Date of Award

January 2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Civil Engineering

First Advisor

Yeo Lim

Abstract

While responding to a wet weather flow event, stormwater pipe systems experience complex transient flow in which both open channel and pressurized flow regimes may coexist. The resulting transient flows may induce significant positive and negative pressure surges that can be intense enough to compromise the integrity of the system such as pipe rupture or flooding the streets and damage to properties. Unfortunately, available off-the-shelf software such as InfoWorks, Mike Urban, etc. are not comprehensive enough to capture all features of the resulting transient flows. When the elastic feature of the flow system becomes of significant importance, these models fail to capture the magnitude and track of the resulting waterhammer pressures as they produce extensive spurious numerical oscillations that compromise the accuracy of the results and in some cases cause the computer simulation to crash. The existing models are also incapable of capturing water column separation that may occur whenever the negative pressure in the conduits falls to the water vapor pressure. Thus far, several models have been proposed to improve transient flow modeling in sewer pipe systems, but none of them succeeded in addressing the aforementioned issues. This research proposes an innovative one-dimensional numerical model to address part of the shortcomings associated with the existing state-of-the-art models. The model calculates both cavitating and pressurized flow using a single set of equations that governs unsteady flow in open channel flow. The first order Godunov type finite volume method is utilized to numerically solve the equations. A customized Harten, Lax, and van Leer (HLL) Riemann solver is proposed to calculate the fluxes at the computational cell boundaries and to dissipate potential post-shock oscillations generated when the cavity is collapsed and the open channel flow beneath the cavity is switched back to pressurized flow. The numerical results are then validated using the data obtained from the experiment, other numerical models, CFD analysis, 1D-CFD analysis conducted as part of this thesis, and analytical solutions. The results show that the model can successfully capture water hammer and column separation in the sewer conduit systems with any conduit cross-sectional shapes. A unique feature of the proposed model is that it can concurrently account for waterhammer, cavitating flow, and free surface flow regimes; this makes the proposed model superior to the existing models. It is also found that the results obtained from the proposed 1D are comparable to those obtained from a comprehensive CFD analysis

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