Assessing equilibrium clear water scour around single cylindrical piers

The objective of this research is to investigate the pertinence of existing approaches to assess the onset of the equilibrium phase of scour at single cylindrical piers in experimental studies. The results of five long-lasting experiments are reported. The discussion has profusely shown that common methods used to decide on whether a given scour experiment has reached the equilibrium phase may be erroneous. It has also shown that known predictors of time to equilibrium may imply significantly wrong predictions of equilibrium depth. Finally, it seems that, typically, 7 days-long scour depth records adjusted though a 6-parameters polynomial function and extrapolated to infinite time render robust vales of the equilibrium scour depth at single cylindrical piers

Pier shape and alignment effects on local scour

Bridge piers may have several horizontal shapes and be built with different alignment angles towards the flow direction. The effects of pier shape and alignment have been studied by only a few researchers, the most well-known being Laursen and Toch [1956]. In the present study, 55 long-duration laboratory tests were run under steady, clearwater flow close to the threshold for initiation of sediment motion, to address the effect of shape and skew-angle on the equilibrium scour depth. Five different pier shapes were considered: circular, rectangular square-nose, rectangular round-nose, oblong and piles group; the tested skew-angles were 0, 30, 45, 60, and 90°. Relevant contributions were achieved on the effect of shape at skewed piers and performance of the equation suggested by Richardson and Davis [2001] to account for the pier alignment factor.info:eu-repo/semantics/publishedVersio

A Numerical Study of the Effect of Vortex-Induced Vibrations on a Circular Cylinder Mounted under Elastic Support

Vortex Induced Vibration (VIV) of structures is of practical interest to many fields of engineering. The particular case of a rigid cylinder mounted under elastic supports and constrained to oscillate in a single direction is modelled using OpenFOAM’s two-dimensional Reynolds-averaged Navier-Stokes (RANS) equations with k-ω SST turbulence model. The model aimed for relativelly low Reynolds numbers (2500 ≤ Re ≤ 15000) and the results were compared with Khalak and Williamson’s experimental results with the intent of also evaluating maximum amplitude to diameter ratio, A/D, achieving good agreement between both computational and experimental data. Lift and drag coefficients,

Erosões localizadas junto de pilares de pontes sobre leitos aluvionares

Esta comunicação reúne contribuições recentes de estudos dos autores sobre os efeitos da altura relativa do escoamento, da dimensão relativa dos sedimentos do leito, do tempo, da forma dos pilares e do seu ângulo de viés em relação à direção do escoamento na profundidade de equilíbrio de cavidades de erosão que se desenvolvem junto de pilares simples. Estas contribuições baseiam-se em campanhas experimentais de características únicas, no sentido em que foram sistematicamente conduzidas com durações superiores às da vasta maioria dos trabalhos publicados na literatura. A caracterização de parte daqueles efeitos é claramente mais completa e rigorosa por comparação com o que se encontra publicado em literatura da especialidade enquanto, noutros casos, se confirmam resultados anteriormente publicados. Sugerem-se critérios de previsão da profundidade de erosão que incorporam as novas contribuições dos autores.info:eu-repo/semantics/publishedVersio

Erosões localizadas junto de pilares simples: efeito do diâmetro relativo do sedimento na profundidade de equilibrio de cavidades de erosão

A comunicação apresenta os resultados preliminares de ensaios experimentais, sobre erosões localizadas junto a pilares cilíndricos isolados, realizados nos Laboratórios de Hidráulica das Faculdades de Engenharia da Universidade da Beira Interior (UBI) e da Universidade do Porto (FEUP). Nesse âmbito, foram realizados treze ensaios com o objectivo de analisar o efeito do diâmetro relativo do sedimento e da profundidade relativa do escoamento de aproximação na profundidade de equilíbrio das cavidades de erosão normalizada pelo diâmetro do pilar. Os ensaios foram realizados em condições de leito fixo (i.e., sem transporte sólido generalizado) e com durações compreendidas entre 4,1 e 12,9 dias. O conjunto de ensaios foi definido de modo a que a gama de parâmetros utilizada fosse o mais alargada possível, perspectivando, desta forma, tirar conclusões mais abrangentes do que as correspondentes à maioria dos trabalhos existentes neste domínio. As séries temporais do desenvolvimento da profundidade máxima das cavidades de erosão em pilares cilíndricos isolados foram analisadas e tratadas de acordo com metodologia proposta por Lança et al. (2010). Os resultados revelam que há uma forte dependência entre a profundidade de equilíbrio das cavidades de erosão em pilares cilíndricos isolados e o diâmetro relativo do sedimento, confirmando os resultados apresentados por Sheppard et al. (1995; 1999; 2004). Contrariando o instituído por alguma literatura da especialidade de referência, foi observado que a profundidade de equilíbrio das cavidades de erosão normalizada pelo diâmetro do pilar decresce com o diâmetro relativo do sedimento para valores superiores a ~100. Este efeito é possivelmente uma das causas da sobrestimação da profundidade de equilíbrio das cavidades de erosão obtidas através de fórmulas de uso reconhecido e que foram determinadas com base em trabalhos laboratoriais

Erosões localizadas em pontes submersas

Nesta comunicação analisam-se os efeitos da submersão de uma ponte na profundidade máxima da cavidade de erosão junto de um pilar cilíndrico, para escoamentos sem transporte sólido generalizado. Comparam-se os resultados obtidos com equações publicadas na literatura, tendo-se concluído que a formulação proposta por MELVILLE & COLEMAN [2000] é a mais adequada, apresentando um desvio inferior a 10%

Summary of in-stream energy production devices

Renewable energy is more important as the time advances. The need to replace fossil fuels such as coal and oil is a big concern in the European union which has established goals of 20% of share of energy from renewable sources in whole European union. The importance of small energy production devices increases when we think of this goal, so energy can reach every citizen, even in a remote village which is kilometers away from the main power source. In-stream devices are optimal for remote sources, which almost always have a water source in the proximities. In-stream turbines can generate enough power to a common house and because it does not require any sort of head nor dam it is easy to mount. Its efficiency is around 40% for most recent in-stream turbines. The most recent technology in this area, the vortex induced vibration devices are still in development reaching 20-30% efficiency when a single device is working, reaching up to 40% when arrayed in some exact positions.info:eu-repo/semantics/publishedVersio

Velocity Field Analysis of a Channel Narrowed by Spur-dikes to Maximize Power Output of In-stream Turbines

Decentralized energy is growing in importance with time. The electricity being needed even in the most remote places, far from power stations, increases the importance of small power production devices such as micro-hydro devices like turbines. In this research, the velocity field in a meandering channel is studied in its natural conditions and with the introduction of spur-dikes, structures that prevent bank erosion, a natural phenomenon observed in meandering channels, with the use of computational fluid dynamics software. With the objective of improving the power production by investigating the changes of the flume velocities with the introduction of spur-dikes, one test without any spur-dike and three tests with it were conducted. Good results were reached, with velocities increasing between 10 to 20% with the introduction of these structures. In certain cases, the increase in power production can reach up to 85% than in a normal situation without spur-dikes in the river.info:eu-repo/semantics/publishedVersio

Local scour at single piers revisited

The paper summarizes recent contributions of the authors on the effects of relative flow depth,relative sand size, time and fluid viscosity, on the scour depth at single piers. These contributions rely on unique experiments in the sense that they are systematically longer than the vast majority of those found in the literature. The characterization of the effects of relative sand size and time is further improved as compared with existing literature while the effect of the relative flow depth confirms previous findings. New predictors are suggested. Viscous effects conveyed by the approach flow seem non-negligible; this is a new contribution that deserves further research.info:eu-repo/semantics/publishedVersio

Effect of spacing and skew-angle on clear-water scour at pier alignments

Pier alignments, defined as single-row pier groups, displayed normal to main bridges’ axes, are frequently used to support bridge decks. Different alignments configurations, characterized by different combinations of piers’ shape and spacing and skew-angle of the alignment to the flow direction, lead to different interactions with the flow field and to different scour depths. Twenty six long lasting – 7 to 15 days – laboratory experiments were run under steady clear-water flow conditions, close to the threshold condition of beginning of sediment motion, to address the effect of pier spacing and skew-angle on the equilibrium scour depth. Alignments consisted of four cylindrical piers spaced of 1, 2, 3, 4.5 and 6 pier diameters; tested skew-angles were 0◦, 15◦, 30◦, 45◦ and 90◦. The main contribution of the paper derives from the long duration of the experiments. The functional relation of issued equilibrium scour depth with pier spacing and skew-angle is established and the dependence of the traditional group correction factor on the same variables is defined