Departamento de Ciências Aeroespaciais
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Percorrer Departamento de Ciências Aeroespaciais por Objetivos de Desenvolvimento Sustentável (ODS) "12:Produção e Consumo Sustentáveis"
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- Dual-Purpose Star Tracker and Space Debris Detector: Miniature Instrument for Small SatellitesPublication . Beltran Nadal Arribas; Maia, João G.; Castanheira, João Pedro Conceição ; Filho, Joel Alves Costa ; Melício, Rui; Gordo, Paulo Romeu Seabra; Onderwater, Hugo; Duarte, Rui; Silva, André Resende Rodrigues daThis paper presents the conception, design and real miniature instrument implementation of a dual-purpose sensor for small satellites that can act as a star tracker and space debris detector. In the previous research work, the authors conceived, designed and implemented a breadboard consisting of a computer laptop, a camera interface and camera controller, an image sensor, an optics system, a temperature sensor and a temperature controller. It showed that the instrument was feasible. In this paper, a new real star tracker miniature instrument is designed, physically realized and tested. The implementation follows a New Space approach; it is made with Commercial Off-the-Shelf (COTS) components with space heritage. The instrument’s development, implementation and testing are presented.
- E-Kerosene Potential for Commercial Aviation DecarbonizationPublication . Quaresma, Guilherme da Silva Nheu; Magalhães, Leandro Barbosa ; Ferreira, Ana Filipa; Silva, André Resende Rodrigues daReducing greenhouse gas emissions from aircraft transport is crucial to achieving climate goals. In this sense, the present study looks into the suitability of e-fuels such as e-kerosene in reducing CO2 emissions. The Fleet System Dynamic Model is employed to examine data and predict future trends in line with the Committee on Aviation Environmental Protection. While the findings suggest that achieving carbon-neutral growth is possible, it might take longer than current forecasts indicate. For instance, considering an e-fuel production rate of 15%, it is possible to cut emissions by half around 2060 concerning 2005 levels.
- Mechanical and Piezoresistive Sensing of GFRP Modified with MWCNTs under Monotonic and Cyclic Loading for Structural Health MonitoringPublication . Limpo, Joana Valente; Pereira, João Pedro Nunes; Silva, Abílio Manuel Pereira da; Parente, João Miguel NunesFiber-reinforced composites, specifically polymer fiber-reinforced composites, have gained increased popularity among scientists and engineers. This results from their optimized properties, including mechanical strength, reduced weight, low density, chemical inertness, freedom in design, and good response to fatigue, among many others. This is reflected in many sectors, including the aeronautical and aerospace fields, where these composites have been replacing the more traditional materials, like metal. However, despite all the advantages of composites, due to their nature, some behavioral aspects, especially damage-wise, are not fully understood, hindering their use for certain functions. One of those functions is the structural health monitoring of components, which goal is to have components and structures be able of in situ monitor of their own condition, without the disadvantages of embedded sensors. With this in mind, this study analyzed the impact of the addition of varying carbon nanotube concentrations, 0.3 wt% and 0.4 wt% MWCNTs, to find an optimized concentration for better piezoresistive properties. Beyond that, the 0.3 wt% and 0.4 wt% MWCNT-reinforced laminates were subjected to multiple flexural tests, from monotonic to cyclic, and with increased deformation, to mimic possible in service conditions and preview their possible behavior under each situation. SEM imaging was done post testing, to link the mechanical and electrical data obtained with the damage suffered by the specimens. Overall, the results pointed to better mechanical properties for the samples with 0.3 wt% nanotubes, which can be a sign of poor interface properties for the higher nanoparticle concentration. On the other hand, the electrical data concluded the samples with 0.4 wt% MWCNT were the most sensitive and presented more stable results. In summary, by adding carbon nanotubes to the glass-fiber-reinforced laminates, it was possible to create a material with self-sensing capabilities, and real-time monitoring of the structure was achieved. The mechanical data reinforced the importance of manufacturing and dispersion processes, especially with increasing nanoparticle concentrations and the electrical resistance results concluded there is a relation between a material’s damage and electrical signal.
- Mitigating Dynamic Stall with a Movable Leading-Edge: the NACA0012-IK30 WingPublication . Camacho, Emanuel António Rodrigues ; Silva, André Resende Rodrigues da ; Marques, Flávio D.One major problem that affects rotor blade aerodynamics is dynamic stall, characterized by a series of events where transient vortex shedding negatively affects drag and lift, leading to abrupt changes in the wing’s pitching moment. The present work focuses on the mitigation of such effects by using a modified NACA0012 airfoil: the NACA0012-IK30 airfoil, used previously for thrust enhancement in flapping propulsion. An experimental rig is designed and built to study the advantages of a time-varying pitching leading edge on a plunging wing, more specifically its influence on the aerodynamic coefficients over time. Results indicate that when the wing is not experiencing significant stall, the movable leading edge does not hold considerable influence on drag or lift. However, it can reduce the pitching moment intensity by indirectly shifting the pressure center. Contrarily, when the wing is under proper dynamic stall, the movable leading edge truly improves the aerodynamic characteristics while operating at smaller effective angles of attack. This study contributes to the long-standing discussion on how to mitigate the adverse effects of dynamic stall by providing an innovative yet simple solution.
- Predicting airfoil dynamic stall loads using neural networksPublication . Camacho, Emanuel António Rodrigues ; Silva, André Resende Rodrigues da ; Marques, Flávio D.Dynamic stall is an aerodynamic regime characterized by loss of airfoil lift, drag increment, and abrupt changes in the pitching moment. Such effects can couple with structural dynamics where perturbations can be easily amplified, making this a critical phenomenon that jeopardizes operational safety. Hence, there is always the need to constantly study the basics of dynamic stall and provide newer predictive models that can take advantage of the current interest peak in artificial intelligence. The present work builds upon that need, exploring the ability of a simple feed-forward network to predict the oscillation cycle of a pitching airfoil experiencing from light to deep stall of a NACA0012 airfoil close to a Reynolds number of approximately 1.1x10^6. The proposed neural network uses the angle of attack and its rate of change as inputs, then estimates the whole aerodynamic cycle at once, outputting an aggregated vector of drag, lift, and pitching moment coefficients. The training phase was conducted using a database containing several conditions obtained from experimental tests, with a strict convergence criterion of R^2=0.99 for both training and test datasets. Results show that the neural network, even in the least-performing conditions, can capture the aerodynamics and overall tendencies, even if some dynamics are underrepresented in the training dataset. The present work brings down the complexity of methodology while demonstrating that a simplistic architecture can still offer an accurate dynamic stall model.
- Splashing correlation for single droplets impacting liquid films under non-isothermal conditionsPublication . Rodrigues, Daniel de Almeida Vasconcelos ; Barata, Jorge Manuel Martins ; Silva, André Resende Rodrigues daThe droplet impact phenomenon onto liquid films is predominant in a variety of modern industrial applications, including internal combustion engines and cooling of electronic devices. These are characterised by heat and mass transfer processes, such as evaporation, condensation and boiling. However, studies regarding droplets and liquid films under non-isothermal conditions are scarce in the literature and do not explore temperature-dependent phenomena. Due to this, the main objective of this work is to evaluate the influence of temperature on the splashing occurrence of single droplets impinging onto liquid films under the presence of a heat flux. The crown evolution is evaluated qualitatively to provide insight regarding breakup mechanisms. Water, n-heptane and n-decane are the fluids considered for the current study, as these provide a wide range of thermophysical properties and saturation temperatures. The splashing dynamics are evaluated by varying the droplet impact velocity and dimensionless temperature of the liquid film. Qualitative results show that an increase in the liquid film temperature leads to the transition from spreading to splashing, which is less evident for fuels in comparison with water. For water and n-heptane, the formation of cusps on the crown rim is promoted, which is associated with ligament breakup. For n-decane, the crown rims are relatively homogeneous in terms of shape and size, whereas the atomisation process varies a function of the liquid film temperature. Visually, the secondary droplets exhibit a greater size in comparison with lower temperatures. Transitional regimes display some irregularities, such as splashing suppression/reduction, which require further attention. In terms of splashing correlation, the authors propose to develop a non-splash/splash boundary for both iso- and non-isothermal conditions. Results show that the splashing threshold is dependent on the thermophysical properties and the dimensionless temperature of the liquid film.