ISEL - Eng. Mecan. - Artigos
Permanent URI for this collection
Browse
Browsing ISEL - Eng. Mecan. - Artigos by Title
Now showing 1 - 10 of 343
Results Per Page
Sort Options
- 2019 world of shipping Portugal. An international research conference on maritime affairs editorial “Leading the shipping industry into the future”Publication . Paixão Casaca, Ana Cristina; Loja, M.A.R.Background, the context and purpose of the study: The current Editorial addresses the evolutionary path of the shipping industry. It mentions its role throughout the years, identifies the leading market segments, refers to the different operational modes due to the inherent nature of the cargoes they carry and lists some trends that appear to have been shaping the maritime industry. Within the scope of this background, the Editorial claims that all maritime market segments face the same future challenges and lists a range of international legislation released by the International Maritime Organisation which industry players must comply with. Findings, the main results: Not/aplicable. Conclusions, brief summary and potential implications: The Editorial concludes by stating that the maritime industry will benefit from the implementation of innovative solutions and further claims that wrong decisions will have severe impacts on the finances of the shipping companies and the environment. Moreover, it presents in a brief way the papers published in this Special Issue, which were selected among the ones presented at the 2019 World of Shipping Portugal, an International Research Conference on Maritime Affairs, 21–22 November 2019, that took place at Hotel Riviera, in Carcavelos, Portugal.
- 2021 World of shipping Portugal: an international research conference on maritime afairs editorialPublication . Paixão Casaca, Ana Cristina; Loja, M.A.R.Currently, the shipping industry is at a crossroads. Although it has overcome numerous technological barriers and fnance and economic crises over the years, the industry is facing its most prominent challenge, which rests on fnding the most feasible solutions to deal with industry decarbonisation until 2050. Within this scope, the current Editorial addresses the issue of sulphur emissions that the industry faced with the entrance of the sulphur regulation on 1 January 2020 and draws attention to the road that the industry players need to cover to decarbonise the shipping industry. Innovative measures like the Poseidon Principles or the Sea Cargo Charter are in place, and industry players are coming together to fnd feasible solutions. Within this regulatory environment, the shipping industry also had to deal with the COVID-19 Pandemic. However, some market segments, such as the container and dry bulk ones, have managed to survive, which is not the case with the tanker market. Altogether, these events draw the industry to deal with the market, technology, and regulatory challenges and risks whose outcome is yet to be seen. The Editorial concludes by presenting briefy the papers published in this Special Issue, which were selected among the ones presented at the 2021 World of Shipping Portugal, an international research conference on maritime afairs, 28–29 January 2021, that took place online from Portugal to the World due to the Covid-19 pandemic.
- 3D nickel foams with controlled morphologies for hydrogen evolution reaction in highly alkaline mediaPublication . Siwek, K. I.; Eugénio, S.; Santos, Diogo; Moura E Silva, Teresa; MONTEMOR, FATIMAWater electrolysis is the cleanest method for hydrogen production, and can be 100% green when renewable energy is used as electricity source. When the hydrogen evolution reaction (HER) is carried out in alkaline media, nickel (Ni) is a low cost catalyst and an interesting alternative to platinum. Still, its performance has to be enhanced to meet the high efficiency of the nobler metals, an objective that requires further tailoring of the surface area and morphology of Ni-based electrode materials. Unlike commercially available porous Ni, these features can be easily controlled via electrodeposition, a one-step process, taking advantage of the dynamic hydrogen bubble template (DHBT). Generally, changes in surface porosity and morphology have been mainly achieved by altering the main parameters, such as the current density or the deposition time. However, very scarce work has been done on the role of supporting electrolyte (i.e., its concentration and composition) in tailoring the foam features and consequently their catalytic activity. Hence, this approach paves the way to optimum design of metallic foam structures that can be obtained only with modifications in the electrolytic bath. In this work, 3D Ni foams are obtained from different composition baths by galvanostatic electrodeposition in the hydrogen evolution regime on stainless steel current collectors. Their porosity and morphology are analysed by optical microscopy and SEM. The electrochemical performance is evaluated by cyclic voltammetry, while catalytic activity towards HER and materials' stability in 8 M KOH are tested using polarisation curves and chronoamperometry measurements, respectively. The recorded high currents and extended stability of the Ni foams with dendritic morphology demonstrate its outstanding performance, making it an attractive cathode material for HER in highly alkaline media. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.
- 3D printing of abdominal immobilization masks for therapeutics: dosimetric, mechanical and financial analysisPublication . Duarte, Jessica; Loja, M.A.R.; Portal, Ricardo; Vieira, Lina OliveiraMolding immobilization masks is a time-consuming process, strongly dependent on the healthcare professional, and potentially uncomfortable for the patient. Thus, an alternative sustainable automated production process is proposed for abdominal masks, using fused deposition modelling (FDM) 3D printing with polylactic acid (PLA). Radiological properties of PLA were evaluated by submitting a set of PLA plates to photon beam radiation, while estimations of their mechanical characteristics were assessed through numerical simulation. Based on the obtained results, the abdominal mask was 3D printed and process costs and times were analyzed. The plates revealed dose transmissions similar to the conventional mask at all energies, and mechanical deformation guarantees the required immobilization, with a 66% final cost reduction. PLA proved to be an excellent material for this purpose. Despite the increase in labour costs, a significant reduction in material costs is observed with the proposed process. However, the time results are not favorable, mainly due to the printing technique used in this study.
- Adaptive empirical distributions in the framework of inverse problemsPublication . Silva, Tiago; Loja, Amélia; Carvalho, Alda; Maia, Nuno. M.; Barbosa, JoaquimThis article presents an innovative framework regarding an inverse problem. One presents the extension of a global optimization algorithm to estimate not only an optimal set of modeling parameters, but also their optimal distributions. Regarding its characteristics, differential evolution algorithm is used to demonstrate this extension, although other population-based algorithms may be considered. The adaptive empirical distributions algorithm is here introduced for the same purpose. Both schemes rely on the minimization of the dissimilarity between the empirical cumulative distribution functions of two data sets, using a goodness-of-fit test to evaluate their resemblance.
- Aerodynamic study of a drag reduction system and its actuation system for a formula student competition carPublication . Loução, Ricardo; Duarte, Gonçalo O.; J. G. C. Mendes, M.This work presents a computational fluid dynamic (CFD) analysis of a drag reduction system (DRS) used in a Formula Student competition vehicle, focusing on the interaction between the triple wing elements, as well as on the electrical actuators used to provide movement to the upper two flaps. The S1123 wing profile was chosen, and a 2D analysis of the wing profile was made. The trailing edge was rounded off to conform to Formula Student competition safety rules, resulting in around a 4% decrease in the lift coefficient and around a 12% increase in the drag coefficient for an angle of attack of 12°, compared to the original wing profile. The multi-element profile characteristics are: wing main plate with 4°, first flap 28°, and second flap 60°. To evaluate the wing operation, end plates and electrical linear actuators were added, generating a maximum lift coefficient of 1.160 and drag coefficient of 0.397, which provides around a 10% reduction in lift and a 9% increase in drag compared to the absence of the linear actuators. When activating the DRS, the flap rotation generates about a 78% decrease in the aerodynamic drag coefficient and 53% in the lift coefficient for the minimum aerodynamic drag setting.
- Alpha-Co(OH)(2)/carbon nanofoam composite as electrochemical capacitor electrode operating at 2 V in aqueous mediumPublication . Della Noce, Rodrigo; Eugénio, Sónia; Silva, Maria Teresa Oliveira de Moura e; Carmezim, M. J.; Montemor, Maria de FátimaIn this work, alpha-Co(OH)(2) is electrodeposited onto carbon nanofoam forming a composite electrode operating in a potential window of 2 V in aqueous medium. Prior to electrodeposition, the carbon nanofoam substrate is subjected to a functionalization process, which leads to an increase of about 40% in its specific capacitance value. Formation of cobalt hydroxide clusters onto the functionalized carbon nanofoam by pulse electrodeposition further enhances the specific capacitance of the electrode. The combination of these factors with an enlarged working potential window, results in a material with specific capacitance close to 300 F g(-1) at current density of 1 A g(-1), considering the total mass loading of the composite. This suggests the potential application of the prepared composites in high energy density electrochemical supercapacitors. (c) 2015 Elsevier B.V. All rights reserved.
- Aluminum-to-steel cladding by explosive weldingPublication . Carvalho, Gustavo; Galvão, Ivan; Mendes, Ricardo; Leal, Rui; Loureiro, AltinoThe production of aluminum-carbon steel and aluminum-stainless steel clads is challenging, and explosive welding is one of the most suitable processes to achieve them. The present work aims to investigate the coupled e_ect of two strategies for optimizing the production of these clads by explosive welding: the use of a low-density interlayer and the use of a low-density and low-detonation velocity explosive mixture. A broad range of techniques was used to characterize the microstructural and the mechanical properties of the welds, specifically, optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, electron backscatter di_raction, microhardness and tensile-shear testing with digital image correlation analysis. Although aluminum-carbon steel and aluminum-stainless steel have di_erent weldabilities, clads with sound microstructure and good mechanical behavior were achieved for both combinations. These results were associated with the low values of collision point and impact velocities provided by the tested explosive mixture, which made the weldability di_erence between these combinations less significant. The successful testing of this explosive mixture indicates that it is suitable to be used for welding very thin flyers and/or dissimilar materials that easily form intermetallic phases.
- An assessment of thermally influenced and delamination-induced regions by composites drillingPublication . Loja, Amélia; Alves, M. S. F.; Bragança, Ivo; Rosa, R. S. B.; Barbosa, Inês; Barbosa, JoaquimThe connection among different structural components may be promoted by several means. Among these, if one considers mechanical connections, it becomes often necessary to drill the components. When these structures are total or partially made of composite materials, this drilling operation imposes a particular care, due to its heterogeneous character highly prone to delamination or fibre pulling-out. Under these circumstances, not only will the stiffness and strength of the material be reduced in the drilled region neighbourhood, but ultimately a more worrying situation may arise if specific conditions exist to enable propagation and subsequent failure. It is therefore important to improve the drilling processes efficiency from the damage minimization perspective. To this purpose, the characterization of the drilling parameters influence in a cross-relation to measurable resulting effects may be a relevant contribution. With the present work, one intends to characterize how different drilling parameters may affect the surrounding region, either from an induced damage quantification perspective as well as from a thermally affected area characterization. The information acquisition of the affected areas was carried out both through scans and thermographic digital videos and images. A set of illustrative cases is presented to support the conclusions.
- An assessment of thick nanocomposite plates' behavior under the influence of carbon nanotubes agglomerationPublication . Craveiro, D.S.; Loja, AméliaThe influence assessment of carbon nanotubes (CNTs) agglomeration on CNT-reinforced composite (CNTRC) thick plates' behavior is the main aim of the present work. CNTs are known to agglomerate into clusters even for relatively low volume fractions, which imposes the need to characterize the effects this may introduce in structures behavior, also knowing that recent works have concluded that neglecting agglomeration phenomenon may lead to an overestimation of the mechanical properties of nanocomposites. Hence, it matters to understand how the arising of these clusters may affect the static and free vibrational behaviors of low side-to-thickness nanocomposite plates. To this purpose, the nanocomposite plate properties' estimation is performed by using the two-parameter model of agglomeration based on the Eshelby-Mori-Tanaka approach, while for behavioral analyses one considers a Higher-order Shear Deformation Theory (HSDT) based on the displacement field of Kant, implemented through the finite element method. The analyses developed consider a set of parametric studies involving the assessment of the influence of side-to-side ratios, side-to-thickness ratios, boundary conditions, and CNTs' distributions along the thickness. The results obtained allow concluding that the transverse deflections and fundamental frequencies of these structures are significantly influenced by the CNTs' agglomeration.