Obtenção de um modelo de elementos finitos simplificado para representação de juntas rebitadas em análise dinâmica de estruturas usando uma ferramenta de updating

ResumoNeste artigo é proposto um modelo de elementos finitos simplificado para representação de juntas rebitadas em análise dinâmica de estruturas. O rebite é modelado com elementos que combinam mola e amortecedor. Vários modelos numéricos são estudados com diferentes quantidades de rebites (um, 2, 3 e 5) e diferentes quantidades de elementos mola‐amortecedor (4, 6, 8, 12, 16 e 20) por cada rebite. Amostras constituídas por 2 placas de alumínio ligadas entre si por diferentes quantidades de rebites (um, 2, 3 e 5) são construídas e submetidas a análise modal experimental, a fim de serem conhecidas as suas características modais – frequências naturais e formas naturais de vibração. É usada uma metodologia de melhoramento de modelos de elementos finitos, também conhecido na linguagem anglo‐saxónica por updating, com o fim de obter a melhor representação numérica da junta rebitada relativamente às amostras experimentais. Uma avaliação da melhor representação numérica da junta rebitada é efetuada com base na comparação entre as frequências naturais experimentais e as frequências naturais numéricas, para cada modo de vibração, após aplicação do processo de melhoramento de elementos finitos. Mostra‐se que o modelo de junta composto por 8 e 12 elementos mola‐amortecedor por rebite consegue uma melhor aproximação ao comportamento dinâmico observado experimentalmente. Um valor numérico da constante de rigidez é obtido para as juntas em estudo.AbstractIn this paper, a simplified finite element model to represent a riveted lap joint in structural dynamic analysis field is proposed. The rivet is modeled by spring‐damper combination elements. Several numerical models are studied with different quantities of rivets (1, 2, 3 and 5) and spring‐damper combination elements (4, 6, 8, 12, 16 and 20) per rivet. Experimental samples of two aluminum material plates connected by different quantities of rivets (1, 2, 3 and 5) are built and tested in order to be known its modal characteristics ‐ natural frequencies and mode shapes. A finite element model updating methodology is used in order to get the best numerical riveted lap joint representation relatively to the experimental samples. An evaluation of the best numerical riveted lap joint is carried out based on the comparison between the experimental and numerical resonance frequencies after updating. It is shown that the riveted lap joints composed by eight and twelve spring‐damper combination elements per rivet have the best representation. A stiffness constant value is obtained for the riveted lap joints in stud

Experimental study of twin air impinging jets

This work is devoted to the visualization and characterization of twin air jet flow when impinging vertically to a solid surface, which is important to understand the phenomenon relevant to Vertical/Short Take-Of and Landing (V/STOL) type of aircraft when they are operating on short distances from the ground, landing or taking-off, and could be helpful to improve the performance and stability of this kind of aircrafts. The major concern of this work is characterizing the fountain upwash region, which is a distinctive fan-shape flow that is formed on the collision region. The parameters analysed on this work are the separation distance between the jets and the jet height. Have been observed significant changes in the flow pattern and properties in the fountain upwash region due to the changes in the parameter studied. To be possible the realization of this work an experimental facility has been built. The facility supports an adjustable mechanical system which can accommodate twin stainless steel barrels with different diameters, which are the jets. Within this mechanical system, the barrels horizontal distance and height can be independently adjusted. The working fluid is the air, and to be possible the flow visualization a seeding generator have been projected and built. The flow visualization has been supported by an algorithm developed on the “Image Processing toolbox of Matlab” software, where have been made the post processing of the images.Este trabalho baseia-se na visualização e caracterização do escoamento desenvolvido por dois jactos paralelos e verticalmente disposto em relação a uma superfície sólida. Estes fenómenos estão associados com aeronaves de descolagem e aterragem vertical ou curta (V/STOL – vertical/short take-of and landing). Particularmente, interessa a caracterização da região conhecida como “fountain upwash”, que é uma forma característica do escoamento que se forma na região da colisão. Os parâmetros analisados neste trabalho foram a distância horizontal entre os jactos e a altura destes à superfície de impacto. Foram observados diferenças significativas no padrão e propriedades do escoamento na região de “fountain upwash” devido à variação dos parâmetros em estudo. Para a realização deste estudo foi construída uma instalação experimental. A instalação é ajustável mecanicamente, contendo dois tubos de aço, com diâmetro variável. O sistema mecânico permite o ajustamento, independentemente, a distância horizontal entre os jactos e a altura dos mesmos. Como neste trabalho se vai trabalhar com ar, para ser possível visualizar o escoamento é necessário marcar o escoamento. Nesse sentido foi desenvolvido um gerador de “seeding”. Para uma melhor e mais precisa visualização do escoamento foi desenvolvido um algoritmo no “Matlab” usando “Image Processing toolbox”, onde as imagens captadas foram pós processadas

Building up Undergraduate Skills – empirical evidence from a Portuguese University

This study presents preliminary results of the PSP Project, addressing students' soft skills development within the context of HEI. Theoretical framework is grounded in Person-Environment Fit theories (Rounds & Hesketh, 1994), and also in Evans (2001) starfish model. Study 1 aimed to identify Economics and Business graduates' Market-Valued Skills Profile, collecting data through semi-structured interviews with HR managers and former students focus groups. Study 2 assessed students' confidence level regarding skills using a self-report questionnaire (Miles & Grummon, 2006). Career development representations were also assessed (Savickas, 2002; Gonçalves, 2006). Additional data was collected through open-ended questions focusing on work and other extracurricular experiences. Results from Study 1 highlight soft skills as multidimensional construct where different interrelated skills contribute to graduates' employability. Study 2 reveals students' positive self-perception regarding those skills, although limited vocational experiences were reported.Soft Skills, Career development, higher education students; employability

EU ETS effects on emissions of European Union industries

This article contributes to the literature by analyzing how has the EU ETS allowance price affected the CO2 emissions of the EU industries, analyzing eight economic activity sectors for the three EU ETS phases (2005-2020). Estimations were performed using both a sample of 33 and 23 European countries through panel estimations. From the results, it was inferred that only in the sectors manufacture of paper and paper products (mpp) and manufacture of other nonmetallic mineral products (monmp) the impact of CO2 allowances prices has lead to the reduction of emissions intensity significantly, meaning that they reduce the emissions amount whenever the price of these allowances goes up. Therefore, the effect of allowances prices on emissions intensity is heterogeneous among sectors and the implementation phase of the EU ETS is relevant to explain emissions intensity reductions (phase 3) or increases (phases 1 and 2). Policymakers, thus should devote more attention to the other sectors where prices do not reveal a negative nor significant impact on emissions intensity.info:eu-repo/semantics/acceptedVersio

Land use intensity and land occupation of utility-scale photovoltaic power plants in continental Portugal

Details about Portuguese PV stations are scarce: no public access is provided to project files and environmental impact assessments (EIA) - public-domain information - are mandatory only for power plants of 50 MW or higher capacity, a small minority. In our research, we measured the land use intensity (LUI) of utility-scale PV power plants in continental Portugal and estimated their future land occupation from the capacity additions forecast by the government and from the expected future improvements in LUI due to the increase in PV panel efficiency. A novel method, with land occupation depending simultaneously on the evolution of capacity and panel efficiency, was developed for the purpose. We found 3.336 ha/MW for the average LUI of all stations in operation in continental Portugal, with the LUI varying with mounting type. For land occupation by PV plants in 2050 we found large areas albeit small when compared with other land cover types, e.g. 30 000 hectares would be 1.3% and 0.9% of the current areas dedicated to agriculture and forestry, respectively. However, with EIAs required only for large stations there will be opportunities for land-use conflicts and deep landscape alterations.info:eu-repo/semantics/acceptedVersio

The effectiveness of environmental taxes in reducing CO2 emissions in passenger vehicles: The case of Mediterranean countries

The transport sector is the biggest source of CO2 emissions in Europe. It is responsible for over a quarter of all greenhouse gas emissions. Passenger vehicles, alone, account for nearly 41% of these emissions, resulting in human health impacts. To meet the Paris climate commitments, cars and vans should be decarbonized until 2050. Such a transformation requires general changes, such as how the vehicles are owned, taxed, and driven. The European Federation for Transport and Environment revealed that Mediterranean countries tend to emit less per vehicle compared to the northern and central Europeans. Intriguingly, this does not necessarily correspond to motorization rates. In this article, we assess whether the observed reductions in CO2 emissions in the Mediterranean countries can be attributed to vehicle taxation on CO2 emissions. We apply panel data econometric techniques using data on annual registrations from 2008 to 2018 and model the demand for new-vehicle purchases and their responsiveness to changes in both CO2-based taxation and circulation tax. Our results show the determinants of new-vehicle demand and the change in the emissions rate in each country under the taxation currently adopted. We found that fiscal policies can have an important role in reducing the emission in the Mediterranean countries.info:eu-repo/semantics/publishedVersio

Immune Reconstitution Inflammatory Syndrome: Opening Pandora's Box

One of the purposes of antiretroviral therapy (ART) is to restore the immune system. However, it can sometimes lead to an aberrant inflammatory response and paradoxical clinical worsening known as the immune reconstitution inflammatory syndrome (IRIS). We describe a 23-year-old male, HIV1 infected with a rapid progression phenotype, who started ART with TCD4+ of 53 cells/mm(3) (3,3%) and HIV RNA = 890000 copies/mL (6 log). Four weeks later he was admitted to the intensive care unit with severe sepsis. The diagnostic pathway identified progressive multifocal leukoencephalopathy, digestive Kaposi sarcoma, and P. aeruginosa bacteraemia. Five weeks after starting ART, TCD4+ cell count was 259 cells/mm(3) (15%) and HIV RNA = 3500 copies/mL (4 log). He developed respiratory failure and progressed to septic shock and death. Those complications might justify the outcome but its autopsy opened Pandora's box: cerebral and cardiac toxoplasmosis was identified, as well as hemophagocytic syndrome, systemic candidiasis, and Mycobacterium avium complex infection. IRIS remains a concern and eventually a barrier to ART. Male gender, young age, low TCD4 cell count, and high viral load are risk factors. The high prevalence of subclinical opportunistic diseases highlights the need for new strategies to reduce IRIS incidence.info:eu-repo/semantics/publishedVersio

Clean and dirty technologies under environmental policy

This paper aims is to study the contributions of environmental policies to the production of ecological goods, when consumers are indifferent between ecological and dirty goods. It develops a Schumpeterian R&D growth model with endogenous directed technological change. By solving the transitional dynamics numerically and by removing the scale effects, it is shown that, through the price channel, when green firms and green research are supported by policy and/or dirty activities are taxed, technological progress leads to relatively more production of ecological goods and environmental quality improvements. Furthermore, if there is a positive change in the green technological environment, it strongly fosters R&D towards quality improvement of ecological goods, increasing their production.info:eu-repo/semantics/publishedVersio

TK diffusion under market-based instruments between different environmental countries

Using an endogenous Schumpeterian R&D growth model, this paper intends to analyse how international trade of intermediate goods can affect the structure and diffusion of technological knowledge between ecological and dirty countries. Each country is assumed to have different environmental quality levels and different available technological knowledge and to be able of conducting R&D activities (innovative in ecological-country and imitative in dirtycountry). We concluded that under international trade, there is a higher probability of successful imitation that improves the Dirty-country ability to benefit from Ecological-country innovations. This induces an efficient allocation of production in the Dirty-country, where marginal cost is lower, and increases the ecological goods production in the Ecological-country. Furthermore, subsidies, by promoting technological knowledge progress, lead to a permanent increase in the world steady-state growth rate.info:eu-repo/semantics/acceptedVersio

Technological diffusion between different environmental countries

Using an endogenous Schumpeterian R&D growth model, this paper intends to analyse how international trade of intermediate goods can affect the structure and diffusion of technological knowledge between ecological and dirty countries. Each country is assumed to have different environmental quality levels and different available technological knowledge and to be able of conducting R&D activities (innovative in ecological-country and imitative in dirty-country). We concluded that under international trade, there is a higher probability of successful imitation that improves the Dirty-country ability to benefit from Ecological-country innovations. This induces an efficient allocation of production in the Dirty-country, where marginal cost is lower, and increases the ecological goods production. Furthermore, subsidies, by promoting technological knowledge progress, lead to a permanent increase in the world steady-state growth rate.info:eu-repo/semantics/acceptedVersio