Corrosion of steel in reinforced concrete structures is a large problem facing engineers today. The marine environment is considered to be the most severe owing to the high levels of chlorides available, and so structures located here are particularly vulnerable to chloride attack and chloride induced corrosion of steel. In order to intervene and address the concern of premature deterioration in the marine environment, design guidelines and frameworks have been developed and implemented. For example, the Eurocode (EN 206, 2013) provides three class designations in order to predict the severity of potential steel corrosion. The three exposure zones, namely i) structures exposed to airborne salts but not in direct contact with sea water, ii) submerged structures, and iii) structures in the tidal, splash and spray zones are given here in order of increasing assumed probability of corrosion. However, it has been found through condition assessments of structures along the Atlantic Ocean and Indian Ocean coasts of Southern Africa that structures in the tidal zone generally show no signs of corrosion damage despite having high levels of chlorides at the depth of reinforcement. Often, on a structure where both zones have the same cover to reinforcing, the splash and spray zone will show significant damage while the tidal zone shows no signs of reinforcement corrosion. These findings challenge the existing idea that the tidal zone can be characterised as the most severe exposure zone. In order to further understand the mechanisms of reinforcement corrosion within different marine environmental conditions, a total of 36 corrosion cells were manufactured with dimensions of 120 × 122 × 380 mm and placed in simulated marine environmental conditions. These three environmental conditions included submerged, cyclic wetting and drying, and periodic splashing. In order to simulate the submerged environment, the cover surface of the specimens were permanently saturated with a 5% NaCl solution while for the splash zone concrete specimens were sprayed with 5% NaCl solution every second day. The tidal zone attempted to simulate natural tidal conditions by exposing the corrosion cells to 12 hour cycles consisting of 6 hours wetting and 6 hours drying All 36 corrosion cells were connected to a data logger where the voltage was measured weekly across a resistor of 100Ω. Ohm’s law was then used to determine the current flowing through the circuit. The concrete cover depth was varied in the corrosion cells (10, 20 and 30 mm) as well as the w/b ratio (0,5 and 0,8). The corrosion current resulting from these corrosion cells were used to infer relationships between all 3 parameters (cover depth, w/b ratio, and exposure conditions) and their influence on the corrosion current. Three companion moisture specimens were cast per mix in order to establish moisture profiles in the different exposure zones. From these specimens, the relative humidity of the concrete at different cover depths and w/b ratio’s could be determined for corrosion cells located in differentexposure conditions. Companion cubes were also cast with the corrosion cells in order to determine the durability index values. The results of the experiments indicate that the exposure condition has a very large impact on the availability of oxygen, and hence the corrosion rate. High relative humidity (or moisture content) in concrete stifles the supply of oxygen to the steel, and hence prevents active corrosion. For concrete submerged and partially or completely saturated with water, oxygen accessibility can become limited at the steel surface. The results obtained conform to the widely accepted principle that submerged concrete is less vulnerable to corrosion as a result of insufficient oxygen supply at the reinforcing steel. For concrete exposed to a 6 hour cycle of wetting and drying, the corrosion rate was significantly lower at higher cover depths due to the short cycle durations, the pores surrounding the steel were still partially or fully saturated with water. As a result, oxygen diffused slower through the cover layer. Consequently, where the concrete in the tidal zone has drying times of about 6 hours and a cover depth exceeding 30 mm, the steel will be deprived of oxygen, and corrosion will be stifled. This means that the concrete in the tidal zone would theoretically perform as if it were permanently submerged (provided sufficient cover depth exists). Specimens exposed to a splash environment performed as expected. A low moisture content showed that oxygen is able to diffuse through the pore system and facilitate corrosion in the specimens. This is owing to the pores around the steel not being saturated with moisture, and oxygen being readily available to participate in the cathodic reaction. In the case of these specimens, the electrical resistivity of the specimens was found to be the main limiting factor in controlling the corrosion rate (and not cathodic control as with tidal and submerged specimens). As a result, it is recommended that the current SANS exposure classification be broadened to include concrete exposed to cyclic wetting and drying (i.e. tidal zone exposure) a separate category, and not be classified as having the same severity as the splash zone. The application of these research findings is in infrastructure that is primarily exposed to only tidal and submerged marine conditions.

Projects are undertaken at Koeberg Nuclear Power Station in South Africa to enhance safety and to contribute to the continuity of power supply in the country. These projects are undertaken in an industry that is regarded as a high risk due to the potential consequence of a nuclear accident. Focus is thus placed on safety culture to prevent such accidents from taking place. Since safety is a key performance indicator in these high-risk industries, and projects are undertaken to improve the overall performance of such organizations, the role which safety culture has on project performance would be of interest. This study investigates how safety culture influences project performance and identifies the respective elements that collectively interact in contributing towards successful project outcomes in the context of Koeberg Nuclear Power Station. The study has found that - Safety culture plays a vital role in safety performance which is a recognized performance indicator of projects in high risk industries. Safety culture itself was found to consist of the elements of safety performance, personal values to safety, safety leadership, safety related interpersonal relations, proactivity to safety, commitment to safety and continuous improvements to safety. These elements with emphasis on safety were related to the project management knowledge areas of Time, Scope, Risk, Quality, Human Resource and Communication Management. The project managers competencies are also included amongst these elements which respectively interact with one another to influence the level of safety culture in a project. The study has revealed that these elements should be worked at by all departments involved in a project to allow the required performance criteria to be achieved. In addition, it reveals that a good safety culture provides flexibility in addressing changing requirements in a project.

The simultaneous localisation and mapping (SLAM) algorithm have been widely used for autonomous navigation of robots. A type of visual SLAM that is popular among the researchers is RGBD SLAM. However processing immense image data to identify and track landmarks in RGBD SLAM can be computationally expensive for smaller robots. This dissertation presents an alternate method to reduce the computational time. The proposed algorithm extracts features from a region of interest (ROI) to track landmarks for RGBD SLAM. This strategy is compared to the traditional method of extracting features from an entire image. The ROI algorithm is implemented via a pre-processing algorithm, which is then integrated into the RGBD SLAM framework. The pre-processing pipeline implements image processing algorithms in three stages to process the data. Stage one uses a ROI algorithm to detect ROIs in an image. For visual SLAM such as RGBD SLAM, objects that are highly detailed are used as landmarks. Hence the ROI algorithm is designed to detect ROIs containing highly detailed objects. Stage two extracts features from the image and stage three uses feature matching algorithms to re-identify a ROI. Once a ROI has been successfully re-identified, it is stored and categorised as a landmark for RGBD SLAM. Scale invariant feature transform (SIFT), speeded up robust features (SURF) and orientated FAST and rotated BRIEF (ORB) are three feature extraction algorithms that are used in stage two. The outcomes from this study revealed that the pipeline was able to successfully create a database of landmarks which can be re-identified in subsequent frames. In addition, the results showed that when the pipeline is configured such that SURF features are used with a bigger ROI, RGBD SLAM produced more accurate results in determining the position of the robot compared to the traditional method of extracting features from an entire image. However, this strategy requires more computational time. The findings further revealed that this strategy still out performs the traditional method when the number of features extracted is reduced. This indicated that this strategy performs more robustly compared to the traditional method in environments that can contain few features. The method presented in this study did not improve the computational time of RGBD SLAM but did improve the accuracy in localizing the robot.

The leaflet material in heart valve prostheses is required to be both flexible and durable to eliminate the need for chronic anticoagulation medication and accommodate younger patients with longer life expectancies. This investigation aims to provide two of the necessary tools to design and test suitably flexible and durable materials for heart valve replacement. These tools address the question of how to model the stress-strain behaviour of polymer networks and thermoplastic polyurethanes in particular, as well as how to practically evaluate the durability of the proposed material. A model for polyurethane stress-strain behaviour is proposed, whereby the number of monomers between crosslinks is suggested to evolve with macroscopic strain. Following the polymer chain entanglement theory, the increase in the number of monomers between crosslinks is further extended to be a function of strain rate, incorporating the viscous effect observed in polyurethanes. A multistation, micro-tensile specimen fatigue tester was developed to evaluate material durability. The proposed equilibrium polyurethane model accurately predicts the experimental data across the full material strain range. The proposed model extension sufficiently captures the rate dependence of polyurethane, however, fails to account for the raised specimen temperatures at high strain rates. The developed fatigue tester is verified to successfully feature selectable variables including test frequency (1 - 20 Hz), amplitude (1 - 6 mm), waveform (Triangular, Sinusoidal, Square and Custom) and environmental temperature control (23 - 50 oC). Less than 10% error in measured force is observed when compared to a commercial tensile tester. The proposed model successfully provides a platform to aid the design of flexible materials suitable for heart valve leaflets. The developed fatigue tester enables the assessment of material durability across a range of test conditions, successfully providing a tool for leaflet material durability analysis and verification.

With the drive to reduce water usage globally, the mining sector must reassess its water usage as it has in the past contributed greatly to environmental degradation due to effluent discharge, tailing disposal and process water seepage into the water-table. Mineral beneficiation entails different unit operations; amongst them is froth flotation. Froth flotation is a multifaceted complex process which is water intensive and to manage water usage, the global mining industries are now recycling water. The recycled water may contain deleterious ions that affect the mineral surface, pulp chemistry and reagent action, hence the need to establish whether threshold concentrations exist beyond which the flotation performance will be adversely affected. This is of paramount importance in informing appropriate recycle streams and allowing simple, cost-effective water treatment methods to be applied. To better understand the influence of water recycling in flotation, a low-grade Cu-Ni-PGM sulphide ore was used. This study investigated the effects of increasing ionic strength as well as increases in specific ion concentrations to determine whether these selected ions had beneficial or deleterious effects on the flotation process. Copper and nickel were the target metals, floated as chalcopyrite and pentlandite, respectively. Their recovery and grade under different conditions was used as a measure to quantify whether a threshold ion concentration existed. The key performance indicators used were: (a) water recovery, (b) solids recovery, (c) valuable metal recovery, (d) grade of the recovered concentrates and (e) electrical conductivity. While a complex background water chemistry of 3 SPW was maintained for the spiking tests, ion spiking was intended to mimic the recycling of water and the most prevalent ions which would likely be recycled and therefore accumulated, such ions as: Ca2+, Mg2+, NO3 - , SO4 2- and S2O3 2-. These ions were chosen based on speculation from relevant literature that they might impact the flotation performance due to their influence on pulp chemistry and reagent interaction. This was achieved by conducting sequential batch flotation and electrical conductivity (EC) tests. Batch flotation tests were performed to investigate the effect of different ionic strength conditions on the overall flotation performance. The same ionic strengths and spiking concentrations were used for froth (or foam) column studies with a focus on tracking the ion concentration distribution between the froth and the slurry (or solution) by means of measuring the EC of each of the froth and the pulp (solution) phases. The differences implied whether the ions were selectively concentrated at the air-water or solids-water interphases in a 3-phase system or likewise at the v bubble surface or within the solution for a 2-phase system. This distribution of ions was linked to the other key performance indicators. Increasing ionic strength; 3, 5 and 10 SPW respectively, resulted in an increase in water recovery in the order 3 SPW < 5 SPW < 10 SPW, indicating an increase in froth stability due to inhibition of bubble coalescence at high ionic strength. There was, however, no significant effect on the valuable metal recovery. Most of the nickel was recovered in the copper circuit which was expected as on-site conditions were not maintained at the laboratory scale, no lime was added to adjust the pH in the copper circuit and an EDTA chelating agent was not included in the nickel circuit. Spiking 3 SPW with 800 ppm Ca2+ results in considerably higher water recovery per unit solids recovered compared to 3 SPW, 5 SPW, 400 ppm Ca2+, 350 ppm Mg2+, 700 ppm Mg2+. 400 ppm Ca2+ resulted in the highest copper and nickel grade and was deemed the threshold for this study while for Mg2+ threshold lies outside of the range considered for this study. 10 SPW shows a decrease in the copper and nickel grade while the copper and nickel recoveries were not significantly impacted. The presence of the Ca2+ and Mg2+ at high concentrations leads to gangue activation which as a consequence will result in decreased grade. 880 ppm NO3 - gave the highest copper and nickel grade compared to 3 SPW while increasing the S2O3 2- from 60 to 78 ppm resulted in an increase in nickel grade. 1200 ppm SO4 2- and 880 ppm NO3 - were deemed the threshold concentration for these anions, above which the flotation performance declines, while for S2O3 2- the threshold lay outside the range considered for this study. This study has shown that the accumulation of ions within plant water, owing to recycling, is, in general, beneficial to flotation. This study has also shown that there is a concentration for each ion beyond which it is no longer beneficial to flotation. While this finding is clearly ore and ion dependent, it gives an indication as to the need for water treatment and considering the threshold concentrations found, may direct operations to suitable treatment methods for their systems.

Speech Recognition is a technology with promising applications. However, the performance of current speech recognizers greatly limit their widespread use. Approaches to reducing the word error rate have mainly been associated with statistical techniques. As a consequence, speech recognition results can still contain sentences that are nonsensical. The method proposed here, is to analize the output of any chosen speech recognition system, in order to determine whether a sentence contains syntactic or semantic errors. This is done via a software agent that uses the information from its knowledge base to attempt to correct the errors found. A system was implemented with a small vocabulary speaker-independent continuous speech recognition system, with limited sentence structures. The achieved increase in speech recognition accuracy, shows that there are bene ts in using this approach.

Word processed copy. / Includes bibliographies. / Power system stability is defined as the condition of a power system that enables it to remain in a state of operating equilibrium under normal operating conditions and to regain an acceptable state of equilibrium after being subjected to a finite disturbance. In the evaluation of stability, the focus is on the behavior of the power system when subjected to both large and small disturbances. Large disturbances are caused by severe changes in the power system, e.g. a short-circuit on a transmission line, loss of a large generator or load, loss of a tie-line between two systems. Small disturbances in the form of load changes take place continuously requiring the system to adjust to the changing conditions. The system should be capable of operating satisfactorily under these conditions and successfully supplying the maximum amount ofload. This dissertation deals with the use of Power System Stabilizers (PSS) to damp electromechanical oscillations arising from small disturbances. In particular, it focuses on three issues associated with the damping of these oscillations. These include ensuring robustness of PSS under changing operating conditions, maintaining or selecting the structure of the PSS and coordinating multiple PSS to ensure global power system robustness.

Bibliography: leaves 63-68. / This thesis is part of the greater study and looks into understanding the ferric leaching sub-process by establishing an effective way of measuring the rate of the chemical leach process.

Bibliography: leaves 158-168.

This thesis gives a detailed presentation of a formulation for thin shells, and its finite element approximation, with the goal of modelling soft, thin biological tissues. The rigorous but complex theory due to Simo and Fox (1986) is presented in an accessible manner, with detailed derivations where appropriate. The presentation is confined to small strains and linear elasticity, with the constitutive theory extended to take account of transverse isotropy. The finite element formulation is given in such a way as to make various implementational aspects clear. Implementation has been carried out in deal.II, an open source library of finite element code. Substantial detail is given about how the shell formulation was implemented; this includes preprocessing, programming of the solution algorithm, and post-processing of results. The formulation is tested against a series of benchmark problems for flat plates and cylindrical shells, under a variety of loading conditions, and compared with results in the literature. II Two example problems in biomechanics are considered: the problem of arterial clamping, and the modelling of a prosthetic aortic valve. In the case of the clamped artery, the deformed shape for a range of clamp depths compares well with results in the literature obtained using a three-dimensional formulation. The addition of helical fibre families orientated in the same manner as two different arterial layers significantly altered the resulting deformations and agreed qualitatively with those in the literature. Using the geometric and material parameters given in earlier studies of prosthetic aortic valve leaflets, the shell solution algorithm was used to simulate a leaflet with and without transverse isotropy. The deformed leaflet behaved as expected for a diastolic state and showed a significant increase in load carried by the aortic wall with the inclusion of fibres. The work concludes with suggestions for extensions to include, for example, large strains and nonlinear material models.