Masters Degrees (Mechanical Engineering)

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Accelerated environmental degradation of GRP composite materials.
(2004) Dlamini, Power Madoda.; Von Klemperer, Christopher Julian.; Verijenko, Viktor.
The use of fibre reinforced polymer composites and development of structural composites has expanded rapidly in the Southern African region over the past ten years. The long-term effect of placing these materials outdoors in the Southern African climate is unknown with exposure data for these materials being primarily European and North American based. This study intends to take a broad-based study to the problem of environmental degradation of advanced composite structures. This work is intended to study different degradation mechanisms. Work performed includes: a study of literature on degradation and protective measures; identification of dominant degradation mechanisms; manufacture of specimens; accelerated environmental testing; and an assessment of the effect of the exposure on the chemical properties The goal of this work is to produce information, which can be subsequently used to determine the rate of damage, methods of suitable protection and necessary maintenance intervals for polymer composite components. The approach was: to simulate outdoor exposure within a reduced period of time; to establish correlation of results with actual outdoor exposure; and to determine how the gel coats compare with other protective methods. As part of the objectives of the study (i.e. to assess the durability of polymer matrix composites materials subjected to environmental exposure), an experimental study was carried out to establish the durability of specific gel coats against ultraviolet (DV) and moisture degradation. An investigation of the effectiveness of the various protective measures has begun with a review of selected gel coats available as a protective coating. Laminates with these gel coats have been set up for both accelerated and natural exposure tests. 3000, 2500, 2000, 1600, and 800 hours of accelerated DV exposure tests were performed on polyester GRP laminates with gel coats. No measurable strength loss occurred on protected laminates; there was significant increase in yellowness on un-protected laminates; all protected specimens showed a fair retention of gloss; fibre prominence occurred on unprotected laminates; and the glass transition of samples had dropped from the normal polyester glass transition temperature range.
Aerodynamic modelling and further optimisation of solar powered vehicle.
(2016) Lawrence, Christopher Jon.; Bemont, Clinton Pierre.; Veale, Kirsty Lynn.
Computational fluid dynamics was used to optimise the aerodynamics of a solar powered vehicle via the addition of airflow alteration devices that interact with the boundary layer airflow. These features were designed, manufactured and applied to the vehicle while ensuring that the bulk geometry remained unmodified. The modifications had to be added to the vehicle non-invasively, and had to allow for removal during race conditions. The solar vehicle raced in both the Sasol Solar Challenge (SASC) which took place in September 2014 and the Bridgestone World Solar Challenge (WSC) which took place in September 2015. Aerodynamic drag is the single largest energy loss experienced by a solar vehicle; it is therefore essential that the aerodynamics of these vehicles be highly refined if they are to be competitive. The UKZN solar vehicle placed first in South Africa in the SASC and 13th in the WSC - indisputably outstanding results. The features to be refined were chosen to reduce aerodynamic drag caused by the wheel spokes as well as the canopy due to these being high turbulence zones and having high curvatures respectively. The principles applied were to reduce turbulence caused by the wheel spokes by adding to the wheel geometry, and adding turbulence to the canopy airflow through the use of a technique commonly known as flow tripping. While turbulence caused by the wheels is undesirable, the turbulence added by flow tripping is desirable as it reduces the size of the separated region of airflow behind the canopy, allowing for a net reduction in aerodynamic drag. Wheel geometry alteration was done via the addition of smooth and dimpled covers, so as to mitigate the turbulence caused by the wheel spokes. Many techniques were considered to trip the airflow on the canopy, it was found that vortex generators of specific geometry and dimensions would reduce drag more effectively. Another airflow altering device, a NACA duct, was designed and manufactured. This duct was placed on the canopy to allow airflow into the driver compartment which enabled adherence to race rules and allowed for driver cooling and ventilation. Each wheel cover was manufactured from two layers of carbon fibre to allow a net gain in efficiency with regards to rolling resistance and drag reduction when considering weight added by the wheel covers. The vortex generators and NACA duct were 3-D printed using ABS plastic. The wheel covers and NACA duct were applied to the car for the World Solar Challenge while only the wheel covers were applied for the Sasol Solar Challenge. The vortex generators were not applied due to the efficiency gain from the application being uncertain at the time of the race. A gain in aerodynamic efficiency with the addition of wheel covers to a front wheel was shown through CFD testing. The drag was reduced by approximately 0.5 Newtons (5 %) relating to translational forces and 0.02 Newtons per meter (44 %) percent with regards to rotational forces. The addition of vortex generators resulted in a drag reduction ranging from approximately zero to three percent when considering straight airflow and crosswinds respectively.
Analysis of residual stresses and distortions resulting from multi-pass welding of nozzles to cylindrical pressure vessels.
(2012) Zondi, Mthobisi Clyde.; Adali, Sarp.
The purpose of the present study is to obtain insight into the formation, behaviour and magnitude of welding-induced residual stresses and distortions resulting from welding nozzles onto cylindrical pressure vessels. A hybrid methodology that comprises numerical analysis, experimental measurements and empirical calculations is used in the present study. The welding process induces a high thermal gradient on the material due to non-uniform temperature distribution; thereby causing the portion of the material that is exposed to high temperatures to expand. However, the relatively cooler material portion that is away from the weld pool resists such expansion, thereby subjecting the structure to stresses and distortions around the fusion zone (FZ) and the heat-affected zone (HAZ). Over the last two decades a number of studies have been done in an effort to predict the effect of welding-induced residual stresses on the integrity of welded structures. However, to this end, such studies have focussed on analysing residual stresses on bead-on-plate, plate-to-plate and [to a less extent] on pipe-to-pipe weld joints. Fewer studies have looked at nozzle-cylinder joints of pressure vessels as is the case in this study. The second chapter gives a detailed review of applicable literature. The constitutive model described in the third chapter includes a two-phase sequentially-coupled thermo-mechanical analysis, which incorporates metallurgical effects. The non-linear transient problem is solved using an axisymmetric 2D model with ‘element birth’ technique, developed on ABAQUS. The first phase comprises the thermal analysis based on Goldak’s moving heat source model that is used to determine temperature histories. The second phase is a sequel stress/strain analysis wherein the temperature fields are used as input loads. The results discussed in chapters three and four show that there is a high concentration of residual stresses close to the weld centre-line, and these die down as distance away from centre-line increases. It is also shown that the inside surface is under tensile stresses, while the outer surface is under compressive stress, whose magnitude approaches yield strength of the material. Axial deflections of up to 0.384mm and radial shrinkage of 0.0237mm are observed. Distortion decreases as distance away from weld centre-line increases. Minimum axial shrinkage, which is close to zero, is observed at the restrained end. The analytical results show adequate corroboration and agreement with the experimental measurements. A number of mitigation techniques are suggested in order to alleviate the impact of residual stress and distortions on fatigue performance of welded structures.
An automated apparatus for non-contact inspecting of mass produced custom products.
(2009) Davrajh, Shaniel.; Bright, Glen.
The evolution of the manufacturing industry may be viewed as proceeding from Dedicated Manufacturing Systems (DMS) to Reconfigurable Manufacturing Systems (RMS). Customer requirements change unpredictably, and so DMS are no longer able to meet modern manufacturing requirements. RMS are designed with the focus of providing rapid response to a change in product design, within specified part families. The movement from DMS to RMS facilitates mass-production of custom products. Custom parts require inspection routines that can facilitate variations in product parameters such as dimensions, shape, and throughputs. Quality control and part inspection are key processes in the lifecycle of a product. These processes are able to verify product quality; and can provide essential feedback for enhancing other processes. Mass-producing custom parts requires more complex and frequent quality control and inspection routines, than were implemented previously. Complex, and higher frequencies of inspection negatively impact inspection times, and inherently, production rates. For manufacturers to successfully mass-produce custom parts, processes which can perform complex and varying quality control operations need to be employed. Furthermore, such processes should perform inspections without significantly impacting production rates. A method of reducing the impact of high frequency inspection of customized parts on production rates is needed. This dissertation focuses on the research, design, construction, assembly, and testing of a Non- Contact Automated Inspection System (NCAIS). The NCAIS was focused on performing quality control operations whilst maintaining the maximum production rate of a particular Computer Integrated Manufacturing (CIM) cell. The CIM cell formed part of a research project in the School of Mechanical Engineering, University of KwaZulu-Natal; and was used to simulate mass-production of custom parts. Two methods of maintaining the maximum production rate were explored. The first method was the automated visual inspection of moving custom parts. The second method was to inspect only specified Regions of Interest (ROIs). Mechatronic engineering principles were used to integrate sensor articulation, image acquisition, and image processing systems. A specified maximum production rate was maintained during inspection, without stoppage of parts along the production line occurring. The results obtained may be expanded to specific manufacturing industries.
Automatic calibration of a tool-changing unit for modular reconfigurable machines.
(2011) Collins, James.; Bright, Glen.
Modern trends in customer demand have resulted in the development of a class of manufacturing system known as Reconfigurable Manufacturing Systems (RMS). Reconfigurable systems are designed around the idea that they must be able to be reconfigured in both their production capacity as well as in the machining processes they perform. A subset of the RMS paradigm is a group of machines called Modular Reconfigurable Machines (MRMs). Modular machines are built up from different hardware modules. They offer the user the possibility of only purchasing the required tooling for the specific need at the time. As reconfigurable machines are able to offer flexibility in machining functions, their ability to have easy access to a variety of machine tools would greatly influence their effectiveness and production capacity. This project presents a machine tooling system that would provide MRMs with an efficient way to change tools. A major requirement of the unit was that it should automatically calibrate itself in terms of its position relative to the machine it was servicing. In order for the unit to realize this requirement, it needed a method that would provide it with real-time 3D tracking of the spindle with which it was interacting. Commercially available systems that offer this facility are very costly. A popular gaming controller, the Nintendo Wii remote, was used to provide the tool-changing unit with a very economical real-time 3D tracking capability. This dissertation details the design, implementation and testing of the positioning system for the tool-changing unit.
Autonomous materials handling robot for reconfigurable manufacturing systems.
(2010) Butler, Louwrens Johannes.; Bright, Glen.
The concept of mass producing custom products, though extremely beneficial to the commercial, and retail industries, does come with some limitations. One of these is the occurrence of bottlenecks in the materials handling systems associated with reconfigurable manufacturing systems tasked with achieving the goal of mass customisation manufacturing. This specific problem requires the development of an intervention system for rerouting parts and materials waiting in line, around bottlenecks and/or work flow disruptions, to alternative destinations. Mobile robots can be used for the resolution of bottlenecks, and similar disruptions in work flow, in these situations. Embedding autonomy into mobile robots in a manufacturing environment, releases the higher level production management systems from routing of parts and materials. The principle of the inverted pendulum has recently become popular in mobile robotics applications, and is being implemented in research projects around the world. The use of this principle produces a two-wheeled mobile robot that is able to actively stabilise itself while in operation. The dissertation is focused on the research, design, assembly, testing and validation of a two-wheeled autonomous materials handling robot for application in reconfigurable manufacturing systems. This robot should be dynamically or statically stable during different phases of operation. The mechatronic engineering approach of system integration has been used in this project in order to produce a more reliable robotic system. The application of the inverted pendulum principle requires that a suitable control strategy be formulated. It also necessetates the ues of sensors to track the state of the robot. Control engineering theory was used to develop an optimal control strategy that is robust enough to cope with varying payload characteristics. The Kalman filter is employed as state estimation measure to improve sensor data. For a mobile robot to be deemed autonomous, one of the requirements is that the robot should be able to navigate through its environment without colliding with obstacles in its path, and without human intervention. A navigation system has been designed, through field specific research, to enable this. The robot is also required to communicate with remote computers housing production management systems as well as with mobile robots that form part of the same materials handling system. Performance analysis and testing proves the feasibility of a mobile robot system.
Autonomous mobile materials handling platform architecture for mass customisation.
(2008) Walker, Anthony John.; Bright, Glen.
In order to facilitate the materials handling requirements of production structures configured for Mass Customisation Manufacturing, the design of requisite materials handling and routing systems must encompass new conceptual properties. Materials handling and routing systems with the capacity to support higher-level management systems would allow for mediated task allocation and structured vertical integration of these systems into existing manufacturing execution and management systems. Thus, a global objective in designing a materials handling and routing system, for such production configurations. is to provide a flexible system mechanism with minimal policy on system usage. With the recent developments in mobile robot technologies, due to various advancements in embedded system, computational, and communication infrastructures, mobile robot platforms can be developed that are robust and reliable, with operating structures incorporating bounded autonomy. With the addition of materials handling hardware, autonomous agent architectures, structured communication protocols and robotic software systems, these mobile robot platforms can provide viable solution mechanisms in realising real-time flexible materials handling in production environments facilitating Mass Customisation Manufacturing. This dissertation covers the research and development of a materials handling and routing system implementation architecture, for production environments facilitating Mass Customisation Manufacturing. The materials handling and routing task environment in such production structures is characterised in order to provide a well defined problem space for research purposes. A physical instance of a functional subset of the architecture is constructed consisting of a semi-autonomous mobile robot platform equipped with the infrastructure for materials handling and routing task execution. The architecture orientates the mobile robot platform in such a way as to present a collection of functional units, integrated and configured for a range of applications, and prevents viewpoints in the sense of monolithic mobile robots less susceptible to reconfiguration and stochastic utilisation.
Autonomous sea craft for search and rescue operations : marine vehicle modelling and analysis.
(2011) Onunka, Chiemela.; Bright, Glen.; Stopforth, Riaan.
Marine search and rescue activities have been plagued with the problem of risking the lives of rescuers in rescue operations. With increasing developments in sensor technologies, it became a necessity in the marine search and rescue community to develop an autonomous marine craft to assist in rescue operations. Autonomy of marine craft requires a robust localization technique and process. To apply robust localization to marine craft, GPS technology was used to determine the position of the marine craft at any given point in time. Given that the operational environment of the marine was at open air, river, sea etc. GPS signal was always available to the marine craft as there are no obstructions to GPS signal. Adequate cognizance of the current position and states of an unmanned marine craft was a critical requirement for navigation of an unmanned surface vehicle (USV). The unmanned surface vehicle uses GPS in conjunction with state estimated solution provided by inertial sensors. In the absence of the GPS signal, navigation is resumed with a digital compass and inertial sensors to such a time when the GPS signal becomes accessible. GPS based navigation can be used for an unmanned marine craft with the mathematical modelling of the craft meeting the functional requirements of an unmanned marine craft. A low cost GPS unit was used in conjunction with a low cost inertial measurement unit (IMU) with sonar for obstacle detection. The use of sonar in navigation algorithm of marine craft was aimed at surveillance of the operational environment of the marine craft to detect obstacles on its path of motion. Inertial sensors were used to determine the attitude of the marine craft in motion.
Bio-mechatronic implementation of a portable upper limb rehabilitative exoskeleton.
(2011) Naidu, Dasheek.; Stopforth, Riaan.; Bright, Glen.; Davrajh, Shaniel.
The rationale behind this research originates from the lack of public health care in South Africa. There is an escalation in the number of stroke victims which is a consequence of the increase in hypertension in this urbanising society. This increase results in a growing need for physiotherapists and occupational therapists in this country which is further hindered by the division between urban and rural areas. The exoskeleton device has been formulated to encapsulate methodologies that enable the anthropomorphic integration between a biological and mechatronic limb. The physiotherapeutic mechanism was designed to be portable and adjustable, without limiting the spherical motion and workspace of the human arm. The exoskeleton was portable in the sense that it could be transported geographically and is a complete device allowing for motion in the shoulder, elbow, wrist and hand joints. The avoidance of singularities in the workspace required the implementation of non-orthogonal joints which produces extensive forward kinematics. Traditional geometric or analytical derivations of the inverse kinematics are complicated by the nonorthogonal layout. This hindrance was resolved iteratively via the Damped Least Squares method. The electronic and computer system allowed for professional personnel, such as an occupational therapist or a physiotherapist, to either change an individual joint or a combination of joints angles. A ramp PI controller was established to provide a smooth response in order to simulate the passive therapy motion.
Broadband solar radiometric measurements in the greater Durban area.
(2011) Kunene, Khulisile.; Brooks, Michael John.; Roberts, Lancian Willett.
This work comprises a radiometric study of Durban‟s solar resource, utilizing data from the Howard College campus of the University of KwaZulu-Natal (UKZN), and the Solar Thermal Applications Research Laboratory (STARlab) at Mangosuthu University of Technology (MUT), located 17 km away. The study has three aims: first to establish a solar radiometric monitoring network for the greater Durban area, comprising the UKZN Howard College and Westville stations, and the STARlab facility at MUT. The UKZN Westville station is under refurbishment and should be operational by the end of 2011. Data from this station are not included in the study. The instrumentation and acquisition software in use at Howard College and STARlab are described. The stations record global horizontal irradiance (GHI), direct normal irradiance (DNI) and diffuse horizontal irradiance (DHI), measured by an unshaded pyranometer, a normal incidence pyrheliometer and a pyranometer shaded with a stationary band respectively. Second, to test a number of existing radiometric models against measured data gathered at the stations. Radiometric models assist in estimating missing components of radiation at stations that do not measure all three components separately, for reasons of cost. The models investigated included Erbs et al. (1982), Orgill and Hollands (1977), Reindl et al. (1990), Boland et al. (2001), and Skartveit and Olseth (1987) and correction models by Drummond et al. (1956), Le Baron et al. (1990), Batlles et al. (1995), and Muneer and Zhang (2000) to correct the shadow band effect. Third, to compare data from the two operational stations and to investigate potential spatial differences in sun strength arising from micro-climate effects in the greater Durban area. This takes the form of a statistical analysis of the differences in radiometric data recorded simultaneously at the UKZN and STARlab stations. The study found that the recorded difference in GHI over one year was 0.72%, which lies within the instrument measurement accuracy. Therefore no measurable radiometric differences due to microclimate could be detected and, for the period in which data were collected, measurements from Howard College could be used to estimate irradiance patterns for MUT, and vice versa.
Buckling of short, thin-walled cylinders, as applied to storage tanks.
(2001) Du Poujol, Geraldine Touche.; Bodger, Robert.; Adali, Sarp.
This is an investigation of the buckling characteristics of short, thin-walled cylinders. This study was required as large storage tanks, which were converted from Boating roof to fixed roofed tanks, were found to buckle when severe atmospheric temperature drops and thus pressure differentials occurred. These severe ambient temperature changes are characteristic of the Highveld in South Africa where the tanks in question are situated. Since this modification is an uncommon procedure, codes of practice for storage vessels do not cover this type of cylinder. For the same reason, research performed in this field is limited. Buckling due to axial loading, lateral external pressure, hydrostatic pressure and a combination of axial loading and hydrostatic pressure are explored in this study. To compare with and verify theory, existing research for each case is examined, and the Finite Element Analysis package MSC Nastran used to determine trends. In some cases, to the best of the author's knowledge, no research exists and numerical analysis is performed to establish the relationships present in those cases. The study is extended to include the design of imperfect cylinders, as defined in the tank code AD Merkblatter where it is stated as being dependant on the major and minor diameters of the imperfect section . The study is also extended to the case of variable wall thickness cylinders, where the thickness variation is symmetrical about the axis of the cylinder.
Buckling of woven fibre and graphene platelet reinforced nanocomposite laminates.
(2021) Sewnath, Kiren.; Adali, Sarp.; Drosopoulos, Georgios A.
Composite materials are known for exhibiting high specific stiffness, strength and light weight. Their properties can be optimized by designers for a specific application. They currently have many applications in various industries such as aerospace, automotive and building industries. Fibre reinforced polymer composites are a large portion of the composite material market. The use of such materials has many advantages. Recently, nanosized reinforcements such as carbon nanotubes and graphene nanoplatelets have also been used as filler materials in composites. Graphene is one of the strongest materials available today and exhibits excellent mechanical properties. The study presented here is an investigation into the buckling of a woven glass fibre and graphene nanoplatelet reinforced epoxy composite. A laminate analogy is utilised. The analytical equations governing these types of laminates are presented and incorporated into Matlab, a computer simulation software that makes use of matrix implementations. The programme is then used to investigate the effects of various design parameters on the buckling load, by generating 2D and 3D graphs. In this study, a laminate analogy is used for the woven glass fibres whereby undulation of the fibres is neglected, and the composite is regarded as an assembly of cross-ply laminates with woven fibres orientated at 90° to each other. The Halpin-Tsai equations are used to incorporate the graphene nanoplatelets into the epoxy matrix. The laminate that is investigated consists of 4 plies, each reinforced by woven glass fibres and graphene nanoplatelets. The laminate is symmetric about its midpoint, such that the two outer layers are identical, and the two middle layers are identical. Layer thicknesses are non-uniform and the reinforcements are distributed non-uniformly in the layers. The thickness ratio of the laminate is defined as the ratio of the total width of the outer layers to the entire laminate thickness. The governing equations of classical laminate theory for buckling of a simply-supported rectangular plate under biaxial loading are used to predict the critical buckling load of the laminate. The bending-twisting coupling terms are neglected. The results generated display the influence of various design parameters on the buckling load. The design parameters investigated are the woven glass fibre volume fraction, woven glass fibre orientation, woven glass fibre balancing coefficient, graphene platelet weight fraction, laminate thickness ratio and laminate aspect ratio. The results show that the graphene nanoplatelets have a greater effect on the buckling load than the woven glass fibres. High graphene content can obscure the effect of the woven fibre orientation and laminate aspect ratio on the buckling load. At low graphene contents, a more concentrated fibre distribution in a single direction (warp or weft) is preferred for the buckling load. At higher graphene content, a more evenly balanced distribution is preferred. Furthermore, for high thickness ratios, more focus must be placed in the reinforcements in the outer layer of the laminate for a cost-effective design.
Case study of bird streamer caused transient earth faults on a 275KV transmission grid.
(2001) Taylor, Paul.; Hoch, Derek A.
This thesis discusses the results of an investigation that was initiated in January 1996 to determine the root cause of the increasing fault trend in respect of transient earth faults on the 275 kV transmission grid in KwaZulu-Natal, South Africa. Historically it was thought that the persistently poor performance of this network was caused by pollution faults. This network was reinsulated with silicone composite insulators, and cane fire as well as veld fire management programmes were introduced. These projects did not result in a consistently decreasing fault trend on this 275 kV transmission grid. The burn marks caused by the power arcs, which were identified in this study, appeared to indicate that air gap breakdown was occurring. Birds were also observed in close proximity to the faulted towers. Consequently it was thought that bird streamers caused the transmission line faults. Welded rod bird guards designed to prevent bird streamer faults were installed on eighteen 275 kV transmission lines. The accumulative length of these transmission lines is 932 km. The implementation of this initiative coincided with a 73% reduction in the total number of transient earth faults. This improvement in performance indicates a strong statistical correlation showing that a large number of the transient earth faults on the transmission grid are related to bird streamers. Bird streamer induced faults were identified by means of the following diagnostic techniques: • Burn mark analysis • Time-of-day analysis Bird streamer line faults have been observed on I string, V string and strain jumper assemblies on the 275 kV power lines. However, on the 400 kV power lines bird streamer faults have only been observed on V string assemblies. Experimental work involved simulated bird streamers and determining the minimum flashover distance for AC system voltages. Electric field measurements by means of a capacitive probe were undertaken at the ground plane. The electric field measurements at the ground plane under bird streamer intrusion confirm that if the streamer is moved away from the live tower hardware, the electric field enhancement at the ground plane decreases below the background streamer propagation field. This case study determined that in order to prevent bird streamer faults the bird streamer must be moved away from the live tower hardware. The distance it must be moved is at least 900 mm for 275 kV power lines and 1 100 mm for 400 kV lines.
CFD Modelling and performance evaluation of a forced convection mixed-mode solar grain dryer with a preheater.
(2021) Angula, Johannes Penda.; Inambao, Freddie Liswaniso.
Solar drying of agricultural food products as an art of food preservation has been in existence since the 17th century. In most tropical and subtropical countries, the drying process of harvested agricultural products such as grains is mainly carried out using the method of open-air drying or sun drying to preserve the harvest. With the advances of technology over time, new solar drying methods such as indirect and mixed-mode solar drying are evolving. Mixed-mode solar dryers are among the most efficient solar drying methods for improving the harvest and storage of grains. One of the advances in the development of solar dryers is the use of computational fluid dynamics (CFD) and computer-aided design (CAD) codes to model, simulate, and analyze dryer systems' performance. This study was conducted in two phases. The first phase entailed the use of CAD and CFD codes to model and simulates a forced convection mixed-mode solar grain dryer integrated with a preheater. A 3D model was developed with great accuracy using SolidWorks code and, the CFD simulation was carried out using ANSYS Fluent code. In the second phase, an experiment was conducted using an existing indirect solar dryer which was modified and converted to a mixed-mode solar dryer suitable for the study. The modeling and simulation results were validated against experimental results to evaluate the dryer system' performance. The study was conducted at various airflow speed and preheater temperatures ranging from 0.5 m/s to 2 m/s and 30 ℃ to 40 ℃, respectively. The type of grains used in the experiment were corn grains whereby 72 freshly harvested maize ears/cobs were dried. The study was conducted under the weather conditions of Durban, South Africa, at the University of KwaZulu-Natal. This study aimed to investigate solar drying technologies towards performance enhancement of a forced convection mixed-mode solar grain dryer that incorporated a preheater through modeling and optimization. This approach was followed in order to develop a better understanding of the effects of forced convection and air preheating on airflow distribution and temperature distribution within a solar dryer. The results from both the CFD modeling and experiment were satisfactory, resulting in a correlation with a maximum relative error of 16.3 %. The dryer system's performance results indicated a maximum thermal efficiency of 58.8 % with a corresponding drying rate of 0.0438 kg/hr. The minimum thermal efficiency for the dryer system was 47.7 %, with a corresponding drying rate of 0.0356 kg/hr. The fastest drying time of maize ears was achieved in 4 hours and 34 minutes from an initial moisture content of 24.7 % wb to 12.5 % wb. At the same time, open-sun drying yielded the slowest drying time of 15 hours from an initial moisture content of 27.3 % wb to 12.7 % wb. There was a significant improvement in the dryer system's performance, whose initial efficiency was 36 % when operating as an indirect solar dryer. These results are a clear indication that using a solar dryer system in mixed-mode operation with forced convection and the assistance of a preheater or backup heater can significantly improve drying processes and increase food preservation. The study further presents design concepts of incorporating cost-effective solar thermal energy storage systems that can be implemented to optimize solar dryers. In this case, solar energy can be harvested and stored during peak sunshine hours and made available for usage during off-peak sunshine hours.
Closed-loop throttle control of a hybrid rocket motor.
(2018) Velthuysen, Timothy Johnathan.; Brooks, Michael John.; Pitot de la Beaujardiere, Jean-Francois Philippe.
Hybrid rocket motors produce thrust by reacting a solid fuel with a liquid oxidizer inside a combustion chamber. This approach has certain advantages over conventional solid propellant rockets including improved safety and the potential for thrust control, while also being less expensive than liquid propellant engines. Liquefying hybrid fuels, such as paraffin wax, regress at a faster rate than the conventional solid fuels like HTPB that are dominated by vaporization at the solid-gas interface. Non-classical theory is still in its infancy, however, and more work is required to validate performance models experimentally, especially where throttling of the oxidizer mass flowrate is incorporated. While hybrid motor throttlabilty remains a subject of considerable interest, there has been little investigation of throttling in motors that use high regression rate, liquefying fuels such as paraffin wax. This study proposes a closed-loop thrust control scheme for paraffin wax/nitrous oxide hybrid rocket motors using a low-cost ball valve as the controlling hardware element. There are a number of advantages to throttling hybrid rocket motors but the most important is to enforce a constant thrust curve throughout the burn. A test facility and laboratory scale hybrid rocket motor utilizing paraffin wax as fuel and nitrous oxide as oxidiser were used for experimental testing. Using a mathematical model of a laboratory-scale hybrid rocket motor, the controller constants for a PID controller were obtained and tested through experimental testing. Open-loop testing was first done in order to determine the control authority of the ball valve over the oxidiser mass flowrate, as well as characterize the oxidiser mass flowrate in relation to each valve angle value. Closed-loop testing was undertaken to verify and refine the controller constants obtained via the laboratory-scale model. The tests prompted a redesign of the injector and additions to the LabVIEW™ controller regime. Using results from the open-loop tests a feed-forward lookup table was developed to allow for the controller to move to a specified angle quickly and thereby remove nonlinearities present in flow control using ball valves. Three successful closed-loop tests were done where the controller causes the thrust of the motor to track a predetermined thrust or chamber pressure set point with a reasonable degree of accuracy. The set-point profile of the first test was a constant thrust throughout the burn while the second test had a ramp set-point profile. The final test used chamber pressure as the feedback variable and had a step-down set-point profile. This study demonstrates that thrust control can be exercised over a paraffin wax/nitrous oxide hybrid rocket motor, using a low-cost ball valve as the control element to modulate the oxidiser mass flowrate.
Combustion studies of biodiesel fuel from moringa, jatropha and restaurant oil.
(2016) Onuh, Emmanuel Idoko.; Inambao, Freddie Liswaniso.
Biodiesel is a renewable alternative to finite diesel and, has the capacity to reduce emission and broaden energy access particularly in sub-Saharan Africa where economic growth has been, to some extent, constrained by global warming and a lack of universal access to sustainable source of energy. In the transport sector, a niche exist for biodiesel derived from non-edible feedstock such as waste oil, jatropha and moringa in sub-Saharan Africa. Extraction of oil from jatopha and moringa were achieved via manual as well as soxhlet method using normal hexane, petroleum ether and distilled gasoline. A numerical property prediction scheme was implemented (and validated with experimental data) to obtain the thermo- physical as well as the transport properties of the resulting fuel for the various samples. This prediction scheme reduced the number of experimentation for property determination from nine to one per sample. The pure fuel samples were evaluated in a 3.5kw diesel engine to determine their performance and emissions. The Brake Specific (BS in g/kWh) emissions across the full load spectrum were benchmarked against the United State Environmental Protection Agency (US, EPA) and the European Union (EU) emission caps. This study is a follow-up to an earlier work by Eloka Eboka which focused on the determination of optimal production process for biodiesel using different technique and catalyst. In that work, the engine test was a qualitative evaluation of different mixture ratio forming new hybrids and the engine test protocol did not follow the ISO 8178-4:2006 test cycle categorization nor was the emission benchmarked against the EPA/EU emission caps (both of which were implemented in this study). The extraction results not only confirmed normal hexane solvent and soxhlet method as the optimal means of extraction (with a 37.1% and 51.8% yield for moringa and jatropha respectively) but, gave hint of the potential of distilled Gasoline as a viable solvent (with a 40.2% and 34.1% yield for moringa and jatropha respectively). The validated numerical prediction scheme reduce research cost and time without compromising accuracy. The performance and emission revealed that the Brake specific fuel consumption (BSFC) and brake thermal efficiencies for both diesel and the biodiesels only differ marginally (±4% and ±5 respectively at peak load). Carbon monoxide (CO), unburnt hydrocarbon (UHC) and particulate matter (PM) emissions (in part per million-ppm) showed decreasing trend with load increase and were lower than those of diesel. Oxides of nitrogen (NOX) emission for the biodiesel were lower than those of diesel. The Brake Specific (BS) emission results in comparison to the EU and EPA regulation showed various level of compliance and non-compliance to the emission limits. The result also showed that samples with higher proportion of unsaturated FAME have poorer engine performance and results in higher unwanted emission than saturated FAME. In broad terms, engine retrofitting and novel design could effectively bridge the performance and emission gaps observed between diesel and biodiesel. A multi-blend (saturated and unsaturated FAME) and multi-strategy (Modular kinetic and premix/DI) was recommended as a remediation strategy. For numerical prediction purpose, a 3D CFD with multi zone and detailed chemistryusing KIVA-3V code was proposed.
A comparative study on the effects of internal vs external pressure for a pressure vessel subjected to piping loads at the shell-to-nozzle junction.
(2003) Maharaj, Ashveer.; Adali, Sarp.; Von Klemperer, Christopher Julian.
This investigation seeks to perform a comparative study between the combined effects of internal pressure and piping loads versus external pressure and piping loads on a pressure vessel. There are currently several well-known and widely-used procedures for predicting the stress situation and the structural stability of pressure vessels under internal pressure when external piping loads (due to thermal expansion, weight, pressure, etc.) are applied at the nozzles. This project familiarises one with several international pressure vessel design Codes and standards, including AS ME (American Society of Mechanical Engineers) pressure vessel code sections and WRC (Welding Research Council) bulletins. It has been found that many vessels are designed to operate under normal or steam-out conditions (in vacuum). The combined effect of the external atmospheric pressure and the piping loads at the nozzle could be catastrophic if not addressed properly - especially when the stability of the structure is a crucial consideration, i.e. when buckling is a concern. The above-mentioned codes and standards do not directly address procedures or provide acceptance criteria for external loads during vacuum conditions. The approach to the study was, firstly, to investigate the effects of internal pressure and piping loads at the shell-to-nozzle junction. Theoretical stresses were compared with Finite Element results generated using the software package MSC PATRAN. Finite Element Methods provide a more realistic approach to the design of pressure vessels as compared to theoretical methods. It was necessary to determine if the theoretical procedures currently used were adequate in predicting the structural situation of a pressure vessel. Secondly, the buckling effects of vessels subjected to external atmospheric pressure and piping loads were also investigated. Buckling of the shell-to-nozzle region was explored with the aid of Finite Element software. The results gained were used to develop appropriate procedures for the design of vessels under external atmospheric pressure and piping loads. The design is such that it indicates if buckling will occur at the shell-to-nozzle junction. These design procedures form the basis for future exploration in this regard.
Computational fluid dynamic modelling of baffled open volumetric receiver operation.
(2020) Jo Mathew, Mathew.; Pitot De La Beaujardiere, Jean-Francois Philippe.; Brooks, Michael John.
An Open Volumetric Receiver (OVR) is a type of solar energy receiver that is able to heat atmospheric air volumetrically via a porous absorber exposed to concentrated solar radiation, through which the air flows. OVRs have the potential to attain higher operational efficiency than tubular or cavity type receivers, and they have been extensively investigated for use in concentrating solar power (CSP) plants. In CSP applications, the hot air leaving the OVR is typically passed through a heat recovery steam generator to generate steam for the plant’s steam turbine, after which it is returned to the OVR. Here, it is injected back into the atmosphere near the receiver inlet where some of the warm return air is re-entrained along with fresh air entering it. The amount of air that is re-entrained into the OVR is quantified by the air return ratio, and the higher this ratio, the lower the energy lost from the receiver. One of the factors limiting the operational efficiency of OVRs is fairly poor ARR performance, in the region of 50 % for state-of-the-art OVR designs. This research aims to evaluate the effectiveness of the addition of the vertical air flow baffles in improving the air re-entrained performance of an OVR. The evaluation was carried out numerically using Ansys Fluent Computational Fluid Dynamics (CFD) modelling software. Prior to the core investigation, cold and hot flow validation studies were conducted with respect to a generalized porous absorber and an arrangement of HiTRec-II OVR modules. The corresponding CFD models were successfully validated against experimental data and the methodology used to model the HiTRec-II modules was used to model an arrangement of SolAir OVR modules and modified arrangements incorporating air flow baffles of varying lengths. OVR air re-entrainment performance was evaluated in terms of the module air outlet temperature. The performance of the SolAir modules was evaluated when exposed to wind at varying magnitude and direction. The results from this study were used as a baseline against which the performance predicted for the SolAir modules modified with baffles (of different lengths) could be compared. A comparison of the results indicates that there is a clear increase in mean module air outlet temperature, when air flow baffles are incorporated with the lowest being 2.5 % and highest being 60.7 % increase in the temperature among the wind conditions and baffle lengths investigated for the study. The increase in the temperature also implies an improvement in air re-entrainment and thus OVR efficiency. The results also suggested the existence of an optimal baffle length for the receiver modules, beyond which the air outlet temperature drops and the OVR efficiency deteriorates.
The computational investigation of the wind-induced vibration of overhead conductors.
(2013) Athol-Webb, Avern Malcolm.; Bright, Glen.; Loubser, Richard Clive.
The reliable transmission of high-voltage electricity through overhead electrical conductors is a cornerstone of the modern industrialised world. Any situation or phenomenon that impedes the functioning of this network warrants investigation. An example of which is the occurrence of aeolian vibration. This is caused by airflow over the conductor breaking off into alternating turbulent vortices. These vortices can cause an alternating lift force on the conductor, resulting in unwanted vibrations and damaging fatigue loading. The Vibration Research Testing Centre (V.R.T.C.) of the University of Kwa-Zulu Natal is investigating the effects of this problem experimentally by oscillating an overhead conductor in a test facility. An electrodynamic shaker is used in a frequency and amplitude range equivalent to that produced by measured wind power input. This method is limited because only a single point force input to the conductor is possible as well as the limited span length. The aim of this research was to investigate the effects of aeolian vibrations and to develop a model that can verify the results of the V.R.T.C. This model can also be used to analyse scenarios that cannot be experimentally tested. A mathematical simulation of an overhead conductor subject to various wind power and single point oscillator inputs was developed. The mathematical simulation was performed using the MATLAB computing environment in the form of a finite element model. The model consists of a number of beam elements, arranged linearly to form a cable model, with suitable end conditions and driving inputs. The system was solved using a varying time-step 4th order Runge-Kutta solving method. The results of the model were compared to tests performed at the V.R.T.C. on a sample conductor length.
Condition monitoring of a rotor bearing system.
(2011) Grobler, Herbert Alfred.; Bright, Glen.; Loubser, Richard Clive.
The key objective for this research was to construct an experimental test rig along with a finite element model. Both had to accommodate a certain extent of misalignment and unbalance to provide induced vibrations in the system. Misalignment and unbalance was then varied in magnitude to identify the effect it has on the system. The next variable was the rotor speed and its effects. Finally the experimental and theoretical results were compared and the slight differences have been outlined and described. A rotor supported by two bearings with a disk attached to the middle and a three jaw coupling at the one end was considered for this research. The three jaw coupling consists out of two hub elements with concave jaws and a rubber element that fits in-between the jaws. The rotor-bearing system was subjected to unbalance at the disk and both angular and parallel misalignment at the coupling. Misalignment was achieved by offsetting the centre of rotation of the rotor and the motor shaft. Finite element analysis, along with Lagrange method, was used to model the behaviour of the system. A mathematical model for the three jaw coupling was derived to simulate its behaviour. The second order Lagrange model was reduced to a first order and solved using the Runge-Kutta method. Experimental results were obtained from a test rig and used to validate the theoretical results. Time domain and frequency spectrum were used to display the results.

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