ENIDH - EMM - Artigo Científico
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- Vibrations of functionally graded material axisymmetric shells.Publication . Moita, J. S.; Araújo, A. L.; Correia, V. F.; Soares, C. M. M.The free-vibration analysis of functionally graded materials (FGM) axisymmetric plate-shell type structures are presented in this work. A numerical solution is obtained by expanding the variables in Fourier series in the circumferential direction and using conical frustum finite elements in the meridional direction. The finite element model, having two nodal circles and ten degrees of freedom per node, is based in the Kirchhoff-Love theory that include the transverse shear deformations by introducing a penalty function, and using one Gauss point integration scheme which gave excellent results for both thin and thick axisymmetric plate/shells structures. The reduced number of finite elements, which are required to model even complex structures, combined with the use of a small number of discrete layers to model the continuous variation of the mechanical properties through the thickness of the structure, result in an extremely low computational time required for FGM applications. An in-house program has been developed, and applications in a variety of axysimetric shells are solved, including circular plates. The solutions obtained are discussed and compared with solutions obtained by alternative models.
- Optimization of Metal–Ceramic Functionally Graded Plates Using the Simulated Annealing Algorithm.Publication . Franco Correia, Victor; S. Moita, J.; Moleiro, F.; M. Mota Soares, C.This work involves the design optimization of metal–ceramic through the thickness of functionally graded material (FGM) plates subjected to thermomechanical loadings. Constrained optimization was performed for minimum mass and minimum material cost of the FGM plates. The design process of FGM plate structures requires a good choice of metal and ceramic materials and the adequate definition of the components volume fractions through the thickness direction in order to accomplish a certain structural behavior, while optimizing the material costs and/or the plate mass. Here, the optimization problems are solved with the simulated annealing (SA) algorithm, not requiring the calculation of the derivatives of the objective or constraint functions. Constrained single objective optimization cases are studied, and validated with alternative solutions, considering the p-index and the FGM plate thickness as design variables. New optimization cases, involving additionally the metal and ceramic materials as design variables, are presented both for benchmark purposes and to demonstrate the suitability of the SA algorithm to solve those optimization problems.
- ENIDH desenvolve Projeto de I&DPublication . Assunção, M.; Franco, V.; Marat, R.; Fazenda, P.
- Parvifloron D from Plectranthus strigosus Cytotoxicity Screening of Plectranthus spp. ExtractsPublication . Garcia, C.; Ntungwe, C.; Rebelo, A.; Bessa, C.; Stankovic, T.; Dinic, J.; Díaz-Lanza, A.; Reis, C.; Roberto, A.; Pereira, P.; Cebola, M. J.; Saraiva, L.; Pesic, M.; Duarte, N.; Rijo, P.The Plectranthus genus is commonly used in traditional medicine due to its potential to treat several illnesses, including bacterial infections and cancer. As such, aiming to screen the antibacterial and cytotoxic activities of extracts, sixteen selected Plectranthus species with medicinal potential ere studied. In total, 31 extracts obtained from 16 Plectranthus spp. were tested for their antibacterial and anticancer properties. Well di usion method was used for preliminary antibacterial screening. The minimum inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of the five most active acetonic extracts (P. aliciae, P. japonicus, P. madagascariensis var. “Lynne”, P. stylesii, and P. strigosus) were determined. After preliminary toxicity evaluation on Artemia salina L., their cytotoxic properties were assessed on three human cancer cell lines (HCT116, MCF-7, and H460). These were also selected for mechanism of resistance studies (on NCI-H460/R and DLD1-TxR cells). An identified compound—parvifloron D—was tested in a pair of sensitive and MDR-Multidrug resistance cancer cells (NCI-H460 and NCI-H460/R) and in normal bronchial fibroblasts MRC-5. The chemical composition of the most active extract was studied through high performance liquid chromatography with a diode array detector (HPLC-DAD/UV) and liquid chromatography–mass spectrometry (LC–MS). Overall, P. strigosus acetonic extract showed the strongest antimicrobial and cytotoxic potential that could be explained by the presence of parvifloron D, a highly cytotoxic diterpene. This study provides valuable information on the use of the Plectranthus genus as a source of bioactive compounds, namely P. strigosus with the potential active ingredient the parvifloron D.
- Deformable MRI-Ultrasound registration using correlation-based attribute matching for brain shift correction: accuracy and generality in multi-site data.Publication . Machado, I.; Toews, M.; Luo, J.; Unadkat, P.; Essayed, W.; George, E.; Teodoro, P.; Carvalho, H.; Martins, J.; Golland, P.; Pieper, S.; Frisken, S.; Golby, A.; Wells, W.; Ou, Y.Intraoperative tissue deformation, known as brain shift, decreases the benefit of using preoperative images to guide neurosurgery. Non-rigid registration of preoperative magnetic resonance (MR) to intraoperative ultrasound (iUS) has been proposed as a means to compensate for brain shift. We focus on the initial registration from MR to predurotomy iUS. We present a method that builds on previous work to address the need for accuracy and generality of MR-iUS registration algorithms in multi-site clinical data. High-dimensional texture attributes were used instead of image intensities for image registration and the standard difference-based attribute matching was replaced with correlation-based attribute matching. A strategy that deals explicitly with the large field-of-view mismatch between MR and iUS images was proposed. Key parameters were optimized across independent MR-iUS brain tumor datasets acquired at 3 institutions, with a total of 43 tumor patients and 758 reference landmarks for evaluating the accuracy of the proposed algorithm. Despite differences in imaging protocols, patient demographics and landmark distributions, the algorithm is able to reduce landmark errors prior to registration in three data sets (5.37±4.27, 4.18±1.97 and 6.18±3.38 mm, respectively) to a consistently low level (2.28±0.71, 2.08±0.37 and 2.24±0.78 mm, respectively). This algorithm was tested against 15 other algorithms and it is competitive with the state-of-the-art on multiple datasets. We show that the algorithm has one of the lowest errors in all datasets (accuracy), and this is achieved while sticking to a fixed set of parameters for multi-site data (generality). In contrast, other algorithms/tools of similar performance need per-dataset parameter tuning (high accuracy but lower generality), and those that stick to fixed parameters have larger errors or inconsistent performance (generality but not the top accuracy). Landmark errors were further characterized according to brain regions and tumor types, a topic so far missing in the literature.
- Flexural testing and analysis of fullstrain-fields in sandwich composites.Publication . Marat-Mendes, R.; Martins, R.; Garcia, A.; Reis, L.The objective of this work was to characterize the full-field flexural behavior of composite sandwich beams. Finite element analysis was used to estimate the behavior of sandwich beams under three- and four-point-bending tests and were compared with experimental results obtained via digital image correlation and strain-gauges. Two different polyurethane core thicknesses and two different sandwich lengths were used to simulate short- and long-beam. Two distinct sandwich beams were used by means of two different faces: aluminum and basalt fiber reinforced polymer composite. Full-strain-fields and flexural displacements results were obtained showing that BFRP sandwiches exhibited higher flexibility and higher capacity of absorption energy than the aluminum specimens however with a higher prospect of core shear failure. For both face materials short-beams present higher strains than the long-beams and 4PB test specimens showed negative strain distribution in the upper side of the specimen and positive in the underside contrary to 3PB that presents positive strain distribution along the fulfilled. Moreover, results show that the strain distribution in not symmetric. Obtained experimental results are in good agreement with estimations; the digital image technique attested to be a complementary method to strain gages measurements in experimental full-strain-fields analysis.
- 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.
- Ordinary differential equations with singular coefficients: An intrinsic formulation with applications to the Euler-Bernoulli beam equation.Publication . Dias, N. C.; Jorge, C.; Prata, J. N.
- Failure analysis of a crankshaft of a helicopter enginePublication . Afonso Fonte, M.; Freitas, M.; Infante, V.A detailed analysis of a crankshaft failure belonging to a helicopter engine is presented. The main objective of this work was to analyze the characteristics of the failure and determine the root cause of the failure of the crankshaft. In order to determine the causes of the crankshaft failure, a material analysis was performed, followed by a detailed observation of the failure mechanisms through macroscopic, microscopic and microstructural examinations of the fracture surface. A preliminary observation of the fractured crankshaft indicates that this failure occurred by a fatigue process where the fracture surface shows obvious signs of cyclic propagation mechanisms. The existence of a large number of beachmarks indicates significant crack growth characterized by the effect of successive starts and stops of the engine by the operating conditions. These beachmarks cover about two-thirds of the total area of the fracture surface and the uniform geometric pattern of the crack front, along the entire propagation zone, allows to conclude that the fatigue process occurred from a loading state consisting essentially of cyclic bending stresses between the crankweb and the main journal of the crankshaft. No original defect was observed either on the surface or inside the material that could be the source of the crack initiation and growth and subsequent final fracture of the component. The analysis of the shell bearings applied to the main journal revealed a significant damage, with fractured location lugs, that are believed to be at the origin of the crack initiation of the crankshaft.
- Failure mode analysis of a damaged diesel motor crankshaftPublication . Afonso Fonte, M.; Reis, L.; Freitas, M.A case study of a catastrophic failure of a diesel motor crankshaft is presented. The aim of this failure analysis is to investigate the root cause of this important mechanical component. This crankshaft belonged to a particular vehicle (140 cv, at 4000 rpm, 1968 cm3 displacement) that fractured after 180,000 km and 8 years in service. The motor was disassembled, and the crankpin No. 3 and the main bearing cap No. 4 were broken. Defects of material and machining defects were not found at the crack initiation sites by optical and SEM microscope. Results shown that the crankpin and the main bearing cap clearly failed by fatigue, and the root cause seems to be related with deficient tightening of the main bearing cap No. 4, which fractured due to a crack developed on the its outer side. The main journal No. 4 did run out of support, and the crankthrow No. 3 increased the alternating stress amplitude, whereby an inevitable catastrophic crankshaft failure happened.