Thesis (M. Eng.(Mechanical))--University of Pretoria, 2003. / Includes summary. Includes bibliographical references (leaves 87-90).

Pregnancy is an unique period in a woman’s life in which her body undergoes rapid and drastic changes. Historically, physical activity was thought to be dangerous during pregnancy and women were recommended to avoid engaging in most physical activities. Mechanical efficiency, the ratio of external work and energy required to perform a task, is an important consideration when addressing the safety of physical activity, but also when defining recommendations to this population. Currently, there is limited literature that characterizes the change in mechanical efficiency across pregnancy. Of the available literature, suboptimal methodologies were employed, resulting in conclusions that conflict with what would be expected. The purpose of this thesis was to characterize mechanical efficiency across gestation and to compare with non-pregnant women. Women performed a standardized treadmill task in early, mid, and late pregnancy, and energy dynamics were measured. Results showed that energy requirements and external work performed increased over time, and that these were in relation to gestational weight gain. Pregnant women did not exhibit a change in the efficiency of performing a walking task. Overall, these results add to the current literature that supports women’s engagement in physical activity during pregnancy.

Drilling is one of the most commonly used material removal processes for producing holes in the manufacturing industry. Despite the long history of design and developments of hole making tools, the modern twist drill, which undertakes most of the hole making tasks, is largely based on Morse’s geometrical design patented in 1863. however, considerable improvements in the technological performance of drilling operations as assessed by the forces, power, drill-life and hole quality have been achieved through the use of stronger and more wear resistant tool materials, better selection of the salient drill point features and improvements in drill manufacturing methods involving increased automation and geometrical control of drill variability. A variety of drill point modifications and designs have also been proposed and made commercially available although the modern conventional general purpose twist drill design still remains the standard product of drill manufacturers commonly available in stock. The improvement of the technological performance of twist drills has traditionally been the domain of the drill manufacturers who provide technical information and advice often in the form of machining feed and speed recommendations for use in practice. Such machining recommendations or data may also be found in special handbooks which sometimes include drilling performance data such as thrust, torque and power requirements or the expected drill-life in the form of tables, monographs or empirical equations which include the obvious process variables such as the feed and speed. (For complete introduction open document)

Thesis (M.S.)--Ohio University, March, 1997. / Title from PDF t.p.

Thesis (Ph. D.)--University of Washington, 1996. / Vita. Includes bibliographical references (leaves [275]-299).

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 227-233).

Due to a relative high thermal efficiency, the gas turbine engine has wide ranging applications in various industries today. The aerospace and power generation sectors are probably the best known. One method of increasing the thermal efficiency of a gas turbine engine is to increase the turbine inlet temperature. This increase in temperature will result in an additional thermal load being placed on the turbine blades and in particular the nozzle guide vanes. The higher temperature gradients will increase the thermal stresses. In order to prevent failure of blades due to thermal stresses, it is important to accurately determine the magnitude of the stresses during the design phase of an engine. The accuracy of the thermal stresses mainly depends on two issues. The first is the determination of the heat transfer from the fluid to the blade and then secondly the prediction of the thermal stresses in the blade as a result of the thermal loading. In this study the flow and heat transfer problem is approached through the use of computational fluid dynamics (CFD). The principal focus is to predict the heat transfer and thermal stresses for steady state cases for both cooled and uncooled nozzle guide vanes through numerical modelling techniques. From the literature, two studies have been identified for which experimental data was available. These case studies can therefore be used to evaluate the accuracy of using CFD to simulate the thermal loading on the blades. One study focused only on solving heat transfer whilst the other included thermal stress modelling. The same methodology is then applied to a three-dimensional application in which flow and heat transfer was solved for a nozzle guide vane of a commercial gas turbine engine. The accuracy of results varied with the choice of turbulence model but was, generally within ten percent of experimental data. It was shown that the accurate determination of the heat transfer to the blade is the key element to accurately determine the thermal stresses. / Dissertation (M Eng (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

This master's thesis is concerned with the mechanical efficiency of cranktrain contact pairs in a combustion engine. In the introductory part, the fundamental terminology relating to the cranktrain is presented along with the specification of the areas of mechanical losses, greasing modes and types of wear. The following chapters describe the possibilities of eliminating mechanical losses of the cranktrain and the calculation methods that can be utilized to mathematically solve mechanical losses. The practical part includes the proposal of a calculation model and its use in the analysis of the cranktrain of Skoda 1.2 HTP engine. The last part of this thesis comprises modified alternatives of the standard cranktrain focusing on the elimination of mechanical losses. The evaluation of the results is presented in the conclusion of this thesis.

Large amounts of energy from heat sources such as waste-eat and geothermal energy are available worldwide but their potential for useful power-generation is largely untapped. This is because they are relatively low temperature difference (LTD) sources, in the range from 100 to 200 °C, and it is thermodynamically diffcult, for theoretical and practical reasons, to extract useful work at these temperatures. This work explores the suitability of a Stirling engine (SE) to exploit these heat sources. Elsewhere much work has been done to optimise Stirling engines for high temperature heat sources, but little is known about suitable engine layouts, and their optimal design and operational aspects at lower temperature differences. With the reduced temperature difference, changes from conventional engine designs become necessary and robust solutions for this novel application have to be identified. This has been achieved in four major steps: identification of a suitable engine type; thermodynamic optimisation of operating and engine parameters; optimisation of mechanical efficiency; and the development of conceptual designs for the engine and its components informed by the preceding analysis. For the optimisation of engine and operating parameters a model was set up in the commercial Stirling software package, Sage, which also has been validated in this thesis; suitable parameter combinations have been identified. This work makes key contributions in several areas. This first is the identification of methods for better simulating the thermodynamic behaviour of these engines. At low temperature differences the performance of Stirling engines is very sensitive to losses by fluid friction (and thus frequency), adiabatic temperature rise during compression, and the heat transfer from and to the surroundings. Consequently the usual isothermal analytical approaches produce results that can be misleading. It is necessary to use a non-isothermal approach, and the work shows how this may be achieved. A second contribution is the identification of the important design variables and their causal effects on system performance. The primary design variable is engine layout. For an engine having inherently low efficiency due to the low temperature difference it is important to choose the engine layout that provides the highest power density possible in order to minimise engine size and to save costs. From this analysis the double-acting alpha-type configuration has been identified as being the most suitable, as opposed to the beta or gamma configurations. An-other key design variable is working fluid, and the results identify helium and hydrogen as suitable, and air and nitrogen as unsuitable. Frequency and phase angle are other design variables, and the work identifies favourable values. A sensitivity analysis identifies the phase angle, regenerator porosity, and temperature levels as the most sensitive parameters for power and efficiency. It has also been shown that the compression work in low-temperature difference Stirling engines is of similar magnitude as the expansion work. By compounding suitable working spaces on one piston the net forces on the piston rod can be reduced significantly. In double-acting alpha-engines this can be achieved by choosing the Siemens as opposed to the Franchot arrangement. As a result friction and piston seal leakage which are two important loss mechanisms are reduced significantly and longevity and mechanical efficiency is enhanced. Design implications are identified for various components, including pistons, seals, heat exchangers, regenerator, power extraction, and crankcase. The peculiarities of the heat source are also taken into account in these design recommendations. A third key contribution is the extraction of novel insights from the modelling process. For the heat exchangers it has been shown that the hot and cold heat exchangers can be identical in their design without any negative impact on performance for the low-temperature difference situation. In comparison the high temperature applications invariably require different materials and designs for the two heat exchangers. Also, frequency and phase angle are found to be quite different (lower frequency and higher phase angle) from the optimum parameters found in high temperature engines. Contrary to common belief the role of dead volume has been found to play a crucial and not necessary detrimental role at low temperature differentials. Taken together, the work is positioned at the intersection of thermodynamic analysis and engineering design, for the challenging area of Stirling engines at low temperature differences. The work extracts thermodynamic insights and extends these into design implications. Together these help create a robust theoretical and design foundation for further research and development in the important area of energy recovery.

The problem of this study concerns the reduction of spasticity in physically handicapped persons with CP. The hypotheses tested were: that there would be no significant difference between the mechanical efficiency (ME) of persons with spastic CP following application of the TENS Unit and following application of the placebo unit; that there would be no significant difference between the ME of males with spastic CP, following application of the TENS Unit or the placebo unit, and the ME of females with spastic CP, following application of the TENS Unit or the placebo unit; and that there would be no significant interaction between the treatment factor and the gender category.