Marcelo Giulian Marques

Pressure extrema in energy-dissipating structure using block maxima: case study

Knowledge of hydrodynamic processes is essential for engineers who assess the stability of energy dissipation structures undergoing extreme pressure fluctuations caused by turbulence during high discharge. Methods are in particular required to evaluate the frequencies of occurrence of extreme pressures. This work explores the use of the generalized extreme value (GEV) distribution to represent frequencies of instantaneous pressures recorded in a structure designed for energy dissipation by a hydraulic jump in a hydroelectric power station at Porto Colombia in central Brazil. The goodness of fit of the GEV distribution was evaluated using probability plots and the Kolmogorov–Smirnov test. The results indicate that it is appropriate for studying the maximum and minimum pressures for a range of discharges corresponding to Froude numbers between 3.88 and 6.42.

Analysis of the longitudinal distribution of pressures near the ends of the vertical and horizontal faces in stepped spillway of slope 1V: 0.75H

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.

Longitudinal distribution of extreme pressures in a hydraulic jump downstream of a stepped spillway

The overflow system of a dam safely controls the water level of a reservoir. The design of these structures should predict the damage caused by the action of the turbulent flow to which they are subject to. The combination formed by a stepped spillway followed by a stilling basin promotes a considerable portion of the energy dissipation in the actual chute of the stepped spillway but it is not sufficient to completely avoid the risk of damaging the basin. In this paper, we analyze the longitudinal distribution of extreme pressures in a stilling basin downstream of a stepped spillway. The study was based on the instant pressure data from the tests carried out in a physical model in the Laboratório de Obras Hidráulicas in IPH/UFRGS. Thus, it was found that the pressure behavior is similar to that observed in studies involving smooth chute spillways, except in the area surrounding the base of the stepped spillway, where high pressure fluctuations may occur. This happens as a result of the impact caused by the flow in the dissipation structure, which is not observed downstream of smooth chute spillways due to the existence of a vertical concordance curve between the spillway and the stilling basin.

Dimensionless curves of centrifugal pumps for water supply systems: development and case study

Centrifugal pumps are widely used in water supply systems and account for more than 90% of the electricity consumption of water pumping stations. Studies that seek to generalize the characterization of performance curves of centrifugal pumps are extremely useful. A study was carried out on the dimensionless characteristics of the operating conditions of centrifugal pumps for preliminary design estimations of water supply systems aiming at energy efficiency. The research consisted of the analysis of performance curves of centrifugal pumps from which data was collected regarding the point of maximum yield (PMY). The curves and the equations obtained were made dimensionless so that the information could be extrapolated to other situations. A case study was conducted in the Water Supply System of Vale Campus of the Federal University of Rio Grande do Sul (UFRGS) to demonstrate the application of those equations and curves developed. The dimensionless equations were useful to determine which discharge should be adopted so that the system would be more efficient hydro and energetically and, also, to determine how much more energy would be consumed in the case of alteration of the point of operation of the pump by a throttling valve.

Macro-turbulent characteristcs of pressures in hydraulic jump formed downstream of a stepped spillway

A bacia de dissipacao tem como finalidade dissipar, atraves de ressalto hidraulico, a energia do escoamento junto a base do vertedouro. Por ser um fenomeno turbulento que provoca amplas flutuacoes de pressao junto ao fundo da bacia, o ressalto hidraulico pode comprometer a estrutura do dissipador por mecanismos como fadiga, subpressao e cavitacao. A utilizacao de vertedouros em degraus permite a dissipacao de uma parte da energia ainda durante o escoamento da agua pela calha, o que possibilita a reducao das dimensoes e do custo da estrutura da bacia de dissipacao. O presente artigo apresenta a analise das distribuicoes longitudinais da pressao media, das flutuacoes de pressao e dos coeficientes de assimetria e curtose, oriundas de ensaios realizados em modelos fisicos hidraulicos. Foi feita uma comparacao das caracteristicas das pressoes obtidas em uma bacia de dissipacao a jusante de um vertedouro em degraus (para numeros de Froude entre 5 e 8) com dados observados em uma bacia de dissipacao a jusante de um vertedouro de calha lisa, com raio de concordância entre a calha e a bacia (para numeros de Froude compreendidos entre 4,5 e 10). A partir dessa analise pode-se concluir que, diferentemente do ocorrido na bacia de dissipacao com calha lisa, as pressoes medias e flutuacoes de pressao observadas na bacia de dissipacao a jusante de calha em degraus tem seu maximo no ponto mais proximo ao pe do vertedouro. O desenvolvimento longitudinal dos coeficientes de assimetria e curtose possibilitaram determinar as posicoes de inicio do descolamento do escoamento, de fim do rolo e de fim da influencia do ressalto hidraulico no escoamento.

Surface drainage system for dry docks in shipyards - Case study of Estaleiro Rio Grande (Technical Note)

This study aims to present a methodology for the design of a surface drainage system for dry docks in shipyards, taking into account the rainfall intensity at the site, the damping capacity of the hydraulic structures (drainage channels) and the pumping capacity of the pumping system. A case study of a dry dock owned by Estaleiro Rio Grande, located at the state of Rio Grande do Sul, is presented. The results obtained indicate alternatives for channel and submersible pump sizing. These pumps would be used to control the dry dock flooding after an intense rainfall event.

Método de determinação de pressões em bacias de dissipação a jusante de vertedores tipo salto esqui

This paper discusses the action of jets formed in ski jump spillways on pre-excavated stilling basins, with special emphasis on hydrodynamic pressures and their characterization in the bottom of the basin. Experimental trials were performed on a physical model built in the Hydraulic Works Laboratory of IPH (Institute of Hydraulic Research)/UFRGS (Federal University of Rio Grande do Sul), applying different flows and depths, to study the action of the jets in stilling basins. The dynamic pressures observed in the physical model were compared with those calculated by a theoretical model in order to evaluate its application in engineering projects. Large pressure magnitude differences were observed in shallow water beds, while differences in pressure distribution were observed along the stilling basin bottom, especially when in deep water beds. Changes in the values of the parameters that regulate the shape of the pressure bulb formed by the jet were proposed, in combination with the use of a pressure damping coefficient, allowing to significantly improve the distribution and magnitude of the pressures calculated due to the action of jets in the stilling basin bottom. The results were satisfactory until a certain distance after the peak pressure caused by the jet. After this point, the hydraulic jump effects prevail and should be investigated in future studies.

Eclusas de Navegação: Caracterização das Pressões a Jusante das Válvulas de Enchimento e Esvaziamento para Operação a 60% e 70% de Abertura

Hydraulic problems in the filling and emptying systems, especially close to the valves, are among the major limitations to increasing the lock lift. This study provided a better understanding of the flow dynamics downstream from lock valves. This was achieved by conducting an experimental investigation in the Laboratório de Obras Hidráulicas of the Instituto de Pesquisas Hidráulicas at the Universidade Federal do Rio Grande do Sul. The behavior of the data showed that, for an equal ∆ , the conditions of 60% and 70% of valve opening would result in the lowest mean pressures for the culvert base and roof, respectively. For Reynolds greater than3 10 , it was possible to characterize the behavior of the mean and extreme pressures along the culvert base and roof by the relationship between dimensionless coefficients of position and pressure. Key-words: Navigation lock, reverse radial gate, reverse tainter gate, extreme pressures, experimental hydraulics.

Numerical analysis of flow downstream of a reverse Tainter gate

The reverse Tainter gates are frequently used in flow control for fi lling and emptying systems of high lift navigation locks. In order to better understand the dynamics of the downstream flow of this gate, a research that seeks to associate the numerical modeling with experimental analysis is being conducted in order to identify the characteristics of the flow and to enable the development of solutions that avoid damage to the structure, since they are subject to several harmful hydraulic phenomena. This paper presents some of the results obtained in the numerical simulations of flow through a reverse Tainter gate. Cases in steady flow condition were studied for different volumetric flow rates and percentages of gate opening. The numerical results of average pressures at the bottom and at the top of the downstream conduit of the gate were compared with the results obtained in the experimental model. The results obtained with the numerical model are in agreement with the experimental results. Key words: navigation locks, reverse Tainter gate, numerical simulation, CFX.

Efeito de Escala nos Valores de Pressão Média junto ao Fundo em Bacias de Dissipação por Ressalto Hidráulico Submergido

Hydraulic jumps are widely used as a form of energy dissipation downstream from hydraulic structures. Knowledge regarding average pressure values, pressure fluctuation and extreme values at the bottom of stilling basins is very important for designers seeking a more efficient and economic sizing. This paper aims to present the scale and laboratory effects on the average pressure values from experimental data of three partial reduced physical models (geometric scale of 1:100, 1:50 and 1:32) and from measurements performed at UHE Porto Colombia (owned by Furnas Centrais Eletricas S.A.). Suggestions of minimal scales are presented to be used in reduced models for average pressure evaluation along hydraulic jump stilling basins