Doctoral Degrees (Mechanical Engineering)

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Modelling and empirical characterisation of environmental degradation of FRP laminates in southern Africa.
(2010-10-29) Sookay, N. K.
As polymeric composite materials are being increasingly used in Southern Africa, there is a
Molecular simulation and modeling of the phase equilibria of polar compounds.
(2006) Clifford, Scott Llewellyn.; Ramjugernath, Deresh.; Bolton, Kim.
The initial phase of the project involved an investigation into the modeling of binary carboxylic acid vapour-liquid equilibrium (VLE) data. This stemmed from the Masters research that led into the current study, in which the conventional gamma-phi formulation of VLE was found to inadequately describe the complicated acid chemistry. In an effort to correctly describe the dimerization occurring in both the liquid and vapour phases, the chemical theory of vapour-phase imperfections was applied. The chemical theory technique allowed the experimental liquid-phase activity coefficients to be accurately calculated by taking the vapour phase dimerization into account. Once these activity coefficients had been determined, standard Gibbs excess energy models were fitted to permit analysis of the VLE data's thermodynamic consistency. In addition, the typical bubble-point iteration scheme used for VLE data regression was adapted to include the chemical theory expressions necessary for satisfactory modeling of the carboxylic acids. The primary focus of this study was to determine the ability of currently available computer simulation techniques and technology to correctly predict the phase equilibria of polar molecules. Thus, Monte Carlo simulations in the NVT- and NPT- Gibbs ensembles were used to predict pure component and binary phase equilibrium data (respectively), for a variety of polar compounds. The average standard deviations for these simulation results lay between 1 and 2 % for the saturated liquid densities, and varied between 5 and 10 % for the saturated vapour pressures and densities. Pure component data were simulated for alcohols, carboxylic acids, hydrogen sulfide (ELS), sulfur dioxide (SO2) and nitrogen dioxide (NO2). For H2S, S02 and NO2, a potential model parameterized as part of this project was used to describe the molecular interactions. All the other compounds were simulated using the TraPPE-UA force field. The simulation results for the alcohols and acids showed a consistent saturated vapour pressure over-prediction of 5 - 20 % depending on the species and the system temperature. The liquid density predictions were, in general, good and on average differed from experiment by 1 - 2 %. The critical temperatures and densities were estimated from the pure component data by fitting to the scaling law and the law of rectilinear diameters. They were found to lie within 1 and 2 % of the experimental values for the carboxylic acids and alcohols, respectively. Clausius-Clapeyron plots of the saturated vapour pressures allowed the critical pressure and normal boiling points to be determined. The critical pressures were, as expected, over-predicted for both compound classes and the normal boiling points were under-estimated somewhat for the acids, but deviated from experiment by less than 0.5 % for the alcohols. A Lennard-Jones 12-6 plus Coulombic potential energy surface was parameterized for H2S, SO2 and NO2. For FbS, the proposed force field offers improved saturated vapour pressure and vapour density predictions when compared to the existing NERD force field, and comparable accuracy with the recent models of Kamath and co workers. SO2 and NO2 had not previously been parameterized for a Lennard-Jones 12-6 based force field. For SO2, there was excellent agreement with experimental data. In the case of NO2, the saturated liquid density predictions were very good, but the vapour pressures and densities were over-predicted. Binary VLE simulations were carried out for systems consisting purely of carboxylic acids, and also for H2S and SO2 with a selection of alkanes and alcohols. The liquid and vapour composition predictions were good for the acid systems, but the anticipated pressure and temperature deviations were observed in the isothermal and isobaric simulations, respectively. The H2S + alkane systems were generally good, as were the SO2 + alkane systems. For both H2S and SO2, the systems involving an alcohol displayed a characteristic pressure over-estimation. The azeotropes were, in most cases, predicted fairly well; the exception was the SO2 + methane binary. A sensitivity analysis of the Lennard-Jones unlike interaction parameters was also conducted. It was demonstrated that even minor changes to these parameters can have a significant effect on the final simulation results. The considerable affect that these parameters have on the simulation outputs was emphasized by studying the influence of different combining rules on the H2S + methane and H2S + ethane binary systems. Analysis of the radial distribution functions indicated that hydrogen bonding and dimerization were occurring in the alcohol and carboxylic acid systems, respectively. The H2S, SO2 and NO2 distribution functions showed little sign of any association, except for a small plateau in that of SO2. A radial distribution function from one of the carboxylic acid binary simulations was also analysed, and supported the assumption made in the chemical theory modeling work of using a geometric mean (instead of twice the geometric mean, which is favoured by some researchers) to determine the heterodimerization constant, KAB-
Molecular simulation of vapour-liquid equilibrium using beowulf clusters.
(2010-11-01) McKnight, Tyrone J.
This work describes the installation of a Beowulf cluster at the University of KwaZulu-Natal
Finite element solutions of optimization problems with stability constraints involving columns and laminated composites.
(2006) Cagdas, Izzet Ufuk.; Adali, Sarp.
The primary aim of this study is to assess the applicability and performance of the finite element method (FEM) in solving structural optimization problems with stability constraints. In order to reach this goal, several optimization problems are solved using FEM which are briefly described as follows: The strongest column problem is one of the oldest optimization problems for which analytical solutions exist only for some special cases. Here, both unimodal and bimodal optimization of columns under concentrated and/or distributed compressive loads with several different boundary conditions and constraints are performed using an iterative method based on finite elements. The analytical solutions available in the literature for columns under concentrated loads and an analytical solution derived for simply supported columns under distributed loads are used for verification purposes. Optimization results are presented for fibre-reinforced composite rectangular plates under inplane loads. The non-uniformity of the in-plane stresses due to stress diffusion and/or in-plane boundary conditions is taken into account, and its influence on optimal buckling load is investigated. It is shown that the exclusion of the in-plane restraints may lead to errors in stability calculations and consequently in optimal design. The influences of the panel aspect ratio, stacking sequence, panel thickness, and the rotational edge restraints on the optimal axially compressed cylindrical and non-cylindrical curved panels are investigated, where the optimal panel is the one with the highest failure load. The prebuckling and the first-ply failure loads of the panels are calculated and minimum of these two is selected as the failure load. The results show that there are distinct differences between the behaviour of cylindrical and non-cylindrical panels. The formulations of the finite elements which are used throughout the study are given and several verification problems are solved to verify the accuracy of the methodology. The computer codes written in Matlab are also given in the appendix sections accompanied with the selected codes used for optimization purposes.
Development of high strength material for smart aircraft bolt.
(2005) Vugampore, Jean-Marie Vianney.; Verijenko, Belinda-Lee.
Scientists are constantly seeking new and convenient non-destructive damage assessment techniques. In fact, a global market has developed for structural health monitoring products. Many of the currently available techniques are expensive and difficult to implement. An inexpensive alternative is technology based on strain memory alloys. These materials encompass a vast array of alloys, from austenitic stainless steels through to the extremely high strength TRIP steels. All, however, have in common the transformation from paramagnetic austenite to ferromagnetic martensite upon application of strain. The degree of ferromagnetism can be directly correlated to the peak strain undergone by the material. Strain memory alloys are not as expensive to manufacture as some smart materials, and in addition are capable of bearing significant load, and it is therefore possible to manufacture entire components from these alloys, thereby producing what is known as a smart component, i.e. one that is capable of doing the job of an ordinary component while at the same time assessing its own peak damage levels. A possible application of this technology is that of wing bolts for the Hercules e130 aircraft. The material usually used to manufacture the aircraft wing bolts is HSLA steel (AISI 4340). A strain memory alloy was therefore developed to match the mechanical properties of 4340 steel, while also having the requisite properties to perform the self damage-assessment. Ultra high strength TRIP steels were identified as possible candidates, and four alloys selected for investigation. These alloys were melted and then thermo-mechanically processed using a rolling operation. All alloys were tensile tested and magnetic susceptibility monitored. The final material selected possesses an ultimate tensile strength (UTS) of between 1270 and 1500 MPa with 10 to 12% elongation. The stress / strain induced transformation begins to occur before the yield point, which is important because bolts must be replaced before they fail. Compression tests were also performed, and yielded similar results to those of the tensile tests, with martensitic transformation again beginning before plastic yield. The strain induced phase transformation was confirmed not only by magnetic susceptibility measurements, but also by metallographic inspection before and after testing. A subscale Smart bolt was designed, manufactured and tested for magnetic sensitivity using a smart washer.
Contractible arms elevating search and rescue (Caesar) robot : improvements and modifications for urban search and rescue (Usar) robots.
(2010) Stopforth, Riaan.; Bright, Glen.; Harley, Ronald G.
Rescuers have lost their lives in events requiring them to go into dangerous areas that have unstable structures and gases. Robots are necessary for search and rescue purposes, to access concealed places and environments to which fire fighters and rescue personnel cannot gain entry. Robots that were previously used encountered problems with communication, chassis design, traction and sensory systems. Improvements are required for the successful localization of victims. Research on improvements in these areas were carried out for the use in the CAESAR (Contractible Arms Elevating Search And Rescue) robot. Contributions were made in the area of Urban Search And Rescue (USAR) robots focusing on antenna design, communication protocols, chassis design, traction system and artificial intelligence on decisions relating to gas danger levels for humans and the robot. The capabilities of CAESAR is audio, video and data communication irrespective of the orientation of the robot and the antennas. Penetration of radio frequencies through building material is possible. Reliable data communication is achieved with the designed Robotics Communication Protocol (RCP). The chassis is designed to have traction on unstable terrain and autonomously transform flipper arms for the best orientation. Materials for the body were selected and constructed to be able to withstand the unstable environments and high temperatures which they will encounter. The control station display gives the rescuers immediate indication of the gas concentrations detected by the on-board gas sensors. Developed analytical models determine the danger of the gas concentrations for victims, rescuers and the robots.
Investigation and design of wet-mill equipment and process technology.
(2003) Smith, Lisa Noelle.; Bodger, Robert.; Adali, Sarp.
need to dry-mill the wheat into flour, and as a result, the total cost of conversion from wheat to bread is reduced. The resulting product has been perceived as being more filling than normal bread and it is also more nutritious and more affordable. The wet-mill concept was developed in a laboratory environment and no process methodology or equipment has existed to enable the technology to be used in a real bakery environment. The focus of this research was to design the particular equipment required for a medium plant-bakery production facility based on the wet-mill technology. Due to severe overcapacity in the bread-making industry, the research focuses on how best to integrate this equipment into an existing production facility. Three broad areas are investigated: • Product Development • Process Design • Machine Design The aim of the Product Development phase was to create a recipe that would withstand the rigours of the plant bakery environment, while at the same time satisfying consumer demand for taste and texture. The Process Design phase ensured that any new equipment had the capacity to match the throughput rate of the rest of the plant bakery, so that wet-mill dough could seamlessly continue downstream. Process control variables were examined to ensure that a consistent quality product was delivered. Inbound material handling was also investigated and designed to ensure safe and uncontaminated delivery of perishable raw material. Since the end product is edible, hygiene design requirements were also considered by completing a HACCP study to ensure a consumer-safe product. The Machine Design phase involves the development and design of a completely new food machine: a vertical wet-mill cutter. Many ideas are evaluated and a prototype machine, based on the optimal design, was built to test the concept. This prototype was then used to define process and design constraints for a scaled, large plantbakery machine. The final detailed design of a plant bakery wet-mill cutter was then completed. It includes drive, belt, bearing and pneumatic cylinder selection, and shaft and blade design. Safety considerations were an important part of the design process and production facility. Conformity to OHS Act regulations required investigation into the safe operation of the designed equipment with particular reference to driven and rotating machinery sub-regulations of the Act. A hazard analYSis and operability study was also undertaken. Lastly, the research calculates a financial valuation of the project to ascertain whether a plant baker should be interested in implementing wet-mill technology. The research concludes with a discussion of the various successes of the three research areas, and states any further investigation that may be required before full implementation.
Finite element modelling of smart TRIP steel sensors and systems.
(2003) Jonson, David.; Verijenko, Viktor.; Adali, Sarp.
Transformation Induced Plasticity (TRIP) steels undergo a phase transformation when subjected to high levels of mechanical strain. This transformation from a paramagnetic austenitic parent phase to a ferromagnetic martensitic phase is irreversible and the resultant magnetic properties may therefore be used as a measure of strain history. The transformation behaviour of TRIP steels has been recognised as a potential smart characteristic and various proposals have appeared aimed at producing a structure that performs its primary structural function as well a strain sensing function simultaneously. However the strain induced nature of the transformation implies that transformation will occur in areas of high stress concentration and therefore engineered stress concentration features will be required to provide a consistent measure of the changes in the magnetic properties of the material as a function of applied load. In order to predict the performance of smart TRIP steel sensors, an analysis method capable of quantifying the effectiveness of a component in its dual role as structure and sensor is needed. The thesis addresses the development of a methodology for correlating the changing magnetic permeability of TRIP steel sensors and structures with martensitic transformation behaviour. The prediction of the deformation behaviour including transformation is implemented by considering a mechanical analysis based on the finite element method and a constitutive model incorporating strain-induced martensitic transformation kinetics. .Extensions to the model which allow for a wide range of deformation rates and temperatures are also discussed. In order to demonstrate the application of the methodology, an analysis of a simple tensile element used in strain measurement applications is presented. The analysis also includes the effect of temperature on the performance of the sensor. An analysis of a design proposal for a smart aircraft bolt is also included to investigate the effects of geometry, particularly engineered stress concentrations, and sensor placement.
Low velocity impact energy absorption of fibrous metal-matrix composites using smart materials.
(2003) Gopal, Ajith Karamshiel.; Adali, Sarp.
In general, the basic concept of an intelligent material is defined as the multifunctional material that has a sensor, a processor and an actuator function in the material that allows it to maintain optimum conditions in response to environmental changes. Despite the fact that these materials have demonstrated varying degrees of success in shape and position control, active and passive control of vibration and acoustic transmission of materials subjected to dynamic loads, impact damage and creep resistance in structures and have been applied in industries from aerospace to biomechanics to civil engineering structures, very little literature is available on the subject. Thus, the objective of this dissertation is to add to the fundamental understanding of the behaviour of these special materials by investigating the possibility of a magnetostrictive SMA hybrid metalmatrix composite beam with piezoelectric actuator, to enhance the materials load attenuation and energy absorption characteristics under low velocity impact loading. The methodology employed in this investigation is driven by two primary factors. The first is the unique approach that the author puts forward to attempt to simplify the characterisation of damage in not just metal matrix composites, but in materials in general. The second factor is the lack of available literature on smart material energy absorption as well as a lack of precise theory for short fibre composites. The methodology includes an extensive literature review, the development of an analytical model, based on the new damage modulus approach, verification of the model using experimental results presented by Agag et. aI., adjustment of the model to include smart material effects and finally numerical simulation using the MATLAB® software to predict the effect of smart materials on the energy absorption capacity of the material under impact. The results show that the damage modulus (ED) is a material characteristic and can be derived from the stress strain diagram. Further, it takes into account degradation of the material through the plastic region, up to the point just before ultimate failure. Thus, ED lends itself to the simplification of many damage models in terms of a reducing sustainable load and energy absorption capacity. Only the energy consumed through material rupture remains to be characterised. The results also show that smart fibres diminish the capacity of the beam to sustain a load, but increase the displacement to failure. Thus, for a compatible substrate material, this increased displacement translates to a significant enhancement of energy absorption characteristics. The effect of prestrain on energy absorption is also considered and there appears to be a definite turning point where the dissertation thus achieves its objective in investigating the ability of smart materials to enhance the energy absorption characteristics of regular fibre reinforced metal-matrix composite materials subject to low velocity impact loading. Of equal importance to the achievement of this objective is the introduction in the dissertation of the unique damage modulus that goes to the foundation of material characterisation for mechanical engineering design and has profound implications in damage theory and future design methodologies. Significant learning has taken place in the execution of this PhD endeavour and this dissertation will no doubt contribute to other investigations in the field of smart materials.
Smart materials for structural health monitoring.
(2003) Verijenko, Belinda-Lee.; Adali, Sarp.
A new philosophy in structural health monitoring was explored, with the view to the creation of a smart mining bolt: one which would bear the normal load of any bolt used in South African gold mining tunnels, but at the same time be capable of monitoring its own level of damage. To this end, a survey of various smart materials currently used in structural health monitoring applications, was conducted, and a group known as strain memory alloys isolated as holding the most promise in this regard. Strain memory alloys give an indication of peak strain based on an irreversible transformation from paramagnetic austenite to ferromagnetic martensite, which occurs in direct proportion to the amount of strain experienced by the material. A measurement of magnetic permeability can therefore be correlated to peak strain. An extensive study of the alloying chemistry, material processing and transformation characteristics was therefore carried out, including an analytical model for the quantification of the energy associated with martensitic nucleation, at a dislocation-disclination level. The conditions within typical South African gold mining tunnels were evaluated, and a smart mining bolt design produced, based on the loading and environmental conditions present. Several material formulations were then proposed, melted, tested and evaluated against the relevant strength, corrosion and transformation criteria. A suitable material was selected and further tested. A working prototype bolt has been produced, and in situ tests of complete bolts, are scheduled to take place shortly.
Best practice for personnel, material and rock transportation in ultra deep level gold mines.
(2003) Rupprecht, Steven Michael.; Verijenko, Viktor.
Ultra deep mining presents many challenges to the mining engineer, one of which is the logistics to support mining operations quickly and efficiently. Typically, Witwatersrand gold mines operate at depths in excess of 2000 m with stoping taking place to 3500 m and investigations underway to mine to a depth of 5000 m. As mining progresses deeper and further from the shaft, the role of logistics becomes increasingly important if production targets are to be achieved. Access to the workings is often via sub vertical and even tertiary subvertical shaft systems with working faces as far as five kilometers from the shaft. It is inevitable therefore, that distance will negatively impact the working time available at the stope face, material transportation and distribution, as well as the removal of broken ore. Possible solutions to these logistical problems may be found in the use of different transportation systems or by applying sound design and operational principles to transportation systems, both in the horizontal and instope areas. This thesis investigates the challenges of logistics for ultra deep level gold mining in the Witwaterstrand basin for mining layouts planning to mine between 3000 m and 5000 m underground with typical horizontal distances of over 3000 m. The transportation needs analysis recognised that vertical transportation is a wellmanaged and organised system and is mainly the same for both shallow and deep level operations. As a result of this, the thesis only focuses on the logistical issues of the horizontal and in-stope processes. The literature review indicates that the majority of work previously conducted on transportation focused around the area of horizontal transportation with limited inputs to in-stope transportation systems. The review concludes that the traditional locomotive transportation system is the most applicable mode of horizontal transportation. Thus, special emphasis is given to trackbound transportation. An integrated approach is taken towards mine transportation advocating that underground logistics be considered as equally important as any other discipline, Le. rock engineering, ventilation, etc. In addition, the transportation process should consider each area equally important. All to often, the transportation of rock is considered of paramount importance over the transportation of personnel and material. Thus, the planning any transportation system should incorporate personnel, material and rock. To enable this, scheduling, communication and control are important with special attention required for transfer points in the transportation system. As each site has its own particular requirement, thus the final transportation systems must be drawn up based on the specific requirements of each mine. A guideline is proposed for the design of ultra deep level underground transport systems for personnel, material and rock transportation. Thus, providing mining engineers with sufficient information and data to select an appropriate transportation system to meet specific mine requirements. The thesis highlights areas requiring consideration by mine engineers when designing a transportation system from shaft to the working face.
Crashworthiness modelling of thin-walled composite structures.
(2003) Morozov, Konstantin E.; Verijenko, Viktor.
This thesis is concerned with the study of the crashworthiness of thin-walled composite structures. Composites are being used more and more in different fields of engineering, particularly, in aerospace and automotive industries because of their high strength-to-weight and stiffness-to-weight ratios, quality and cost advantages. More and more metal parts in cars for instance become or are already replaced by new advanced materials. Composite materials are included in these new advanced materials with the following advantages: weight reduction, corrosion resistance, aesthetics and style, isolation and the ability to integrate several parts into one single structural component. The introduction of new composite structural components (body panels, bumpers, crash absorbers, etc.) requires the development and implementation of new approaches to structural analysis and design. Crashworthiness is one of the foremost goals of aircraft and automotive design. It depends very much on the response of various components which absorb the energy of the crash. In order to design components for crashworthy structures, it is necessary to understand the effects of loading conditions, material behaviour, and structural response. Due to the complexity of the material structure (matrix reinforced with fibres) and specific mechanical properties the nature of transforming the collision kinetic energy into material deformation energy differs from that of conventional metal alloys. The energy absorption mechanics are different for the advanced composites and depend on the material structure (type of reinforcement) and structural design. The primary function of the energy absorption for the composites belongs to the progressive crushing of the materials themselves and structural components (beams, tubes, etc.) made of such materials. Since the mechanics of composite materials and structural components differs substantially from the conventional applications there is a need to develop an appropriate way of modelling and analysis relevant to this problem. Currently there are a large variety of design approaches, test results, and research investigations into the problem under consideration depending on the type of composite material and design geometry of the parts. It has been found that in general an application of fibre reinforced plastics (FRP) to vehicle compartments can satisfy the structural requirements of the passenger compartment including high strength and light weight. Implementation of new advanced composite materials provides the opportunity to develop designs of reliable structural composite parts in high volume for improved automotive fuel economy. Structural optimisation and crashworthiness of composite components should be incorporated into design calculations to control the mechanical performance. The introduction which follows describes the aims of the present study of the crashworthiness modelling and simulation of the structural response of thin-walled composite components which are subjected to various loading conditions relevant to vehicle design. The research programme undertaken within the framework of this project includes development and validation of the modelling and simulation methodology applicable to the crashworthiness analysis of thin-walled composite structures. Development of computerised dynamic modelling of structural components offers the capability of investigating the design parameters without building the actual physical prototypes. In this approach, the dynamic behaviour of the structure is simulated for specified external inputs, and from the corresponding response data the designer is able to determine its dynamic response characteristics, and estimate the crashworthiness of the structure in vehicle engineering applications.
Smart structural health monitoring of mining support units.
(2003) Apsey, Jason.; Verijenko, Viktor.
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.
Influence of wagon structure on the vertical response of freight.
(2002) Loubser, Richard Clive.; Kaczmarczyk, Stefan.; Adali, Sarp.
Historically, wagons have been designed according to the American Association of Railroads specifications. These require that wagons be designed to withstand a static load between the couplers of 350 tons. This implies that the structure has a certain stiffness. In order to improve load to tare ratio, there has been talk of reducing the end load specifications. This implies that the stiffness of the wagon will reduce. Using more flexible wagons implies that the freight will probably be exposed to a harsher dynamic environment. There is a trade off between the cost of packaging and the cost of protection devices installed in the vehicle. If handling damage can be prevented then an understanding of the dynamic environment will assist in reducing the packaging requirement. This research looked at the dynamic characteristics of an existing design of wagon using modal analysis. The results from the modal analysis were extended to be inputs to the time domain freight model. Various analytical models of the freight were developed depending on the configuration and dynamic properties. Special consideration was given to a cylinder with its axis transverse to the wagon. The modal model was modified to accommodate the change in mass imposed by the freight. The various sources of dynamic excitation were explored, namely inputs from the coupler and from the bogie. Data from shunting yard simulations were used to generate spectra as input to the wagon model. The objective was to use modal techniques to be able to take individual components, form them into a complete model and make informed decisions about the suitability of a certain configuration for traffic.
Optimum design of grid structures of revolution using homogenised model.
(2000) Slinchenko, Denys.; Verijenko, Viktor.; Adali, Sarp.
The present study involves analysis and design optimisation of lattice composite structures using symbolic computation. The concept of a homogenised model is used to represent heterogeneous composite isogrid structure as a homogeneous structure with the stiffness equivalent to the original grid structure. A new homogenisation technique is developed and used in the present study. The configuration of a unit cell and the geometrical parameters of the ribs of a composite isogrid cylinder are optimised subject to a strength criterion in order to maximise externally applied loading to provide maximum strength and stiffness of the structure as a whole. The effects of tension and torsion on the optimum design are investigated. Special purpose computation routines are developed using the symbolic computation package Mathematica for the calculation of equivalent stiffness of a structure, failure analysis and calculation of optimum design parameters. The equivalent stiffness homogenisation approach, in conjunction with optimum search routines, is used to determine the optimal values of the design variables. The numerical approach employed in the present study was necessitated by the computational inefficiency and conventional difficulties of linking the optimiser and the FEM analysis package for calculating the stress resultants used in the optimisation process. These drawbacks were successfully overcome by developing special purpose symbolic computation routines to compute stress resultants directly in the program using a new homogenisation approach for the model with equivalent stiffness. In the design optimisation of cylindrical isogrids the computational efficiency of the optimisation algorithm is improved and good accuracy of the results has been achieved. The investigation on the basis of failure analysis shows that the difference in the value of the maximum load applied to the optimal and non-optimal isogrid structure can be quite substantial, emphasising the importance of optimisation for the composite isogrid structures. The computational efficiency of optimisation algorithms is critical and therefore special purpose symbolic computation routines are developed for its improvement. A number of optimal design problems for isogrid structures are solved for the case of maximum applied load design.
The development of instrumentation for the direct measurement of heat loss from man in a normal working mode.
(1974) Hodgson, T.; Bindon, Jeffrey Peter.; Reed, M.
Based on a theoretical analysis of the heat transfer process between the human body and its environment, graphs are presented for determining the theoretical skin surface temperatures and sweat rates as a function of the physiological conductance, under certain assumed environmental conditions with regard to air temperature, relative humidity and wind speed. In addition, the development of unique measuring techniques for the direct measurement of the evaporative and radiative heat transfer rates between a human body in a natural working position and its environment as well as the development of a low-cos~ radiometer for the measurement of the emissivity and temperature of human skin are described. The heat loss measuring equipment was installed in the horizontal test section of the climatic chamber of the Human Sciences Laboratory of the Chamber of Mines. Basically the evaporative heat loss measuring system consists of two air-sampling probes, for sampling the air on the upstream and downstream sides of the body , a double circuit heat exchanger, for equalising the dry- bulb temperatures of the two air samples and a differential humidity- measuring system incorporating electrical resistance hygrometero, for measuring the difference in specific humidity between the two air samples. In addition, a steam generator is provided for introducing a known amount of steam at a predetermined rate into the wake of the body. Since the output of the humidity-measuring system is linearly related to the evaporative heat loss rate, the unknown rate of evaporation of moisture from the human body can be determined relatively easily from a knowledge of the respective outputs of the humidity-measuring system due to the moisture evaporation rate of the human body and the known vapour production rate by the steam generator. The direct- measuring instrument for determining the radiation energy exchange rate of a working subject is in the form of a rotating hoop. The inside and outside surfaces of the hoop are lined with thermal radiation-sensing elements, so connected as to measure the net radiation energy exchange between the subject and the surroundings. The hoop integrates over the circular strip formed by the elements and upon rotation, integrates the radiation over the total 4n surface enveloping the subject . While the interposition of a surface between the body and its surroundings must of necessity influence the radiation exchange, the method introduces a small surface only . The significance of the evaporative and radiative heat loss measuring techniques which were successfully used in animate studies, is reflected in the, hitherto unknown, accuracy regarding partial calorimetric studies . The low- cost radiometer for measuring the skin temperature and emissivity is equipped with two non-selective thermal radiation detectors in the form of semi-conductor thermocouples. The one radiation-sensing element faces a built-in reference black body. The other detector, which can be temperature controlled, is used to detect the incoming radiation from the target. The output of the radiation-sensing elements which is sufficiently high to be measured on a recorder without the use of a chopper-amplifier system, can either be measured differentially or the output of the radiation-sensing element facing the target can be measured separately; for the purpose of temperature and emissivity measurements, respectively. The unique facility of being able to vary the temperature of the radiation detector enabled a new method of determining the emissivity of a surface to be developed. As a result, accurate measurements of the emissivities of samples of excised skin could be carried out. An improvement in the response of the radiometer would, however, be necessary for the rapid determination of the emissivity of . living skin by this means. The accuracy with which surface temperatures could be determined by means of the radiometer compared favourably with more sophisticated radiometers.
Non-stationary responses on hoisting cables with slowly varying length.
(1999) Kaczmarczyk, Stefan.; Adali, Sarp.
Cables in hoisting installations, due to their flexibility, are susceptible to vibrations. A common arrangement in industrial hoisting systems comprises a driving winder drum, a steel wire cable, a sheave mounted in headgear, a vertical shaft and a conveyance. This system can be treated as an assemblage of two connected interactive, continuous substructures, namely of the catenary and of the vertical rope, with the sheave acting as a coupling member, and with the winder drum regarded as an ideal energy source. The length of the vertical rope is varying during the wind so that the mean catenary tension is continuously varying. Therefore, the natural frequencies of both subsystems are time-dependent and the entire structure represents a non-stationary dynamic system. The main dynamic response, namely lateral vibrations of the catenary and longitudinal vibrations of the vertical rope, are caused by various sources of excitation present in the system. The most significant sources are loads due to the winding cycle acceleration/deceleration profile and a mechanism applied on the winder drum surface in order to achieve a uniform coiling pattern. The classical moving frame approach is used to derive a mathematical model describing the non-stationary response of the system. First the longitudinal response and passage through primary resonance is examined. The response is analyzed using a combined perturbation and numerical technique. The method of multiple scales is used to formulate a uniformly valid perturbation expansion for the response near the resonance, and a system of first order ordinary differential equations for the slowly varying amplitude and phase of the response results. This system is integrated numerically on a slow time scale. A model example is discussed, and the behaviour of the essential dynamic properties of the system during the transition through resonance is examined. Interactions between various types of vibration within the system exist. The sheave inertial coupling between the catenary and the vertical rope subsystems facilitates extensive interactions between the catenary and the vertical rope motions. The nature of these interactions is strongly non-linear. The lateral vibration of the catenary induces the longitudinal oscillations in the vertical system and vice-versa. In order to analyze dynamic phenomena arising due these interactions the nonlinear partial-differential equations of motion are discretised by writing the deflections in terms of the linear, free-vibration modes of the system, which result in a non-linear set of coupled, second order ordinary differential equations with slowly varying coefficients. Using this formulation, the dynamic response of an existing hoisting installation, where problematic dynamic behaviour was observed, is simulated numerically. The simulation predicts strong modal interactions during passage through external, parametric and internal resonances, confirming the autoparametric and non-stationary nature of the system recorded during its operation. The results of this research demonstrate the non-stationary and non-linear behaviour of hoisting cables with slowly varying length. It is shown that during passage through resonance a large response may lead to high oscillations in the cables' tensions, which in turn contribute directly to fatigue damage effects. The results obtained show also that the non-linear coupling in the system promotes significant modal interactions during the passage through the instability regions. The analysis techniques presented in the study form a useful tool that can be employed in determining the design parameters of hoisting systems, as well as in developing a careful winding strategy, to ensure that the regions of excessive dynamic response are avoided during the normal operating regimes.
The effect of tip clearance and tip gap geometry on the performance of a one and a half stage axial gas turbine.
(1996) Kaiser, Ivan.; Bindon, Jeffrey Peter.
In a previous work of a similar nature, the performance of a low speed axial turbine with a second stage nozzle was examined with respect to the effect of the variation of tip clearance for various tip shapes. Present findings suggest some interesting phenomena, including the effect of tip clearance on the flow within the rotor and show that poor resolution from a transducer and insufficient data points in the critical tip region, where a high velocity peak was found, were responsible for a number of incorrect conclusions in the original study. In terms of blade tip geometry, a standard flat tip shape was found to deliver only a marginally better performance when compared to a double squealer tip and the two streamlined shapes previously investigated. Although contemporary opinion suggests that a streamlined tip should increase the leakage flow and hence cause greater mixing losses, the machine efficiency was not significantly reduced. This is an exciting result since it suggests that a streamlined tip shape can be used to alleviate the problem of blade tip burnout without significantly reducing machine efficiency. When the single stage performance in the absence of a second nozzle was examined, slightly different trends were obtained. The low entropy tips produced slightly lower mixing loss, suggesting that the internal gap loss is an important parameter in determining the rate at which the leakage jet mixes downstream of the rotor. The flow behind the rotor (ie time averaged) was found to be in remarkable agreement with linear cascade data when time averaged even though the latter did not include any effects of relative motion. An increase in clearance was seen to reduce the Euler work and also to cause a deficit of mass flow across the remainder of the blade right down to the hub. The leakage flow was also seen to induce a flow blockage which resulted in a higher driving pressure across the rotor for the same mass flow rate. As in the previous study, the second stage nozzle efficiency was seen to be independent of tip clearance or tip shape and was moderately better than that of the first nozzle. However, the improvement was not found to be as large, due to a previously undetected very thin ring of high energy leakage fluid. When this is taken into account, the efficiency of the second stage nozzle is comparable to the first. The second nozzle was seen to have a flow straightening effect on the poorly deflected, high energy leakage flow, causing a rapid mixing process within these downstream blade passages. The growth of secondary flow was reduced at both the hub and the tip and this is believed to result in a slight decrease in loss. The outlet flow was closer to design conditions than that of the first stage nozzle.
Analysis and design optimization of laminated composite structures using symbolic computation.
(1994) Summers, Evan.; Adali, Sarp.; Verijenko, Viktor.
The present study involves the analysis and design optimization of thin and thick laminated composite structures using symbolic computation. The fibre angle and wall thickness of balanced and unbalanced thin composite pressure vessels are optimized subject to a strength criterion in order to maximise internal pressure or minimise weight, and the effects of axial and torsional forces on the optimum design are investigated. Special purpose symbolic computation routines are developed in the C programming language for the transformation of coordinate axes, failure analysis and the calculation of design sensitivities. In the study of thin-walled laminated structures, the analytical expression for the thickness of a laminate under in-plane loading and its sensitivity with respect to the fibre orientation are determined in terms of the fibre orientation using symbolic computation. In the design optimization of thin composite pressure vessels, the computational efficiency of the optimization algorithm is improved via symbolic computation. A new higher-order theory which includes the effects of transverse shear and normal deformation is developed for the analysis of laminated composite plates and shells with transversely isotropic layers. The Mathematica symbolic computation package is employed for obtaining analytical and numerical results on the basis of the higher-order theory. It is observed that these numerical results are in excellent agreement with exact three-dimensional elasticity solutions. The computational efficiency of optimization algorithms is important and therefore special purpose symbolic computation routines are developed in the C programming language for the design optimization of thick laminated structures based on the higher-order theory. Three optimal design problems for thick laminated sandwich plates are considered, namely, the minimum weight, minimum deflection and minimum stress design. In the minimum weight problem, the core thickness and the fibre content of the surface layers are optimally determined by using equations of micromechanics to express the elastic constants. In the minimum deflection problem, the thicknesses of the surface layers are chosen as the design variables. In the minimum stress problem, the relative thicknesses of the layers are computed such that the maximum normal stress will be minimized. It is shown that this design analysis cannot be performed using a classical or shear-deformable theory for the thick panels under consideration due to the substantial effect of normal deformation on the design variables.
Optimisation of the process parameters of the resin film infusion process.
(1999) Von Klemperer, Christopher Julian.; Verijenko, Viktor.
The resin film infusion process or RFI is a vacuum assisted moulding method for producing high quality fibre reinforced components. The goals of this research have been to investigate this new process, with the aim of determining how the process could be used by the South African composites industry. This included factors such as suitable materials systems, and optimum process parameters. The RFI process is a new composite moulding method designed to allow fibre reinforced products to be manufactured with the ease of pre-preg materials while still allowing any dry reinforcement material to be used. The high pressures required for traditional manufacturing methods such as autoclaves, matched dies and R TM can be avoided while still having very accurate control over the fibre / resin ratio. Moreover, the RFI process is a "dry" process and hence avoids many of the environmental and health concerns associated with wet lay-up and vacuum bag techniques. Furthermore the simple lay-up process requires less skill than a wet lay-up and vacuum bag method. Through a combination of mathematical modelling and physical testing, a material system has been identified. The primary process parameters were identified and a strenuous regime of testing was performed to find optimum values of these parameters. These results were finally feed back into the development of the mathematical model.

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