Conference Proceedings (Electrical and Electronic Engineering)
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- ItemAdaptive estimation of speech parameters(IEEE, 1994) Basson, J. A. L.; Du Preez, J. A.Linear predictive coding (LPC), and transformations of it, is currently the most popular way of analysing speech signals. Major limitations of using a frame-based technique are that each frame is analysed in isolation of the rest while assuming the excitation source to be a white noise process. In order to reduce computation time, an all pole model is usually employed. In this project an adaptive algorithm is proposed for speech signal analysis. The algorithm is based on the recursive least squares method with a variable forgetting factor. A pole-zero model is used to estimate the anti-formants present in certain sounds (i.e. nasals and nasalized vowels). This method offers better detection of poles and zeros in stationary environments and faster tracking of pole and zero frequencies in nonstationary signals than other sequential methods. An effective input estimation algorithm eliminates the influence of pitch on the parameter estimates by assuming the input to be a white noise process or a pulse sequence.
- ItemAn adaptive transportation prediction model for the informal public transport sector in Africa(IEEE, 2014-10) Ndibatya, I.; Booysen, Marthinus J.; Quinn, J.The informal public transport sector in Sub-Saharan Africa is responsible for transporting the overwhelming majority of the workforce. Often, passengers have to wait for hours for taxis to coincidentally pass by to pick them up, making the transport mode notoriously inefficient. Despite its relevance and impact, the sector is afforded little attention in terms of regulation, development and organization, giving rise to a complex and inefficient system that affects millions of people. In fact, little is known about the industry. To advance understanding of this system, minibus taxis were equipped with tracking devices in this study. Tracking data was then used to develop a model that describes the transport network – essentially finding patterns in the apparent chaos for the potential benefit of its users. The adaptive model uses unsupervised learning to predict the informal stages in the city and provide travelers with intelligence on the best time and place to get transport, thereby reducing the waiting time at the taxi rank and the informal roadside stops. Experimental results show 70.4% model accuracy in dynamically learning the taxi behavior and accurately predicting the best places to get taxis at a given time of the day.
- ItemAnalytical prediction of rotor eddy current loss due to stator slotting in PM machines(IEEE Xplore, 2001-08) Wills, Dominic A.; Kamper, Maarten J.Certain types of PM electric machines are particularly susceptible to the proliferation of eddy currents flowing within the solid conducting regions in the rotor. These eddy currents can be induced by current winding harmonics, but also by the interaction of the static rotor magnetic field with the permeance variation of the slotted stator known as ‘slotting’. This work focuses on the analytical calculation of eddy current loss that occurs in the conducting regions within a rotor under no-load conditions. The results are compared with finite element analysis and measured results from a machine test. Good agreement is achieved between the three methods of comparison.
- ItemAutomated landing of an intelligent unmanned aerial vehicle in crosswind conditions using total energy control(2014-12-10) Le Roux, C. T.; Engelbrecht, J. A. A.ENGLISH ABSTRACT: This paper presents the development, implementation and verification of a flight control system for the automated landing of an intelligent unmanned aerial vehicle (UAV) in crosswind conditions. There is an increasing number of commercial opportunities for UAVs in business, agriculture, industry and mining, the emergency services and security services. The major barrier to commercialisation of UAVs is the certification process, where automated take-off and landing is a key feature required. The automated landing system presented in this paper uses a longitudinal control system based on the total energy control system (TECS), and a lateral control system that combines a heading and guidance controller with a cross-track error controller. A software state machine is used to advance the flight control system through the different stages of the automated landing. The TECS architecture allows the airspeed and flight path angle to be decoupled, while the Cross-Track Controller uses a limited integrator to drive the cross-track error to zero in the presence of crosswind. The automated landing system is implemented on a UAV with an on-board computer, sensors and actuators, and is verified in simulation and with practical flight tests. The hardware simulation results show that the UAV is able to land autonomously in crosswinds up to 3.6 metres per second, with a landing accuracy of 3.50 metre in-track and 0.12 metre cross-track.
- ItemBalancing runtime space- and time complexity in synthetic database driven hand posture reconstruction systems(PRASA, 2010-11) De Villiers, H. A. C.; Niesler, T. R.; Van Zijl, L.Hand posture reconstruction systems based on large databases of synthetically rendered images of a 3D hand model offer a simple and flexible means of exploiting domain knowledge to provide training data. Such systems may also be applied to other domains in the posture reconstruction field by changing the model under consideration. Typically, the index structures used to answer similarity queries at runtime explicitly contain the prerendered feature data. However, the combinatorial explosion resulting from the multiple degrees of freedom available to the human hand severely limits the complexity of feature data that may be embedded into the index structure. The system presented in this paper exploits real-time objectspace rendering techniques to rebalance the preprocessing and runtime workloads such that the space complexity of the database relative to the number of degrees of freedom is greatly reduced. A prototype of the database subsystem is implemented and its properties investigated to obtain insight into its scaling behaviour.
- ItemA comparison of Quad-tree and Voronoi-based spatial partitioning for dynamic load balancing(2014-12) Van Greunen, M.; Engelbrecht, H. A.ENGLISH ABSTRACT: Massively multi-user virtual environments (MMVEs) face scalability challenges, one being the large number of concurrent users interacting in the virtual environment (VE). Spatial partitioning addresses this problem by distributing partitions of the VE, and their associated users, to separate servers. Users dynamically migrate between partitions as they move within the VE and server load imbalances occur when users flock to popular locations (such as cities or boss arenas). Dynamic Load Balancing can be achieved by dynamically scaling the VE partitions and migrating users to underloaded servers. In this paper, we assume an MMVE has load balancing and focus on comparing two spatial partitioning methods, namely Quad-trees and Voronoi diagrams, using OverSim, an extension of the OMNeT++ simulation package. We evaluate each approach using the number of messages sent between servers, the distribution of users across servers and the number of servers in use as performance metrics. We conclude that a Voronoi based system is better in distributing the load across multiple servers, but has a greater computational cost than a Quad-tree based system.
- ItemA comparison of simple low-power wedge-type X-band waveguide absorbing load implementations(IEEE, 2007-11) Stander, T.; Van der Walt, P. W.; Meyer, P.; Steyn, W.Two inexpensive waveguide absorbing loads are constructed and measured, each using a single thin resistive sheet absorber supported by styrofoam walls, and 50mm in length. It is found that a V-cut wedge displays less reflection than a tapered wedge, with -30 dB reflection across a band 8.5 - 12.4 GHz.
- ItemContemporary wind generators(Energy Research Centre, 2015) Akuru, Udochukwu Bola; Kamper, Maarten J.It is believed that wind energy is growing at a very rapid rate, especially in the last few years. When compared with other sources of renewable energy in the energy portfolio, it becomes evident that the bulk is wind energy-based. However, there are some backlogs to full manifestation of this technology ranging from initial high cost to performance and reliability issues, among others. But in spite of these bottlenecks, new research trends have been assertive in seeking out a sustainable solution for harnessing wind energy for power generation -especially in the design and construction of wind generators. In order to motivate and prime a sustainable energy mix among stakeholders, this paper is a shot at appraising the theory of these innovative wind generators towards ecological sustainability, economy, efficiency, and employment creation.
- ItemDecarbonising South Africa’s paratransit with hydrogen: a simulated case study(2023-07-10) Abraham CJ; Zenner T; Booysen MJ; Rix AJAs fuel prices climb and the global automotive sector migrates to more sustainable vehicle technologies, the future of South Africa’s minibus taxis is in flux. The authors’ previous research has found that battery electric technology struggles to meet all the mobility requirements of minibus taxis. They investigate the technical feasibility of powering taxis with hydrogen fuel cells instead. The following results are projected using a custom-built simulator, and tracking data of taxis based in Stellenbosch, South Africa. Each taxi requires around 12 kg of hydrogen gas per day to travel an average distance of 360 km. 465 kWh of electricity, or 860 m2 of solar panels, would electrolyse the required green hydrogen. An economic analysis was conducted on the capital and operational expenses of a system of ten hydrogen taxis and an electrolysis plant. Such a pilot project requires a minimum investment of € 3.8 million (R 75 million), for a 20 year period. Although such a small scale roll-out is technically feasible and would meet taxis’ performance requirements, the investment cost is too high, making it financially unfeasible. They conclude that a large scale solution would need to be investigated to improve financial feasibility; however, South Africa’s limited electrical generation capacity poses a threat to its technical feasibility. The simulator is uploaded at: https://gitlab.com/eputs/ev-fleet-sim-fcv-model.
- ItemDesign and development of a satellite based water resources monitoring system(2014-12) Mafukidze, Harry; Wolhuter, RiianENGLISH ABSTRACT: The Faculty of Forestry and Woodscience at Stellenbosch University has a requirement to monitor and record water resources and environmental data at remote sites, not within reach of any mobile services. The current solution consists of a standalone data logger based monitoring system. This system, however, is not ideal as it does not provide data in real time and has high costs and other problems servicing the particular sites. This paper presents an alternative satellite based WSN (Wireless Sensor Network) solution to this problem. The system described in this paper comprises a WSN with a three-part framework. The first part consists of sensor nodes monitoring rainfall, air temperature, air humidity, ambient light, wind speed, wind direction, soil temperature and soil moisture. Communication from these nodes to the central gateway is based in the wireless ISM band. The second part contains an Iridium satellite communications module, a gateway with a Linux based SBC (Single Board Computer) for collecting, storing and sending data from sensor nodes and forwarding such data via the SBD (Short Burst Data) satellite messaging service. The third part consists of the MS (Master Station), which is used for displaying sensory and site information. The system is solar powered and measurements indicate that the system meets an overall standby time of at least three days, as stated in the project requirements. It has been tested continuously in an actual deployment situation and is performing well. This new satellite based monitoring system is certainly an improvement and a reliable alternative to the one used up to now.
- ItemEvaluation of the energy model of a horizontally-mounted electric water heater through internal temperature measurement(Institute of Electrical and Electronics Engineers, 2017) Leeuwner, L. L.; Naude, N. H.; Roux, M.; Booysen, M. J.The resource-constraint energy sector faces an insatiable demand for energy, which necessitates improvements in efficiency. One key sector that has potential for savings is residential water heating, which makes up 32% of household energy. Previous studies have proven that with effective scheduling up to 29% savings can be achieved for a nominal consumption pattern. The model that was used to estimate the savings, calculates the energy usage for a given hot water consumption pattern and given heating schedule for a horizontally mounted water heater. This two-node model is used to aid user-informed scheduling and auto- scheduling, but was developed as a black-box model, validating the energy and not the internal temperatures, which could be misleading. This paper evaluates the accuracy of the model by performing temperature measurements inside the horizontal electric water heater. Moreover, two aspects neglected by the model are investigated: The node state transfer usage threshold, and the inter-nodal thermal resistance. The results show that the model significantly underestimates the stratification that occurs naturally. This underestimation also severely affects the modelled energy consumption and hides limitations of the model, preferring a lower threshold and higher inter-nodal resistance. The results also show that Legionella growth in the EWH could be a concern despite a high set point.
- ItemICT-enabled solutions for smart management of water supply in Africa(2014-12) Nel, P. J. C.; Booysen, Marthinus J.; Van der Merwe, B.ENGLISH ABSTRACT: Pervasive and ubiquitous technologies that include mobile device applications, machine to machine communications, and cloud computing, are increasingly used for cost-effective data aggregation and information dissemination. Recently, this trend has started to gain momentum in the water sector and is being used for various management and monitoring tasks, such as remote leakage detection, automated meter reading and enhanced usage feedback to water users. This paper analyses the challenges faced by various stakeholders (consumers, utilities, etc.) in the water supply industry. Application of the said technologies is then proposed to address these unique challenges and the varying data needs of all stakeholders. An example solution, with a mobile device application and supporting cloud computing solution, is developed and presented as a proof-of-concept to further illustrate the potential use of ICT for water supply management.
- ItemThe impact of average speed over distance (ASOD) systems on speeding patterns along the R61(2014-12-10) Ebot Eno Akpa, N. A.; Booysen, Marthinus J.; Sinclair, M.ENGLISH ABSTRACT: Speeding is considered to be a major contributing cause of road fatalities in Sub-Saharan Africa and South Africa in particular. The minibus taxi industry is a vibrant yet partly informal sector of public transport in South Africa, which has been associated with speed-related road fatalities. Although countermeasures have been implemented to address speeding, they have not led to significant reduction in road fatalities and adherence to legal speed limits. Among the countermeasures deployed on some highways is the Average Speed Over Distance (ASOD) system which uses cameras to enforce speed limits. In this paper, historical probe data is used to evaluate the impact of the ASOD system on speed profiles of passenger vehicles. The data also consists of speed, time and location information gathered by navigation and fleet management devices that were installed in minibus taxis. The evaluation is based on spatial differentiation (the impact on the enforcement site with ASOD versus the control site without ASOD) and time differentiation (the impact before and during ASOD enforcement). For passenger vehicles, the results show that the presence of ASOD systems caused a reduction in mean speeds and ensured compliance with speed limits at enforcement and control sites. On the other hand, the system appears to have no influence on minibus taxis, with high, yet similar average speeds measured in the enforcement and control sites during ASOD enforcement.
- ItemInformal public transport -- Safety measures(2014-07) Zeeman, A. S.; Booysen, Marthinus J.The informal transport industry in Sub-Saharan Africa is notoriously dangerous, leading to many fatalities annually. This paper presents an innovative way of monitoring driver behaviour, in real-time, by taking into account road design standards and vehicle dynamics. A theoretical model is presented that combines acceleration and speed data into an erratic driving detection algorithm. The model presents a novel use of commonly used civil engineering principles, used in road design. Evaluation of the models, using actual minibus taxi data, demonstrates that it successfully detect reckless driving. An online platform is presented to visualise the tracked vehicle and the driving behaviour.
- ItemAn intelligent water heater with wi-fi access to support demand-side management(2015-01) Brown, J. W. K.; Booysen, Marthinus J.In the current climate of energy shortages and attempts to reduce electricity consumption, demand-side management has proven to be effective and popular. One implementation of demand-side management has been to provide the end-user with control over the ubiquitous houshold water heater (called geysers in South Africa). This paper presents a novel way to interact with water heaters, in which water heater control and monitoring is provided on a website that is accessible through a Wi-Fi hotspot interface. Both of these are hosted by the processor that controls electricity supply, tank temperature, and water supply; and monitors electricity consumption, water consumption, inlet, outlet and tank temperatures. The proposed system also provides protection against inevitable mechanical failure of the water heater, by detecting leaks and bursts, and by stopping water and electricity supply in such scenarios. This paper shows that the proof of concept is realisable in terms of cost, functionality, and energy savings.
- ItemModelling of inter-stop minibus taxi movements : using machine learning and network theory(2014-12) Ndibatya, Innocent; Booysen, Marthinus J.ENGLISH ABSTRACT: Minibus taxis provide affordable alternative transport for the majority of urban working population in Sub- Saharan Africa. Often, these taxis do not follow predefined routes in their endeavours to look for passengers. Frequently, they stop by roadsides to pick up passengers and sometimes go off the main route in an attempt to fill the taxi with passengers to make the trip profitable. In addition, the destinations are changed from time to time depending on the driver. This uncoordinated movement creates a web of confusion to would-be passengers. The key aspects that are not clear to the passengers include; where to get a taxi, the waiting time and the travel time to the destination. These conditions leave taxi passengers at a very big disadvantage. In this research, we applied the concepts of machine learning and network theory to model the movements of taxis between stops. The model can be used to compute the waiting times at the stops and the travel times to a specified destination. Twelve minibus taxis were tracked for 6 months. Density-based clustering was used to discover the formal and informal taxi stops, which were modelled into a flow network with the significant stops as nodes and the frequency of departures between nodes as edges representing the strength of connectivity. A data driven model was developed. From the model, we can predict the time a passenger will have to wait at a stop in order to get a taxi and the trip duration.
- ItemMonte-Carlo Tree Search Parallelisation for Computer Go(ACM Publishers, NY, USA, 2012) Van Niekerk, Francois; Kroon, R. Steve; van Rooyen, Gert-Jan; Inggs, Cornelia P.ENGLISH ABSTRACT: Parallelisation of computationally expensive algorithms, such as Monte-Carlo Tree Search (MCTS), has become increasingly important in order to increase algorithm performance by making use of commonplace parallel hardware. Oakfoam, an MCTS-based Computer Go player, was extended to support parallel processing on multi-core and cluster systems. This was done using tree parallelisation for multi-core systems and root parallelisation for cluster systems. Multi-core parallelisation scaled linearly on the tested hardware on 9x9 and 19x19 boards when using the virtual loss modi cation. Cluster parallelisation showed poor results on 9x9 boards, but scaled well on 19x19 boards, where it achieved a four-node ideal strength increase on eight nodes. Due to this work, Oakfoam is currently one of only two open-source MCTS-based Computer Go players with cluster parallelisation, and the only one using the Message Passing Interface (MPI) standard.
- ItemNumerical calculation on iron and pulsation losses on induction machines with open stator slots(2007) Germishuizen J. J.; Jockel, A.; Kamper M. J.Pulsation losses, which are very difficult to measure, are present in every squirrel cage induction motor and depend mainly on the geometrical design. This paper primarily deals with the question whether these losses can be calculated by means of numerical methods. For this purpose two induction motors that only differ in the slot design are measured at no- and full-load and compared with the computed results.
- ItemPerformance evaluation of a centrifugal pump system under variable speed operation(SAIEE, 2013) Kuhn, C.; Randewijk, P. J.ENGLISH ABSTRACT: The aim of this research project investigates the performance of a centrifugal pump system under variable speed operation. Operating a pump under variable speed operation brings the affinity laws into play. These equations were firstly investigated before it was applied to the overall investigation of pump performance. Distinction is made between three types of systems, a system with high static head (lift system), the second system is a high loss system with no- or little static head and the third is a mixed type system. The “correct” affinity laws were then used to apply to a system with a minimum pressure requirement. The theory proved accurate and was confirmed by practical findings. It has been found that both the pump and the VSD experience a slight drop in efficiency for small changes in speed. A maximum of 5% drop occurred in the efficiency of the pump for a 30% reduction in speed. Further reductions in speed resulted in a more rapid drop in efficiency.
- ItemPresentation of a home automation solution with potential for seamless integration and vast expansion(2014-12) Sawyer, G.; Booysen, M. J.ENGLISH ABSTRACT: The ever-increasing existence of electronic systems and devices within the residential environment, along with the human desire to simplify life and daily routine, is generating increased interest in the field of Home Automation and intelligent environments. A large variety of HA solutions have been conceptualised or developed. However, many of these solutions are designed by experts and therefore require professionals to install and/or operate them. Furthermore they lack the potential for seamless integration into an already functioning home environment. This paper presents a HA solution with seamless integration potential. The system can be installed and configured without professional skills or physical alteration of the environment itself. There is also large potential for the expansion of the systems capabilities and functions due to the hardware and software platforms utilised. This paper concludes with an analysis of performance tests results, and a discussion of the potential avenues for expansion.