Bruno Brunone

Pipe system diagnosis and leak detection by unsteady-state tests. 1. Harmonic analysis

As shown in Part 1, the analysis of a pressure signal in the frequency domain can give items of information for leak detection even though, moving from time to frequency domain, interesting information about the arrival time of pressure waves are lost. To overcome this limitation and to widen the applicability of transient-test based methodologies for leak detection, the wavelet transform of laboratory experimental data is used. Such data consist of pressure time histories acquired at one measurement section during transients in a single pipe system. The wavelet transform is used to detect local singularities in the pressure time history due to the presence of a leak. The discontinuity occurrence in time reveals the arrival time of the leak reflected pressure wave and is the basis for leak location.

Detecting leaks in pressurised pipes by means of transients

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...

Numerical analysis of one-dimensional unsaturated flow in layered soils

Abstract The paper deals with numerical solutions to the Richards equation to simulate one-dimensional flow processes in the unsaturated zone of layered soil profiles. The equation is expressed in the pressure-based form and a finite-difference algorithm is developed for accurately estimating the values of the hydraulic conductivity between two neighboring nodes positioned in different soil layers, often referred to as the interlayer hydraulic conductivity. The algorithm is based upon flux conservation and continuity of pressure potential at the interface between two consecutive layers, and does not add significantly to simulation run time. The validity of the model is established for a number of test problems by comparing numerical results with the analytical solutions developed by Srivastava and Yeh29 which hold for vertical infiltration towards the water table in a two-layer soil profile. The results show a significant reduction in relative mass balance errors when using the proposed model. Some specific insights into its numerical performance are also gained by comparisons with a numerical model in which the more common geometric averaging operator acts on the interlayer conductivities.

In-Line Pipe Device Checking by Short-Period Analysis of Transient Tests

In this paper, the results of laboratory transient tests concerning the interaction between a pressure wave and an in-line device are discussed. Transients are generated by means of a fast and complete closing of an end valve, and pressure measurements are carried out just upstream of the maneuver valve. The main effect of the device on the pressure time-history—hereafter referred to as pressure signal—is a sharp increase caused by the pressure wave reflection. Three experimental setups are considered, in which different in-line devices are installed (i.e., a ball valve, a butterfly valve, and different-sized orifices). The pressure signal is analyzed in the time domain, and a reliable evaluation of the device location is obtained by means of wavelet functions. Furthermore, on the basis of the value of the pressure increase, the status of the device can be determined; experimental results are synthesized in a dimensionless diagram. Finally, criteria for using the obtained results in other pipe systems are...

Experimental Evidence of Hysteresis in the Head-Discharge Relationship for a Leak in a Polyethylene Pipe

The relationship between leak outflow from a damaged pipe and flow condition inside the pipe plays a crucial role in pressurized pipe systems management. As an example, this relationship is used in leakage reduction techniques based on pressure control and in leak detection techniques based on inverse analysis. To explore the relationship between total head inside the pipe and leak outflow for a single leak in a polyethylene pipe, tests were carried out at the Water Engineering Laboratory of the University of Perugia. These tests point out that the viscoelastic nature of the pipe material gives rise to a hysteretic behavior of the investigated relationship, i.e., the outflow depends not only on the synchronous total head but also on the total head time history and variation rate.

Wall Shear Stress in Transient Turbulent Pipe Flow by Local Velocity Measurement

The modeling of unsteady wall shear stress plays a crucial role in the analysis of fast transients in pressurized pipe systems, since it allows to evaluate transient energy dissipation properly. The main aim of this paper is to give a contribution to the understanding of transient pressurized flow dynamics in turbulent regime by measuring not only pressure but also the instantaneous axial velocity profile at two sections of the laboratory pipe. Specifically, by means of ultrasonic Doppler velocimetry—a completely nonintrusive technique—instantaneous velocity gradients at pipe wall are measured allowing to evaluate the time history of the actual wall shear stress by coupling velocity measurements to a two-zone stress model. As a result, the behavior of accelerating and decelerating flows with respect to the corresponding steady ones, i.e., with the same value of the discharge, is pointed out. Due to the characteristics of the laboratory pipe—a 352-m long high density polyethylene pipe—transients phenomena ...

Decay of Pressure and Energy Dissipation in Laminar Transient Flow

In the present paper, some peculiar characteristics of transient laminar flow are dis-cussed. After presenting a review of the existing literature, attention is focused on tran-sient energy dissipation phenomena. Specifically, results of both laboratory and numericalexperiments are reported, the latter by considering one-dimensional (1D) along withtwo-dimensional (2D) models. The need of modifying a criterion for simulating unsteadyfriction proposed some years ago by one of the writers, and extensively used for water-hammer calculations, is pointed out. Differences between accelerating and deceleratingflows as well as between transients in metallic and plastic pipes are also highlighted.@DOI: 10.1115/1.1839926#Keywords: Transient, Laminar, Energy, Dissipation, Viscoelasticity

Experimental Investigation of Coupled Frequency and Time-Domain Transient Test–Based Techniques for Partial Blockage Detection in Pipelines

AbstractPartial blockages commonly exist in pressurized pipeline systems, and the rapid remediation of such faults is required to reduce the wastage of energy as well as to maintain the serviceability of the pipe network. Numerous transient test–based techniques (TTBT) have been developed for detecting pipe defects, with each technique providing different advantages. Two previously developed techniques—pressure signal analysis (PSA) and frequency response analysis (FRA)—are experimentally tested in this study on systems of different pipe material and characteristics. Each method is validated using the experimental data, and the results show that PSA is most accurate for locating the blockage while FRA is most accurate for determining the radial constriction and length of the blockage section. To take advantage of the different strengths of the techniques, a coupling of the two methods is proposed. Experimental application results reveal that both detection accuracy and calculation efficiency are improved ...

Potential of Transient Tests to Diagnose Real Supply Pipe Systems: What Can Be Done with a Single Extemporary Test

In this paper, the reliability of a transient test-based technique as a powerful tool in the management of real supply pipe systems is shown. The pressure signal acquired during the first phase of the single completed test has been analyzed on the basis of extensive research activity performed in the previous years in the field of transient test-based techniques and refined on the basis of numerical and laboratory tests. Specifically, the wavelet transform, which allows the automatic detection of singularities in noisy pressure signals, and a Lagrangian model, which evaluates the causes of discontinuities, are efficiently coupled for analyzing the pressure signal acquired in the described pipe system. As a result, the topology of such a system has been checked, and its functioning conditions have been determined. Moreover, the unwanted status of an in-line valve—certified by the manager as fully open but actually partially closed—has been pointed out.

Is the leak head–discharge relationship in polyethylene pipes a bijective function?

Traditional characterization of the leak head–discharge relationship in pipeline systems relies on the use of power law functions to explain the increase in leakage rate with pressure when network and laboratory data are analysed. However, recent studies addressed that the leak behaviour is complex and influenced by pipe material and leak geometry. The experimental tests, carried out at Water Engineering Laboratory of the University of Perugia (WEL), Italy, show that the leak head–discharge relationship on polyethylene pipes is not a bijective function since it gives rise to different discharge values with respect to one value of the pressure. To explore this issue, two viscoelastic models of a leak in a polyethylene pipe are introduced and compared with other leakage models. The results show that the viscoelastic behaviour reflects the leak head–discharge relationship, and care should be taken in the use of bijective relationships.