Conforming finite elements with embedded strong discontinuities

A kinematically consistent approach for embedded discontinuitie

Time-dependent modelling of quasi-brittle materials with a strong discontinuity approach

The time-dependent behaviour of quasi-brittle materials can have a significant effect on serviceability and ultimate failure. E.g., in the case of concrete structures, the presence of cracking can evolve, propagate and gradually widen over time, therefore significantly changing the stress state and expected structural response. The development of models that can account for the discrete nature of cracking whilst predicting time-dependent behaviour can be of interest to many practical applications. The discrete strong discontinuity approach (DSDA) has been validated as a reliable approach for simulating the cracking phenomenon by directly embedding the traction-separation constitutive relation within finite elements, therefore enriching standard finite element models with the ability to capture cracks, where material can separate without the need for remeshing. This work presents a generalisation to account for the long-term behaviour of cracked quasi-brittle materials, more specifically creep and shrinkage. To this end, a rate-type creep is first applied through a number of kelvin units; the interaction of the resulting response from the Kelvin chain system, shrinkage, and discrete cracking is developed to obtain a suitable constitutive model for the discrete crack simulations. Finally, the formulation is deployed on a finite element code where the performance of the proposed model is assessed through representative numerical examples

Flexural response of HSC girders strengthened with non- and prestressed CFRP laminates

An experimental programme was carried out to characterise the flexural response of prestressed highstrength concrete (HSC) girders strengthened with CFRP laminates. For that purpose, four beams with 20 m span were subjected to four-point bending loads and the effectiveness of two distinct strengthening strategies was analysed. The following testing situations have been considered: one girder was externally strengthened with CFRP laminates, whereas one was externally strengthened with prestressed CFRP laminates; the two remaining girders were left unstrengthened and were used as control. The monitoring system included the measurement of deflections at critical sections, strains in pre-selected points of the concrete girder and CFRP laminates and the applied loading, respectively using displacement transducers, strain gages and load cells. Herein, the tests are thoroughly described and the most relevant results and conclusions are presented

Crack growth modelling: enriched continuum vs. discrete models

Failure in quasi-brittle materials usually appears in the form of narrow bands called fracture process zones, where all inelastic deformation takes place, while the surrounding bulk material outside those areas typically unloads elastically. This localised nature of failure is the main source of size effects in these materials, since the width of the fracture process zone is a material property that does not scale with the size of the material volume. An adequate description of localised failure and associated size effects requires both size and behaviour of the fracture process zone and neighbouring material to be properly taken into account. In this study, we present two alternative approaches for modelling localised failure and simulating fracture propagation using finite element methods. In the first approach, an embedded crack appears at a constitutive level by enriching the kinematics of constitutive models, while in the second one this is done at the finite element level using cohesive interface elements. The advantages and shortcomings of both are presented through one numerical example on the failure of fibre-reinforced composite materials

Comportamento à rotura de vigas de betão de alta resistência reforçadas com CFRP

O presente artigo encontra-se inserido num projeto que visa caracterizar o comportamento de vigas de Betão de Alta Resistência (HSC) reforçadas com laminados de CFRP (Carbon Fiber Reinforced Polymer). Para o efeito, foi definido um programa experimental que compreende o reforço de uma viga fabricada em HSC e o seu ensaio em flexão até à rotura. A realização de um estudo numérico prévio permitiu concluir que a aplicação de pré-esforço aos laminados de CFRP aumentaria de forma considerável a eficiência do reforço. Sendo assim a viga pré-esforçada de grande vão (20 m), fabricada com um betão de resistência à compressão de 120 MPa e de secção transversal em I (com altura de 0.5 m e largura de 0.30 m) foi reforçada com laminados de CFRP pré-esforçados. A operação de reforço das vigas foi precedida do carregamento das mesmas com uma carga correspondente a uma combinação quase permanente de ações, mantida constante durante a operação de reforço, de forma a simular o reforço de elementos estruturais em aplicações correntes de engenharia civil. Após reforço, a viga foi ensaiada até à rotura por flexão. Os resultados deste estudo foram comparados com os obtidos em ensaios à rotura de duas vigas de HSC não reforçadas com as mesmas dimensões e condições de ensaio, apresentando-se as principais conclusões

O IMPACTO DA PESCA ACESSÓRIA DO ARRASTO CAMAROEIRO NA REPRODUÇÃO DE PEIXES NO NORDESTE DO BRASIL

In the west coast of Rio Grande do Norte many small-scale fisheries targeting mostly shrimp but accidentally catch a large number of fish. Our aim was to evaluate the Ichthyofauna composition and distribution in Potiguar Basin, northeastern Brazil, in order to elucidate the impact of bycatch on fish reproduction. The study area was divided into four stretches (A, B, C and D), and we sampled 1,426 specimens classified into 10 orders, 23 families and 49 species. We obtained biometric data and gonadal tissue in order to determine the reproductive aspects of the studied fish. Stretch A had the highest values of evenness and dominance; the highest values of abundance, biomass, richness and diversity were found in stretches B, C and D. Analysis based on faunal similarity revealed three groups: I (found in stretches B and D), II (C), and III (A). In regards to reproductive phase, 76.3% of the specimens were classified as 'immature’, 16.7% as ‘maturing’ and 7% as ‘mature’. Through the anatomical and histological analyzes of the gonads and the size of first maturation, we verified that the species Pomadasys corvinaeformes, Menticirrhus littoralis and Larimus breviceps were negatively related to fishing activity; on the other hand, Pellona harroweri was positively related. Our findings indicate that the incidental capture of some non-target species can affects predominantly individuals considered immature, i.e. without reproductive potencial, an indicative of non-sustainable fishing in region.Keywords: coastal zone; diversity; ichthyofauna; reproductive stages; sexual maturity.Na costa oeste do Rio Grande do Norte, muitas pescarias de pequena escala têm como alvo principal camarões, mas acidentalmente capturam um grande número de peixes. Nosso objetivo foi avaliar a composição e distribuição da ictiofauna na Bacia Potiguar, Nordeste do Brasil, a fim de elucidar o impacto das capturas acessórias na reprodução dos peixes. A área de estudo foi dividida em quatro trechos (A, B, C e D), e foram amostrados 1.426 espécimes classificados em 10 ordens, 23 famílias e 49 espécies. Obtivemos dados biométricos e tecido gonadal para determinar os aspectos reprodutivos dos peixes estudados. O Trecho A apresentou os maiores valores de equitabilidade e dominância; os maiores valores de abundância, biomassa, riqueza e diversidade foram encontrados nos trechos B, C e D. A análise baseada na similaridade faunística revelou três grupos: I (trechos B e D), II (C) e III (A). Em relação à fase reprodutiva, 76,3% dos espécimes foram classificados como “imaturos”, 16,7% como “em maturação” e 7% como “maduros”. Através das análises anatômicas e histológicas das gônadas e do tamanho da primeira maturação, verificamos que as espécies Pomadasys corvinaeformes, Menticirrhus littoralis e Larimus breviceps foram negativamente relacionadas à atividade pesqueira; Por outro lado, Pellona harroweri estava positivamente relacionada. Nossos achados indicam que a captura incidental de algumas espécies não-alvo pode afetar predominantemente indivíduos considerados imaturos, ou seja, sem potencial reprodutivo, um indicativo de pesca não sustentável na região.Palavras-chave: diversidade, estágios reprodutivos, ictiofauna, maturidade sexual, zona costeira

Power Allocation, Relay Selection, and User Pairing for Cooperative NOMA Systems with Rate Fairness

Funding Information: This research was partially funded by Fundac¸ão para a Ciência e Tecnologia under the Projects CoSHARE (PTDC/EEI-TEL/30709/2017), UIDB/04111/2020, IF/00325/2015, and UIDB/50008/2020.Assuming a cooperative non-orthogonal multiple access (NOMA) system with rate fairness in a scenario with multiple users and arbitrary relays, this paper investigates adaptive power allocation (PA), relay selection (RS), and user pairing (UP) policies. Specifically, two adaptive PA optimization problems are formulated, one at the base station (BS) and another at the selected relays. Closed-form expressions for the power allocation factors are derived as well as an algorithm that provides the optimal solution at the BS. In order to show the superiority of the proposed study, our results are compared with other benchmark schemes in terms of outage probability, Jain's fairness index, and average sum rate.publishersversionpublishe

Monitoring steel fibre orientation in self-compacting cementitious composite slabs during pouring with dynamic X-ray radiography

This paper presents a new technique based on dynamic X-ray radiography that can be used to assess fibre orientation during pouring of steel fibre reinforced cementitious composites. Synthetic examples were used to assess the suitability and robustness of the technique, which was shown to provide reliable measurements of fibre orientation even when the signal-to-noise ratio is relatively high. A study was then carried out on the effect of formwork aspect ratio, time/duration of pouring, and rebar placement on the fibre orientation while pouring self-compacting cementitious composite slabs. Results demonstrated the ability of the technique in monitoring the movements of fibres while pouring, and the strong effect of the flow in inducing preferential fibre alignment within the slabs. Fibre orientation was found to vary progressively over time and could take about half of the duration of pouring to fully stabilise.University of Sydney - Sydney Research Accelerator (SOAR) programm

Effect of pollution by particulate iron on the morphoanatomy, histochemistry, and bioaccumulation of three mangrove plant species in Brazil

In Brazil, some mangrove areas are subjected to air pollution by particulate iron from mining activities. However, the effect of this pollutant on mangrove plants is not well known. This study aimed to comparatively analyze the morphoanatomy, histochemistry, and iron accumulation in leaves of Avicennia schaueriana, Laguncularia racemosa, and Rhizophora mangle. Samples were collected from five mangrove sites of Espírito Santo state, each of which is exposed to different levels of particulate iron pollution. The amount of particulate material settled on the leaf surface was greater in A. schaueriana and L. racemosa, which contain salt glands. High iron concentrations were found in leaves of this species, collected from mangrove areas with high particulate iron pollution, which suggests the foliar absorption of this element. None of the samples from any of the sites showed morphological or structural damage on the leaves. Scanning electron microscopy (SEM) coupled to X-ray diffraction rendered a good method for evaluating iron on leaves surfaces. A histochemical test using Prussian blue showed to be an appropriate method to detect iron in plant tissue, however, proved to be an unsuitable method for the assessment of the iron bioaccumulation in leaves of A. schaueriana and R. mangle. So far, this study demonstrates the need of evaluating the pathway used by plants exposed to contaminated particulate matter to uptake atmospheric pollutants.Fil: Pereira Arrivabene, Hiulana. Universidade Federal do Espírito Santo; BrasilFil: da Costa Souza, Iara. Universidade Federal do São Carlos; BrasilFil: Oliveira Có, Walter Luiz. Associação Educacional de Vitória; BrasilFil: Moreira Conti, Melina. Universidade Federal do Espírito Santo; BrasilFil: Wunderlin, Daniel Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Ciencia y Tecnología de Alimentos Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Ciencia y Tecnología de Alimentos Córdoba; ArgentinaFil: Rozindo Dias Milanez, Camilla. Universidade Federal do Espírito Santo; Brasi

On the secrecy performance of mixed RF/UOW communication system

In this paper, the secrecy performance of a dual-hop mixed radio-frequency/underwater optical wireless communication (RF/UOWC) system is investigated. The considered system consists of one single antenna source node (S) communicating with one destination node (D), considered as the legitimate receiver, through the help of one amplify-and-forward (AF) relay node R equipped with multiple antennas for reception. Specifically, the relay receives the incoming signal from S via an RF link, applies maximal-ratio combining (MRC) technique, amplifies the output combined signal with a fixed gain, and then forwards it to D via an UOWC link. The transmission protocol is performed under the eavesdroppers’ attempt to overhear the RF link (i.e., SR). We derive an exact closed-form expression for the secrecy intercept probability (IP) in terms of the Fox’s H-function, or in terms of the Meijer’s G-function as a particular case. The derived secrecy performance metric is evaluated in terms of various channel and system parameters, and corroborated by Monte-Carlo simulation method. Our derived analytical formulas present an efficient tool to highlight the impact of some system and channel parameters on the secrecy performance, namely the number of relay antennas, number of eavesdropping nodes, relay gain, fading severity of RF links, and water turbulence severity of the UOWC link