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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Parallel robot design incorporating a direct end effector sensing system.

Shaik, Ahmed Asif. January 2007 (has links)
This dissertation details the development of a parallel robot with an integrated direct end effector sensing system, from concept to prototype model and includes details of research, design, simulation, construction, assembly and testing. Current research in parallel robots is insufficient as compared to serial type machines, even though their existence has been known for some time. The reasons are the difficulty in conceptualising unique parallel mechanisms, achieving machines that are capable of high accuracy, solving their complex kinematics, dynamics and control problems. There are many advantages of parallel machines that rival the serial type, and these warrant further studies. The second aspect of this project was the design of a direct end effector sensor system. Many existing automated multi-axis machines operate under overall 'open loop' control. The exact position in space of the end effector or tool head, for those machines, is not sensed directly but is calculated by software monitoring sensors on actuator axes. This sensor system and robot structure was designed specifically for use in the agricultural and general food processing/packaging industries. The accuracy and repeatability of such a machine and its sensor system are in the millimetre range. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.
2

Crush simulation and experimental model validation for laminated composite structures.

Thomson, Vaughan Allen. January 2004 (has links)
The primary aim of this study is to develop a modelling approach useful for modelling the response of thin-walled fibre reinforced composite components (particularly laminates) to crushing loads, with the overall direction being towards a reliable methodology for modelling crash scenarios involving composite structures. As such, experimental work is completed in order to characterise the material being studied, as well as to obtain physical data for the crushing of a composite component. The results of numerical modelling are compared with the experimental data in order to evaluate the performance of the implemented models. A review of published literature for the progressive damage modelling of laminated composite materials provides the background for selection of a material model for modelling the real behaviour of the elementary ply of the laminated material. This model is to be implemented into a Finite Element code using a material characterisation process that is based on the material's experimentally recorded behaviour. Experimentation to investigate the effect of variations in reinforcement orientation and distribution on the crush response of a composite demonstrator component is also undertaken. This experimentally recorded data provides information on the physical response of a real composite component under varied load cases and with varied internal structure. Capturing of data in this way provides a wider scope of physical data for comparison with the predictions of the simulation algorithm and opens the door for further developments aimed at optimising a component's crash response through manipulation of internal structure. Simulation of the demonstrator component's response to a constant velocity crushing load shows the predictions resulting from the underlying modelling methodology and comparison of the predicted response with the data recorded from physical testing provides a basis for evaluating the performance of the models, as applied. With a known level of confidence provided through the experimental validation program, modelling of the demonstrator's response to impact loading conditions provides predictions of the demonstrator crash response. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.
3

The performance of a one and a half stage axial turbine including various tip clearance effects.

Morphis, George. January 1993 (has links)
The necessary clearance at the tip of unshrouded rotors of axial turbines allows fluid to leak from the pressure to the suction side of the blade and produces an important component of loss that is ultimately responsible for approximately 25 % of the total turbine rotor losses. Leakage fluid can pass through the tip clearance gap with either high or low loss generation. It has been customary in turbine design to employ high loss designs since it is only by the creation of loss that the gap mass flow rate can be restricted. The present work, however examined the effect of streamlined tips that have low entropy generation within the tip and high leakage flows. An axial turbine followed by a second stage nozzle (ie one and a half stages) was designed, built and instrumented and used to evaluate performance with particular reference to the understanding of tip clearance effects in a real machine and possible benefits of streamlined low loss rotor tips. A radiused pressure edge was found to improve the performance of a single stage and of a one and a half stage turbine at the selected tip clearances. This was in contrast to previous cascade results where mixing losses reduced the benefits of such tips. Clearance gap flow appears to be similar to other turbine flow where the loss mechanism of separation must be avoided. Loss formation within and downstream of a rotor is more complex than previously realized and does not appear to obey the simple rules used to design for minimum tip clearance loss. For example, approximately 48 % of the tip leakage mass flow within a rotor may be a flat wall-jet rather than a vortex. Second stage nozzle efficiency was significantly higher than first stage nozzle efficiency, and even increased with tip clearance. This was a surprising result since it means that not only was there a reduction in secondary flow loss but also that rotor leakage and rotor secondary flows did not generate significant downstream mixing loss. The manner in which the second nozzle responds to the complex leakage flows presented to it and how it completes the formation of tip clearance loss for various rotor tip clearances was identified. The tangentially averaged relative rotor flow in the tip clearance region differed radically from that found in cascades which was seen to be underturned with a high axial velocity. There was evidence rather of overturning presumably caused by secondary flow. Axial velocity followed an almost normal endwall boundary layer pattern with almost no leakage jet effect. Cascade tip clearance models are therefore not accurate in predicting leakage flows of real rotors. The reduction in second stage nozzle loss was seen to occur near the hub and tip confirming a probable reduction in secondary flow loss. Nozzle exit loss contours showed that the leakage flow suppressed the formation of the classical secondary flow pattern and that a new tip clearance related loss phenomenon existed on the suction surface. The second stage nozzle reduced the hub endwall boundary layer below that of both the first nozzle and that behind the rotor. It also appeared to rectify the secondary and tip clearance flows to the extent that a second stage rotor would experience no greater flow distortion than the first stage rotor would. Radial flow angles behind the second stage nozzle were found to be much smaller than those measured in a previous study of low aspect ratio, untwisted blades. / Thesis (Ph.D.)-University of Natal, Durban, 1993.
4

Modelling of carbon nanotubes and carbon nanotube-reinforced polymers with applications to composite structures.

01 November 2010 (has links)
Owing to their exceptional mechanical and physical properties, carbon nanotubes seem to / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2006.
5

The measurement of axial turbine tip clearance flow phenomena in a moving wall annular cascade and in a linear cascade.

05 January 2011 (has links)
On unshrouded axial flow turbine rotors, the tip clearance, required for thermal expansion and manufacturing limitations, allows fluid to leak from the pressure side to the suction side of the blade. This flow across the blade tip causes a large proportion of the overall rotor loss. In this work, the flow was visualized, microscopic static pressures taken and flow field measurements were done in the blade tip region to investigate the complex nature of tip clearance flows. An annular turbine cascade with a rotating outer casing was used to simulate the relative motion at the tip of an axial rotor. It was found that relative motion did not have a significant effect on the basic structure of the micro-flow, even though it reduced the leakage mass flow rate which is important as far as mixing loss formation is concerned. The existence of a narrow, very low pressure depression, caused by the flow remaining attached around the sharp pressure corner edge, was confirmed. The width and pressure of the separation bubble were found to be strongly dependent on gap size but the relationship was not linear. The point at which the separation bubble reattaches was seen to coincide with a slight rise in static pressure. The separation bubble which caused the majority of the internal gap loss, and which was thought to contribute to the mixing loss, was shown to disappear when the pressure corner was given a radius of 2,5 gap widths.A linear cascade was used to evaluate the performance of two blade tip shapes that substantially reduced internal gap loss and to compare them to a standard sharp or flat tip blade. A method whereby linear cascade data was analyzed as if it were a rotor with work transfer, was used to evaluate the performance of the various blade tip geometries. It was found that both modified tips increased the mixing loss due to the extra leakage mass flow rate. The first tip with the radiused pressure corner was seen to have a lower efficiency than the flat tip blade. A second tip that was contoured to shed flow in a radial direction and thus decrease the leakage mass flow rate through the gap was seen to significantly increase the overall efficiency. / Thesis (M.Sc.)-University of Natal, Durban, 1989.
6

Designing optimisation of a cane haulage vehicle.

Cowling, Simon L. January 2008 (has links)
The sugar industry transports in excess of 20 million tons of sugarcane per annum, equating to approximately 800 000 road consignments. This entails substantial expenditure on vehicle capital and operational costs. There exists substantial scope to redesign vehicle configurations to reduce the vehicles tare mass and optimise the process of cane transportation. These modifications could potentially save the industry approximately Rl36 million per annum, and in addition will increase a vehicles lifespan, performance and speed. This project is one aspect of a larger project organised by the South African Sugarcane Research Institute, with the general aim of optimising the entire sugarcane transportation system. Aspects of this particular project include literature research as well as field investigation into the various sugarcane transportation systems in South Africa and throughout the world. The design of a cane haulage vehicle will be analysed and optimised, using tools such as finite element analysis. The aims of this project include the investigation of the engineering design issues with respect to vehicle/trailer configurations, and the design of an optimised cane haulage vehicle which increases the efficiency of raw sugarcane transportation in South Africa. / Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2008.
7

Experimental and theoretical analysis of heat transfer on a transonic blade.

Essa, Zaahir Ahmed. January 2008 (has links)
This dissertation involves the experimental and numerical analysis of heat transfer on a transonic high turning angle gas turbine blade, which has been performed on the supersonic cascade experimental facility at the University of KwaZulu-Natal (UKZN), as part of the continuous research and development project run under ARMSCOR. Efforts have been made to keep constant maintenance on the experimental rig. This now functional rig was used to generate experimental results, which were used to validate numerical models created using the commercially available computational fluid dynamics (CFD) package of FLUENT. The facility at UKZN is a continuously running cascade system, which consists of a plenum run under vacuum pressure and houses a four-blade cascade. One of these SMR-95 turbine blades is instrumented with thin-film gauges, which allow heat transfer measurement via a heat transfer analogy through electrical circuit boards. This blade is interchangeable with an instrumented blade with pressure tappings along its span for pressure distribution tests. This facility was used to validate flow measurements, and results compared to previous test data conducted on the rig, using two pressure transducers, a scanivalve and a data acquisition system with LabView software. The method of generating heat transfer measurement results involved pre-chilling the test blade in a cooling box, before rapidly plunging it directly into a hot-air stream. Re-instrumented and more sensitive thin-film gauges would react resistively according to the temperature change. The heat transfer coefficient distribution was calculated using LabView. The turbulence intensity at the inlet of the cascade was varied using a grid of rods of varying diameter. For 15% turbulence intensity, there was a 16% overall increase in heat transfer on the pressure side, and 25% increase on the suction side. For 25.5% turbulence intensity, there was an overall increase of 23% on the pressure side and 40% on the suction side. The results compared favourably to that of previous results generated by Stieger (1998). The experimental results were used to validate and compare to the CFD model developed in FLUENT. Improvements were made with the meshes developed previously, and results obtained showed that the general trend of distribution was similar, although certain models varied in the correct prediction of magnitude. This research includes a comprehensive study of various methods of numerical heat transfer measurement techniques, which would be used to replace the current ageing electrical heat transfer analogue method used at UKZN. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2008.
8

Trip steels as smart sensor alloys.

Bemont, Clinton. 06 October 2014 (has links)
Upon deformation, TRIP steels undergo progressive irreversible transformation from paramagnetic austenite to more thermodynamically stable, ferromagnetic αʹ-martensite. The change in magnetic permeability is readily detectable, and since TRIP steels also have excellent mechanical properties, this presents the opportunity for implementing cheap, robust structural health monitoring systems. However, the extent of martensitic transformation in TRIP steels is affected not only by the degree of deformation, but by environmental temperature at the time of deformation and strain rate. This creates inherent inaccuracy when implementing TRIP steels as sensor materials. In this thesis it has been demonstrated that it is possible to design TRIP steels that are less susceptible to these factors, show good deformation induced transformation, and can function simultaneously as sensors and structural elements. As-cast alloys were tested in compression, while annealed, hot-rolled and warm-rolled alloys were tested primarily in tension. There was considerable variation between alloys in rate of transformation with deformation. Martensitic transformation was evaluated magnetically and correlated with optical and scanning electron microscopy and X-ray diffraction results. Changes in magnetisation and magnetic permeability curves with deformation were characterised to ensure optimal electronic monitoring. Equations from literature for determining characteristic transformation temperatures, Ms and Md30 were evaluated experimentally for the alloy range of interest, and the best equations were selected to aid in the design of high alloy TRIP steels exhibiting strong transformation and low temperature sensitivity. Temperature sensitivity between alloys was found to vary as predicted. Temperature sensitivity was also compared in annealed, hot rolled and warm rolled conditions; the annealed condition showed the lowest sensitivity, and this is thought to be related to lower dislocation densities. Mining was targeted as a primary industry for application of these sensor systems because of the pressing need for greater safety and more efficient structural support at low cost. Two distinct devices for monitoring the structural health of mines were designed, built and tested, and a third was developed for the aerospace industry. Better understanding and control of the temperature sensitivity of martensitic transformation in TRIP steels is expected to aid not only structural health monitoring, but also the application of such materials to other areas of technology, such as sheet forming and high impact resistance applications. Although there are limitations on the extent to which TRIP steel transformation characteristics can be controlled, it was shown that they can be manipulated to enable successful implementation of new alloys for smart load or damage sensors. Practical, robust, low cost structural health monitoring sensors based on the smart properties of TRIP steels were shown to be feasible. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.
9

Modelling and empirical characterisation of environmental degradation of FRP laminates in southern Africa.

29 October 2010 (has links)
As polymeric composite materials are being increasingly used in Southern Africa, there is a / Thesis (Ph.D.)-University of KwaZulu-Natal, 2007.
10

Smart structural health monitoring of mining support units.

Apsey, Jason. January 2003 (has links)
In the South African mining industry, the design of tunnel support systems is generally based on empirical methodologies that consider rockmass characteristics as well as the type of loading (e.g. seismic) that the excavation experiences. The design methodologies are by no means infallible, and work is continually being conducted to improve the classification of excavation conditions and thereby improve the selection of a suitable support system. This study is concerned with finding a means to monitor the installed support units rather than with improving the classification methodologies. It is postulated that with the extraction of accurate information describing the state of any support unit at any given time, areas of instability in the tunnel can be readily identified and strengthened~ Also, the information gathered as to the behaviour of the support units in a particular region can be used to assist in understanding the environmental characteristics of that region (rockmass, loading, etc.). A material survey was conducted to identify suitable candidates that could feasibly be used in either a passive (feedback when interrogated) or active (constant feedback) structural health monitoring system. The preferred candidates identified in this study are the group of passive smart materials referred to as TRIP steels, which are a subset of strain memory alloys. TRIP steels exhibit microstructural changes from paramagnetic austenite to ferromagnetic martensite as a function of increasing deformation at a given temperature.. The strength of the magnetic field at critical locations provides an indication as to the health state of the component. Because of their high strengths and ductility, TRIP steels can be used as what amounts to a self-monitoring support unit (interrogation apparatus required). Finite element methods are a practical means of predicting the mechanical and magnetostatic behaviour of TRIP steel structural members once material equations have been established by experiment. / Thesis (Ph.D.)-University of Natal, Durban, 2003.

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