Priscila dos Santos Priebe

The hydrodynamic conditions to which hydraulic structures such as spillways and stilling basins of dams are submitted under given conditions favor the occurrence of cavitation, damaging the concrete surfaces. This damage may be intensified by the cumulative effect of the successive hydrologic events that characterize the operational regime of these structures. Thus, the purpose of the present article is to identify the propensity for damage caused by cavitation by using SpillwayPro software to estimate the hydraulic parameters of flow (mean velocities and cavitation indices) based on information on smooth chute spillways at the Furnas, Luiz Carlos Barreto de Carvalho and Batalha hydroelectric power plants. The results shown were compared to the critical limits of cavitation defined in the literature on photographic records of inspections performed in the field. The highest mean velocities estimated coincided with the zones where the worst potential damage of the structures was identified. Nevertheless, most of the cavitation indices obtained did not present results similar to the limits presented by different authors, and thus do not favor the indication of cavitation risks due to this parameter in the spillways examined.

Stepped spillways can dissipate a great amount of energy during the flow passage over the chute, however these structures have limited operation due to the risk of cavitation damage. The induced aeration may protect the concrete chute through the air concentration near the channel bottom. Furthermore, some research studies have indicated that the presence of air in flows may reduce the mean pressures. The present research aims to analyze mean pressures, air entrainment coefficient and flow behavior over a stepped spillway with aeration induced by two different deflectors, comparing the results to natural aeration flow. Despite the jet impact influence, the induced aeration does not change significantly the mean pressures compared to natural aeration flow. The air entrainment coefficient, as well as the jet impact position, is higher for the deflector with the longer extension and, although air bubbles can be seen throughout the extension of the chute due to the air entrainment through the inferior flow surface, the induced aeration did not anticipate the boundary layer inception point position.

The operation of stepped spillways is limited by a range of discharges due to the risk of occurrence of the cavitation phenomenon and erosion on its steps. Since there is a demand for spillways with the possibility of overflow of greater discharges, the designs seek to increase the air concentration of the flow, which can occur through the installation of piers in the spillway in order to protect the structure from the above mentioned damage. The aim of this work is to analyze flow characteristics and extreme minimum and maximum pressures with non-exceedance probability of 0.1% and 99.9% acting next to the step edges of the spillway with aeration induced by piers through an experimental analysis in a physical model. Based on the results obtained, flow behavior was defined and equations for predicting the extreme pressures that occur along the stepped spillway with aeration induced by piers were proposed.

The possibility of damage due to the phenomenon of cavitation leads the design of stepped spillways considering maximum specific discharges of 15 to 30 m2/s, a limit considerably lower than that practiced on smooth chutes. Aerators promote the insertion of air in the flow, allowing for the increase of specific flow rates. This work analyzes the pressures on the vertical faces of the steps and the air entrainment coefficient in the flow, through an experimental study in a physical model with a stepped chute angle of 53.13o, considering the installation of aerators in different places of the channel. Comparing the tested conditions with the natural aeration, it is concluded that the installation of the aerator does not change the magnitude of the minimum extreme hydrodynamic pressures, but anticipates the beginning of the flow aeration. A new equation is proposed to estimate the air entrainment coefficient, as well as a methodology for forecasting extreme pressures on the vertical faces of the steps, both valid in the range 3.0 ≤ Fr ≤ 6.0.

Stepped spillways have been widely used for flood runoff due to of their constructive advantages and in regards to energy dissipation during the drop, allowing downstream dissipation structures to be designed in smaller dimensions. Due to the need for further studies on the effect of runoff in the chute of the stepped spillway and the analysis of dimensionless numbers used to characterize the longitudinal distribution of the pressures acting on the faces of the steps of a spillway, this study aims to characterize the acting forces on the steps of said spillways. Analyses were performed on a physical model of spillway with a slope of 1V: 0.75H and steps with a height of 6 centimeters. The pressure fields on the steps were analyzed and compared with results found in literature. As a general finding concerning the pressure in the horizontal faces, it was ascertained that the traction and the compression loads have relatively similar magnitudes, the negative pressures being more intense. Regarding the maximum pressures at the horizontal faces of the steps, it should be emphasized that the maximum values of compression have occurred at the end of the chute and that the lower discharges yielded higher values of pressure coefficients.

O objetivo desse trabalho foi avaliar o efeito de diferentes substratos alternativos na produção de mudas de alface (Lactuca sativa L.). No experimento foram avaliados seis diferentes substratos. As variáveis avaliadas foram: número de folhas, comprimento de raiz, altura da muda, massa fresca de parte aérea, massa seca de parte aérea, massa fresca do sistema radicular e massa seca do sistema radicular. Os tratamentos T2: (75% Casca de Arroz Carbonizada + 25% Composto Orgânico Ecocitrus) e T3: (50% Casca de Arroz Carbonizada + 50% Composto Orgânico Ecocitrus) permitiram a obtenção de mudas de alface com boas respostas agronômicas, construindo-se uma opção viável na redução do custo para a produção de mudas de alface para a agricultura familiar.