School of Engineering Includes bibliographical references (leaves 248-256)

"October 2001." Bibliography: leaves 99-103. Establishes several sets of conditioning relating to the variant optimal deign of linear consecutive-k-out-of-n systems and includes a review of existing research in the theory of variant optimal design of linear consecutive-k-out-of-n systems.

The primary objective of the research reported in this thesis was the improvement of safety in helicopters by identifying and, where necessary, developing vibration analysis techniques for the detection and diagnosis of safety critical faults in helicopter transmission systems. A review and, where necessary, expansion of past research is made into (a) the mechanisms involved in the production of vibrations in mechanical systems, (b) the failure modes experienced in geared transmission systems, (c) which failure modes are critical to the safety of helicopters, (d) how the safety critical failure modes affect the vibration signature, and e) the vibration analysis techniques currently used to detect safety critical failures. The effectiveness of the currently available vibration analysis techniques is investigated using in-flight vibration data from Royal Australian Navy helicopters and seeded fault data from a purpose built spur gear test rig. Detailed analysis of techniques for synchronous signal averaging of gear vibration data is undertaken, which includes the development of new methods of modelling and quantifying the effects of synchronous averaging on non-synchronous vibration. A study of digital resampling techniques is also made, including the development of two new methods which provide greater accuracy and/or efficiency (in computation) over previous methods. A new approach to fault diagnosis is proposed based on time-frequency signal analysis techniques. It is shown that these methods can provide significant improvement in diagnostic capabilities over existing vibration analysis techniques. Some limitations of general time-frequency analysis techniques are identified and a new technique is developed which overcomes these limitations. It is shown that the new technique provides a significant improvement in the concentration of energy about the instantaneous frequency of the individual components in the vibration signal, which allows the tracking of small short term amplitude and frequency modulations with a high degree of accuracy. The new technique has the capability of 'zooming' in on features which may span only a small frequency range, providing an enhanced visual representation of the underlying structure of the signal.

Howard J. Chizeck, Alan S. Willsky. / Bibliography: leaf 2. / Caption title. / Supported in part by the Office of Naval Research under Contract no. N00014-77-C-0224 NASA Ames Research Center Grant NGL-22-009-124

An approach for robust design based on stochastic expansions is investigated. The research consists of two parts : 1) stochastic expansions for uncertainty propagation and 2) adaptive sampling for Pareto front approximation. For the first part, a strategy based on the generalized polynomial chaos (gPC) expansion method is developed. Second, in order to alleviate the computational cost of approximating the Pareto front, two strategies based on adaptive sampling for multi-objective problems are presented. The first one is based on the two aforementioned methods, whereas the second one considers, in addition, two levels of fidelity of the uncertainty propagation method.

In this work a new current-sweep stress methodology for quantitatively assessing the mixed-mode reliability (simultaneous application of high current and high voltage) of advanced SiGe HBTs is presented. This stress methodology allows one to quickly obtain the complete damage spectrum of a given device from a particular technology platform, enabling better understanding of the complex voltage, current, and temperature interdependence associated with electrical stress and burn-in of advanced transistors. We consistently observed three distinct regions of mixed-mode damage in SiGe HBTs, and find that hot carrier induced damage can be introduced into SiGe HBTs under surprisingly modest mixed-mode stress conditions. For more aggressively scaled silicon-germanium technology generations, a larger percentage of hot carriers generated in the collector-base junction are able to travel to and hence damage the EB spacer, leading to enhanced forward-mode base current leakage under stress. A new self-heating induced mixed-mode annealing effect was observed for the first time under fairly high voltage and current stress conditions, and a new damage mechanism was observed under very high voltage and current conditions. Finally, as an example of the utility of our stress methodology, we quantified the composite mixed-mode damage spectrum of a commercial third-generation (200 GHz) generation SiGe HBT. It is found that if devices are stressed with either voltage or current alone during burn-in, they can easily withstand extreme over-stress conditions. Unfortunately, devices were easily damaged when stressed with a combination of stress voltage and current, and this has significant implications for the device and circuit lifetime prediction under realistic mixed-signal operating conditions.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 113-116). Also available in electronic version. Access restricted to campus users.

Thesis (M. Phil.)--University of Hong Kong, 1980.

Not available / text

M. Tech. Industrial Engineering. / Aims to improve the maintenance strategy in order to improve Return on Capital Investment (ROCI) in a Fast Moving Consumable Goods (FMCG) environment.