Faculty of Engineering and Built Environment
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Item An investigation into the development of a portable, ultrasonic, density measuring instrument(1987) Hulse, Nigel Douglas; Stewart, A. B.In the gold mining industry, one of the significant physical properties of the mineral slurry is its density and it is important to be able to measure this parameter in most processes. There are many techniques for determining the density of fluids, but because of the hostile, abrasive nature of mineral slurry, very few of these are suitable, This dissertation describes the deveiopment, construction and testing of a portable, ultrasonic, density measuring instrument. The instrument uses an ultrasonic transducer as the primary measuring element, and system operation is based on the fact that the driving impedance of the transducer varies with changes in the physical properties, and hence the characteristic impedance, of the surrounding medium into which the ultrasonic energy is being transferred. The technique may a-Lao be used to measure the relative concentrations of two liquids in a mixture or emulsion, provided that the characteristic impedances of the liquids are sufficiently dissimilar. The electronic circuitry is fairly straightforward, consisting essentially of an oscillator, driving circuit for the transducer and a voltage monitor to provide a d.c. voltage proportional to the impedance of the transducer, and hence to the density of the surrounding medium. Most of the research has been concentrated on the probe design, as the type of transducer, the type and thickness of facing material and the method of construction all contribute to the sensitivity of the instrument. A design of probe assembly has been developed that may be used for both slurry density measurement and the measurement of the ratio of aqueous to organic liquids in emulsion.Item The design of digital signal processing electronics for a steel wire ropetesting instrument(1989) Nair, Dhavan; Scott, R. W.This thesis describes the design work undertaken at the Anglo American Electronics Laboratory to implement an electronic instrumentation system to evaluate the condition of steel wire ropes.Item The development of a hand-held direction finder(1990) Atkinson, John Kevin; Shearer, M. S.This dissertation is primarily concerned with the design in development and performance of a hand-held radio direction finderItem A study to assess the energy savings potential in the ocean going trawler 'Roxana Bank'(1990) Fiddler, David Michael; Gowans, B.; Calder, P.Increasing fuel prices have forced marine engineers and diesel engine manufacturers to look at methods of. reducing fuel consumption without a loss in output power. Engineers are always Investigating the following points: (1) decreasing the specific fuel consumption (2) enabling engines to use worse fuels ... (3) extending part load capability (4) using as much waste heat as possible. The sources of heat loss are investigated and the design of an efficient heat recovery system has been evaluated for Ideal temperature and heat conditions. after taking lnto consideration the various methods of heat recovery that are possible on the fishing trawler MFV Roxana Bank. Sources of heat loss identified by engine manufacturers are found primarily in engine cooling water and exhaust systems. These methods are investigated and extra heat transfer systems have become apparent. The use of exhaust gas boilers in diesel engine installations has become widespread as there is always a demand for heating services regardless of vessel type. The predominant form of heat transfer on the Roxana Bank is by forced convection and fluids must always remain in a turbulent state when passing through heat exchange apparatus. The introduction to heat exchangers shows that a high degree of turbulence in both primary and secondary fluids will the overall heat transfer coefficient and also reduce fouling. The design parameters of the heat recovery systems discussed as suitable for the Roxana Bank require the existing cooling water system to be scrapped and a fresh water system with one central cooler to be designed with a high temperature and a low temperature circuit together with a variable speed pump arrangement. should be fitted with such central cooling systems for a number of reasons. The central cooler system Is discussed In detail and it is shown that existing ships and/or new buildings The heat recovery system requires a certain degree of automation to prevent undercooling of the main engine systems and to maintain set Inlet and outlet temperatures to makers specifications. After attending the Roxana Bank on the 09/10 November 1989, the monitored operati~g parameters show a marked deviation to the Ideal temperatures, particularly In the cylinder cooling water circuit ... temperatures. The adverse effects these deviations have on the heat recovery and combined engine load fluctuations found on the Roxana Bank show that steady state heat recovery Is difficult to achieve on this particular type of vessel. Through calculation it Is shown that the envisaged steam turbine alternator is not practical due to the combination of low feed water inlet temperatures to the boiler and insufficient driving steam. The consequence of the reduction in electrical load on the power take off alternators have on the exhaust gas mass flow rates due to reduced engine load are also discussed. A brief mention is also made of organic fluid and thermal oil systems as a form heat recovery and possibilities for efficient heat transfer using these systems. ii Recommendations are made to Irvin and Johnson with regards to a centralised cooling system and the benefits that can be realised with regard to more efficient heat exchanger operations, but that heat recovery on the Roxana Bank from the proposed sources is not a viable proposition.Item Preaging techniques as a means of stabilising thermoelectric drift in nickel-chromium/nickel-aluminium thermocouples for use in an aluminium heat treating furnace(1991) Hart, Roderick William Wenham; Smuts, D. J.This dissertation is primarily concerned with investigating and improving the degree of accuracy and precision that may be achieved from temperat~re measurements made utilising nickel-chromium/nickel-aluminium (Type K) thermocouples. The practice of heat treating extruded aluminium section creates specific metallurgical properties within section. Development of specialised aluminium alloys has necessitated the use of treatment temperatures,- close to the limit beyond which the alloy experiences undesirable, permanent, metallurgical change. This situation has demanded urgent attention to, in quality assurance terms, the, 'fitness for purpose', of primary temperature sensors. The most established of these sensors, the Type thermocouple, has known problems relating to calibration stability and drift. The substantial amount of furnace control instrumentation and cabling dedicated to measurement from Type K sensors precludes the simple conversion to an alternate sensor type. The more practical option of applying calibration correction factors to existing measuring systems is only feasible if sensor stability characteristics permit measurement traceability to' be established within required uncertainty limits.Item Factors affecting brinelling and its detection in cylindrical roller element bearings(1992) Smith, Brian Holman; Rae, G. J.; Coertze, Dirk J.Brinelling exists ID two fonns, namely true brinelling and false brinelling. Bearing damage due to false brinelling is a common problem and is known to occur on powerstations in Eskom.An example of false brinelling has recently been identified on the ejector pump motors at I.ethabo Pow'er station. True brinelling does not pose a problemto Eskom,and has therefore not been included in this study False brinelling is a special form of fretting and is found to occur in stationary roller element bearings subject to vibration. The vibration creates load fluctuations and varying degrees of relative motion within the bearings. As a result, small depressions or flutes are fonned in the race (Plate 1.1) which eventually lead to increased operational vibration and premature bearing failures. Previous studies do not makeany reference to factors affecting false brinelling in horizontally mounted bearings. The need for a better understanding of false brinelling has increased with the cold storage and partial cold storage of under utilized powerstations. This investigation approachesthe problemof false brinelling froma new angle. Horizontally mountedbearings have been used for testing as opposed to vertically mountedbearings used by other researchers. The effects of static bearing load, impedance,vibration amplitude and direction on false brinelling have been investigated. The study has shown that bearing impedanceand load do not have a significant influence on the rate of bearing damage,while vibrationItem Stress evaluation of a monolithic refractory concrete rotary calciner lining for Tioxide Southern Africa(1993) Ilbury, M. W.; Stone, Nigel A.; Coertze, Dirk J.Item The construction, development and evaluation of a portable ferro- precipitator(1994) Sunjka, Ivan; Coertze, Dirk J.; Rawlins, MarkThis dissertation is concerned with the construction of the locally developed Ferro-precipitator which can be utilised outside a laboratory environment. The American developed Ferrograph machine, besides being expensive (R42 000 + GST in 1984), can only be used inside a dust free, temperature controlled room. As lubricants in machinery moving parts play an important role in their performance and durability many methods of evaluating the health of machines have been devised, but none by themselves can give a complete picture of what is happening inside the machine. Various methods of oil analysis have been studied in this dissertation for comparison and/or complementary purposes, so as to establish the role of the Ferro-precipitator in the context mentioned. Spectrometric, Debris and Radio Tracer methods are based on quantitative aspects of wear particle analysis, whereas the Magnetic Plug method shows visibly large wear particles in the very high wear pattern range. A further aspect to consider is the fact that the Spectrometric analysis method, which is the most common and comprehensive method available in South Africa, is laboratory orientated. This means that an oil sample has to be taken from a machine and then sent to a laboatory for analysis. Besides being time consuming from the time the samples are taken to the time when the results are known, the Spectrometric analysis method is also very expensive. The Ferro-precipitator that has been developed, is sensitive to particle size and to the rate at which these particles are generated. This is due to the phenomenon that a varying magnetic field strength will attract different size ferrous particles accordingly. This concept was validated by manufacturing ferrous particles of various sizes, firstly by grinding and secondly by sieving. These particles, in both cases, were passed through the Ferro-precipitator in a medium of oil, and graphs of density versus distance along the slide were plotted. The graphs showed distinct variations between particle sizes. The manufactured particles were also statistically evaluated by establishing the correlation between the machined and/or the sieved particles to the optically measured particles. The sensitivity of the Ferro-precipitator was further demonstrated by comparing results obtained from an engine test carried out under controlled conditions using the Spectrometric method. If developed further, the Ferro-precipitator .could, be used in the field, which would eliminate the time lost due to samples being sent ot a laboratory. Also the cost of the machine would be a fraction of the price of the Ferrograph and/or the Spectrometer. An in-depth study of particle morphology can be carried out on the wear particles deposited on the slide, with the aid of a Scanning Electron microscope using its X-Ray attachment. The potential for such a study was demonstrated on the engine test performed for this dissertation.Item Controlling the feedrate of material from a vibratory pipe conveyor using an electro-magnetic vibrator and load cell system(1994) Janse van Vuuren, Gary Peter; Eitelberg, E.This work presents a novel way of controlling the feed rate of raw material from a vibratory pipe feeder system. The system consists of a hopper, feeder pipe, electromechanical vibrator and a loadcell which measures the mass of the complete system. Raw material is gravity fed onto the vibrating pipe whose amplitude of vibration controls the amount of material fed.Item Development of an interface monitor to operate over a data transmission line(1994) Crankshaw, Brett Robert; Bajic, Vladimir B.; Galbraith, Bruce G.One of the telecommunication facilities provided by Telkom S.A. is connection to the National and International X.25 data network. This network follows the international data protocol standard based upon the CCITT Recommendation X.25. The network allows data calls to be made from the X.25 user in very much the same fashion as a caller on the Public Switched Telephone Network (PSTN), in that the caller must specify the number of the called user on the network in order to be connected. It is in this environment, specifically in the testing and maintaining of these data circuits, that this study is based.Item An investigation into exterior illumination of buildings(1995) Wimbush, J. C.; Martins, M."The nature of light is only describable by enumerating its properties and founding them on the simplest possible principles. As these principles transcend our ordinary experiences, they must be cast in a purely logical, that is to say, mathematical form. But that is never enough, for, though logic tells us what deductions must be right, it does not tell us what will be interesting, and so gives no guidance as to the direction the theory will take. In choosing this direction, much help is derived from analogies and models which are often loose and incomplete but without which no proper understanding of the subject can be acquired. We shall, therefore, describe, largely by means of analogies, the behaviour of light and this is the 'real' nature of light. "Item Cost effective electrical reticulation of the rural areas in Transkei at the district of Lady Frere (Nkolonga)(1995) Booi, Bongani Mpumelelo; Khumalo, J.The purpose of this study is to investigate the most cost effective way of electrifying rural areas in the Transkei concentrating in the district of Lady Frere. One Administrative Area (A.A) was used for research. Questionnaires were send to people of this area where a like rat format was followed. For the purpose of this study, 20 families were randomly selected for investigation.Item Optimal design of symmetric angle-ply laminates subject to nonuniform buckling loads and in-plane restraints(Elsevier, 1996) Walker, Mark; Adali, Sarp; Verijenko, Viktor E.Optimal buckling designs of symmetrically laminated rectangular plates under in-plane uniaxial loads" which have a nonuniform distribution along the edges are presented. In particular, point loads, partial uniJorm loads and nonuniform loads" are considered in addition to uniform O' distributed inplane loads" which provide the benchmark solutions. Poisson's effect is" taken into account when in-plane restraints are present along the unloaded edges. Restraints give rise to in-plane loads" at unloaded edges which lead to biaxial loading, and may cause premature instability. The laminate behaviour with respect to fiber orientation changes significantly in the presence of Poisson's eJfi, ct as compared to that o/'a laminate where this" ~Jfect is neglected. This change in behaviour has significant implications Jor design optimisation as the optimal values of design variables with or without restraints differ substantially. In the present study, the design objective is" the maximisation of the uniaxial buckling load by optimally determining the fiber orientations. The )qnite element method, coupled with an optimisation routine, is employed in analysing and optimising the laminates. Numerical results are given for a number of boundary conditions and fi)r uniJormly and non-uniformly distributed buckling loads.Item Optimization of symmetric laminates for maximum buckling load including the effects of bending-twisting coupling(Elsevier, 1996) Walker, Mark; Adali, Sarp; Verijenko, Viktor E.Finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates subjected to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximization of the biaxial buckling load by determining the fibre orientations optimally, with the effects of bending-twisting coupling taken into account. The finite element method coupled with an optimization routine is employed in analysing and optimizing the laminated plate designs. The effects of boundary conditions, the number of layers and bending-twisting coupling on the optimal ply angles and the buckling load are numerically studied.Item Multiobjective optimization of laminated plates for maximum prebuckling, buckling and postbuckling strength using continuous and discrete ply angles(Elsevier., 1996) Adali, Sarp; Walker, Mark; Verijenko, Viktor E.The optimal design of uniaxially loaded laminated plates subject to elastic in-plane restraints along the unloaded edges are given for a maximum combination of prebuckling stiffness, postbuckling stiffness and buckling load. The results are also obtained for biaxially loaded plates without elastic restraints. The method of solution involves defining a design index comprising a weighted average of the objective functions and identifying candidate configurations which have to be optimized and compared to determine the best stacking sequence. This multiobjective approach leads to improved prebuckling, buckling and postbuckling performance. A similar approach is adopted in the case of discrete ply angles with the provision that these angles can only take predefined values. From a manufacturing viewpoint, using only certain fibre orientations such as 0, ± 45 and 90 ° is advantageous and cost-effective. The multiobjective design results are compared to single objective ones, and the effect of various problem parameters on the optimal designs are numerically studied. It is observed that the resulting trade-off among the different objectives are not severe leading to well-balanced laminates with regard to the range of loads they are required to carry. A comparison of continuous and discrete optimization indicates that both designs lead to comparable load carrying capacity, with regard to different objectivesItem Optimal design of symmetrically laminated plates for maximum buckling temperature(Taylor & Francis, 1997) Walker, Mark; Reiss, Talmon; Adali, Sarp; Verijenko, Viktor E.The optimal designs of laminated plates subject to nonuniform temperature distributions are givenfor maximum bucklingtemperature. The method ofsolution involves the finite element method based on Mindlin plate theory and numerical optimization: A computational approach is developed that involves successive stages of solution for temperature distribution, buckling temperature, and optimalfiber angle. Three different temperature loadingsare consideredand various combinations of simply supported and clamped boundary conditionsare studied. The effectofplate aspectratioon the optimal fiber angle and the maximum buckling temperature is investigated. The influence of bending-twisting coupling on the optimum design is studied by considering plates with an increasing number of layers.Item Hierarchical identification of large-scale system models(1997) Jankovic, Boris R.; Bajic, Vladimir B.In this study we propose a new concept and methodology of hierarchical identification. The need for such a methodology comes from the fact that identification of large-scale systems (LSSs) by one-shot approach may be numerically very complex. The analysis of LSSs is, in general, not approached by the one-shot methodologies normally associated with non-LSSs. The proposed method of hierarchical identification can be therefore viewed as an extension of LSS methodologies to system identification. LSS methodology aims at breaking up the initial, complex problem into a set of smaller size subproblems.Item Optimal design of symmetrically laminated plates for minimum deflection and weight(Elsevier, 1997) Walker, Mark; Reiss, Talmon; Adali, SarpThe minimum deflection and weight designs of laminated composite plates are given. The finite element method using Mindlin plate theory is used in conjunction with optimisation routines in order to obtain the optimal designs. Various boundary conditions are considered and results are given for varying aspect ratios and for different loading types. Comparative results are presented for minimum weight priority design as an alternative to minimum deflection/minimum weight priority design to investigate the effect of priority on the deflection and weight.Item An investigation into the feasibility of the use of an electrostatic technique for the measurement of mass flow rate of pneumatically conveyed solids(1997) Hole, Evan D.; Bajic, Vladimir B.This report details the findings of work carried out over the course of 1994 and 1995 to determine if it is feasible to use an electrostatic technique for the measurement of mass flow rate of pneumatically conveyed solids. This includes results from tests done on a flow rig and at various power stations.Item Design of a non-linear analog PID controller(1997) Govender, Poobalan; Bajic, Vladimir B.In this study we propose an analogue nonlinear PID controller with antiwindup and dead-time compensation to optimise the control of loops experiencing degradation in the control performance as a result of dead-time and saturation nonlinearity. Loops containing a significant dead-time are notoriously difficult to control. The proposed controller optimises the control of loops experiencing the negative effects of saturation and dead-time.