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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
431

An empirical study of flood wave impact pressures to determine the effectiveness of new seawall designs using a dam-break approach

Adegoke, P. B. January 2014 (has links)
Coastal flooding and erosion, a major consequence of coastal natural events can result in physical devastation, threats to human health and safety, detrimental effects on ecosystems, and severe economic losses to individuals and to society. These potentially devastating consequences are therefore justifying efforts to reduce both their occurrence and severity. Seawalls of varying slopes with wave energy dissipaters to create various degrees of roughness on their surfaces have been proposed as a potential evolution in the design of coastal defences. This present study therefore aimed at investigating the energy dissipating ability, in terms of impact pressures, of newly designed seawalls which incorporate unique energy dissipaters, with the ultimate goal of predicting the effectiveness of these new designs. To achieve these aims, a novel technique for generating floodwater waves has been developed and applied to new seawall models. A Low Cost Wave Tank (LCWT) with water release gate mechanism (dam-break method) was primarily designed and constructed for this purpose. Apart from the smooth surface wall model, geo-grid materials of varying textures and grit sizes have been used to model different degrees of surface roughness with each model subjected to varying wave heights and wall angles. The experimental tool and technique had been found to be effective and relatively economical while the gate release system represented a good approximation of instantaneous dam-break problem. The innovative imaging system (IS) and the sensor signal capture (SSC) techniques used for estimating flow velocity were found to be in close agreement with the commonly used PIV method, thus, could be a useful laboratory scheme for analysing hydrodynamics model studies. The study has also found the location of maximum impact pressures for the vertically inclined smooth surface wall model, to be varied from that of sloping forms which is in agreement with the propositions of most previous researchers. The maximum impact pressures have been found to be about 1.4 to 40 times the hydrostatic pressure which is within the range previously suggested by other researchers. Also, angle 75o appeared to be the best sloping position for the wall models investigated and in general, IMACTS wall seemed the most superior surface in terms of energy dissipation in vertical form. This implies that the harder the surface of the defence wall or/and the higher the degree of surface roughness the greater the energy of the floodwater waves that would be dissipated. Again, the predictive model equations proposed in this study are useful for the purposes of assessment of the suitability of the seawalls and the mitigation against flood hazards.
432

Proposta de uma metodologia para projeto construção e adequação de tubo de sucção numa turbina Michel-Baki

Perez, Edgar Paz [UNESP] January 2003 (has links) (PDF)
Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2003Bitstream added on 2014-06-13T18:59:52Z : No. of bitstreams: 1 perez_ep_me_guara.pdf: 1116117 bytes, checksum: 2ae25303ba483b9f7ccbf3d2f842125f (MD5) / A turbina Michell-Banki é basicamente uma máquina de ação, sendo que a característica mais importante das turbinas de ação é a não existência do tubo de sucção. A instalação do tubo de sucção numa turbina causa o aumento da queda disponível e como conseqüência, aumenta a potência gerada e a rotação da turbina. No presente trabalho propõe-se a instalação de um tubo de sucção numa turbina Michell-Banki, visando alcançar as melhorias já indicadas acima, lembrando que ao colocar o tubo de sucção aparece um grau de reação na máquina. Foi feito uma análise mecânica-hidráulica da turbina Michell-Banki proposta, com o objetivo de encontrar as equações que permitem calcular os diversos elementos da turbina. Desta maneira o trabalho apresenta uma metodologia para projeto de uma turbina Michell-Banki com tubo de sucção. Também são apresentadas as formas de traçar o rotor, o injetor e a pá diretriz. Finalmente o trabalho apresenta ainda as recomendações para a execução de projeto e construção da turbina. / The turbine Michell-Banki is basically an action machine, and the important characteristic of the action turbines is the no existence of the suction tube. The installation of the suction tube in a turbine increases the available fall and as consequence, it increases the generated power. The rotation of the turbine is also increased by increasing the available fall. In the present work it's proposed the installation of a suction tube in a Michell-Banki turbine, aiming to reach the improvements already indicated above, remembering that when placing the suction tube a reaction degree appears in the machine. It was done an mechanical and hydraulics analysis of the Michell-Banki turbine with the objective of finding the equations that allow to calculate the several elements of the turbine proposed, and thus presenting a methodology for project of a turbine. Finally I described the way of drawing the rotor, the injector and the guideline shovel, as well as it is also recommended the process that should be followed to build the turbine.
433

An investigation into the effect of lateral hillslope inputs on floodplain hydraulic model predictions

Charlton, Rosemary Anne January 1995 (has links)
In recent years there has been a growing interest in the contemporary floodplain environment which has come from a number of fields including civil engineering, hydrology, geomorphology and ecology. A major advance in civil engineering has been the development of two-dimensional hydraulic models capable of a high degree of spatial representation. These models were originally developed for engineering applications although recent developments, such as their application to longer reach lengths, mean that these models are very powerful predictive tools with potential for application in many different fields. Two-dimensional floodplain hydraulic models can be viewed as a platform for further development through the incorporation of additional components to represent specific processes. For the case of the application of these models in hydrology, whilst the models provide a good representation of floodplain processes in a hydraulic context, catchment hydrology is essentially treated as a black box. The only input to the system is the upstream input hydrograph (occasionally rainfall over the floodplain surface and tributary inflows are included) and output only occurs at the downstream boundary. The floodplain is assumed to be impermeable and any input from the hillslopes bordering the reach is ignored. This investigation examines the significance of contributions to the floodplain from the hillslopes bordering the reach. In order to do this, the zero flux boundary condition at the hillslope-floodplain interface is relaxed. A two-dimensional floodplain inundation model, RMA-2, is set up for a 14 km reach of the River Culm in Devon. A distributed hillslope hydrology model, VSAS3 is set up for a section of the hillslopes bordering the reach. This model is coupled to RMA-2 using a simple external coupling mechanism whereby water produced by VSAS3 is applied to elements along the edge of the RMA- 2 finite element mesh. A sensitivity analysis is carried out using this coupled scheme to identify some of the range of hillslope environments which may contribute a significant volume of lateral inflow to the floodplain. Five key hillslope parameters are selected and altered over a range of values. It has been shown that hillslope inflows can have a significant effect on the predictions made by RMA-2, both in terms of changes to the predicted output hydrograph and localised changes in depth and inundation extent. It has also been shown that the timing of the hillslope inflow peak relative to the arrival of the floodwave from upstream is of great importance. The addition of inflows has also been found to affect the calibration of the floodplain inundation model.
434

Uma contribuição à melhoria do processo de fresamento em 5 eixos de pás de turbinas hidráulicas / A contribution to the improvement of the milling process in 5 axis for blades of hydraulic turbines

Lacerda, Rafael Segantin, 1979- 25 August 2018 (has links)
Orientador: Anselmo Eduardo Diniz / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-25T10:42:27Z (GMT). No. of bitstreams: 1 Lacerda_RafaelSegantin_M.pdf: 5082934 bytes, checksum: 9288c8f97c6d45416ba8bc96895fc01d (MD5) Previous issue date: 2014 / Resumo: A fabricação de pás de turbinas hidráulicas representa uma das atividades mais importantes no processo de fabricação do rotor de uma usina hidrelétrica e corresponde a uma parcela considerável do custo de produção do mesmo. Devido às características geométricas e requisitos hidráulicos destes componentes, as operações de fresamento em cinco eixos são altamente solicitadas e se destacam pela versatilidade e rapidez que proporcionam para o processo produtivo. Todavia, o fresamento de pás de turbinas hidráulicas apresenta alguns pontos críticos relacionados com a qualidade superficial, qualidade dimensional e os custos da operação de usinagem. A taxa de remoção de material, a variação das condições de fresamento diretamente relacionada com os parâmetros de corte e a necessidade de se reduzir os ciclos de produção são itens que fazem o estudo detalhado desta operação ter importância fundamental para a utilização das modernas tecnologias de usinagem. O objetivo deste trabalho é identificar as condições de corte mais adequadas para o processo de fresamento em cinco eixos de pás de turbinas hidráulicas. Para isto, o processo de fabricação foi monitorado e ensaios foram realizados para comparação entre diferentes estratégias de fresamento e parâmetros de corte. Durante estes ensaios observaram-se os parâmetros elétricos do motor da máquina e também a coloração dos cavacos, para estabelecer uma relação entre estes parâmetros e o real desgaste sofrido pela ferramenta, a fim de se ter um método direto e prático para definição de seu fim de vida. As principais conclusões deste trabalho são que a variável de entrada mais influente na vida da ferramenta dentre as testadas foi a estratégia de corte (concordante ou concordante / discordante) e para estas ferramentas, o desgaste de flanco (VB) foi o principal determinante para o fim de vida da aresta de corte. Em adicional, a observação da potência consumida e da coloração do cavaco realizada pelo operador, mostrou-se adequada para determinar o momento de troca da ferramenta neste tipo de fresamento em desbaste. Palavras chave: fresamento em cinco eixos, pás, turbinas hidráulicas e desgaste de flanco / Abstract: The manufacturing process of blades for hydraulic turbines is one of the most important activities to fabricate a runner for a hydraulic power plant and is responsible for a considerable portion of the production cost thereof. Due to the geometric characteristics and hydraulic requirements in these components, the milling operations in five axis is highly appreciated and offer the versatility and speed for the production process. However, the milling process for blades of hydraulic turbines present some critical issues related to the surface quality, dimensional quality and machining costs. The rate of material removal, the variation of milling conditions directly related with cutting parameters and the need to reduce production cycles are items that make a detailed study of this operation has high importance on the application of the most modern machining technologies. The objective of this work is to identify the most suitable cutting conditions for five axis milling in blades of hydraulic turbines. For this, the manufacturing process was monitored and tests were performed in order to compare different milling strategies and cutting parameters. During these tests was observed the electrical parameters of the machine motor and also the colors of the chips to establish a relationship between these parameters and the actual wear suffered by the tool in order to have a derictly and practical method to define the end of the tool life. The main conclusions are that the most influential variable in the tool life among those tested was the cutting strategy (Up Milling or Up Milling / Down Milling) and for these tools, the main determinant for the end of life is the flank wear (VB) of the cutting edge. In additional, the observation of the power consumption and the colors of the chips performed by the operator, with the goal of determining the exactly time to exchange the tool was adequate for this type of rough milling. Keywords: five axis milling, blades, hydraulic turbines and flank wear / Mestrado / Materiais e Processos de Fabricação / Mestre em Engenharia Mecânica
435

A Framework for the Analysis of Coastal Infrastructure Vulnerability under Global Sea Level Rise

O'Brien, Patrick S. 24 February 2018 (has links)
<p> The assumption of hydrologic stationarity has formed the basis of coastal design to date. At the beginning of the 21<sup>st</sup> century, the impact of climate variability and future climate change on coastal water levels has become apparent through long term tide gauge records, and anecdotal evidence of increased nuisance tidal flooding in coastal areas. Recorded impacts of global sea rise on coastal water levels have been documented over the past 100 to 150 years, and future water levels will continue to change at increasing, unknown rates, resulting in the need to consider the impacts of these changes on past coastal design assumptions. New coastal infrastructure plans, and designs should recognize the paradigm shift in assumptions from hydrologic stationarity to non-stationarity in coastal water levels. As we transition into the new paradigm, there is a significant knowledge gap which must address built coastal infrastructure vulnerability based on the realization that the underlying design assumptions may be invalid. </p><p> A framework for the evaluation of existing coastal infrastructure is proposed to effectively assess vulnerability. The framework, called the Climate Preparedness and Resilience Register (CPRR) provides the technical basis for assessing existing and future performance. The CPRR framework consists of four major elements: (1) datum adjustment, (2) coastal water levels, (3) scenario projections and (4) performance thresholds. The CPRR framework defines methodologies which: (1) adjust for non-stationarity in coastal water levels and correctly make projections under multiple scenarios; (2) account for past and future tidal to geodetic datum adjustments; and (3) evaluate past and future design performance by applying performance models to determine the performance thresholds. The framework results are reproducible and applicable to a wide range of coastal infrastructure types in diverse geographic areas. </p><p> The framework was applied in two case studies of coastal infrastructure on the east and west coasts of the United States. The east coast case study on the Stamford Hurricane Barrier (SHB) at Stamford CT, investigated the navigation gate closures of the SHB project. The framework was successfully applied using two performance models based on function and reliability to determine the future time frame at which relative sea level rise (RSLR) would cause Navigation Gate closures to occur once per week on average or 52 per year. The closure time analysis also showed the impact of closing the gate earlier to manage internal drainage to the Harbor area behind the Stamford Hurricane Barrier. These analyses were made for three future sea level change (SLC) scenarios. </p><p> The west coast case study evaluated four infrastructure elements at the San Francisco Waterfront, one building and three transportation elements. The CPRR framework applied two performance models based on elevation and reliability to assess the vulnerability to flooding under four SLC scenarios. An elevation-based performance model determined a time horizon for flood impacts for king tides, 10 and 100-year annual exceedance events. The reliability-based performance model provided a refinement of results obtained in the elevation-based model due to the addition of uncertainty to the four infrastructure elements. </p><p> The CPRR framework and associated methodologies were successfully applied to assess the vulnerability of two coastal infrastructure types and functions in geographically diverse areas on the east and west coasts of the United States.</p><p>
436

River Hydraulics on a Steep Slope Can a 2D Model Push the Limits of the Hydrostatic Assumption?

Newmiller, Jeanette Eileen 18 April 2018 (has links)
<p> The Saint-Venant shallow water equations are commonly used to model river hydraulics. The equations utilize a hydrostatic assumption with a recommendation to limit use to a bed slope less than 1:10, vertical to horizontal. This recommended limit was made in an era when calculations were performed by hand and therefore minimized by performing a one-dimensional analysis with the distance between river stations maximized. Current technology makes a more detailed analysis accessible. </p><p> This study investigates the effects of applying a two-dimensional hydraulic model that utilizes the Saint-Venant shallow water equations without correction for non-hydrostatic conditions to a bed slope of 1:8. By doing so it was hoped to show that there exists an effective and economical method for engineers to analyze hydraulic effects in these conditions. </p><p> A comparative analysis of the results from the 2D model and a 3D non-hydrostatic model was utilized to investigate the theoretical limit of slope on the hydrostatic assumption. The models consisted of an existing 2D model previously developed for an engineering study and a 3D model developed for this study, which employed a novel approach to approximate the effects of surface roughness. The analysis compared model results for depth, velocity, and flow rate at nine cross sections on the study reach. While the findings from the research are not conclusive they do illustrate that a well resolved 2D model is able to push the 1:10 slope limit on the hydrostatic assumption for the shallow water equations. It was found that a uniform flow applied to the 2D model and allowed to come to steady state maintained a relatively consistent flow rate throughout the length of the reach. This demonstrates that the model did not produce any artificial gains or losses. Surprisingly, the 2D model accomplished this while the 3D model did not. </p><p> These findings are important in locations where the accepted methods of 3D non-hydrostatic modeling would be computationally cumbersome and cost prohibitive. The lack of efficient and affordable analysis tools rated for steep slopes leads to the construction of facilities with unknown hydraulic risk to life and property. Fully verifying the methods of this study would provide needed support to hydraulic engineers for these conditions. </p><p> Concurrent to the research for this thesis, was the development of a series of lessons on introductory hydraulic engineering for middle school students. Engineering is characterized by its hands on, real world application of science and math and is rooted in a tradition of disseminating knowledge through mentorship. Many engineering topics provide opportunity to spark the minds of our youth. The final chapter of this paper is a summary of this work. It is included it here to encourage more engineers to share their work with the next generation.</p><p>
437

Retention performance and hydraulic design of constructed wetlands treating runoff waters from arable land

Koskiaho, J. (Jari) 29 August 2006 (has links)
Abstract Agriculture is the main source of nitrogen (N) and phosphorus (P), which are the nutrients accelerating the eutrophication of waters in Finland. Hence, mitigation measures are needed to reduce the nutrient loading from the arable land. Since Finland's accession to the EU in 1995 and the subsequent adaptation to its agri-environmental policy, constructed wetlands (CWs) have been one of the mitigation measures for which farmers may receive agri-environmental subsidies. The aim of this study was to find out how efficiently such CWs are able to retain the loading and how they should be designed and dimensioned in order to optimize their performance. Particular attention was paid to CW hydrology and hydraulics, since the dynamics of the water flowing through a CW is the major factor governing retention. Water quality and flow measurements were made in three CWs located in agricultural watersheds in southern Finland during 1999-2002. Hydraulic properties were examined in 2 of the CWs by simulations with 2-dimensional hydrodynamic and water quality models. According to the calculations of material fluxes, the maximum annual retention was 72% for solid material (TSS), 67% for total P and 40% for total N. The lowest retentions were slightly negative, because the CW with the smallest CW-to-watershed area ratio (0.5% in the Alastaro CW) sometimes acted rather as a source than a sink of nutrients. The highest percent retentions were found in the Hovi CW with the largest CW-to-watershed area ratio (5%). In terms of mass per CW area, the Hovi CW retained 25 kg of total P and 300 kg of total N per one hectare per one year. In the Hovi CW also dissolved reactive P retention was high (49% in situ and 34% in laboratory microcosm experiments), obviously due to high contents and low P saturation of Al and Fe oxides of the CW soil. The basic underlying reason behind the high retentions of both dissolved nutrients and particulate matter in the Hovi CW was the long water residence time coupled with high hydraulic efficiency. In the deep part of the Hovi CW, near-bottom increase of dissolved O2 was found in phase with diurnal temperature changes. The oxygen transport by this kind of convective circulation of CW water inhibited near-bottom anoxia and thus decreased the risk of P desorption. According to the hydrodynamic simulations coupled with simulated tracer tests made for the Hovi CW, a 40% improvement in hydraulic efficiency was achieved by baffles directing the main flow to optimally exploit the CW area. The rectangular, elongated shape of the Alastaro CW also showed fairly high hydraulic efficiency. Hydrodynamic simulations were also coupled with a sediment transport model, which proved to be a useful method in predicting the change of TSS concentrations in CWs. Hourly datasets of inflow and outflow revealed high attenuation of runoff peaks in the well-designed and -dimensioned Hovi CW. The hourly outflow modeled with the reservoir routing method corresponded to the observed with a reasonable accuracy. When carefully designed, painstakingly implemented and wisely located, CWs may – even in cold climate – efficiently contribute to agricultural water pollution control.
438

Attenuating amplitude of pulsating pressure in a low-pressure hydraulic system by an adaptive Helmholtz resonator

Kela, L. (Lari) 27 April 2010 (has links)
Abstract The adaptive Helmholtz resonator for decreasing harmonic pulsating pressure in a low-pressure hydraulic system is presented in this study. Adaptivity is executed by both open loop and closed loop controls so that continuous -20dB attenuation of the peak-to-peak value of the amplitude of pressure is reached. The study begins by a theory review including the theory of effective bulk modulus, sound velocity measurements, adjustable dynamic vibration absorbers and control methods of dynamic vibration absorbers. The main target of the paper, the Helmholtz resonator, is presented in its own chapter, albeit it is noted to be one application of the dynamic vibration absorber. The review is completed by the analytical model of the hydraulic pipe with a T-filter or Helmholtz resonator. After the theory review, the test equipment and its characteristics are presented. The main parts of the test equipment were a main pipe and an adjustable Helmholtz resonator, which were both developed for this study. Certain properties of the hydraulic oils used were determined experimentally to increase understanding of the system. The experimental section includes sound velocity measurements, sonic bulk modulus definitions, measurements of the resonant frequencies of the adaptive Helmholtz resonator in the test equipment, and tests of the open loop and closed loop control of the resonator. Control is verified to maintain -20dB attenuating of pressure pulsations in the system. The presented Helmholtz resonator and controls are available for installation into a hydraulic system to damp out harmonic vibrations at low frequency. For example, the roll in the size press of a paper machine might become excited to vibrate at its resonance frequency after the paper wad has washed through the nip. In that case, tuned Helmholtz resonators in the hydraulic cylinders of the size press would damp out the pulsating pressures, and if the resonators are adaptive, as presented in this study, they can operate in a wider frequency range.
439

Chemical Interactions of Hydraulic Fracturing Biocides with Natural Pyrite

Consolazio, Nizette A. 01 September 2017 (has links)
In conjunction with horizontal drilling, hydraulic fracturing or fracking has enabled the recovery of natural gas from low permeable shale formations. In addition to water, these fracking fluids employ proppants and up to 38 different chemical additives to improve the efficiency of the process. One important class of additives used in hydraulic fracturing is biocides. When applied appropriately, they limit the growth of harmful microorganisms within the well, saving energy producers 4.5 billion dollars each year. However, biocides or their harmful daughter products may return to the surface in produced water, which must then be appropriately stored, treated and disposed of. Little is known about the effect of mineral-fluid interactions on the fate of the biocides employed in hydraulic fracturing. In this study, we employed laboratory experiments to determine changes in the persistence and products of these biocides under controlled environments. While many minerals are present in shale formations, pyrite, FeS2(s) is particularly interesting because of its prevalence and reactivity. The FeII groups on the face of pyrite may be oxidized to form FeIII phases. Both of these surfaces have been shown to be reactive with organic compounds. Chlorinated compounds undergo redox reactions at the pyrite-fluid interface, and sulfur-containing compounds undergo exceptionally strong sorption to both pristine and oxidized pyrite. This mineral may significantly influence the degradation of biocides in the Marcellus Shale. Thus, the overall goal of this study was to understand the effect of pyrite on biocide reactivity in hydraulic fracturing, focusing on the influence of pyrite on specific functional groups. The first specific objective was to demonstrate the effect of pyrite and pyrite reaction products on the degradation of the bromine-containing biocide, DBNPA. On the addition of pyrite to DBNPA, degradation rates of the doubly brominated compound were found to increase significantly. DBNPA is proposed to undergo redox reactions with the pyrite surface, accepting two-electrons from pyrite, and thus becoming reduced. The primary product is the monobrominated analogue of DBNPA, 2-monobromo-3-nitrilopropionamide (or MBNPA). The surface area-normalized first-order initial degradation rate constant was found to be 5.1 L.m-2day-1. It was also determined that the dissolution and oxidation products of pyrite, FeII, S2O32- and SO42- are unlikely to contribute to the reduction of the biocide. Taken together, the results illustrate that a surface reaction with pyrite has the ability to reduce the persistence of DBNPA, and as a consequence change the distribution of its reaction products. The second objective was to quantify the influence of water chemistry and interactions with pyrite on the degradation of the sulfur-containing biocide. Dazomet readily hydrolyzes in water due to the nucleophilic attack of hydroxide (OH-) anions. Thus the half-life of dazomet during the shut-in phase of hydraulic fracturing will decrease with increasing pH: 8.5 hours at pH 4.1 to 3.4 hours at pH 8.2.Dazomet degradation was rapidly accelerated upon exposure to the oxidized pyrite surface, reacting five times faster than hydrolysis in the absence of pyrite at a similar pH. The products measured were identical to those identified on hydrolysis (methyl isothiocyanate and formaldehyde) and no dissolved iron was detected in solutions. This suggests that the dithiocarbamate group in dazomet was able to chemisorb onto the oxidized pyrite surface, shifting the electron density of the molecule which resulted in accelerated hydrolysis of the biocide. The third objective explored the reactivity of various biocide functional groups due to the addition of pyrite. Several elimination mechanisms were identified, and tied to the reactivity of the specific functional group involved. The addition of pyrite led to accelerated degradation of dibromodicyanobutane. This is because the bromine (-Br) group is easily reduced. For methylene bis(thiocyanate), hydrolysis was a noteworthy elimination mechanism since the thiocyanate (-SCN) functionality is a good leaving group. Benzisothiazolinone and methyl isothiazolinone were stable at low pH due to the stabilizing donor-acceptor interactions between the organic biocides’ carbonyl (–C=O) groups and salts in the solution. This body of work has illustrated that pristine pyrite can undergo redox reactions with brominated biocides used in hydraulic fracturing, reducing their persistence and altering the product distribution. This will change the efficacy and the risks associated with the use of these biocides in shales containing pyrite, particularly at lower pH where organic compounds are more stable to hydrolysis. However, at higher pH hydrolysis becomes more important, and additional studies will need to be conducted to investigate the pyrite contribution under these conditions. Conversely, the FeIII surface groups on oxidized pyrite can catalyze the hydrolysis of dazomet and may do so for other labile, sulfur-containing biocides as well. Overall, this research has shown that the physicochemical properties (such as the acid dissociation constant and the standard reduction potential) that govern the environmental reactivity of a molecule can be used to anticipate its reactivity in hydraulic fracturing.
440

Characterisation of natural radioactivity in Karoo Basin groundwater prior to shale gas exploration

Botha, Ryno January 2017 (has links)
Magister Scientiae - MSc / The prospect of unconventional shale-gas development in the Karoo Basin (South Africa) has created the need to obtain baseline data on natural radioactivity in Karoo groundwaters. The Karoo Basin groundwater radiological baseline developed through this study could serve as a reference to research potential future radiological contamination effects due to hydraulic fracturing. The major naturally occurring radioactive material (NORM) studied was radon (222Rn), in particular in-water activity concentrations; however, supplementary radium (226Ra and 228Ra) in-water activity concentrations and uranium (238U) in-water concentrations measurements were also made. A total of 53 aquifers across three provinces were sampled for groundwater and measured, with three measurement series from 2014 to 2016. The aquifers were categorized as shallow, mixed, or deep source. The radon-in-water baseline of the Karoo Basin can be characterised by a minimum of 0.6 ± 0.9 Bq/L, a maximum of 183 ± 18 Bq/L and mean of 41 ± 5 Bq/L. The radon-in-water levels from shallow sources (with water temperature < 20 °C) were systematically higher (40 Bq/L) than for deep sources (with water temperature > 20 °C). The natural fluctuations in radon-in-water levels were predominantly associated with shallow aquifers compared to almost none observed in the deep sources. The uranium in-water baseline can be characterised by a minimum of below detection level, a maximum of 41 μg/L, and the mean of 5.10 ± 0.80 μg/L. Similar to radon-in-water levels, uranium in-water levels for shallow sources were systematically higher than for deep sources. The limited (six aquifers) radium (228Ra and 226Ra) in-water activity-concentration measurement results were very low, with a maximum of 0.008 Bq/L (226Ra) and 0.015 Bq/L (228Ra). The 228Ra/226Ra ratio baseline were characterised by a minimum of 0.93, a mean of 3.3 ± 1.3, and a maximum of 6.5. The radium isotopes’ activity concentration ratio is an isotopic tracer for hydraulic fracturing wastewater. Pollution and contamination (radiological), due to unconventional shale gas development, in water resources has been noticed in the Marcellus Basin (United States). Consequently, developing and improving continuous baseline monitoring are of importance to study the environmental radiological effect of hydraulic fracturing.

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