Generalized Flexible Method for Simulating Transient Pipe Network Hydraulics

Characteristic solution methods, namely the method of characteristics (MOC) and wave characteristics method (WCM), are widely used for simulating transient pipe network flows. Because the MOC computes solutions at interior nodes, it features higher spatial resolution, whereas the WCM makes simplifications that yield more efficient computations. Practical analyses require numerical methods that are both accurate and computationally efficient. To benefit from the advantages of the two approaches, a generalized characteristic method (GCM) is developed in this paper by combining a flexible friction approximation with a variable reach scheme. Significantly, computational savings are realized by selectively providing greater accuracy and higher resolution solutions only where needed via more interior reaches and higher order solutions; further, the new method reduces to either of the MOC and WCM, thereby showing their intrinsic similarities. Multiple examples compare and contrast the numerical methods. From these, unsteady friction effects and, more importantly, spatial resolution are shown to be directly affected by the interior reach treatment, thus exposing a limitation for solution methods with too few interior reaches. Overall, the key contribution of this work is a methodology featuring a similar degree of accuracy to the MOC, but with a computational cost better than that of the WCM.