ETD Collection

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Browsing ETD Collection by Faculty "Faculty of Engineering and Built Environment"

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    An exploratory model of water and solute excretion in animals
    (2022) Letts, Robyn
    "What goes in must go out" is the dictum of mass balance, and excretion. All animals need to take in nutrients and excrete excess and waste products; how they achieve this depends on the capacity of their individual excretory systems and their tolerance to survive in a particular environment. Avoiders seek refuge from extreme or highly fluctuating environmental conditions, conformers are able to follow the environment, while regulators keep their internal environment in terms of volume and osmolarity approximately constant. A systems’ analysis of excretion was performed across the animal spectrum. Taking inspiration from comparative biology, a bottom-up, exploratory and indeed, evolutionary approach to modelling was followed where the multiple iterations each represent an increasing level of structural complexity to meet increasing functional constraints, just as in the biology it aims to imitate. Acknowledging that results need to be considered with the high level of abstraction in mind; interest lies in modes of behaviour and signature trends rather than point prediction. Nonetheless, this has led to the emergence of a number of contributions and hypotheses in the field of renal physiology, worthy of further research. It was found that, no matter the complexity of animal being considered, a single continuously-stirred tank satisfactorily provides the core of the model. The mean residence time of the tank alone was found to determine sensitivity of the response to disturbances in water and solute inflow, implying a need for more sophisticated excretory control in a volume- and osmo-regulating animal with a smaller mean residence time compared to that with a higher mean residence time, simply based on size relative to flow. Through similar argument, it is suggested that higher than expected infant drug sensitivity is due to reduced mean residence time when compared with older children and adults, and not necessarily organ immaturity. Simple volume or pressure feedback on the outflow of the tank was found to be sufficient in describing volume regulation at the level of cells; and pressure diuresis and natriuresis in primitive animals such as the hagfish through to long-term arterial pressure control in sophisticated mammals, emphasising its inherent utility. In addition, a possible explanation for the exponential shape of the renal urinary output or renal function curve in humans is suggested. Unintentionally, simply considering increasing regulatory requirements of excretion and iteratively building in requisite structure on the tank outflow, led to the development of a multiple-separator, series-parallel model that has clear analogies with that of differential intrarenal blood flow and nephron heterogeneity as present in the kidneys of birds and mammals, incidentally the only animals able to elucidate concentrated urine. Interestingly, variable flow between parallel separators and distal series water reabsorption have direct renal analogues; i.e. vascular and tubular receptors for antidiuretic hormone, respectively. Similar trends in electrolyte imbalance and volume- and osmo-dysregulation that are exhibited in the syndrome of inappropriate antidiuresis and exercise-associated-hyponatremia were achieved. In addition, a hypothesis regarding the proposed action of loop diuretics was made based on model findings; that a shunt in flow towards the diluting branch of the parallel separator arrangement causes the same trend in volume depletion and electrolyte imbalance (i.e. potassium-losing). In addition, the developed tank-separator-recycle architecture (as present in the kidneys of birds and mammals) provides a mechanism for achieving energetically "passive" urine concentration; i.e. one in which all energy is derived externally from blood pressure. Real-time visualisation of blood flow to cortical and medullary regions of human kidneys under administration of both antidiuretic hormone and a loop diuretic with non-invasive phase-contrast MRI or ultrasound is suggested to provide falsifiability for the proposed contribution of flow redistribution to the urine concentrating mechanism in mammals.
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    The application of dynamic anisotropy in the kriging estimation process to improve resource estimation on a folded and undulating stratiform copper deposit
    (2019) Tembo, Zifa
    This research study was motivated by the geological complexity of Konkola orebody. It is a well-known fact that the geological complexity of an orebody will add to the risk associated with the Mineral Resource estimation of the deposit. In this research report the applicability of Ordinary Kriging with a dynamic search ellipse is investigated on the Konkola copper orebody where traditionally Ordinary Kriging with a fixed global oriented search ellipsoid is applied in the resource estimation. The regional and local geology of the mine was studied including prominent structures that had potential to affect the final estimates. Exploratory Data Analyses were carried out and the orebody was domained into three zones based on grade variation and structural orientation. Variograms, capturing the spatial correlation of the Total Copper % (TCu%), were calculated and modelled for the individual zones, this was followed by a kriging neighbourhood optimisation process. Grade interpolation was done using both the interpolation techniques and the estimate results were compared to the input sample data. An analysis on the financial benefits of adopting Ordinary Kriging with dynamic search was also conducted. This research study concludes that it is beneficial to domain the orebody and to use Ordinary Kriging with a Dynamic Anisotropic search approach for resource estimation and therefore recommends that Konkola Mines adopt this methodology to improve its resource estimation and save costs.
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    Using the dem to relate drop ball tests to semi-autogenous grinding
    (2019) Samukute, Shwarzkopf Oliver
    The Drop Ball Test (DBT) is a common quality control procedure used in many grinding media-manufacturing units to evaluate the quality of manufactured balls by subjecting a sample to an impact fracture test. Whilst DBTs have provided reasonable data over many years, the quantitative comparison of the energy that the balls are subjected to during the DBT and in high impact loading environments such as Semi-Autogenous Grinding (SAG) mills remains a grey area. The Discrete Element Method (DEM) is a numerical technique that can provide a much more detailed description of the grinding media collision behaviour in both DBTs and SAG mills. The DEM allows simulation of the collision behaviour in various systems that involve interaction of many particles. The DEM model applied in this work uses a spring-sliderdashpot to calculate contact forces and the net resultant is used to compute acceleration, velocity and distance moved by the particles by applying Newton’s laws of motion. The objective of this work was to quantify the energy that grinding balls are exposed in both the DBT and SAG environments. Using the DEM, simulations where conducted in both environments to evaluate extent of ball impact loading. The impact energy spectra obtained from the DEM simulation of various ball sizes in the DBT was used to quantify the energy the balls are subjected to. The data showed that larger 125mm steel balls are exposed to relatively higher energy levels and have higher probability of fracture than smaller 115mm and 100mm balls. From the SAG mill simulations, ball trajectories were evaluated to determine the energy that the grinding media is exposed to. Increasing ore:ball ratios showed the extent of ore cushioning and reduction in energy that the balls are exposed to. Using the DBT data and DEM impact energy spectra obtained from both the DBT and SAG simulations, empirical models were developed that attempt to predict ball fracture in the DBT and try to relate ball fracture in the DBT to ball endurance in the SAG environment. A reasonable estimation of the energy that the balls are exposed in both the DBT and SAG mill was achieved. However, establishment of simulation parameters that specifically apply to the material of ball construction is recommended for future studies. From the results analysed, it was concluded that a more accurate determination of simulation parameters of the specific material of construction has the prospect of achieving improved ball fracture predictions