Showing 10 results for Kashefipour
A. Moradi Sabz Koohi, S. S.m. Kashefipour, M. Bina,
Volume 15, Issue 56 (sumer 2011)
Abstract
Drops are the most important and common hydraulic structures used as energy dissipators in irrigation networks and erodible waterways. Dissipation of energy occurs in two different ways. One portion belongs to the geometric form of the structure (briefly called loss due to structure), whereas the other occurs due to happening of hydraulic jump downstream of the structure. The dimensions of drop structure and downstream stilling basin can be optimized if geometric and hydraulic characteristics are recognized properly. In this research, the effects of drop geometry and hydraulic characteristics on the loss due to structure were investigated. At first, the effective dimensionless parameters were specified. 14 physical models of more common drops including straight, inclined and stepped drops were then built in 2 heights of 51.5 & 25.5 centimeters and 2 bed slopes of 26.6 & 33.7 degrees. The number of steps in stepped models was chosen equal to 3 and 7. With establishment of 90 flow rate, the energy losses were compared. The results showed that in the range of variable parameters, the straight drop has the maximum amount of energy dissipation.
F. Kooti, S. M. Kashefipour, M. Ghomeshi,
Volume 16, Issue 59 (spring 2012)
Abstract
In this paper, velocity profiles were analyzed under different conditions such as bed slope, discharge and concentration of density current, and water entrainment. Experiments were carried out in a tilting flume with the density currents being provided using salt and water solution. Results showed that the above mentioned factors have significant effects on the velocity profile characteristics. Dimensionless velocity profiles were also provided and compared for sub-critical, critical and supercritical flow conditions and the results showed that for supper critical conditions the velocity profiles are generally thicker due to the more ambient water entrainment. The coefficients of velocity profile equations were also derived for the jet and wall zones, which showed good agreements with the experimental measurements. Relative values of the velocity profile characteristics were also calculated in order to have a better understanding about the velocity profile structure.
R. Ghobadian, M. Zare, S. M. Kashefipour,
Volume 16, Issue 60 (Summer 2012)
Abstract
Development of precise and simple methods in flood simulation has greatly reduced financial damage and life loss. Various methods and procedures have been implemented based on Saint-Venant's one-dimensional equation governing unsteady flows. To simplify the solution for these flows, analytical and numerical methods have been used. In the present study, a new method that provides the optimal outcome is introduced using non-linear programming. Penalty function has also been used to convert nonlinear programming (NLP) constrained problems into unconstrained optimal issues. To verify the accuracy of decision variables, the study covered 60 cross-sections of Gharasu River and 25-year flood hydrographs. After determining the model correctness, the 50 and 100-year flood hydrograph were routed in 18 Kilometers. The results were statistically compared with hydraulic and Muskingum hydrological methods. To sum up the routed hydrographs introduced by NLP method were very close to the hydrographs produced by dynamic wave method. The R2 of calculated discharge of routed hydrograph by NLP and dynamic wave method were 0.948, 0.990, and 0.989, respectively, with the return period of 25, 50 and 100-year flood being 0.989. It can be concluded that NLP method is more accurate than Muskingum method, especially when predicting the peak discharge of flood hydrograph.
S. Baghbanpour* and S. M. Kashefipour, ,
Volume 16, Issue 61 (fall 2012)
Abstract
Rivers as a main sources of supplying water for urban areas, agriculture and industry, are very important. This point reveals the necessity of the control, improvement and solving the problems of rivers, especially all problems relating to water quality. In this study, transport of the suspended sediment is numerically modeled. The Saint-Venant hydrodynamic equations and also advection-dispersion equation (ADE) are applied for modelling flow and suspended sediment transport. It is necessary to choose appropriate empirical and/or semi-empirical equation to accurately estimate the equilibrium suspended sediment discharge, as well as the appropriate equation describing longitudinal dispersion coefficient. In this research, 5 and 6 equations were applied in the ADE for estimating equilibrium suspended sediment discharge and longitudinal dispersion coefficient, respectively. 30 combinations of these equations were made and the final model was run for each of them separately. Comparison of the predicted suspended sediment concentrations and the corresponding measured values at the survey site, Abdelkhan Station, for the calibration and verification periods showed that the combination of the Van Rijn's equilibrium suspended sediment equation and the Fischer's longitudinal dispersion equation performed very well. The maximum percentages of errors in estimation of suspended sediment concentrations were 19.56% and 26.3% for the calibration and verification periods, respectively.
M. Toozandehjani, M. Kashefipour,
Volume 16, Issue 62 (Winte - 2013 2013)
Abstract
One of the usual ways to dissipate excess energy in the dam's downstream is hydraulic jump. Hydraulic jump is a rapidly varied flow, in which the flow conditions change from supercritical to sub-critical with a large amount of energy loss. In this research, a combination of two water jets in the form of overflow dam and underflow through a slot on the body of an ogee dam with the USBR standard was established in order to decrease the length and sequent depth in a hydraulic jump. In these experiments, the underflow from the slot was designed with three out passages of 0, 45, and 90 degrees in respect horizontal line. Six different discharge ratios were used for each slot and the effect of each experiment conditions on decreasing of the length and sequent depth of hydraulic jump was investigated. The results showed that the confluence of two jets with 45 degrees from the slot had the maximum effect on the reducing of the length of hydraulic jump and sequent depth, and when 26 percent of the total discharge passed through the slot as underflow, it caused the length of hydraulic jump to be reduced by 50 percent in comparison with the classic jump. This slot not only decreases the length and sequent depth of hydraulic jump but also the sediment behind the dam can be evacuated through it. Moreover, it increases the discharge coefficient.
E. Jasemi Zargani, S. M. Kashefipour,
Volume 21, Issue 3 (Fall 2017)
Abstract
Spur dikes are the most common hydraulic structures for river bank protection. Since the construction of this structure causes higher velocities around it, this structure is exposed to erosion. Riprap around the structure nose is one of the most common and economic way to protect spur dike. The main aim of this study is to investigate the riprap stability in a mild 90 degrees bend. Experiments were conducted in a laboratory flume with a 90 degree bend. After specifying the critical spur dike along the bend, this spur and one before and one after it were protected by riprap. The variables were the length of the structure, spur space, riprap size, Froude number, and the amount of submergence, and 205 experiments were carried out in this flume. Finally an experimental equation was developed based on the flow and geometric parameters of submerged spur dike, which can be applied for designing the riprap size.
R. Khankhani Zorab, S. M. Kashefipour,
Volume 22, Issue 1 (Spring 2018)
Abstract
The purpose of this study was to evaluate two perforated sills in the stilling basin and their impact on characteristics of the hydraulic jump, such as the length of the roller of hydraulic jump, decrease in the secondary depth of the hydraulic jump, and the required tailwater depth. Also, the optimal distance of two perforated sills from the beginning of the stilling basin with a fixed height for the perforated sill and ratios of the opening of holes equal to 50% were determined. The experiments were carried out in the form of 48 tests for different discharges in the range of 47 to 145 lit/s and for Froude numbers in range of 3.6 to 11.2. The results of the experiments on two perforated sills showed that they could only reduce the length of the roller of the hydraulic jump to an acceptable level, with the distance between them providing the conditions to create a stable jump; also, the length of roller of jump was not decreased by reducing the distance between the sills. Also, they decreased the secondary depth of the forced hydraulic jump up to 27.8%, which was less than the secondary depth of the free hydraulic jump; the length of roller was up to 76.9 % less than the length of the roller of the free hydraulic jump for the Froude number of 11.2.
E. Yabbarepour, M. Shafai Bajestan, S. M. Kashefipour,
Volume 22, Issue 4 (Winter 2019)
Abstract
Channels and surface water are ways for the transfer of pollutants to the environment and human. When any pollutant is spilled into the channel, the pollutant concentrations are decreased after the travel. Reducing the distance is an engineering expedient. To reduce the distance, mixing in water should be increased. Thus, the main goal of the present study was to investigate the effect of the triangular vane on transverse mixing used for control bank erosion. Experiments were carried out in an 80cm width flume. The vane, which was triangular, was made of Plexi-glass with a 30% width of the flume length, 15cm height and 50cm far from the tracer injection. Salt solution was used as the soluble tracer. The experiment was carried out to investigate the effect of the triangular vane for two conditions: with and without vane. The transverse mixing (ez) and complete mixing length were estimated for the two conditions of with and without vane. The results showed with installing the triangular vane, the transverse mixing was increased up to 2.5 and the length of mixing was decreased by 60%, as compared with the tests of no vane.
A. Sharifnezhad, M. Kashefipour, M. Ghomeshi,
Volume 23, Issue 1 (Spring 2019)
Abstract
Study of Turbidity Current, as one of the most important phenomena affecting the sedimentation in the reservoirs of dams, is essential. Since most of the research studies have been conducted under experimental conditions on rigid beds, the effect of erodible bed and the formation of the bed form on the turbidity current specifications is not yet clear. Therefore, in this Research, the study of the turbidity current in two conditions of rigid and mobile bed was conducted in order to determine water entrainment specification and the effective hydraulic parameters. The results showed that water entrainment changes depended on the variation of bed roughness and the type of bed form. Also, water entrainment of turbidity current was initially reduced by about 25% with the change in the bed shear stress, relative to the rigid bed, due to formation of small bed forms; then, it increased by about 30%, forming the larger bed forms; finally it decreased with increasing the flow strength and removing the bed forms. In addition, comparison of the results of the present study with previous research showed that the formation of bed forms increased water entrainment in a constant Richardson number up to 50%.
E. Shaker, S. M. Kashefipour, M. Shafai Bajestan,
Volume 23, Issue 4 (winter 2020)
Abstract
Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph’s parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion’s ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph’s peak led to increasing depth erosion from 7% to 22%.
