Water quality modelling in pipelines including the impact of hydraulic transients.

摘要

The quality of water delivered by a distribution network may degrade for many reasons. This research studies one potential cause that arises from the connection between water quality parameters and the hydraulic conditions experienced by a pipe system. More specifically, pressure and velocity variations associated with hydraulic transients or water hammer conditions, particularly through leaks and rapid device adjustments, have the potential to cause water quality degradation.; To deal with the complexity of the interrelated threats and challenges to water quality conditions, an integrated approach to the analysis of water distribution system is required. To this end, this thesis presents a water quality modelling approach that is superimposed on a comprehensive hydraulic simulator. The result is an analysis tool that permits the consideration of a wider range of hydraulic conditions than is currently permitted by the conventional steady-state (or near steady-state) approaches.; The challenge of approximating both the advection equation (AE) and the advection-dispersion equation (ADE) arises from the nature of the governing partial differential equations, which is characterized by a hyperbolic non-dissipative advective term, a parabolic diffusive term and a reaction/decay mechanism. In most pipeline applications, the numerical transport scheme has been coupled to a steady or nearly steady hydraulic model. The numerical challenge overcome here was to couple the transport equations to a fully unsteady, method of characteristics (MOC) based, hydraulic solution.; This thesis presents two successful finite difference schemes, one for the solution of the advection-reaction equation (ARE) and the other for the advection-dispersion-reaction equation (ADRE), both under transient or waterhammer conditions. The numerical properties of consistency, stability and convergence of the proposed models are investigated, both analytically and through several numerical case studies.; The case studies investigated revealed some water quality implications as a consequence of dynamic conditions in the pipeline system. However, many transient simulations showed no dramatic differences compared to results from a quasi-steady formulation in an extended period simulation. Depending on the properties of the system being analyzed, the effects of advection, compressibility and reaction are evident at various stages in the modelled response. The most serious water quality implications arise from a possible transient intrusion scenario.; This contribution represents the first rigorous attempt to evaluate water hammer effects on the water quality evolution of a pipe system.