Journal of Hydraulic Structures
Volume:6 Issue: 2, Spring 2020

In this study, the performance of the algorithms of whale, Differential evolutionary, crow search, and Gray Wolf optimization were evaluated to operate the Golestan Dam reservoir with the objective function of meeting downstream water needs. Also, after defining the objective function and its constraints, the convergence degree of the algorithms was compared with each other and with the absolute optimal values obtained from GAMS nonlinear programming method (19.41). These values together with each algorithm optimization results were ranked using six multi-criteria decision-making methods of TOPSIS, VICOR, Linmap, Codas, ELECTRE and Simple Additive Weighting after obtaining the performance evaluation criteria of each algorithm (Reliability, reversibility, and vulnerability). Finally, integration methods (Mean, Borda, and Copland techniques) were used to evaluate the performance of decision models. The results showed that the mean responses of the gray wolf, the whale, differential evolutionary, and crow search algorithms were 1.08, 1.49, 1.29 and 1.19 times the absolute optimal response and the answers’ coefficient of variation obtained by Gray Wolf algorithm was 113.2, and 1.43 times smaller than the whale, differential evolutionary, and crow search algorithms, respectively. Moreover, all integration techniques indicated the superiority of the gray wolf algorithm. Then, the Crow search, Differential evolutionary, and whale algorithms were ranked second to fourth, respectively. On the other hand, the use of these methods in solving the problem of Golestan Dam reservoir optimization was considered appropriate due to the similarity of the results obtained from the integration techniques with the results of TOPSIS, VICOR and Linmap methods.

This study examines the relations of structures and shapes of streambed evolution after dam break floods. A flume was used to simulate dam-break floods with variations of initial upstream water levels and variance, from uniform to graded, of the bed sediments. Detailed measurements of the evolution and composition were made during these experiments. The data indicate that intense scour occurred immediately downstream of the “dam break” in both uniform and graded sediments. The resulting bed surfaces of graded sediments showed coarse-fine-coarse structures in the areas with the lowest scour and highest deposition and various type of cluster (i.e. line and heap). This pattern was not observed in beds of uniform sediment. The scour hole changes from circular to oval-shaped in both uniform and graded sediments with increasing bed slopes. Keywords: Dam break, Experimental, Bed-surface composition, Graded and uniform sediment, Scour.

The presence of several convergent meanders is a basic characteristic of natural flowing rivers. It is important to construct bridge piers in different geometric shapes at convergent meanders. The formation of secondary flows at meanders and their enhancement by the convergence effect can bring complexities and irregularity in the erosion pattern around bridge piers. The present study experimentally and numerically investigates the effects of the geometric shapes of bridge piers on local scour around piers at a 90° convergent meander. Tests were carried out within a channel with a 90° convergent meander and a centerline radius of 170 cm. Cylindrical piers with the diameters of 40 and 60 mm and cubic piers with the sizes of 40*40 and 60*60 mm were placed at the center of the meander, investigating scour in clear-water conditions. Also, a three-dimensional SSIIM-2 model was employed to simulate the problem and compare the results to the experimental ones. The results indicated that the shapes and sizes of the piers affected the scour depth, and the maximum scour depth was estimated to be smaller around the cylindrical piers than around the cubic piers in all the tests. Moreover, convergence-induced contraction along with the placement of the piers at the meander enhanced scour around the piers. The numerical SSIIM-2 results were found to be in a good agreement with the experimental results.

Ground motions records of the past higher magnitude (Mw>5) earthquakes have indicated that ground motions recorded at the closest distance of the near-fault are very different from those recorded from a higher distance from the site of the far-fault. Forward directivity and fling effect are the essential characteristics of the near-fault earthquakes; these can cause potentially high damage during earthquakes. Hence, to understand the effect of the far-fault and near-fault on the performance of the structure is vital to reduce the damage and perform an efficient response. In this paper, an attempt is made to evaluate the effects of far-fault and near-fault ground motions on the seismic performance of the concrete gravity dam incorporating the dam-reservoir-foundation interaction. An arbitrary gravity dam is considered as numerical example. In this, eight different earthquake records are considered for time history analyses. The seismic performance of the dam is evaluated using the cumulative-overstress-duration (COD) and demand-capacity ratio (CDR). The results obtained show the importance of the near-fault ground motion effect on the seismic performance of the concrete gravity dam.

The critical depth is a hydraulic factor of the flow, it plays a particularly important role in studying and designing for open channels, especially during identification of water surfaces and analyzing to determine the phenomenon of a hydraulic jump in open channel. In practice, when calculating the critical depth, only the rectangular and isosceles triangle channels have the theory equation, in other circumstances in calculating by semi empirical equations. This paper presents the general method to compute the critical depth of trapezoidal channel, the case study methodology was chosen to analyze the application of existing formulas and then offering a new equation to compute the critical depth based on the optimization algorithm in MS Excel software. This new equation will help to obtain more accurate result, which relative error of the equation is less than 0.61%, this equation has a simple structure, easy to calculate with small errors to meet the conditions to quickly calculate the critical depth, this equation is also suitable for teaching–learning and studying in the field of hydraulics.

Prevention of water loss for the Urmia Lake due to the drought is environmentally crucial for the lake basin and it seems that, the analysis of the historical process of factors governing the water mass balance equation for the catchment leading to the lake can provide insights on what has to be done. In order to do that, statistical significance for potential breaking points and rate of changes over time points of precipitation and runoff for 25 hydrological basin stations based on the data regarding Annual precipitation and Annual runoff related to the whole span of the lake basin from 1977 to 2019 has been studied and surveyed using Mann-kendall test, Petit test and Sen’s Slope Estimator. For all hydrological basinstations breaking points have been observed in the water discharge time points from 1993 to 2005 and the decline of water discharge. Significant increase in precipitation in the entire Urmia catchment area of about 0.16 mm at a indicates its stability during the study period. The annual runoff of the studied basins into Lake Urmia in the two time periods before and after the discharge drop were estimated at 4.671 and 1.885 billion cubic meters per year, respectively, indicating volume reduction of 2.786 billion cubic meters (59.6%). Looking at the Lake Urmia sub-basins annual discharge reduction data, it can be seen that Zarrinehroud with the largest share of 34.5% and Mahparishai with smallest share of 0.2%, and the rest in between, contribute to the occurrence of draught for Lake Urmia.