Browsing by Author "Gryzagoridis, Jasson"
Now showing 1 - 20 of 24
Results Per Page
Sort Options
- ItemOpen AccessAspects of holography(1989) Findeis, Dirk Michael; Findeis, Dirk Michael; Gryzagoridis, JassonThis study was aimed at broadening the knowledge of aspects of holography by examining three areas of importance, namely: i) qualitative holographic nondestructive testing, as applicable to flaw detection, ii) quantitative holographic interferometry and iii) white-light transfer reflection holography, with particular emphasis on the multiplexing principle. The objects used to evaluate the viability of qualitative holographic nondestructive testing were various carbon fibre airframe sections, a ceramic tube and a ceramic mould. The real-time and double-exposure holographic techniques were used to investigate the objects. Hot air was employed as the stress application medium. The results obtained clearly show the viability of holography as a nondestructive testing technique for the detection of debonds, delaminations, cracks, etcetera. In the second part of the study, the zero-order and fringe-counting techniques were applied to a cantilever loading experiment as a means of quantitatively determining the cantilever's displacement. It was determined that displacements with an accuracy of circa 85 % could be obtained by using the abovementioned techniques. In the final part of this study the transfer and multiplexing principles were rigorously examined. As a result, it was found that when reflection holograms were used as masters, excessively dim transfer holograms were produced. Transmission masters produced much brighter transfer holograms and displayed the capability of individually reproducing the images recorded. However, the angle of visibility of the individual images produced was found to be unsatisfactory and therefore warrants further investigation.
- ItemOpen AccessAspects of laminar free convection from a vertical plate(1972) Gryzagoridis, Jasson; Boyle, W PThe thesis is comprised of a number of aspects pertaining to the phenomenon of laminar free convection from a vertical plate. A survey of literature is presented which brings out the fact, that the phenomenon although it has been investigated to a large extent, still gives rise to widespread dispute and uncertainties which need careful examination. An analytical approach is presented showing that the hydrodynamic boundary layer is equal to the thermal boundary layer. In the past it was simply assumed to be so, in order to limit the computations, and the assumption was justified by the excellent agreement between calculations and experimental data. An analysis is presented showing the analogy existing between the Grashof and Reynolds numbers, as it is expected in the case of low velocities and considerable temperature differences, i.e. in free convection. An extensive experimental investigation pertaining to average heat transfer rates from a vertical plate at low Grashof numbers is presented and provides the necessary evidence in a much disputed region. It is shown conclusively that as far as average heat transfer rates are concerned, the agreement with the already accepted relationship can be extended to Grashof numbers as low as 10.
- ItemOpen AccessComparative study of non-destructive testing methods of defect detection on aircraft(2007) Musonda, Vincent; Gryzagoridis, JassonThere is currently an increase in the usage of composite materials both in civilian and military aircraft because of their mechanical resistance, high toughness, reduced weight and immunity to corrosion. Any damage in the fibers of these composites requires an evaluation in order to ensure the integrity of aircraft structures. Composite materials are subject to various degrees of damage during their service life and therefore maintenance of these light-weight structures is a new challenge for non-destructive testing (NDT) which requires techniques that respond with a high probability of detection of defects on such high-specific strength materials. In this thesis, Digital shearography and Infrared Thermography (IRT) techniques are employed to test aircraft composite materials. Background information on the techniques has been presented and the literature survey has confirmed the use of these techniques on aircraft structures. Much of the inspection work reviewed in the literature has focused on qualitative evaluation of the defects rather than quantitative.
- ItemOpen AccessComputer generated 3D animated holographic stereograms(1997) Reed, Brandon Ian; Gryzagoridis, JassonThis thesis describes the process of creating and displaying a computer generated 3D animated holographic stereogram. The objective of the project was to create a computer generated 3-dimensional model and animate it to perform some action using an animation program. This animated object would then be transferred to holographic film in the form of incremental component views of that object, resulting in a holographic stereogram that displays both parallax as well as animation.
- ItemOpen AccessDefect and fracture detection using acoustic emission monitoring(2006) Mckuur, Gerswynn; Gryzagoridis, JassonThis thesis is a consolidation of work that investigates the flaw detection capabilities of Acoustic Emission (AE) technology applied to metal alloys and composite materials. The thesis explores the background to AE and how it is applied to flaw detection and fracture characterisation. In preliminary tests, a steel pressure vessel and a filament wound composite pressure vessel were used in hydro proofing tests. Each of the vessels had existing flaws/defects in them. The locations of these flaws were known. Acoustic emission sensors were placed on the surface of the vessels, the vessels were subjected to a pressurising programme, and the AE equipment was used in order to confirm the locations of these flaws.
- ItemOpen AccessDevelopment of a portable low-cost digital shearography system(2008) Pitman, Barry; Findeis, Dirk; Gryzagoridis, JassonShearography is an optical non-destructive testing technique that is well-suited, but not limited, to testing composite materials. The method takes advantage of the special properties of lasers, namely their high coherence length and monochromatic light, to detect flaws such as cracks, debonds and delaminations in materials.
- ItemOpen AccessElectronic Speckle Pattern Interferometry (ESPI) NDE of cracks in pressure vessels with FEA modelling(1997) Myles, John Robert; Gryzagoridis, JassonThis dissertation describes the results of an attempt to simulate the Electronic Speckle Pattern Interferometric fringe patterns observed around a crack or combination of cracks in a pressure vessel by finite element methods. Electronic Speckle Pattern Interferometry (ESPI) is a coherent optical measurement technique that produces a contour map of the surface displacement of an object when it is stressed. The sensitivity of the techniques is of the order of half the Wavelength of light. The objective of the study was to determine a procedure for the modelling of interferometric fringes by finite elements. The finite element model may then be used to study the effects of crack geometry on fringe patterns and produce a library of reference fringe patterns for comparison with experimental fringe patterns found for unknown flaws. The approach to the problem was to simulate the fringe patterns for a crack free cylinder and compare these with these observed experimentally. The FE model modulus of elasticity was than to be calibrated to minimise uncertainty in the exact value of the elastic modulus. Once the model was calibrated, various cracks and combinations of cracks were introduced into both the physical cylinders and the FE model and fringe patterns obtained were compared. The experimental results for the cracks and combinations of cracks were compared with the finite element predictions at a range of loads.
- ItemOpen AccessEvaluation of film, jacket and internal cooling during fermentation of grape juice(1994) Steenkamp, Zaldeus Johannes; Gryzagoridis, JassonThe work described in this thesis deals with analytical and experimental aspects of water-film cooling, jacket cooling and internal cooling, which are the three predominant types of fermentation cooling found in the South African wine industry. During the past decades questions were constantly raised concerning the thermal efficiency of equipment used in the above mentioned types of fermentation cooling. These questions were particularly asked when a wine cellar expanded operations, or after product damage had occurred. The thesis presents the work that was carried out along the following aspects: 1. The building of models which will enable simulation of each type of fermentation cooling under different running conditions for various sizes of available equipment. 2. The experimental work on all three main types of fermentation cooling under different running conditions to confirm the validity of the mathematical models. 3. The comparison of analytical or predicted results of the performance (cooling capacity, pressure drop and effectiveness of the three types of fermentation cooling) with the experimental or measured values.
- ItemOpen AccessFlow interference between groups of three and four equispaced cylinders(1989) Sayers, A T; Gryzagoridis, JassonThis thesis is a study of the interference forces acting on one cylinder comprising a group of three and four cylinders when situated in a free stream flow. The spacing of the cylinders was such that the lines joining their axes formed an equilateral triangle, and a square respectively. The study is split into two parts, (a) potential flow over the groups of cylinders (b) real flow over the groups of cylinders. Bound with copies of the authors' published papers.~Bibliography: pages 132-137.
- ItemOpen AccessHeat and mass transfer characteristics: design and optimisation of absorption refrigeration machines(1995) Vicatos, George; Gryzagoridis, JassonAn extensive literature study on the subject of absorption refrigeration has revealed that there is no proven methodology that can be used to design, optimise and size a plant. On the contrary there are numerous methods which analyse the performance of an existing plant from collected data. These methods however, do not provide any means of predicting how the analysed plant would perform if one or more of its working conditions should change. This work provides a complete design for an ammonia-water absorption refrigeration plant. The ranges of the working conditions in the evaporator and condenser are from -5°C to -55°C and from 5°C to 45°C respectively. For any combination of temperatures within these ranges, the temperature of the generator is optimised for maximum performance of the plant. Depending on the refrigeration capacity, the components are sized and designed. The proper design of the various components takes into account both heat and mass transfer correlations, something which has not been considered in the past as a necessary step for absorption refrigeration machines. Literature indicates that there is a vast amount of research into the absorption of gases into liquids and two-phase flows through tubes of various sections. The correlations cited in these studies have been used in designing the absorption column, evaporator and generator. The proposed optimisation method is a novel approach in designing a plant and stems from the fact that the performance of the absorption refrigerator reaches a maximum at a specific generator temperature. For this, optimisation curves have been developed, which for a particular combination of evaporator and cooling environment temperatures, both the optimum generator temperature and the maximum performance of the plant are predicted. The equations used in the computerised simulation procedure are based on the well-established enthalpy-concentration chart for the ammonia-water mixtures. Thus the properties of the mixture at various points in the plant are accurately predicted. Published computerised procedures in the past have been proven inaccurate in predicting the properties of the mixtures at near pure-ammonia concentrations. The validity of the simulation model is verified by tests performed on a laboratory size absorption plant. The plant was built from design parameters predicted by the simulation model for a refrigeration capacity of 1 kW at -l5°C evaporator coil and 25°C condensate temperatures. Thereafter the unit was operated for a range of evaporator conditions while the generator temperature was varied.
- ItemOpen AccessHolographic determination of mechanical properties and behaviour of materials(1991) Sher, Arnold; Gryzagoridis, JassonThis study, which was primarily experimental, was aimed at investigating the feasibility and development of experimental procedures using holographic interferometry to determine different material properties such as: i) Modulus of Elasticity (E) ii) Poisson's ratio (v) (which included a study into the Modulus of Rigidity. (G)) iii) creep behaviour at room temperature. The Elastic Modulus (E) was determined from the relationship E=v²p, where v is the velocity of a longitudinal wave propagating in a long rod and p is the density of the rod. The technique of double-exposure holographic interferometry was used to record longitudinal waves propagating in long brass and steel rods. The waves were initiated by striking the end of the rod with a pendulum. From the pulsed laser interferograms obtained, the distance travelled by the wave in a known time could be measured and thereby the velocity (v) could be calculated. Experimental results indicate that it is feasible fo use holographic interferometry when dynamically determining the Elastic Modulus. The values produced for brass and steel compared favourably with the ones obtained from the ultrasonic velocity technique.
- ItemOpen AccessThe in-service non-destructive evaluation of wooden transmission line poles(1998) Prestage, Brendan Paul; Gryzagoridis, JassonThis thesis covers the research undertaken on behalf of the ESKOM TRI Group into the In-service Non-Destructive Evaluation of Wooden Transmission Line Poles. The aim of this work was the development of an effective pole tester that could be used to test the integrity of wooden transmission line poles in situ. The pole testing method that ESKOM uses at present is both time and labour intensive and it is envisaged that this research will contribute to the establishment of a faster, cheaper and more effective alternative. The research began with a literature survey of past investigations. Previous research in this area followed two distinct approaches. The first approach concentrated on mechanical testing procedures. For example the physical bending of the pole and measuring its bending stress (the effect that this bending has on the single fibres in the pole is not documented). The present ESKOM pole tester follows this approach. The second approach has been in the field of true "non-destructive" testing. Procedures using x-rays, magnetic resonance imaging and vibration analysis have all been considered in the past by investigators. The present investigation followed the approach of vibrations analysis. The process involved impacting the pole and measuring its vibration response. The response was then used to analyse the pole's behaviour. The state of integrity of the pole determined its vibration characteristics.
- ItemOpen AccessAn investigation into the fibre instrument feed for the Southern African Large Telescope (SALT)(2001) Sessions, Nicholas James Adam; Gryzagoridis, JassonThis thesis is an investigation into the Fibre Instrument Feed (FlF) for SALT. Its goal is to provide the groundwork that will lead to the detailed design and manufacture of such an instrument that is to be completed by the time SALT is commissioned in mid-2004.
- ItemOpen AccessLow cost solar powered water pump(1985) Vouzas, George; Gryzagoridis, JassonThe study describes the development of a prototype solar energy powered water pump. The system was developed in an attempt to meet the following requirements and constraints: Cheap, convenient and easy manufacture, reliability and low maintanance of the system, no auxiliary power requirements, and minimum running costs. The literature survey indicated that a number of pumping systems have been studied in the past, with variable successes, based on numerous thermodynamic cycles. Our system operates on the combination of two constant volume and two constant pressure processes, on a working fluid which expands due to input heat from the sun, and contracts due to heat rejection to the pumped water. This expansion and contraction of the fluid is utilized to move flexible bellows, resulting in the pumping action. The thermodynamic and heat transfer aspects of the system have been modelled and the results were compared with the experimental data. A number of working fluids were attempted and the final results show very good agreement between the theoretical and experimental results for Freon 113. Lack of detailed thermodynamic data did not allow similar comparison for Methanol. Yet, experiments on another fluid (Cyclohexane) were abandoned because the fluid was found to be incompatible with the bellows material.
- ItemOpen AccessMotor vehicle air-conditioning : utilising the exhaust gas energy to power an absorption refrigeration cycle(1997) Wang, Shiyi; Gryzagoridis, JassonIt is a well-known fact that a lot of heat energy associated with the exhaust gases from an engine is wasted. The work described in this thesis attempts to use the energy from the motor car's exhaust gases to power an air-conditioning system. Thus the waste heat can be utilised and shaft power conserved by replacing the traditional compression refrigeration system, used for air-conditioning a motor car, with an absorption unit. The thesis deals with some theoretical aspects of the absorption refrigeration cycle as well as practical aspects of motor car air-conditioning. A fair amount of research on absorption refrigeration has concentrated on the choice of the combinations absorbent and refrigerant. The need for the combination to be suitable for this special application is self evident. The use of aqua-ammonia, one of the oldest and most widely used combinations for absorption refrigeration systems, to chill water which is used as a secondary fluid, goes a long way in ensuring that ammonia does not get released in the passenger space. An added bonus is that this choice of refrigerant does not have potentially an adverse environmental influence (i.e. ozone layer etc.).
- ItemOpen AccessMultiple lift tube bubble pumps to increase the capacity of diffusion absorption refrigerators(2004) Bennett, A J; Gryzagoridis, Jasson; Vicatos, GeorgeIncludes bibliographical references.
- ItemOpen AccessA new product development practices model for small and medium engineering enterprises(2010) Jacobs, Keith; Gryzagoridis, JassonThe work presented here describes the development and validation of a diagnostic New Product Development Practices (NPDP) Model for the sustainability of Small and Medium Engineering Enterprises (SMEEs). A review of the literature regarding the sustainability of SMEEs, supported with the data gathered through the case study of a sample of SMEEs, led to the creation of a model. The model consists of unique elements such as the Innovative Engine and an environment called the Innovative Space. This model was used to shape further data collection instruments since it represented the ideal status in terms of sustainability potential or a measure of a particular SMEE. Comprehensive data relating to the various components of the NPDP model were gathered from 18 SMEEs. The SMEEs were chosen from a governmental database of small enterprises in the manufacturing sector of the Western Cape. Analysis of the data yielded a classification of these SMEEs in terms of their sustainability potential. This depended on the level of their NPDP as compared with the ones indicated by the proposed model. On the assumption that proof of sustainability of a SMEE is in its “growth”, the 18 SMEEs were re-visited after a period of three years, i.e.: from the original data collection that informed the model and subsequent classification. Data regarding their growth was collected. Analysis of this latest set of data revealed that most companies performed as expected, based on their potential for sustainability within a range of “growth factor” values.
- ItemOpen AccessA novel compact Shearographic NDT system(2005) Andhee, Avinash; Findeis, Dirk; Gryzagoridis, JassonThere is a need in industry and the NDT (Non-destructive Testing) community for quick, reliable, user-friendly and cost-effective compact NDT systems that can be used on a wide variety of materials and structures, for quality assurance and maintenance. Designing and building a compact Shearographic NDT system will enhance the capability of inspection during quality assurance and maintenance routines as well as reduce inspection time. Older compact Shearographic systems, which have been tested satisfactorily both under laboratory and field conditions at the NDT Laboratory at the University of Cape Town, have a rather restricted field of view. This is due to the proprietary shearing optics being placed in front of the camera lens, which in other words means that the field of view can only be increased by using a relatively small focal length camera lens which results in having to increase the size of the shearing optics. This would make the compact Shearographic device much larger which is counter-productive since technology enables/directs research and development toward more compact devices.
- ItemOpen AccessThe performance of an integral greenhouse solar air-heater(1984) Bam, Peter Jonathan; Gryzagoridis, JassonThe Baird-type solar collector is a solar air-heater, utilising black shade-cloth as the absorber, that is incorporated as part of the roof of a greenhouse. It is intended to be used, in conjunction with a heat storage device, to provide greenhouse heating (and cooling), and so to assist in maintaining an optimum greenhouse plant-cultivation environment. An analysis of a Baird-type integral greenhouse solar collector is presented in this thesis. This has involved designing and building a solar simulator, which was used to test the performance of a model of a greenhouse-integral solar collector. The experimental results thus derived were compared with results generated using a theoretical heat-transfer model of the solar collector and show that, on average, the theoretical model was capable of predicting the model solar collector heat-gain to within six percent of the measured values. Predictions of performance were made for various input conditions, such as high and low values of inlet-air temperature, different ground temperatures, different mass-flowrates and radiation intensities. Although subject to the input conditions, the results indicated an efficiency of solar energy collection of about 35 percent for the model greenhouse solar collector. The theoretical model was used (with appropriate modifications), to predict the performance of a "life-size" Baird-type greenhouse integral solar collector. Predictions were made for average conditions in the Cape Peninsula for the months of January and June. Assuming zero windspeed, a collector efficiency of approximately 42 percent is anticipated for most of the January day and approximately 33 percent for most of the June day.
- ItemOpen AccessA qualitative holographic study of hemipelvic and acetabular deformation caused by different hip prostheses(1989) Spirakis, Athanasios Apostolou; Gryzagoridis, JassonAseptic loosening of the components is probably the most common long-term complication resulting in failure of Total Hip Arthroplasty. The mechanical behaviour of bone under load is one of the contributory causes of loosening encountered at the prosthesis/cement/bone interface. The present study dealt with a series of invitro experiments conducted on epoxy resin models of human hemi-pelves with different commercially available acetabular components implanted in them. These are used for the construction of simplified models of the artificial hip joint (three-dimensional) and of the prosthesis/cement/bone acetabular interface (two-dimensional). Loading conditions for the models included tensioning of the simulated abductor muscles for the hemi-pelvic and femoral loading for the prosthesis/cement/bone interface study. The experimental method employed was real-time holographic interferometry, a stress analysis technique recently used in the biomechanical field, which permitted whole-field simultaneously inspection of deformation patterns. The holographic interferograms were interpreted in a qualitative rather than a quantitative manner. The models do not exactly represent the in-vivo situation. Since this study identified high stresses both in the hip bone as well as in the interface (prosthesis/bone) it is suggested that these stresses are implicated in the mechanical pathogenesis of loosening. The observed changes in stress levels detected in our models could serve as a guide for future designs of acetabular prostheses as well as guide a in surgical techniques.