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- ItemA 10 GHz oversampling delta modulating analogue-to-digital converter implemented with hybrid superconducting digital logic(Stellenbosch : Stellenbosch University, 2001-03) Fourie, Coenrad Johann; Perold, W. J.; De Swardt, J. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: Rapid Single Flux Quantum (RSFQ) logic cells are discussed, and new cells developed. The expected yield of every cell is computed through a Monte Carlo analysis, and where necessary these cells are optimized for use in a complex system. A mathematical study of the Josephson junction and SQUIDs (Superconducting Quantum Interference devices) as switching elements precede a discussion on the operation of RSFQ and COSL (Complementary Output Switching Logic.) These logic families are implemented in low temperature niobium technology, and require liquid helium cooling. A 10 GHz oversampling delta modulating analogue-to-digital converter is then designed and constructed using RSFQ and COSL building blocks in a hybrid configuration. The design emphasis is on devising ways to test the operation of RSFQ with limited equipment. Yield analysis procedures on the complex system are discussed, followed by a detailed discussion on the circuit layout and layout problems. Software routines are developed to calculate the required dimensions of layout structures.
- Item10 kW L-Band planar power combiner(Stellenbosch : University of Stellenbosch, 2006-12) Fourie, Gerhardus Johannes; Van Niekerk, C.; Van der Walt, P. W.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.This thesis relates to the design and characterization of a 10 kW L-band power combiner consisting of 8 input ports. The design is implemented in a non-radial planar transmission line architecture and operates between 1.2 and 1.4 GHz. Because of the ultra high power requirements for the combiner, special attention is given to the power handling capabilities of the transmission lines and the other components involved. Simulated S-parameter models of connector to stripline transitions and a one to four-way junction, as well as measured S-parameter models of high power terminations are incorporated in the final design. A 10 kW combiner was built and measured at low power only due to time constraints and the limited availability of high power sources. Satisfactory results were obtained in terms of the graceful degradation of unit amplifiers, port mismatches and power combining efficiency.
- Item16th INTERNATIONAL CONFERENCE ON HEAT TRANSFER, FLUID MECHANICS AND THERMODYNAMICS: 3D PRINTED MINIATURE COOLER FOR ELECTRONICS THERMAL MANAGEMENT ONLINE, 8 – 10 AUGUST 2022(ASTFE, 2022-08-08) Imtiaz, Nida; Wahid, Mazlan Abdul; Kamaruzaman, Natrah Binti; Ng, Kim Choon; Xu, Ben Bin; Shahzad, Muhammad WakilThe global Central Processing Units (CPUs) are expected to grow at a significant CAGR of 3.6% by 2028. The major factors driving the growth are increasing demand for high processing power CPUs in various applications such as personal computers, servers, and portable computers, among others; growing adoption of enterprise systems that require high-performance CPUs with faster processing speed; and rise in the number of CPU cores per chip over time. However, thermal management is a crucial issue to maintain their performance with increasing processing speed and number of CPU cores per chip. The conventional fans/blowers are unable to maintain required temperature and hence deteriorate CPU performance. We proposed an innovative miniature indirect evaporator cooler for thermal management and local cooling of electronic boards, CPU and Graphics Processing Unit (GPU). In proposed unit, the humidity of supply air is maintained by separating dry and wet channels via thin copper film that also provide good heat transfer properties. Thin water layer is maintained through wick surface in wet channel to extract heat from supply air flowing in dry channel. In order to achieve the objectives and evaluate the performance, miniature indirect evaporator cooler is designed and most of parts are fabricated using 3D printing facility. Extensive experiments are conducted at assorted temperature to map the performance for various electronic units applications. The result shows that the 200mm x 150mm cell with 5 dry and wet channels can achieve up to 40–45Watt cooling capacity. Based on 3D printed modular design, it has flexibility to improve capacity to match application requirements. The proposed miniature cooler can be employed for electronic thermal management and maintain low temperature to enhance their efficiency and improve processing speed.
- ItemA 22.2 GHz Antenna for water vapour radiometry(Stellenbosch : Stellenbosch University, 2019-04) Cerfonteyn, William; De Villiers, D. I. L.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: For this thesis a low-cost antenna solution for a low-cost water vapour radiometry system is designed. The most important specifications for the antenna is that it has to have a -20 dB sidelobe level, a 3° -3 dB beamwidth and have to be electronically steerable. It also has to be low-cost. The first design that is considered is the phased array solution as it can be electronically steered. Since components can be etched onto the design the manufacturing cost is also reduced. The number of elements required for this design to reach the specifications is determined to be more than 16x16 elements, and thus proves to be cost impractical. The analysis is tested by designing a 1x4 and 2x2 multilayered aperture coupled patch antenna array with a corporate feed network, to both test if a better antenna element design can improve the results, and if the analysis is accurate in determining the impracticality of an array design. This also proves that the array design is infeasible. A reflector solution is then considered. The reflector system is designed to statically observe in a few specified directions, removing the need for electronic steering. Two parabolic reflectors and a conical horn is designed. The reflectors are combined through interpolation into one larger reflector. After the horn design proves to be ineffective, a new horn is considered that almost allows the reflector system to meet the specifications. Finally the system is measured, but unfortunately the measured result proves that the physical system does not meet all the specifications. The sidelobe level is around -16 dB, however, the -3 dB beamwidth is well below 3°.
- Item2D Edge-based finite elements for guided and scattered wave problems(Stellenbosch : Stellenbosch University, 1999-03) Hansmann, Riana Helena; Davidson, D. B.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This thesis may be divided into two parts: the first describes the Finite Element Method (FEM) and its application to guided wave problems. The second part is devoted to scattering configurations, specifically the use of the Boundary Element Method (BEM) and the hybrid Finite Element Method-Boundary Element Method (FEM-BEM) to obtain solutions for scattering problems. The formulations are restricted to two dimensions throughout the thesis. A variational formulation is introduced and the implementation of boundary conditions is described. The use of vector approximation functions for the Finite Element Method is explained and the advantages highlighted. The properties of these functions are derived and graphical representations are given. A comparison between a lower order and higher order approximation is made. This is applied to problems which demonstrate the capabilities of the Finite Element Method such as ridged waveguides and circular waveguides containing eccentric dielectric rods. Results obtained compare well to analytic solutions, in the cases where these are available. An integral equation for scattering problems is derived. This relates the tangential field components on a contour enclosing a scattering object to the scattered fields and enables a solution to be obtained when the tangential components on the contour are known. It is shown how the interior region enclosed by the contour is discretised and how the Finite Element Method can be coupled with the Boundary Element Method by imposing continuity conditions on the enclosing contour. The resulting system of equations obtained may be solved. Solutions for scattering from perfectly conducting cylinders are obtained and compare well to analytic results.
- Item2D Modelling of turbulant transport of cohesive sediments in shallow reservoirs(Stellenbosch : University of Stellenbosch, 2006-12) De Villiers, J. W. L.; Basson, G. R.; University of Stellenbosch. Faculty of Engineering. Dept. of Civil Engineering.Modelling of the transport of fine cohesive sediments, as found in most South African reservoirs, has not been well developed. This is because the transport processes that are involved are complex and the theories not as implicit as the traditional equilibrium transport theories for coarse non-cohesive sediment. Advection and dispersion are found to be the processes that best describe the transport of fine sediments in turbulent flow conditions. A two-dimensional modelling tool, MIKE 21C, which simulates reservoir hydrodynamics and cohesive sediment transport processes with an advection-dispersion model, was evaluated in this thesis. The creation of such a numerical model involves the setting up of a suitable curvilinear grid and requires data on the bathymetry, recorded inflows as well as water levels. It also requires sediment characteristic parameters and transport parameters. These parameters have to be specified by the user based on previous studies and field measurement data. MIKE 21C was applied to laboratory flume tests and reservoir case studies in the field in order to determine the effects that these parameters have on the sediment transport in a series of sensitivity studies. Ranges were determined within which these parameter values should fall. A procedure was also developed through which reservoir sedimentation models can be calibrated.
- ItemA 3-axis attitude control system hardware design for a CubeSat(Stellenbosch : Stellenbosch University, 2014-12) Gerber, Jako; Steyn, W. H.; Stellenbosch University. Faculty of Engineering. Department of Electrical and Electronic Engineering.ENGLISH ABSTRACT: With CubeSats becoming popular as a cheap alternative to larger satellites, the need for advanced miniature attitude determination and control systems (ADCS) arises to meet the pointing requirements of satellite operations such as earth imaging and orbit maintenance. This thesis describes the design of a complete ADCS for use on CubeSats. A previously designed CubeSat on-board-computer, CubeComputer, and ne sun and nadir sensor, CubeSense, is incorporated in the design. The remaining requirements with regard to sensors and actuators were met by CubeControl, an additional module, the design, manufacturing and testing of which are described. CubeControl can implement magnetic control with the use of a magnetometer and three magnetorquers. It is also capable of driving three reaction wheels for accurate active 3-axis stabilization.
- Item3-Axis geomagnetic magnetometer system design using superconducting quantum interference devices(Stellenbosch : Stellenbosch University, 2014-04) Kilian, Anton Theo; Fourie, C. J.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: This work discusses the design of a 3-axis Geomagnetometer SQUID System (GSS), in which HTS SQUIDs are used unshielded. The initial GSS installed at SANSA was fully operable, however the LN2 evaporation rate and SQUID orientation required improving. Magnetic shields were also developed in case the SQUIDs would not operate unshielded and to test the system noise with geomagnetic variations removed. To enable removing the double layer shield from the probes while the SQUIDs remain submerged in LN2, the shield was designed to disassemble. The shields proved to be effective, however due to icing the shields could not be removed without removing the SQUIDs from the LN2.
- Item3-D face recognition(Stellenbosch : Stellenbosch University, 1999-12) Eriksson, Anders; Weber, D.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical & Electronic Engineering.ENGLISH ABSTRACT: In recent years face recognition has been a focus of intensive research but has still not achieved its full potential, mainly due to the limited abilities of existing systems to cope with varying pose and illumination. The most popular techniques to overcome this problem are the use of 3-D models or stereo information as this provides a system with the necessary information about the human face to ensure good recognition performance on faces with largely varying poses. In this thesis we present a novel approach to view-invariant face recognition that utilizes stereo information extracted from calibrated stereo image pairs. The method is invariant of scaling, rotation and variations in illumination. For each of the training image pairs a number of facial feature points are located in both images using Gabor wavelets. From this, along with the camera calibration information, a sparse 3-D mesh of the face can be constructed. This mesh is then stored along with the Gabor wavelet coefficients at each feature point, resulting in a model that contains both the geometric information of the face as well as its texture, described by the wavelet coefficients. The recognition is then conducted by filtering the test image pair with a Gabor filter bank, projecting the stored models feature points onto the image pairs and comparing the Gabor coefficients from the filtered image pairs with the ones stored in the model. The fit is optimised by rotating and translating the 3-D mesh. With this method reliable recognition results were obtained on a database with large variations in pose and illumination.
- Item3D printing of eco-friendly concrete incorporating recycled plastic waste (RESIN8) as fine aggregate(Stellenbosch : Stellenbosch University, 2022-12) Oosthuizen, Jandré Daniel; Babafemi, Adewumi John; Walls, Richard Shaun; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH BSTRACTS: Plastic waste is a massive environmental issue worldwide which cannot be solved in a simple manner. Sand being a natural resource is limited in nature in contrast to the abundance of waste plastics in our environment. This study, therefore, investigates the suitability of creating an eco-friendly 3D printable concrete where recycled plastic waste, in the form of Resin8, is incorporated by replacing different percentages of fine aggregates. Replacement values of 5%, 10% and 15% of natural sand by volume are investigated, which are further characterized by varying Resin8 particle sizes. Particle sizes of Resin8 included are sub-5 mm, sub-1 mm and a combination of the two by mixing them by equal proportions (50/50). The concrete incorporating recycled plastic waste (Resin8) was compared to, and tested against a reference concrete mix which is the standard 3DPC mix at Stellenbosch University. Samples of each concrete mix were also mould cast into 160 x 40 x 40 mm prisms from the same concrete mix that were used for printing to investigate the effect the printing process had on the mechanical properties of the concrete. The rheology, slump flow (workability), buildability, air content and density are some of the fresh properties that were investigated. The mechanical properties of the different concrete mixes were investigated by means of flexural (4-point bending) and compression tests. Due to the anisotropic nature of 3DPC, the printed samples were tested in two different directions; D1 and D3. Porosity analysis by means of Computed Tomography (CT) scans were done on printed and cast samples of the reference mix as well as all sub-1 mm Resin8 printed samples to compare and investigate the effect of Resin8 on the microstructure of the printed concrete. Scanning Electron Microscopy (SEM) analysis was conducted on sub-5 mm and sub-1 mm Resin8 particles used in this study, as well as on the 3D printed samples of the reference mix and all replacement percentages of the combination Resin8 mixes after 28 days. All mixes containing Resin8 performed adequately for use in 3DPC based on characterisation of its fresh properties. It was observed that mixes containing Resin8 were more flowable, which has been validated by an increase in slump flow value when compared to the reference mix, while the buildability was negatively affected by the increased flowability. A lower density was obtained as the percentage of Resin8 replacement increased as expected due to the lower relative density of Resin8 compared to sand. Both the flexural and compressive strength decreased as the Resin8 replacement increased. However, an increase in interlayer bond strength was observed in all Resin8 mixes compared to the reference mix, which could possibly be as a result of excess pore water at the interlayer region due to the hydrophobic nature of plastics. The printing process had little effect on the performance of the 3DPC mixes based on similar flexural and compressive strength results achieved for orientation D3 and the mould cast samples, while orientation D1 yielded the best results. Considering the results obtained in this research, the addition of Resin8 into 3D printable concrete is a feasible option and could potentially lead to great reductions of waste plastics in our natural environment even for low replacement volumes.
- Item3D Printing of rapid setting ordinary concrete mixtures(Stellenbosch : Stellenbosch University, 2021-12) Gunzel, Friedhelm Stefan; Combrinck, Riaan; Kruger, Pienaar Jacques; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: In recent years, significant research and development has gone into 3D printed concrete. This construction technique requires no formwork as in ordinary construction projects. The addition of admixtures increases the complexity of 3D printable mixtures in comparison to ordinary concrete mixtures in which cement, water and aggregate are the main constituents. In this study, more ordinary concrete mixtures are used for 3D printing in order to minimise the complexity of 3D printable mixtures. The combination of a more ordinary concrete mixture with the efficiency of 3D printing as a construction technique, combines the benefits of both construction techniques. The aim was to 3D print ordinary concrete mixtures that have improved buildability characteristics due to a rapid setting behaviour. Three types of rapid setting behaviours were tested in this study: false setting, ordinary Portland cement (OPC) cement replacement with belitic calcium sulfoaluminate (BCSA) cement and flash setting. The study was conducted in two phases. The first phase was used to characterise the three rapid setting mixtures. Compressive strength, hydration temperature development, setting time and early age compressive strength were tested for the characterisation. In the second phase, the three rapid setting mechanisms were printed in a 3D printer to determine the buildability of the three rapid setting mechanisms. In addition to buildability, the economic feasibility of the rapid setting mixtures was analysed. It was found that false setting does not significantly influence the mechanical characteristics of concrete. The early age strength gain is not as rapid as for flash setting or with the addition of BCSA cement. Flash setting improves the early ages strength gain of concrete but reduces the long-term compressive strength development. Replacing OPC cement with BCSA cement improves the early age strength gain and does not impact the mechanical properties significantly. Higher cement replacement rates increased the intensity of the rapid setting mechanisms, shorter setting times and higher early age strength was improved. From the buildability study it was found that flash setting has the largest positive impact on the buildability characteristics of 3D printed concrete. The buildability could be increased by 321% with flash setting. OPC cement replacement with BCSA cement resulted in a buildability increase of 214%. False setting was found to be the least effective rapid setting mechanism with a 35% increase in buildability. Flash setting and BCSA replacement are cost effective methods to improve the buildability of 3D printed concrete. False setting is found too expensive to induce and the compressive strength gain at early ages is little compared to the other two rapid setting mechanisms. The aim of this study was achieved by 3D printing rapid setting ordinary concrete mixtures. Significant buildability improvements could be made, and the rapid setting ordinary concrete mixtures are beneficial for the rapid construction of 3D printed components or structures.
- Item3D tracking between satellites using monocular computer vision(Stellenbosch : University of Stellenbosch, 2005-03) Malan, Daniel Francois; Steyn, W. H.; Herbst, B. M.; University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.Visually estimating three-dimensional position, orientation and motion, between an observer and a target, is an important problem in computer vision. Solutions which compute threedimensional movement from two-dimensional intensity images, usually rely on stereoscopic vision. Some research has also been done in systems utilising a single (monocular) camera. This thesis investigates methods for estimating position and pose from monocular image sequences. The intended future application is of visual tracking between satellites flying in close formation. The ideas explored in this thesis build on methods developed for use in camera calibration, and structure from motion (SfM). All these methods rely heavily on the use of different variations of the Kalman Filter. After describing the problem from a mathematical perspective we develop different approaches to solving the estimation problem. The different approaches are successfully tested on simulated as well as real-world image sequences, and their performance analysed.
- Item3D turning analysis of a Bipedal Robot(Stellenbosch : Stellenbosch University, 2022-04) Pretorius, Dean; Fisher, Callen; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: There is stark contrast between the abilities of legged locomotion found in nature, and locomotion found in lab environments. This performance gap is indicative of a large knowledge gap. Roboticists are required to bridge these gaps to truly invite robots to detach from their support rigs, and actuate within the real world. In this thesis, non-planar contact and discontinuous locomotive dynamics were modeled as a trajectory optimization problem. Consequently, this made understanding the complexities of legged locomotion more tractable. Understanding, and being able to leverage, contact is crucial to successful legged locomotion. Therefore, a comprehensive investigation was conducted into non-planar contact dynamics using a monopod robot. Here, methods of modeling the Coulomb friction cone in contact implicit trajectory optimization were implemented. Literature suggests replacing the friction cone with a polyhedral approximation thereof. However, this method is known to underestimate the resultant friction in non-planar environments. This thesis presents a novel method of modeling the 3D friction cone and compares it to an implementation of the polyhedral approximation. Results from this comparison show that the novel method was significantly more computationally efficient than the polyhedral approximation, without underestimating the friction cone. Dynamic bipedal locomotion remains a struggle for most robotic platforms. Robotics literature provides few examples of robots achieving agile, dynamic locomotion. Therefore, trajectories realizing non-planar dynamic bipedal motion were generated. Experiments were conducted into acceleration, steady-state, deceleration, and rapid turning off the sagittal plane. Optimal trajectories displayed the robot walking at speeds resulting in a Froude number less than 0.5, and running at speeds resulting in a higher Froude number. This is consistent with dynamic gaits found in nature. A sliding-mass velocity profile emerged when conducting long-time-horizon trajectories where the robot accelerated from a rest position and decelerated back to rest after completing multiple steps in a periodic steady-state gait. Additionally, when turning off the sagittal plane, slip occurred at least 93.32% of the duration of contact, and turn overshoot is present in all turn trajectories.
- Item3D-feature recogntion from measured data(Department of Industrial Engineering, Stellenbosch University, 1999) Janssens, M.; Van Wijck, W.; Du Preez, N. D.ENGLISH ABSTRACT: This paper presents a method to automatically extract analytical entities like planes, spheres and cylinders from a file containing a cloud of points. The method facilitates the manipulation and reduction of large data sets and the evaluation of it. It can be used as a design tool, a quality control tool, data-processing tool or a data reduction tool. From a database of points, the user can automatically extract a subset of points belonging to an analytical entity of interest, within a predefined but adjustable level of confidence. If necessary, the dimensional parameters of the entity can also be calculated. The method is based on the subtle statistical properties of the least-squares technique that makes it compliant with the strict regulations in the co-ordinate measuring arena. Its robustness guarantees the applicability to less accurate environments than precision engineering.
- ItemA computational architecture for real-time systems(Stellenbosch : Stellenbosch University, 2000-12) Mostert, Sias; Du Plessis, J. J.; Halang, W. A.; Stellenbosch University. Faculty of Engineering. Dept.of Electrical and Electronic Engineering.ENGLISH ABSTRACT: The engineering of dependable real-time systems for mission critical applications is a resource intensive and error prone process. Achieving dependability requires a general consensus on the correctness of a system with regard to its intended function. For a consensus to be achieved, the properties of the system must be well understood which, in turn, requires consensus on a rigorously defined computational architecture. There is currently no single agreed upon computational architecture at the application level which can serve as a common denominator for the design and implementation of real-time systems. It is the thesis of this dissertation that a rigorous computational architecture, applicable from design to implementation, enables engineers to better understand software for real-time systems. To substantiate this claim, the real-time data flow architecture RDF with its notation allowing the description of complete systems from design to implementation will be explored. Four distinct research areas for improving the engineering process of real-time systems are dealt with in the dissertation: 1) the development of an architecture for real-time systems being suitable for design and implementation in software and hardware, 2) the consolidation of a number of graphical languages into a graphical notation for functional specification, design and construction of real-time systems, 3) the development of a simple processor architecture for the execution of real-time applications, and 4) and the evaluation of the architecture in the framework of a microsatellite case study. In particular, the following original contributions are made: 1) the firing semantics of data flow systems are expanded to include disjunctive firing semantics in a novel way in addition to the classical conjunctive firing semantics, 2) the inherent real-time data flow property, Le. that a receiving task must be ready to receive the next incoming message when it is sent, is extended to the synchronous data flow model, 3) a notation for describing all properties of real-time systems is defined 'with the real-time data flow language RDF as base language, 4) two hardware processor architectures are introduced that offer one-to-one correspondence between design and implementation and, thus, reduce the semantic gap between design language and program execution, and 5) the class of systems that can be modelled with data flow architectures is shown to include control systems and data flow systems. The language set and processor architecture were applied to certain aspects of the SUNSAT microsatellite project.
- ItemA concentrating solar power value proposition for South Africa(Energy Research Centre, University of Cape Town, 2013) Gauche, Paul; Von Backstrom, Theodore W.; Brent, Alan C.Concentrating solar power (CSP) offers the potential for a high degree of localization and an alternative strategy to meet electricity demand for South Africa in a future of uncertain conventional resources. The integrated resource plan (IRP) makes strides to introduce renewables to the electricity generation system by 2030, but we argue that the proposed energy mix is too reliant on resources that are not only unsustainable but also at risk in the short to medium term. Coal and other conventional resources may be more limited than originally anticipated, which if true, requires action to be taken soon. CSP is currently the only sustainable and dispatchable energy technology that could domestically supply a significant portion of South Africa’s electricity needs. A balanced mix of PV, wind and CSP can provide the energy supply needed in South Africa, but steps are required soon to take advantage of the localization potential and excellent sustainable energy resources.
- ItemA data and modelling framework for strategic supply chain decision-making in the petro-chemical industry.(Stellenbosch : Stellenbosch University, 2006-12) Van Schalkwyk, Willem Tobias; Bekker, James; Stellenbosch University. Faculty of Engineering. Dept. of Industrial Engineering.ENGLISH ABSTRACT: The research was initiated by an opportunity within the petro-chemical company Sasol to explore, improve and integrate various analytical techniques used in the modelling, design and optimisation of supply chains. Although there is already a strong focus on the use of analytical applications in this environment, the lack of both modelling integration and analytical data availability has led to less than optimal results. This document presents an exploration into the supply chain planning landscape, and in particular strategic planning in the petro-chemical environment. Various modelling methodologies and techniques that support strategic supply chain decision-making are identified, followed by an in-depth analysis of the data requirements for effectively constructing each of these models. Perhaps the biggest hurdle in the continual use of modelling techniques that support strategic supply chain decision-making, remains the extent of the data gathering phase in any such project. Supply chain models are usually developed on an ad hoc project basis, each time requiring extensive data gathering and analysis from transactional data systems. The reason for this is twofold: 1) transactional data are not configured to meet the analytical data requirements of supply chain models, and 2) projects are often done in isolation, resulting in supply chain data that end up in spreadsheets and point solutions. This research proposes an integrated data and modelling framework, that aspires to the sustainable use of supply chain data, and continual use of modelling techniques to support strategic supply chain decision-making. The intent of the framework is twofold: 1) to enable the design of new supply chains, and 2) to ensure a structured approach for capturing historical supply chain activities for continued review and optimisation. At the heart of the framework is the supply chain analytical data repository (SCADR), a database that maintains supply chain structural and managerial information in a controlled data model. The motivation behind developing a database structure for storing supply chain data is that a standard encoding method encourages data sharing among different modelling applications and analysts. In the globalised environment of the 21•t century, companies can no longer ensure its market position solely by its own functional excellence ... in the new economy, whole business ecosystems compete against each other for global survival (Moore, 1996). This motivates the ever-increasing importance of supply chain management, which necessitates the use of advanced analytical tools to assist business leaders in making ever more complex supply chain decisions. It is believed that the integration of information requirements for multiple optimisation/ modelling initiatives in a structured framework (as presented in this research) will enable sustainability and improved strategic decision-making for the petro-chemical supply chain.
- ItemA multi-mode attitude determination and control system for small satellites(Stellenbosch : Stellenbosch University, 1995-12) Steyn, Willem Hermanus; Schoonwinkel, A.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: New advanced control techniques for attitude determination and control of small (micro) satellites are presented. The attitude sensors and actuators on small satellites are limited in accuracy and performance due to physical limitations, e.g. volume, mass and power. To enhance the application of sophisticated payloads such as high resolution imagers within these confinements, a multi-mode control approach is proposed, whereby various optimized controller functions are utilized during the orbital life of the satellite. To keep the satellite's imager and antennas earth pointing with the minimum amount of control effort, a passive gravity gradient boom, active magnetic torquers and a magnetometer are used. A "cross-product" detumbling controller and a robust Kalman filter angular rate estimator are presented for the preboom deployment phase. A fuzzy controller and magnetometer full state extended Kalman filter are presented for libration damping and Z-spin rate control during inactive imager periods. During imaging, when high performance is required, additional fine resolution earth horizon, sun and star sensors plus 3-axis reaction wheels are employed. Full state attitude, rate and disturbance estimation is obtained from a horizon/sun extended Kalman filter. A quaternion feedback reaction wheel controller is presented to point or track a reference attitude during imaging. A near-minimum time, eigenaxis rotational reaction wheel controller for large angular maneuvers. Optimal linear quadratic and minimum energy algorithms to do momentum dumping using magnetic torquers, are presented. A new recursive magnetometer calibration method is designed to enhance the magnetic in-flight measurements. Finally, a software structure is proposed for the future onboard implementation of the multi-mode attitude control system.
- ItemThe absence of a creative focus in the conventional engineering design process : identifying research opportunities to address this(SAIIE, 2016-05) Oosthuizen, Louzanne; Vlok, P. J.ENGLISH ABSTRACT: This paper synthesizes an overview of various models of the engineering design process with an overview of the most relevant theories within the field of creativity studies to conclude that (i) creativity plays a role throughout the engineering design process, and it is possible to incorporate creativity into the engineering design process in a systematic manner; (ii) doing so, at the very least, holds significant potential for economic benefit; and (iii) due to the complex interplay between creativity and the wide range of factors that influence it, organisational climates and management practices cannot simply be assumed to support creativity effectively. It is proposed that organisations be managed proactively to support creativity in engineering design. For this study, a structured literature search protocol was implemented to determine whether there is any evidence in the literature that engineering organisations are being managed proactively with this in mind; none was found. Two opportunities for future research are suggested based on these findings: (i) the development of a framework to guide the proactive management of engineering organisations to support creativity; and (ii) the development of mechanisms for measuring creativity in engineering organisations and engineering design.
- ItemAccelerated testing of an asphalt pavement with the third-scale model mobile load simulator (MMLS3)(Stellenbosch : Stellenbosch University, 2000-12) Walubita, Lubinda F.; Van de Ven, M. F. C.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.ENGLISH ABSTRACT: Accelerated pavement testing (APT) is the application of a wheel loading, to a prototype or actual layered, structural pavement system to determine pavement response and performance under controlled, accelerated accumulation of damage in a compressed time period. It is a tool used for the evaluation of performance of new pavement materials, distress mechanisms, pavement distress, and selection of rehabilitation strategies. In this study, the research work that was done in Jacksboro, Texas (USA) with the third-scale Model Mobile Load Simulator (MMLS3) as part of the APT programme of the Texas Department of Transportation (TxDOT) is presented. The primary objective was to evaluate the performance ofthe different asphalt concrete (AC) materials (Dustrol and Remixer) used on highway US 281, in terms of rutting and distress due to wet trafficking. The other objective was to investigate the difference in rutting between the MMLS3 and the full-scale Texas Mobile Load Simulator (TxMLS). The scope of the study included fieldwork, laboratory work and theoretical analysis. On average, the performance of the layer from the Dustrol process was found to be poorer than that of the Remixer process. The Dustrol process was more susceptible to moisture damage and less resistant to permanent deformation compared to the Remixer process. The MMLS3 and TxMLS permanent deformations in the upper 90 mm surface layers correlated well in terms of the respective vertical stresses imposed by the two APT devices, after allowing for the difference in environmental conditions during trafficking. Overall, the study demonstrated that the MMLS3, used in conjunction with nondestructive field and laboratory testing, is a significant cost-effective APT device that can be used for evaluating the response and performance of the (surface) layers of full-scale, in-service pavements.