ENIDH - EMM - Artigo Científico
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- 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.
- Modified binary PSO for feature selection using SVM applied to mortality prediction of septic patientsPublication . Vieira, Susana M.; Mendonça, Luís F. Mendonça; Farinha, Gonçalo J.; Sousa, João Miguel da CostaThis paper proposes a modified binary particle swarm optimization (MBPSO) method for feature election with the simultaneous optimization of SVM kernel parameter setting, applied to mortality prediction in septic patients. An enhanced version of binary particle swarm optimization, designed to cope with premature convergence of the BPSO algorithm is proposed. MBPSO control the swarm variability using the velocity and the similarity between best swarm solutions. This paper uses support vector machines in a wrapper approach, where the kernel parameters are optimized at the same time. The approach is applied to predict the outcome (survived or deceased) of patients with septic shock. Further, MBPSO is tested in several benchmark datasets and is compared with other PSO based algorithms and genetic algorithms (GA). The experimental results showed that the proposed approach can correctly select the discriminating input features and also achieve high classification accuracy, specially when compared to other PSO based algorithms. When compared to GA, MBPSO is similar in terms of accuracy, but the subset solutions have less selected features.
- The Stream‐basedService‐Centered Calculus: a Foundation for Service‐Oriented ProgrammingPublication . Cruz-Filipe, L.; Lanese, I.; Ravara, A.; Vasconcelos, V.We give a formal account of stream-based, service-centered calculus (SSCC), a calculus for modelling service-based systems, suitable to describe both service composition (orchestration) and the protocols that services follow when invoked (conversation). The calculus includes primitives for defining and invoking services, for isolating conversations (called sessions) among clients and servers, and for orchestrating services. The calculus is equipped with a reduction and a labelled transition semantics related by an equivalence result. SSCC provides a good trade-off between expressive power for modelling and simplicity for analysis. We assess the expressive power by modelling van der Aalst workflow patterns and an automotive case study from the European project Sensoria. For analysis, we present a simple type system ensuring compatibility of client and service protocols. We also study the behavioural theory of the calculus, highlighting some axioms that capture the behaviour of the different primitives. As a final application of the theory, we define and prove correct some program transformations. These allow to start modelling a system from a typical UML Sequence Diagram, and then transform the specification to match the service-oriented programming style, thus simplifying its implementation using web services technology.
- Multipliers, linkages and influence fields among the sectors of the Portuguese maritime clusterPublication . Simões, A.; Salvador, R.; Guedes Soares, C.The main objective of this paper is to present the multiplier effects on the Portuguese economy of the main maritime sectors and their comparison with other economic sectors, in particular the key activities of which they are suppliers or buyers. One way of evaluating economic activities, which is adopted in this paper, is through the sectorial linkage indices and their interdependence, displaying their direct, indirect and induced effects, which can be quantified with the use of the Leontief (input-output) matrix. Based on the input-output matrix, one obtains the interconnection coefficients, the multiplying factors and the influence fields. Based on the values of the interdependence coefficients, the economic activities are analyzed and classified by its importance to the national economy. The paper identifies a broadly diversified productive structure, with several key sectors, which, if stimulated, can significantly boost the growth of other sectors and the overall economy.
- Hierarchical MPC for Multi-Commodity Transportation NetworksPublication . Nabais, João Lemos; Negenborn, Rudy R.; Carmona-Benítez, Rafael Bernardo; Mendonça, Luís Filipe; Botto, Miguel AyalaTransportation networks are large scale complex systems spatially distributed whose objective is to deliver commodities at the agreed time and at the agreed location. These networks appear in different domain fields, such as communication, water distribution, traffic, logistics and transportation. A transportation network has at the macroscopic level storage capability (located in the nodes) and transport delay (along each connection) as main features. Operations management at transportation networks can be seen as a flow assignment problem. The problem dimension to solve grows exponentially with the number of existing commodities, nodes and connections. In this work we present a Hierarchical Model Predictive Control (H-MPC) architecture to determine flow assignments in transportation networks, while minimizing exogenous inputs effects. This approach has the capacity to keep track of commodity types while solving the flow assignment problem. A flow decomposition of the main system into subsystems is proposed to diminish the problem dimension to solve in each time step. Each subsystem is managed by a control agent. Control agents solve their problems in a hierarchical way, using a so-called push-pull flow perspective. Further problem dimension reduction is achieved using contracted projection sets. The framework proposed can be easily scaled to network topologies in which hundreds of commodities and connections are present.
- Influence of Milling and Abrasive Waterjet Cutting on the Fatigue Behaviour of DP600 Steel SheetPublication . Duarte, Pedro; Infante, Virgínia; Freitas, Manuel deThe observation of cracks in mechanical parts shows that cracks often initiate on cutting edges. A lot of effort has been done to developing theories to predict fatigue behaviour of welds. However for the cut-edges available data is very scarce on the fatigue behaviour. This paper presents the results obtained in fatigue tests on DP600 dual-phase steel sheet specimens, under three types of cutting edges processes: milling with two cutting parameters and abrasive waterjet cutting. The tests were carried out using smooth specimens (Kt=1)and with a fatigue constant amplitude loading with R=0.1. Surface roughness and residual stresses induced by these different cutting conditions were measured and analysed. It was found that the fatigue strength of the abrasive waterjet cutting specimens was smaller than the predicted fatigue strength of the milling specimens and these may be attributed to the surface roughness induced by the cutting process. Finally failure mechanisms were studied with the scanning electron microscope (SEM) at fracture surfaces, including the identification of the fatigue crack initiation region. It was also observed that fatigue crack initiation takes place on the cut-edges.
- Participative Approaches to the Portuguese Maritime ClusterPublication . Simões, A.; Salvador, R; e Guedes Soares, CAs a public good, sea must be enjoyed and preserved according to the will of the majority of citizens. In order to do that, marine and maritime resources management must be accomplished through participative and democratic processes that increase the probability of correct decisions. The development of a participative sea-related process ought to facilitate the emergence of more creative and reality-adjusted solutions. The paper presents both the results of an inquiry launched to the seventy members (companies and public institutions) of the “Maritime Economy Entrepreneurship Forum” (MEEF) and the synthesis of a Delphi panel–type methodology based on fifteen maritime experts’ opinions. Based in these results, the authors propose a strategy in line with the UNESCO “Community-Based Strategy” (CBS).
- 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.
- New approach for analysis of complex multiaxial loading pathsPublication . Anes, V.; Reis, L.; Li, B.; Fonte, M.; Freitas, M.Experimentally, it has been proven that the stress level needed to cause fatigue failure in pure shear is less than the axial one. This fact has led to consider a stress scale factor between shear and axial stress in order to reduce different applied stresses to the same shear stress space or principal stress space to facilitate the yielding analysis or fatigue damage evaluations. In this way most of multiaxial fatigue models use a stress scale factor to consider the fatigue damage contributions from the axial and shear stress components regarding the material strength degradation. Much efforts were made to quantify the effective shear and axial stress amplitudes under a three-dimensional stress state, however, the combined damage resulted from those amplitudes have been reduced to a constant value. In some cases, the approaches used proved to be inadequate, leading to compute the same equivalent stress for different loading paths with different fatigue lives. In this work it is performed a series of multiaxial fatigue tests on a high-strength steel in order to determine the multiaxial fatigue strength under proportional and non-proportional loading conditions. A stress scale factor function was mapped based on the experimental results using as arguments, the axial stress amplitude and the stress amplitude ratio, which has proven to be sensitive to the loading path nature. Using the stress scale factor surface an equivalent shear stress was defined and it was used in the fatigue life correlation. Results indicate that the stress scale factor (ssf) is not a constant value and it is strongly dependent on stress amplitude level and loading path shape. The equivalent stress was successfully applied to proportional and non-proportional loading paths with satisfactory results.
- 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.