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Call number: LD2668 .T4 1959 C53

University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

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No description available.

Thesis (MTech (Electrical Engineering))--Cape Peninsula University of Technology, 2009 / Traditional high voltage power transformers feature sensors measuring basic parameters from oil and gas and are limited to on-site monitoring. Unforeseen failures and breakdowns on these transformers have led to extensive financial losses even with planned maintenance schedules in place. A distinct need has arisen to actively monitor and identify causes of such failures. However, no or little infrastructure exists for effective remote condition monitoring. Wireless sensor networks can be introduced to actively monitor and identify causes of such failures. Sensor motes in the network are battery operated and therefore constrained by limited energy in these batteries. An alternative to battery-powered sensor motes is the conversion of available energy harvested from the surrounding environment into useable electrical energy powering the sensor motes. The primary objective of this research was to examine methods to harvest energy from both the environment and high voltage power transformer. A low cost and feasibly sized hybrid energy harvesting power management prototype was successfully developed that enabled sustained sensor mote operation for prolonged condition monitoring of high voltage transformers. The sensor mote utilised a piezoelectric cantilever to generate usable electrical energy from the transformer tank vibration. Together with solar energy harvesting, the system allowed for a battery-less self-sustained wireless sensor mote capable of autonomously monitoring its surroundings. The power management system's modular architecture provided for the inclusion of additional energy harvesting techniques. This allowed condition monitoring solutions not exclusively for power transformers but proposed an extensible condition monitoring solution for various applications.

M.Ing. / In the drilling process, the majority of hole inaccuracies can be corrected with the use of secondary hole operations. Hole location errors cannot be corrected as their magnitude is determined at the beginning of penetration of the drill point into the material. This thesis investigates the influence of the drill bending stiffness on the hole location error when drilling with ordinary twist drills. Infrared sensors were developed for the drill point location measurements, the initial wandering of the drill and the final hole location error. Also investigations were made into the on-line monitoring of the drilling process using acoustic emission in the audio range. The acoustic signal was transformed to the frequency domain and related to the torque and the thrust magnitudes. The relationships in the acoustic emission, torque and thrust and chip formation between drilling low carbon steel and aluminium were determined.

Includes bibliographical references. / This project was commissioned in order to provide engineers with the necessary knowledge of steel wire winder ropes so that they may make accurate decisions as to when a rope is near the end of its useful life. For this purpose, a knowledge base was compiled from the experience of experts in the field in order to create an expert system to aid the engineer in his task. The EXSYS expert system shell was used to construct a rule-based program which would be run on a personal computer. The program derived in this thesis is named ROPES, and provides information as to the forms of damage that may be present in a rope and the effect of any defects on rope strength and rope life. Advice is given as to the procedures that should be followed when damage is detected as well as the conditions which would necessitate rope discard and the urgency with which the replacement should take place. The expert system program will provide engineers with the necessary expertise and experience to assess, more accurately than at present, the condition of a winder rope. This should lead to longer rope life and improved safety with the associated cost savings. Rope assessment will also be more uniform with changes to policy being able to be implemented quickly and on an ongoing basis as technology and experience improves. The program ROPES, although compiled from expert knowledge, still requires the further input of personal opinions and inferences to some extent. For this reason, the program cannot be assumed infallible and must be used as an aid only.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The majority of power stations in South Africa are located in coal rich, but arid regions where wet-cooled condenser systems are not feasible from an environmental and economic perspective. Consequently the focus on power generation cooling has shifted towards dry-cooling systems using air-cooled steam condensers (ACSC). The steam passing through the ACSC units is cooled by an air-draught, mechanically induced by large diameter axial flow fans. Consequently the effectiveness of the cooling is impacted by the performance of these fans, which ultimately affects the overall efficiency of the power plant. However, due to the large diameters (> 10 m) of these fans, their performance is predicted based on small scale test results using the fan scaling laws. The objective of this project was to develop a methodology which accurately predicts the fan performance of more than one fan configuration using computational fluid dynamics (CFD) software and validating the results with experimental tests. Four fans were considered in this study of which three were scaled fan models of large air-cooled axial fans. The performance of the scaled fan models (L1-, L2- and N-fan) were measured in a type A, BS 848 standard fan test facility. The geometries of the fans were scanned three-dimensionally to obtain the models for simulation purposes. The other fan considered was an 8- bladed axial fan designed by Bruneau (1994) and referred to as the B-fan. Simulations were carried out for the L2-, N- and B-fan for different computational domains while implementing the multiple reference frames (MRF) and steady RANS approach. Three variations of the k-ε turbulence model were also investigated. Noticeable differences were found between the experimental and numerical results of the B-fan. Good correlations between the numerical and experimental fan static pressure, fan power and fan static efficiency were found for the two scaled model fans over a large operating range. The performance of the full scale fans, however, did not correlate well with the performance of the scaled models. It is concluded that accurate simulations of axial fans are possible although these domains require a large number of mesh elements. It is recommended that further research is carried out to investigate the relationship between full scale and small scale fan models. / AFRIKAANSE OPSOMMING: Die meerderheid steenkool kragstasies in Suid-Afrika is geleë in droë, maar steenkool ryke streke waar natverkoelde kondensor stelsels uit ʼn omgewings en ekonomiese perspektief nie geskik is nie. Die fokus in kragopwekking verkoeling het dus verskuif na droë-verkoelings stelsels en spesifiek die gebruik van lugverkoelde stoomkondensors (LVSKs). Die stoom in LVSK eenhede word verkoel deur atmosferiese lug wat meganies geïnduseer word deur groot aksiaalvloeiwaaiers. Die effektiwiteit van die verkoelingsproses word gevolglik beïnvloed deur die werksverrigting van hierdie waaiers wat uiteindelik die algehele effektiwiteit van die kragstasie beïnvloed. As gevolg van hierdie waaiers se grootte word hulle werksverrigting egter bepaal op grond van kleinskaal toetsresultate en deur gebruik te maak van die waaierskaleringswette. Die hoofdoelwit van hierdie projek was om ‘n metodiek te ontwikkel wat die werksverrigting van ʼn aksiaalwaaier akkuraat kan voorspel vir ʼn verskeidenheid opstellings, deur gebruik te maak van berekenings vloei meganika (BVM) sagteware en die resultate eksperimenteel te verifieer. Die projek het vier waaiers ondersoek waarvan drie van hierdie waaiers geskaleerde modelle van groot lugverkoelde aksiaalwaaiers was. Die werksverrigting van die geskaleerde waaiers (L1-, L2- en N-waaier) was met ‘n tipe A, BS 848 standaard waaier toetsfasiliteit gemeet. Die geometrie van dié waaiers was ook drie-dimensioneel opgemeet vir simulasie doeleindes. Die B-waaier, ‘n 8 lem aksiaalwaaier, wat ontwerp is deur Bruneau (1994) was slegs numeries ondersoek. Die L2-, N- en Bwaaier was gesimuleer in verskillende berekeningsdomeine deur gebruik te maak van die multi verwysingsraamwerk en gestadigde vloeiberekenings benaderings. Drie k-ε turbulensie modelle was ook ondersoek. Merkbare verskille tussen die eksperimentele en numeriese resultate van die Bwaaier was waargeneem. Goeie korrelasie tussen die eksperimentele en numeriese resultate van die geskaleerde waaiers vir ‘n wye bedryfsbestek was gevind. ‘n Vergelyking tussen die volskaal en kleinskaal waaiers se werksverrigting het egter beduidende afwykings aangetoon. Deur gebruik te maak van ‘n groot aantal selle in die berekeningsdomein was dit moontlik om ʼn verskeidenheid aksiaalvloeiwaaiers akkuraat te simuleer. Verdere navorsing wat die verhouding tussen volskaal en kleinskaal waaiers ondersoek woord aanbeveel.

Made available in DSpace on 2015-03-26T12:31:38Z (GMT). No. of bitstreams: 1 texto completo.pdf: 1500306 bytes, checksum: 7a203d595a99d75855e1b0a051251811 (MD5) Previous issue date: 2007-04-02 / Hand logging systems were the first adopted, mostly, in the exploitation of native forests, with no concern with the rationalization and productivity of such activities. In Brazil, the first activities of forest harvesting were carried out along the coast, at that time of discovery, when the main traded species was brazilwood. Machine selection and development of operating systems constitute a great challenge to the reduction of costs and dependence on labor in harvesting operations and forest transport. The general objective of this research was to optimize the forest harvesting system, and the specific ones were to evaluate the technical and economic characteristics of the machines, simulate the tractive effort of the Skidder and to develop an electronic device for automatic demarcation of wood bucking point. The technical analysis was based on a study of times and movements to identify and analyze the phases of the operating cycle of each studied machine and their delays. The economic analysis consisted of determining machine operating and production costs. Feller-Buncher and Slacher data were evaluated in a complete randomized design, with six replications, in a split-plot arrangement, with the phases of the machine operating cycle in whole plots and the levels of productivity 100, 200 and 300 m³ ha-1 in subplots. Data were subjected to analysis of variance and the Tukey test at 5% of probability. To evaluate the effect of the times spent in the operating cycle by the Skidder at the productivity levels of 100, 200 and 300 m³ ha-1 and the dragging distances of 100, 200 and 300 m, as well as evaluating the significant interactions, a randomized block design was used, in a 6x3x3 factorial arrangement (six operations, three productivities and three dragging distances), with four replications. Data were subjected to analysis of variance and the Tukey test at 5% of probability. To model the dynamic behavior of the skidding tractor we used the model proposed by the Standard 497.4 (ASAE, 2000), developing a piece of software to predict the efficiency behavior of traction, force and the available potency on the log tong of the Skidder. To accomplish the simulations, a piece of software was developed using the programming language VISUAL BASIC version 6.0. To simulate the Skidder tractive effort, the program was supplied with data on wheel characteristics, tire specifications, operational parameters and soil properties. The control of bucking length used a TP 02 WEG programmable counter, working through a pulse generator based on an inductive proximity sensor M12 X 1 CC in metal housing, with protection against short circuit and automatic rearming. The results led to the conclusion that the Feller-Buncher recorded the highest production cost and was the most important machine within the system, with productive capacity based on its productivity, i.e., 6,197.93, 10,623.09, and 18,328.99 m³ month-1, when working in forests of 100, 200 and 300 m³ ha-1 respectively. The simulation model generated values for simulated traction force similar to the experiments of dragging heights, with the maximum height giving the largest effort. The results were conclusive, since for 6 to 9% skidding, there were no significant differences, independently of the dragging height, and at maximum height the tractor showed the largest effort. The values found for the log lengths when electronically measured and by the standard log were close to the required and showed no significant differences. The sensor was not automatically capable of reset the values when the operator surpassed the required length. The time values were not satisfactory, being the ones electronically measured above those measured with the standard log. The device produced no bucking times feasible for its use, needing adjustment. For optimization, the system should work in a 300 m³ ha-1 forest with dragging distance up to 200 m, with volumes of bunches larger than the currently in use. / Os sistemas de colheitas manuais foram os primeiros a serem adotados, em sua maioria, na exploração de florestas nativas, sem a preocupação com a racionalização e produtividade das atividades. No Brasil, as primeiras operações de colheita florestal foram realizadas ao longo da costa, na época da descoberta, e a principal espécie comercializada foi o pau-brasil. A seleção de máquinas e o desenvolvimento de sistemas operacionais constituem o grande desafio para a redução dos custos e da dependência de mão-de-obra nas operações de colheita e transporte florestal. Esta pesquisa teve como objetivo geral otimizar o sistema de colheita florestal, sendo os objetivos específicos: avaliar as características técnicas e econômicas das máquinas, simular o esforço tratório do trator Skidder e desenvolver um dispositivo eletrônico para marcação automática do ponto de traçamento da madeira. A análise técnica do sistema consistiu de um estudo de tempos e movimentos, com os objetivos de identificar e analisar os elementos do ciclo operacional de cada máquina estudada, bem como suas interrupções. A análise econômica consistiu na determinação dos custos operacionais e da produção das máquinas. Para avaliar os valores do Feller-Buncher e da Garra Traçadora, foi empregado um delineamento estatístico inteiramente casualizado com seis repetições, em esquema de parcelas subdivididas. Adotaram-se como parcelas as operações que compõem o ciclo operacional das máquinas e, como subparcelas, os níveis de produtividade da floresta de 100, 200 e 300 m3 ha-1. Os valores foram submetidos à análise de variância e ao teste de Tukey a 5% de probabilidade. Para avaliar o efeito dos tempos gastos nas operações do ciclo operacional do Skidder nas produtividades de 100, 200 e 300 m3 ha-1 e nas distâncias de arraste de 100, 200 e 300 m, assim como avaliar suas interações quando significativas, utilizou-se um delineamento estatístico em blocos casualizados em esquema fatorial 6 x 3 x 3, sendo seis operações, três produtividades e três distâncias de arraste, com quatro repetições. Os valores foram submetidos à analise de variância e ao teste de Tukey a 5% de probabilidade. Para modelagem do comportamento dinâmico do trator arrastador Skidder, implementou-se o modelo proposto pela Standard 497.4 (ASAE, 2000), desenvolvendo um programa computacional para predizer o comportamento da eficiência de tração, da força e da potência disponível na pinça do trator Skidder. Para realizar as simulações, utilizou-se a linguagem de programação VISUAL BASIC, versão 6.0. Para a simulação do esforço tratório do Skidder, foram fornecidos ao programa as características dos rodados motrizes, as especificações dos pneus, os parâmetros operacionais e as propriedades do terreno. E para o controle do ponto de traçamento dos toretes foram utilizados: um contador controlador programável linha TP 02, marca WEG, que funciona através de um gerador de pulsos baseado em sensor de proximidade do tipo indutivo, modelo M 12 X 1 CC, com invólucro metálico, proteção contra curto-circuito e rearme automático. De acordo com os estudos, concluiu-se que: o Feller-Buncher registrou o maior custo de produção dentro do sistema e foi a máquina principal do sistema, cuja capacidade produtiva se baseou na sua produtividade, com capacidade de 6.197,93; 10.623,09; e 18.328,99 m3 mês-1, trabalhando em florestas de 100, 200 e 300 m3 ha-1, respectivamente. O modelo de simulação apresentou valores de força de tração simulados semelhantes aos dos experimentos da altura de arraste, sendo a máxima altura o maior esforço. Os resultados foram conclusivos, uma vez que, para uma patinagem de 6 a 9%, os valores não apresentaram diferenças significativas, independentemente da altura de arraste, sendo que na altura máxima o trator apresentou seu maior esforço. Os valores encontrados nos comprimentos dos toretes quando medidos pelo dispositivo eletrônico e pela tora-padrão ficaram próximos do desejado e estatisticamente não apresentaram diferenças. O sensor utilizado não foi capaz de zerar automaticamente os valores quando o operador ultrapassou a medida desejada. Os valores de tempo não foram satisfatórios, sendo os medidos pelo dispositivo superiores ao mensurados com a tora-padrão. O dispositivo não apresentou valores de tempo de traçamento que viabilizasse sua utilização, necessitando de ajustes principalmente quanto ao tempo de traçamento. Para otimização do sistema, concluiu-se que este deve trabalhar em floresta de 300 m3 ha-1 e com distância de arraste de até 200 m.