مجله هیدرولیک
سال چهاردهم شماره 1 (بهار 1398)

In the present research, the flow over asymmetric rectangular Pianokey weirs with optimum geometrical ratio is modelled using experimental and numerical modeling. Effects of the water head on discharge distribution pattern over the weir crest is also studied. Effect of the relative height (P/Wu) is investigated on the efficiency of the Pianokey weir by changing the width of the unit key and keeping constant the weir height. The results showed that the weir efficiency increases by decreasing the relative weir height. Available analytical equations in the literature have been applied to compute the discharge passing over the hydraulically optimum weir and also the discharge coefficient for a given approach water head. Differences between the experimental and computed discharge coefficient values are considerable and thus the accuracy of the available equations is not sufficient. In this study, new equations have been developed to compute the discharge coefficient and discharge portions of the inlet key crest, outlet key crest and also the side crest of the asymmetric geometrically optimum Pianokey weirs against approach flow head. The consistency of the results of the new equations with experimental results is considerably higher than the results of available analytical equations in the literature.

One of the most important problems, in the field of hydraulic science, is the study of the behavior of sediment particles and the morphology changes in water flows above sediments. In this research, twophase flow of water-sediment is modeled using the fully Lagrangian SPH method in weakly compressible form. One of the features of the SPH method is the ability to model large deformation, the interface between two phases, as well as particle tracing in multiphase models. In this study, the open-source SPHysics2D code is used where pressure is explicitly calculated using the equation of state. In order to investigate the behavior of sediment, the viscoplastic non-Newtonian model of Herschel -Bulkley Papanastasiou (HBP) has been used. Here, the water-sediment interface is modeled using Owen’s equation where a harmonic mean is used for the viscosity. Due to the density difference between phases, a modified method is used for the continuity and momentum equations. Moreover, an experimental data of the granular dam-break was used to validate the viscoplastic model, and also an experimental data of the dam-break over a moveable bed (water-sediment simulation)was utilized to study the performance of the two-phase flow model. The results indicated that the model of the present study has a high potential for simulating water-sediment systems.

In the present research, effects of a porous spur-dyke on the hydraulic characteristics of the flow in an open-channel have been numerically studied through non-linear Forschheimer model. The numerical simulations were performed in Flow3D package using RNG k-epsilon turbulence closure model. During simulations of the porous spur-dyke, suitable Friesheimer non-linear coefficients were determined for various cases with the sensitivity analysis. The sensitivity analysis and comparisons of the numerical results with the results of the physical model showed that most of parameters are completely dependent to Friesheimer non-linear term and the proposed software range for Friesheimer nonlinear coefficient is not suitable. The results showed that by increasing of the porosity of the porous spur dyke, the flow velocity and also the effect area of the maximum velocity will decrease. Also, by increasing of the porosity of the porous spur dyke, the upstream water depth of the spur dyke will decrease and the downstream water depth of the spur dyke will increase. It was also observed that by increasing of the porosity of the porous spur dyke, the maximum value of the velocity decreases and the minimum value of it increases.

Local scour around bridge pier is a major factor of bridge destruction and increase in maintenance and operation cost. In addition, due to higher extension of wake region around rectangular bridge pier, more local scour depth occurs in comparison to circular bridge pier. In the present study, a new semiempirical approach was developed for calculation of local scour depth at the upstream face of round nose and tail rectangular bridge pier during hydrograph event (unsteady flow condition). In this method, in each time step, the volume of scour hole or in other words the volume of sediment transport was calculated using a sediment transport equation (MPM). Then, scour depth was determined form the volume of scour hole by simplifying the shape of it. In order to examine the accuracy of the present method, experimental data from different sources were selected. Results showed that the sediment transport equation should be modified in order to determine the volume of transported sediment around bridge pier in an unsteady flow condition. The modification factor applied to sediment transport equation was a function of hydrograph characteristics such as time to peak, duration and time from peak to base flow as well as hydrograph peak flow intensity. For example, by decreasing the time to peak, the modification factor increased (more sediment transport). Finally, the comparison of calculated scour depth based on present method and experimental data showed the acceptable accuracy of present method in comparison to other empirical equation with maximum discrepancy of lower than 10%.

Generally, natural open channels have sections in which by increasing the water level, the crosssectional area will be increased considerably. These sections have consisted of relatively wide floodplains. In compound channels with asymmetric cross-sections, the hydraulic behavior of the flow would be complicated. Rating curves estimation in compound channels is one of the most critical issues of river engineering. In the current study, a new approach based on the concept of the crosssectional isovel contours is introduced for the estimation of rating curves in compound channels. To extract the exponent values of the governing parameters, minimization approach is used to the difference between the observed and estimated data. In this method, in order to set up the rating curves in various cross-sections, it is only requisite to have the flow information at a reference water level. The results show that the proposed method has a good accuracy for predicting rating curves in asymmetric compound channels even in compound channels with different floodplain levels.

In this research، the evaluation of cavitation threshold detection and the automation of the detection process with regard to the Remaining Useful Life (RUL) of the Sefidrood power plant turbine، has been studied. The input of generated model by MATLAB program includes data driven from kaplan hydro turbine located on Tarik hydro power plant. The proposed model is based on 61 features resulting from 6 cavitation sensitivity parameters and 17 operational conditions. For training in MATLAB program, 12 individual data sets and 4095 unique combinations were created and 408 data were selected for examination. The training data combined with sensor rating and cavitation sensitivity feature were employed to predict the cavitation and the best training data set with 98% accuracy. The results showed that the use of a fully automated process for sensitivity determination and cavitation classification was more suitable than the use of a process based on manually selected thresholds. Furthermore, considering the operational conditions and RUL, the automation of determination of cavitation threshold without human intervention was much more accurate.

An air-bubble screen is an innovative technique for riverbank protection along the bends which improve the navigation conditions in the alluvial rivers. In this research, the effects of this structure on a 90° mild and long bend on the bed morphology and flow pattern have been investigated. To this end, the experiments were carried out with three angles 0, 45, 90 degree and four Froude numbers of 0.37, 0.41, 0.45, 0.47 combined with three air discharge. Experiments performed in a mild bend using clearwater showed that the bubble screen was able to redistribute the velocity patterns and bed morphology in the bend. In addition, the results showed that maximum bend scouring is reduced about 47% andoccurs further away from the outer bank and high velocity zone shifted toward the center of the channel. The results showed that the maximum and minimum scour depths in outer bank with 0 and 90 degrees angles respectively. Also, by increase of air discharge ratio the maximum scour depth was decreased.

In this study, the impacts of skew angle of two bridge piers with respect to the flow direction on the equilibrium scour depth in front of the piers under clear water condition is investigated. For this purpose, the piers are aligned with four different skew angles with respect to the flow direction. Additionally, to obtain the equilibrium scour depth in front of the piers, the experiments are performed until reaching the equilibrium time. The results show that increasing the skew-angle increases the equilibrium scour depth and time. The minimum and maximum equilibrium scour depths at both piers occur at the skew-angles of 0 and 60 degree, respectively. Regarding the analysis of the results, the maximum equilibrium scour depths in front of the piers, for the skew angles less than 28 degree occur at the upstream pier while for the skew angles greater than 28 degree is shifted to the downstream pier. In the following, formula are provided to estimate the scour depths in front of the piers, utilizing the Semi-logarithmic linear regression method and observed data.

The most important step for prevention of flood’s destructive effects is determining the flood-prone areas over the catchment. There are several approaches for flood prioritization and flood hazard mapping when it comes to flood subject, but the distributed and GIS-based methods are one of the best ones and widely used. Most of the studies that have carried out on this topic were based on analytical hierarchy process (AHP) or fuzzy analytical hierarchy process (FAHP) for estimating the weight of factors affecting the formation of the flood. These methods depend on experts comments and owing to their unfamiliarity with all factors that affect the flood formation, it maybe leads to significant biases in the final results and unreasonable analyses. On this basis, a new method which considers the interaction between the effective factors is used in this study. Finally, by using a linear combination the flood hazard map is created for the study area and divided into five classes including very high, high, moderate, low and very low. Verification of this approach by using recorded destructive floods at different hydrometric stations indicates that the performance of this method, especially onidentifying areas with very high and high hazard levels, is very remarkable. For example, the results of distributed approach in Shirgah-Talar, Razan-Noor, SoleimanTange, Ghoran-Talar and Doab-Challos hydrometric stations are completely matched with recorded historical floods that most of them have the return periods higher than 50-year and 100-year. One of the great advantages of this approach is that it can predict and determine the spatial pattern of flood-prone areas which is more important especially for local authorities and persons who are in areas with high danger of floods. After identifying the flood-hazard areas, the local authorities can set preventive measures for reducing flooddamages, design evacuation plans and run campaigns such as posters and maps to inform the residents about the hazardous areas.

Most of the bridges breakdown is due to scour around the foundation of bridge during the floodwater. Accordingly, an improved model is needed to estimate the depth of scour around the bridge pier, for minimizing the possibility of failure. Since the scour in the bridge pier is a complex function of floor materials specification, fluid characteristics, flow specification and basic geometry, thus experimental equations cannot estimate the scour depth accurately. In this paper, artificial intelligence approaches have been used to estimate scour depth. In order to evaluate the performance of the mentioned method, laboratory data has been used in two cases with dimension and dimensionless data.First, an appropriate artificial neural network model is proposed and then optimized using the genetic algorithm. The mean correlation coefficient for dimensionless data were 0.97 at the testing stage. In this model, the neural network optimized by genetic algorithm, the root mean square error value, is 0.094. The results show that the recursive artificial neural network and genetic algorithm has a much better performance in estimation of scour depth around the bridge pier in substrate with sticky sediments in comparison to experimental equations.