ENIDH - EMM - Artigo Científico
Permanent URI for this collection
Browse
Recent Submissions
- Optimization on Elastoplasticity of Functionally Graded Shells of Revolution, under Axisymmetric LoadingPublication . Moita, J. S.; Araújo, A. L.; Correia, V.F.; Soares, C.M.M.; Herskovits, J.Depending on the load level, structures can experience a material nonlinearity known as elastoplasticity, which has an important role in the behaviour of structures. In order to avoid the elastoplastic behaviour, it is necessary to find the optimal thickness distribution, which corresponds to the minimum mass that provides an elastic behaviour for a certain load level. The elastoplasticity analysis of functionally graded axisymmetric shells under axisymmetric mechanical loading, and the subsequent optimization, was performed by using a simple conical frustum finite element model with two nodal circles; three degrees of freedom per node, which was based on Kirchhoff’s theory allowing for shear deformation; and using a reduced numerical integration procedure that is essential for its success when applied to thin shells. The formulation accounts for the calculation of the displacements and through-thickness stress distribution, including the effective stress. In this work, the thickness was the design variable in the optimization procedure and the mass was the objective function that needed to be minimized subject to a constraint imposed on the effective stress. The optimization solutions were obtained by using a feasible arc interior point gradient-based algorithm. Some illustrative examples were performed, and the corresponding results are presented and discussed.
- An existence and uniqueness result about algebras of Schwartz distributionsPublication . Dias, Nuno Costa; Jorge, Cristina; Prata, João Nuno
- Free Vibrations Analysis of Composite and Hybrid Axisymmetric ShellsPublication . Moita, José S.; Araújo, A. L.; Correia, Victor Franco; Soares, C. M. MotaThe free vibration of laminated composite (C) and hybrid axisymmetric shell structures, consisting of a composite laminated material sandwiched between two functionally graded material laminas (F1/C/F2), is analysed in the present work. The numerical solutions are obtained by expanding the variables in Fourier series in the circumferential direction and using conical frustum finite elements in the meridional direction. The implemented finite element is a simple conical frustum with two nodal circles, with ten degrees of freedom per nodal circle. This model requires only a reduced number of finite elements to model the geometry of axisymmetric structures, the integration procedures use one Gauss point, and the through the thickness properties variation in FGM laminas is modelled by a small number of virtual layers, resulting a very high computational efficiency. The in-house developed code presents very good solutions when compared with results obtained by alternative available models.
- On a Recent Conjecture by Z. Van Herstraeten and N. J. Cerf for the Quantum Wigner EntropyPublication . Dias, Nuno C.; Prata, João N.We address a recent conjecture stated by Z. Van Herstraeten and N. J. Cerf. They claim that the Shannon entropy for positive Wigner functions is bounded below by a positive constant, which can be attained only by Gaussian pure states. We introduce an alternative definition of entropy for all absolutely integrable Wigner functions, which is the Shannon entropy for positiveWigner functions. Moreover, we are able to prove, in arbitrary dimension, that this entropy is indeed bounded below by a positive constant, which is not very distant from the constant suggested by Van Herstraeten and Cerf. We also prove an analogous result for another conjecture stated by the same authors for the R´enyi entropy of positive Wigner functions. As a by-product we prove a new inequality for the radar-ambiguity function (and for the Wigner distribution) which is reminiscent of Lieb’s inequalities.
- Uncertainty principle via variational calculus on modulation spaces.Publication . Dias, N.C.; Luef, Frank; Prata, João .We approach uncertainty principles of Cowling-Price-Heis-enberg-type as a variational principle on modulation spaces. In our discussion we are naturally led to compact localization operators with symbols in modulation spaces. The optimal constant in these uncertainty principles is the smallest eigenvalue of the inverse of a compact localization operator. The Euler-Lagrange equations for the associated functional provide equations for the eigenfunctions of the smallest eigenvalue of these compact localization operators. As a by-product of our proofs we derive a generalization to mixed-norm spaces of an inequality for Wigner and Ambiguity functions due do Lieb.
- MediBot: An Ontology-Based Chatbot to Retrieve Drug Information and Compare its PricesPublication . Avila, Caio Viktor S.; Franco, Wellington; Venceslau, A. D. P.; Rolim, Tulio Vidal; Vidal, Vania M. P.; Pequeno, Valéria M.In this article, we present the MediBot. MediBot is a chatbot for querying drugs information. The presented system acted as a single access point for natural and simplified information retrieval of drugs, prices, and its risks. The chatbot has two modes of operation: Quick Response and Interactive modes. The first answers questions asked in natural language, while the second has three interactive tasks, namely Browser, Query, and Price Comparison. We present here the system architecture, the Linked Data Mashup’s construction process, and Chatbot MediBot’s activities modes, focusing on the new Price Comparison’s task. This task presents the best prices for medicines and their best potential substitutes extracted in real-time from the Web with the help of the information obtained from a linked data mashup.
- Assessment of Replacement of Metal Parts by BFRP Composites into a Highly Efficient Electrical PrototypePublication . Marat-Mendes, R.; Ribeira, D.; Reis, L.This work intends to evaluate the use of epoxy composite materials reinforced with basalt fibers as replacement to metallic mechanical parts of a highly efficient electrical prototype. The analysis of the behavior of the original metallic bracket was made and an optimization process was carried out in order to achieve the most suitable geometry and stacking sequence if produced in composite material. Finite element analysis using Siemens NX12 and experimental tests to the produced composite part were performed in order to access it. It was verified that the total weight of the composite part shows a 45% reduction. The composite part shows a higher deformation than the metallic one due to basalt fiber’s higher flexibility. However, the advantages added by the new component largely compensate for the disadvantages that may have been added without compromising its performance. Obtained results show that the use of basalt fiber reinforced composites as the material of mechanical parts of a highly efficient electrical prototype that is a good alternative.
- Mechanical and thermal buckling of functionally graded axisymmetric shellsPublication . Moita, J. S.; Araújo, A. L.; Soares, C. M. M.; Correia, V. F.The buckling analysis of functionally graded materials (FGM) axisymmetric plate-shell type structures under mechanical and termal loading is 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 includes the transverse shear deformations by introducing a penalty function, which corresponds to the first order shear deformation theory (FSDT), is suitable for both thin and thick axisymmetric plate/shell 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, results in an extremely low computational time required for FGM buckling applications. An in-house program has been developed, and applications in a variety of axisymmetric shells are solved, including circular plates. The solutions obtained in mechanical and thermal buckling are discussed and compared with alternative models.
- Boundaries and profiles in the Wigner formalismoPublication . Dias, N. C.; Prata, J. N.We consider a quantum device contained in an interval in the context of the Weyl–Wigner formalism. This approach was originally suggested by Frensley and is known to be plagued with several problems, such as non-physical and non-unique solutions. We show that some of these problems may be avoided if one writes the correct dynamical equation. This requires the (non-local) infuence of the potential outside of the device and the inclusion of singular boundary potentials. We also discuss the problem of imposing boundary conditions on the Wigner function that mimic the efect of the external environment. We argue that these conditions have to be chosen with extreme care, as they may otherwise lead to non-physical solutions
- Partial Traces and the Geometry of Entanglement; Sufficient Conditions for the Separability of Gaussian States.Publication . Dias, N. C.; Gossan, M. de; Prata, J. N.The notion of partial trace of a density operator is essential for the understanding of the entanglement and separability properties of quantum states. In this paper, we investigate these notions putting an emphasis on the geometrical properties of the covariance ellipsoids of the reduced states. We thereafter focus on Gaussian states and we give new and easily numerically implementable sufficient conditions for the separability of all Gaussian states. Unlike the positive partial transposition criterion, none of these conditions is however necessary.