Zheng Yi Wu

Battle of the Water Networks II

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

MULTI OBJECTIVE OPTIMIZATION OF SENSOR PLACEMENT IN WATER DISTRIBUTION SYSTEMS

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.

EFFICIENT PRESSURE DEPENDENT DEMAND MODEL FOR LARGE WATER DISTRIBUTION SYSTEM ANALYSIS

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.

PROGRESSIVE OPTIMIZATION APPROACH FOR CALIBRATING EPS HYDRAULIC MODELS

This paper presents a solution method and the results for Battle Water Calibration Network (BWCN) problem. It is solved in a progressive manner of optimizing model parameters with sound engineering judgments. The model calibration has been completed by undertaking multiple steps, including (1) constructing the initial Extended Period Simulation (EPS) model with the given model and SCADA data; (2) calibrating for static and fire flow test data; and (3) calibrating EPS model for given SCADA data over 167 hours. The calibration tasks were iteratively conducted per District Meter Area (DMA), verified and then fine tuned for the whole system. While the field data contained some noise, good model calibration has been achieved for BWCN.

Determining the Best Way to Model Distribution Flushing

Modeling of distribution system flushing consists of adding demands to the model to simulate the open hydrants and observing the response of the system. However, the details of setting up flushing events bring up a number of issues that will be addressed in this paper. Most models do not explicitly include hydrants and their laterals in the model but simulate flushing as occurring at junction nodes near the hydrants. The paper shows that most of the head loss during flushing occurs in the hydrant itself, primarily as a conversion of pressure head to velocity head. As such, the error involved in simulating flushing at a junction node rather than at the location of the hydrant or hydrant tap is small. This paper discusses modeling practice in planning flushing operation. Conventional flushing (i.e. with no valve operation) is shown to do an adequate job in flushing a system in most cases and modeling can help engineers to identify situation where unidirectional flushing can yield significant improvement or flushing by operating hydrants alone will not be successful.

ENHANCEMENTS FOR MODELING TARGET HYDRAULIC HEAD BY AUTOMATIC CALCULATION OF VARIABLE PUMP SPEED

To analyze a system of maintaining a fixed hydraulic head at a location for delivering adequate water supply with little or no storage, a conventional hydraulic model could be applied with constant speed pumps. However, modelers would need to iteratively adjust pump speed for each variable speed pump (VSP) to identify the appropriate speed factors at each time step. No doubt, this is a time consuming task, specially, when there are multiple VSPs installed in a system. This paper presents a technically enhanced approach that extends the hydraulic network model to automatically calculate the pump speed that is to deliver a prescribed hydraulic head. The improvement allows engineer to model not only a single VSP without rule-based control, but also multiple VSPs with simple and logic controls. The desired control head can be specified at any location in a system. This feature offers great flexibilities and modeling capabilities for engineers to efficiently analyze a variety of scenarios for the systems where VSPs are installed.