Mechanical Engineering

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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.
The measurement of axial turbine tip clearance flow phenomena in a moving wall annular cascade and in a linear cascade.
(1989) Morphis, George.; Bindon, Jeffrey Peter.
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.
The use of discrete event simulation techniques to optimize a proposed factory layout.
(1989) Gokal, Manooj.; Guthrie, A. M.
This project has proved conclusively that discrete event simulation techniques can be used to simulate, on computer, a complex stochastic materials handling system. The packing, automatic palletising and warehousing departments of a large powders manufacturing factory was used as an example to investigate the capabilities of computer simulation. The company intends to increase the number of packing machines from seven to eleven, and has embarked on productivity improvement projects that aims to increase the average packing efficiency from the current 50%, to 60% with a long term goal of 70%. Due to the stochastic nature of the run and stop durations of the packing machines, it was impossible to predict the effect of the increased throughput on the palletising system by conventional means. The system was modelled on computer using the SIMAN simulation language. Extensive research was initially carried out in order to determine the operating parameters of the system. The generation of cases from the packing machines in the program was verified against actual production runs. Various alternatives were analyzed to assist in decision making on the expansion of the palletising system in order to accommodate the increased throughput expected from the packing floor. The simulation was therefore used to increase the capacity of the automatic palletising system at minimal cost while meeting demands from the packing floor. It was established that the only capital expenditure required would be about R500 000 to increase the capacity of a palletiser and to provide a pallet conveyor to transport 40% of the pallets to direct despatch.
Communication, mapping and navigational aspects for a free-ranging, automated guided vehicle.
(1992) Asbury, James.; Katz, Z.
A free-ranging automated guided vehicle incorporating navigation and radio communication for use in a fully automated flexible manufacturing system has been developed. A vehicle, operating as a complete subsystem, was built and tested in an integrated control environment and proved to have promising results. various radio communication techniques are examined and the design and testing of a low cost, wireless, two way communication link is detailed. A novel, flexible infrared navigation technique was developed and incorporated into the AGV subsystem. Path planning and a flexible real time path modification system was formulated using an innovative program with an interpolative visual display unit and digitiser. Data transfer to and from the vehicles in a real time integrated system is covered. System integration for an free-ranging automatic guided vehicle is discussed covering aspects of communication, mapping and navigation. Specific needs for a free-ranging automatic guided vehicle, are presented. The unique design features of navigation and mapping outlined in this thesis has resulted in a low cost, free-ranging, autonomous automatic guided vehicle.
Modelling saturated tearing modes in tokamaks.
(1992) McLoud, Willem Stephanus.; Sherwell, David.; Hellberg, Manfred Armin.
In this thesis a model for saturated tearing mode islands is developed. The equations for the mode amplitudes are essentially those of R B White et al,after a pertubation expansion has been made. It is well known that these equations are not then analytic at the mode rational surface. In our model this problem is overcome when a suitable choice of the axisymmetric current density perturbation is added to the unperturbed equilibrium current density profile. The modelled axisymmetric current density perturbation flattens the unperturbed profile locally at the rational surface and is sufficient to induce an island. No modelling in the interior of the island is necessary. The axisymmetric perturbation has a free variable which adjusts the amount of local flattening. However, when the boundary conditions are taken into account, this free parameter is determined, and the problem becomes an eigenvalue problem. The boundary condition thus determines the amount of local flattening at the rational surface. The saturated island widths are determined using D.' (W) criterion. The model allows for non axsymmetric plasma surface in a simple way, requiring careful choice of D (W). The different criteria are compared to establish the validity of the use of such criteria for perturbed boundaries. In the cylindrical approximation, one or two modes may be included in the model. In the case of two modes, non-linear coupling via the current density profile is introduced. Toroidal coupling between modes can also be simply introduced. Two modes that are toroidally coupled are considered, but mode-mode coupling is ignored. The emphasis falls in large part on the boundary conditions. Various boundary conditions can be considered because distortion of the plasma surface can be fixed by wall effects, plasma rotation, external DC coil currents, plasma rotation with external coil currents, etc. Of particular interest is the case of toroidally coupled modes, coupled in turn to these external conditions as this is the first study of such a nature. Results flowing from the study include among others that: for the special case of circular boundaries the model agrees reasonably with the results of R B White et al. No significant difference was found between the D. I (W) criterion of P H Rutherford, which is valid for circular boundaries, and that of A H Reiman, which is also valid for perturbed boundaries, when the boundary is perturbed significantly. Toroidally coupled islands do not increase in size if the boundary condition of that particular mode is not changed. If a coil current of particular helicity is switched on, it will only affect the mode of that particular helicity. Toroidally induced sideband islands have approximately the same width as natural tearing islands when the size of the natural island is large.
The performance of a one and a half stage axial turbine including various tip clearance effects.
(1993) Morphis, George.; Bindon, Jeffrey Peter.
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.
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.
The optimal design of laminated plates for maximum buckling load using finite element and analytical methods.
(1994) Walker, Mark.; Adali, Sarp.; Verijenko, Viktor.
In the first part of the study, finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load by determining the fibre orientations optimally with the effects of bending-twisting coupling taken into account. The finite element method coupled with an optimisation routine is employed in analysing and optimising the laminated plate designs. The effect of boundary conditions, the number of layers and bending-twisting coupling on the optimal ply angles and the buckling load are numerically studied. Optimal buckling designs of symmetrically laminated rectangular plates under in-plane uniaxial loads which have a nonuniform distribution along the edges are presented in the second part of the study. In particular, point loads, partial uniform loads and nonuniform loads are considered in addition to uniformly distributed in-plane loads which provide the benchmark solutions. Poisson's effect is taken into account when in-plane restraints are present along the unloaded edges. Restraints give rise to in-plane loads at unloaded edges which lead to biaxial loading, and may cause premature instability. The laminate behavior with respect to fiber orientation changes significantly in the presence of Poisson's effect as compared to that of a laminate where this effect is neglected. This change in behavior has significant implications for design optimisation as the optimal values of design variables with or without restraints differ substantially. In the present study, the design objective is the maximisation of the uniaxial buckling load by optimally determining the fiber orientations. Numerical results, determined using the finite element method, are given for a number of boundary conditions and for uniformly and non-uniformly distributed buckling loads. In the third part of the study, finite element solutions are presented for the optimal design of symmetrically laminated rectangular plates with central circular cut-outs subject to a combination of simply supported, clamped and free boundary conditions. The design objective is the maximisation of the biaxial buckling load by determining the fiber orientations optimally. The effect of boundary conditions and bending-twisting coupling on the optimal ply angles and the buckling load are numerically studied. The results are compared to those for laminates without holes. The fourth part of the present study gives optimal designs of symmetrically laminated angle-ply plates, which are obtained with the objective of maximising the initial post buckling stiffness. The design involves optimisation over the ply angles and the stacking sequence to obtain the best laminate configuration. The stacking sequence is chosen from amongst five candidate designs. It is shown that the best configuration depends on the ratio of the in-plane loads in the x and y directions. Results are also given for two additional configurations which do not exhibit bending-twisting coupling. The final section of the present study deals with the optimal design of uniaxially loaded laminated plates subject to elastic in-plane restraints along the unloaded edges for a maximum combination of prebuckling stiffness, postbuckling stiffness and buckling load. This multiobjective study illustrates that improved buckling and post buckling performance can be obtained from plates which are designed in this fashion. The multiobjective results are also compared to single objective design results.
Computational and analytical modelling of composite structures based on exact and higher order theories.
(1995) Tabakov, Pavel.; Adali, Sarp.; Verijenko, Viktor.
The objective of the present study is the computational and analytical modelling of a stress and strain state of the composite laminated structures. The exact three dimensional solution is derived for laminated anisotropic thick cylinders with both constant and variable material properties through the thickness of a layer. The governing differential equations are derived in a such form that to satisfy the stress functions and are given for layered cylindrical shell with open ends. The solution then extended to the laminated cylindrical shells with closed ends, that is to pressure vessels. Based on the accurate three-dimensional stress analysis an approach for the optimal design of the thick pressure vessels is formulated. Cylindrical pressure vessels are optimised taking the fibre angle as a design variable to maximise the burst pressure. The effect of the axial force on the optimal design is investigated. Numerical results are given for both single and laminated (up to five layers) cylindrical shells. The maximum burst pressure is computed using the three-dimensional interactive Tsai-: Wu failure criterion, which takes into account the influence of all stress components to the failure. Design optimisation of multilayered composite pressure vessels are based on the use of robust multidimensional methods which give fast convergence. Transverse shear and normal deformation higher-order theory for the solution of dynamic problems of laminated plates and shells is studied. The theory developed is based on the kinematic hypotheses which are derived using iterative technique. Dynamic effects, such as forces of inertia and the direct influence of external loading on the stress and strain components are included at the initial stage of derivation where kinematic hypotheses are formulated. The proposed theory and solution methods provide a basis for theoretical and applied studies in the field of dynamics and statics of the laminated shells, plates and their systems, particularly for investigation of dynamic processes related to the highest vibration forms and wave propagation, for optimal design etc. Geometrically nonlinear higher-order theory of laminated plates and shells with shear and normal deformation is derived. The theory takes into account both transverse shear and normal deformations. The number of numerical results are obtained based on the nonlinear theory developed. The results illustrate importance of the influence of geometrical nonlinearity, especially, at high levels of loading and in case when the laminae exhibit significant differences in their elastic properties.
High temperature fatigue crack growth behaviour of TIMETAL 21S in an oxidizing environment.
(1995) Ferreira, Jacques Henri.; Aghion, E. E.
The high temperature fatigue crack growth behaviour of the newly developed, metastable titanium-based alloy, TIMETAL 21S, was investigated in an inert and an oxidizing environment. The investigation adopted a two pronged approached, namely, to initially establish the pure microstructural behaviour under oxidizing and inert environments at various elevated temperatures, and consequently, to establish the environmental effects on the fatigue crack growth behaviour in the various environments at high temperature. The effect of the oxidizing environment on the metastable alloy and on the mechanical and chemical events occurring at the fatigue crack were studied by using optical and scanning electron microscopy, including ED X analysis, x-ray diffraction, and Auger Electron Spectroscopy (AES) . For the microstructural investigation, the TIMETAL 21S samples were exposed for 5 hours to a pure argon and argon + 20% O2 environment at 300°C to 750°C in increments of 50°C. The results showed that in the oxidizing environment a more homogeneous nucleation of the alpha phase had occurred at higher temperatures and that the oxide Ti02, in addition to the alpha case, had predominantly formed on the exposed surfaces. AES analysis showed that dissolution of the oxygen into the alloy occurred even at low temperatures. An LEFM approach was used to investigate fatigue crack growth rate (FCGR) of C(T) specimens at 375°C, 450°C, 550°C and 620°C in the argon and argon + 20% oxygen environment. The crack growth rates were monitored using load-line compliance and the beachmarking method - a method by which beach marks were impressed on the fracture surface to track the progressing crack. The results showed that the crack growth rates were lower in the oxidizing environment and was influenced by a synergistic effect of the temperature, stress intensity at the crack tip and the environment. In addition to the phenomena of crack tip shielding (a process whereby the effective crack tip driving force experienced at the crack tip was locally reduced), other mechanisms such as slip character modification and secondary cracking ahead of the crack tip, leading to crack tip blunting and branching, had to be incorporated to fully explain the crack growth behaviour. The tests conducted in the inert environment effectively excluded the effect of oxygen on the crack growth behaviour and substantiated that various mechanisms ultimately determined the FCGR in TIMETAL 21S at elevated temperatures.
Finite element and analytical solutions for the optimal design of laminated composites.
(1996) Reiss, Talmon.; Adali, Sarp.; Walker, Mark.
The present study involves the analysis and design optimisation of composite structures using analytical and numerical methods. Five different problems are considered. The first problem considers the design of laminated plates subject to non-uniform temperature distributions. The plates are optimised for maximum buckling temperature using the fibre angle as the optimising variable. The method of solution involves the finite element method based on Mindlin theory for thin laminated plates and shells, and numerical optimisation. A computational approach is developed which involves successive stages of solution for temperature distribution, buckling temperature and optimal fibre angle. Three different temperature loadings are considered and various combinations of simply supported and clamped boundary conditions are studied. The effect of plate aspect ratio on the optimal fibre angle and the maximum buckling temperature is investigated. The influence of bending-twisting coupling on the optimum design is studied by considering plates with increasing number of layers. The second problem concerns the optimal design of composite pressure vessels. Finite element solutions are presented for the design of hemispherically and flat capped symmetrically laminated pressure vessels subjected to external pressure. The effect of vessel length, radius and wall thickness, as well as bending-twisting coupling and hybridisation on the optimal ply angle and buckling pressure are numerically studied. Comparisons of the optimal fibre angles and maximum buckling pressures for various vessel geometries are made with those for hybrid pressure vessels. In the third problem, the multiobjective design of a symmetrically laminated shell is obtained with the objectives defined as the maximisation of the axial and torsional buckling loads. The ply angle is taken as the optimising variable and the performance index is formulated as the weighted sum of individual objectives in order to obtain Pareto optimal solutions of the design problem. Single objective design results are obtained and compared with the multiobjective design. The effect of weighting factors on the optimal design is investigated. Results are given illustrating the dependence of the optimal fibre angle and performance index on the cylinder length, radius and wall thickness. In the fourth problem, the optimal layup with least weight or cost for a symmetrically laminated plate subject to a buckling load is determined using a hybrid composite construction. A hybrid construction provides further tailoring capabilities and can meet the weight, cost and strength constraints while a non-hybrid construction may fail to satisfy the design requirements. The objective of the optimisation is to minimise either the weight or cost of the plate using the ply angles, layer thicknesses and material combinations as design variables. As the optimisation problem contains a large number of continuous (ply angles and thicknesses) and discrete (material combinations) design variables, a sequential solution procedure is devised in which the optimal variables are computed in different stages. The proposed design method is illustrated using graphite, kevlar and glass epoxy combinations and the efficiency of the hybrid designs over the non-hybrid ones are computed. Finally, the minimum deflection and weight designs of laminated composite plates are given in the fifth and last problem. The finite element method is used in conjunction with optimisation routines in order to obtain the optimal designs, as was the procedure in the first problem. Various boundary conditions are considered and results are given for varying aspect ratios and for different loading types.
Investigation into on-line optimization of cutting tool geometry.
(1996) Bosch, Christiaan Wilhelm.; Katz, Z.
Metal cutting is an important process used to manufacture components with machined surfaces or holes. Due to the wide usage o f this manufacturing process, research with the aim to optimize the cutting processes is important. Improving cutting techniques even mild)s can result in major cost savings in high volume production. Better machining practices will result in products of better precision and of greater useful life . Benefits can also be had from increasing the rate of production and producing a bigger variety of .. products with the tools available. The area of metal cutting has been researched widely by people like Tourrett, Taylor, Cohen, Davis and many others to find improved techniques and methods. This project was conducted to improve cutting conditions by ensuring that the tool geometry is always optimal . The effect of tool geometry on cutting performance has been discussed in detail by many researchers, but the practical application of these theories is an area that needs further attention. For this project a device was developed to vary the tool geometry with stepper motors on command from the controller. This device was used for research into the viability of varying tool geometry during machining to obtain different cutting conditions. Stepper motors ensure high accuracy in the control of tool geometries. The ease of controlling stepper motors, also simplified the controlling program and communication devices a lot. Rotating the stepper motors results in rotation o f the tool holder around the tool tip. Tool angles are varied without affecting the other cutting parameters like the depth o f cut, metal removal rate and cutting speed. With these cutting parameters staying the same, the change in tool geometry should result in a change in the power consumed during cutting and the force required for cutting . Other measurements for cutting performance like temperature of the tool and workpiece and the acoustic print of the tool will also change. Results prove that cutting force measurement can be used effectively to measure the optimal cutting conditions . The back rake angles and side rake angles have the biggest influence of all the tool angles on metal cutting . This is demonstrated by a number of researchers [28] as discussed in section 2 . 2. This thesis proves how the on-line changing of tool geometry, ensures the optimal cutting conditions.
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.
The influence of sulphidizing attack on the mechanism of failure of coated superalloy under cyclic loading conditions.
(1998) Govender, Gonasagren.; Aghion, E. E.
A systematic study of the effect of sulphidizing atmosphere on the High Temperature Low Cycle Fatigue (HTLCF) properties of coated and uncoated unidirectionally solidified MARM002 nickel base superalloy was performed at 870°C. The coating systems investigated were, aluminide coating, three types of platinum modified aluminide coatings, and platinum coating. The creep-plasticity mode of the strain range partitioning method was used for creep-fatigue loading. A constant loading regime (Strain range 6.6 x 10-3 ) was used to test the samples in argon, air and Ar + 5%S02 and a lower strain range of3.8 x 10-3 was used to investigate the creep-fatigue properties in Ar + 5%S02 only. The results were analysed using scanning electron microscopy including spot analyses (SEM-EDS), Auger electron spectroscopy (AES) and X-ray diffraction (XRD) techniques. The synergistic effect of sulphidizing environment and the creep fatigue loading (Strain range - 0.66%) resulted in accelerated failure in all the materials systems tested, except for the TYPE I platinum aluminide coated sample. This coating displayed a "self-healing" mechanism which enhanced its fatigue life under sulphidizing conditions. In general, the coatings had an adverse effect on the fatigue properties of the material systems. This was due to the poor mechanical properties of the coating. The mechanical properties of the coating was influenced by the coating microstructure and the chemical composition. The modification of the NiAI zone with platinum in the platinum aluminide coatings improved the fatigue properties of the coating by altering the crack propagation mechanism in the NiAl zone. The higher the platinum content in this region the more brittle it became. The platinum modified aluminide coating showed an improvement in the corrosion fatigue properties in the S02 containing environment at the higher strain range when compared with the uncoated, aluminide coated and platinum coated samples. However, at the lower strain range all the coating systems performed worse than the uncoated alloy. This was mainly due to the brittle failure of the coating. The platinum modified aluminides performed the worst due to the presence of brittle platinum aluminide phases. The interdiffusion and interaction of platinum with the substrate alloying elements, resulted in this coating being ineffective for corrosion protection. The resultant coating layer produced poor corrosion-fatigue properties. Although the coating systems did show evidence of resistance to sulphidation and oxidation there were relatively ineffective under the combination of sulphidizing environment and fatigue loading due to their poor mechanical properties. The mechanism of sulphidation was consistent for all the material systems tested with oxidation proceeding first and sulphidation proceeding at the corrosion scale/substrate interface. The crack propagation in the coating and substrate was controlled by the sulphidation attack at the crack tip and failure of the oxide scales formed in the cracks.
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.
A mechanistic evaluation and design of tunnel support systems for deep level South African mines.
(1999) Haile, Andrew Thurlo.; Verijenko, Viktor.; Adali, Sarp.
The design of support systems, comprising rock bolt reinforcement and fabric containment components for tunnels in deep level mining environments does not currently cater well for adverse rock mass conditions. This often results in periodic failure of the support system, particularly under dynamic (rockburst) conditions with the potential for total collapse of the excavation. The design of support systems is currently based either on empirical design guidelines often not applicable to this environment or simple mechanistic models. This thesis details a methodology for the rational design of tunnel support systems based on a mechanistic evaluation of the interaction between the components of a support system and a highly discontinuous rock mass structure. This analysis is conducted under both static and dynamic loading conditions. Due to the highly complex and variable nature of the rock mass structure and the dynamic loading environment, a large component of the practical work on the evaluation of the mechanisms of rock mass deformation and support interaction is based on rockburst case studies. The understanding gained from these investigations is further evaluated by means of laboratory testing of the performance of the components of the support systems and numerical modelling of the interaction of the components of the support system with the rock mass. Due to the complex nature of this design environment the methodology developed in this thesis is but a step towards our greater understanding of the behaviour of the rock mass, and the interaction of support systems in the stabilisation of tunnel excavations. However, in comparison to the current design, this methodology now allows the design engineer to make better estimations of the anticipated demand on the different components of the support systems, under a defined rock mass environment on engineering principles. This understanding will give the design engineer greater flexibility, and confidence to design the appropriate tunnel support system for a specific rock mass and loading condition based on the often limited availability of different support units in the underground mining environment.
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.
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.
Coriolis effect on the stability of convection in mushy layers during the solidification of binary alloys.
(2000) Govender, Saneshan.; Vadasz, Peter.;
We consider the solidification of a binary alloy in a mushy layer subject to Coriolis effects. A near-eutectic approximation and large far-field temperature is employed in order to study the dynamics of the mushy layer in the form of small deviations from the classical case of convection in a horizontal porous layer of homogenous permeability. The linear stability theory is used to investigate analytically the Corio lis effect in a rotating mushy layer for, a diffusion time scale used by Amberg & Homsey (1993) and Anderson & Worster (1996), and for a new diffusion time scale proposed in the current study. As such, it is found that in contrast to the problem of a stationary mushy layer, rotating the mushy layer has a stabilising effect on convection. For the case of the new diffusion time scale proposed by the author, it is established that the viscosity at high rotation rates has a destabilising effect on the onset of stationary convection, ie. the higher the viscosity, the less stable the liquid. Finite amplitude results obtained by using a weak non-linear analysis provide differential equations for the amplitude, corresponding to both stationary and overstable convection. These amplitude equations permit one to identify from the post-transient conditions that the fluid is subject to a pitchfork bifurcation in the stationary case and to a Hopf bifurcation associated with the overstable convection. Heat transfer results were evaluated from the amplitude solution and are presented in terms of the Nusselt number for both stationary and overstable convection. They show that rotation enhances the convective heat transfer in the case of stationary convection and retards convective heat transfer in the oscillatory case, but only for low values of the parameter X I = 8 Pr ~ 0 So· The parameter 1/ X I represents the coefficient of the time derivative term in the Darcy equation. For high X I values, the contribution from the time derivative term is small (and may be neglected), whilst for small X I values the time derivative term may be retained.
Cordless linear synchronous motor material handling system for computer integrated manufacturing.
(2000) Lindsay, Craig Vaughn.; Bright, Glen.; Hippner, Maciej.
Advanced material handling systems' impact on flexible manufacturing systems (FMS) have increased the efficiency and work rate over conventional manufacturing assemblies. The interaction of automated guided vehicles (AGVs), roller conveyors and conveyor belts with robots and machine tools forms highly sophisticated assembly operations. Whilst material handling in FMS today is conventionally used to transport assembly units from one work station to another, it does not take an active role in the manufacturing process. With manufacturers implementing more advanced manufacturing principles to perform agile manufacturing, there is a growing need to implement "smarter" material handling systems that would perform essential, integral roles in the assembly process. This research outlines the development of a cordless linear synchronous motor (CLSM) material handling system. The CLSM incorporates a permanent magnet courier that moves without tether restrictions on an integrated reverse air bearing system which eliminates friction. The CLSM provides a material handling system with enhanced travel, flexibility and accuracy. The CLSM material handling system is designed to integrate with overhead manipulators and part feeders to form a comprehensive flexible manufacturing system. This research covers the 2-D finite element modeling (FEM) used to determine the CLSM's optimal parameters. The development of the motor windings design and construction, together with the control system for the CLSM, is also covered. The CLSM novel air bearing system is outlined and compared to other conventional linear bearing systems. The possible impact of the CLSM on current manufacturing systems is explored to determine the validity of the research project and possible further research opportunities.

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