The purpose of this study is to develop and demonstrate a novel process for heat recovery from hot exhaust gases. This process involves direct contact of a hot gas with a countercurrently flowing vibrofluidized bed of cold solid. Based on a simple heat-transfer model, an "apparent" heat-transfer coefficient between the air and solid was calculated. The temperature profile of the air as a function of heat-exchanger length was used to determine the "apparent" area for heat transfer in the model. Analysis, based on factorial-design experiments, showed that increasing the airflow rate and applied vibrational intensity, as well as decreasing the baffle height of the system served to increase the "apparent" heat-transfer coefficient. Increasing the solid flow rate produced higher heat-transfer coefficients only when the baffle was lowered past a certain "critical" height. Under optimum conditions investigated, a gas-to-bed heat-transfer coefficient of about 270 W/m²-K was obtained with a heat exchanger length of 0.71 m. "Cold-flow" experiments of the system were used to explain the heat-transfer trends. A condition analogous to "flooding" determined the operating range of the "flowing" vibrofluidized-bed heat exchanger. As a result of this work, significant progress has been made on the evolutionary development of a vibrofluidized-bed heat exchanger to be used for future heat recovery. / M.S.

The object of this thesis is to establish the necessary design criteria for a number of special feedback networks which were required to allow the final development of the Strip Mining Industry's first Automatic Crowd-Hoist Regulator. The introduction considers the purpose and needs for such a regulator by briefly outlining the present manual dipper loading operation. Section IV and Appendix 1 presents the analytical system requirements which are basically determined from an analysis of the system's inherent mechanical oscillatory frequency. Section VA is concerned with the development of the hoist and crowd motion transfer functions which are necessary to accomplish the stability analysis of the system. A general determinantal solution is obtained based on linear analysis to allow expression of the motion transfer functions as a factored polynomial. In section VB, the development of the necessary Crowd-Hoist feedback circuits is accomplished in terms of the system parameters defined from the analysis of the oscillatory mechanical system. Section VIA outlines the procedures to be followed in going from the basic mechanical system parameters to the specific control system hardware. The general requirements for a Bode analysis of the system GR is defined in section VIB, including the general procedures to follow in the utilization of the two lead compensation circuits provided. / M.S.

The purpose of this study was to record the results of experiments made in the construction of archery equipment at North Texas State Teachers College in the school sessions from 1938 to 1940.

The advancement of Very Large Scale Integration (VLSI) technology has reduced the size and increased the speed of information processing circuits. Consequently, power supplies for such circuits have had to meet increasing demands for power, yet simultaneously decrease in size. This need for higher power density in the supplies can be met with higher circuit operating frequencies and by using high-density circuit fabrication techniques. Generally, when the conversion frequency of conventional Pulse-Width-Modulated (PWM) supplies approaches 1 MHz, the switching loss becomes very large. This sharply reduces the efficiency of the supply. A quasi-resonant topology reduces much of this loss. For a Zero-Current-Switched (ZCS) Quasi-Resonant Converter (QRC) the turn-off loss is nearly eliminated. It was the objective of the research reported here to combine the quasi-resonant technology with thick-film hybrid microelectronics technology to produce a high density dc-dc converter. For this research endeavor an off-line, half-bridge ZCS-QRC was used. The circuit processed 300V and up to 20A with switching frequencies in the 1MHz to 2MHz range. The voltage and current levels exemplify the high electric field and current densities that must be considered in the design of most QRC circuits that process power up to 100W. Only available materials for thick-film hybrid processing were used although some characteristics were modified. No special magnetic or capacitive components, or semiconductors were developed. To combine technologies the following were performed: 1. identification of critical power electronic circuit and hybrid component parameters such as maximum voltages and currents, thermal and electrical component impedances; 2. assessment of thick-film hybrid microelectronic materials and their compatibility in circuits having high voltage and current levels; 3. development of a complete thick-film power hybrid process; and 4. design, fabrication and evaluation of a power hybrid QRC that has high power-processing density. / Ph. D.

This is a study to design and construct a suitable and effective mechanical device for storing, dispensing, and accounting for small tools and equipment used in industrial arts laboratories.

A review of behavioral rock properties used for input to the finite element method are summarized. Rock properties presented in the literature were primarily obtained from laboratory specimens. Methods to determine applicable field properties via testing, calculations and empirical correlations are included. Suggested behavioral properties of the structural concrete-to-rock interface are proposed. Specific property values, resulting from the literature review, are presented as input for a finite element parametric evaluation of navigation structures. / Master of Science

No description available.

During the design of sports equipment, the main focus is usually on physical performance attributes, neglecting key subjective factors such as feel and comfort. The personal protective equipment worn in sport is a typical example, where injury prevention has taken precedence over user comfort, but it is anticipated that with a new approach to the design process, comfort can be improved without sacrificing protection. Using cricket leg guards and taekwondo chest guards as an example, this study aimed to develop a systematic method for assessing user perceptions and incorporating them into the design process. Players perceptions of the factors that influence the comfort of cricket leg guards and taekwondo chest guards were elicited through the use of co-discovery sessions, focus groups and individual interviews, and analysed through an inductive process to produce a comfort model. The relative importance of each different comfort dimension was identified through the use of an online questionnaire utilising the analytical hierarchy process method. Through the combination of these methods, six general dimensions were identified with a weighting regarding the amount to which each one determines a user's perceived comfort. For both cricket and taekwondo, the majority of players ranked Fit as the most important factor affecting comfort. Experimental procedures were developed to objectively test the Fit of cricket leg guards, with regards to batting kinematics, running performance and contact pressure. These methods were combined with subjective assessments of leg guard performance, to determine if there was a relationship between users perceived comfort and objective test results. It was found that shot ROM and performance were not significantly affected by cricket leg guards, despite perceptions of increased restriction whilst wearing certain pads. Wearing cricket leg guards was found to significantly decrease running performance when compared to running without pads (p<0.05). In addition, it was found that the degree of impedance depended on pad design and could not solely be attributed to additional mass. These results correlated with the subjective assessment of three different leg guards, with respondents identifying the pad which had the largest influence on their running biomechanics and impeded their performance the most, as the most restrictive pad. Contact pressure under the pad and straps was also measured for four different leg guards whilst running. The results found that the top strap applied the greatest amount of pressure to the leg, especially at the point of maximum knee flexion. The peak pressure under the top strap was found to reach up to three times that of any other area of the pad. These results were reflected in the subjective assessment of the leg guards, with all nine subjects identifying the top strap as an area of discomfort for certain pads. The results also suggested there was a preference for pads with a larger more consistent contact area, as pad movement was perceived to increase when contact area variation was greater. Finally the results from this research were used to develop a product design specification (PDS) for a cricket leg guard, specifying size, mass, contact pressure and shape. The PDS was used to develop a concept design which would maximise comfort, whilst maintaining protection.

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2017 / In the mining industry, communications systems are important for ensuring personnel safety and optimizing the mining processes underground. Achieving robust and reliable through-the-air (TTA) communication systems has always been a challenge in the underground mining environment due to harsh and dynamic conditions. TTA requires radio channel characterization for efficient designing and deploying of the communications systems. The literature covers the statistical radio propagation of a room and pillar coal mine, a longwall coal mine, CANMET Gold mine, Camborne School of Mines hard rock mine tunnel, MUZ Coal mine, an iron-ore mine and a lead-zinc mine with linearly polarized antennas at different frequencies. [Abbreviated Abstract. Open document to view full version] / MT 2017

A research report submitted to the faculty of Engineering and the built environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. Johannesburg, August 2016 / There has been much interest in using the Microsoft Xbox 360 Kinect cameras for visual servo control applications. It is a relatively cheap device with expected shortcomings. This work contributes to the practical considerations of using the Kinect for visual servo control applications. A comprehensive characterisation of the Kinect is synthesised from existing literature and results from a nonlinear calibration procedure. The Kinect reduces computational overhead on image processing stages, such as pose estimation or depth estimation. It is limited by its 0.8m to 3.5m practical depth range and quadratic depth resolution of 1.8mm to 35mm, respectively. Since the Kinect uses an infra-red (IR) projector, a class one laser, it should not be used outdoors, due to IR saturation, and objects belonging to classes of non- IR-friendly surfaces should be avoided, due to IR refraction, absorption, or specular reflection. Problems of task stability due to invalid depth measurements in Kinect depth maps and practical depth range limitations can be reduced by using depth map preprocessing and activating classical visual servoing techniques when Kinect-based approaches are near task failure. / MT2017