Development of a framework for fast transient analysis in sewer systems – S-TAF

The changes in the hydraulic engine that were introduced in SWMM 5.1.013 included enabling a pressurization algorithm that is based on the Preissmann slot. The underlying idea of the Preissmann slot is to introduce a fictitious narrow slot at the top of the closed conduits. Thus enables pressures values to exceed the maximum depth, while still enabling the use of the Saint-Venant equations that are designed for open-channel flows only. However, research has demonstrated that models based on Preissmann Slot and other mixed flows conceptual model can simulate closed pipe transient flows. Building from earlier research contributions that involved much denser spatial discretization, we apply SWMM and the Preissmann slot to represent a range of closed pipe transient flows, some of which involving fast transients. This framework, referred to as S-TAF (SWMM Transient Analysis Framework), applies custom versions of SWMM5 DLLs to enable much faster acoustic wavespeed values that are anticipated in closed conduit flows. This work presents the potential of S-TAF along with existing shortcomings, but it demonstrates that SWMM, with proper setup, can represent a wider range of flow conditions that initially conceived.

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