Transient conditions in closed conduits have traditionally been modeled as 1D flows with the implicit assumption that velocity profile and friction losses can be accurately predicted using equivalent 1D velocities. Although more complex fluid models have been suggested, there has been little direct experimental basis for selecting one model over another. This paper briefly reviews the significance of the 1D assumption and the historical approaches proposed for improving the numerical modeling of transient events. To address the critical need for better data, an experimental apparatus is described, and preliminary measurements of velocity profiles during two transient events caused by valve operation are presented. The velocity profiles recorded during these transient events clearly show regions of flow recirculation, flow reversal, and an increased intensity of fluid turbulence. The experimental pressures are compared to a water hammer model using a conventional quasi-steady representation of head loss an...

Reliable and quick techniques are needed to locate and estimate leaks in pressurised pipe systems in order to reduce water loss as much as possible. The aim of the present paper is to show that the use of unsteady-state tests, which give rise to small overpressure, can be considered as an appropriate method. During these tests, it is necessary to record the pressure-time history - the ‘pressure signal’ - in just one section of the pipe, the ‘measurement section’. On the basis of a thorough laboratory investigation, the influence on the pressure signal of size and shape of small leaks, along with discharge conditions and initial flow regime, is analysed. Some remarks about the possible applicability of the obtained results to pipes of different material can be found. A reliable criterion is provided for a first-approximation estimation of leak size, based on the results of an inverse method procedure concerning pressure signals.

In this paper, the reliability of transients due to pump trip as a powerful tool for the pre-localization of anomalies in real pipe systems is tested. The examined pipe system is part of the one supplying the city of Milan, Italy and is managed by Metropolitana Milanese SpA (MM). The characteristics of such a system can be considered as intermediate between those of classical transmission mains and distribution systems because of its several branches. A Lagrangian model simulating pressure wave propagation is used to evaluate the pipe pressure wave speed – associated with a genetic algorithm – and to locate possible anomalies – associated with wavelet analysis. The results of the diagnosis of the pipe system are corroborated by repairs executed by MM in the area where possible anomalies have been pre-localized.

Transient tests can be reliably used for the diagnosis of pressurized pipe systems. As a matter of fact, the pressure signals acquired during these tests can reveal the presence of anomalies, e.g., leaks, since any irregularity in the pipe gives rise to reflected waves which in turn create discontinuities in the observed signal at the measurement section. In order to make the most of the interpretation of the pressure signals, as well as to improve the effectiveness of the location of leaks, wavelet analysis—a powerful tool within the realm of harmonic analysis—can be used. It aids in the diagnosis of pressure pipe systems by better exposing pressure signal discontinuities and precisely determining the arrival time of the pressure waves reflected by leaks, thus locating the leak itself. Since many wavelet transforms are available and the choice is driven by the specific application, both continuous and discrete wavelet transforms are considered in the paper, comparing different mother wavelets. Then the r...