Water supply systems (WSS) experience blockages during their life time due to physical and/or chemical processes (e.g. material deposition, tubercles (rust), scales, plaque, bio-fouling and inadvertently throttled inline valves, and air intrusion). Such blockages result in wastage of energy and financial resources, reduction in carrying capacity, and increased potential for contamination. This research investigates the physics of wave-blockage interaction in WSS by analytical, numerical and experimental means. Both shallow blockages (i.e., blockages with small radial protrusion) and severe blockages (i.e., blockages with large radial protrusion) are studied. The principle of action invariance shows that w_m E_m is conserved for small blockages implying Δw_m / w_m = -ΔE_m / E_m , where...[ Read more ]

Water supply systems (WSS) experience blockages during their life time due to physical and/or chemical processes (e.g. material deposition, tubercles (rust), scales, plaque, bio-fouling and inadvertently throttled inline valves, and air intrusion). Such blockages result in wastage of energy and financial resources, reduction in carrying capacity, and increased potential for contamination. This research investigates the physics of wave-blockage interaction in WSS by analytical, numerical and experimental means. Both shallow blockages (i.e., blockages with small radial protrusion) and severe blockages (i.e., blockages with large radial protrusion) are studied. The principle of action invariance shows that w_m E_m is conserved for small blockages implying Δw_m / w_m = -ΔE_m / E_m , where w_m and E_m are the eigenfrequency and total energy of the m^th mode and Δw_m and ΔE_m its eigenfrequency and energy shift due to the blockage. The change in energy is shown to be equal to the work of the radiation pressure during the formation of the blockage. In addition, it is found that a small blockage reduces the potential energy, but increases the kinetic energy of all modes. For a severe blockage, the pipe system is decoupled into two independent subsystems: a subsystem that involves the blockage and another that involves the intact pipe section. The decoupling is lost when the blockage length is such that the fundamental frequencies of the two subsystems are close or equal, resulting in resonance which means that waves within the subsystem involving the blockage are able to penetrate (transmit) to the second subsystem and vice-versa. It is shown that the assumption of small blockage is applicable when the blockage occupies 30% of the crossectional area. The assumption of severe blockage is applicable when the blockage occupies 30% of the crossectional area or larger provided that the decoupling assumption is valid. When the blockage and the remainder of the pipe system are coupled, perturbation theory is successfully used to derive a simple frequency relation for the case of a blockage with large radial extent. This study also reveals that Bragg’s resonance plays a key role where the wave-blockage interaction is minimal for certain frequencies and maximal for others. The spacing between consecutive Bragg’s resonance frequencies, where maximal interaction occurs, scales as the wavespeed divided by the blockage length. Therefore, a wideband frequency of the transient generator is required to capture the signature of a short blockage. However, the use of high frequency waves (HFW) excites radial and azimuthal waves and renders the classical one-dimensional water-hammer (WH) theory invalid. Unlike classical WH theory, the resulting wave field is highly dispersive. Therefore, this thesis examines and reviews the behaviour of HFW in water-filled pipes and how they interact with blockages. As a result, a high-order numerical scheme has been developed and tested. The results show the strong effects of multi-paths on the propagation of high HFW in WSS and highlight that such waves, althgouh provide the required resolution, have a low range of detectability. Thus, a double pronged approach, where low frequency waves are used for reconnaissance and HFW are used for the localization is desirable in the future.