Basic Research Of Event Model For Water Distribution System Based On Transient Flow Analysis

At this phase, the primary method of water distribution system analysis is extended period analysis such as Epanet software model. The time scale of this method is general hours, and the state of pipelines analyzed is characteristic status of that period time, not real-time status, it is only "expectations" state, and can not satisfy requirements of the analysis for network mechanical equipment control movements and junction water demand variation. Changes in the status of the network are essentially according to variation of the state of network components. If variation process of components states and its impacts on network state are known, the real-time model of pipelines can be built to describe real-time variation of pipelines status. Variation of component status is commonly detected by using SCADA system and estimated by some algorithms. The new conception: event-driven model is introduced to describe variation process of components'states and its' impacts on network states.The event-driven model for water distribution system abstracts and encapsulates logics of analysis of transient flow induced by components'status variations. This paper completes several innovative works listed below based on event-derived model analysis for water distribution system.(1) The framework for water distribution system model is constructed based on object-oriented analysis and design principle and also based on requirement of model design and software engineering methodology.The most category components of the network are in detailed analyzed and related classes are designed, these are basic and important part for constructing event-driven model.(2) The database tables are designed for water distribution model system, it mostly include:static data tables of model elements,dynamic data tables of model elements,data tables of physical units, analysis options and fluid characteristics, etc.(3) Water consumptions and demand categories are analyzed for water distribution system. It is important to accurately estimate water demand and it is the basic prerequisite to construct the events-driven model. Water demands temporal and spatial distributions are analyzed, and the related methods are presented of junction demand computation.(4) Continuity equation and motion equation are deduced. using characteristic method, the two partial differential equations can be converted to two ordinary differential equations along two characteristic lines, and these two ordinary differential equations can be integrated along characteristic lines to get time series for fluid flow rate and head .The methods for treatment of different boundary conditions are given (including pipe connection with junction, pump, valve, reservoir, tank etc.). Methods of sectioning for pipelines are discussed (including rigid method, wave velocity adjustment, interpolation method, etc). Finally, history of research of wall shear stress models is briefly reviewed.(5) The conceptions of event and event-driven model are presented, events prototype and structure are given. Multi-event model can be simulated using event pool structure, the mechanism for firing events and event types are analyzed. Related conceptions in modern control theory are induced to reflect fluid transient flow characteristics (delay time, rise-time, peak value time, maximum amplitude value, transition time, surge time etc.)(6) The impacts are analyzed on pipelines system of events triggered by variation of component status. Several cases listed for demonstration pipelines system are studied: pump shut off analysis, pump restart up analysis, pump speed adjustment analysis, junction abnormal demand analysis, and valve open (close) analysis, etc.