Browsing by Author "Van Zyl, J E"

Now showing 1 - 7 of 7
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    An analysis of leakage parameters of individual leaks on a pressure pipeline through the development and application of a standard procedure
    (2015) Malde, Rahil; Van Zyl, J E
    Water is a vital and scarce resource. Providing a sustainable and efficient means of transporting water is essential to the wellbeing of humankind. Most water distribution systems worldwide are ageing and deteriorating, as a result, leakage is a common problem. Modern water distribution systems use a variety of methods to minimise leakage, one of them is pressure management. However, the relationship between leakage and pressure is a complex one. The goals of this study were to develop a standard experimental procedure to determine the leakage parameters of a pipe with an individual leak, and to test a series of pipes using the newly developed procedure to determine their leakage parameters. There have been numerous experimental investigations into the leakage parameters; however, these investigations have variation in their methodologies. Therefore, developing a standard procedure will provide a consistent method for the accurate determination of the leakage parameters. Leakage parameters are important as they help to improve the understanding of the relationship between leakage and pressure. They are also important for use in the two main equations used to relate leakage and pressure, i.e. the N1 equation and the FAVAD equation. The determination of a variety of leakage parameters will help to determine whether both equations explain the behaviour of a variety of pipe samples, and which equation is better suited for use in leakage prediction.
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    Apparent water loss due to consumer meter inaccuracies in selected areas of South Africa
    (2012) Couvelis, Frank Alan; Van Zyl, J E
    Apparent losses form an important component of the International Water Association's water balance. While apparent losses look like real losses to a municipality, this is not actually the case. The main components of apparent losses are water meter under-registration and unauthorised consumption. Water utilities in South Africa and internationally are becoming increasingly aware of the importance of good meter management practices based on the vast amount of literature published and work done by municipalities in recent years. Water meters are known to increasingly under-register as they age and register consumption. They register consumption the least accurate at low flowrates and their accuracy in this range deteriorates the fastest. This study investigates the extent of the apparent loss problem in selected areas of South Africa due to meter inaccuracy in a number of different ways, including an inspection of new residential consumer meters, interrogation of a metering database, flow logging of domestic consumers with and without an Unmeasured Flow Reducer (UFR) installed and a compilation of reports on bulk consumer meters. It was found that 16 % of 402 properties investigated in the City of Cape Town had an on-site leakage and their median flowrate was 10 litres/ hour. In Bloemfontein, it was found that 28 % of the 167 properties investigated had an on-site leakage with a median flowrate of 20 l/h. An investigation into the performance of 15 mm positive displacement meters based on eThekwini's water meter database showed that the under-registration from these meters increase by 0.36 %-points per year and 0.9 %-points per 1000 kL registered. Flow logging of domestic consumers with and without UFRs, showed that there was no genuine improvement in meter accuracy with meters that had UFRs installed in-line with it. However, there were only 8 properties (3 of which having a UFR installed) in the study that were investigated and no statistical conclusive conclusions could be made. Bulk meter audits in Ekurhuleni and Tshwane showed apparent losses of 18 % and 19 % respectively.
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    Development and testing of experimental equipment to measure pore pressure and dynamic pressure at points outside a pipe leak
    (2015) Bailey, Nicholas David; Van Zyl, J E
    Leaks in water distribution mains are a major issue throughout the world. The amount of water lost through these leaks is unacceptable for a resource, which is becoming ever scarcer. Little is known about the fundamentals, which exist outside leaking water distribution mains. The se fundamentals are the interaction between the leaking water and the soil surrounding the distribution main. This interaction is known as the leak - soil interaction. Research has found that a phenomenon called internal fluidisation typically occurs in the soils outside of leaks in distribution mains. Internal fluidisation is a complex interaction between the leak and the surrounding soil, whereby the soil losses its intermolecular bonding and becomes displaced by the water jet generated by the leak. It is believed that this complex phenomenon causes large energy losses. Subsequently, many water leaks are not able to propagate to the ground surface where they will be visible. This leads to many such leaks being undetected below the ground surface. The objective of this study was to develop an experimental setup, which simulated the internal fluidisation phenomenon. The setup consisted primarily of an orifice, simulating a leak in a distribution pipe; surrounded by ballotini (glass beads), as the soil medium surrounding the pipe; and the measurement instruments, which were Pitot tubes. When using the experimental setup, pore pressures and dynamic pressures around the leak and therefore within the ballotini bed were measured using two Pitot tubes. The accuracy and repeatability of these measurements were also of importance and were investigated. The accuracy of the measurements were dependant on the precision of the Pitot tubes in taking measurements. They were found to have an error of up to 4.1 %, although the experiment to test for the accuracy was not fool proof. The repeatability of the measurements was found to have a 3.8 % average difference between the previous and repeated measurements. The measuring of the pore pressures and dynamic pressures resulted in the following findings, which were the most important in the study: There were large vertical velocities found in the fluidized zone, where outside of this zone they were significantly smaller. The largest pore pressure was found to occur near the top of the fluidised zone. The pore pressures in the bed from a certain distance away from the orifice had a linear distribution, illustrating that Darcy water flow was present. High energy existed in the fluidised zone where it was greatest nearest the orifice and decreased to the top of the fluidised zone. In the ballotini bed outside of the fluidised zone the energy was found to be considerably smaller and decreased further away from the orifice.
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    The effect of viscoelastic deformation in pipe cracks on leakage response to variations in pressure
    (2014) Ssozi, Eva Nantongo; Van Zyl, J E; Reddy, B Daya
    Water is an important and increasingly scarce resource in the world today. Unfortunately, a lot of water is lost through leakage since most distribution systems are deteriorating. Therefore research in leakage management is necessary in order to improve the utilization of water resources. Leakage may be reduced by managing the water pressure in water distribution systems. One of the important factors affecting the pressure-leakage relationship is pipe material behaviour (Van Zyl & Clayton 2007; Greyvenstein & Van Zyl 2007). The pressure – leakage relationship has been described by several relationships such as the Torricelli equation, the Fixed and Variable Area Discharge (FAVAD) concept and the conventional equation. Pipe material behaviour affects leakage parameters in the pressure-leakage relationship such as the leak area and the leak exponent (Cassa et al. 2010). For this project, the pressure-leakage relationships in High Density Polyethylene (HDPE) and Polyvinylchloride (PVC) pipes are investigated. HDPE and PVC are polymeric materials and therefore exhibit a viscoelastic response to applied stress and applied strain. Viscoelastic responses include creep, relaxation, hysteresis and time dependency. When these pipes experience stresses due to water pressures, failure and fracture may occur as leaks. The viscoelastic properties of these materials therefore affect how the leaks respond to pressure change. The effect of viscoelastic deformations in leaks was investigated using Finite Element Analysis (FEA) software, Abaqus. Round holes and longitudinal cracks were represented as individual leaks in HDPE and PVC pipes in Abaqus. Pressure was applied to each pipe model for different time periods, and the deformed leak areas were obtained. Further analysis was carried out to determine the effects of pressure on leak parameters such as the gradient of the leak area-pressure relationship, leak exponent and the leakage number. The analysis shows that viscoelastic deformations have an effect on the pressure-leakage relationship. A linear relationship exists between the leak area and pressure for all time periods investigated and therefore gradients could be obtained. Deformed leak areas, gradients and leak exponents all increased with time and therefore confirmed that the time dependency of viscoelastic materials affected the pressure-leakage relationship. The leakage exponents for both materials were found to vary between 0.5 and 1.5 for both HDPE and PVC. HDPE also exhibited higher leak exponents, gradients and larger deformed leak areas than PVC for the same leaks. It was also found that leakage in viscoelastic materials may be analysed using the leakage number, developed for elastically deforming materials by Van Zyl & Cassa (2013).
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    Optimal risk-based design of bulk water supply systems
    (2010) Vlok, Gustav; Van Zyl, J E
    Bulk water supply systems generally consist of a source of water, a conveyor (feeder pipe, canal etc.) and a storage facility. Designing bulk water supply systems includes the sizing of these components to ensure a functional system...The study follows the same methods that have been used by researchers at the University of Johannesburg in recent years. A Monte Carlo simulation method is used through the use of the Mocasim II software.
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    Priority water research questions for South Africa developed through participatory processes
    (2014) Siebrits, R M; Winter, K; Barnes, J; Dent, M C; Ekama, G; Ginster, M,; Harrison, J; Jackson, B; Jacobs, I; Jordaan, A; Kasan, H C; Kloppers, W; Le Roux, R; Maree, J; Momba, M N B; Munnik, A V; O'Keeffe, J; Schulze, R; Silberbauer, M; Still, D; Van Zyl, J E
    This paper describes a collaborative process of identifying and prioritising current and future water research questions from a wide range of water specialists within South Africa. Over 1 600 questions were collected, reduced in number and prioritised by specialists working in water research and practice. A total of 59 questions were finally proposed as an outcome of the study and are categorised under the themes of change, data, ecosystems, governance, innovation and resources. The questions range in scale, challenge and urgency, and are also aligned with prevailing paradigms in water research. The majority of the questions dealt with relatively short- to medium-term research requirements and most focused on immediate issues such as water supply, service delivery and technical solutions. Formulations of long-term research questions were sparse, partly because some of the principles and methods used in this study were difficult to apply in the South African context, and also because researchers are influenced by addressing what are believed to be the more immediate, short-term water-related challenges in South Africa. This is the first initiative of its kind to produce a comprehensive and inclusive list of research priorities for water in South Africa.
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    The relationship between consumer demand and pressure in a selected pressure managed zone in Cape Town
    (2020) Alves De Sousa, Melissa; Van Zyl, J E
    Water is a basic need and a limited resource across the world. Climate change, pollution, population growth, irrigation and urban development, among others, contribute to the issues faced with respect to availability of quality of water resources and security of water supply for consumption. Pressure management, is the most common and feasible demand management initiative implemented by the City of Cape Town Metro. The main focus of these initiatives is to reduce water losses within the water distribution system. Influence of pressure on water consumption is also observed, but has not been as well investigated as with leakage-pressure relationships. This study aims to assess the impact of change in system pressure on consumer water demand. To do this a pressure managed DMA and Control DMA was identified. The billed consumption data was analysed for 11 months before and 11 months after the pressure management period. A control DMA served to verify that the consumption reduction was as a result of pressure management and not any other intervention. Furthermore, this study involved the collection and analyses of the logged system flow data prior to and post commissioning of pressure management. Pressure is not fixed and varies overtime. The Average Zone Pressure was not available from logged data and was calculated by simulating the hydraulic model to reflect the system conditions prior and post commissioning of the pressure managed DMA. Following that, an investigation into how the leakage responds to pressure was performed. Since the latter affects the demand response to pressure. It was then decided to separate the leakage from consumption. In order to do this, various leakage parameters were calculated and randomly distributed across the system. To analyse the leakage before and after pressure management, two types of models were used, namely 1) Epanet Model (based on the Orifice Equation) and 2) the Epaleaks Model (based on the Modified Orifice Equation). N3 is the coefficient of elasticity. This coefficient represents the relationship between pressure and flow rate. Normal N3 analysis was performed on the available data. N3 was calculated for the system consumption, based on the logged data and a sample of the billed consumption records. The power regression model suggests an N3 of approximately 0.05 to 0.06 for the system based on a sample of filtered billed consumption data. However, in the case of the entire system's end use consumption the N3 value is approximately 0.4. Overall, the N3 values compared reasonably well with other studies in the range of 0.04 to 0.29 and in some cases ≈0.5.