Mechanical Engineering

Permanent URI for this communityhttps://hdl.handle.net/10413/6533

Browse

Now showing 1 - 20 of 218

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 and design optimization of laminated composite structures using symbolic computation.
(1994) Summers, Evan.; Adali, Sarp.; Verijenko, Viktor.
The present study involves the analysis and design optimization of thin and thick laminated composite structures using symbolic computation. The fibre angle and wall thickness of balanced and unbalanced thin composite pressure vessels are optimized subject to a strength criterion in order to maximise internal pressure or minimise weight, and the effects of axial and torsional forces on the optimum design are investigated. Special purpose symbolic computation routines are developed in the C programming language for the transformation of coordinate axes, failure analysis and the calculation of design sensitivities. In the study of thin-walled laminated structures, the analytical expression for the thickness of a laminate under in-plane loading and its sensitivity with respect to the fibre orientation are determined in terms of the fibre orientation using symbolic computation. In the design optimization of thin composite pressure vessels, the computational efficiency of the optimization algorithm is improved via symbolic computation. A new higher-order theory which includes the effects of transverse shear and normal deformation is developed for the analysis of laminated composite plates and shells with transversely isotropic layers. The Mathematica symbolic computation package is employed for obtaining analytical and numerical results on the basis of the higher-order theory. It is observed that these numerical results are in excellent agreement with exact three-dimensional elasticity solutions. The computational efficiency of optimization algorithms is important and therefore special purpose symbolic computation routines are developed in the C programming language for the design optimization of thick laminated structures based on the higher-order theory. Three optimal design problems for thick laminated sandwich plates are considered, namely, the minimum weight, minimum deflection and minimum stress design. In the minimum weight problem, the core thickness and the fibre content of the surface layers are optimally determined by using equations of micromechanics to express the elastic constants. In the minimum deflection problem, the thicknesses of the surface layers are chosen as the design variables. In the minimum stress problem, the relative thicknesses of the layers are computed such that the maximum normal stress will be minimized. It is shown that this design analysis cannot be performed using a classical or shear-deformable theory for the thick panels under consideration due to the substantial effect of normal deformation on the design variables.
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.
Best practice for personnel, material and rock transportation in ultra deep level gold mines.
(2003) Rupprecht, Steven Michael.; Verijenko, Viktor.
Ultra deep mining presents many challenges to the mining engineer, one of which is the logistics to support mining operations quickly and efficiently. Typically, Witwatersrand gold mines operate at depths in excess of 2000 m with stoping taking place to 3500 m and investigations underway to mine to a depth of 5000 m. As mining progresses deeper and further from the shaft, the role of logistics becomes increasingly important if production targets are to be achieved. Access to the workings is often via sub vertical and even tertiary subvertical shaft systems with working faces as far as five kilometers from the shaft. It is inevitable therefore, that distance will negatively impact the working time available at the stope face, material transportation and distribution, as well as the removal of broken ore. Possible solutions to these logistical problems may be found in the use of different transportation systems or by applying sound design and operational principles to transportation systems, both in the horizontal and instope areas. This thesis investigates the challenges of logistics for ultra deep level gold mining in the Witwaterstrand basin for mining layouts planning to mine between 3000 m and 5000 m underground with typical horizontal distances of over 3000 m. The transportation needs analysis recognised that vertical transportation is a wellmanaged and organised system and is mainly the same for both shallow and deep level operations. As a result of this, the thesis only focuses on the logistical issues of the horizontal and in-stope processes. The literature review indicates that the majority of work previously conducted on transportation focused around the area of horizontal transportation with limited inputs to in-stope transportation systems. The review concludes that the traditional locomotive transportation system is the most applicable mode of horizontal transportation. Thus, special emphasis is given to trackbound transportation. An integrated approach is taken towards mine transportation advocating that underground logistics be considered as equally important as any other discipline, Le. rock engineering, ventilation, etc. In addition, the transportation process should consider each area equally important. All to often, the transportation of rock is considered of paramount importance over the transportation of personnel and material. Thus, the planning any transportation system should incorporate personnel, material and rock. To enable this, scheduling, communication and control are important with special attention required for transfer points in the transportation system. As each site has its own particular requirement, thus the final transportation systems must be drawn up based on the specific requirements of each mine. A guideline is proposed for the design of ultra deep level underground transport systems for personnel, material and rock transportation. Thus, providing mining engineers with sufficient information and data to select an appropriate transportation system to meet specific mine requirements. The thesis highlights areas requiring consideration by mine engineers when designing a transportation system from shaft to the working face.
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.
Combustion studies of hybrid nanoadditive doped waste cooking oil biodiesel and its blends in compression ignition engine.
(2021) Maverengo, Hilton.; Inambao, Freddie Liswaniso.
South Africa, among the developing nations in sub-Saharan Africa lacks technologies for converting crude biooil into biodiesel to run fuel CI engines. The country has also struggled to identify a suitable feedstock that can be used for biodiesel production. This research was therefore aimed at analysing the suitability of mixed waste cooking oil (WCO) biodiesel doped with hybrid nano particles as a viable fuel for diesel engines. The utilization of WCO as feedstock for biodiesel is garnering attention since it does not impact on the food supply chain and provides a solution to the challenges associated with its disposal. Biodiesel acceptance has been hampered by three main issues. These are related to higher production costs linked to feedstock, higher nitrogen dioxide emissions, and a lack of economic evaluation of technologies incorporating different alcohols and catalysts. This research performed investigations to develop solutions to circumvent all these challenges. Regarding high feedstock cost, WCO was identified to present an easily available solution since it is acquired at a low cost and its usage helps to solve the disposal problem. Manufacture, assessment, and engine testing of biodiesel from WCO was conducted to evaluate its viability as a potential feedstock for biodiesel. From the derived results, WCO oil has higher oil yields and excellent fuel properties and therefore is a viable feedstock to create biodiesel. Transesterification, a biodiesel creation measure, was performed utilizing methanol and NaOH or KOH as catalysts. This feedstock showed some favourable engine exhaust emission behaviour, but on engine performance considerable shortfalls were noted when evaluated against fossil diesel (FD) fuels. Lower brake thermal efficiency and higher fuel consumption were noted when the neat fuel blends with fossil diesel were tested in two-cylinder compression ignition engines. Higher NOx emissions were also noted with WCO and its blends when evaluated against FD. Three options are available to dealt with the above problems, namely, engine modification, exhaust after-treatment, and fuel reformulation. Fuel reformulation is the most promising due to its easy implementation and cheaper cost. The researcher’s search for the most relevant solution resulted in identification of hybrid nanoparticles consisting of cerium oxide and aluminium oxide as the most appropriate solutions. WCO biodiesel and its blends were doped with nanoparticles and tested in two-cylinder compression ignition (CI) engines and results compared with those of FD. From the experimental analysis, addition of hybridized nano additives improved BTE by a maximum value of 6.22 % compared to FD fuel when evaluated against load. A maximum decrease in BSFC of 10.20 % was noted with hybrid nano fuel WCO20A50C50 compared to FD fuel. A significant reduction in NOX of 25.62 % was found compared to FD. CO, unburnt hydrocarbons (UBHC) and smoke opacity were reduced by 36.8 %, 27.8 % and 17.68 % respectively compared to FD. WCO20A50C50 produced the most superior characteristics of all the fuels tested in this research. To understand the combined impact of hybrid nanoparticles and other engine conditions on performance and emissions, design of experiments (DOE) using the response surface method (RSM) was performed to model and optimize WCO20 performance and emissions parameters. This was accomplished by utilizing a variable compression engine and selecting three variables, namely, hybrid nanoparticle blends (fuel blend), compression ratio (CR) and load as input parameters, while the analyzed responses were brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), nitrogen oxides (NOX), unburnt hydrocarbons (UBHC), carbon monoxide (CO) and smoke. The outcomes from this investigation showed that RSM is a viable technique for improvement of the parameters of biodiesel blends doped with nanoparticles in diesel engines. Considering the intricacy of biodiesel production measures, process development, technical assessment, and advancement of biodiesel according to the entire chain, is fundamental for improving its performance and increasing its global adoption. A detailed biodiesel process flow design was developed and economic assessment incorporating material performed. The designed plant is expected to produce 16.88 tons per annum. The cost of biodiesel was evaluated based on researched cost variables and plant data which resulted in a biodiesel production cost of ZAR10.10 per kg giving a total production cost of ZAR10,100.00 (US$673.33) per ton. A CaO ethanolysis catalysed process was shown to be the most appropriate process for WCO production – the reaction was faster and produced a high yield. South Africa, among the developing nations in sub-Saharan Africa, has a huge capacity to produce its own renewable fuels but at present there is an absence of localized and effective applicable techniques for converting crude bio-oil into biodiesel to run fuel CI engines. Therefore, the discoveries of the present doctoral study are important because they demonstrate that it is viable to convert WCO to biodiesel and that its properties can be enhanced with the addition of nano particles, thereby demonstrating that its performance is even better than that of FD. Furthermore, a more sustainable CaO catalysed ethanolysis, with superior yields and locally produced in comparison to methanolysis, has been effectively developed and evaluated, as per the objectives of the thesis.
Communication, mapping and navigational aspects for a free-ranging, automated guided vehicle.
(1992) Asbury, James.; Katz, Z.
A free-ranging automated guided vehicle incorporating navigation and radio communication for use in a fully automated flexible manufacturing system has been developed. A vehicle, operating as a complete subsystem, was built and tested in an integrated control environment and proved to have promising results. various radio communication techniques are examined and the design and testing of a low cost, wireless, two way communication link is detailed. A novel, flexible infrared navigation technique was developed and incorporated into the AGV subsystem. Path planning and a flexible real time path modification system was formulated using an innovative program with an interpolative visual display unit and digitiser. Data transfer to and from the vehicles in a real time integrated system is covered. System integration for an free-ranging automatic guided vehicle is discussed covering aspects of communication, mapping and navigation. Specific needs for a free-ranging automatic guided vehicle, are presented. The unique design features of navigation and mapping outlined in this thesis has resulted in a low cost, free-ranging, autonomous automatic guided vehicle.

Browse

Browsing Mechanical Engineering by Title