Masters Degrees (Mechanical and Mechatronic Engineering)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/781

Browse

Now showing 1 - 20 of 631

Accounting for proof test data in Reliability Based Design Optimization
(Stellenbosch : Stellenbosch University, 2015-03) Ndashimye, Maurice; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Recent studies have shown that considering proof test data in a Reliability Based Design Optimization (RBDO) environment can result in design improvement. Proof testing involves the physical testing of each and every component before it enters into service. Considering the proof test data as part of the RBDO process allows for improvement of the original design, such as weight savings, while preserving high reliability levels. Composite Over-Wrapped Pressure Vessels (COPV) is used as an example application of achieving weight savings while maintaining high reliability levels. COPVs are light structures used to store pressurized fluids in space shuttles, the international space station and other applications where they are maintained at high pressure for extended periods of time. Given that each and every COPV used in spacecraft is proof tested before entering service and any weight savings on a spacecraft results in significant cost savings, this thesis put forward an application of RBDO that accounts for proof test data in the design of a COPV. The method developed in this thesis shows that, while maintaining high levels of reliability, significant weight savings can be achieved by including proof test data in the design process. Also, the method enables a designer to have control over the magnitude of the proof test, making it possible to also design the proof test itself depending on the desired level of reliability for passing the proof test. The implementation of the method is discussed in detail. The evaluation of the reliability was based on the First Order Reliability Method (FORM) supported by Monte Carlo Simulation. Also, the method is implemented in a versatile way that allows the use of analytical as well as numerical (in the form of finite element) models. Results show that additional weight savings can be achieved by the inclusion of proof test data in the design process.
ADHD screening tool: investigating the effectiveness of a tablet-based game with machine learning
(Stellenbosch : Stellenbosch University, 2019-04) Swarts, Romano; Fourie, Pieter Rousseau; Van den Heever, David Jacobus; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: This study investigated the effectiveness of a tablet-based game that incorporated machine learning to screen participants between the ages of six and twelve years for ADHD inattentive subtype. Prior to the design and development of the ADHD screening tool, a thorough investigation of the literature was conducted. Additionally, existing ADHD screening tools and cognitive training tools were identified. This research project implemented lessons learned from the literature, as well as input from medical professionals and the DSM-V diagnostic criteria. The ADHD screening tool presents a patient-testing interface in the form of a tablet-based game with a cloud-based machine learning classifier. The cloud-based classifier is integrated with an algorithm, and together they can discriminate between ADHD and non-ADHD patients with a sensitivity of 100i% and specificity of 87.5i%. The device used for testing was a single, internet connected, commercially available tablet. No additional hardware is required.
Aerodynamic characteristics of a mission-adaptive stealthy air inlet
(Stellenbosch : Stellenbosch University, 2003-12) Marais, Louwrens; Thiart, G. D.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: The aerodynamic performance of a mission-adaptive air inlet for a stealthy unmanned aircraft was examined using CFX 5.5, a commercial Computational Fluid Dynamics package. In order to ensure that the numerical results were reliable, the package was validated against a number of flow situations for which previously-known results exist. This was done for both external and internal flow, and in all cases the conclusion could be made that the code produces realistic results. The simulation of the inlet was done in two steps. A first-order design was simulated using robust simulation parameters: the focus was on obtaining a "picture" of the flow into the inlet, not on the quantitative values of flow variables. On account of the results of these simulations, the design was suitably modified. This second-order design was then simulated using more accurate simulation parameters, and the results analysed in detail. Comparative simulations between the two design iterations showed that their pressure recoveries are similar, but that the distortion of the velocity profile at the engine compressor face is lower for the second-order design than for the first-order design over a significant portion of the operational range. When compared with an idealized theoretical analysis, the numerical results showed that the performance of the inlet was severely degraded at most operating conditions. This is mainly due to the effects of flow separation ahead of the inlet capture plane. To alleviate this problem, recommendations for the modification of the design are proposed. This thesis demonstrates that CFD is a valuable tool for both qualitative and quantitative evaluation of performance during the design process of an air inlet.
Aerodynamic damping of an oscillating fan blade: Numerical fluid structure interaction analysis
(Stellenbosch : Stellenbosch University, 2017-03) Peters, Christian Dietrich; Els, D. N. J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH SUMMARY: The thesis’ main objective is to determine the dynamic ﬂow phenomena that dampen a fan blade’s oscillation amplitude using numerical ﬂuid structure interaction (FSI) simulations. The observed ﬂow eﬀects include the formation and shedding of leading edge vortices, downwash and the added mass eﬀect. Leading edge vortices are a major damping contributor and are dependent on the blade’s eﬀective angle of attack. The aim of the thesis is to ﬁnd a suitable method that is capable of simulating the aerodynamic damping of an axial fan used in an air cooled condenser unit. Therefore, three diﬀerent numerical models are used to perform the FSI simulation and are compared according to their accuracy, robustness and computational cost. The aerodynamic damping of an oscillating fan blade was experimentally investigated by Basson (2015) and his results are used to validate the three numerical models. The three methods used are a mesh-based FSI simulation, a simpliﬁed one dimensional beam model coupled with a heuristic ﬂow model and a meshless FSI simulation. The mesh based and meshless FSI simulations are both suitable for modelling the entire air cooled condenser fan unit, whereas the simpliﬁed 1D beam model is incapable of doing so.
Aerodynamic development of a contra-rotating shrouded rotor system for a UAV
(Stellenbosch : Stellenbosch University, 2015-03) Geldenhuys, Heinrich Jacques; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Unmanned aerial vehicles with vertical take-off and landing capabilities have received extensive attention worldwide in the last decade. Their low detectability, high manoeuvrability in confined spaces, and their capability for out-of-sight operations make them practical solutions for an array of military and civilian missions. The main advantage of shrouded rotors in hover and low speed conditions is the decreased blade tip induced drag when the tip gap is small enough. A well-designed shroud augments the rotor thrust in hover and low axial flight conditions. It also provides noise reduction and safety. A contra-rotating rotor system eliminates the need for separate anti-torque devices, thus producing a smaller footprint and a more compact vehicle. In this study a more efficient coaxial rotor for the ducted coaxial rotor system as published by (Lee 2010) was developed. The first phase of the design process consisted of the selection and numerical analysis of the best suited parent airfoils for the rotors by using XFOIL and XFLR 5. The second phase dealt with the design of a counter-rotating rotor system for the existing cambered shroud as published by (Lee, 2010), using the DFDC-070ES2a two dimensional code, specifically written for ducted rotor optimization. The final phase of the study dealt with the Computational Fluid Dynamic (CFD) verification of the design in ANSYS-CFX 15.07. A comparison between the CFX predictions of the newly designed rotor system and the reference design indicates a 33% improvement in hover thrust at the design power input.
Aerodynamic optimisation of a small-scale wind turbine blade for low windspeed conditions
(Stellenbosch : Stellenbosch University, 2006-12) Cencelli, Nicolette Arnalda; Von Bakstrom, T. W.; Denton, T. S. A.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronical Engineering
ENGLISH ABSTRACT: Wind conditions in South Africa determine the need for a small-scale wind turbine to produce useable power at windspeeds below 7m/s. In this project, a range of windspeeds, within which optimal performance o the wind turbine is expected, was selected. The optimal performance was assessed in terms of the Coefficient of Power(Cp), which rates the turbines blade's ability to extract energy form the avalible wind stream. The optimisation methods employed allowed a means of tackling the multi-variable problem such that the aerodynamic characteristics of the blade were ideal throughout the wind speed range. The design problem was broken down into a two-dimensional optimisaion of the airfoils used at the radial stations, and a three-dimensional optimisation of the geometric features of the wind rotor. by means of blending various standard airfoil profiles, a new profile was created at each radial station. XFOIL was used for the two-dimensional analysis of these airfoils. Three-dimensional optimisn involved representation of the rotor as a simplified model and use of the Blade Element Momentum(BEM) method for analysis. an existimg turbine blade, on which the design specifications were modelled, was further used for comparative purposes throughout the project. The resulting blade design offers substantial improvements on the reference design. The application of optimisation methods has successfully aided the creation of a wind turbine blade with consistent peak performance over a range of design prints.
An affordable robotic-assisted rehabilitation device for the treatment of stroke and spinal cord injury.
(Stellenbosch : Stellenbosch University, 2018-03) Basson, Ariel; Muller, Jacobus Hendrik; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Please refer to full text for abstract
Aiming strategies for small central receiver systems
(Stellenbosch : Stellenbosch University, 2015-03) Grobler, Annemarie; Gauche, Paul; Smit, Willie; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Concentrating solar power as a sustainable energy technology is considered favourable in South Africa due to the high solar resource and the integration possibilities with the current electricity grid. Considering the various concentrating solar power technologies, the central receiver system is thought to be one of the most promising due to its high capacity factor and cost-efficient thermal storage capabilities. These thermal systems are able to reach high temperatures (more than 1000°C have been shown), and to obtain such temperatures, a high solar flux is required. This is achievable by aiming all of the heliostats at the centre of the target. High flux gradients over the receiver surface area and between the outer and inner surfaces of the receiver material can exist. These thermal gradients account for differences in temperatures on the receiver which result in thermal stresses leading to elastic and potentially plastic deformation of the material. To eradicate the thermal stresses, the aim points of the heliostats can be managed such that the flux density distribution over the receiver aperture is decreased and homogenised. The primary objective of this thesis is to develop an aiming strategy specifically for small experimental heliostat fields. To reach this objective, a simulation platform was developed to model any heliostat field and receiver, and an analysis was conducted to compare analytical flux prediction methods to ray tracing. At high incidence angles of between 30° and 60°, the standard deviations of the circular Gaussian flux approximation methods were found to differ between approximately 10 % and 30 % from the ray traced results. A novel method, the Gaussian mixture model, was suggested and deviated less than 4 % from the ray traced results when considering the standard deviation of the flux profile. Two basic aiming strategies were developed using the Tabu search and Genetic algorithm optimisation methods. These two strategies make use of approximate method of flux prediction. Experiments were conducted to investigate static aiming strategies on physical systems and to identify factors that could have an effect on the experimental results. Finally a method of implementing the aiming strategy on a dynamic system was proposed. By implementing both optimisation methods to complement each other, a new aiming strategy was developed that proved to provide better homogenisation of the flux distribution than either of the two methods alone. The accuracy of the final predicted flux distribution was improved by using the Gaussian mixture model as the flux distribution approximation method.
Air turbine design study for a wave energy conversion system
(Stellenbosch : University of Stellenbosch, 2010-03) Ackerman, Paul Henry; Von Backstrom, T. W.; Van Niekerk, J. L.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
Alternative methods of material handling within a reconfigurable manufacturing station.
(Stellenbosch : Stellenbosch University, 2017-03) Deacon, Matthew Marc; Basson, A. H.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: This thesis contributes to evaluating methods of material handling within a reconfigurable manufacturing station, as alternative to a six degree of freedom articulated robot arm. This research follows the design process of formulating the design requirements, considering different concepts and evaluating them, designing a selected concept in detail, validating the concept using test data and then applying the concept to a broader application. A few material handling methods are briefly considered before focusing on the use of a Cartesian robot. Different configurations of a Cartesian robot were considered. As part of the design analysis, a model was developed which allows for the input of various station parameters and provides an estimate of the station’s throughput and cost. This estimation model was implemented in MathCAD and split into two parts: a throughput estimate and a cost estimate. The inputs into the model are the process module configuration and the target kinematics. The model includes load and force calculations for each axis and component selection, as an input to the cost estimate. A control system was developed, based on the PROSA architecture and implemented in C#. The design and implementation of this control system is discussed in this thesis. To be able to validate the research results, a case study is used as an example implementation of the material handling method. However, the design is not limited to the case study, but rather provides a model for any process station with similar transport requirements. The model was validated using a test setup in the Automation Laboratory that uses Festo components. The model therefore only provides for Festo components at this stage, but can easily be expanded upon if other manufacturers are to be considered. After the model was validated, it was applied to the case study, including drive selection, to provide an estimate throughput and cost. These estimates are then compared to previous research that used a six degree of freedom articulated arm robot for a similar case. Other applications, different from the case study, of the model are also discussed.
Analysing the performance of a compressor impeller for a micro gas turbine
(Stellenbosch : Stellenbosch University, 2019-04) Bindeman, Marco; Van der Spuy, S. J.; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: This project sets out to numerically evaluate the performance of micro gas turbine (MGT) compressor impellers and to improve the 1-Dimensional (1-D) mean-line code developed for the in-house analysis of these impellers. The objective for the improvement of the code is to accurately predict the performance of both radial flow and mixed-flow impellers. The possible applications for MGTs are numerous. They find specific application for the propulsion of unmanned aerial vehicles (UAVs). Mixed-flow compressors offer the opportunity to reduce the frontal area of a MGT engine while maintaining a high pressure ratio and ensuring a high thrust-to-weight ratio. The use of mixed-flow impellers in MGTs are thus attractive. Although detailed aerodynamic design is normally based on two- and three-dimensional viscous flow analysis, 1-D analysis with empirical work input and loss models is the basis for most aerodynamic performance analyses. Using 1-D mean-line flow analyses also allows the researcher to analyse multiple geometries in a short time span, while only analysing the best performing geometries with 3-D Computational Fluid Dynamics (CFD). Two areas of the mean-line code were identified for improvement. A new slip factor formulation taking both radial and axial flow components into account was implemented. Secondly, an alternative location for the inter-blade throat area was proposed, considering the area between a main blade and splitter blade, as opposed to the area close to the inducer section which is effectively between the main blades. The code was adapted to calculate the throat parameters for the alternative location and two iterations. of the code were subsequently created. The first employing the new slip factor and the second employing both the new slip factor and an alternative throat location. Three diferent impellers, of which one impeller is a mixed-flow impeller, were analysed using the adapted mean-line code and the results were validated with 3- dimensional CFD. The newly adapted 1-D mean-line code was found to predict the performance of the mixed-flow impeller reasonably well. The mean-line code over predicted both the pressure ratio and isentropic efficiency (total-to-total) by 1.6% and 2.8% respectively, while also predicting a larger operating range. The pressure ratio of the centrifugal impellers was under predicted on average by 15%, while the the isentropic efficiency was predicted within 3%. It was however found that a blade outlet angle of 90 adversely affected the performance prediction of the code.
The analysis and optimization of an axial compressor
(Stellenbosch : Stellenbosch University, 2015-12) Hamman, Richard Alan; Venter, Gerhard; Van der Spuy, Johan; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Axial compressors are widely used in a variety of contexts. When compared to centrifugal compressors, axial compressors offer higher pressure ratios and efficiencies. Due to the complex relationship between blade shape and compressor performance, as well as the sensitivity of axial compressors to massflow rates, the design of an axial compressor is a challenging problem. These design difficulties can be circumvented using numerical design optimization. In this work, meta-model based design optimization (MBDO), a variant of numerical design optimization, is used to develop replacement blades for a low speed axial compressor. Two numerical models were developed: a low fidelity, computationally inexpensive single stage model and a high fidelity, computationally expensive three stage model. For reasons of computational cost, the single stage model was used to evaluate the objective function in the optimization process. An optimized blade design was developed, which delivered a 9:83% increase in pressure coefficient over the original design, when evaluated with the single stage model. This increase was not sustained when evaluating the optimized design with the three stage model. After investigation, the cause was found to be a high incidence angle near the hub and shroud, just outside the range in which incidence angle was constrained in the design problem. To compensate for this, the blade angles were manually adjusted, in order to lower the incidence angle. The adjusted blades delivered an increase of 8:54% over the original design, when evaluated with the three stage model.
The Analysis of an organic rankine cycle for smaller concentrated solar powered systems.
(Stellenbosch : Stellenbosch University, 2018-12) Karsten, Louis; Dinter, Frank; Hoffmann, Jaap; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Small-scale energy consumers (500 kWe – 5 MWe), that are situated in off-grid areas are often left reliant on fossil fuels (like diesel generators) to meet their energy needs. The International Energy Association (IEA) however attempts to decarbonise the entire energy system and has set certain goals for the renewable energy sector. Most renewable energy sources offer only intermitted power solutions for small-scale off-grid applications and storing electrical energy for this scale becomes expensive. Concentrated solar power (CSP) can offer a non-intermitted solution by having the added benefit of thermal energy storage (TES). However, the critical barrier to the widespread usage of small-scale CSP is the lack of optimised and economically competitive technology. Steam Rankine cycles are typically integrated with CSP in large-scale applications but the thermodynamic properties of steam however prohibit water being used as suitable working fluid in lower temperature and lower power output applications. The aim of this thesis is therefore to determine whether the integration of an organic Rankine cycle (ORC), with a smaller CSP system can result in a feasible energy solution for off-grid applications. The first step taken was to determine the technical feasibility of solar integrated organic Rankine cycle (SORC) technology. It was proven feasible by the operation of existing small-scale SORC plants. ORC’s and CSP as separate types of technology are being used in various industries. The integration of CSP with an ORC is however considered an immature technology. A small-scale application in the higher DNI region of South Africa was identified to use as case study. Black Mountain mine near the town Aggeneys was selected by using a multi criteria decision analysis tool. Even though Black Mountain mine is grid-connected, it is still a viable case study to analyse whether an SORC can be a feasible solution for a mine. In proving so, the proposition then exists to use a SORC for future mining developments in off-grid areas. A SORC was theoretically analysed by looking at the solar field, TES and power block separately. The theory developed was then combined to create a model for a SORC. The simulation was conducted on MatLab and the design point was resultantly determined at a plant efficiency of 12.8 % and a turbine inlet pressure and evaporating temperature of 2858.8 kPa and 186 °C respectively. The simulation was then expanded to run over a period of one year and a maximum capacity factor of 83 % was recorded. The lowest achievable levelised cost of electricity (LCOE) was 16.7 $c/kWh at a solar multiple (SM) of 1.7 and TES size of 6 hours. The conclusion was reached that SORC’s are economically competitive with diesel generators but cannot solely meet the required energy demand and must therefore utilise auxiliary energy sources.
Analysis of evaporative coolers and condensers
(Stellenbosch : Stellenbosch University, 1988) Dreyer, Andre Alexis; Erens, P. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: In this report various mathematical models for the thermal evaluation of evaporative coolers and condensers are presented. These models range from the exact model based on the work by Poppe [84P01] to the simplified logarithmic models based on the work of McAdams [54Mcl] and Mizushina et al. [67MI1], [68MI1]. Various computer programs were written to perform rating and selection calculations on cross-flow and counterflow evaporative coolers and condensers. Experimental tests were conducted on a cross-flow evaporative cooler to determine the governing heat and mass transfer coefficients. The experimentally determined coefficients were cqrrelated and these correlations are compared to the existing correlations. The two-phase pressure drop across the tube bundle was also measured and a correlation for two-phase pressure drop across a tube bundle is presented.
Analysis of gearbox loads in large air-cooled condensers.
(Stellenbosch : Stellenbosch University, 2017-03) Lombard, Charles Henry Ochse; Els, Daniel Nicolaas Johannes; Muiyser, Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Operational gearbox loading, in an air-cooled condenser (ACC), is measured and analysed in this investigation. Measurements are recorded during the start, stop and normal operational periods of the gearbox. Interaction between gearbox input and output torsion and bending experienced by the output shaft, are the primary focus of the study. Secondary areas of investigation include gearbox vibration, temperature, shaft speeds and power consumption of the motor. Correlations are also drawn between gearbox loading and wind conditions. Industry has noted that the gearboxes used in the ACC of large coal red power stations, are responsible for most of the unit down-time, which motivated the above mentioned investigation. This investigation is part of a collaboration between Stellenbosch University and various industry partners. The knowledge gained from this study may be used to optimize selection criteria, design of ACC gearbox components, and to improve operation and maintenance information. Previous research has not yet published data that was obtained from the input shaft of such a gearbox, as working conditions complicate this task. A previously developed measurement system is customized to meet the requirements of this investigation. Strain gauges are used to measure torsion on both gearbox shafts as well as bending on the output shaft. The data is transmitted from the rotating shafts by means of radio frequency and it is recorded by using a very specialized data acquisition system. Gearbox shaft speed, vibration and temperature are measured with proximity sensors, accelerometers and a thermal camera. The power supply of the motor is measured with an oscilloscope and current transformers. The data from the various sensors are time synchronized before recording. The accelerometers and the thermal camera were calibrated beforehand, while the same was not possible for the strain gauges. Fundamental strain theory was used to determine the measured torsion and bending on the output shaft. The accuracy of the input shaft measurements are quanti ed by means of nite element analysis, statistical analysis and laboratory testing. Vibration analysis is then also performed on the input shaft to investigate the relationship between temperature and elastic modulus. Firstly, start-up measurements showed that the induction motor draws up to 7:89 times the rated power. During this period, gearbox torque was measured to be roughly four times higher than the operational torque. Secondly, analysis of the normal operational data showed that strain measurement is a ected by shaft temperature, while frequency spectrum analysis proved that torsional vibrations are transferred through the gearbox. Correlations were also drawn between output shaft bending and varying wind conditions. Lastly, stop period measurements were able to show reverse loading of the gearbox, as the fan drives the motor during that period. This study succeeded in acquiring and analysing data from the input shaft of an operational ACC gearbox , which has never been done before. It was also established that absolute strain gauge measurements are not possible without knowing the exact material properties of the test sample.
Analysis of reinforcement designs for specials in steel pipelines.
(Stellenbosch : Stellenbosch University, 2017-03) Barry, Reginald Murray; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering
ENGLISH ABSTRACT: This thesis relates to the analysis of reinforced steel pipe specials (tees and lateral tees) for bulk water pipelines. Pipe specials provide a means of dividing and/or uniting ows. Finite element (FE) analyses are performed to evaluate the, experimentally obtained, American Water Works Association's (AWWA) M11 design model that is commonly used. Modelling considerations are discussed with emphasis on stress-strain behaviour, boundary conditions and geometry. The material non-linear behaviour of steel is described, with emphasis on the selection of suitable numerical analysis tools. The purpose of reinforcements for large diameter steel specials are explained and the types of reinforcements are described in detail. Emphasis is placed on the development of a large number of simulated 45 degree lateral tees. Possible model variations and alternative types of reinforcements are brie y looked at. The development of adjustment parameters for M11 designed reinforcements are discussed, with consideration to the mechanical properties of modern steels. The results of physical testing were used to validate the numerical models developed in this study. The deformed shape of the pressurised test piece used in the validation process corresponds to the numerical model and strain measurements correlate well with simulated strains.
An analysis of the respiratory dynamics of preterm infants
(Stellenbosch : Stellenbosch University, 2019-04) Bester, Maretha; Van den Heever, David Jacobus; Dellimore, K. H.; Joshi, Rohan; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: Poor understanding of preterm infant physiology attributes to the high infant mortality rates, as well as its corresponding financial burden. Prematurity compromises the respiratory and regulatory systems of infants. This manifests itself in characteristic respiratory dynamics consisting of apneas, periodic breathing and regular breathing. These dynamics, if captured, quantified and visualised have potential to track maturational changes in infants. This can aid physicians in the difficult task of assessing a preterm infant’s level of physiological maturity and offer insight into the infant’s regulatory systems. The primary objective of this study was to develop a transition model representing the behaviour of and temporal relationship between the different respiratory states of preterm infants. Secondary objectives consisted of the following: Analysing 2 – 5 s cessations, their contribution to breathing cessation and relationship to apnea; temporally tracking the respiratory stability of preterm infants; and studying the relationship between breathing cessations and heart rate behaviour. Transition models were developed that adequately represented the respiratory dynamics of preterm infants. It showed that respiratory events are related in time, but that periodic breathing rarely precedes apnea of prematurity. On average 9% of breathing cessation and less than 1% of periodic breathing was found in the dataset. It was found that the contribution of short cessations were large, and that there is a temporal periodicity to the percentage cessations in the respiratory signal. Coupling between the respiratory and cardiac systems could be observed, with an apparent common temporal periodicity between some heart rate variability measures and percentage cessation in breathing signal. In conclusion, all objectives were successfully addressed and greater insight was gained into the physiology of preterm infants. Future value exists in applying these analyses on a larger, more longitudinal and clinically annotated dataset.
Analysis, design and manufacturing of solarised gas turbine compressor
(Stellenbosch : Stellenbosch University, 2019-04) Schommarz, Timmo Marc; Von Backstrom, T. W.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering (CRSES)
ENGLISH ABSTRACT: An existing three-dimensional fluid mechanical design of a compressor is reviewed and compared to mean-line simulation results obtained using the Comp- Aero® compressor design code. Mean-line simulation results give a compressor total-to-static pressure ratio of 3.2. The three-dimensional CFD analysis performed using ANSYS CFX® calculates a total-to-static pressure ratio of 3.4. This is an increase of 31% from the pressure ratio of the currently installed compressor (2.6). ANSYS Mechanical® is used to perform finite element analyses for deformation, stress and vibrational behaviour. The maximum calculated axial deflection is 0.24 mm. The calculated maximum equivalent stress is 218 MPa. All vibration modes occur at frequencies higher than the operating speed of the compressor. The first damped frequency occurs at 837 Hz which represents and over-speed condition of 9.24%. Over-speed simulations to 110% operating speed calculate a maximum stress in the impeller of 264 MPa. This is 1.8 times less than the yield strength of Aluminium 7075 which was used to manufacture the part. Axial forces due to the increased outlet pressure of the compressor are calculated. The total load on the angular contact bearing increased from 376 N, as experienced with the old compressor, to 955 N when using the new compressor. The new impeller and diffuser are designed using the Autodesk Inventor® CAD program. The components are machined using five- and three-axis computer-aided milling.
Analytical and a numerical ground resonance analysis of a conventionally articulated main rotor helicopter
(Stellenbosch : University of Stellenbosch, 2007-03) Eckert, Bernd; Van Niekerk, J. L.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
The helicopter is a prime example of a nonlinear multi-body dynamic system that is subjected to numerous forces and motions to which the system must react. When a helicopter, with a conventionally articulated rotor head, is resting on the ground with its rotor spinning, a condition called ground resonance can develop. Ground resonance is a specific self-excited oscillation of the helicopter and is caused by the interaction between the main rotor blades and the fuselage structure. Inertia forces of the blades perform an out-of-phase lagging motion, which reacts with the elastic landing gear of the helicopter. For certain values of the main rotor angular velocity, the frequency of these inertia forces coincides with a natural vibration frequency of the fuselage structure. If this occurs, the inertia forces of the lagging blades produce oscillations of the fuselage, which then further excite the lagging motion of the blades. This interaction is responsible for an instability of conventionally articulated main rotor helicopters, which is called ground resonance. The ground resonance phenomenon is investigated by means of a classical analytical approach in which the ground resonance equations are derived from Euler-Bernoulli beam theory and verified with results in literature. These equations are required to discuss ground resonance stability in further detail and determine the specific regions in which the phenomenon occurs. These results are incorporated in a simplified numerical model using an elastic multiple-body dynamics analysis program called DYMORE to simulate the South African Rooivalk Combat Support Helicopter. DYMORE is a program that offers nonlinear multi-body dynamic analysis code, using the finite element method, which was specifically developed for helicopter modelling. The complexity of helicopter modelling generally requires large amounts of computing power to ensure reasonable processing time. In order to prevent excessive computational time, the numerical model will be simplified in terms of aerodynamic and structural aspects. The scope of the numerical investigation is, therefore, limited to the ground resonance phenomenon without the effect of aerodynamic forces and representing the fuselage as multi-body beam structures of specified stiffness.
Analytical modelling and optimization of a thermal convective microfluidic gyroscope
(Stellenbosch : University of Stellenbosch, 2010-03) Vosloo, Surika; Groenwold, A. A.; University of Stellenbosch. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
ENGLISH ABSTRACT: This thesis deals with the mathematical optimization of the detecting chamber of a thermal convective microfluidic gyroscope and the comparison of several different optimization strategies. An analytical model is developed for the gyroscope and some design considerations are discussed. Sequential approximate optimization strategies are explained and compared to each other by implementing test problems fromthe literature. The optimization problem is formulated from the analytical model and implemented using the different optimization strategies. Results are presented and compared to find the most effective optimization strategy. A sequential approximate optimization algorithm is implemented in MATLAB and tested using the gyroscope design problem and common test problems from the literature. Results and iteration history are compared with an existing FORTRAN implementation.

Browse

Browsing Masters Degrees (Mechanical and Mechatronic Engineering) by browse.metadata.type "Thesis"

Results Per Page

Sort Options