Submitted by Priscila Oliveira (priscila.b.oliveira@ufes.br) on 2016-07-12T14:57:59Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissert João Gabriel M Silva (versao final).pdf: 2801701 bytes, checksum: 21e33695f6b8ed99e66a7beaa76c8188 (MD5) / Approved for entry into archive by Patricia Barros (patricia.barros@ufes.br) on 2016-07-18T12:31:54Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissert João Gabriel M Silva (versao final).pdf: 2801701 bytes, checksum: 21e33695f6b8ed99e66a7beaa76c8188 (MD5) / Made available in DSpace on 2016-07-18T12:31:54Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) Dissert João Gabriel M Silva (versao final).pdf: 2801701 bytes, checksum: 21e33695f6b8ed99e66a7beaa76c8188 (MD5) / Teve-se por objetivo determinar a transição do lenho juvenil e adulto e avaliar a qualidade da madeira para a produção de serrados de duas espécies de mogno africano (Khaya ivorensis e Khaya senegalensis). O material pesquisado (19 anos de idade) foi proveniente de plantios experimentais da Reserva Natural Vale, Linhares, ES, Brasil. Foram mensuradas a altura comercial, o diâmetro à altura do peito – DAP e a deformação residual longitudinal (método CIRAD – FORÊT). Após o corte das árvores, foram retirados discos na altura do DAP e toras ao longo do fuste, sendo o topo inferior das toras da base fotografado. A morfologia das fibras e vasos foi analisada por meio de estudo microscópico do lenho; o ângulo das microfibrilas mensurado empregando a microscopia de luz polarizada; a densidade aparente, determinada pela técnica de densitometria de raios X; e a densidade básica e a contração volumétrica, determinadas em acordo com normas técnicas vigentes. As rachaduras de topo das toras foram mensuradas utilizando um software analisador de imagens e os defeitos das tábuas secas também foram examinados. Por intermédio da variação radial do comprimento das fibras e da frequência de vasos foi possível demarcar o ponto de transição entre o lenho juvenil e adulto para as duas espécies de mogno africano. O lenho juvenil correspondeu a maior porção do diâmetro do fuste (altura do DAP) e suas propriedades foram mais variáveis e inferiores ao lenho adulto, para ambas espécies de mogno africano. Não houve diferenças da deformação residual longitudinal, índice de rachaduras de topo de toras e tábuas e deslocamento da medula entre as espécies. Todavia, foram verificadas nas toras e tábuas da espécie de K. ivorensis as maiores dimensões de rachaduras, enquanto o maior índice de empenamentos foi observado nas tábuas de K. senegalensis. / The aim of this work was determine the transition from juvenile and mature wood and evaluate the wood quality for the lumber production of two species of African mahogany (Khaya ivorensis and Khaya senegalensis). The material researched (19 years old) was from experimental plantation of Vale Natural Reserve, Linhares, ES, Brazil. Were measured at commercial height, diameter at breast height - DBH and the longitudinal residual strain (method CIRAD- FORÊT). After cut the trees, discs at the height of DBH and logs were removed along the stem, being the top bottom of the logs photographed. The morphology of fibers and vessels was analyzed by microscopic study of wood; the microfibril angle measured using by polarized light microscopy; apparent density, determined by the technique of X-ray densitometry; and basic density and volumetric shrinkage, determined in accordance with current technical standards. The end splits of the logs were measured using an images analyzer software and defects of dried boards also were examined. Through the radial variation of fiber length and frequency of vessels was possible to demarcate the point of transition between the juvenile and mature woods for the two species of African mahogany. The juvenile wood corresponded the highest portion of diameter of the stem (height DBH) and its properties were more variable and inferior than the mature wood, for both species of African mahogany. There were not differences of longitudinal residual strain, index end splits of logs and boards and displacement of the pith between species. However, were observed in the logs and boards of the species K. ivorensis the larger splits, while the highest index warping was observed in the boards of the species K. senegalensis.

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2015 / Made available in DSpace on 2015-12-29T03:03:30Z (GMT). No. of bitstreams: 1 336508.pdf: 7700720 bytes, checksum: ca8d978347b029e8c911f7a051c5039f (MD5) Previous issue date: 2015 / Com a exploração de poços de óleo e gás em alto mar com reservatórios de alta pressão e altas temperaturas, os problemas associados com a transferência de calor tem se tornado de maior relevância. Os novos cenários de produção apresentam com frequência desafios relacionados à garantia do escoamento, perfuração, completação e recondicionamento do poço. O hidrocarboneto a altas temperaturas escoa pelo tubo de produção aquecendo toda a região adjacente. Como consequência do gradiente de temperatura radial observado, a pressão do fluido confinado nos anulares formados pela geometria do poço aumenta, levando ao cenário de falha do poço conhecido como Annular Pressure Build-up (APB). Este trabalho utiliza modelos de escoamento bifásico e transferência de calor para simular um poço de produção típico da região do pré-sal, e avaliar a transferência de calor e o aumento de pressão no anular. São utilizados modelos de escoamento de fases separadas e de padrões de escoamento para a solução do escoamento no interior do tubo de produção. As propriedades termodinâmicas e de transporte da mistura de hidrocarbonetos são calculadas utilizando o software Multiflash, em conjunto com as equações da conservação da quantidade de movimento e energia integradas através do método de Runge-Kutta de quarta ordem utilizando o software Matlab para determinar as frações de vazio pressão e temperatura locais. Um modelo de resistências térmicas é utilizado para resolver a transferência de calor na direção radial do poço, considerando as diversas camadas formadas pelo tubo de produção, revestimentos, camadas de cimento e as regiões anulares associadas. Condições de contorno são definidas com o gradiente geotérmico da formação rochosa e dados de temperatura e pressão na entrada do tubo de produção no fundo do poço. A formação rochosa adjacente ao poço é modelada de forma transiente através da simplificação da equação da difusão de forma a englobar o efeito de aquecimento do poço com o tempo de produção. Uma estimativa do aumento de pressão do anular é feita através da expansão do fluido confinado no anular, associado com um modelo estrutural de deformação das paredes do anular. Os resultados foram validados com dados experimentais de pressão e temperatura na cabeça do poço e no sensor de fundo de poço (PDG). Uma análise de possíveis causas e métodos de controle do APB foi feita.<br> / Abstract : Heat transfer issues in offshore wells have become more relevant in recent years with the exploration of high-pressure, high-temperature reservoirs. New production scenarios often present challenges related to flow assurance, well drilling, completion and workover. When the high-temperature reservoir fluid flows through the tubing string toward the wellhead, the entire borehole is heated. As a result of the radial temperature gradients, the fluid pressure in the sealed annular space between tubes increases, posing a well integrity failure scenario known as annular pressure build up (APB). This work addresses the use of two-phase flow and heat transfer models to simulate a typical pre-salt oil well, and evaluate the heat transfer and the annular pressure build up. Separate two-phase models and a flow-pattern-based model were used to solve the hydrocarbon fluid flow. The thermodynamic and transport properties of the hydrocarbon mixture were calculated using the Multiflash package and were solved together with the momentum and energy equations using the 4th order Runge-Kutta algorithm available in Matlab to determine the local vapor mass fraction and the equilibrium temperature. A thermal resistance network was used to model the heat transfer in the radial direction in the concentric multistring well geometry composed by the tubing, casing, cemented layers and associate annular regions. Boundary conditions were defined based on the geothermal gradient, the hydrocarbon flow rate and pressure at the bottomhole. The adjacent rock formation was modelled using a pseudo steady state approximation of the diffusion equation, considering the well heating along the production time. An estimate of the annular pressure build up was made considering the annular trapped fluid expansion coupled with a structural wall deformation model. Results were validated with pressure and temperature experimental data at the wellhead and permanent downhole gauge (PDG). An analysis of APB possible causes and control methods was made.

Made available in DSpace on 2016-06-02T20:36:43Z (GMT). No. of bitstreams: 1 4957.pdf: 21190527 bytes, checksum: 413709070fb6756ed5ca83e7f9d98b89 (MD5) Previous issue date: 2013-02-12 / Financiadora de Estudos e Projetos / In this work, were studied nanoparticles colloidal systems ZrO2 were using coarse grained models in order to observe the influence of the interaction potential between nanoparticles and the solvents in the system coloidal structure at chemical equilibrium. The molecular dynamics (MD) method was applied to propagate the system trajectories from an optimized initial structure. The interaction energy values allowed the evaluate of which systems reached the colloidal stability and which converged to aggregates with different morphologies just by self-organization mechanisms. The analysis based of the radial distribution function allowed us to relating the nanoparticles superficial faces with the morphologies of aggregates for the correlations peak positions. The radial pair distribution plots and the average of interaction energy determined the interaction potential effect of the solvent in the colloidal systems structure at equilibrium. The colloidal stability was favored when the interaction potential of nanoparticles was equivalent to the interaction potential of the solvent, i.e., almost attractive nanoparticles in almost attractive solvent and attractive nanoparticles in attractive solvents. In other hand, the variation of solvent s interaction potential, using almost attractive nanoparticles in attractive solvent and attractive nanoparticles in almost attractive solvent, leaded systems to form nanoparticles aggregates with different morphologies, depending on the interaction between nanoparticles. Almost attractive nanoparticles formed a nanobunch, whereas attractive nanoparticles formed a nanorod. Gibbs energy of the nanoparticles aggregation process in each system was calculated, which indicated concordance between the thermodynamic of the aggregation process or of colloidal stabilization and the equilibrium systems obtained by molecular dynamic. / Neste trabalho, foram estudados sistemas coloidais de nanopartículas de óxido de zircônio (ZrO 2) utilizando modelos coarse grained a fim de se observar a influência do potencial de interação entre as nanopartículas e o solvente na estrutura coloidal do sistema no equilíbrio químico. O método de dinâmica molecular (MD) foi utilizado para propagar as trajetórias dos sistemas a partir de uma estrutura inicial otimizada. Os valores de energia de interação permitiram avaliar quais sistemas atingiram a estabilidade coloidal e quais convergiram para agregados com diferentes morfologias apenas por mecanismos de auto-organização. A análise das funções de distribuição radial de pares permitiu relacionar a combinação das faces superficiais das nanopartículas com as morfologias dos agregados a partir das posições dos picos de correlação. Os gráficos de distribuição radial de pares e a média das energias de interação determinaram o efeito do potencial de interação do solvente na estrutura coloidal dos sistemas no equilíbrio. A estabilidade coloidal foi favorecida quando o potencial de interação das nanopartículas foi equivalente ao potencial de interação do solvente, ou seja, nanopartículas pouco atrativas em solvente pouco atrativo e nanopartículas atrativas em solvente atrativo. Por outro lado, variando o potencial de interação do solvente, com nanopartículas pouco atrativas em solvente atrativo e nanopartículas atrativas em solvente pouco atrativo, os sistemas formaram agregados de nanopartículas com diferentes morfologias dependendo da interação entre as nanopartículas. Nanopartículas pouco atrativas formaram um nanobunch, nanopartículas atrativas formaram um nanorod. A energia de Gibbs do processo de agregação das nanopartículas em cada sistema foi calculada, tendo indicado uma concord ancia entre a termodinâmica do processo de agregação ou de estabilização coloidal com os sistemas em equilíbrio obtidos por meio da dinâmica molecular.

Modern gas turbine engines run at extremely high temperatures which require the high pressure turbine blades to be extensively cooled in order to reach life requirements. This must be done using the minimum amount of coolant in order to reduce the negative impacts on the cycle efficiency. In the design process the cooling configuration and stress distribution must be carefully considered before verification of the design is conducted. Improvements to all three of these blade design areas are presented in this thesis which investigates internal cooling systems in the form of ribbed, radial passages and leading edge impingement systems. The effect of rotation on the heat transfer distribution in ribbed radial passages is investigated. An engine representative triple-pass serpentine passage, typical of a gas turbine mid-chord HP blade passage, is simulated using common industrial RANS CFD methodology with the results compared to those from the RHTR, a rotating experimental facility. The simulations are found to perform well under stationary conditions with the rotational cases proving more challenging. Further study and simulations of radial passages are undertaken in order to understand the salient flow and heat transfer features found, namely the inlet velocity profile and rib orientation relative to the mainstream flow. A consistent rib direction gives improved heat transfer characteristics whilst careful design of inlet conditions could give an optimised heat transfer distribution. The effect of rotation on the heat transfer distribution in leading edge impingement systems is investigated. As for the radial passages, RANS CFD simulations are compared and validated against experimental data from a rotating heat transfer rig. The simulations provide accurate average heat transfer levels under stationary and rotating conditions. The full target surface heat transfer in an engine realistic leading edge impingement system is investigated. Experimental data is compared to RANS CFD simulations. Experimental results are in line with previous studies and the simulations provide reasonable heat transfer predictions. A new method of combined thermal and mechanical analysis is presented and validated for a leading edge impingement system. Conjugate CFD simulations are used to provide a metal temperature distribution for a mechanical analysis. The effect of changes to the geometry and temperature profile on stress levels are studied and methods to improve blade stress levels are presented. The thermal FEA model is used to quantify the effect of HTC alterations on different surfaces within a leading edge impingement system, in terms of both temperature and stress distributions. These are then used to provide improved target HTC distributions in order to increase blade life. A new method using Gaussian process regression for thermal matching is presented and validated for a leading edge impingement case. A simplified model is matched to a full conjugate CFD solution to test the method's quality and reliability. It is then applied to two real engine blades and matched to data from thermal paint tests. The matches obtained are very close, well within experimental accuracy levels, and offer consistency and speed improvements over current methodologies.

Orientador: José Luiz Gasche / Banca: André Luiz Seixlack / Banca: Paulo Eduardo Lopes Barbieri / Resumo: Devido à solubilidade mútua entre o fluido refrigerante e o fluido lubrificante usados em sistemas de refrigeração por compressão de vapor, eles formam uma mistura homogênea que influencia tanto os processos de transferência de calor no evaporador e no condensador, como os processos de lubrificação e de selagem de vazamentos no interior do compressor. O vazamento de refrigerante através da folga radial de compressores rotativos de pistão rolante é de particular importância para o bom desempenho do compressor, uma vez que ele influencia significativamente a eficiência volumétrica do compressor, chegando a somar cerca de 30% das perdas totais de refrigerante. No presente trabalho foram desenvolvidos modelos de escoamento de misturas óleo-refrigerante através desta folga, incluindo a mudança de fase do refrigerante devida à variação da sua solubilidade no lubrificante. A solução da equação da energia constitui uma evolução do processo de modelagem deste escoamento em relação aos modelos até então desenvolvidos. Quatro modelos diferentes foram usados para simular o escoamento: modelo de escoamento bifásico homogêneo isotérmico, modelo de escoamento bifásico isotérmico com formação de espuma, modelo de escoamento bifásico homogêneo não-isotérmico e modelo de escoamento bifásico homogêneo não-isotérmico com termo de força inercial. O estudo foi realizado para três misturas óleo-refrigerante: óleo éster Freol a10 e refrigerante R134a, óleo éster EMKARATE RL10H e refrigerante R134a e óleo mineral SUNISO 1 GS e refrigerante R12. Para todos os modelos e misturas, realizou-se um estudo paramétrico envolvendo as principais variáveis do problema: pressão de entrada, temperatura de entrada, vazão de mistura e valor da folga mínima... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Due to the mutual solubility between the refrigerant and lubricant of refrigeration systems using mechanical compression of vapor, they form a homogeneous mixture which influences the heat transfer processes in the evaporator and condenser as well as the compressor lubrication and refrigerant leakage. The refrigerant leakage through the radial clearance of rolling piston compressors plays an important role to the volumetric efficiency in this type of compressor, in which it represents about 30% of the total refrigerant loss. In the present work several models to predict the lubricant-refrigerant mixture flow through this clearance, including the refrigerant phase change due to the reduction of the refrigerant solubility in the lubricant, are developed. Four different models were developed to simulate the flow: isothermal homogeneous two-phase flow, isothermal two-phase flow with foam formation, non-isothermal homogeneous two-phase flow and non-isothermal homogeneous two-phase flow containing inertial force. The simulations were performed for three mixtures: ester oil Freol a10-refrigerant R134a, ester oil EMKARATE RL10H-refrigerant R134a, and mineral oil SUNISO 1 GS-refrigerant R12. The influences of the inlet pressure, inlet temperature, mixture mass flow rate, and minimal clearance were analyzed for all mixtures. The results showed that it is important to consider the foam formation, the inertial force, and the solution of the energy equation in the flow modeling. Concerning the volumetric efficiency of the compressor the ester oil Freol a10-R134a was the best mixture because it produced the lowest refrigerant leakage. / Mestre

Submitted by Automa??o e Estat?stica (sst@bczm.ufrn.br) on 2017-03-09T19:22:31Z No. of bitstreams: 1 OdailsonCavalcanteDeOliveira_TESE.pdf: 2506082 bytes, checksum: 1c97e15b1c237711152fe45d82d8809b (MD5) / Approved for entry into archive by Arlan Eloi Leite Silva (eloihistoriador@yahoo.com.br) on 2017-03-10T22:41:06Z (GMT) No. of bitstreams: 1 OdailsonCavalcanteDeOliveira_TESE.pdf: 2506082 bytes, checksum: 1c97e15b1c237711152fe45d82d8809b (MD5) / Made available in DSpace on 2017-03-10T22:41:06Z (GMT). No. of bitstreams: 1 OdailsonCavalcanteDeOliveira_TESE.pdf: 2506082 bytes, checksum: 1c97e15b1c237711152fe45d82d8809b (MD5) Previous issue date: 2016-09-01 / Neste trabalho ser? apresentada uma estrat?gia de controle utilizando uma rede com fun??es de base radial (rede RBF) com adapta??o em modo dual. O objetivo da estrat?gia ? utilizar a capacidade aproximativa da rede RBF no controle de sistemas n?o-lineares desconhecidos, ou conhecidos com incertezas. O controle proposto utiliza a estrutura do Controle Adaptativo por Modelo de Refer?ncia (MRAC) e uma rede RBF cujos par?metros s?o ajustados em tempo real atrav?s de uma adapta??o em modo dual, o que permitir? um r?pido transit?rio e um sinal de controle suave em regime permanente. A adapta??o em modo dual dos par?metros da rede RBF ? feita usando a fun??o tangente hiperb?lica, que durante o transit?rio proporcionar? um comportamento similar ao controle por estrutura vari?vel, e durante o regime permanente atuar?o as leis integrais do MRAC reguladas pela fun??o secante hiperb?lica. A tangente hiperb?lica ? usada no lugar da fun??o sinal das leis chaveadas para reduzir o fen?meno de chattering. A fun??o secante hiperb?lica ? usada para regular a lei integral, aumentando seu efeito em regime permanente e reduzindo durante o transit?rio, evitando oscila??es na resposta do sistema. Ser?o apresentadas uma prova de estabilidade baseada na teoria de Lyapunov para a rede RBF em modo dual e compara??es atrav?s de simula??es. / This work presents a control strategy using a network with radial basis function (RBF network) with adaptation in dual mode. The objective of the strategy is to use the approximate capacity of the RBF network to control nonlinear systems with unknown parameters or with uncertainties. The proposed control uses the structure of Model Reference Adaptive Control (MRAC) and a RBF network whose parameters are adjusted in real time in dual mode, which will allow a fast transient and a smooth control signal in steady state. The dual mode adaptive method of RBF network parameters uses the hyperbolic tangent function, which during the transient provides a similar behavior to variable structure control, and integral laws of MRAC that are regulated by a hyperbolic secant function during steady state. A hyperbolic tangent is used instead of signal function what reduces the chattering phenomenon. A hyperbolic secant is used to regulate the integral law, increasing its effects on steady state and reducing on transient time. It is presented a Lyapunov proof for dual mode method and comparisons through simulations.

O presente trabalho tem por objetivo propor uma metodologia para o dimensionamento da potência tracionária em função do percurso percorrido por veículos elétricos, assim como realizar o projeto básico de uma máquina elétrica para suprir a carga tracionária exigida. Os cálculos foram realizados através de um algoritmo onde o usuário insere as variáveis mecânicas do veículo e recebe a potência e conjugado necessários, e o projeto elementar da máquina que deverá equipar o veículo. Realizou-se um estudo de caso a partir de uma scooter elétrica para validar os resultados, foi projetada uma máquina brushless dc com fluxo radial e rotor externo. Os resultados experimentais atenderam as espectativas de conjugado de 46 Nm, o máximo conjugado estático atingiu 48 Nm e a rotação a vazio obteve valor de 613 rpm à tensão nominal. Os ensaios de frenagem regenerativa com supercapacitores apresentaram resultados promissores com 50% da energia mecânica recebida durante a frenagem entregue na partida do veículo. / The present study aims to propose a methodology for the design of power traction depending on the distance traveled by electrical vehicles, and perform the basic design of an electrical machine to supply the traction load required. The calculations will be performed through an algorithm where the user enters the mechanical variables of the vehicle and receives the power and torque required and the basic machine design that should equip the vehicle. A case study was conducted for an electric scooter considering the designed dc brushless machine with radial flow and external rotor in order to validate the results. The experimental results met the target of 46 Nm of torque, the maximum static torque 48 Nm was reached, and the no-load rotation obtained was 613 rpm at nominal voltage. Regenerative braking tests with super capacitors showed a promising result: 50% of the received mechanical energy during braking was delivered to the vehicle starting.

Orientadores: Anamaria Gomide, Jorge Stolfi / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Computação / Made available in DSpace on 2018-08-13T10:58:35Z (GMT). No. of bitstreams: 1 Pereira_DanilloRoberto_M.pdf: 891270 bytes, checksum: 71a9debc6a10f8de7083dd3e33c649a6 (MD5) Previous issue date: 2009 / Resumo: A geração de imagens fotorrealisticas e um desafio importante em computação gráfica. Um ingrediente critico para a obtenção do realismo esta o modelo de iluminação. Em 1986, Jim Kajiya apresentou uma equação integral que define o fluxo de luz (radiosidade) num ambiente de maneira precisa; contudo, ate recentemente, os métodos conhecidos para a resolução dessa equação tinham custo computacional e complexidade de implementação elevados. Em 2008, Jaako Lehtinen desenvolveu uma técnica relativamente simples e eficiente para o calculo da iluminação global em cenas virtuais, usando elementos finitos definidos por pontos de amostragem. Neste projeto de Mestrado, implementamos esse método, e comparamos o resultado usando três tipos diferentes de bases: uma base radial, uma base radial normalizada e uma base de Shepard. Alem da comparação visual, calculamos a radiosidade "exata" para uma cena simples e comparamos quantitativamente esse resultado com os resultados do método de Lehtinen com cada uma das três bases. / Abstract: The generation of realistic images is a major challenge in computer graphics. A critical ingredient for realistic rendering is the lighting model. In 1986, Jim Kajiya presented an integral equation that precisely defines the light flow (radiosity) in a virtual environment; however, until recently, the known methods for solving that equation had high computational cost and implementation complexity. In 2008, Jaako Lehtinen developed a relatively simple and efficient technique for the computation of global illumination in virtual scenes, using finite elements defined by sampling points. In this Masters project, we implemented that method, and compared the results using three different types of bases: a radial basis, a normalized radial basis, and a Shepard basis. Besides visual comparison, we computed the "exact" radiosity for a simple scene and compared quantitatively that result with the results obtained by Lehtinen's method with each of the three bases. / Mestrado / Computação Grafica / Mestre em Ciência da Computação

Wireless Sensor Networks (WSNs) refer to a group of spatially deployed devices which are used to monitor or detect phenomena, and have the ability to relay sensed data and signalling wirelessly. Positioning information in WSNs is absolutely crucial to perform tasks such as intelligent routing, data aggregation and data collection optimally. A need exists for localisation algorithms which are scalable, distributed, energy efficient and easy to deploy. This research proposes a beaconless Cluster-based Radial Coordinate Establishment (CRCE) positioning algorithm to locate sensor nodes relative to a local coordinate system. The system does not make use of Global Positioning System (GPS) or any other method to provide apriori position information for a set of nodes prior to the CRCE process. The objective of CRCE is to reduce energy consumption while providing a scalable coordinate establishment method for use in WSNs. To reduce energy consumption during the node positioning process, the research focuses on minimising the number of message exchanges in the network by implementing a cluster-based network topology and utilising the potential of geographically distributed processors. A radial coordinate convergence process is proposed to achieve scalability as the number of sensors in the network increases. Three other localisation algorithms are investigated and compared to CRCE to identify the one best suited for coordinate establishment in WSNs. Two of these comparison algorithms are published in the literature and the other is a modified version of one of the published algorithms. The results show a significant decrease in the number of messages that are necessary to establish a network-wide coordinate system successfully, ultimately making it more scalable and energy efficient. In addition, position based algorithms, such as location based routing, can be deployed on top of CRCE. / Dissertation (MEng (Computer Engineering))--University of Pretoria, 2006. / Electrical, Electronic and Computer Engineering / unrestricted

Growth release of trees following canopy disturbances is of interest to ecological scientists and forest managers. Using dendroecological techniques, I examined growth release of canopy and subcanopy trees following the formation of natural, fine-scale canopy gaps in old-growth, western red cedar-western hemlock forests of coastal British Columbia. I aimed to quantify detailed information on release of the three shade-tolerant tree species that constitute these stands: western red cedar (Thuja plicata), western hemlock (Tsuga heterophylla), and Pacific silver fir (Abies amabilis). As a first step, I calibrated the radial-growth averaging method to account for regional-scale variability and capture a more complete range of growth releases that may occur following the formation of fine-scale gaps in the study stands. A 25% threshold, 5-year moving average, and 10-year window emerged as appropriate parameters for detecting releases using radial-growth averaging. Basal area increment was also the most appropriate growth index for detecting releases. Establishing these empirically-based criteria was important for quantifying the magnitude and duration of releases. Tree diameter and growth rate prior to release were the most important predictors of the magnitude and duration of releases, but identity of the tree species and distance from the gap center were also important predictors. Western hemlock and Pacific silver fir were often growing slowly both in the canopy and subcanopy, giving them tremendous potential to release. For these species, releases were generally intensive and persistent. In contrast, western red cedar were often growing quickly both in the canopy and subcanopy, giving them less potential to release. Compared to western hemlock and Pacific silver fir, western red cedar releases were less intensive and persistent. Patterns related to distance from the gap center emerged for trees growing along the north-south axis of gaps. Regardless of species, increasing distance from the gap center resulted in decreasing magnitude and duration of releases. However, patterns for duration were complex, as the distance effect was greater for trees north of the gap center. Information on growth release of trees is useful for reconstructing the history of past canopy disturbances, elucidating mechanisms of tree species coexistence, and assessing and predicting stand changes due to forest management in coastal British Columbia. / Arts, Faculty of / Geography, Department of / Graduate