Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 176-182). Also available via the Internet.

Mode of access: Internet via World Wide Web. Available http://hdl.handle.net/1947/9738. / "November 2008" Includes bibliographical references.

Thesis (M.S.)--University of North Texas, Dec., 2009. / Title from title page display. Includes bibliographical references.

Thesis (MTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 1998 / The purpose of this study was to perform an investigation into advances in the field of opto-electronics and to develop a suitable lightwave sensor, for application in smart structures research. Included in the scope of this research was the theoretical development and analysis of an appropriate technology to lead to an implementation of such sensors. This project forms part of an overall plan to gain experience in optoelectronic (photonic) sensor design. In research done previously in smart structure monitoring, piezo-electric techniques with the usual electrical interconnections was used. In a highly distributed sensor system the problems of electromagnetic interference, the tribo-electric effect and noise could be problematic. In this research, opto electronic techniques were thoroughly researched and an improvement on laser based fibre-optic interferometers was made. A non monochromatic lightwave interferometer was developed from theory and a prototype tested. The results suggests that an interferometric sensor can be operated with a non monochromatic source by using a second interferometer to modulate the frequency spectrum of the light before it is detected by a photodetector. Various test and measurement circuits for improved photodetector performance were evaluated, as well as a study of signal processing techniques that would be of use for an upgrade of the project where specific feature detection and analysis using the sensor is envisaged. A specification for a computer based data acquisition system was developed to do initial tests. The project should continue, with the sensor head being improved and all the necessary signal processing routines programmed into a Labview based data acquisition system.

Thesis (DTech (Electrical Engineering))--Peninsula Technikon, Cape Town, 2002 / In the last decade, the South Amcan Electricity Supply Commission would have had their ability to serve an ever demanding public severely tested. With the dilemma of providing electricity supply through hazardous environmental conditions, and with prospects of supplying power even beyond South Afiican borders, the need for a comprehensive damage and power delivery assessment strategy becomes all the more relevant. The rapid growth being made in the evolution of so called "intelligent" structures, with inherent sensor, actuator and control mechanisms built in can have direct influence on a power distribution network. At least in the foreseeable future, the impact ofphotonic sensors with inherent miniaturization, a foremost candidate in Smart System technology, can play a vital role in damage assessment of a potentially large network such as that found in the supply ofelectricity. Smart systems are nonliving systems that integrate the functions of sensing, actuation, logic and control, to respond adaptively to changes in their condition or environment to which they are exposed, in a useful and usually repetitive manner. Sensors are a fundamental part of the evolution of such systems and form the basis for the topic of this dissertation. The use ofoptical fiber sensors is increasing widely mainly due to their (a) miniature size, (b) remote signal processing ability, and (c) multiplexing capabilities. Because of the above features a variety of optical fiber sensing techniques has evolved over the years having potential for a myriad of applications. In this work a systems model and equations was developed for modeling the propagation of light in a optical waveguide, in order to study a Fabry Perrot sensor topology for application as a miniaturised sensor in a new type of smart structure, namely a smart electrical power system.

Linear vibration absorbers are a valuable tool used to suppress vibrations due to harmonic excitation in structural systems. Limited evaluation of the performance of nonlinear vibration absorbers for nonlinear structures exists in the current literature. The state of the art is extended in this work to vibration absorbers in their three major physical implementations: the mechanical vibration absorber, the inductive-resistive shunted piezoelectric vibration absorber, and the electronic vibration absorber (also denoted a positive position feedback controller). A single, consistent, physically similar model capable of examining the response of all three devices is developed. The performance of vibration absorbers attached to single-degree-of-freedom structures is next examined for performance, robustness, and stability. Perturbation techniques and numerical analysis combine to yield insight into the tuning of nonlinear vibration absorbers for both linear and nonlinear structures. The results both clarify and validate the existing literature on mechanical vibration absorbers. Several new results, including an analytical expression for the suppression region's location and bandwidth and requirements for its robust performance, are derived. Nonlinear multiple-degree-of-freedom structures are next evaluated. The theory of Nonlinear Normal Modes is extended to include consideration of modal damping, excitation, and small linear coupling, allowing estimation of vibration absorber performance. The dynamics of the N+1-degree-of-freedom system reduce to those of a two-degree-of-freedom system on a four-dimensional nonlinear modal manifold, thereby simplifying the analysis. Quantitative agreement is shown to require a higher order model which is recommended for future investigation. Finally, experimental investigation on both single and multi-degree-of-freedom systems is performed since few experiments on this topic are reported in the literature. The experimental results qualitatively verify the analytical models derived in this work. The dissertation concludes with a discussion of future work which remains to allow nonlinear vibration absorbers, in all three physical implementations, to enter the engineer's toolbox. / Ph. D.

Active control of sound radiation from vibrating structures has been an area of much research in the past decade. In Active Structural Acoustic Control (ASAC), the minimization of sound radiation is achieved by modifying the response of the structure through structural inputs rather than by exciting the acoustic medium (Active Noise Control, ANC). The ASAC technique often produces global far-field sound attenuation with relatively few actuators as compared to ANC. The structural control inputs of ASAC systems are usually constructed adaptively in the time domain based on a number of error signals to be minimized. One of the primary concerns in active control of sound is then to provide the controller with appropriate ``error'' information. Early investigations have implemented far-field microphones, thereby providing the controller with actual radiated pressure information. Most structure-borne sound control approaches now tend to eliminate the use of microphones by developing sensors that are integrated in the structure. This study presents a new sensing technique implementing such an approach. A structural acoustic sensor is developed for estimating radiation information from vibrating structures. This technique referred to as Discrete Structural Acoustic Sensing (DSAS) provides time domain estimates of the radiated sound pressure at prescribed locations in the far field over a broad frequency range. The structural acoustic sensor consists of a set of accelerometers mounted on the radiating structure and arrays of digital filters that process the measured acceleration signals in real time. The impulse response of each filter is constructed from the appropriate radiation Green's function for the source area associated with each accelerometer. Validation of the sensing technique is performed on two different systems: a baffled rectangular plate and a baffled finite cylinder. For both systems, the sensor is first analyzed in terms of prediction accuracy by comparing estimated and actual sound pressure radiated in the far field. The analysis is carried out on a numerical model of the plate and cylinder as well as on the real structures through experimental testing. The sensor is then implemented in a broadband radiation control system. The plate and cylinder are excited by broadband disturbance inputs over a frequency range encompassing several of the first flexural resonances of the structure. Single-sided piezo-electric actuators provide the structural control inputs while the sensor estimates are used as error signals. The controller is based on the filtered-x version of the adaptive LMS algorithm. Results from both analytical and experimental investigations are again presented for the two systems. Additional control results based on error microphones allow a comparison of the two sensing approaches in terms of control performance. The major outcome of this study is the ability of the structural acoustic sensor to effectively replace error microphones in broadband radiation control systems. In particular, both analytical and experimental results show the level of sound attenuation achieved when implementing Discrete Structural Acoustic Sensing rivaled that achieved with far-field error microphones. Finally, the approach presents a significant alternative over other existing structural sensing techniques as it requires very little system modeling. / Ph. D.

This thesis presents algorithms to utilize the wireless bandwidth efficiently and at the same time meet the quality of service (QoS) requirements of the users. In the proposed algorithms we present an adaptive frame structure based upon the airlink frame loss probability and control the admission of call requests into the system based upon the load on the system and the QoS requirements of the incoming call requests. The performance of the proposed algorithms is studied by developing analytical formulations and simulation experiments. Finally we present an admission control algorithm which uses an adaptive delay computation algorithm to compute the queuing delay for each class of traffic and adapts the service rate and the reliability in the estimates based upon the deviation in the expected and obtained performance. We study the performance of the call admission control algorithm by simulation experiments. Simulation results for the adaptive frame structure algorithm show an improvement in the number of users in the system but there is a drop in the system throughput. In spite of the lower throughput the adaptive frame structure algorithm has fewer QoS delay violations. The adaptive call admission control algorithm adapts the call dropping probability of different classes of traffic and optimizes the system performance w.r.t the number of calls dropped and the reliability in meeting the QoS promised when the call is admitted into the system.

Thesis (MTech (Mech. Eng.))--Peninsula Technikon, 1999. / Word processed copy. Summary in English. Includes bibliographical references (leaves 72-75). Also available online.

Thesis (MS )--Montana State University--Bozeman, 2008. / Typescript. Chairperson, Graduate Committee: Douglas S. Cairns. Includes bibliographical references (leaves 142-147).