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No / Two novel reduced-size, printed spiral antennas are proposed for use in personal communications mobile terminals exploiting the “big low earth orbit” (Big-LEO) satellite system (uplink 1.61–1.63 GHz; downlink 2.48–2.5 GHz). The two proposed antenna give 3.12―6.25% bandwidth at lower resonant mode of 1600MHz, while at the higher resonant mode of 2450MHz a bandwidth of around 6% is obtained. The experimental and simulated return losses of the proposed antennas show good agreement. The computed and measured gains, and axial ratios are presented, showing that the performance of the proposed two antennas meets typical specifications for the intended applications.

Variable speed motor drives are being rapidly deployed for a vast range of applications in order to increase efficiency and to allow for a higher level of control over the system. One of the important areas within the field of variable speed motor drives is the system's operational boundary. Presently, the operational boundaries of variable speed motor drives are set based on the operational boundaries of single speed motors, i.e. by limiting current and power to rated values. This results in under-utilization of the system, and places the motor at risk of excessive power losses. The constant power loss (CPL) concept is introduced in this dissertation as the correct basis for setting and analyzing the operational boundary of variable speed motor drives. The control and dynamics of the permanent magnet synchronous motor (PMSM) drive operating with CPL are proposed and analyzed. An innovative implementation scheme of the proposed method is developed. It is shown that application of the CPL control system to existing systems results in faster dynamics and higher utilization of the system. The performance of a motor drive with different control strategies is analyzed and compared based on the CPL concept. Such knowledge allows for choosing the control strategy that optimizes a motor drive for a particular application. Derivations for maximum speed, maximum current requirements, maximum torque and other performance indices, are presented based on the CPL concept. High performance drives require linearity in torque control for the full range of operating speed. An analysis of concurrent flux weakening and linear torque control for PMSM is presented, and implementation strategies are developed for this purpose. Implementation strategies that compensate for the variation of machine parameters are also introduced. A new normalization technique is introduced that significantly simplifies the analysis and simulation of a PMSM drive's performance. The concepts presented in this dissertation can be applied to all other types of machines used in high performance applications. Experimental work in support of the key claims of this dissertation is provided. / Ph. D.

The first objective of this thesis was to assess the effect of casting orientation on bond strength in pretensioned prestressed concrete members. The "top strand effect" was evaluated through transfer and development length tests of prestressed concrete beams. Eight beams were cast with normal orientation, while four beams were cast with inverted orientation so that a significant depth of fresh concrete was placed below prestressing strands. Discrete transfer lengths were determined at the ends of each beam by measuring concrete surface strains. Inverted casting orientation caused an average 70 percent increase in transfer length. Some transfer lengths in beams with inverted casting orientation exceed current ACI and AASHTO code provisions. All measured transfer lengths were less than 90 strand diameters (45 in. for 0.5 in. diameter strands). Ranges of development length were determined through iterative load testing. The top strand effect on development length was more qualitative than quantitative. Ranges of development length in normal beams were conservatively less than code provisions. Ranges of development length in beams with inverted casting orientation were much closer to and sometimes exceeded code provisions. It is recommended that ACI and AASHTO code provisions for the development length of prestressing strand be modified to include the same magnification factors that are specified for the development length of deformed bars with twelve or more inches of fresh concrete placed below. The second objective of this thesis was to compare experimentally measured prestress losses to theoretical calculations. Theoretical prestress losses were calculated according to PCI and AASHTO Refined methods. These methods produced similar results. Prestress losses were experimentally measured by vibrating wire gages and flexural load testing. Vibrating wire gages were used to monitor internal concrete strains. Two methods were used to reduce vibrating wire gage data: an upper/lower bound method and a basic method. The upper/lower bound method produced distorted data that was unreasonable in some cases. The basic method was more reasonable, but resulted in some prestress loss measurements that were greater than theoretical predictions. Flexural load testing was used to back calculate prestress losses from crack initiation and crack reopening loads. Prestress losses measured by crack initiation loads were generally greater than theoretical values. Losses measured by crack reopening loads were distorted. The distortion was attributed to difficulty in isolation of the correct crack reopening load. Large measurements of prestress losses by the basic vibrating wire gage and crack initiation methods suggested that losses occurred between the time when concrete was poured and prestress transfer occurred. Such losses are not accounted for in current code provisions. More research is recommended to determine the magnitude of these additional losses and their effect on design. / Master of Science

Losses induced in a single-mode fiber due to periodic spatial deformations along the fiber axis have been investigated spectrally. Deformation losses in several single-mode fibers were found to be strongly wavelength dependent. This wavelength dependence was characterized by narrow attenuation bands in the transmission spectra of periodically deformed fibers. The attenuation bands were shown to shift as the spatial deformation period was varied. The amplitude and location of the attenuation bands were recorded as the number and amplitude of spatial deformations on the fiber were varied. The backreflected spectra of deformed fibers were also studied. Applications of wavelength dependent losses in periodically perturbed single-mode fibers are proposed. In particular, a self-referenced, intensity-based, fiber sensor is suggested. A distributed sensor is proposed using several sets of deformations with different periods induced on the same fiber to measure the same physical measurand at multiple locations along the length of the fiber. Based on this scheme, a multiplexed fiber sensor is envisioned, capable of measuring different physical variables on the same fiber. Optical notch filters can be made by using the notch-like characteristic of each attenuation band. Methods to induce permanent, periodic, axial deformations on an optical fiber are discussed. Spectral investigation of two-mode fibers with photo-induced refractive index changes is suggested. The proposed investigations would eliminate the need for external deformers to perturb the fiber and yield an intrinsic fiber sensor for sensing different physical variables. / Master of Science

The research conducted was part of a project sponsored by the Virginia Department of Transportation and the Virginia Transportation Research Council. One PCBT-53 girder was fabricated with lightweight, self-consolidating concrete. An additional composite cast-in-place lightweight concrete deck was added at the Virginia Tech Structures and Material Laboratory. The project had two specific goals. The first was to experimentally determine the shear strength of the bridge girder. The initial tests focused on the web-shear strength of the girder, and the second tests focused on the flexure-shear strength. The theoretical predictions for the web shear strength were all conservative when compared to the experimentally measured failure strength. The theoretical predictions of the flexure-shear strength were typically unconservative because during the flexure-shear test the girder reached the nominal flexural strength, and a failure occurred in the previously damaged region of the beam. Shear strength was also predicted using the design material properties. Results from these calculations suggested that the equation for the steel contribution to shear strength proposed in the NCHRP Simplified Method were unconservative. Further investigation into the results from the web-shear test showed that the maximum nominal shear strength calculated using the AASHTO LRFD Specifications was typically unconservative. Test results from this project suggested that the constant multiplier of 0.25 used in the LRFD equation for Vnmax may be too high. Further research may be needed to accurately quantify an upper limit on the shear strength. Additionally, predictions of the initial web-shear cracking load were conservative when using the AASHTO Standard Specifications and the NCHRP Simplified Method. The initial web-shear crack angle was under-predicted using the AASHTO LRFD Specifications. The second goal was to monitor the change in prestress over time (and hence the prestress loss) occurring in the PCBT-53 girder. Prestress losses were experimentally measured by vibrating wire gages (measured changes in concrete strain) and flexural load testing. Measured prestress losses were compared to a theoretical prediction calculated using the AASHTO Refined Method. The amount of prestress recorded at any given time using vibrating wire gages was greater than predictions from the AASHTO Refined method. The effective prestress measured just prior to deck placement was higher than the theoretical prediction, and the measured effective prestress at the time of testing was also higher than the theoretical effective prestressing force. The effective prestress value calculated using the flexural crack initiation method was significantly lower than the effective prestress values predicted by both the code provisions and the vibrating wire gages; however, the effective prestress value calculated using the flexural crack re-opening method corresponded very well with the effective prestress values predicted by the code provisions and measured by the vibrating wire gages. The discrepancy in the crack initiation effective prestress values may be due to prestress losses occurring between placement of the concrete and transfer of the prestress force. These losses are not taken into account when using current code provisions to estimate prestress losses. Additional research is recommended to determine if these losses occur in bulb-tee girders, and if so, to quantify them. Finally, from test results within the scope of this research project, design of prestressed bulb-tee girders with lightweight, self-consolidating concrete is practical. The current AASHTO LRFD Specifications provided conservative results when predicting the shear strength of the PCBT-53. Additionally, prestress losses in PCBT girders fabricated with lightweight, self-consolidating concrete were less than those predicted using the AASHTO Refined method. / Master of Science

The first objective of this thesis was to determine the effect of using self-consolidating concrete versus normal concrete on transfer and development lengths, and flexural strengths of prestressed members. Three small rectangular members were made, two cast with SCC mixes and one cast with a conventional mix, to determine the transfer length of each mix. Transfer lengths of both ends of each member were determined by measuring the concrete surface strains. The change in the transfer length was monitored by determining the transfer length of each member at prestress release, 7 days after release, and 28 days after release. All concrete mixes had lower than code determined transfer lengths at prestress release. Each concrete mix showed between a 12 to 56 percent increase in transfer length after 28 days. One SCC mix exceeded the ACI code stipulated 50 strand diameters 7 days after prestress transfer. The other SCC mix was consistently below the transfer length of the conventional concrete. Separate development length members were cast in a stay-in-place steel form used for creating structural double tees. Each development length member was a stub tee. Iterative load testing was performed to determine the development length of each SCC and conventional mix. Development lengths for both SCC mixes were approximately 20 percent shorter than ACI and AASHTO code predictions. A development length for the conventional concrete was not determined due to non-repeating test data. The flexural strength of each member was determined during load testing. All concrete mixes achieved higher than the ACI predicted strengths. The second objective of this thesis was to experimentally measure prestress losses and compare these experimental values to theoretical models. Crack initiation and crack reopening tests were performed to experimentally determine the prestress losses in each member. Three theoretical models were evaluated, the sixth edition PCI Design Handbook suggested model, a 1975 PCI Committee on Prestress Losses model, and the AASHTO LRFD prestress loss model. The crack initiation experimental values tended to be between 10 and 15 percent lower than theoretical models. In general, the crack reopening prediction of the effective prestress had a good correlation with theoretical models. This suggests crack reopening tests can be used as predictors of effective prestress, and as such, predictors of prestress losses in future experimental research. Additionally, the concrete type was shown to affect the prestress losses determined in the development length members. The SCC members tended to have higher effective prestress forces than the conventional concrete members, and thus had less prestress losses due to creep and shrinkage than the conventional concrete members. / Master of Science

Accurate camber prediction in prestressed concrete bridge beams is important to all parties involved in bridge design and construction. Many current prestress loss prediction methods, necessary for proper camber calculation, were developed many years ago and are predicated on assumptions that may no longer be valid as higher strength concrete, wider beam spacing, and longer span lengths become more commonplace. This throws into question which models are appropriate for use in camber calculation by the bridge engineers and contractors of today. Twenty-seven high-strength concrete modified 79 in. Bulb Tee beams with a design compressive strength of 9,000 psi were periodically measured to determine camber growth. Most available models for concrete creep and shrinkage were used to calculate creep and shrinkage strain. The modulus of elasticity equation of each model was used to predict modulus of elasticity of the studied mix. The Shams and Kahn compressive strength and modulus of elasticity equations were modified in order to approximate measured modulus of elasticity. The creep, shrinkage, and modulus of elasticity equations were used as inputs to an incremental time step method. The time-dependent change in beam curvature calculated by the time step method was used to calculate theoretical camber using the Moment-Area method. Predicted camber, using inputs from each considered model, was then compared with measured camber to determine the most accurate camber prediction models. Season of casting was also examined to determine what, if any, affect ambient temperature has on camber growth. For the studied beams, the Shams and Kahn Model for creep, shrinkage, and modulus of elasticity, used as inputs for an incremental time step analysis, were found to most accurately predict camber values. Lower concrete compressive strength was observed for test cylinders from beams cast in summer versus beams cast in winter. Differences in beam deflection based on season of casting showed mixed results. / Master of Science

Propagation of a Gaussian beam in a layered periodic structure is studied analytically, numerically, and experimentally. It is demonstrated that for a special set of parameters the acoustic beam propagates without diffraction spreading. This propagation is also accompanied by negative refraction of the direction of phase velocity of the Bloch wave. In the study of two-dimensional viscous phononic crystals with asymmetrical solid inclusions, it was discovered that acoustic transmission is nonreciprocal. The effect of nonreciprocity in a static viscous environment is due to broken PT symmetry of the system as a whole. The difference in transmission is caused by the asymmetrical transmission and dissipation. The asymmetrical transmission is caused solely by broken mirror symmetry and could appear even in a lossless system. Asymmetrical dissipation of sound is a time-irreversible phenomenon that arises only if both energy dissipation and broken parity symmetry are present in the system. The numerical results for both types of phononic crystals were verified experimentally. Proposed devices could be exploited as collimation, rectification, and isolation acoustic devices.

[pt] Esta dissertação investiga uma nova metodologia, baseada em técnicas inteligentes, para a redução das perdas comerciais relativas ao fornecimento de energia elétrica. O objetivo deste trabalho é apresentar um modelo de inteligência computacional capaz de identificar irregularidades na medição de demanda e consumo de energia elétrica, considerando as características sazonais não lineares das curvas de carga das unidades consumidoras, características essas que são difíceis de se representar em modelos matemáticos. A metodologia é baseada em três etapas: categorização, para agrupar unidades consumidoras em classes similares; classificação para descobrir relacionamentos que expliquem o perfil da irregularidade no fornecimento de energia elétrica e que permitam prever a classe de um padrão desconhecido; e extração de conhecimento sob a forma de regras fuzzy interpretáveis. O modelo resultante foi denominado Sistema de Classificação de Unidades Consumidoras de Energia Elétrica. O trabalho consistiu em três partes: um estudo sobre os principais métodos de categorização e classificação de padrões; definição e implementação do Sistema de Classificação de Unidades Consumidoras de Energia Elétrica; e o estudo de casos. No estudo sobre os métodos de categorização foi feito um levantamento bibliográfico da área, resultando em um resumo das principais técnicas utilizadas para esta tarefa, as quais podem ser divididas em algoritmos de categorização hierárquicos e não hierárquicos. No estudo sobre os métodos de classificação foram feitos levantamentos bibliográficos dos sistemas Neuro-Fuzzy que resultaram em um resumo sobre as arquiteturas, algoritmos de aprendizado e extração de regras fuzzy de cada modelo analisado. Os modelos Neuro-Fuzzy foram escolhidos devido a sua capacidade de geração de regras lingüísticas. O Sistema de Classificação de Unidades Consumidoras de Energia Elétrica foi definido e implementado da seguinte forma: módulo de categorização, baseado no algoritmo Fuzzy C-Means (FCM); e módulo de classificação baseado nos Sistemas Neuro-Fuzzy NEFCLASS e NFHB-Invertido. No primeiro módulo, foram utilizadas algumas medidas de desempenho como o FPI (Fuzziness Performance Index), que estima o grau de nebulosidade (fuziness) gerado por um número específico de clusters, e a MPE (Modified Partition Entropy), que estima o grau de desordem gerado por um número específico de clusters. Para validação do número ótimo de clusters, aplicou-se o critério de dominância segundo o método de Pareto. No módulo de classificação de unidades consumidoras levou-se em consideração a peculiaridade de cada sistema neuro-fuzzy, além da análise de desempenho comparativa (benchmarking) entre os modelos. Além do objetivo de classificação de padrões, os Sistemas Neuro-Fuzzy são capazes de extrair conhecimento em forma de regras fuzzy interpretáveis expressas como: SE x é A e y é B então padrão pertence à classe Z. Realizou-se um amplo estudo de casos, abrangendo unidades consumidoras de atividades comerciais e industriais supridas em baixa e média tensão. Os resultados encontrados na etapa de categorização foram satisfatórios, uma vez que as unidades consumidoras foram agrupadas de forma natural pelas suas características de demanda máxima e consumo de energia elétrica. Conforme o objetivo proposto, esta categorização gerou um número reduzido de agrupamentos (clusters) no espaço de busca, permitindo que o treinamento dos sistemas Neuro-Fuzzy fosse direcionado para o menor número possível de grupos, mas com elevada representatividade sobre os dados. Os resultados encontrados com os modelos NFHB-Invertido e NEFCLASS mostraram-se, na maioria dos casos, superiores aos melhores resultados encontrados pelos modelos matemáticos comumente utilizados. O desempenho dos modelos NFHB-Invertido e NEFCLASS, em relação ao te / [en] This dissertation investigates a new methodology based on intelligent techniques for commercial losses reduction in electrical energy supply. The objective of this work is to present a model of computational intelligence able to identify irregularities in consumption and demand electrical measurements, regarding the non-linearity of the consumers seasonal load curve which is hard to represent by mathematical models. The methodology is based on three stages: clustering, to group consumers of electric energy into similar classes; patterns classification, to discover relationships that explain the irregularities profile and that determine the class for an unknown pattern; and knowledge extraction in form of interpretable fuzzy rules. The resulting model was entitled Electric Energy Consumers Classification System. The work consisted of three parts: a bibliographic research about main methods for clustering and patterns classification; definition and implementation of the Electric Energy Consumers Classification System; and case studies. The bibliographic research of clustering methods resulted in a survey of the main techniques used for this task, which can be divided into hierarchical and non-hierarchical clustering algorithms. The bibliographic research of classification methods provided a survey of the architectures, learning algorithms and rules extraction of the neuro-fuzzy systems. Neuro-fuzzy models were chosen due to their capacity of generating linguistics rules. The Electric Energy Consumers Classification System was defined and implemented in the following way: a clustering module, based on the Fuzzy CMeans (FCM) algorithm; and classification module, based on NEFCLASS and Inverted-NFHB neuro-fuzzy sytems. In the first module, some performance metrics have been used such as the FPI (Fuzziness Performance Index), which estimates the fuzzy level generated by a specific number of clusters; and the MPE (Modified Partition Entropy) that estimates disorder level generated by a specific number of clusters. The dominance criterion of Pareto method was used to validate optimal number of clusters. In the classification module, the peculiarities of each neuro-fuzzy system as well as performance comparison of each model were taken into account. Besides the patterns classification objective, the neuro-Fuzzy systems were able to extract knowledge in form of interpretable fuzzy rules. These rules are expressed by: IF x is A and y is B then the pattern belongs to Z class. The cases studies have considered industrial and commercial consumers of electric energy in low and medium tension. The results obtained in the clustering step were satisfactory, since consumers have been clustered in a natural way by their electrical consumption and demand characteristics. As the proposed objective, the system has generated an optimal low number of clusters in the search space, thus directing the learning step of the neuro-fuzzy systems to a low number of groups with high representation over data. The results obtained with Inverted-NFHB and NEFCLASS models, in the majority of cases, showed to be superior to the best results found by the mathematical methods commonly used. The performance of the Inverted-NFHB and NEFCLASS models concerning to processing time was also very good. The models converged to an optimal classification solution in a processing time inferior to a minute. The main objective of this work, that is the non- technical power losses reduction, was achieved by the assertiveness increases in the identification of the cases with measuring irregularities. This fact made possible some reduction in wasting with workers and effectively improved the billing.