ENIDH - EMM - Artigo Científico
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- Active-passive damping in functionally graded sandwich plate/shell structuresPublication . Moita, J.S; Araújo, A.L; M. Franco Correia, V.; Mota Soares, C.M; Herskovits, J.; ElsivierIn this work, a simple and efficient finite element model is applied to the vibration analysis of active–passive damped multilayer sandwich plates/shells with a viscoelastic core, sandwiched between functionally graded material (FGM) layers, and including piezoelectric layers. Both the FGM and the piezoelectric layers are modelled using the classical plate theory and the core is modelled using Reddy’s third-order shear deformation theory. The sandwich finite element is obtained performing the assembling of N “elements” through the thickness, by using specific assumptions on the displacement continuity at the interfaces between layers. To achieve a mechanism for the active control of the structural dynamics response, a feedback control algorithm is used, coupling the sensor and active piezoelectric layers. The dynamic analysis of the sandwich plate/shell structures is conducted in the frequency domain to obtain the natural frequencies and the loss factors of the viscoelastic core and in time domain for the steady state harmonic motion. For both analyses, a finite element code has been implemented. The model is applied in the solution of some illustrative examples and the results are presented and discussed.
- AIS Based Shipping Routes Using the Dijkstra AlgorithmPublication . Silveira, P.; Teixeira, A.P.; Guedes Soares, C.This paper proposes an approach for identifying and characterizing shipping routes using information contained in Automatic Identification System messages broadcasted by ships and recorded by the coastal Vessel Traffic Service centre. The approach consists of using historical Automatic Identification System data to build a graph, where nodes are cells of a grid covering the geographical area being studied and the weights of directional edges are inversely related to ship movements between cells. Based on this graph, the Dijkstra algorithm is used to identify a potential safe route, assumed to be the most used route by ships between two locations. A second graph is created simultaneously, with the same nodes and edges, but with edge weights equal to the average speed of transitions between cells, thus allowing the determination of the average speed profile for any possible path within the graph. The proposed approach is applied to two scenarios: an approach to the port of Lisbon and the entry through the fairway to a RO-RO terminal in the port of Setubal in Portugal.
- An overview on how failure analysis contributes to flight safety in the Portuguese Air ForcePublication . Duarte, Diogo.; Marado, Bruno.; Nogueira, João.; Serrano, Bruno.; Infante, Virgínia.; Moleiro, Filipa.Failure analysis has been, throughout the years, a fundamental tool used in the aerospace sector, supporting assessments performed by sustainment and design engineers mainly related to failure modes and material suitability. The predicted service life of aircrafts often exceeds 40 years, and the design assured life rarely accounts for all in service loads and in service environmental menaces that aging aircrafts must deal with throughout their service lives. From the most conservative safe-life conceptual design approaches to the most recent on-condition based design approaches, assessing the condition and predicting the failure modes of components and materials are essential for the development of adequate preventive and corrective maintenance actions as well as for the accomplishment and optimization of scheduled maintenance programs of aircrafts. Moreover, as the operational conditions of aircrafts may vary significantly from operator to operator (especially in military aircraft), it is necessary to access if the defined maintenance programs are adequate to guarantee the continuous reliability and safe usage of the aircrafts, preventing catastrophic failures which bear significant maintenance and repair costs, and that may lead to the loss of human lives. Thus being, failure analysis and material investigations performed as part of aircraft accidents and incidents investigations arise as powerful tools of the utmost importance for safety assurance and cost reduction within the aeronautical and aerospace sectors. The Portuguese Air Force (PRTAF) has operated different aircrafts throughout its long existence, and in some cases, has operated a particular type of aircraft for more than 30 years, gathering a great amount of expertise in: assessing failure modes of the aircrafts materials; conducting aircrafts accidents and incidents investigations (sometimes with the participation of the aircraft manufacturers and/or other operators); and in the development of design and repair solutions for in-service related problems. This paper addresses several studies to support the thesis that failure analysis plays a key role in flight safety improvement within the PRTAF. It presents a short summary of developed analysis and studies using optic and electronic (MEV) microscopy, material chemical composition analysis and Non Destructive Testing (NDT) to solve problems related to operation, maintenance and design issues. Additionally, it presents the investment that has been made by the Portuguese Air Force in the last two decades, to increase the flight safety through the implementation of powerful aircraft configuration management tools, and structural condition assessment methodologies based on strain measurements, NDT evaluation programs and, more recently, on Structural Health Monitoring systems in their fleets.
- Antioxidant Capacity and Identification of Bioactive Compounds of Myrtus communis L. Extract Obtained by Ultrasound-Assisted ExtractionPublication . Pereira, P.; Cebola, M.J.; Oliveira, M.C.; Bernardo-Gil, M. G.Ultrasound-assisted extraction was used to investigate the polyphenolic compounds, particularly anthocyanins, present in myrtle alcoholic extracts. This type of extract is typical in the making of liqueurs obtained from herbs or plants, especially medicinal plants. The leaf extracts were found to contain flavonoids from the quercetin and myricetin families. Besides these, the berry extracts also showed the presence of anthocyanins, hydrolysable tannins and quinic acid. The antioxidant capacity was studied using the ORAC and TEAC methods and the polyphenol content was measured using the Folin–Ciocalteu method. The results showed that the values produced by the ORAC and TEAC methods were in agreement and that the antioxidant capacity correlated with the polyphenol content. The results showed that the leaf extracts exhibited higher antioxidant capacity than the berry extracts. The extraction method was easily implementable, and proved to be a swift method for obtaining bioactive compounds from vegetable matrices.
- Bell operator and Gaussian squeezed states in noncommutative quantum mechanicsPublication . Bernardini, Alex E.; Bastos, Catarina.; Bertolami, Orfeu.; Costa Dias, Nuno.; Prata, João Nuno.We examine putative corrections to the Bell operator due to the noncommutativity in the phase space. Starting from a Gaussian squeezed envelope whose time evolution is driven by commutative (standard quantum mechanics) and noncommutative dynamics, respectively, we conclude that although the time-evolving covariance matrix in the noncommutative case is different from the standard case, the squeezing parameter dominates and there are no noticeable noncommutative corrections to the Bell operator. This indicates that, at least for squeezed states, the privileged states to test Bell correlations, noncommutativity versions of quantum mechanics remain as nonlocal as quantum mechanics itself.
- Benchmark exact solutions for the static analysis of multilayered piezoelectric composite plates using PVDFPublication . Moleiro, F; Soares, C.M. Mota; Soares, C.A. Mota; Reddy, J.N.The three-dimensional (3D) exact solutions developed in the early 1970s by Pagano for simply supported multilayered orthotropic composite plates and later in the 1990s extended to piezoelectric plates by Heyliger have been extremely useful in the assessment and development of advanced laminated plate theories and related finite element models. In fact, the well-known test cases provided by Pagano and by Heyliger in those earlier works are still used today as benchmark solutions. However, the limited number of test cases whose 3D exact solutions have been published has somewhat restricted the assessment of recent advanced models to the same few test cases. This work aims to provide additional test cases to serve as benchmark exact solutions for the static analysis of multilayered piezoelectric composite plates. The method introduced by Heyliger to derive the 3D exact solutions has been successfully implemented using symbolic computing and a number of new test cases are here presented thoroughly. Specifically, two multilayered plates using PVDF piezoelectric material are selected as test cases under two different loading conditions and considering three plate aspect ratios for thick, moderately thick and thin plate, in a total of 12 distinct test cases. (C) 2013 Elsevier Ltd. All rights reserved.
- Composition of Myrtus communis L. Essential Oils as Affected by Climatic ConditionsPublication . Pereira, Paula.; Cebola, Maria João.; Bernardo-Gil, M.GMyrtus Communis L. (Myrtaceae family), commonly known as myrtle, possesses a set of qualities that make it very interesting for the pharmaceutical, nutraceutical and cosmetic industries. In this work, myrtle was studied over a period of three years (2006-2008), encompassing the main stages of the development cycle of the plant. The influence of climatic conditions, such as temperature and rainfall, on the chemical composition and yield of the essential oils obtained from leaves and berries was studied. The leaves and berries essential oils were obtained by Clevenger distillation and analysed by GC and GC-MS. The results show that the major components were limonene+1,8-cineole, myrtenyl acetate, α-pinene and linalool. Over the three year period of study, a decrease in the composition of the most volatile compounds (α-pinene and limonene+1,8-cineole) was observed, the reverse being found for linalool and myrtenyl acetate. The highest value for the yield of the leaves’ essential oils was observed in the third year (0.64%, w/w), whereas that same year the lowest yield (0.07%, w/w) of fruit was observed. These results were likely due to an atypically high record for rainfall in April and May of that year. The highest value of the berry essential oils (0.14%, w/w) was obtained in the second year.
- Crankshaft failure analysis of a boxer diesel motorPublication . Fonte, M.; Anes, V.; Duarte, P.; Reis, L.; Freitas, M.This paper reports a failure mode analysis of a boxer diesel engine crankshaft. Crankshafts are components which experiment severe and complex dynamic loadings due to rotating bending combined with torsion on main journals and alternating bending on crankpins. High level stresses appear on critical areas like web fillets, as well as the effect of centrifugal forces and vibrations. Since the fatigue fracture near the crankpin-web fillet regions is one of the primary failure mechanisms of automotive crankshafts, designers and researchers have done the best for improving its fatigue strength. The present failure has occurred at approximately 2000 manufactured engines, and after about 95,000 km in service. The aim of this work is to investigate the damage root cause and understand the mechanism which led to the catastrophic failure. Recommendations for improving the engine design are also presented.
- Crankshaft failure analysis of a motor vehiclePublication . Fonte, M.; Li, Bin; Reis, L.; Freitas, M.A case study of a crankshaft catastrophic failure of a motor vehicle and its failure analysis is presented. The crankshaft suffered a mechanical seizure on the crankpin no. 2 after 3 years in service. It was repaired and after 30,000 km the vehicle had a damage again, with a catastrophic failure on the same crankpin. A transversal macrograph of the crankpin revealed that the crankpin was rectified and filled with a metal alloy for the same nominal diameter. Two fatigue cracks growing to the center of the crankpin where the final fracture occurred. The symmetric semi-elliptical crack front profile confirms the effect of a pure mode I under alternating bending. The catastrophic failure was a consequence of the inadequate repairing by a non-authorized manufacturer.
- A damage parameter for HCF and VHCF based on hysteretic dampingPublication . Lage, Y.; Cachão, H.; Reis, L.; Fonte, M.; Freitas, M. de; Ribeiro, A.The fatigue limit of materials, due to the improvement of fatigue life of structures and mechanical components should be extended from the traditional 106–107 cycles up to 109 and more, but with traditional testing hardware this is a difficult technical task due to the length of time needed for the completion of tests. Ultrasonic fatigue testing machines seem to be adequate for very high cycle fatigue (VHCF) tests. We propose here to evaluate the behavior of the hysteretic damping in an attempt to associate that with damage parameter. The approach here presented is based on the fact that the fatigue issue can be understood in terms of the energy available for irreversible process triggering. This nonconservative energy will be involved in micro-structural changes in the material before being dissipated as thermal energy. In fact, the balance between the energy supplied to and returned by the material is positive and the hysteretic damping factor represents the inelastic fraction of energy in each cycle. Aiming at building a model to correlate the hysteretic cycle parameters and the fatigue process, both energy loss and material response of the specimens are measured during the fatigue test. The fatigue tests are carried out with an ultrasonic machine test, operated at 20 kHz with amplitude or temperature control, under HCF and VHCF for copper specimens. The results show the behavior of hysteretic damping parameter during fatigue life, the equivalent dissipated energy per cycle and a good correlation between the hysteretic damping factor parameter and the fatigue process S–N curve, suggesting that factor as a promising fatigue life parameter useful for some cases of fatigue life prediction.