Nonunique Steady States in Water Distribution Networks with Flow Control Valves

It is shown that the quasi-steady-state approach to water-distribution-system simulation, which is adopted in most of the currently available hydraulic simulators, may result in nonunique solutions (in terms of nodal pressures) in the practically occurring case of a network section fed through a flow control valve whose setting is equal to the sum of the required demands in the section (this being true both for demand-driven and pressure-driven analyses). This paper presents an algorithm that allows one to determine whether nonunique solutions occur and, if so, to determine the nodal pressure range in which they lie. The algorithm is illustrated by the example of an operating city water distribution network.