40 research outputs found

    Test method for determination of air content of hardened concrete

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    Increased air content has been reported from drilled samples in the frost resistance concrete throughout Finland. Elevated air content has been measured at up to 15 percent which has resulted in inadequate compressive strength in various structures. However, the test method which is used to determine the air content in hardened concrete is not standardized. This thesis presents the results of measurements of air content in fresh and hardened concrete by using different methods and techniques. However, the absolute or true air content in concrete is always unknown. Therefore, the results do not show the correctness of measurement but the correlations between them. This thesis focuses on the measurement of air content in hardened concrete with different methods. The aim of this study was to draw a correlation between the methods and evaluate the performance of each method compared to a standardized method. A research was carried out in the Literature Review, which consisted of the hypothesis of air voids, the influence of air content, factors affecting the air content, and the methods for measurement of air content in hardened concrete. The Laboratory Work comprised of the preparation of nine different concretes in three groups of water-cement ratios and different air contents ranging from 2% to 10% by volume. A total of sixteen cores were drilled from each cast block. Their densities were measured. From the theoretical density and measured density, the Calculated method was conducted to measure air contents. A total of 65 cores, from the nine concrete, were examined with the Pressure Saturation method. A Thin Section round robin test was organised for 54 samples from the middle of the blocks. Based on the results, the Calculated method has good correlation with fresh concrete 0.98 R2 with ± 1.4% of error from the average within a standard deviation of nine blocks. However, this method is giving a false result if the concrete is inhomogeneous and cannot be used in in-situ cases since the mix-design of the concrete is not necessarily known. The Pressure Saturation method had a good correlation with fresh concrete and Calculated method with R2 of 0.96 and 0.98. The standard deviation of the method shows that the maximum error which was conducted is ± 1.2% from the mean value. Thin Section within a round robin test analysis proved that the results are unreliable due to problems with a relatively large variation of results regarding total air content. This is due to the high coefficient of variation of entrapped air (27% to 129%) in certain concretes. However, the average total air content results of Thin Section have a good correlation between the fresh concrete air content and Pressure Saturation

    Numerical Analysis of a Single Droplet Combustion: Jet-A1, N-Dodecane, N-Hexadecane

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    There has been an increase in concerns about the planet earth and its resources throughout the past decades. The dependency on fossil fuels created a critical dilemma since transportation is currently fueled by traditional, not sustainable power sources. The originated climate crisis on fossil fuels demands action from mankind, specifically concerning the research on alternative ways of fueling the current methods of transportation. The implementation of Biofuels in transportation encourages future scientists and engineers as a realistic option among other different paths constructed to develop sustainable fuels. The study of the injection, impinging, evaporation, and combustion allows the improvement of the burning characteristics assuming a specific fuel within a combustion chamber. These investigations of the combustion and evaporation procedures improve the burning droplet performance and thus reduce the emitted emissions under the same circumstances. This study intends to numerically simulate the single droplet evaporation and combustion of fuel droplets in a drop tube furnace (DTF) that has the capacity of varying the ambient temperature. The numerical approach simplifies the physical phenomena by employing an Eulerian-Lagrangian approach, considering a discrete and a continuous phase, which is further accomplished while running in a CFD software. The continuous phase is computed recurring to a turbulence modeling, while the dispersed phase is separately computed using the discrete phase model. The computation of the combustion phenomenon is deeply related to the evaporation of the discrete phase employing the non-premixed combustion provided by the operating software. There is a 2D planar simplification of the 3D axisymmetric experimental cylinder followed by the respective discretization of the mathematical equations and pressure-velocity coupling. This work numerically simulates the burning phenomenon of n-dodecane, jet fuel, and nhexadecane single droplets. The obtained results of the droplet size reduction relating to time display agreement with the d 2 law and respective experimentally obtained data. The acquired outcomes also allow the establishment of correlations between the combustion characteristics and the droplet physics properties, such as velocity, displaying a reduction of the droplet velocity alongside the shrink of the droplet diameter. This information is visible for different temperature environments and fuels, suggesting a physical association. Besides this interpretation, the imposed droplet initial velocity variations (1.0 m/s until 1.3 m/s) do not affect the combustion characteristics outcomes. This study demonstrates a precise relation between the ambient temperature of the drop tube furnace (DTF) and the improvement of the combustion process and burning properties. Additionally, the chemical composition of the fuels influences the combustion characteristics and their performances. Overall, the numerical performed simulation can be improved and thus approximate the implemented simulation to the occurring physical event, allowing the development of the additional knowledge in this thematic.As preocupações relativamente ao planeta Terra e os seus recursos naturais têm vindo a aumentar nas últimas décadas. A dependência de combustíveis fósseis provocou um problema delicado, visto que o transporte atualmente é essencialmente abastecido por fontes de energia tradicionais e não sustentáveis. A crise climática originada devido à utilização de combustíveis fósseis exige ações da humanidade, especificamente no que se refere à pesquisa de formas inovadoras de abastecer os atuais meios de transporte. A implementação de biocombustíveis nos transportes atuais, desperta o interesse dos cientistas e engenheiros como uma opção viável entre os distintos possíveis caminhos para se desenvolver opções de combustíveis sustentáveis. O estudo de fenómenos como a injeção, a colisão de gotas, a evaporação e a combustão permite a melhoria das características de queima de um determinado combustível dentro da câmara de combustão, porém o estudo da combustão e da evaporação revela ser a forma mais eficiente para reduzir as emissões e melhorarando significativamente o desempenho da queima. Este estudo pretende simular numericamente a evaporação e combustão de gotículas de combustível dentro de um forno tubular com capacidade de variar a temperatura ambiente. A abordagem numérica simplifica os fenómenos físicos, empregando uma abordagem EulerLagrange realizada com auxílio de um software de Dinâmica de Fluidos Computacional (DFC). A fase contínua é calculada recorrendo a um modelo de turbulência, enquanto a fase dispersa é calculada separadamente utilizando um modelo de fase discreta. O cálculo do fenómeno de combustão está profundamente relacionado à evaporação da fase discreta empregando posteriormente o modelo de combustão fornecida pelo software utilizado. Adicionalmente, existe uma simplificação 2D do domínio e a respetiva discretização das equações matemáticas em conformidade com o acoplamento pressão-velocidade do modelo numérico. Neste trabalho o fenómeno de queima de gotas é simulado para gotas isoladas de n-dodecano, jet fuel e n-hexadecano. Os resultados obtidos relativamente à evolução temporal do diâmetro da gota mostram concordância com a lei d 2 e respetivos dados obtidos experimentalmente. Os resultados adquiridos também permitem uma correlação das características da combustão e a dinâmica das gotas, apresentando uma redução entre velocidade das gotas e a respetiva redução do diâmetro das gotas. Esta relação ocorre para diferentes temperaturas do meio continuo e utilizando diferentes combustíveis, sugerindo uma associação física. Além dessa interpretação, a variação da velocidade inicial da gota não afeta os resultados das características de combustão. Durante o estudo é demonstrada uma relação entre a temperatura ambiente do forno tubular e a indução do processo de combustão bem como as propriedades de queima da gota. Além disso, as composições químicas dos combustíveis utilizados aparenta influenciar as características de combustão da gota e o seu desempenho global na câmara de combustão. De uma forma geral, a simulação numérica poderá ser optimizada em trabalhos futuros e aproximar a simulação ao fenómeno fisico, permitindo assim o desenvolvimento de conhecimentos nesta temática

    Transitioning power distribution grid into nanostructured ecosystem : prosumer-centric sovereignty

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    PhD ThesisGrowing acceptance for in-house Distributed Energy Resource (DER) installations at lowvoltage level have gained much significance in recent years due to electricity market liberalisations and opportunities in reduced energy billings through personalised utilisation management for targeted business model. In consequence, modelling of passive customers’ electric power system are progressively transitioned into Prosumer-based settings where presidency for Transactive Energy (TE) system framework is favoured. It amplifies Prosumers’ commitments into annexing TE values during market participations and optimised energy management to earn larger rebates and incentives from TE programs. However, when dealing with mass Behind-The-Meter DER administrations, Utility foresee managerial challenges when dealing with distribution network analysis, planning, protection, and power quality security based on Prosumers’ flexibility in optimising their energy needs. This dissertation contributes prepositions into modelling Distributed Energy Resources Management System (DERMS) as an aggregator designed for Prosumer-centered cooperation, interoperating TE control and coordination as key parameters to market for both optimised energy trading and ancillary services in a Community setting. However, Prosumers are primarily driven to create a profitable business model when modelling their DERMS aggregator. Greedy-optimisation exploitations are negative concerns when decisions made resulted in detrimental-uncoordinated outcomes on Demand-Side Response (DSR) and capacity market engagements. This calls for policy decision makers to contract safe (i.e. cooperative yet competitive tendency) business models for Prosumers to maximise TE values while enhancing network’s power quality metrics and reliability performances. Firstly, digitalisation and nanostructuring of distribution network is suggested to identify Prosumer as a sole energy citizen while extending bilateral trading between Prosumer-to- Prosumer (PtP) with the involvements of other grid operators−TE system. Modelling of Nanogrid environment for DER integrations and establishment of local area network infrastructure for IoT security (i.e. personal computing solutions and data protection) are committed for communal engagements in a decentralise setting. Secondly, a multi-layered Distributed Control Framework (DCF) is proposed using Microsoft Azure cloud-edge platform that cascades energy actors into respective layers of TE control and coordination. Furthermore, modelling of flexi-edge computing architecture is proposed, comprising of Contract-Oriented Sensor-based Application Platform (COSAP) employing Multi-Agent System (MAS) to enhance data-sharing privacy and contract coalition agreements during PtP engagements. Lastly, the Agents of MAS are programmed with cooperative yet competitive intelligences attributed to Reinforcement Learning (RL) and Neural Networks (NN) algorithms to solve multimodal socio-economical and uncertainty problems that corresponded to Prosumers’ dynamic energy priorities within the TE framework. To verify the DERMS aggregator operations, three business models were proposed (i.e. greedy-profit margin, collegial-peak demand, reserved-standalone) to analyse comparative technical/physical and economic/social dimensions. Results showed that the proposed TE-valued DERMS aggregator provides participation versatility in the electricity market that enables competitive edginess when utilising Behind-The-Meter DERs in view of Prosumer’s asset scheduling, bidding strategy, and corroborative ancillary services. Performance metrics were evaluated on both domestic and industrial NG environments against IEEE Standard 2030.7-2017 & 2030.8-2018 compliances to ensure deployment practicability. Subsequently, proposed in-house protection system for DER installation serves as an add-on monitoring service which can be incorporated into existing Advance Distribution Management System (ADMS) for Distribution Service Operator (DSO) and field engineers use, ADMS aggregator. It provides early fault detections and isolation processes from allowing fault current to propagate upstream causing cascading power quality issues across the feeder line. In addition, ADMS aggregator also serves as islanding indicator that distinguishes Nanogrid’s islanding state from unintentional or intentional operations. Therefore, a Overcurrent Current Relay (OCR) is proposed using Fuzzy Logic (FL) algorithm to detect, profile, and provide decisional isolation processes using specified OCRs. Moreover, the proposed expert knowledge in FL is programmed to detect fault crises despite insufficient fault current level contributed by DER (i.e. solar PV system) which conventional OCR fails to trigger

    Assessing the Vitality of Urban Trees using Remote Sensing and Deep Learning

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    Abstract The use of Convolutional Neural Networks (CNN) has been widely implemented in forestry-related tasks as species classification, crown detection and mortality identification. The usage of several sources as images, point clouds and elevation models have generated relevant results in different forested areas, but unfortunately these studies have not been focused on urban trees. Therefore, the objective of this study is to investigate the performance of CNN for classifying the vitality of urban trees, which are increasingly affected and stressed by the Urban Heat Island Effect. Aerial and Sentinel-2 images are sampled for feeding the CNN model. The prediction of the vitality classes shows a precision of 74,69%, especially for the most represented class (healthy trees). The achieved results allow to better understand the performance of a CNN network for determining the vitality of trees in an urban context where diversity of vegetation patterns can represent a big challenge for classification tasks

    Quality of service differentiation for multimedia delivery in wireless LANs

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    Delivering multimedia content to heterogeneous devices over a variable networking environment while maintaining high quality levels involves many technical challenges. The research reported in this thesis presents a solution for Quality of Service (QoS)-based service differentiation when delivering multimedia content over the wireless LANs. This thesis has three major contributions outlined below: 1. A Model-based Bandwidth Estimation algorithm (MBE), which estimates the available bandwidth based on novel TCP and UDP throughput models over IEEE 802.11 WLANs. MBE has been modelled, implemented, and tested through simulations and real life testing. In comparison with other bandwidth estimation techniques, MBE shows better performance in terms of error rate, overhead, and loss. 2. An intelligent Prioritized Adaptive Scheme (iPAS), which provides QoS service differentiation for multimedia delivery in wireless networks. iPAS assigns dynamic priorities to various streams and determines their bandwidth share by employing a probabilistic approach-which makes use of stereotypes. The total bandwidth to be allocated is estimated using MBE. The priority level of individual stream is variable and dependent on stream-related characteristics and delivery QoS parameters. iPAS can be deployed seamlessly over the original IEEE 802.11 protocols and can be included in the IEEE 802.21 framework in order to optimize the control signal communication. iPAS has been modelled, implemented, and evaluated via simulations. The results demonstrate that iPAS achieves better performance than the equal channel access mechanism over IEEE 802.11 DCF and a service differentiation scheme on top of IEEE 802.11e EDCA, in terms of fairness, throughput, delay, loss, and estimated PSNR. Additionally, both objective and subjective video quality assessment have been performed using a prototype system. 3. A QoS-based Downlink/Uplink Fairness Scheme, which uses the stereotypes-based structure to balance the QoS parameters (i.e. throughput, delay, and loss) between downlink and uplink VoIP traffic. The proposed scheme has been modelled and tested through simulations. The results show that, in comparison with other downlink/uplink fairness-oriented solutions, the proposed scheme performs better in terms of VoIP capacity and fairness level between downlink and uplink traffic

    An Afrocentric exploration of South African cultural-religious narratives of depression

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    The perceptions of causes of depression are diverse, formulated from many different factors such as personal experiences, education, generational and cultural influences, and religious beliefs. While there is a large body of literature on both depression and religion and culture, there is a limited amount available that synthesizes the findings of multiple different studies, finding key common themes. Therefore, this review aimed to develop a comprehensive understanding of how religious and cultural narratives describe and influence depression. As a result, a meta-ethnography was carried out to synthesise existing literature on cultural-religious narratives of depression within a South African context. Five published journal articles were sampled for translation and synthesis. From this process, three key themes were developed, namely Conflictual Coexistence, Observation-Based Discernment, and Status or Stigma. The result is a lens that is formed through a mixture of traditional cultural religious traditions and beliefs interconnected with contemporary ways of understanding and being. This framework for diagnosing and treating a mental illness is heavily reliant on observable symptoms. As a result, status or stigma can be attached to multiple aspects of the situation surrounding an individual with or suspected of having a mental illness. Stigmatisation can be noted to form a cycle that becomes inclusive of prognosis, finance/employment and not being able to fulfil culturally held expectations. As a result, future research, and therapeutic intervention of this mental disorder within this demographic will be better informed.Thesis (MSoc) -- Faculty of Social Sciences and Humanities, 202
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