1,721,025 research outputs found
More realistic water distribution network design using pressure-driven demand and leakage
No full textThe traditional optimization paradigm used in system design focuses on network cost minimization and the maintenance of nodal pressures by relying on a demand-driven simulation of the network. This article describes a more realistic optimal design approach in which simulations are conducted with a pressure-driven model in order to assess unsupplied network demand and actual leakage flow rates. Reliability, within the context of unsatisfied demand and leakage, serves as an additional objective criterion in the optimization formulation. The assumption of a maximum network deterioration level is revisited and shown to be useful for improving reliability in the face of escalating leakage
Supporting decision on energy vs. asset cost optimization in drinking water distribution networks
Full text linkOne of the challenges for water utilities is the optimal asset design ( i. e. maximum power of pump systems, tank volumes and pipe diameters) of water distribution networks (WDN) while optimizing operational efficiency ( i. e. energy consumption and cost). Besides the classical minimization of capital cost while providing sufficient supply service, the operational sustainability is an emerging issue. As the reduction of each component of capital and energy costs are conflicting with each other, the optimization problem is multi-objective. This work presents the study of the robustness of solutions of the Pareto set as a further element to support the decision
Advancements in water distribution network simulation by Enhanced GGA
No full textThe advent of information technology and geographical information systems in water industry allows a detailed description of Water Distribution Network (WDN) topology and its boundary conditions. However, the complexity of network analysis and the mathematical problem size related to the hydraulic simulation considerably increase, especially for large WDN. The present paper introduces a network simplification strategy based on a correction paradigm adopted by Giustolisi and Todini in the Enhanced Global Gradient Algorithm (EGGA). Starting from the original topology of the analyzed WDN, the proposed strategy identifies the serial nodes/sections (i.e. those adjacent to two nodes/pipes only) which are iteratively removed from network topological representation. Therefore, the new network topology contains only those nodes joining three or more pipes or the terminal nodes of branched sections. Such a topological simplification results into a lower dimension of the topological matrices underlying the hydraulic simulation model. This way the WDN analysis can be performed using the EGGA formulation increasing computational efficiency, especially for large-size networks, without forfeiting energy and mass balances of the original hydraulic system. The paper reports the general formulation of EGGA and the strategy is tested on two large-size networks (of 1,461 and 12,513 internal nodes). The results are compared with those obtained using the original WDN topology and the classic Global Gradient Algorithm (GGA). Thus, it has been demonstrated that the EGGA strategy of simplification allows achieving a computational efficiency while correctly representing the hydraulic behaviour of the network
Accounting for Local Water Storages in Assessing WDN Supply Capacity
Full text linkAbstractIn many real WDNs, as in the Mediterranean area, customers are traditionally supplied by local water storages (i.e. roof or basement tanks) fed from the top by service pipes of the urban WDN through volume-controlled orifices. The present contribution shows that the prediction of WDN water supply capacity achieved by a model accounting for the filling/emptying of local tanks, is different from both classical demand-driven analysis and the pressure-driven analysis based on Wagner's demand-pressure relationship at each node. The WDNetXL system (www.hydroinformatics.it) is used to perform multiple simulation runs to assess WDN capacity under increasing demand scenarios
Application of model tree and Evolutionary Polynomial Regression for evaluation of sediment transport in pipes
No full textPrediction of critical velocity for sediment deposition is a significant component in design of sewer pipes. Because of the abrupt changes in velocity and shear stress distributions, traditional equations based on regression analysis can fail in evaluating sediment transport efficiently. Therefore, different artificial intelligence approaches have been applied to investigate sediment transport in sewer pipes. This study proposes two different approaches to predict the critical velocity for sediment deposition in sewer networks: Model Tree (MT) and the Evolutionary Polynomial Regression (EPR), a hybrid data-driven technique that combines genetic algorithms with numerical regression. The hydraulic radius, average size of sediments, volumetric concentration, total friction factor, and non-dimensional sediment size were considered as input parameters to characterize sediment transport in clean sewer pipes. The
present study implements data collected from different works in literature. The proposed modeling approaches are compared to some benchmark formulas from literature, and discussed from the accuracy and knowledge discovery points of view, highlighting the advantage of both proposed techniques. Results indicated that both techniques have similar accuracy in predictions, but EPR allows to physical validation of returned formulas, allowing identifying the most influent inputs on the phenomenon at stake
Optimal water distribution network design accounting for valve shutdowns
No full textThe hydraulic system functioning is determined by the boundary conditions (e.g. network topology, pipe resistances/diameters, tank levels, status of control devices, status of pumps, etc.). Shutdown of isolation valves, in order to detach a portion of the hydraulic network for planned or unplanned works, generates abnormal working conditions due to the induced topological modification of the network, which may reduce the hydraulic capacity of the water system with respect to the portions still connected. Thus, a challenge for network design is to optimize diameters versus system management under abnormal working conditions, i.e. accounting for the isolation valve system. To this purpose, a methodology for optimal system design accounting for valve shutdowns is herein presented. As the optimization asks for the evaluation of network configurations that can be generated by the isolation valve system, a strategy to reduce the computational burden is required. In fact, the analysis of a large number of network configurations could be required in real-world applications. A strategy to evaluate only the critical configurations, i.e. those ones for which the hydraulic capacity becomes insufficient to satisfy water requests in the still connected network, and dominating configurations, i.e. those ones which are the most critical, is presented. The optimization procedure is explained and discussed using a small size network and the computational efficiency is demonstrated using a large size network
Generalizing WDN simulation models to variable tank levels
Full text linkIn water distribution network (WDN) steady-state modelling, tanks and reservoirs are modelled as nodes with known heads. As a result, the tank levels are upgraded after every steady-state simulation (snapshot) using external mass balance equations in extended period simulation (EPS). This approach can give rise to numerical instabilities, especially when tanks are in close proximity. In order to obtain a stable EPS model, an unsteady formulation of the WDN model has recently introduced. This work presents an extension of the steady-state WDN model, both for demand-driven and pressure-driven analyses, allowing the direct prediction of head variation of tank nodes with respect to an initial state. Head variations at those nodes are introduced as internal unknowns in the model, the variation of tank levels can be analyzed in the single steady-state simulation and EPS can be performed as a sequence of simulations without the need for external mass balances. The extension of mass balance at tank nodes allows the analysis of some technically relevant demand components. Furthermore, inlet and outlet head losses at tank nodes are introduced and large cross-sectional tank areas are allowed by the model and reservoirs become a special case of tanks. The solution algorithm is the generalized GGA (G-GGA), although the proposed WDN model generalization is universal
A decision support tool for operational optimization in WDNetXL
No full textThe pumping energy is a relevant element of WDN operational costs. If tanks are used to store water, pumping optimization generally results into a less number of working pumps during the daylight hours when the electricity tariff is generally higher. Nevertheless, optimal solutions should also account for leakage component of demand which increases with pressure. In addition, the optimization of water distribution networks sometimes may require also resizing/upgrading of existing asset elements including pipes, tanks and pumps.
Starting from the Battle for Water Networks II problem, this contribution presents a practical decision support tool for WDN operational optimization as new tailored function in the WDNetXL system (www.hydroinformatics.it). Capital cost and/or operational cost and/or non-revenue water can be simultaneously minimized accounting for different decision variables like controls for pumps, pipe diameters, tank sizes and pumping stations. The WDNetXL system also facilitate analysis and successive refinement of solutions according to engineering expertise
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