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Pivot weirs are one of the most important structures for regulating the water level in rivers and canals. These weirs are constructed with one or more gates in a row in the waterways. Changing the angle of each gate is done individually with an independent system. Based on available information, the hydraulic performance of this type of weirs (especially in several gates and different angles) in different operational conditions has not been investigated. In present study, pivot weirs with two gates are simulated using Ansys CFX software with the angles of 27.8 to 90 degree and the discharges between 40 to 130 L/s. Further, the importance of the open space between the two adjacent weirs with different angles (lack of retail wall) and its hydraulic behavior have been studied. The model was calibrated based on valid laboratory data and using the K-? turbulence model. Therefore, the weirs with equal angles were studied in the first step. In this case, the effective discharge angle coefficient was studied and its maximum value compared to the vertical angle was obtained 1.076 for the angle of 52°. Furthermore, relationships for discharge coefficient versus upstream water depth were developed. In the next step, the effective length of the crest was found to be increases by 30% under unequal angles operation and the discharge coefficient raised by 1.3 to 2.4 times. Also, it was recognized that, in case of two weirs with unequal angles, about 26% to 69% of the flow passes through the distance between the two weirs. Therefore, the performance of unequal angles operation seems to be more effective in controlling the water level and discharge in different conditions and especially in flood events. [ABSTRACT FROM AUTHOR]

Articulated concrete block mattress revetment (ACB Mats) is an appropriate revetment for shore protection and breakwater. ACB Mats act as an integrated and flexible revetment against waves. There is a necessary need of investigation due to the lack of exact ACB Mat design relations in the estimation of hydrodynamic processes including wave run-up and run-down parameters. In the present study, using proper laboratory equipment, run-up and run-down processes were investigated under irregular waves and also granular and geotextile filters’ conditions. In this study, wave run-up and run-down estimation relations in ACB Mat revetment with the open area were explored for the first time. As the obtained results showed, relative maximum wave run-up and rundown are desirable for all conditions. Using a geotextile layer under ABC Mat caused a 14% increase in relative wave run-up values compared to granular filter. Further, in the run-down process, geotextile filter caused a 40% decrease in relative wave run-down values. The intensive decrease in run-down value occurred due to the outflow rate of the water from inside the filter with delay during water attack toward downward, which can be effective on structure stability significantly and should be considered in designs. [ABSTRACT FROM AUTHOR]

In this study, pressure fluctuation and also the effect of entrance flow conditions on the pressure fluctuation on the bed of compound flip buckets used in the Gotvand dam in Iran are investigated experimentally. For this purpose, Pressure fluctuations on the buckets are measured in the entrance flow Froude number range of 3.5–7.5. Results show that mean of pressure decreases and pressure fluctuation increases when depth and discharge of the entrance flow increase or Froude number decreases. Furthermore, mean of pressure is maximum at the beginning and also minimum at the end of the buckets. The pressure fluctuation is maximum at the beginning and end of the buckets. In contrast, the pressure fluctuation is minimum at thalweg of the buckets. Therefore, this can be concluded that deflection of the flow streamlines is on the effect of the changing of the buckets bed and also impact of high-speed water flow at the beginning of the buckets can cause that the maximum value of mean and fluctuation of pressure occurred at the beginning of the buckets. [ABSTRACT FROM AUTHOR]

Armor is a pavement made of erosion-resistant materials like a stone or concrete that is constructed to protect breakwater, coasts, and other coastal line features against erosion. These armors are a kind of protective layer made of stone or concrete, used in breakwater constructions or coastal lines, arrayed with specific regular or irregular pattern on the breakwater or the coast. The antifer concrete blocks have almost cubic form, often changed into frustum by adding inclined plates to their sides. One of the most important advantages of these armors is their diversified regular and irregular placement patterns. In this study, using the physical modeling and different tests, the stability level of antifer concrete blocks was evaluated considering the decrease of the armor weight. Results of this study show that by a 10% decrease in the block weight, the failure graph slope is increased and the damage is intensified. [ABSTRACT FROM PUBLISHER]

Flip buckets are usually placed at the end of chute spillways or outlet conduits of high dams. The projected jets from these buckets jump into plunge pools to dissipate the destructive energy of plunging jets. Compound flip bucket is a special bucket with a non-zero degree of cross sectional slope, followed by a curvature in its longitudinal direction. These structures are very suitable for restricted geometries and conditional topographies. Although, studies of flow over flip buckets turn back to many years and there are valuable information for simple buckets, but still there are uncertainties regarding the flow over compound flip buckets. Therefore, in this study the hydraulic parameters such as pressure, velocity and depth of flow on these structures are presented. Two chute spillways with their flip buckets were used to check the pressure distribution and its variation with different hydraulic characteristic along the compound flip buckets. The scaled model of Gotvand dam (south of Iran) at Water Research Institute of Iran was used for this study. The Froude number varies in the range of 3.5 to 7.5. The results are presented in the form of dimensionless equation, which was calibrated based on the present results. The location of maximum dynamic pressure and pattern of flow obstruction on the bed of the compound flip bucket is also presented. [ABSTRACT FROM AUTHOR]

In this research a direct numerical simulation (DNS) of turbulent flow is performed in a geometrically standard case like plane channel flow. Pseudo spectral (PS) method is used due to geometry specifications and very high accuracy achieved despite relatively few grid points. A variable time-stepping algorithm is proposed which may reduce requirement of computational cost in simulation of such wall-bounded flow. Channel flow analysis is performed with both constant and varied time-step for 128 × 65×128 grid points. The time advancement is carried out by implicit third-order backward differentiation scheme for linear terms and explicit forward Euler for nonlinear convection term. PS method is used in Cartesian coordinates with Chebychev polynomial expansion in normal direction for one non-periodic boundary condition. Also Fourier series is employed in stream-wise and span-wise directions for two periodic boundary conditions. The friction Reynolds number is about Ret=175 based on a friction velocity and channel half width. Standard common rotational form was chosen for discritization of nonlinear convective term of Navier-Stocks equation. The comparison is made between turbulent quantities such as the turbulent statistics, Reynolds stress, wall shear velocity, standard deviation of (u) and total normalized energy of instantaneous velocities in both time-discretization methods. The results show that if final decision rests on economics, the proposed variable time-stepping algorithm will be proper choice which satisfies the accuracy and reduces the computational cost. [ABSTRACT FROM AUTHOR]