Browsing by Subject "Masters"

Now showing 1 - 5 of 5
  • Thumbnail Image
    Item
    Open Access
    "But I want to teach?": A critical discourse analysis of the 2018 Funza Lushaka Bursary Agreement Form
    (2023) Watson, Carla; Omar, Yunus; Badroodien Nur-Mohammed
    Despite efforts by the government, the quality and retention of teachers in South African schools remain challenges. This minor dissertation explores the discourse(s) in the Funza Lushaka Bursary Agreement Form (NSFAS, 2018) and its impact on bursary holders, including newly qualified teachers. It asks two central research questions: (1) how does this document impact the bursary holders? and (2) to what extent does the discourse(s) it uses exert power over its applicants? The research approach adopted for the study is qualitative. The Funza Lushaka Bursary Agreement Form is analysed using Norman Fairclough's theory of critical discourse analysis and Michel Foucault's theories on embedded power and use of time to demonstrate control. This approach is supplemented by Bigo's (2018) concept of silence and its intended and unintended consequences.
  • No Thumbnail Available
    Item
    Open Access
    Control of Rapid Acceleration in a Planar Legged Robot
    (2023) Mailer, Christopher; Patel, Amir; Govender Reuben
    This thesis details the hardware and control design of Kemba: a planar legged robot intended for investigating bounding and explosive, agile manoeuvres. The robot incorporates both pneumatically actuated knees for powerful, compliant, and impact resistant actuation, and proprioceptive electric actuators at the shoulder and hip for high bandwidth torque control and foot placement. Kemba is capable of bounding at up to 1.7m/s with a full flight phase, jumping just under 1mhigh (2.2 times it's nominal leg length), and accelerating from rest into a top speed bound in only 2 strides and under half a second, demonstrating its agility. Stable bounding and acceleration is achieved using a discrete body oscillation stabiliser, and the more dynamic jumping and somersault motions are generated using offline nonlinear trajectory optimisation. The optimal jumping motion was executed on the physical robot while the somersault is currently still limited to simulation. Due to the unique design and actuator combination, contact implicit trajectory optimisation served as a vital tool for motion identification and controller design. In addition to the robot dynamics and unilateral contact constraints, a more tractable pneumatic actuator model was developed which enabled the numerically stiff, discontinuous air dynamics and discrete valve switching to also be incorporated into the trajectory optimisation formulation. Trajectories resulting from optimisation were accurate enough to be implemented directly on the hardware in the case of the jump motion, and also crucially inform the design of the accelerate from rest controller. The results presented in this work indicate that Kemba is a robust and agile platform, well suited for future work in understanding dynamic manoeuvres and optimal control
  • No Thumbnail Available
    Item
    Open Access
    Investigation of the effect of hydrocarbon spillages and their interaction with alteration minerals on the flotation of UG2 PGE ore
    (2023) Tshinavhe, Thendo Arthur; Becker, Megan; Mcfadzean Belinda
    With growing safety, low productivity and operational cost concerns in the local PGE mining industry, mechanized mining is becoming more frequent to address these challenges and offer easy access to ore bodies compared to conventional mining methods. The heavy-duty machinery used may contaminate the ore because of oil inadvertently leaking from their hydraulic components during mining. Such contaminants have been anecdotally linked to the reduction of downstream flotation performance. Anecdotal evidence suggests that such problems are further exacerbated in the presence of phyllosilicate alteration minerals (serpentine, chlorite and talc) from weathered or altered ores. The near-surface Two Rivers Platinum (TRP) UG2 ore is routinely exposed to hydrocarbon contamination when the underground ore is excavated and transported to surface, resulting in reduced PGE flotation recoveries. Therefore, this study aimed to decouple the effects of oil contaminants on the flotation performance of PGE bearing ores and further establish the interaction mechanism(s) between oil and phyllosilicate alteration minerals. Two ores of varying alteration degrees (normal and altered UG2) were utilized to assess the effects of oil. Batch flotation tests were conducted to decouple the effect of oil on the flotation performance of the two UG2 ores by varying the oil dosage from 0 to 500 g/t, followed by conducting supplementary experiments in which the key interests were on column froth stability, rheology, and oil adsorption tests. These were performed to understand the mechanism(s) leading to the reduced flotation performance. Quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) was utilized to characterize the bulk mineralogy as well as PGM. The bulk mineralogy was validated with quantitative X-ray diffraction (QXRD). The last phase on the study involved using sodium metasilicate (1500 g/t) and a degreaser (500 g/t) as a potential mitigation measure to the deleterious effect of oil on flotation performance. As was expected, the QEMSCAN bulk mineralogy recorded a higher percentage of the phyllosilicate alteration minerals (serpentine, chlorite, and talc) in the altered UG2 (9.1 wt.%) relative to the normal UG2 (6.2 wt.%), consistent with the observations of alteration during sampling. Talc contributed around half of the total phyllosilicate alteration minerals in both ores; however, it was slightly higher in the altered UG2 compared to the normal UG2 (5.8 wt.% versus 3.8 wt.%). Therefore, the altered ore was expected to experience more severe detrimental flotation effects. The results of batch flotation tests indicated a decrease in Pt (~3 g.t) and Pd (~3 g/t) concentrate grades in the normal ore with increasing oil dosage with no significant negative effects on recovery (Pt increased by 4% and Pd was constant). In contrast, the oil resulted in detrimental effects to both Pt and Pd recovery for the altered ore, where a recovery loss of 6% Pt and 12 % Pd were observed. The concentrate grades remained unaffected. The addition of oil increased the froth stability for both ores (34% in the normal ore and 47% in the altered) as well as the pulp viscosity (including pure talc). The increase in viscosity was greater in the altered ore. The oil adsorption study on the two feeds revealed that most of the iv oil coats the particles with no preferential adsorption between the two ores (nearly the same concentration). The oil adsorption study on the concentrate and the tails showed no preferential recovery to either the concentrate or tails in the normal ore whereas more selective recovery of the oil-coated particles to the tails was observed for the altered ore. The observed decrease in grade in the normal ore due to oil contamination was attributed to oil improving the froth stability which caused excess entrainment of gangue materials and thereby diluting the concentrate grade. The decrease in recovery in the altered ore was ascribed to oil forming particle agglomerates (particularly complex talc agglomerates) which increased the pulp viscosity and subsequently resulting in poor gas dispersion and reduced particle-bubble collision. After understanding the mechanisms in each ore, batch flotation with sodium metasilicate and a degreaser were conducted in the presence of oil, as a potential mitigation measure. Sodium metasilicate (SS) improved the grades in the normal ore floats and had no detrimental effect toward the recovery (constant recoveries, no loss in Pt and Pd). For the altered ore, both the grade and recovery (Pt-8% and Pd-5%) were improved by the adding of SS. The effects on the grade were most noticeable at low oil concentration (0 and 300 compared to 500 g/t). For the degreaser, only the flotation experiments with the degreaser were performed due to laboratory technical problems-new flotation cell was used. Thus, there was no comparison with the no degreaser condition. The trends (% difference between 0 g/t and 500 g/t) were compared to the no degreaser (oil only) conditions conducted in the first cell. The degreaser was shown to improve 2E grade and recovery in both ores. However, the improvement in flotation performance was unquantified. The deleterious effects were successfully mitigated when using sodium metasilicate due to its beneficial effects in reducing pulp viscosity as well as improving the froth drainage. With the degreaser, the flotation performance was not quantified. Therefore, this study demonstrated that, SS can be implemented to mitigate the viscous effects caused by oil spillages and alteration minerals (particle agglomeration) in mechanized mines. However, SS should not be implemented blindly as other downstream processes should be considered (settling in the thickener). To implement the degreaser, more tests need to be conducted.
  • No Thumbnail Available
    Item
    Open Access
    The response of a structural target to oblique fragment and blast loading
    (2023) Van Der Merwe, Pierre; Chung Kim Yuen, Steeve; Govender, Reuben; Cloete, Trevor
    An improvised explosive device (IED) can be defined as a homemade bomb which is used to target humans and structures [1]. IEDs commonly have dual damaging effects, a high-pressure blast wave that propagates outwards from the point of detonation as well as blast induced fragments. The blast induced fragments include the casing of the IED and added components to increase its lethality and destructive power. Examples of these added components can include but not limited to nails, pieces of glass, nuts, bolts and ball bearings [2]. Fragments, released upon the detonation of the device, are propelled outwards at high velocities and different directions with devastating effects on structures or human lives. Investigating the fragment effect is vital to develop better protection. Two sets of experiments were undertaken in this study, projectile impact experiments and blast experiments. The impact loading of an IED was investigated by performing projectile impact experiments to infer the average impact velocity of the ball bearing during the blast experiments. Impact loading caused by IEDs is complex and often contains numerous fragments. Typical fragments were simplified to a ball bearing propelled using a two-stage gas gun towards a Domex 700 steel target plate. The velocity of the ball bearing and the orientation angle of the target plate was varied. A numerical study was undertaken to further study oblique impact of a ball bearing on a Domex 700 target plate and to investigate experimental uncertainty. Blast experiments were carried out using a cylindrical charge with an embedded ball bearing representing a simplified IED to investigate the response of a target plate experiencing oblique detonation by varying the angle of the explosive. The mass and geometry of the explosive and the placement of the ball bearings were kept constant. For the projectile impact experiments, it was found that an increase in the target plate orientation angle was associated with a decrease in the maximum deflection experienced by the target plate. In contrast, for the blast experiments, the target plate deflection increased as the orientation angle of the explosive charge increased up to 15°. The effect of the orientation angle of the explosive charge decreases for charge orientation angles larger than 15°.
  • No Thumbnail Available
    Item
    Open Access
    Volcanic skyscapes
    (2025) Pretorius, Pieter Cilliers; Gain, James
    Explosive volcanic eruptions are some of the most visually impressive natural phe-nomena, and are frequently represented in visual media such as films or games, usually with a bespoke, one-off solution. Existing plume models treat the atmo-sphere as a static boundary, while existing atmosphere models are not designed for the extremes present in a plume. We present the first general-purpose model with bi-directional interaction between a volcano plume and the atmosphere. The atmo-sphere is modelled as sparse layers of 2D Eulerian grids, while the plume dynamics are modelled with Lagrangian disks and spheres. We enable the transfer of physi-cal quantities such as ash, moisture, temperature, and wind velocity between these submodels. Volumetric animations are generated through procedural upsampling using noise functions, specifically tuned to the physical processes in play, to create a complete volcanic skyscape. Our model depicts most of the relevant facets arising from plume and atmosphere interactions, such as ash rain, embedded bell, cap, and skirt clouds, shockwave effects, and volcanic lightning.