The influence of the boundary conditions on low-velocity impact composite damage

The objective of this work was to study the influence of the boundary conditions on low-velocity impact behaviour of carbon-epoxy composite plates. Experimental work and numerical analysis were performed on [04,904]s laminates. The influence of different boundary conditions on the impacted plates was analysed considering rectangular and square plates. The X-radiography was used as a non-destructive technique to evaluate the internal damage caused by impact loading. A three-dimensional numerical analysis was also performed considering progressive damage modelling. The model includes three-dimensional solid elements and interface finite elements including a cohesive mixed-mode damage model, which allows simulating delamination between different oriented layers. It was verified that plate’s boundary conditions have influence on the delaminated area. Good agreement between experimental and numerical analysis for shape, orientation and size of the delamination was obtained.

Controlador Boundary-Scan

A crescente complexidade dos sistemas electrónicos associada a um desenvolvimento nas tecnologias de encapsulamento levou à miniaturização dos circuitos integrados, provocando dificuldades e limitações no diagnóstico e detecção de falhas, diminuindo drasticamente a aplicabilidade dos equipamentos ICT. Como forma de lidar com este problema surgiu a infra-estrutura Boundary Scan descrita na norma IEEE1149.1 “Test Access Port and Boundary-Scan Architecture”, aprovada em 1990. Sendo esta solução tecnicamente viável e interessante economicamente para o diagnóstico de defeitos, efectua também outras aplicações. O SVF surgiu do desejo de incutir e fazer com que os fornecedores independentes incluíssem a norma IEEE 1149.1, é desenvolvido num formato ASCII, com o objectivo de enviar sinais, aguardar pela sua resposta, segundo a máscara de dados baseada na norma IEEE1149.1. Actualmente a incorporação do Boundary Scan nos circuitos integrados está em grande expansão e consequentemente usufrui de uma forte implementação no mercado. Neste contexto o objectivo da dissertação é o desenvolvimento de um controlador boundary scan que implemente uma interface com o PC e possibilite o controlo e monitorização da aplicação de teste ao PCB. A arquitectura do controlador desenvolvido contém um módulo de Memória de entrada, um Controlador TAP e uma Memória de saída. A implementação do controlador foi feita através da utilização de uma FPGA, é um dispositivo lógico reconfiguráveis constituído por blocos lógicos e por uma rede de interligações, ambos configuráveis, que permitem ao utilizador implementar as mais variadas funções digitais. A utilização de uma FPGA tem a vantagem de permitir a versatilidade do controlador, facilidade na alteração do seu código e possibilidade de inserir mais controladores dentro da FPGA. Foi desenvolvido o protocolo de comunicação e sincronização entre os vários módulos, permitindo o controlo e monitorização dos estímulos enviados e recebidos ao PCB, executados automaticamente através do software do Controlador TAP e de acordo com a norma IEEE 1149.1. A solução proposta foi validada por simulação utilizando o simulador da Xilinx. Foram analisados todos os sinais que constituem o controlador e verificado o correcto funcionamento de todos os seus módulos. Esta solução executa todas as sequências pretendidas e necessárias (envio de estímulos) à realização dos testes ao PCB. Recebe e armazena os dados obtidos, enviando-os posteriormente para a memória de saída. A execução do trabalho permitiu concluir que os projectos de componentes electrónicos tenderão a ser descritos num nível de abstracção mais elevado, recorrendo cada vez mais ao uso de linguagens de hardware, no qual o VHDL é uma excelente ferramenta de programação. O controlador desenvolvido será uma ferramenta bastante útil e versátil para o teste de PCBs e outras funcionalidades disponibilizadas pelas infra-estruturas BS.

Survey of trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) in retail samples of flavoured and bottled waters

Concentrations of eleven trace elements (Al, As, Cd, Cr, Co, Hg, Mn, Ni, Pb, Se, and Si) were measured in 39 (natural and flavoured) water samples. Determinations were performed using graphite furnace electrothermetry for almost all elements (Al, As, Cd, Cr, Co, Mn, Ni, Pb, and Si). For Se determination hydride generation was used, and cold vapour generation for Hg. These techniques were coupled to atomic absorption spectrophotometry. The trace element content of still or sparkling natural waters changed from brand to brand. Significant differences between natural still and natural sparkling waters (p<0.001) were only apparent for Mn. The Mann–Whitney U-test was used to search for significant differences between flavoured and natural waters. The concentration of each element was compared with the presence of flavours, preservatives, acidifying agents, fruit juice and/or sweeteners, according to the labelled composition. It was shown that flavoured waters generally increase the trace element content. The addition of preservatives and acidifying regulators had a significant influence on Mn, Co, As and Si contents (p<0.05). Fruit juice can also be correlated to the increase of Co and As. Sweeteners did not provide any significant difference in Mn, Co, Se and Si content.

Fractional generalization of memristor and higher order elements

Fractional calculus generalizes integer order derivatives and integrals. Memristor systems generalize the notion of electrical elements. Both concepts were shown to model important classes of phenomena. This paper goes a step further by embedding both tools in a generalization considering complex-order objects. Two complex operators leading to real-valued results are proposed. The proposed class of models generate a broad universe of elements. Several combinations of values are tested and the corresponding dynamical behavior is analyzed.

Elements of scalable data processing

Cooperating objects (COs) is a recently coined term used to signify the convergence of classical embedded computer systems, wireless sensor networks and robotics and control. We present essential elements of a reference architecture for scalable data processing for the CO paradigm.

Modeling of the lung impedance using a fractional order ladder network with constant phase elements

The self similar branching arrangement of the airways makes the respiratory system an ideal candidate for the application of fractional calculus theory. The fractal geometry is typically characterized by a recurrent structure. This study investigates the identification of a model for the respiratory tree by means of its electrical equivalent based on intrinsic morphology. Measurements were obtained from seven volunteers, in terms of their respiratory impedance by means of its complex representation for frequencies below 5 Hz. A parametric modeling is then applied to the complex valued data points. Since at low-frequency range the inertance is negligible, each airway branch is modeled by using gamma cell resistance and capacitance, the latter having a fractional-order constant phase element (CPE), which is identified from measurements. In addition, the complex impedance is also approximated by means of a model consisting of a lumped series resistance and a lumped fractional-order capacitance. The results reveal that both models characterize the data well, whereas the averaged CPE values are supraunitary and subunitary for the ladder network and the lumped model, respectively.

Fractional electrical impedances in botanical elements

Fractional calculus (FC) is no longer considered solely from a mathematical viewpoint, and is now applied in many emerging scientific areas, such as electricity, magnetism, mechanics, fluid dynamics, and medicine. In the field of dynamical systems, significant work has been carried out proving the importance of fractional order mathematical models. This article studies the electrical impedance of vegetables and fruits from a FC perspective. From this line of thought, several experiments are developed for measuring the impedance of botanical elements. The results are analyzed using Bode and polar diagrams, which lead to electrical circuit models revealing fractional-order behaviour.

The use of the boundary element method in the analysis of single lap joints

The most common techniques for stress analysis/strength prediction of adhesive joints involve analytical or numerical methods such as the Finite Element Method (FEM). However, the Boundary Element Method (BEM) is an alternative numerical technique that has been successfully applied for the solution of a wide variety of engineering problems. This work evaluates the applicability of the boundary elem ent code BEASY as a design tool to analyze adhesive joints. The linearity of peak shear and peel stresses with the applied displacement is studied and compared between BEASY and the analytical model of Frostig et al., considering a bonded single-lap joint under tensile loading. The BEM results are also compared with FEM in terms of stress distributions. To evaluate the mesh convergence of BEASY, the influence of the mesh refinement on peak shear and peel stress distributions is assessed. Joint stress predictions are carried out numerically in BEASY and ABAQUS®, and analytically by the models of Volkersen, Goland, and Reissner and Frostig et al. The failure loads for each model are compared with experimental results. The preparation, processing, and mesh creation times are compared for all models. BEASY results presented a good agreement with the conventional methods.

An optimal boundary fair scheduling

Nowadays, many real-time operating systems discretize the time relying on a system time unit. To take this behavior into account, real-time scheduling algorithms must adopt a discrete-time model in which both timing requirements of tasks and their time allocations have to be integer multiples of the system time unit. That is, tasks cannot be executed for less than one time unit, which implies that they always have to achieve a minimum amount of work before they can be preempted. Assuming such a discrete-time model, the authors of Zhu et al. (Proceedings of the 24th IEEE international real-time systems symposium (RTSS 2003), 2003, J Parallel Distrib Comput 71(10):1411–1425, 2011) proposed an efficient “boundary fair” algorithm (named BF) and proved its optimality for the scheduling of periodic tasks while achieving full system utilization. However, BF cannot handle sporadic tasks due to their inherent irregular and unpredictable job release patterns. In this paper, we propose an optimal boundary-fair scheduling algorithm for sporadic tasks (named BF TeX ), which follows the same principle as BF by making scheduling decisions only at the job arrival times and (expected) task deadlines. This new algorithm was implemented in Linux and we show through experiments conducted upon a multicore machine that BF TeX outperforms the state-of-the-art discrete-time optimal scheduler (PD TeX ), benefiting from much less scheduling overheads. Furthermore, it appears from these experimental results that BF TeX is barely dependent on the length of the system time unit while PD TeX —the only other existing solution for the scheduling of sporadic tasks in discrete-time systems—sees its number of preemptions, migrations and the time spent to take scheduling decisions increasing linearly when improving the time resolution of the system.

Desenvolvimento de um Controlador de Boundary Scan (Ieee 1149.1)

Mestrado em Engenharia Electrotécnica e de Computadores - Área de Especialização em Automação e Sistemas

Desenvolvimento de programa em linguagem Matlab® para cálculo pelo método de elementos finitos

Para o projeto de qualquer estrutura existente (edifícios, pontes, veículos, máquinas, etc.) é necessário conhecer as condições de carga, geometria e comportamento de todas as suas partes, assim como respeitar as normativas em vigor nos países nos quais a estrutura será aplicada. A primeira parte de qualquer projeto nesta área passa pela fase da análise estrutural, onde são calculadas todas as interações e efeitos de cargas sobre as estruturas físicas e os seus componentes de maneira a verificar a aptidão da estrutura para o seu uso. Inicialmente parte-se de uma estrutura de geometria simplificada, pondo de parte os elementos físicos irrelevantes (elementos de fixação, revestimentos, etc.) de maneira a simplificar o cálculo de estruturas complexas e, em função dos resultados obtidos da análise estrutural, melhorar a estrutura se necessário. A análise por elementos finitos é a ferramenta principal durante esta primeira fase do projeto. E atualmente, devido às exigências do mercado, é imprescindível o suporte computorizado de maneira a agilizar esta fase do projeto. Existe para esta finalidade uma vasta gama de programas que permitem realizar tarefas que passam pelo desenho de estruturas, análise estática de cargas, análise dinâmica e vibrações, visualização do comportamento físico (deformações) em tempo real, que permitem a otimização da estrutura em análise. Porém, estes programas demostram uma certa complexidade durante a introdução dos parâmetros, levando muitas vezes a resultados errados. Assim sendo, é essencial para o projetista ter uma ferramenta fiável e simples de usar que possa ser usada para fins de projeto de estruturas e otimização. Sobre esta base nasce este projeto tese onde se elaborou um programa com interface gráfica no ambiente Matlab® para a análise de estruturas por elementos finitos, com elementos do tipo Barra e Viga, quer em 2D ou 3D. Este programa permite definir a estrutura por meio de coordenadas, introdução de forma rápida e clara, propriedades mecânicas dos elementos, condições fronteira e cargas a aplicar. Como resultados devolve ao utilizador as reações, deformações e distribuição de tensões nos elementos quer em forma tabular quer em representação gráfica sobre a estrutura em análise. Existe ainda a possibilidade de importação de dados e exportação dos resultados em ficheiros XLS e XLSX, de maneira a facilitar a gestão de informação. Foram realizados diferentes testes e análises de estruturas de forma a validar os resultados do programa e a sua integridade. Os resultados foram todos satisfatórios e convergem para os resultados de outros programas, publicados em livros, e para cálculo a mão feitos pelo autor.

Fate Hazardous elements in soils surrounding a coal-fired power plant complex

Proceedings of the 13th International UFZ-Deltares Conference on Sustainable Use and Management of Soil, Sediment and Water Resources - 9–12 June 2015 • Copenhagen, Denmark

Trace Elements in Ambient Air at Porto Metropolitan Area—Checking for Compliance with New European Union (Eu) Air Quality Standards

Because of the scientific evidence showing that arsenic (As), cadmium (Cd), and nickel (Ni) are human genotoxic carcinogens, the European Union (EU) recently set target values for metal concentration in ambient air (As: 6 ng/m3, Cd: 5 ng/m3, Ni: 20 ng/m3). The aim of our study was to determine the concentration levels of these trace elements in Porto Metropolitan Area (PMA) in order to assess whether compliance was occurring with these new EU air quality standards. Fine (PM2.5) and inhalable (PM10) air particles were collected from October 2011 to July 2012 at two different (urban and suburban) locations in PMA. Samples were analyzed for trace elements content by inductively coupled plasma–mass spectrometry (ICP-MS). The study focused on determination of differences in trace elements concentration between the two sites, and between PM2.5 and PM10, in order to gather information regarding emission sources. Except for chromium (Cr), the concentration of all trace elements was higher at the urban site. However, results for As, Cd, Ni, and lead (Pb) were well below the EU limit/target values (As: 1.49 ± 0.71 ng/m3; Cd: 1.67 ± 0.92 ng/m3; Ni: 3.43 ± 3.23 ng/m3; Pb: 17.1 ± 10.1 ng/m3) in the worst-case scenario. Arsenic, Cd, Ni, Pb, antimony (Sb), selenium (Se), vanadium (V), and zinc (Zn) were predominantly associated to PM2.5, indicating that anthropogenic sources such as industry and road traffic are the main source of these elements. High enrichment factors (EF > 100) were obtained for As, Cd, Pb, Sb, Se, and Zn, further confirming their anthropogenic origin.