Waste Management. II: Illustrative Applications}, volume={128}, ISSN={0733-9372 1943-7870}, url={http://dx.doi.org/10.1061/(asce)0733-9372(2002)128:10(993)}, DOI={10.1061/(asce)0733-9372(2002)128:10(993)}, abstractNote={A companion paper described the development of the integrated solid waste management (ISWM) model that considers cost, energy, and environmental releases associated with management of municipal solid waste. This paper demonstrates the application of the ISWM model to a hypothetical, but realistic, case study. Several solid waste management (SWM) scenarios are studied, including the variation in energy and environmental emissions among alternate SWM strategies; the effect of mandated waste diversion (through recycling and other beneficial uses of waste such as combustion to recover energy) on environmental releases and cost; the tradeoff between cost and the level of waste diversion; and the tradeoff between cost and greenhouse gas emissions. In addition, the flexibility of the model is illustrated by the identification of alternate SWM strategies that meet approximately the same objectives using distinctly different combinations of unit processes. This flexibility may be of importance to local solid waste management planners who must implement new SWM programs. Use of the model illustrates the potential impact of solid waste management policies and regulations on global environmental emissions.}, number={10}, journal={Journal of Environmental Engineering}, publisher={American Society of Civil Engineers (ASCE)}, author={Solano, Eric and Dumas, Robert D. and Harrison, Kenneth W. and Ranjithan, S. Ranji and Barlaz, Morton A. and Downey Brill, E.}, year={2002}, month={Oct}, pages={993–1005} }
 @article{solano_ranjithan_barlaz_brill_2002, title={Life-cycle-based solid waste management. I: Model development}, volume={128}, DOI={10.1061/(asce)0733-9372(2002)128:10(981)}, abstractNote={This paper describes an integrated solid waste management (ISWM) model to assist in identifying alternative SWM strategies that meet cost, energy, and environmental emissions objectives. An SWM system consisting of over 40 unit processes for collection, transfer, separation, treatment (e.g., combustion, composting), and disposal of waste as well as remanufacturing facilities for processing recycled material is defined. Waste is categorized into 48 items and their generation rates are defined for three types of sectors: single-family dwelling, multifamily dwelling, and commercial. The mass flow of each item through all possible combinations of unit processes is represented in a linear programming model using a unique modeling approach. Cost, energy consumption, and environmental emissions associated with waste processing at each unit process are computed in a set of specially implemented unit process models. A life-cycle approach is used to compute energy consumption and emissions of CO, fossil- and biomas...}, number={10}, journal={Journal of Environmental Engineering (New York, N.Y.)}, author={Solano, E. and Ranjithan, S. R. and Barlaz, Morton and Brill, E. D.}, year={2002}, pages={981–992} }
 @article{harrison_dumas_solano_barlaz_brill_ranjithan_2001, title={Decision support tool for life-cycle-based solid waste management}, volume={15}, DOI={10.1061/(ASCE)0887-3801(2001)15:1(44)}, abstractNote={Existing solid waste management (SWM) planning software provides only limited assistance to decision makers struggling to find strategies that address their multifarious concerns. The combinatorial nature (many waste items and many management options) and multiple objectives of the SWM problem severely constrain the effectiveness of a manual search process using these tools. Recognizing this, researchers have proposed several optimization-based search procedures. These methods, however, enjoy limited use due to the substantial expertise required for their application. This paper presents a new computer-based decision support framework that addresses these limitations. The new framework integrates process models that quantify the life-cycle inventory of a range of pollutants and costs for an extensive municipal solid waste system, an optimization search procedure that identifies strategies that meet cost and environmental objectives and site-specific restrictions, and a user-friendly interface that facilitates utilization of these components by practitioners. After describing the software design, the use and value of the tool in typical waste management scenarios is demonstrated through a hypothetical, but realistic, case study in which several alternative SWM strategies are generated and examined.}, number={1}, journal={Journal of Computing in Civil Engineering}, author={Harrison, K. W. and Dumas, R. D. and Solano, E. and Barlaz, Morton and Brill, E. D. and Ranjithan, S. R.}, year={2001}, pages={44–58} }
 @article{loughlin_ranjithan_brill_baugh_2001, title={Genetic algorithm approaches for addressing unmodeled objectives in optimization problems}, volume={33}, ISSN={["0305-215X"]}, DOI={10.1080/03052150108940933}, abstractNote={Abstract Public sector decision-making typically involves complex problems that are often not completely understood. In these problems, there are invariably unmodeled issues that can greatly impact the acceptability of solutions. Modeling to Generate Alternatives (MGA) is an approach for addressing unmodeled issues in an optimization context. MGA techniques are used to generate a small number of good, yet very different, solutions to optimization problems. Because these solutions are different in decision space, they may differ considerably in performance when unmodeled objectives are considered. Many problems are sufficiently complex that traditional optimization solution procedures, and therefore traditional MGA techniques, are not readily applicable. Two techniques for performing MGA using genetic algorithms (GAs) are investigated and compared. One of these techniques, which uses specialized MGA operators, is shown to produce solutions that are both better in quality and more different. This technique is also demonstrated for a realistic air quality management problem.}, number={5}, journal={ENGINEERING OPTIMIZATION}, author={Loughlin, DH and Ranjithan, SR and Brill, ED and Baugh, JW}, year={2001}, pages={549–569} }
 @article{loughlin_ranjithan_baugh_brill_2000, title={Application of genetic algorithms for the design of ozone control strategies}, volume={50}, ISSN={["2162-2906"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-0034195231&partnerID=MN8TOARS}, DOI={10.1080/10473289.2000.10464133}, abstractNote={ABSTRACT Designing air quality management strategies is complicated by the difficulty in simultaneously considering large amounts of relevant data, sophisticated air quality models, competing design objectives, and unquantifiable issues. For many problems, mathematical optimization can be used to simplify the design process by identifying cost-effective solutions. Optimization applications for controlling nonlinearly reactive pollutants such as tropospheric ozone, however, have been lacking because of the difficulty in representing nonlinear chemistry in mathematical programming models. We discuss the use of genetic algorithms (GAs) as an alternative optimization approach for developing ozone control strategies. A GA formulation is described and demonstrated for an urban-scale ozone control problem in which controls are considered for thousands of pollutant sources simultaneously. A simple air quality model is integrated into the GA to represent ozone transport and chemistry. Variations of the GA formulation for multiobjective and chance-constrained optimization are also presented. The paper concludes with a discussion of the practicality of using more sophisticated, regulatory-scale air quality models with the GA. We anticipate that such an approach will be practical in the near term for supporting regulatory decision-making.}, number={6}, journal={JOURNAL OF THE AIR & WASTE MANAGEMENT ASSOCIATION}, author={Loughlin, DH and Ranjithan, SR and Baugh, JW and Brill, ED}, year={2000}, month={Jun}, pages={1050–1063} }
 @inproceedings{ranjithan_barlaz_brill_dumas_harrison_kosmicki_solano_1998, title={Development of alternative solid waste management options with economic and environmental considerations: A mathematical modeling approach}, number={1998 Oct.}, booktitle={International Solid Waste Association 1998 World Congress, Charlotte, NC, Oct. 26-29, 1998}, author={Ranjithan, S. R and Barlaz, M. A. and Brill, E. D. and Dumas, R. D. and Harrison, K. W. and Kosmicki, B. A. and Solano, E.}, year={1998} }
 @inproceedings{loughlin_ranjithan_brill_baugh_fine_1998, title={Prototype decision support tool for developing tropospheric ozone control strategies}, booktitle={Water resources and the urban environment-98: Proceedings of the 1998 National Conference on Environmental Engineering. ASCE Joint 25th Annual Conference on Water Resources Planning and Management and 1998 National Conference on Environmental Engineering, Chicago, IL, June 7-10,1998}, publisher={Reston, VA: American Society of Civil Engineers}, author={Loughlin, D. and Ranjithan, S. and Brill, E. D. and Baugh, J. and Fine, S.}, year={1998} }
 @article{baugh_caldwell_brill_1997, title={A mathematical programming approach for generating alternatives in discrete structural optimization}, volume={28}, ISSN={["0305-215X"]}, DOI={10.1080/03052159708941125}, abstractNote={Structural design, like other complex decision problems, involves many tradeoffs among competing criteria. While mathematical programming models are increasingly realistic, there are often relevant issues that cannot be easily captured, if at all, in a formal system. This paper describes an approach to modelling that recognizes these limitations and allows a designer to explore unmodelled issues in a joint human-computer cognitive system. A prototype based on this approach is presented for topological truss optimization, and three modelling techniques are contrasted for their effectiveness in producing “different” alternatives. The results show that alternatives produced using these techniques are good with respect to modelled objectives, and yet are different, and often better, with respect to interesting objectives not present in the model.}, number={1-2}, journal={ENGINEERING OPTIMIZATION}, author={Baugh, JW and Caldwell, SC and Brill, ED}, year={1997}, pages={1–31} }
 @inbook{brill_1997, title={Effluent charges and transferable discharge permits}, booktitle={Design and operation of civil and environmental engineering systems}, publisher={New York: Wiley}, author={Brill, E. D.}, editor={C. ReVelle and McGarity, A. E.Editors}, year={1997}, pages={657–690} }