Author(s): Moez Louati; Mohamed S. Ghidaoui
Keywords: Blockage; Eigenfrequency shift; Unsteady pipe flow
Abstract: Blockages are ubiquitous in water supply systems and their presence often results in wastage of energy and poor system performance and safety. The source of blockages are many and include material deposition, tubercles (rust), scales, plaque, bio-fouling and inadvertently throttled inline valves, and air intrusion. Previous research showed that the presence of blockages induces a shift in the resonant frequencies (eigenfrequencies) of the pipe system. Past research focussed on developing inverse problem techniques that use eigenfrequency shift information to identify blockages. This paper constitutes a first but modest attempt to shed greater light on the forward problem, for only if this forward problem is understood can one hope to address the issues that arise in connection with its inversion. In particular, the aim is to understand the interaction between a blockage and the eigenfrequencies. Such understanding is promising to improve the accuracy and the convergence rate of inverse techniques for TBDDM (Transient-Based Defects detection techniques) and cross-sectional pipe assessment. The theoretical model considered in this work consists of a reservoir-pipe-valve system containing a single interior blockage with small radial protrusion (shallow blockage). The eigenfrequency shift variation is analyzed by studying the variation of the work of radiation pressure at the blockage boundaries.