Pipeline distribution systems account for the vast majority of the physical infrastructure in the water industry. Their effective management represents the primary challenge to the industry, from both an operational and public health standpoint. Biofouling has a ubiquitous presence within these systems, and it can significantly impede their efficiency, through an increase in boundary shear caused by characteristic changes in surface roughness dynamics. Nonetheless, conventional pipeline design practices fail to take into account such effects, partially because research findings that could contribute to upgraded and optimised design practices appear inconsistent in the literature. The overall aim of this study was to improve the current scientific understanding of biofouling within water and wastewater pipelines; for the purpose of instigating a step-change in pipeline design theory by incorporating biofouling, thereby enabling future pipelines to be as sustainable as possible. The nature of the problem, necessitated the need for a multidisciplinary approach, based upon engineering and microbiological principles and techniques. The primary focus of this study was to investigate the impact of biofouling on surface roughness, mean flow structure and sediment transport within wastewater systems. To this effect biofilms were incubated with a synthetic wastewater on a High Density Polyethylene pipe, within a purpose built pipeline facility for 20 days, at three steady-state flow regimes, including the average freestream velocities of 0.60, 0.75 and 1.00 m/s. The physico-chemical properties of the synthetic wastewater were purposely designed to be equivalent to the properties associated with actual wastewater found within typical European sewers. The impact of biofouling on flow hydrodynamics was comprehensively identified using a series of static pressure tappings and a traversable Pitot probe. Molecular and image analysis was also undertaken to support the observations derived from the aforementioned measurements, particularly with regards to the structural composition and mechanical stability of the biofouled surfaces. The study has confirmed that the presence of a low-form gelatinous biofilm can cause a significant increase in frictional resistance and equivalent roughness, with increases in friction factor of up to 85% measured over the non-fouled values. The reported increases in frictional resistance resulted in a reduction in flow rate of up to 22% and increased the pipe’s self-cleansing requirements. The structural distribution of a biofilm was shown to play a key role in its overall frictional capacity and strength, which in turn was found to be a function of the biofilms conditioning shear. In particular, it was found that a biofilm conditioned at higher shear will have less of an impact on a pipe’s overall frictional resistance, although, will be stronger and more difficult to remove than a biofilm conditioned at lower shear. The biofilm’s impact on frictional resistance was found to be further compounded by the fact that traditional frictional relationships and their derivatives are not applicable to biofouled surfaces in their current manifestation. In particular, the von Kármán constant, which is an integral aspect of the Colebrook-White equation is non-universal and dependent on Reynolds Number for biofouled surfaces. It was found that the most suitable manner to deal with the dynamic and case-specific nature of a biofouled surface was to quantify it using a series of dynamic roughness expressions, the formulation of which were the culmination of this study, and should be the focus for further research. The influence of different plastic based pipe materials and flow regimes on biofilm development within drinking water distribution systems was also briefly investigated using a series of flow cell bioreactors and molecular analysis techniques. Keywords: Biofilm; biofouling; pipe; hydraulic efficiency; equivalent roughness; von Kármán constant; Colebrook-White equation; drainage network; wastewater; drinking water.

A new approach to solve shallow water flow problems over highly irregular geometry both correctly' and efficiently is presented in this thesis. Godunov-type schemes which are widely used with the finite volume technique cannot solve the shallow water equations correctly unless the source terms related to the bed slope and channel width variation are discretized properly, because Godunov-type schemes were developed on the basis of homogeneous governing equations which is not compatible with an inhomogeneous system. The main concept of the new approach is to avoid a fractional step method and transform the shallow water equations into homogeneous form equations. New definitions for the source terms which can be incorporated into the homogeneous form equations are also proposed in this thesis. The modification to the homogeneous form equations combines the source terms with the flux term and solves them by the same solution structure of the numerical scheme. As a result the source terms are automatically discretized to achieve perfect balance with the flux terms without any special treatment and the method does not introduce numerical errors. Another point considered to achieve well-balanced numerical schemes is that the channel geometry should be reconstructed in order to be compatible with the numerical flux term which is computed with piecewise constant initial data. In this thesis, the channel geometry has been changed to have constant state inside each cell and, consequently, each cell interface is considered as a discontinuity. The definition of the new flux related to the source terms has been obtained on the basis of the modified channel geometry. A simple and accurate algorithm to solve the moving boundary problem in two-dimensional modelling case has also been presented in this thesis. To solve the moving boundary condition, the locations of all the cell interfaces between the wet and dry cells have been detected first and the integrated numerical fluxes through the interfaces have been controlled according to the water surface level of the wet cells. The proposed techniques were applied to several well-known conservative schemes including Riemann solver based and verified against benchmark tests and natural river flow problems in the one and two dimensions. The numerical results shows good agreement with the analytical solutions, if available, and recorded data from other literature. The proposed approach features several advantages: 1) it can solve steady problems as well as highly unsteady ones over irregular channel geometry, 2) the numerical discretization of the source terms is always performed as the same way that the flux term is treated, 3) as a result, it shows strong applicability to various conservative numerical schemes, 4) it can solve the moving (wetting/drying) boundary problem correctly. The author believes that this new method can be a good option to simulate natural river flows over highly irregular geometries.

No description available.

Hydraulic fracturing has become increasingly popular in the United States during the last ten years. It is a process that is used for the majority of new oil and gas wells, and is used to access the abundance of natural gas in the US. The largest shale bed is the Marcellus Shale which spans the area underneath many states in the Northeast, primarily New York and Pennsylvania. Policy and science have failed to keep up with the boom in fracking that has occurred across the US, which has led the process to be regulated at varying levels of stringency and a lack of understanding of the potential risks associated with fracking. New York decided that the potential adverse effects of fracking outweighed the economic benefits of job creation and increased tax revenue. New York was the 2nd state in the US that banned fracking, and the decision can be attributed to the unique environmental and political factors present. There were six major environmental reasons that New York decided to ban fracking: decreased respiratory health, drinking water contamination, soil contamination, seismic activity, climate change, and boomtown economic effects. Drinking water contamination is especially important in New York because New York’s reservoirs provide water for over 17 million people. These six environmental factors are not unique to New York, but their impact would be more widely felt than in many other states where fracking occurs. The political factors in New York are also critical to understand. New York is a blue state that is being governed by Governor Cuomo who after his re-election desperately needed to re-align with the left wing of New York’s democratic party. The analysis completed in this paper demonstrates that New York is unique in many ways and the decision to ban hydraulic fracturing there may not be easily replicable in other states.

Hydraulic fracturing is a physically complex phenomenon, and there are many variables, both environmental and operational, that affect the overall success of a fracture treatment. Amongst the operational variables, the process of proppant selection is key to ensuring that the induced fractures remain open and permeable. A variety of physical mechanisms act to degrade the permeability of a given proppant packing after deposition in a fracture, the most important of which is the magnitude of the confining stress. The goal of this work is to understand how mixtures of unlike proppants behave under various stress conditions. Specifically, the permeability and conductivity of various mixtures of unlike proppants are measured as a function of confining stress. A secondary investigation is also made into the dependence of permeability on the areal concentration of proppant. Choices of proppants are restricted to those which are currently most common in industry, in terms of both material and size. To that end, mixtures consisted of primarily ceramics and sands with appropriate grain size distributions. Additionally, a light-weight plastic proppant was included in the study. Simple laboratory methods are employed to measure the permeability of the various proppant packings. Values obtained from direct experimentation are compared with values obtained from an independent analytical model. Given the assumptions which are inherent in the analytical model, the experimental and analytical results are in satisfactory agreement. Also, a correlation is developed for single proppants and binary mixtures which predicts permeability as a function of stress, grain size, material, and weight fraction. One key conclusion is that for a binary mixture of proppants, the mixture permeability will not generally be a weighted linear combination of the pure proppant permeabilities. In other words, the permeability of a mixture comprised of 50% (by weight) of one component and 50% of the second component will generally not be halfway between the permeabilities of the single components. A hypothesis is presented which posits that there are threshold weight fractions for each proppant pair that control the permeability of the mixture. / text

Currently microseismic monitoring is widely used for fracture diagnosis. Since the method monitors the propagation of shear failure events, it is an indirect measure of the propped fracture geometry. Our primary interest is in estimating the orientation and length of the ‘propped’ fractures (not the created fractures), as that is the primary driver for well productivity. This thesis presents a new Low Frequency Electromagnetic Induction (LFEI) method that has the potential to estimate the propped length, height, orientation of hydraulic fractures, and vertical distribution of proppant within the fracture. The proposed technique involves pumping electrically conductive proppant (which is currently available) into the fracture and then using a specially built logging tool to measure the electromagnetic response of the formation. Results are presented for a proposed logging tool that consists of three sets of tri-directional transmitters and receivers at 6, 30 and 60 feet spacing respectively. The solution of Maxwell’s equations shows that it is possible to use the tool to determine both the orientation and the length of the fracture by detecting the location of these particles in the formation after hydraulic fracturing. Results for extensive sensitivity analysis are presented in this thesis to show the effect of different propped lengths, height and orientation of planar fractures in a shale environment. Multiple numerical simulations, using a state-of-the-art electromagnetic simulator (FEKO) indicate, as this work show, that we can detect and map fractures up to 250 feet in length, 0.2 inches wide, and with a 0 to 45 degree of inclination with respect to the wellbore. Special cases such as proppant banking, non-symmetrical bi-wing fractures, and wells with steel casing in place were studied. / text

No description available.

No description available.

This thesis takes top tensioned vertical riser interaction as its main study object. It has its focus on the understanding of the mechanism about potential instability of the risers caused by the interaction and the prediction of potential collision. Started from two-dimensional cylinder interaction cases, and later extended into the three-dimensional riser scenarios, the problem is investigated comprehensively. The study covers fluid force prediction, stability analysis, continuation investigation and dynamics simulation. The study disclosed the mechanism of the potential collision when the flow velocity reaches a certain critical value, and provides a robust tool to predict the threshold for the riser collision. Additionally, the investigation shows the difference between marine riser interaction and the similar interaction occurs in other engineering disciplines, such as power transmission lines, heat exchangers etc. Also provided in this thesis are valuable information regarding the riser dynamics should collision occur. The research will be beneficial to the marine riser designers and operators.

The design aspects of offshore jacket structures are presented and discussed with a special emphasis on the different factors which affect wave loading calculations for these structures. An up-to-date review of a large amount of data on the hydrodynamic coefficients obtained from Laboratory experiments and wave projects is presented and the main data are tabulated. To assess the different aspects of the wave loading a set of computer programs were developed and used to perform various comparative studies for the existing methods of wave loading estimation. The analysis of the wave loading was carried out using a jacket structure of 119 members having 73m x 73m base representing a typical offshore platform, assumed to be working in 150m of water. The general method of wave loading calculation is based on Morison's equation taking into account the phase differences between the velocities and accelerations of the wave particles. The relative positions of the different members in space and time when the wave passes through the jacket were also considereG. Besides the drag and inertia forces, the lift (transverse) forces are also taken into account. The kinematics of the flow can be determined using Airy (linear) wave theory, Stokes 2nd order theory or Stokes 5th order theory. Constant drag and inertia coefficients (CD, CM), as recommended by Lloyd's Register of Shipping (LR), Det Norkse Veritas (DnV) and Bureau Veritas (I3V),can be used. Alternatively, variable hydrodynamic coefficients (CD, CM, CL) from Sarpkaya's experimental data for smooth and rough cylinders can be used. The drag interference effect and the current effect can be included in the calculations. Various interpretations as to how to apply Morison's equation in the design were examined which have shown the importance of taking full account of both the relative positions in space and time of the different members of the structure as well as the phase relationships in the wave. A comparison was made between the results of calculations using the recommended coefficients (CD, CM) of LR, DnV and BV which has shown that even small variations in these coefficients leads to appreciable differences in the loading estimation of up to 45%. The approach using variable coefficients (Sarpkaya's data), which are related to the local Reynolds number (Re) and Keulegan-Carpenter number (K) at the different points of the structure, was compared with the method of adopting constant coefficients (as recommended by LR) showed differences up to 26% in the wave loading estimation between the two methods. The effects of surface roughness, as well as the transverse (lift) forces, on the wave loading were also investigated and found to be very significant (eg 43% to 56% in the surge force) and should be considered in design. Three wave theories (Airy, Stokes 2nd order, Stokes 5th order) were compared in terms of wave profile, horizontal and vertical velocities and accelerations. The results have shown that the differences in predicting the wave kinematics by Airy and Stokes theories are large. The wave forces on the individual members as well as the total forces and moments on the complete structure calculated by the fifth order theory, showed 30-60% differences when compared with the results based on Airy theory. The experimental data on the interference effect between the cylindrical members were reviewed. The effect on the jacket loading was examined using some experimental data and found to be 6-9% reduction in the loading for rough cylinders. However, more experimental investigations are required in this area to deal with this problem properly. The effect of current speed and direction on the wave loading was examined by the commonly used practice of adding the velocity of current vectorially to the wave particle velocity when calculating the drag and lift forces. The results showed that the total forces and moments could be increased by 16-37% for a/1 mls current in the direction of the wave. Several static analyses of the jacket were performed using constant and variable hydrodynamic coefficients and two wave theories (Airy and Stokes 5th order theory). The initial differences in the wave loading due to the different coefficients and wave theories appeared again as appreciable differences in the maximum stress on the different members. This supported the necessity of calculating the wave loading accurately from the beginning. A general review of the reliability analysis method as applied to jacket structures indicated that the modelling of the wave loading needs further improvements to take account of the large uncertainties in the loading especially due to the hydrodynamic coefficients and non-linear loads.