J. E. van Zyl

A numerical investigation into the effect of pressure on holes and cracks in water supply pipes

The effect of water pressure in a pipe on the rate of leakage from leak openings in the pipe is one of the main factors influencing leakage that is still not understood sufficiently. In this study, the behaviours of different types of leak openings (round holes and longitudinal and circumferential cracks) on pressurized pipes were investigated for different pipe materials (uPVC, steel, cast iron and asbestos cement) using finite element analysis. Linear elastic behaviour was assumed. The study found that (1) pipe stresses are significantly affected by a leak opening, and can easily exceed the materials yield strength in the vicinity of the opening; (2) round holes show the smallest expansion with pressure, followed by circumferential cracks and then longitudinal cracks; (3) the areas of all leak openings increase linearly with pressure; (4) longitudinal pipe stresses affect the behaviours of round holes and circumferential cracks, but not that of longitudinal cracks; and (5) the effect of pressure on a leak opening increases exponentially with increasing hole diameter or crack length. An equation is proposed for modelling the effect of pressure on individual leaks.

Modeling Elastically Deforming Leaks in Water Distribution Pipes

AbstractIn this study, the relationship between the conventional power equation and the fixed and variable area discharges (FAVAD) equation for modeling leakage as a function of pressure was investigated. It is shown that different leakage exponent (or N1) values are obtained for the same leak when measured at different pressures. An analytical exploration of the two equations shows that the leakage exponent tends to 0.5 when the system pressure tends to zero, and to 1.5 when the system pressure tends to infinity. A dimensionless leakage number LN is defined as the ratio between the variable and fixed portions of a leak, and it is shown that a single function can be used to describe the relationship between the leakage number and leakage exponent. This model was combined with previous research to accurately predict the leakage exponents of several published studies in cases where elastic deformation occurred.

Modeling the Pressure-Leakage Response of Water Distribution Systems Based on Individual Leak Behavior

AbstractPressure management has been used for more than 3 decades to reduce leakage from water distribution systems. While few of these studies have been published, information on the ranges of field study leakage exponents is available. In contrast, several studies on the pressure-leakage relationship of individual leaks have been published, and verified models have been developed for predicting the response of elastically deforming leaks. The main aim of this paper was to determine whether researchers’ current understanding of the pressure-leakage response of individual leaks can be reconciled with the observed pressure-leakage response of district metered areas containing many leaks. To investigate this, a model of the distribution of individual leaks and their parameters was developed based on available literature and expert advice. A repeatability study showed that such a model can indeed produce typical distributions of leakage exponents found in field studies. A sensitivity analysis of the various ...

Numerical Investigation of the Influence of Viscoelastic Deformation on the Pressure-Leakage Behavior of Plastic Pipes

AbstractIt has been well established that leakage from pipes is more sensitive to changes in pressure than the square root relationship predicted by the orifice equation. The main reason for this is that leak areas are not static, but vary with changes in system pressure. While previous studies have shown that the leak area is a linear function of pressure for elastic materials, the effect of the viscoelastic behavior of plastic pipes on the pressure-leakage response is not yet well understood. In this study, finite element analysis was used to investigate the effect of viscoelastic behavior on round holes and longitudinal cracks in both high density polyethylene (HDPE) and polyvinylchloride (PVC) pipes. The standard differential equation for linear viscoelastic deformation was then calibrated to the finite element results, resulting in equations that accurately describe the viscoelastic variation in leak areas as functions of time. The results also showed that the time-dependent behaviors of both pipe ma...

Realistic modeling of leakage and intrusion flows through leak openings in pipes

AbstractThe hydraulics of leakage and intrusion flows through leak openings in pipes is complicated by variations in the leak areas owing to changes in pressure. This paper argues that the pressure...

THE OPEN SOURCING OF EPANET

A proposal was made at the 2009 EWRI Congress in Kansas City, MO to establish an Open Source Project (OSP) for the widely used EPANET pipe network analysis program. This would be an ongoing collaborative effort among a group of geographically dispersed advisors and developers, working on a voluntary basis within an auto-governing organizational structure, which would allow members of the water distribution system modeling community to participate in the program’s development and improvement. After reviewing some key aspects of the OSP development process we discuss what issues these present to establishing an open source project for EPANET. These include justifying the need and benefit of such a project, establishing its membership and organizational structure, identifying the scope of development the project should pursue, and maintaining high quality control standards. Suggestions are made on what options are available to address each of these issues.

ADVANTAGES OF A HYDRAULIC SAINT-VENANT TYPE MODEL WITH PRESSURE-DEPENDENT LEAKAGE

Losses from water distribution systems are reaching alarming levels in many towns and cities throughout the world. Leakage represents a large part, frequently more than 30 %, of the water supplied. One of the major factors affecting leakage is pressure in distribution systems. Consequently, it is important to model the hydraulics of water distribution systems with pressure-dependent leakage included. The objective of this paper is to present and validate an improved formulation of the hydraulic network equations that incorporates pressure-dependent leakage. Particular effort has been made to assess the magnitude of the different terms in the equations, including leakage, inertia and head loss. Moreover, a comparison with an extended period simulation model is performed to determine the impact of pressuredependent demands. The formulation was derived from the Navier-Stokes equations. A system of partial differential equations is solved using a finite-difference method. The feasibility of this method and efficiency of the proposed algorithms are illustrated using a number of case studies.

AN EVALUATION OF DOMESTIC AND NON-DOMESTIC WATER CONSUMPTION IN SOUTH AFRICA

South Africa is a water scarce country that constantly strives to apply its available water resources in the most efficient and equitable manner. Different users including industry, domestic, agriculture and the environment, vie for the available resources and have to be awarded an equitable and adequate share to ensure sustainability in the long term. Proper water demand management in South Africa is thus of critical importance. Researchers, municipal engineers and engineering consultants require good and reliable data and design guidelines on water demand patterns and factors influencing water demand to achieve this aim. The most commonly used South African guideline for municipal water demand was first published in 1983, and is currently included in the document titled Guidelines for human settlement planning and design. The guideline provides upper and lower limits for domestic consumer demands as a function of stand area. In this paper, the authors analyze measured water demand data of more than a million stands (domestic and non-domestic) contained in the treasury data for a cross-selection of South African towns and cities. The main objectives of the study were to evaluate the existing South African domestic demand guidelines and to evaluate the parameters that influence domestic and non-domestic water demand. The main results of the study indicate that the domestic demands of most of the users fall well within the upper and lower limit envelope curves of the South African design guideline although for larger stands the design guideline was found to be conservative. Stepwise multiple variable regressions were applied to domestic and non-domestic consumption data to determine the most significant variables influencing water demand. In a large majority of cases, either the stand area or stand value had the greatest significance. There is strong evidence that both domestic and non-domestic demand increase with increasing, stand area and stand value. In, the case of domestic demand, stand value was used as an indicator for household income level. The study found that inland domestic water demand is significantly and consistently higher than coastal demand. This trend was not observed for non-domestic demand. However, the development level (city vs. small town) was found to have a marked impact on non-domestic demand. The study also found that the frequency distributions of annual average daily demand (AADD) for specific non-domestic user categories seem to have a lognormal distribution. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).

Incorporating the modified orifice equation into pipe network solvers for more realistic leakage modeling

AbstractIt has been well established in several experimental and modeling studies that leak areas are often not fixed, but vary as linear functions of pressure. Replacing this linear equation into ...

Statistical characterisation and estimation of non-domestic water demand

Abstract Estimation of annual average water demand figures is critical for the design and evaluation of water distribution systems. This study evaluated the metered water consumption of more than 67,000 non-domestic consumers in six categories from cities and towns in South Africa. It was found that lognormal distributions provide good descriptions of the annual average daily demand (AADD) distribution in each category. The land use categories Business Commercial, Industrial, Agricultural holdings and Sports & Parks displayed similar median AADDs of between 1.5 and 1.7 kl/property/day. Educational properties used substantially more water (4.7 kl/property/day), while Government & Institutional properties used substantially less water (0.7 kl/property/day). A step-wise regression analyses showed that property size has the greatest impact on water demand for most categories. Finally, a novel statistically based method is proposed for estimating the average AADD of a given number of properties based on an acceptable risk of non-exceedance.