@article{mirghani_mahinthakumar_tryby_ranjithan_zechman_2009, title={A parallel evolutionary strategy based simulation–optimization approach for solving groundwater source identification problems}, volume={32}, ISSN={0309-1708}, url={http://dx.doi.org/10.1016/j.advwatres.2009.06.001}, DOI={10.1016/j.advwatres.2009.06.001}, abstractNote={Groundwater characterization involves the resolution of unknown system characteristics from observation data, and is often classified as an inverse problem. Inverse problems are difficult to solve due to natural ill-posedness and computational intractability. Here we adopt the use of a simulation–optimization approach that couples a numerical pollutant-transport simulation model with evolutionary search algorithms for solution of the inverse problem. In this approach, the numerical transport model is solved iteratively during the evolutionary search. This process can be computationally intensive since several hundreds to thousands of forward model evaluations are typically required for solution. Given the potential computational intractability of such a simulation–optimization approach, parallel computation is employed to ease and enable the solution of such problems. In this paper, several variations of a groundwater source identification problem is examined in terms of solution quality and computational performance. The computational experiments were performed on the TeraGrid cluster available at the National Center for Supercomputing Applications. The results demonstrate the performance of the parallel simulation–optimization approach in terms of solution quality and computational performance.}, number={9}, journal={Advances in Water Resources}, publisher={Elsevier BV}, author={Mirghani, Baha Y. and Mahinthakumar, Kumar G. and Tryby, Michael E. and Ranjithan, Ranji S. and Zechman, Emily M.}, year={2009}, month={Sep}, pages={1373–1385} }
@article{boccelli_tryby_uber_summers_2003, title={A reactive species model for chlorine decay and THM formation under rechlorination conditions}, volume={37}, ISSN={["0043-1354"]}, DOI={10.1016/S0043-1354(03)00067-8}, abstractNote={Chlorine is typically used within drinking water distribution systems to maintain a disinfectant residual and minimize biological regrowth. Typical distribution system models describe the loss of disinfectant due to reactions within the water matrix as first order with respect to chlorine concentration, with the reactants in excess. Recent work, however, has investigated relatively simple dynamic models that include a second, hypothetical reactive species. This work extends these latter models to account for discontinuities associated with rechlorination events, such as those caused by booster chlorination and by mixing at distribution system junction nodes. Mathematical arguments show that the reactive species model will always represent chlorine decay better than, or as well as, a first-order model, under single dose or rechlorination conditions; this result is confirmed by experiments on five different natural waters, and is further shown that the reactive species model can be significantly better under some rechlorination conditions. Trihalomethane (THM) formation was also monitored, and results show that a linear relationship between total THM (TTHM) formation and chlorine demand is appropriate under both single dose and rechlorination conditions. This linear relationship was estimated using the modeled chlorine demand from a calibrated reactive species model, and using the measured chlorine demand, both of which adequately represented the TTHM formation.}, number={11}, journal={WATER RESEARCH}, author={Boccelli, DL and Tryby, ME and Uber, JG and Summers, RS}, year={2003}, month={Jun}, pages={2654–2666} }
@article{tryby_boccelli_uber_rossman_2002, title={Facility location model for booster disinfection of water supply networks}, volume={128}, DOI={10.1061/(ASCE)0733-9496(2002)128:5(322)}, abstractNote={Secondary or postdisinfection is widely used to maintain protective levels of disinfectant within water distribution systems. In contrast to conventional methods that apply disinfectant only at the treatment works, booster disinfection reapplies disinfectant at strategic locations within the distribution system to compensate for the losses that occur as it decays over time. Building on the writers' previous work, this paper addresses the problem of locating disinfectant booster stations that minimize the dosage required to maintain residuals throughout the supply network, and introduces a useful parameterization for disinfectant source types. The model is related to the general fixed-charge facility location problem and is formulated as a mixed integer linear programming problem. Results for an example network show that disinfectant dosage savings are achievable with the adoption of booster disinfection, and that the rate of savings decreases as the number of booster stations utilized increases. Furthermore, booster disinfection may provide a more even distribution of disinfectant concentrations throughout the network, and has the potential to reduce aggregate exposure of the population to chlorine (and its by-products) while simultaneously improving residual coverage in the periphery of the distribution system.}, number={5}, journal={Journal of Water Resources Planning and Management}, author={Tryby, M. E. and Boccelli, D. L. and Uber, J. G. and Rossman, L. A.}, year={2002}, pages={322–333} }