Numerical methods for modeling transient flow in distribution systems
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abstract
The authors compared two numerical methods, one Eulerianâbased, the other Lagrangianâbased, for modeling hydraulic transients in water distribution systems. The method of characteristics (MOC), considered to be the most accurate of the Eulerian methods in its representation of the governing equations, requires a number of steps or calculations to solve a typical transient pipe flow problem. The wave characteristic method (WCM), a Lagrangian approach, tracks movement and transformation of pressure waves and computes new conditions either at fixed intervals or only at times when a change actually occurs. The WCM requires orders of magnitude fewer pressure and flow calculations, allowing large systems to be solved in an expeditious manner. Furthermore, because the method is continuous in both time and space, it is less sensitive to the structure of the network and to the length of the simulation process, resulting in improved computational efficiency. Results indicated that both the MOC and WCM provide fast and accurate results for small pipe systems of short duration transients. However, WCM was superior for transient analysis of large distribution systems because it yields accurate results in a fraction of the computational time required for MOC. Pressure transients can adversely affect the quality of treated water because of potential intrusion by pathogens associated with transient events. Accurate modeling studies can help utility managers determine adequate surge protection, strengthen the integrity of their systems, and minimize costly disruptions to service.
