فهرست مطالب

Journal of Hydraulic Structures
Volume:7 Issue: 4, Winter 2021

  • تاریخ انتشار: 1400/12/26
  • تعداد عناوین: 5
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  • Mojtaba Kheilapoor, Javad Mozaffari *, Seyed Asadolah Mohseni Movahed Pages 1-9
    Labyrinth weirs are one of the kind of nonlinear crest weirs causing the increase of discharge capacity for specified height of water level in canals and dams. In this study, the effects of dentate and orifice labyrinth weirs on increasing the discharge capacity were investigated. Experiments were conducted in a laboratory flume with length of 12 m and width of 0.8 m. The nine experimental models with 15 cm height were used. The results showed that for L/W=2 and H/P=0.2, the discharge coefficient of the orifice-dentate labyrinth weir and the dentate labyrinth weir are 75.6% and 17.5%, more than the simple labyrinth weir, respectively. However, dent and orifice may decrease their efficiency in high heads and the discharge coefficient will be close to simple labyrinth weir. The reason for these changes was increasing the flow interference in downstream of labyrinth weir between dents, orifices and weir with increasing discharge. Also, the result showed the efficiency of orifice and dentate on labyrinth weirs will decrease with increasing the weir magnification (L/W) and they lose their effect.
    Keywords: orifice, Dentate, Magnification Ratio, Experimental model
  • Ehsan Delavari, Mohsen Saadat *, Shamsa Basirat Pages 10-25
    Scour depth around bridge abutment is a crucial parameter to design the protective spur dike. Costly and time consuming experiments make it difficult to evaluate the scour depth in the problems involving scour phenomena. However, soft computing and regression methods may be applied based on the experimental results. In this paper, a set of experiments is performed and a database including 127 records is collected to evaluate the relation between scour depth and five independent variables including abutment length, flow discharge, flow depth, spur dike length and Spur dike distance from abutment to upstream. This paper presents a new application of the multi-layer perceptron neural network (MLP), group method of data handling (GMDH), non-linear regression (NLR) and multiple linear regression (MLR) to predict the scour depth. A sensitivity analysis is also performed to evaluate the influence of each variable on the scour depth. Results indicate that the first three methods are efficient and accurate enough to be applied in practical applications with determination coefficient (R2) above 90%, while, the MLR has shown a poor performance in this paper. It is observed that MLP and GMDH outperform other methods based on the test data. However, explicit equation derived by NLR has a major advantage to be applied in the field applications without skilled operators and computer packages.
    Keywords: Scour depth, protective spur dike, scour around abutment, GMDH, NLR
  • Mahsa Mahmoudi *, Mohammad Ali Banihashemi Pages 26-45
    It is a popular fact that mechanical processes are usually accompanied by the dissipation phenomenon. Therefore, it is not possible to retain the initial energy over a temporal period or a local distance without spending additional energy. Because these motions are accompanied by conversion into heat. In other words, due to some factors such as friction, cross-section changes, etc., there are some energy losses that the process is irreversible, and some of the system's energy is mainly dissipated as heat. In the most cases of the open-channel transitions, the energy losses of turbulent flows are so complex that it is not easy to define specific relationships for them, and the energy losses are usually determined empirically or experimentally. Examining how the mechanical energy loss of three-dimensional turbulent flows can be estimated without measurements is one of the important subjects of this paper. In this study, in order to better understand the mechanism of the energy losses, during a journey from hydrodynamics to hydraulics, the process of the energy loss of turbulent flows and its relationship with the turbulence parameters are examined through theoretical analysis and 3-D numerical simulations. The relationship between the mechanical energy loss and the roughness coefficient is further obtained and investigated. The results are presented in the form of the application of the new analytical relationships in open-channel expansions and determining the contribution of the effective parameters of turbulent flows to the energy loss.
    Keywords: Energy Loss, Turbulent Flows, Theoretical Analysis, Open-Channel Expansions, Numerical simulations
  • Bahram Rezaei *, Mostafa Dolati Mahtaj Pages 46-57
    In rivers with non-prismatic compound cross-sections, due to the change in cross-section along the channel, mass exchange between the main channel and floodplains. Therefore, discharge distribution in non-prismatic compound channels is an important task for river and hydraulic engineers. In this paper, some results of experiments performed in non-prismatic compound channels with skewed and inclined floodplains have been explained. Two skew angles of 3.81o and 11.31o and three discharges were investigated. The effects of relative depth and relative distance on percentage discharge distribution in each sub-section of the skewed compound channels are presented. The experimental results show that the percentage discharge in each sub-section relies upon the parameters like relative depth, relative distance, skew angle, and floodplain side slope. By using the experimental results, multivariable regression models have been developed to estimate the percentage of discharge in the main channel and on the floodplains. Investigations indicate that the regression models presented in this research, in the validation range, can predict the percentage of discharge in each sub-section of the skewed compound channel fairy well. So that for the results used in this research, the coefficient of determination (R2) for predicting discharge regression model in the main channel is 0.96, on the diverging floodplain is 0.92, and on the converging floodplain is 0.91. Also, the mean absolute percentage errors (MAPE) between the calculated and measured value of percentage discharge in the main channel, on the diverging floodplain, and the converging floodplain are equal to 1.47%, 14.29%, and 21.7%, respectively.
    Keywords: Skewed Channels, Inclined Floodplains, Regression model, Discharge Distribution, Percentage of Discharge
  • Shokoofeh Sharoonizadeh, Javad Ahadiyan *, Manouchehr Fathi Moghadam, Mohsen Sajjadi, Mario Di Bacco Pages 58-75
    The high flow velocity downstream of weirs and gates can cause the destruction of erosive beds in rivers or even non-erosive channels. To reduce the flow's kinetic energy, structures are needed to consume this energy. Expansion basins are often used downstream of structures such as weirs, gates, and chutes to increase energy dissipation in hydraulic jumps. Various methods are used to stabilize asymmetric hydraulic jumps in abrupt expanding channels. In this study, the interaction of multiple submerged water jet injection systems with S-type hydraulic jump for stabilizing and stabilizing the hydraulic jump was investigated. The different configurations of the jet system were tested with Froude numbers 7.4, 8.7, and 9.5, and finally, three optimal configurations were selected as configurations 1, 2, and 3. In order to investigate the performance of the jet injection system under other hydraulic boundary conditions, flow velocities downstream of the jet system were measured for three optimal configurations with different depths of the tailwater. Comparison of the results of using a water jet injection system with S-type hydraulic jump showed that the energy and momentum correction coefficients in all different configurations were significantly reduced. The highest relative energy loss was observed in configuration 3, equal to 68.42%. The results showed a good performance of the jet injection system in stabilizing the asymmetric hydraulic jump S and reducing the length of the stilling basin.
    Keywords: Asymmetric Hydraulic Jump, Water Jet Injection System, Expanding Channels, Energy Loss, Stilling basin