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

From colloidal dispersions to colloidal pastesthrough solid–liquid separation processes

Solid–liquid separation is an operation that starts with a dispersion of solid particles in a liquid and removes some of the liquid from the particles, producing a concentrated solid paste and a clean liquid phase. It is similar to thermodynamic processes where pressure is applied to a system in order to reduce its volume. In dispersions, the resistance to this osmotic compression depends on interactions between the dispersed particles. The first part of this work deals with dispersions of repelling particles, which are either silica nanoparticles or synthetic clay platelets, dispersed in aqueous solutions. In these conditions, each particle is surrounded by an ionic layer, which repels other ionic layers. This results in a structure with strong short-range order. At high particle volume fractions, the overlap of ionic layers generates large osmotic pressures; these pressures may be calculated, through the cell model, as the cost of reducing the volume of each cell. The variation of osmotic pressure with volume fraction is the equation of state of the dispersion. The second part of this work deals with dispersions of aggregated particles, which are silica nanoparticles, dispersed in water and flocculated by multivalent cations. This produces large bushy aggregates, with fractal structures that are maintained through interparticle surface– surface bonds. As the paste is submitted to osmotic pressures, small relative displacements of the aggregated particles lead to structural collapse. The final structure is made of a dense skeleton immersed in a nearly homogeneous matrix of aggregated particles. The variation of osmotic resistance with volume fraction is the compression law of the paste; it may be calculated through a numerical model that takes into account the noncentral interparticle forces. According to this model, the response of aggregated pastes to applied stress may be controlled through the manipulation of interparticle adhesion

Lito e tectono-estratigrafia da Unidade do Minho Central e Ocidental: uma proposta de reclassificação

A revisão cartográfica do sector correspondente à unidade parautóctone designada por Minho Central e Ocidental, permitiu identificar novas unidades: autóctones (formação Sobrado); parautóctones (unidades de Torre-Amonde e Vilar de Mouros) e alóctones (Unidades de Vila Mou-Covas e Arga). São propostas correlações destas unidades com outros sectores da Zona Galiza – Trás-os-Montes, nomeadamente, Celorico de Basto, Vila Pouca de Aguiar e Macedo de Cavaleiros.New geological mapping of the parauthocthonous unit of “Minho Central e Ocidental”, allowed the identification of some new units: autochthonous (Sobrado formation); parauthocthonous (TorreAmonde and Vilar de Mouros units) and allochthonous units (Vila Mou-Covas, Arga). Some correlations are established with other sector of Galiza - Trás-os-Montes Zone, namely, Celorico de Basto, Vila Pouca de Aguiar and Macedo de Cavaleiros sectors.(undefined

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

Condições termopluviométricas e fenológicas do cafeeiro arábica no ano agrícola 2007-2008 em Varginha-MG.

Neste trabalho é apresentada uma análise das principais condições termopluviométricas reinantes no ano agrícola 2007-2008 e sua influência nas fases fenológicas do cafeeiro arábica na localidade de Varginha, MG. Pode-se verificar que o ano agrícola 2007-2008 foi caracterizado por uma temperatura média anual de 20,6°C, um índice pluviométrico de 1.701 mm, uma deficiência hídrica de 193 mm, um excedente hídrico de 926 mm e uma taxa de armazenamento médio de água no solo de 69 mm. Os eventos fenológicos mais marcantes neste ano agrícola foram: (a) ausência de chuvas entre os meses de setembro e meados de outubro, acarretou deficiência hídrica elevada prejudicando a floração; (b) crescimento dos ramos dos cafeeiros abaixo da média prevista, consequente da baixa disponibilidade hídrica no solo, principalmente, entre setembro e dezembro

Consumer Behaviour in Fitness Club: Study of the Weekly Frequency of Use, Expectations, Satisfaction and Retention

This study aims to understand the relationship between the weekly frequency of use, expectations, satisfaction and retention of members in a fitness Clubs. In this market it is indispensable to understand the characteristics of faithful members, in order to act appropriately with each segment. Accordingly, the weekly frequency, which a member goes to the gym, their expectations, satisfaction and retention are key variables to understand them. Data was collected with a sample of 146 members. The instrument was constituted by the sample characterization and questions to understand the consumer behaviour in fitness (weekly frequency of use, expectations, satisfaction and retention behaviours). The statistical analysis consisted on descriptive and inferential analyses, using SPSS software. In this study the weekly frequency did not show the explanatory capacity to predict the satisfaction and retention. The relationship between expectations with satisfaction (73%) and retention (64%) was statistically significant. Finally, the relationship between satisfaction and retention (63%) was positive and significant. The results indicated that fitness club managers must act to keep those who are less likely to remain, who aren’t the ones who go less times a week to the club, but those who have a lower satisfaction and, consequently, lower retention.info:eu-repo/semantics/publishedVersio

Simple and complex modelling of timber-framed masonry walls in Pombalino buildings

Timber-framed masonry has been developed as an effective lateral-load resisting system in regions of high seismicity such as Southern Europe. A salient feature of the ‘last generation’ of timber-framed (TF) buildings is the presence of diagonal members that may consist of two diagonal braces. The present study focusses on alternative modelling procedures, ranging from simple to rather complex, for this interesting type of traditional structure. All models are applied to study the behaviour of full-scale specimens of diagonally-braced TF panels. The complex model is based on plasticity with contact surfaces for the connection between timber diagonals and masonry infills. A parametric analysis using this model shows that masonry infills affect only slightly the lateral force carried by this TF panel configuration. Furthermore, two simple modelling techniques are put forward for application in the analysis of large, realistic structures incorporating TF walls. The first one is directly connected to the complex modelling and is based on substructuring. A nine-step procedure is developed and is found to properly reproduce the response of the test specimens. The second simple model is a phenomenological one, developed on the basis of observed behaviour during tests and is a complete hysteretic model; however, for comparison purposes, all models are evaluated here with respect to the prediction of the envelope (pushover) curve for the walls tested under lateral loads

Improving the dynamical behaviour of a laser cutting equipment by using a carbon fibre composite main structural runway frame

In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution. The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented.Adira, S

Improving the dynamical behaviour of a laser cutting equipment by using a carbon fibre composite main structural runway frame

In order to improve the dynamic behaviour of an industrial laser cutting equipment a sandwich solution, using a carbon fibre reinforced polymer (CFRP) and polyester foam core, was implemented to construct its main runway structural frame, which supports the cutting head and major laser beam mirrors and lens. Nowadays, the commercial competiveness of laser cutting equipments is considerable enhanced by their higher cutting speed and precision, as well as, cost. With the recent available higher power laser beam generators and swifter motors quicker and powerful cuts may be already done. However, at accelerations of 3 and 4 g’s already enabled by linear motors, the lack of stiffness and high mass and consequent inertia of the traditional runway structural frames, made from steel and/or aluminium, do not allow achieving high required cutting precisions. Thus, the present study considered replacing those conventional materials by much lighter advanced CRFP composites to improve the dynamic performance of an existing laser cutting equipment. Advanced numeric Finite Element Method (FEM) calculations by using the ANSYS package software were made to verify the static and dynamic behaviours of the new composite structural frame and compare them to simulations made with the currently used steel solution.The composite structural frame processing method has been also studied and defined in this work. Furthermore, the composite laminate has been optimised by defining the better number of stacking layers and fibre orientations to be used, as well as, the foam core thickness. The failure of the new sandwich structural composite runway frame has been verified through the Tsai-Wu criterion. Finally, an economic analysis of the viability of the new composite solution adopted will be also presented