Mechanical Engineering - Theses
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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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ItemSome aspects of turbulent boundary layers( 1969)A detailed experimental programme of two dimensional rough wall turbulent boundary layers developing in zero and arbitrary adverse pressure gradients is used to investigate aspects of turbulent boundary layer development and surface roughness. It is shown that two types of roughness can be clearly distinguished on the basis of the flow variables involved. The more common ‘k’ or ‘sand grain’ type follows the well documented ‘Nikuradse-Clauser’ correlation scheme where the effect of roughness on the flow depends on the size or scale of the roughness elements. The second type of roughness, typified by a smooth wall containing a pattern of narrow cavities, is independent of the scale of the roughness and does not follow• the ‘Nikuradse-Clauser’ correlation scheme. It is shown that previous pipe flow experiments have involved this second type of roughness and these results are used to show that the dependent variable is pipe diameter. This roughness has therefore been named ‘d’ type in this thesis. No length scale associated with the boundary layer could be found to replace pipe diameter except for zero pressure gradient layers. However, it is found that the distance below the crests of the roughness from where the logarithmic distribution of velocity is measured will correlate both types of roughness action. It is shown that a zero pressure gradient turbulent boundary layer developing on a ‘d’ type rough wall conforms to Rotta's condition of precise self preserving flow. The results are used to illustrate several theoretical consequences of this type of flow. Wall shear stresses are determined by measuring in detail, the pressures on the faces of the roughness elements and thereby calculating their form drag. Similarity laws for these pressure patterns are developed for the ‘d’ type results and explicit expressions for the functions are proposed for the zero pressure gradient case. Pressure patterns around 'k' type roughness elements cannot be described by the similarity laws developed here. Theories proposed by several authors to describe the velocity profiles in regions above the logarithmic distribution are compared in detail and critically examined. Some new work related to these theories is introduced. The predictions of mean velocity distribution are tested against an extensive range of experimental data including the results of this thesis. It is shown that all the theories have important shortcomings in their present form and a recommendation for a basis for future work is offered. The problem of the transition of a turbulent boundary layer from a rough (‘d' type) to smooth wall in an adverse pressure gradient is investigated experimentally for two boundary layers. It is found that the outer regions of the boundary layer appear to be unaffected by this change in wall condition whereas the inner flow makes a rapid adjustment to it. This result is at variance to the published work on flow in conduits and for zero pressure gradient boundary layers. An explanation of this is offered. Literature surveys introduce the work in each topic.
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ItemCreative design skills of engineering students( 1972)An investigation has been carried out into the creative design skills of engineering students in the University of Melbourne. In order to tap students' creative abilities, open-ended design problems representative of those encountered by the professional engineer in practice were devised. Students' responses to the problems were then observed and analyzed. The results showed that there were many interesting and apparently important aspects of the students' creative problem-solving behaviour which could be identified and measured, but which were not revealed by performance in conventional university examinations. These aspects of problem-solving appear to be important from the point of view of the students' later professional careers, but further work is needed to confirm this.
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ItemEffect of tool form and workpiece geometry in metal cutting( 1970)A survey on the mechanics of cutting has been carried out. It is shown that little or no work has been done on the cutting analyses of practical three dimensional machining operations such as form cutting or turning. (Appendix A). Thin shear plane deformation analyses are developed for double edged tools. These involve triangular tools performing full depth and chevron type vee grooves as well as lathe cuts. Two alternative yet similar analyses are derived for lathe cuts. A numerical investigation of these analyses is made from which it is shown that the dimensionless power force FP/TA is related to the chip length ratio and is virtually independent of all other variables. Thus variables which alter the chip length ratio will change the forces in machining. These analyses, like all other orthogonal cutting analyses, cannot theoretically predict the chip length ratio although it can be experimentally measured with relative ease and rudimentary equipment. It is also found that there is no theoretical justification for the chip flow rule nc = i in turning. The geometry and specification of lathe tools is studied and the problems and errors in grinding such tools are determined. The difficulty of finding the ‘best’ specification with respect to the theory of cutting is considered by applying the single edge oblique cutting theory and the developed double edged tool analyses. It is shown that no positive conclusion can be achieved without theoretical predictions of the chip length ratio. An experimental investigation is carried out to check the analyses. A series of orthogonal cutting tests is run to form a basis for comparisons with the other cutting operations. Statistical methods such as regression analysis, analyses of variance and co-variance are used to process the data. It is found that the experimental trends for the various tool-work combinations are consistent with those obtained from orthogonal cutting. The measured forces in cutting are shown to be due to cutting-edge forces and deformation forces represented by the analyses of cutting. The shear stress in orthogonal cutting is constant and compares favourably with the constant values found from full depth triangular cuts as well as from higher speed up-milling results. Substantial qualitative and quantitative correlation is achieved between all the tests run showing that the analyses are reasonable representations of the physical case. Methods of using the analyses for predicting the forces in machining are developed and discussed.
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ItemAn investigation of some geometrical and performance aspects of twist drills( 1977)In the last few decades considerable attention has been given to the development of sophisticated machine tools capable of carrying out machining operations with improved overall manufacturing efficiency. Despite these advances in machine tools and associated computer systems, the cutting process and its performance remains a vital element of the manufacturing system. There is a need to establish the relationships between the cutting performance parameters such as forces, power and tool life and the cutting variables which include the tool and work material properties and geometry as well as the cutting conditions. These relationships are required to rationally select the cutting variables for improved, and possibly optimum, manufacturing efficiency. In attempts to relate the cutting performance parameters to the relevant cutting variables the empirical approach has commonly been used. This approach has been applied to the geometrically complex practical machining operations due to the lack of fundamental analyses of these operations. From experimental tests the effect of some cutting variables on various performance parameters have been qualitatively studied. Simple empirical equations have sometimes been found for quantitative prediction purposes. Of the many cutting performance parameters only forces and power and to a lesser extent tool life have been widely considered. In addition turning operations have been extensively studied while other popular operations such as milling and drilling have received comparatively little attention. These empirical techniques have long since been recognized to be time consuming, expensive and relevant to the specific operation studied. Hence the available data, though very useful, have often been limited and incomplete for various common machining operations such as drilling. Recently an alternative analytical approach has been attempted for machining operations such as turning and milling. This approach has followed from fundamental studies and analyses of the mechanics of cutting of the geometrically simple single edge orthogonal and oblique cutting process. The analytical approach, which relies more on the theoretical analyses and less on experimental testing, can account for many geometrical and other variables. In a series of investigations at the University of Melbourne the analytical approach has been shown to yield good qualitative and quantitative force predictions for turning, peripheral milling and machining with form tools. While this alternative approach is promising its potential has not been fully explored. In this thesis the important and popular drilling operation will be studied using the analytical approach. An analysis based on the thin shear zone cutting model will be developed to obtain the relationships between the torque and thrust in drilling, and the relevant twist drill geometrical features and other cutting variables. A method for force prediction will be proposed and experimentally tested. The possibility of adopting an analytical approach for temperature and drill life predictions will also be considered and its practical implications and limitations will be discussed.