FCT: DEMI - Dissertações de Mestrado
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- Application of Natural Language Processing in Aviation Maintenance Management: Teaching machines to classify aircraft zones from maintenance reports using BERTPublication . Lopes, Mariana Mendes; Dinis, DuarteIn the aircraft Maintenance, Repair and Overhaul (MRO) industry the high uncertainty of resources needed for a given operation is a very recurrent problem. This implies that being able to collect and analyze data from past events in order to predict for future operations provides a given company with more stability of outcomes and a competitive advantage in the industry. However, for most companies this is not the case. The heterogeneous manner in which the data is collected and stored causes it to be often disregarded or at least not used in its completeness. In the presented dissertation a NLP model is developed. This model analyses free text fields with the purpose of allowing MRO companies to exploit as much valuable information as possible from the maintenance reports generated throughout its activity. The model will focus on categorizing the zone of the aircraft where each maintenance task was performed. A BERT model was developed based on the existing maintenance reports of a Portuguese MRO. The research was performed with the support of the University of Bergamo, in which another work used the same dataset, but with different NLP models, in order to allow for comparison. An accuracy of 85.69% was obtained with BERT. A sensitivity analysis was also performed, showing that the most adequate combination of hyperparameters consisted in a longer warm-up period for the learning rate, along with low levels of both learning rate and dropout probability. The developed model is intended to be adaptable to other maintenance industries, other than aviation, or even to other economic sectors with due adaptations.
- Development and Validation of a Filament Extrusion System for Precision Diameter ControlPublication . Correia, Miguel Portásio; Duarte, Valdemar; Soares, BrunoThis dissertation addresses the challenge of producing high-quality customized, consistent 1.75 mm diameter filament rolls for additive manufacturing (AM). Inconsistent diameter, which directly impacts print quality and material efficiency, remains a common issue in the polymer extrusion, especially significant when aiming for the industry-standard tolerance of ± 0.05 mm, crucial for achieving dimensional accuracy and reliable print results. While earlier iterations of the developed machine demonstrated functional extrusion, they lacked the essential peripheral mechanisms required for precise control over filament diameter. This project aims to develop a solution by introducing essential auxiliary systems, including a cooling mechanism, puller, diameter sensor, and a closed-loop control system. The proposed modifications allow for real-time adjustments to maintain filament diameter within the required tolerance. The design, development, and testing of these systems are presented, with specific emphasis on optimizing the extrusion parameters. Extrusion was performed using exclusively virgin PLA. Results show that the final machine iteration produces filament with a diameter of 1.75 ± 0.1 mm and a cross-sectional area of 2.43 ± 0.07 mm2. Compared to Prusament PLA Prusa® Orange filament, the extruded filament achieved a tensile strength of 45.8 MPa, while the Prusament filament measured 46.3 MPa. Print quality tests demonstrated that the extruded filament closely matched the Prusament filament, with similar surface finish, dimensional accuracy, and performance in overhangs and bridging. The developed firmware also successfully regulated motor speed, achieving stable filament production and confirming the viability of a cost-effective, in-house extrusion system.
- Integração de Tecnologias de Climatização no Setor da Indústria Farmacêutica: Impacto na Sustentabilidade, Eficiência Energética e Conforto TérmicoPublication . Martins, Leonardo Fernandes; Cardoso, JoãoA presente dissertação tem como principal objetivo, o desenvolvimento de uma solução de AVAC para um edifício em expansão, pertencente a uma unidade industrial do setor farmacêutico e que se encontra localizada em Sintra. O grupo industrial em questão dedica-se à investigação, desenvolvimento e fabrico de novos medicamentos, por isso a solução desenvolvida foi ao encontro dos elevados padrões e exigências característicos deste setor, de forma a não comprometer o desempenho e objetivo das atividades desenvolvidas no edifício. Devido à exigência de tais atividades realizadas neste novo edifício, foi necessário um cuidado rigoroso no dimensionamento dos sistemas, no controlo da qualidade do ar e na garantia das condições ideais de conforto térmico nos diferentes espaços. Ao mesmo tempo, o aumento dos custos dos recursos energéticos e as preocupações ambientais relacionadas às emissões de CO₂, incentivaram o desenvolvimento de uma solução alinhada segundo os princípios da transição energética atual. Essas medidas incluíram, entre outros aspetos, a adoção de sistemas que promovem a recuperação de energia e o controlo remoto dos equipamentos por via de um sistema de gestão técnica centralizada. Outro aspeto relevante, foi a otimização do desempenho dos vãos envidraçados, com o objetivo de reduzir a carga térmica nas escadas exteriores envidraçadas, o que permitiu minimizar o efeito de estufa no seu interior. Por fim, foram desenvolvidas as redes hidráulica e aeráulica, realizada a seleção dos equipamentos de climatização e elaborados os diagramas técnicos da especialidade que complementam o presente estudo.
- Desenvolvimento de um Modelo de Avaliação da Usabilidade de um PortalPublication . Lemos, Bruno Miguel Margarido Alveirinho de; Nunes, IsabelA Ergonomia é a área científica relacionada com a compreensão das interações entre as pessoas e os elementos de um sistema. Inserida nesta área científica encontra-se a usabilidade, que é uma medida da qualidade do uso de produtos e serviços. O objetivo da presente dissertação consiste na implementação da framework User Centered Design ao desenvolvimento de portais, propondo um modelo de avaliação de usabilidade assente na lógica difusa e estimando a usabilidade de um portal através de um indicador. Numa primeira fase pretende-se descrever e analisar o processo de desenvolvimento de portais e identificar as suas limitações. Posteriormente será proposto um processo de desenvolvimento de portais de acordo com a framework User Centered Design, que considera a avaliação da usabilidade em estágios iniciais de desenvolvimento de modo a diminuir o impacto das não- conformidades e a criação de um UCD Charter para auxiliar a equipa de desenvolvimento. De seguida, é desenvolvido um modelo de avaliação da usabilidade do portal, denominado de Índice de Usabilidade, através da lógica difusa, o qual será aplicado em dois momentos de avaliação definidos no processo proposto de desenvolvimento de um portal. Foram ainda identificadas oportunidades de melhoria através da aplicação do modelo proposto de desenvolvimento e do novo modelo de avaliação de usabilidade, que produziram uma qualidade do uso superior segundo as perceções dos utilizadores e que possibilitaram a implementação de um novo processo de desenvolvimento. Comprovou-se que o utilizador deve ser um elemento participativo e ativo no desenvolvimento do portal, com o objetivo de contribuir com a identificação das suas necessidades e perceções, para a melhoria contínua no processo de desenvolvimento.
- DETECTION OF WELD SURFACE DEFECTS WITH COMPUTER VISION TECHNIQUESPublication . Correia, Cláudia Oliveira; Mendes, NunoInspection of welding seams is a critical task in industrial production, as undetected defects can compromise both safety and product quality. This thesis investigates computer vision techniques for the automatic detection and classification of welding surface defects, with the broader objective of identifying the most suitable combination of hardware and methodology for developing an automated visual inspection system. To support this work, a dedicated dataset of weld images was acquired using a custom image acquisition system and preprocessed with specialized techniques. Multiple deep learning models were evaluated for both detection and classification tasks, with particular attention to the effects of data augmentation, class imbalance, and data leakage. Three inspection pipelines were designed and compared: a detection–classification pipeline, a classification-only pipeline, and a hybrid pipeline combining both strategies. The results demonstrated that defect detection based on models such as YOLOv8n, combined with convolutional architectures such as ConvNeXt, achieved consistent per- formance. Hybrid pipelines improved detection for minority defect classes, although limitations persisted for extremely rare categories. The study demonstrates that careful dataset design and augmentation strategies are essential for achieving reliable performance, and that detection-based approaches provide a stronger foundation for automated weld inspection. These findings contribute to the development of a robust computer vision system capable of reducing manual inspection effort and improving quality assurance in industrial welding processes.
- Numerical Analysis of Heat Transfer in Labyrinth Seals of Modern Gas TurbinesPublication . Almeida, Cristiano MiguelPereira de; Brito, Moisés; Garanin, IvanLabyrinth seals play a crucial role in turbomachinery minimising leakage flows at a clearance between stationary and rotating components while avoiding direct mechanical contact. While leakage has been accurately captured by numerical simulations, heat transfer predictions remain significantly more challenging and uncertain. This is particularly critical in modern gas turbines, which operate at inlet temperatures well above the limits of conventional metal alloys. To extend blade life and prevent localised hot spots, it is essential to reliably predict heat transfer coefficients. This dissertation aims to: i) predict the effect of rotor rotation on heat transfer coefficients; and ii) define a proper method for estimating heat transfer coefficients in rotating labyrinth seals. The specific objectives include: comparing different turbulence models, mesh topologies and two Computational Fluid Dynamics (CFD) solvers (Ansys Fluent and Star-CCM+); assessing the thermal impact of different seal designs; investigating modelling strategies aimed at reducing computational cost without compromising accuracy; and analysing the influence of boundary conditions on heat transfer coefficients. To attain these objectives, three geometries exported from literature were modelled and meshed in both CFD softwares. The first, a non-rotating smooth stepped labyrinth seal with a five teeth rotorwas used for mesh parameter selection and hydraulic validation. Smooth and honeycombstepped labyrinth sealswere then employed for thermal validation under static conditions and subsequent heat transfer analyses with and without rotation. The comparison between numerical results and experimental data shows that the numerical tool properly predicts hydraulic and thermal parameters of labyrinth seals. In thermal validation, among the tested approaches, the Linear 𝑇ref Method combined with the 𝑘 − 𝜔 SST turbulence model produced the most reliable results. A cross-validation between Ansys Fluent and Star-CCM+ was performed, revealing acceptable deviations. Subsequent investigations compared heat transfer coefficients between smooth and honeycomb seals. For the smooth seal, additional studies examined the influence of varying thermal boundary conditions on heat transfer coefficients. Under static conditions, honeycomb seals reduce heat transfer, being the impact stronger on stator. At the rotor, honeycomb configurations exhibited slightly lower coefficients and shifted impingement locations with heat transfer coefficient profiles converging to smooth configuration as the ratio between cell diameter and seal clearance decreases. From this observation, a novel modelling aproach capable of reducing computional cost, especially in large circumferential sectors, was proposed. Under rotational conditions, heat transfer coefficients increased in both configurations, but honeycomb revealed better thermal protection at higher rotation rates, as the average heat transfer coefficient at the rotor was reduced 18.13% compared to the smooth case. Thermal boundary condition tests confirmed negligible influence of fluid-wall temperature differences for hotter fluid cases, while heat flux direction under rotation revealed limitations of the Linear 𝑇ref Method, as heat transfer coefficients were lower with increasing rotation in colder fluid cases. To address this, the Adiabatic-Diabatic Linear Method was developed, providing consistent rises in heat transfer coefficients with rotation regardless of heat flux direction when the correct reference frame is applied: Moving Reference Frame (MRF) for colder fluid and Absolute Reference Frame (ARF) for hotter fluid cases.
- Comparação de Dispositivos de Proteção do Choque Hidráulico numa Estação Elevatória (estudo numérico)Publication . Nobre, Ricardo Remédios; Gil, LuísA presente dissertação tem como objetivo o estudo e dimensionamento de dispositivos de proteção contra regimes transitórios numa estação elevatória, assegurando a integridade da instalação face a fenómenos como o golpe de aríete e a cavitação. Para enquadrar o traba- lho, apresentam-se os conceitos fundamentais associados ao escoamento em condutas sob pressão, destacando-se a relevância da implementação de soluções de proteção em sistemas de bombagem. O estudo contempla o dimensionamento de uma estação elevatória em regime per- manente, posteriormente sujeita a simulações transitórias no software AFT Impulse. Foram analisados três cenários de operação considerados críticos: falha súbita de energia, arranque da bomba e saída de serviço. Em cada caso, testaram-se diferentes dispositivos de proteção, nomeadamente válvula de retenção, sistema de by-pass, reservatório hidropneumático e a de- finição de leis de abertura e de fecho de válvulas, avaliando o seu impacto no amortecimento das oscilações de pressão. Os resultados demonstraram que a integração de leis adequadas de abertura e fecho, em conjugação com os dispositivos de proteção, foi determinante para reduzir variações de pressão e evitar cavitação. Entre as soluções analisadas, o reservatório hidropneumático des- tacou-se pela eficácia na atenuação global dos efeitos transitórios. Já o by-pass revelou-se eficaz nos cenários de arranque e de saída de serviço, mas não foi suficiente para eliminar a cavitação na falha de energia. Nestes casos, a sua combinação com válvulas de alívio pode constituir uma alternativa válida em determinados contextos de projeto, devido à simplicidade e ao menor custo de implementação.
- Methodology to define tool usage time based on monitored data in high-speed millingPublication . Guido, Gustavo Mota Lopes Marques; Mourão, António; Madeira, ManuelThis dissertation investigates the complex factors influencing tool life in machining pro- cesses, with a specific focus on operations at Aernnova, a leading aero structures manu- facturing company. The primary objective was to develop a more accurate and reliable method for predicting tool life, thereby improving process efficiency and reducing oper- ational costs in the manufacturing of aluminium thin-walled parts. The research began with a review of traditional theoretical models, such as Taylor’s Tool Life Equation, which were found to have limited applicability due to high variability in tool life data across different machines. To address these challenges, an approach was proposed, incorporating corrected machine air time values and specific operational conditions to compute tool life more accurately with the help of a developed methodology that combined power usage, tool air time and tool usage time. Key findings include the identification of significant discrepancies in tool life predictions when using traditional models, necessitating a more tailored approach that accounts for the specific conditions present at Aernnova. The practical application of this research is expected to result in significant improve-ments in tool management, leading to better quality control, reduced downtime, and lower operational costs for Aernnova. This dissertation contributes to the broader field of manufacturing engineering by showing the importance of combining empirical data analysis with theoretical models to achieve more accurate tool life predictions in complex manufacturing environments.
- Proposta de um Guia de valorização e classificação de produtos excedentes para processos produtivosPublication . Bajanca, Ana Rita Teixeira; Godina, RaduMilhares de milhões de toneladas de lixo são produzidas anualmente e consequentemente outras tantas acabam em aterros que se encontram já sobrecarregados. Esta excessiva produção de resíduos muitas vezes tóxicos, provenientes de uma atividade industrial extremamente poluente, e uma fraca gestão de resíduos, faz com que os especialistas ambientais de todo o mundo, se questionem sobre qual será afinal o futuro do nosso planeta. É neste mesmo conceito que se foca a presente dissertação, que visa desconstruir a forma como os produtores olham para os seus resíduos, expandindo horizontes no sentido da valorização e reutilização dos seus excedentes e, disseminando técnicas de Simbiose Industrial. Desta forma, é proposto um guia de valorização genérico, que ambiciona apoiar os produtores das mais variadas indústrias a tomarem decisões para a valorização dos seus resíduos. São propostas várias etapas distintas que pretendem debloquear as barreiras de classificação e valorização de resíduos, que serão aplicadas na avaliação de resíduos provenientes das indústrias de peixe, para futura aplicação na produção de fertilizantes biológicos, que de forma sustentável e rentável, apresentam grandes potenciais para a fortificação nutricional dos solos.
- Library of Cu-CuAl compositions and mechanical properties produced by wire arc additive manufacturingPublication . Nunes, Beatriz Costa Leandro Dias; Xavier, José; Santos, TelmoAbstract Functionally Graded Material (FGM)s exhibit unique mechanical and physical prop- erties, resulting from gradual variations in their composition and microstructure, which makes them highly applicable in advanced engineering contexts. FGMs are utilised across a variety of industries and are specifically developed for aerospace, maritime, and energy applications. This dissertation forms part of a doctoral thesis in which a Cu-CuAl FGM is being developed. The objective of the present study is to create a library of different Cu- CuAl compositions. The samples for this library, featuring various compositions, are produced using Wire and Wire and Arc Additive Manufacturing (WAAM). WAAM is a technique that enables the production of complex geometries through precise management of material deposition rates, offering substantial benefits compared to traditional methods. The analysis of the samples mechanical behaviour was conducted by performing hardness tests, eddy current tests, and tensile tests with Digital Image Correlation (DIC). The mechanical properties for each Cu-CuAl percentage were calculated based on the strains recorded during the tensile tests, which were obtained using DIC. The results demonstrate that the samples produced by WAAM present a homogeneous mixture of the two alloys across all compositions.