Accounting for directional devices in WDN modeling

This work presents a modification to steady-state Water Distribution Network (WDN) simulation models in order to account for directional devices such as check valves and flow control valves. These devices, allowing water flow control in a definite direction, are important in order to manage the hydraulic system functioning over time by considering the variation of some boundary conditions as for example required demands and tank levels. However, the simulation models are built on the assumption that water can flow in both directions of each pipe in the hydraulic system and the information on directionality of some devices is not automatically allowed. Thus, in WDN models those devices are currently modeled using a heuristic approach, intermixed with solving the problem of steady-state WDN analysis. For this reason, a different approach using content and co-content theory was recently proposed in order to define the conditions that guarantee the existence and uniqueness of the solution. The alternative proposed here presents an adjustment of the energy balance equations to account for flow control valves. Check valves are treated as a special case of flow control valves, while the directionality of pumps, which are equipped with a check valve to avoid reverse flow, is modeled by means of their implicit check valve. Once the status of such directional devices is identified, a topological analysis of the network is performed. The methodology is applied to the demand-driven and pressure-driven analysis of a WDN solved by means of the global gradient algorithm, although it could be easily extended to other algorithms.