Multiple drive belt conveyors are being increasingly incorporated in mining plans worldwide because of their high economic performance and the ease of moving these installations around, especially in underground mines. A typical modern multi-drive conveyor system consists of one or more intermediate drive stations positioned along the upper stretch of the conveyor and a single drive station situated in the lower stretch. Despite the acknowledged cost saving potential of the multiple drive technology, no previous work was reported on the methodology to realize a cost-effective design of multi-drive belt conveyors. This study investigates a design approach for multiple drive belt conveyors with the objective to achieve the lowest life cycle cost of multi-drive belt conveyors for a specified material transport task. For this purpose, an optimization model for the cost-effective design of multi-drive conveyor systems is formulated on the basis of the recommendations of the DIN 22101 and SANS 1313 standards. For a given number of intermediate drive stations, the proposed model optimizes a set of design parameters so that the minimum equivalent annual cost of a conveyor can be attained whilst handling the transport requirements and design conditions. The conveyor parameters optimized in this study are the rated powers of motors, the rated torques of gear reducers, the diameters and wrap angles of drive pulleys, the belt width, the belt speed, the lengths of the belt sections not nestled between drive pulleys, the spacings between idler rolls and the shell diameters and shaft diameters of idler rolls. For benchmark analysis purposes, a similar optimization model is also developed for the single drive technology. Described as mixed integer nonlinear programming (MINLP) problems, the two optimization models are solved using the MIDACO solver embedded in the MATLAB environment. The results of this study show the validity and effectiveness of the design model proposed for multi-drive belt conveyors. The results also indicate that the multiple drive technology is more beneficial for the conveying over long distances. The impact of the possible instability of inflation throughout the project lifetime is also investigated through three hypothetical scenarios, which involve a fixed inflation rate, a higher fluctuating inflation rate and a lower fluctuating inflation rate, respectively. The results of this sensitivity analysis show that the most cost-effective multi-drive belt conveyors obtained under a fixed inflation rate is robust enough against limited fluctuations of this parameter. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Cyber security is a major concern due to global incidents of intrusion. The impact of the attacks on the electricity grid can be significant, resulting in the collapsing of the national economy. Electricity network is needed by banks, government security agencies, hospitals and telecommunication operators. The purpose of this research is to investigate the various types of cyber security threats, including ICT technologies required for safe operation of the smart grid to protect and mitigate the impact of cyber security. The modelling of cyber security using the Matlab/SimPowerSystem simulates the City of Tshwane power system. Eskom components used to produce energy, interconnect to the City of Tshwane power distribution substations and simulated using Simulink SimPowerSystem. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

Potable water is a relatively scarce natural resource. This scarcity is evident on a global scale. For humankind potable water is not only needed to sustain life, but also to engage in activities that maintain and enhance its own comfort and quality of life. These activities contribute to the degradation of water quality and exacerbating water scarcity. Electricity is a resource that needs to be generated, and is used significantly to also maintain and enhance human comfort, and quality of life. The generation of electricity produces a significant amount of greenhouse gases, gases that contribute to climate change. The use of both resources needs to be more ecologically sustainable to reduce the negative impact caused. Wherever possible, the use of these resources should be reduced. University residences utilise substantial amounts of water and electricity. This is because they are commonly designed to accommodate a large number of students. Implementing a behaviour change intervention in a residence therefore has the potential for greater ecological impact if the intervention is successful, due to the large number of people. There are different types of interventions aimed at changing behaviour, with some being active and others passive. Being active or passive is determined by whether or not direct interaction with the subject is required to achieve the desired change. Information provision can be a passive intervention by using posters and pamplets. It can also be active by using Q&A sessions and lectures. The study aimed to determine if the use of a passive behaviour change intervention could result in the reduction of water and electricity consumption in university residences. The passive intervention utilised was prompting in the form of posters. A quasi-experimental design with a mixed methods approach was employed. Quantitative data were meter readings for both electricity and water, while quantitative data were obtained from focus groups. 3 female residences at the University of Pretoria's Groenkloof campus were used in this study. Posters were placed at the points of decision in two of the residences. The third female residence was monitored as the control and no posters were put up in it. Monthly water and electricity meter readings were used to determine if this change had occurred. Focus groups were conducted to understand from the subjects how the intervention had affected them, if at all. Results from this study indicated that water and electricity consumption was reduced, with some reductions being statistically significant and others not. The study, however, cannot confidently predict that the intervention was successful due to various limitations. / Dissertation (MSc)--University of Pretoria, 2018. / Construction Economics / MSc / Unrestricted

The fire behaviour of linear low-density polyethylene composites containing 10 wt.% of different carbon-based fillers was studied. Cone calorimeter tests conducted at a heat flux of 35 kW_m_2 showed that the expandable graphite sample reduced the peak heat release rate by about 50 % while the flake graphite increased the ignition time by about 80 %. Pyrolysis combustion flow calorimetry results were practically identical for all composites. This reveals shortcomings of this bench-scale flammability test method when the flame retardancy mechanisms relies on either the development of physical barrier layer at the surface of the burning sample or on reflecting the incident heat flux. Similarly, it was found that laser pyrolysis-thermogravimetric analysis generated outcomes that did not correlate with the cone calorimeter results at all. In particular, the composite based on expandable graphite performed poorly. The likely explanation is that the aspect ratios of the small samples were such that the barrier effects on which this system relies, was negated by edge effects. / Dissertation (MSc)--University of Pretoria, 2018. / Chemical Engineering / MSc / Unrestricted

The automotive parts supply chain is characterised by expectations of high levels of parts availability, as vehicles are designed to be maintained throughout their life cycles. There is, however, a significant level of unpredictability in demand, requiring suppliers to store sufficient inventory to service demand associated with planned maintenance and unplanned repair events. In this thesis, a supply chain characterisation framework is proposed and confirmed with a series of case studies. The automotive supply chain is characterised as a Class III-P supply chain. This type of supply chain has products with high complexity and long life expectancies, which is augmented through the design of maintenance and repair schedules, requiring a supporting parts distribution supply chain. Automotive part supply continues for 15 years after production of a model ceases, requiring a wide array of items to be available for a significant period of time after the end of vehicle production. The need for parts availability for such a long period results in space constraints within the supply chain. Just-In-Time (JIT) manufacturing results in lean supply chains, but it is shown that the cost for post vehicle production can be high as the volumes required can decrease significantly. To implement JIT in the automotive parts supply chain a MAX/MAX inventory strategy is most commonly followed. The MAX/MAX inventory strategy is implemented with the Maximum Inventory Position (MIP) inventory management method. Deriving the method theoretically and comparing it with the practical implementation shows clear concerns regarding the dimensional consistency of the practical implementation. Using a System Dynamics Simulation Model (SDSM), it is shown that while the theoretical version of the method (MIPTheory) may minimise inventory, it does not maximise parts availability, as measured by allocation fill rate (AFR). The actual implementation (MIPActual) improves the AFR, but increases average inventory levels significantly (as much as 100 times in some cases). While it is accepted that stock-on-hand inventory management policies are inherently unstable, a stock-on-hand policy, Stock Target Setting (STS) was developed and redesigned to be stable. The SDSM showed that the STS method could result in stable behaviour, using the supply chain lead time as a damping factor. Comparison between the three methods in a theoretical set of demand, demand variance, lead time and lead time variance scenarios showed that the STS method improves the AFR above that of MIPTheory and requires significantly less inventory than the MIPActual method. Analysis of the STS method indicates there are some areas for improving the stock target equation, but this has to be performed with sufficient care. Extending the SDSM to use vehicle sales to generate service parts demand, it is possible to evaluate the inventory management methods under non-stationary demand conditions. The STS method is shown to be the preferred method for domestic supplied parts when there is no start-up inventory. For imported parts, the STS method performs better in the long term. The MIPActual method also results in high levels of parts availability. The MIPActual method, however, requires significantly more inventory. In the case of start-up inventory, the STS method is less effective in the short term, but in the long term requires less inventory to maintain an AFR of 100. A practical analysis using actual data show that there are cases where the STS method outperforms the MIP methods, but this is dependent on the demand and lead time behaviour. The study clearly shows that stock-on-hand inventory management policies, such as the STS method developed in this study, have the potential to improve the performance of the automotive parts supply chain. With the STS method, inventory levels can be reduced, reducing the pressure on storage space requirements resulting from the MIPActual results. At the same time, the AFR levels can be maintained. The practical problem in the automotive parts supply chain has clearly been addressed and solved. Significant achievements in the study include the development of a practical supply chain characterisation framework that provides guidance on the supply chain design for specific product classes. The SDSM is a powerful generic tool that can be adjusted for alternative inventory management methods. It can be expanded to evaluate any alternative inventory management method. The STS method showed that the assumption that stock-on-hand inventory management methods are inherently stable is incorrect, opening up the potential to initiate a new research direction towards effective stock-on-hand inventory management methods. The STS method was shown to be a viable alternative for the automotive service parts supply chain. / Thesis (PhD)--University of Pretoria, 2017. / Industrial and Systems Engineering / PhD / Unrestricted

In the long term it is beneficial to a country's economy to exploit the maritime environment surrounding it responsibly. It is also beneficial to protect this environment from poaching and pollution. To achieve this the responsible parties of a country must have an awareness of what is transpiring in the maritime domain. Synthetic aperture radar can provide an image, regardless of weather or light conditions, of the ocean showing most vessels therein. To monitor the ocean, using synthetic aperture radar imagery, at the lowest cost would require large swath synthetic aperture radar imagery. There exists a trade-off between large swath imagery and the image's resolution resulting in the largest swath image having the poorest resolution. Existing research has shown that it is possible to use coarse resolution synthetic aperture radar imagery to detect vessels at sea, but little work has been done on classifying those vessels. This research aims to investigate the coarse resolution classification information gap. This is done by using a dataset of matching synthetic aperture radar and ship transponder data to train a statistical classification algorithm in order to classify or estimate the length of vessels based on features extracted from their synthetic aperture radar image. The results of this research show that coarse resolution (approximately 40 m per pixel) synthetic aperture radar imagery is able to estimate vessel size for larger classes and provides insight on which vessel classes would require finer resolutions in order to be detected and classified reliably. The range of smaller vessel classes is usually limited to ports and fishing zones. These zones can be mapped using historical vessel transponder data and so a dedicated surveillance campaign can be optimised to use higher resolution products in these areas. The size estimation from the machine learning algorithm performs better than current techniques. / Dissertation (MEng)--University of Pretoria, 2017. / Electrical, Electronic and Computer Engineering / MEng / Unrestricted

A gravimeter is an instrument that measures gravitational force Fg (N) or acceleration g (m/s-2). Absolute gravity measurements are preferred in metrology, due to the shortest traceability links to the SI base units of length and time, realising acceleration. The investigation on the suitable method of gravity measurement was performed at the National Metrology Institute of South Africa (NMISA). The free fall gravity measuring system was adopted for development. The metrological need on redefining the kilogramme standard using the watt balance, supported the decision to mandate this project. Free fall gravimeters were researched. The new concept of fully pneumatic controlled vacuum chamber was invented and manufactured. Pneumatic actuators were used on the vacuum chamber to align, launch, capture and reposition the falling test mass. Laser interferometer and high-speed digitiser with embedded accurate clock module, were used in realising displacement and time, through numerical computations. Using stabilised He-Ne Laser red with wavelength =633 nm interferometer, free-falling test mass displacements were traceable to length standard. Interference intensity signal produced from experimental free fall drops were converted to A digital voltage signal enabling processing. Post signal processing algorithms were applied to the signal to extract the displacement and time coordinates of the free-falling object, using a zero-crossing detection method in a LabView environment. The final prototype setup measured the value 9.786041 m/s2 with uncertainty of 0.0000705 m/s2 at the vacuum pressure of 0.05 Pa. It was validated and compared with the Council of Geophysics_ measured value of the site of 9.7860985 m/s2. / Dissertation (MEng)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

The performance of a railway track structure is significantly influenced by ballast shape properties such as roundness, flatness, elongation, sphericity, angularity and surface texture. Railway ballast materials have to comply with several quality requirements and shape properties. Accurate measurement of the shape properties is important for developing and revising specifications for quality control and quality assurance in the selection of ballast materials for railway construction. However, the current test methods for determining these properties have severe shortcomings such as poor repeatability and subjectivity. In addition, they are often based on visual measurements and empirically developed charts, which lack scientific standing. In this study, an advanced three-dimensional (3D) laser scanning was used to quantify the shapes of railway ballast materials from a heavy haul coal line in South Africa. This study complements the current research by the Council for Scientific and Industrial Research (CSIR) that is aimed at introducing advancement and scientific approach (i.e. 3D-laser scanning and numerical techniques) to effectively model the shape of crushed stones i.e. aggregates for roads and ballast for railways used in transport infrastructure. The primary objective was to investigate the effect of ballast particle shape, determined from a modern 3D-laser scanning technique, on the performance characteristics (i.e. shear strength and permanent deformation) of ballast materials. Overall, five ballast materials (four recycled ballast materials from the coal line and one freshly crushed ballast) and one river aggregate were investigated for this study. All six materials were scanned in the 3D-laser scanning system and the data were processed to reconstruct three dimensional models of the ballast and the river pebble particles. The models were further analysed to determine the roundness, flatness, elongation, and sphericity shape properties of the particles. The results obtained were used to develop different charts to characterise ballast shapes. An ANOVA (Analysis of variance) statistical analysis was conducted on the three dimensional data to establish which individual ballast particles contributed significantly to the overall shape parameters. To evaluate the effects of the shape properties on the behaviour of ballast in the track structure, a laboratory testing programme was conducted to determine the settlement behaviour and shear strength of the ballast materials. Repeated load permanent deformation tests were conducted to evaluate the overall settlement behaviour, whereas monotonic static triaxial tests were used to determine the shear strength properties of the ballast materials. The results indicated that ballast materials with low roundness values exhibited low shear strength and high permanent deformation (settlement). Although this was expected, the use of the automated 3D-laser scanning approach introduced a high level of accuracy and confidence in the results. Based on the laser results, a new empirical model was developed to determine the surface area of the ballast materials. The surface area values were further used to develop a chart to assess different particle shapes with varying degrees of roundness. Triaxial tests were conducted to determine the effect of the roundness on the shear strength properties of the materials. A Mohr-Coulomb failure model was successfully developed from the results to represent the individual materials tested. The overall results show that the angle of internal friction decreases with an increase in the roundness index of the particles. More rounded particles have roundness index values of between 1.4 and 1.7 whereas less rounded particles have roundness index values of between 0.8 and 1.3. The outcomes of this study would assist with quality control in the field as to whether or not to replace degraded ballast in the track layer. It is anticipated that this study will enhance improved guidelines, test methods and specifications for the selection of ballast / Dissertation (MEng)--University of Pretoria, 2017. / Civil Engineering / MEng / Unrestricted

Student academic progress has been at the centre of concern to all higher education institutions in South Africa. It is understood that student progress emanates from a range of dynamics that gives students different educational experiences. The student cohort at University of Pretoria (Abdulghani et al., 2014) come from diverse cultural backgrounds in South Africa, aptly called the rainbow-nation, and subsequently bring different levels of proficiency and world experiences to the higher education sector. The student population is like a tapestry interwoven from different cultures and includes students from all 'walks of life', rich and poor, alternative lifestyle and background, as well as students who are disabled, and students who have diverse sexual orientations. The transition from school to university is regarded as a time of extreme stress for students arriving at the university door for the first time. The expectations of students are mostly unknown, but educators know that students entering university come from positions of extreme inequality, not only in terms of schooling, but also of financial and other resources. It is well-documented that in addition to all the other changes, a large number of students arrive at the university lacking the necessary knowledge and skills that will help them cope at university. These are largely students that come from underprivileged schools that still bear the ravages of apartheid education. To assist students in overcoming the lack of these skills and bridging the educational gap, higher education has to address these needs. Hence, it is the intention of this research to "explore the undergraduate Information Technology experience of an extended programme". The research is a four-year longitudinal study of IT students in the extended (four-year) IT degrees at UP, and has analysed interviews conducted with IT graduates in a range of professional settings. Taken together, these components have been designed to expand the researcher's understanding of undergraduate IT experience (extended programmes) and the transition from university to the workplace. Furthermore, it focuses on how students in Information Technology experience their education, how they gain knowledge of what Information Technology is, and what their post-graduation plans are. Based mainly on the theoretical framework of Vincent Tinto (1975), this study provides an analysis of research regarding student experiences, retention and withdrawal in the extended four-year programme (E4YP) in IT. The research methodology used to conduct this study includes a mixed methods approach undertaken from more than one point of view. The researcher used a combination of qualitative and quantitative research features. The data was generated by surveys (online questionnaires and mini-questionnaires), mini-essays and the results of statistical analysis using academic results and Students� Academic Readiness Survey (STARS) scores. The findings of this study paint a portrait of typical first-year students irrespective of study direction. Their experiences and journey during the first-year are fraught with issues such as finance, accommodation, transport, gender inequality, institutional hiccups, loneliness and exhaustion, and difficulty in finding their way around campus. However, many expressed experiencing the euphoria of freedom from school/parental rules, meeting new friends and socialising, and enjoying the general feeling of being a university student. / Thesis (PhD)--University of Pretoria, 2017. / Informatics / PhD / Unrestricted

It is common practice to design heat exchangers that are operated in either the laminar or the turbulent flow regime and not in the transition flow regime. This could mainly be due to a lack of knowledge on the behaviour in the transition flow regime for several reasons. However, due to factors such as design constraints, heat exchangers may indeed operate in the transition flow regime. An experimental study was conducted to determine the lower and upper Reynolds number limits of the transition flow regime, and the characteristics of the heat transfer coefficients and friction factors for annular passages with different geometric dimensions. The inner wall of the annular passage had different degrees of non-uniform temperature, while the outer wall was insulated. Both heated and cooled flow applications with water as fluid (cold fluid and hot fluid respectively) were investigated. The isothermal condition investigation was also conducted for pressure drop. Four horizontal concentric counter-flow tube-in-tube heat exchangers with conventional inlet geometries were considered to obtain the required data. The hydraulic diameters of the test sections were 26.2 mm, 23 mm, 20.2 mm and 17 mm, their respective annular diameter ratios were 0.327, 0.409, 0.386 and 0.483 and their length-to-hydraulic ratios were 193, 221, 251 and 299 respectively. The flow was both hydrodynamic and thermally developing. Test data of laminar, transition and turbulent flow regimes was collected. However, the transition flow regime was the main area of interest for this study. The transition flow regime was found to exhibit either mixed or forced convection types. Average heat transfer coefficients were obtained for both heating and cooling cases, while friction factors were obtained for heating, cooling and isothermal conditions. Uncertainties in the friction factor and Nusselt number were on average below 5.6% and 10.5%, respectively. The geometric size of the annular passage, degree of wall temperature uniformity and direction of the heat flux (heating and cooling cases of annular fluid) had a significant influence on the heat transfer coefficients, friction factors and Reynolds number span of the transition flow regime. New correlations for predicting the transition flow regime Reynolds number spans, Nusselt numbers and friction factors were developed for the transition flow regime and predicted most of the data to within +-10%. / Thesis (PhD)--University of Pretoria, 2017. / Mechanical and Aeronautical Engineering / PhD / Unrestricted