Artigos de Revista

Hydraulic jumps, frequently present in energy dissipation structures, have been thoroughly investigated over the past 70 years.However, studies have focused primarily on the more common and more stable cases of large Froude number jumps. Investigations on low Froude number jumps, usually called transition jumps, are scarce, although they are used in a significant number of run-of-the-river, high-discharge, and low-head dams. This paper addresses the characterization of hydrodynamic pressures of low Froude number jumps.A two-dimensional experimental facility was used for that purpose. Results were compared with those from published studies covering transition jumps and stabilized jumps, to identify differences and similarities between them. The analysis considered common dimensionless statistical parameters, duly nondimensionalized. It was found that, for most of these parameters, low Froude number jumps behave differently from stabilized jumps. This can be attributed mainly to the hydraulic jump

Hydraulic jumps, frequently present in energy dissipation structures, have been thoroughly investigated over the past 70 years. However, studies have focused primarily on the more common and more stable cases of large Froude number jumps. Investigations on low Froude number jumps, usually called transition jumps, are scarce, although they are used in a significant number of run-of-the-river, high-discharge, and low-head dams. This paper addresses the characterization of hydrodynamic pressures of low Froude number jumps.A two-dimensional experimental facility was used for that purpose. Results were compared with those from published studies covering transition jumps and stabilized jumps, to identify differences and similarities between them. The analysis considered common dimensionless statistical parameters, duly nondimensionalized. It was found that, for most of these parameters, low Froude number jumps behave differently from stabilized jumps. This can be attributed mainly to the hydraulic jump

Os materiais metálicos do século XX apresentam propriedades físicas e de resistência à corrosão com interesse para a arquitetura, tendo neste âmbito uma ampla gama de aplicações. Contudo, estão sujeitos a degradação, frequentemente associada às condições de utilização e ambiente de exposição, cujas consequências vão desde alterações estéticas à perda de funcionalidade dos componentes e estruturas em que se encontram aplicados. Neste artigo, descreve-se o comportamento típico de vários materiais metálicos correntemente usados nas edificações, quando usados em componentes de arquitetura exterior, correlacionando-o com a corrosividade ambiental e modos de utilização. O conjunto de informação reunida teve como objetivo contribuir para uma seleção adequada dos metais a aplicar numa determinada obra.

The installation of vibration-based structural health-monitoring systems relying in the study of natural frequencies to assess the condition of civil engineering structures is becoming more and more common. The extraction of these monitoring features can be achieved through automated operational modal analysis, combining output-only identification methods with cluster analyses, and comparing the identified modal properties with references, in a process known as modal tracking. However, changing environmental and operational conditions affect the dynamic behaviour of structures, disturbing the process of modal tracking, which may lead to the loss of important information and to misidentifications. In this context, this paperproposes a new methodology for modal tracking within the scope of automated operational modal analysis, especially prepared for scenarios with strong external influence on modal properties. A concrete arch dam with large variations of some natural frequencies is used as case study, and the proposed methodology is compared to a standard procedure using a quite unique monitoring data set continuously collected for 3 years.

Para caracterizar a resposta de um trecho do quebra-mar de taludes do porto da Ericeira à agitação marítima nele incidente, realizaram-se no canal de ondas irregulares do LNEC um conjunto de ensaios com um modelo reduzido desse mesmo trecho. Nesta comunicação descreve-se a instalação experimental, incluindo os diversos instrumentos utilizados para medir as séries temporais das várias grandezas de interesse e o programa de ensaios, apresentando-se as grandezas medidas num subconjunto dos ensaios considerado mais interessante. Nestas grandezas incluem-se a elevação da superfície livre associada à agitação incidente, o espraiamento ao longo do talude, o volume de água de água galgado, a pressão em vários pontos da superestrutura e a erosão do manto protetor utilizando um sensor cujo funcionamento se baseia na tecnologia Time of Flight.

Neste artigo apresenta-se a formulação e resultados da aplicação de dois modelos descontínuos tridimensionais que simulam a interação hidromecânica. Nestes modelos o comportamento mecânico é simulado de forma idêntica mas o comportamento hidráulico é simulado com duas abordagens diferentes. O primeiro modelo baseia-se numa formulação que admite o escoamento através de elementos planos de interface. O segundo modelo, que se propõe neste artigo, baseia-se numa discretização unidimensional, ocorrendo o escoamento através de elementos de canais. Os modelos hidromecânicos implementados no módulo computacional Parmac3D Fflow são verificados e validados através de exemplos simples, e o modelo proposto é calibrado de modo a serem obtidos, com os dois modelos, os mesmos valores de pressão e de caudal. Foi desenvolvido um modelo hidromecânico de um conjunto barragem/fundação, tendo em consideração a existência de cortina de impermeabilização e de sistema de drenagem na fundação. Salientam-se as vantagens do modelo proposto no estudo do comportamento hidromecânico de fundações de barragens.

Construction and demolition wastes (CDW) are generated at a large scale and have a diversified potential in the construction sector. The replacement of natural aggregates (NA) with CDW recycled aggregates (RA) in construction materials, such as mortars, has several environmental benefits, such as the reduction in the natural resources used in these products and simultaneous prevention of waste landfill. Complementarily, CDW have the potential to capture CO2 since some of their components may carbonate, which also contributes to a decrease in global warming potential. The main objective of this research is to evaluate the influence of the exposure of CDW RA to CO2 produced in cement factories and its effect on mortars. Several mortars were developed with a volumetric ratio of 1:4 (cement: aggregate), with NA (reference mortar), CDW RA and CDW RA exposed to high levels of CO2 (CRA). The two types of waste aggregate were incorporated, replacing NA at 50% and 100% (in volume). The mortars with NA and non-carbonated RA and CRA from CDW were analysed, accounting for their performance in the fresh and hardened states in terms of workability, mechanical behaviour and water absorption by capillarity. It was concluded that mortars with CDW (both CRA and non-carbonated RA) generally present a good performance for non-structural purposes, although they suffer a moderate decrease in mechanical performance when NA is replaced with RA. Additionally, small improvements were found in the performance of the aggregates and mortars with CRA subjected to a CO2 curing for a short period (5 h), while a long carbonation period (5 d) led to a decrease in performance, contrary to the results obtained in the literature that indicate a significant increase in such characteristics. This difference could be because the literature focused on made-in-laboratory CDW aggregates, while, in this research, the wastes came from real demolition activities, and were thus older and more heterogeneous.....

Considering the growing volume of information and services available on the web, it has become essential to provide websites and applications with tools, such as recommender systems, capable of helping users to obtain the information and services appropriate to their interests. Due to the complexity of web adaptation and the ability of multi-agent systems to deal with complex problems, the use of multi-agent approaches in recommender systems has been increasing. In the present work, we make a thorough review of the use of multi-agent-based recommender systems. The review shows the diversity of applications of multi-agent systems in recommender systems, namely on what concerns the diversity of domains, different types of approaches and contribution to the performance improvement of the recommender systems.

This paper presents a multi-criteria decision support methodology for selection and prioritization of rehabilitation intervention in urban water infrastructures considering performance, cost and risk and a long-term perspective. This methodology is divided into three main stages: problem identification, structuring and evaluation. Problem structuring, a crucial stage for the outcomes, includes identifying objectives, selecting scenarios within the analysis period, defining problem options and the problematic type. Problem evaluation includes the selection of assessment metrics, selection of the aggregation method, application of the method and sensitivity and robustness analysis and final recommendations. The methodology is applied to a real case study of a water distribution system, being the different stages presented in detail and obtained results discussed.