Modeling Flow and Pressure Control in Water Distribution Systems Using the Nash Equilibrium
Abstract
Pressure dependent modelling (PDM) for water distribution systems (WDSs) is now widely accepted as being much more realistic than the previously used demand driven modelling (DDM). Steady-state linkflows, q, outflows, c, and heads, h, of a PDM WDS with no controls of flow and pressure in the system can reliably be found as the active set method (ASM) solution of a linear-equality-constrained nonlinear optimization of the system's content. Introducing linkflow controls, such as flow control valves (FCVs) and check valves (CVs) can be handled by imposing box constraints on the decision variables q and c in the optimization and these problems too can be found either by an ASM or an interior point method. The heads in these problems are the Lagrange multipliers in the content model and controlling these cannot be handled simply by imposing constraints on them. In this paper the problem of modelling pressure control devices such as pressure reducing valves (PRVs) is solved by finding the Nash Equilibrium of a model that treats (i) the (global) linkflow constrained content optimization and (ii) the local pressure controls, as players in a competitive, non-cooperative game. While this paper details how to model FCVs and PRVs together, this modelling framework is equally applicable to pressure sustaining valves and variable speed pumps for pressure control without essential modification.
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