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D.Ing. / This study is a numerical investigation into the behaviour of cracks in uPVC pipes under pressure. This study is a continuation of a Masters dissertation which showed that leakage exponents vary significantly from the theoretical orifice exponent of 0.5 for cracks in pipes for different materials. This study looks at the behaviour of cracks in more detail and specifically with regard to the parameters of the pipe and crack. Using Finite Element Analysis the relationship between the pressure head and the leak area in pipes with longitudinal, spiral and circumferential cracks was investigated. It was found that the longitudinal, spiral and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including loading state, pipe dimensions and pipe material properties. The effect that the individual pipe parameters had on the pressure-area slope was investigated. These parameters included the material properties of the pipe (Young’s modulus, Poisson’s ratio and longitudinal stress), the geometry of the pipe (internal diameter and wall thickness) as well as the geometry of the crack (length of the crack and the width of the crack). Once the effect of the pressure-area slope m is known, the link between the conventional leakage exponent N1 and the pressure-area slope m was further investigated and the effect of each parameter on the leakage exponent N1 was found. Using various data techniques the above data was combined and processed to find mathematical relationships that give reasonable descriptions of the pressure-area slopes of longitudinal, spiral and circumferential cracks. Once these equations for the pressure-area slopes were determined it was possible to obtain three new relationships for leakage from longitudinal, spiral and circumferential cracks.

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A mathematical model was developed for the rapid filling of an initially dry pipe. The pipe was assumed to be horizontal and to contain an orifice at the downstream end. The key elements of the model were the momentum equation governing the flow of the water, the thermodynamic equations for the compression and discharge of the entrapped air, and the equations for waterhammer resulting from the impact of the water with the orifice. A computer program of this model was then developed and tested. After initial testing, the model was used to examine the magnitudes of the pressures that could be produced from waterhammer and air compression for various lengths of pipe. The effects that different orifice diameters had on the flow were also analyzed. The results indicated that extremely high pressures can be generated from both waterhammer and air compression during the filling process. These pressures tend to increase as the orifice diameter is reduced. However, below a certain size the orifice constricts the air discharge enough to stop the water prior to its reaching the orifice. This results in an oscillatory behavior of the flow, and the relation between waterhammer and orifice diameter becomes much more difficult to predict. The results also demonstrated that these pressures are significantly reduced for longer pipe lengths, and for pipes with smaller diameters or otherwise offering greater frictional resistance to the flow. / M.S.

Shang Xiandong. / "September 2002." / Thesis (Ph.D.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (p. 141-146). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web. / Abstracts in English and Chinese.

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaf 42. / by Hung Viet Vu. / M.S.