Artigos de Revista

The generation of tidal asymmetries in estuaries is analyzed by examining the differences in celerity at high and low tide. An analytical expression for the difference between ebb and flood durations is introduced and applied to a cross-section composed by a channel flanked by tidal flats. The expression depends on the cross-sectional average of the celerity, for which two approximations are proposed and verified with a numerical model. Results confirm that tidal flats enhance ebb dominance, while large tidal amplitudes promote flood dominance. Maximum ebb dominance occurs for tidal flats at, or above, mean water level, depending on tidal amplitude and the extent of the tidal flats. Finally, qualitative arguments indicate that friction also enhances flood dominance.

Dans le sud de la France, à proximité de la ville de Millau, le raccordement de Clermont-Ferrand à Montpellier par l’autoroute A75 a nécessité la construction d’un ouvrage exceptionnel pour franchir la vallée du Tarn. L’ouvrage est constitué d’un tablier en caisson entièrement avec un platelage orthotrope, le tout entièrement en acier. Il est soutenu par des haubans à des pylônes également en acier. Le montage a été réalisé par lançage sur des palées métalliques provisoires. Ce pont, long de 2460 mètres, est actuellement le viaduc le plus haut du monde. Il possède en effet des piles en béton atteignant 245 mètres de hauteur et son plus haut pylône représente une hauteur totale de 346 mètres au dessus du Tarn. Cet article montre comment a été élaboré le projet de l’un des plus grands ouvrages haubanés à travées multiples de ce début du vingt-et-unième siècle construit dans un site particulièrement difficile.

Apresentam-se modelos preditivos para a ventilação natural, como contribuição para a redução de sistemas AVAC, mantendo a Qualidade do Ar Interior.

O GESTBARRAGENS é o sistema integrado de gestão da informação para o controlo de segurança de barragens de betão que suporta, nomeadamente, os seguintes processos: o processo de observação de grandezas físicas a partir da exploração, manual ou automática, dos sistemas de observação instalados nas barragens; o processo inerente às inspecções visuais realizadas periodicamente por intervenção humana; o processo de gestão e consulta geral da informação de suporte e documental relacionada com as barragens; e o processo de detecção de situações de anomalia nos dados observados que pode implicar a tomada de decisões de modo a garantir a segurança das barragens. Complementarmente, o GESTBARRAGENS apresenta mecanismos avançados de consulta e análise da informação (e.g., suportados por sistemas de informação geográficos e por sistemas de reporting) e mecanismos de sincronização da informação entre as diferentes instâncias do sistema mantidas por entidades distintas (e.g., Autoridade, LNEC, donos de obra). A arquitectura técnica do GESTBARRAGENS adopta ainda um modelo multi-instância, distribuído e federado sempre que tal for conveniente, e adopta modernas tecnologias de desenvolvimento de software, em particular tecnologias ligadas à Internet, sistemas de informação geográficos e computação móvel. Neste artigo apresenta-se a visão geral do GESTBARRAGENS numa perspectiva dos sistemas de informação, e ainda os seus aspectos técnicos informáticos mais distintivos, nomeadamente os aspectos relacionados com: migração de dados legados; suporte à gestão dinâmica de instrumentação; suporte à gestão dinâmica de relatórios; capacidade de representação gráfica dos sistemas de observação das obras e, sobre estes a produção de gráficos representativos do seu comportamento; instalação e funcionamento do sistema segundo um modelo distribuído federativo; e definição de interfaces abertas para permitir a integração do GESTBARRAGENS com sistemas externos, como por exemplo sistemas móveis (e.g., PDA, PDT) usados em campanhas de observação.

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International comparisons are frequently used to assess the road safety performance of a country or to monitor its development over time, at a national or regional level. In most instances either accident or injury risks have to be considered, which results in the need for a quantitative estimation of the amount of travel, namely traffic volumes. Only in special cases may risks be indirectly compared using methods of induced exposure. The required data on traffic volumes is not always readily available. This is especially true if old data or data from several countries for a long period are to be used, as in comparative time series analysis. Several simplifying assumptions can be adopted to bypass this lack of data but often the estimates resulting from these simple assumptions are not entirely satisfactory. Between 1996 and 1998 the European Union (EU) sponsored, within the scope of the 4th Research Framework Programme, a COST Action (COST 329) to analyse and establish a common methodological framework for description and analysis of safety developments—past and future—that could also represent the effect of interventions. Researchers from 14 European countries participated in this action. One activity carried out was the development of a method for estimating the traffic volume of countries where such data is not available, using data on vehicle fleet and fuel sales in the studied country and mathematical models fitted to existing data (from other countries) on fuel consumption, vehicle fleet and traffic volume. In the European context, this method is especially useful for some Eastern and Southern European countries. In this paper the mentioned method is described, the results of its application to Portugal are presented and ways to use it in other countries to estimate their traffic volumes for the period 1980–2000 are described.

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A modeling system to simulate tidally driven morphodynamics is developed and assessed. The system couples an existing shallow water model with a new morphological updating model. Four innovative features to improve the accuracy and efficiency of the system are implemented and tested. First, two alternatives are proposed to update the velocity field without running the hydrodynamic model. Both alternatives, based on an assumption on the behavior of friction, are more accurate than the traditional "continuity correction". Second, hydrodynamic results are provided in the frequency domain. The harmonic synthesis of the velocity time series simplifies interpolation and extrapolation of the hydrodynamic model results and the use of different time steps for the various components of the modeling system. Third, the time-integration of the sediment fluxes is performed with a Runge-Kutta method so the time step adapts in space and time to the flow characteristics. Finally, a criterion to determine the need for a new hydrodynamic simulation is derived, based on the importance of the errors introduced by the outdated flow field relative to those introduced by the sand-transport formulae.

Degradation of water quality in supply and distribution systems is one of the foremost problems that water companies are faced with. It is every day practice in many countries to maintain a residual quantity of a disinfectant such as chlorine throughout the system, in order to ensure the safety of distributed water. However, the chlorine added at the water treatment plant disappears as it travels to the consumer tap, due to reactions in the bulk of the flow and at the pipewalls. This paper analyses the influence on free chlorine bulk decay of several water quality parameters, such as temperature, initial chlorine dosage, organic matter and iron content. The performance of five alternative kinetic models for describing the disinfectant behaviour is also assessed, considering both static and steady-state flow conditions. For the conditions tested, a parallel pseudo-first order model provided the best results. Although, in practice, parallel first order kinetic models fit experimental data better than the classic first order model, most water quality modelling software still relies on the latter as a base choice. The paper discusses practical conditions that may influence model selection for network simulation purposes, and the relevance of the associated errors.