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- Reparação e reabilitação de estruturas portuárias com reduzido impacto ambiental: o caso do Porto de Abrigo da Ilha do Porto Santo (Madeira, Portugal) [Repair and rehabilitation of harbor structures with reduced environmental impact: The case of the shelter harbor of Porto Santo Island (Madeira, Portugal)]Publication . Sousa, Nuno Miguel Barros de; Lopes, Luiz GuerreiroNeste trabalho, são descritas e analisadas as diversas soluções implementadas nas obras de reparação e reabilitação do porto de abrigo da Ilha do Porto Santo, no Arquipélago da Madeira, Portugal. São focados os aspectos essenciais envolvidos nos trabalhos de reabilitação, como o enquadramento climático e geográfico, os estudos preliminares realizados, a caracterização das obras e a solução de reabilitação implementada, que contribuiu para a redução do seu impacto ambiental, assim como a ordem de trabalhos e os meios necessários à sua execução. São também apresentados os resultados da aplicação da metodologia simplificada de cálculo das dimensões e do peso dos blocos de proteção e do enrocamento, bem como da espessura das diferentes camadas por estes formadas, sendo ainda discutidos os aspectos mais e menos positivos desses trabalhos de reabilitação portuária.
- Indirect estimation of flow and suspended sediment concentration and load in small mountain streams: an exploratory study in Ribeira Seca streamPublication . Lobo, Raquel; Lopes, Luiz GuerreiroThe aim of this study was to assess the applicability of indirect techniques for streamflow and suspended sediment concentration estimation and their use in the calculation of suspended sediment transport rate in the small mountain watersheds of Madeira Island, Portugal. Emphasis was given to the application of salt dilution gauging to the indirect determination of the flow rate and the use of water turbidity data to estimate the concentration of suspended sediments. The field and laboratory work carried out are briefly described, and the main experimental results and the field data from the short measurement campaign performed in the Ribeira Seca stream in Faial, on the north side of the island, are presented and discussed. Whilst the measurement campaign carried out was temporally and spatially limited, it was pioneering for Madeira and allowed to verify the applicability of the indirect hydrometric and sedimentometric techniques used in this exploratory study.
- A family of Ehrlich-type accelerated methods with King’s correction for the simultaneous approximation of polynomial complex zerosPublication . Machado, Roselaine Neves; Lopes, Luiz GuerreiroIn this paper, we present a new family of accelerated iterative methods for the simultaneous approximation of simple complex zeros of a polynomial. These simultaneous methods are constructed on the basis of the third order Ehrlich iteration, accelerated by using the so-called Gauss–Seidel approach, and combined with a correction based on King’s family of optimal fourth order iterative methods for solving nonlinear equations. Using King’s correction, the R-order of convergence of the basic accelerated method is increased from at least 3 to at least 6. A numerical example is provided to illustrate the convergence and effectiveness of the proposed family of combined accelerated methods for the simultaneous approximation of simple polynomial zeros.
- Particle swarm optimisation: a historical review up to the current developmentsPublication . Freitas, Diogo; Lopes, Luiz Guerreiro; Dias, Fernando MorgadoThe Particle Swarm Optimisation (PSO) algorithm was inspired by the social and biological behaviour of bird flocks searching for food sources. In this nature-based algorithm, individuals are referred to as particles and fly through the search space seeking for the global best position that minimises (or maximises) a given problem. Today, PSO is one of the most well-known and widely used swarm intelligence algorithms and metaheuristic techniques, because of its simplicity and ability to be used in a wide range of applications. However, in-depth studies of the algorithm have led to the detection and identification of a number of problems with it, especially convergence problems and performance issues. Consequently, a myriad of variants, enhancements and extensions to the original version of the algorithm, developed and introduced in the mid-1990s, have been proposed, especially in the last two decades. In this article, a systematic literature review about those variants and improvements is made, which also covers the hybridisation and parallelisation of the algorithm and its extensions to other classes of optimisation problems, taking into consideration the most important ones. These approaches and improvements are appropriately summarised, organised and presented, in order to allow and facilitate the identification of the most appropriate PSO variant for a particular application.
- Learning programming with robots: a study on students' participation in a virtual community of practicePublication . Santos, Elci Alcione; Lopes, Luiz Guerreirot Nowadays, students learn from the world through a variety of physical and virtual spaces. As one of the priorities of the 21st century is to develop capacities associated with computational thinking and digital literacy, the use of robots in the teaching of programming is becoming more and more usual, since it promotes the development of problem solving, communication and teamwork skills. The purpose of this paper is to analyse and discuss the concept of participation in a virtual community created for the learning of programming with robots. Based on the situated learning theory and the underlying concepts of communities of practice, as well as the effects of technology thereon, we seek a better understanding of learning in these virtual spaces.
- A neural network-based approach for approximating arbitrary roots of polynomialsPublication . Freitas, Diogo; Lopes, Luiz; Dias, Fernando MorgadoFinding arbitrary roots of polynomials is a fundamental problem in various areas of science and engineering. A myriad of methods was suggested to address this problem, such as the sequential Newton’s method and the Durand–Kerner (D–K) simultaneous iterative method. The sequential iterative methods, on the one hand, need to use a deflation procedure in order to compute approximations to all the roots of a given polynomial, which can produce inaccurate results due to the accumulation of rounding errors. On the other hand, the simultaneous iterative methods require good initial guesses to converge. However, Artificial Neural Networks (ANNs) are widely known by their capacity to find complex mappings between the dependent and independent variables. In view of this, this paper aims to determine, based on comparative results, whether ANNs can be used to compute approximations to the real and complex roots of a given polynomial, as an alternative to simultaneous iterative algorithms like the D–K method. Although the results are very encouraging and demonstrate the viability and potentiality of the suggested approach, the ANNs were not able to surpass the accuracy of the D–K method. The results indicated, however, that the use of the approximations computed by the ANNs as the initial guesses for the D–K method can be beneficial to the accuracy of this method
- Algoritmos genéticos híbridos para a resolução numérica de sistemas de equações não linearesPublication . Lopes, Luiz Carlos Guerreiro; Carvalho, André Carlos Ponce de Leon Ferreira de
- Envisat radar altimetry measurements of water level in a semi-arid river with complex morphology: The Lower Save, Southern AfricaPublication . Lopes, Luiz GuerreiroAlthough there are numerous studies on water level changes in large rivers using satellite radar altimetry, there is no altimetry-based published study with specific focus on rivers of semi-arid areas smaller in width and with braided or wandering reaches. Taltimetry to measure water level fluctuations in a river with such characteristics. The lower Save River, a heavily silted river in Southern Africa with a dominant braided pattern, was chosen for this study. The presence of multiple narrow and shallow channels in many sections of the lower Save and the existence of sandbanks, channel bars and small islets represent additional challenges for the processing of altimetry water level measurements. High sampling rate radar altimeter data from the Envisat 35-day exact repeat mission (June 2002 to October 2010) were used in this study. The obtained altimetric water level time series do exhibit a similar variation pattern and show a reasonably good agreement with the nearest river gauge data available, especially when the hydraulic characteristics are similar along the river stretch between both monitoring points and these are not too far apart, and when the return radar signals are not so contaminated by land features. Some of the results are comparable to those from other studies for large rivers, indicating that Envisat radar altimetry can be used to derive water levels for the lower Save, a semi-arid river with relatively small widths and complex channel morphologies.
- Ehrlich-type methods with king’s correction for the simultaneous approximation of polynomial complex zerosPublication . Neves Machado, Roselaine; Lopes, Luiz GuerreiroThere are many simultaneous iterative methods for approximating complex polynomial zeros, from more traditional numerical algorithms, such as the well-known third order Ehrlich–Aberth method, to the more recent ones. In this paper, we present a new family of combined iterative methods for the simultaneous determination of simple complex zeros of a polynomial, which uses the Ehrlich iteration and a correction based on King’s family of iterative methods for nonlinear equations. The use of King’s correction allows increasing the convergence order of the basic method from three to six. Some numerical examples are given to illustrate the convergence behaviour and effectiveness of the proposed sixth order Ehrlich-like family of combined iterative methods for the simultaneous approximation of simple complex polynomial zeros. the advantage of being inherently parallel and avoid the pro cess of deflation, although these iterative methods usually need good initial approximations for all the zeros in order to con verge. In this work, a new family of numerical methods for the si multaneous approximation of simple complex polynomial ze ros is presented. The proposed simultaneous methods are con structed on the basis of the well-known third order Ehrlich– Aberth iteration [1, 6], combined with an iterative correction from the optimal fourth order two-step King’s method for solv ing nonlinear equations [10]
- Avaliação do risco de galgamento de estruturas portuárias: aplicação ao porto de Ponta DelgadaPublication . Pereira, D.; Lopes, L. G.; Reis, M. T.; Fortes, C. J.; Poseiro, P.Neste trabalho, descreve-se a aplicação de uma metodologia para a avaliação do risco de galgamento de estruturas portuárias ao porto de Ponta Delgada, Açores. Esta metodologia envolve, primeiramente, a caracterização da agitação marítima, sendo o estudo da propagação das ondas desde o largo até ao interior do porto feito através do uso combinado dos modelos numéricos WAVEWATCH III, SWAN e DREAMS. Foi considerado um período de estudo de dois anos, entre 2011 e 2012. Os resultados do modelo SWAN foram validados através de comparação com dados in situ medidos por boia-ondógrafo. Com base nos valores fornecidos pelo modelo DREAMS, efetuou-se a determinação do caudal médio de galgamento em cinco secções de estruturas portuárias pré-selecionadas, com recurso à ferramenta neuronal NN_OVERTOPPING2. A avaliação do risco associado ao galgamento para cada secção analisada, a partir da probabilidade de ocorrência de galgamento e das consequências a ele associadas, permitiu a criação de mapas de risco, importantes para o planeamento de operações e de futuras intervenções nos locais em estudo.