Mechanical Engineering - Theses
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ItemMiscibility, morphology and physical properties of blends of polycarbonate with a range of thermoplastic polyesters(University of Melbourne, 1991)This study aims to gain an understanding of the relationship between miscibility, morphology and physical properties of polycarbonate (PC)/thermoplastic polyester blends. Blends of PC with 6 polyesters were prepared. The blends were compounded using a single screw extruder and then injection moulded to form test pieces. A transesterification inhibitor was added to prevent transesterification occurring during the melt processing. The miscibility of the blends was determined using Differential Scanning Calorimetry and Dynamic Mechanical Thermal Analysis. The blends exhibited a range of miscibilities from completely miscible to almost immiscible. The miscibility of some of the blends was found to be dependent on the method of blend preparation, and whether or not transesterification had occurred. Transmission Electron Microscopy of Ruthenium Tetroxide stained sections of the blends was used to study their morphology. As would be expected, the partially miscible blends showed phase separation, whereas the miscible ones did not. The morphology of the partially miscible blends was found to be dependent on the viscosities of the homopolymers and the shear rate applied to the blend during melt processing. Small Angle X-ray Scattering was used to study how the spherulitic morphology of the semicrystalline polyesters was effected by blending them with PC. As the miscibility of the blend increased, an increasing amount of PC became incorporated between the lamellae of crystalline polyester. The resistance to fracture of the blends was determined under both constant strain rate and impact conditions. Tensile tests and Scanning Electron Microscopy of fracture surfaces was used to aid the interpretation of the fracture results. Under constant strain rate conditions, the fracture toughness of the partially miscible blends was dependent on the adhesion between its phases. If the adhesion was poor, the blend had a low resistance to fracture. If the adhesion was good, the fracture toughness was dependent on the morphology of the blend and the relative ductilities of the homopolymers. If the blend consisted of domains of ductile material dispersed through a brittle matrix, its fracture toughness was synergistic. However, if the blend consisted of rigid domains dispersed through a ductile matrix, its resistance to fracture was poor. If the two phases had similar ductilities, the fracture toughness of the blend was additive. Miscible blends were found to have poor resistance to fracture under constant strain rate conditions. These blends had greater than additive densities, indicating that they contain less free volume than their corresponding homopolymers. This results in reduced molecular mobility, which embrittles the material, because it is unable to undergo energy dissipative plastic deformation. The fracture toughness of one particular miscible blend was further reduced by the poor adhesion between the crystalline phase of one of the polymers and the mixed amorphous phase. The impact strength of the blends was found to increase as the miscibility of the blend increased.
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ItemAssembly line sequencing for product-mix( 1971)This thesis is concerned with the sequencing of various models of a product when these are manufactured on one assembly line using product-mix. A simplified model of the assembly line is postulated. Four heuristic algorithms are developed which aim at minimizing assembly line length while avoiding operator interference. Two of these algorithms are used in a factorial experiment to determine the relationship between assembly line length and five factors. These factors are characteristics of the production requirement and workload balance. From the experimental results, empirical equations are developed which are a useful aid in the design of new assembly lines or the balancing of existing assembly lines. The experimental results are also analyzed to determine a range of sequencing problems for which near optimal sequences can be expected using the two algorithms.
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ItemEffects of rotation on turbulent boundary layers and wakes( 1986)This work describes experiments of two simple flow cases with imposed system rotation. The first flow is a boundary layer that develops on the flat vertical side-wall of the working section. A trip-wire causes transition, so that the flow in the boundary layer is fully turbulent. The opposite side-wall has been adjusted so that the pressure gradient is zero. The axis of rotation is parallel to the span of the vertical side-wall. The rotation affects the boundary layers; depending on the direction of rotation the changes can be seen as caused by a stabilisation or destabilisation of the flow. A number of mean flow and turbulence data measured with dynamically calibrated hot-wires are presented, both measured as ordinary boundary-layer profiles and, in the presence of 3-dimensionalities, as contour plots. Similarities between the stabilising/destabilising effects of rotation and density stratification, and also curvature, are pointed out. The second flow is the turbulent wake behind a circular cylinder. Each model used in the study is suspended in the middle of the free stream of the working section, with its axis parallel to the axis of rotation. Since the effects of rotation are found to be negligible close to the cylinder, the wake has been followed for several hundred diameters downstream. There the two initially symmetric sides of the wake have grown asymmetric. The observed effects of rotation are explained in terms of transport equations and alternatively by a qualitative model based on assumed structures underlying the turbulence and their behaviour when subject to rotation.
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ItemModelling heat pump grain drying systems( 1990)Drying is a common process in a number of industries. Products such as furs, wools, textiles, clay, timber, grains, fruits, and vegetables, at some stage, require drying. Review of the literature reveals that commercial dryers are highly inefficient due to various factors. One such factor is that commercial dryers are generally not equipped with heat recovery facilities. Heat pumps can provide a very efficient means of recovering both sensible and latent heat, hence energy loss can be substantially reduced. Furthermore, a heat pump always delivers more heat than the work input to the compressor. These two salient features render heat pump drying a premium alternative for efficient use and conservation of energy in drying industries.
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ItemMotorcycle rider skill assessment( 1983)To determine the differences between the control strategies of skilled and less-skilled riders as they control the lateral and longitudinal motion of a motorcycle, a study of motorcycle handling skills and their assessment was carried out. For the experiments, an instrumented motorcycle was developed which allowed the recording of the various rider/cycle control and response variables while skill tests were being conducted. Riders with a range of riding skills performed a standard skill test and an alternative skill test on the instrumented motorcycle. The experimental data were extensively examined and differences in the control behaviour over the range of riding skills were identified and quantified. A theoretical model was developed describing how less-skilled riders may control the lateral motion of their motorcycle.
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ItemThe form drag of two-dimensional bluff-plates immersed in turbulent shear flows( 1965)The literature concerning bluff-body flows in two-dimensional, incompressible, sheared and unsheared streams is reviewed. It is found that no theory yet exists which can predict the form drag of a bluff body without some recourse to experimental data, even for the simple case of an isolated bluff-plate in an unsheared stream. In the present state of knowledge, and considering the complexity of turbulent shear flows, a theory for the form drag of bluff-plates immersed in turbulent boundary-layers seems remote. A correlation scheme is proposed to relate the form drag of a bluff-plate which is attached to a smooth-wall with the mean-flow characteristics of the naturally-developed, turbulent boundary-layer in which it is immersed. The investigation is limited to smooth-wall flows of the type described by Coles (1956). It is suggested that, for bluff-plates which are small compared with the boundary-layer thickness, the drag might depend only on the “wall variables”: wall shear-stress, fluid density and viscosity, and the plate height.
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ItemLow-Reynolds-number turbulent boundary layers( 1988-12)This thesis documents an extensive experimental investigation into low-Reynolds-number turbulent boundary layers flowing over a smooth flat surface in nominally zero pressure gradients. The way in which these layers are affected by variations in R(theta), i.e. the Reynolds number based on the boundary-layer momentum thickness, type of tripping device used and variations in freestream velocity, each considered independently, are investigated.
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ItemFurther developments of hot wire and laser methods in fluid mechanics( 1974)Some further developments of hot wire and laser methods in fluid mechanics are examined in some detail. Since it is felt that the laser-Doppler method of measuring velocity will eventually supersede the present hot wire methods in many applications, only the response of a hot wire anemometer to temperature fluctuations is considered. This study shows that the constant temperature anemometer is unsuitable for the direct measurement of temperature fluctuations, but that a constant current anemometer operated at very low resistance ratios can be made to work quite well. An appropriate design is developed, calibration methods are outlined for the direct measurement of temperature turbulence and Reynolds heat flux, and it is shown how the possible errors due to end conduction may be eliminated by increasing the length to diameter ratio of the wire filament. In the study of the laser-Doppler velocimeter an optimization procedure is developed, taking into account such factors as particle size, measurement volume size, the width of the Doppler spectrum and the frequency response of the electronic processor. A reference beam system, designed with the aid of this optimization procedure is then used to measure velocity profiles across a vertical line vortex in water. This vortex is produced in a vortex tube with a central outlet.
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ItemThe four bar linkage as a function generator( 1960)Part I: A new concept of the synthesis of the four bar linkage as a function generator is presented. Existing methods of synthesis are examined in the light of this concept, and their advantages discussed. The basis for a new method of synthesis is presented. Part II: A machine which mechanically allows finding the by trial four bar linkage whose polodes are most nearly like the curves which generate the given function exactly has been constructed and calibrated. The apparatus is described and the conditions which indicate a solution are stated. Proof that these conditions are a solution is given. Two simple graphical methods of approximate synthesis have been developed and are used to minimize the trial and error required.
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ItemThe influence of gold-mining on the development of engineering manufacturing in Victoria during the 19th century( 1988)This thesis is a study of how gold-mining contributed to the growth of Victoria's engineering industry prior to 1900. It examines how the demand for the repair and manufacture of mining machinery encouraged local engineering firms to improve their expertise and reputation and to increase their productive capacity. It is argued that the demand for gold-mining machinery provided not only the main initial stimulus for the establishment of the industry during the 1850's and 1860's, but also that it was an important ongoing influence in the later decades of the 19th century, particularly in the non-metropolitan region of Victoria. In the course of this study, extensive use was made of several statistical sources, principally the Statistical Registers of Victoria (for a record of manufacturing establishments and import and export trade), and the Mining Surveyors & Registrars' Statistics (for a record of the quantity of mining machinery employed on the various goldfields). The picture gained from these statistical sources is extended and filled in with descriptive information from newspapers and mining reports which provide a better indication of the effect of technological developments, personal enterprise, and the associations which developed between gold-mining companies and local engineering firms. Ballarat, Castlemaine and Bendigo are identified as the three most important centres in Victoria for the manufacture of mining machinery prior to 1900. However, it is also recognised that a number of important manufacturers existed in Melbourne, and in some smaller country towns such as Clunes, Stawell, Maryborough and Geelong. It is argued that the success of firms in Ballarat, Castlemaine and Bendigo can be largely explained by two factors: the size and continuity of local demand; and the central location of these towns, which minimised the cost of railway freight but still provided convenient access to most of the Victorian goldfields. A discussion of factors such as cost competitiveness, technical innovation, and specialisation of reputation, helps to explain why Victorian firms, both in these towns and elsewhere, came to dominate the supply of mining machinery throughout Victoria by 1900. In the later sections of the thesis, an examination of diversification and the development of export markets explains how the Victorian heavy engineering industry was able to cope with a gradual decline in the demand for mining machinery on many Victorian goldfields after 1875.