جستجوی مقالات مرتبط با کلیدواژه « تلماسه » در نشریات گروه « کشاورزی »

Understanding flow behavior over bedforms is one of the most complex topics in sedimentary engineering. Despite numerous studies that have been conducted on river beds, the understanding of the interaction between flow and bed in turbid and clear waters is still impoverished. The present study mainly focused on simulating clear and turbid flows using SSIIM software. This study modeled the flow through a 12-meter channel with nine consecutive dunes of 1-meter length and 4 cm height. Nine simulations were performed to investigate the effects of flow velocity and flow separation zone in clear and turbid water. Finally, the results were compared with the experimental results of previous researchers using the PIV. The modeling results showed that the length of the flow separation zone increases with increasing velocity, and the highest probability of flow separation occurs at the highest velocity. In turbid flow, flow separation is less than the same flow condition in clear flow, and as fluid density increases, the length of the flow separation zone decreases. This study demonstrates the acceptable functionality of the SSIIM software and its accuracy in estimating flow behavior with and without sediment.

The formation of bed form in alluvial rivers due to sediment transport has a significant effect on the hydraulic parameters of the flow such as bed shear stress. The formation of the bed form and its shape and geometry depends on the bed shear stress. Therefore, the relationship between bed form and flow parameters (such as bed shear stress) is complicated. In the present study; the effect of dune bed forms with different heights on bed shear stress has been investigated. Artificial dunes made by sand-cement mortar with a length of 25 cm and heights of 1, 2, 3, and 4 cm were used. In the tests of this research, flow discharge of 10, 15, 20, 25, and 30 l/s and bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were used. The results showed that with increasing the relative submergence and Δ/λ, the bed shear stress increased in dune-covered beds. The formation of the dune bed form and the increase in its height leads to an increase in the bed shear stress. The bed shear stress in dunes with a height of 1, 2, 3, and 4 cm was, on average, 39, 80, 141, and 146% more than in plane beds, respectively. Moreover, form shear stress for dunes with a height of 1, 2, 3, and 4 cm was, on average, 27.37, 43, 57.11, and 58.74% of the total shear stress, respectively.

Bed shear stress is one of the most important hydraulic parameters to determine the amount of bed and suspended load and the bed and bank scouring in rivers. Bed shear stress depends on bedforms (ripples, dunes, and anti-dunes) in alluvial rivers. In this study, the effect of artificial ripple bedforms on bed shear stress has been investigated. Two types of uniform granulation with average sizes (d50) of 0.51 and 2.18 mm were used to roughen the surface of the artificial ripples. The bedform length and height were 20 and 4 cm, respectively. The angles of its upstream and downstream to the horizon were selected equal to 16.4 and 32 degrees, respectively. Different flow rates (Q= 10, 15, 20, 25, and 30 l/s) and different bed slopes (S= 0, 0.0001, 0.0005, 0.001, and 0.0015) were examined. The results showed that by increasing the particle size on the bed surface, total shear stress (tb ), grain-related bed-shear stress (t¢b ), and form-related bed-shear stress ( t²b )  increase. The value of tb , t¢b , and t²b in bed form roughened by sediment size of 2.18 mm were, on average, 22.38, 30.86, and 22.3% more than the bed form roughened by sediment size of 0.51 mm, respectively.

Accurate estimation of flow resistance, such as Chezy coefficient, is important for calculating the hydraulic flow conditions and sediment transport in open channels. Chezy coefficient is affected by various factors: bed particles size, vegetation, irregularity of waterway cross-section, irregularity of waterway path, scour and sedimentation, presence of obstructions, suspended and bed load, and bed form (Bahrami Yarahmadi & Shafai Bejestan, 2010, 2011). Previous researches, Talebbeydokhti et al. (2006), Omid et al. (2010), Nasiri Dehsorkhi et al. (2011), Chegini & Pender (2012), Kabiri et al. (2014), and Kwoll et al. (2016), have shown that the bed forms can affect the hydraulic or sediment transport characteristics. However, there is a lack of study to investigate the effect of bed forms with different sediment sizes on the Chezy coefficient. Therefore, the present study aims to conduct experiments on a straight channel whose bed is covered with the artificial bed forms made from P.V.C sheet, and on its surface is glued sediment of different sizes in the range of 0.51 and 2.18 mm.

The experiments were performed in a straight flume of 12 m in length and 0.30 m wide (Figure 1). In this study, different flow discharge of 10, 15, 20, 25, and 30 l/s and different bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were tested. Two series of experiments were carried out: plane bed or bed without form and bed covered with form. Each form was made in a triangular shape with a P.V.C sheet. The form's length and height were equal to 20 and 4 cm, respectively, and the angles of its upstream and downstream to the horizon were selected as 16.4 and 32 degrees, respectively. After each form was built, the desired sediment size was glued to their surface. This study used two types of uniform granulation with average sizes (d50) of 0.51 and 2.18 mm. The total number of experiments in the present study was 100. Since in alluvial rivers with bed form, the resistance Chezy coefficient includes the grain Chezy coefficient and the form Chezy coefficient. A formless bed, covered with the same sediment size, was tested to determine the grain Chezy coefficient ((C_b ) ́). The bed with the form was used to determine the total Chezy coefficient (C_b) and the form Chezy coefficient (C_b^''). Ripple and dune form is formed in a lower flow regime, in which the Froude number of the flow is less than 1 (Shafai Bajestan, 2008). In this study, the Froude number values in all tests with bed form were 0.435 to 0.6, indicating a lower flow regime.

Figure 3 shows the changes in the total Chezy coefficient (C_b) against Froude number for sediment-covered substrates of 0.51 and 2.18 mm. It can be seen that as the Froude number increased, the total Chezy coefficient (C_b) increased. In addition, increasing the longitudinal slope of the bed decreased C_b.Figures 4, 5 and 6 illustrate the effect of sediment particles size on (C_b ) ́, C_b^'', and C_b. These figures show that (C_b ) ́, C_b^'', and C_b decreased with increasing particles size. In addition, Figures 5 and 6 show that with increasing R/∆, the total Chezy coefficient (C_b) and the form Chezy coefficient (C_b^'') increased. Calculations showed that the value of C_b^'' in beds with a sediment size of 0.51 mm for slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 was, on average, 14, 12, 12, 15, and 16.4% more than 2.18 mm sedimentary beds, respectively. In addition, the value of C_b in beds with a sediment size of 0.51 mm for slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 was, on average, 15, 13, 13, 16, and 16.5% more than 2.18 mm sedimentary beds, respectively.The results of Table 1 shows that the grain Chezy coefficient ((C_b ) ́) for particles with sizes of 0.51 and 2.18 mm was, on average, 98 and 93% more than the total Chezy coefficient (C_b), respectively. In addition, The form Chezy coefficient (C_b^'') for particles with sizes of 0.51 and 2.18 mm was, on average, 16 and 17% more than the total Chezy coefficient (C_b), respectively.

The results of this study shows that generally with increasing the bed slope and the bed particle size of movable bed sediment channel, the flow resistance increases or the total Chezy coefficient , the form Chezy coefficient and the grain Chezy coefficient decreases. Increasing the bed particle size from 0.51 to 2.18 mm reduced the coefficients of Cb ́, Cb'', and Cb by 15.14, 12, and 12.9%, respectively. Moreover, the value of Cb ́, Cb'', and Cb in sedimentary beds with particles of 0.51 mm were, on average, 18, 14 and 15% more than sedimentary beds with particles of 2.18 mm, respectively.

Determination of flow roughness coefficient in the channels and river hydraulics is necessary for calculating of the discharge, the velocity and the depth of flow. Calculating the exact values of this coefficient is complex and difficult due to the influence of various parameters on it. In this study, using support vector regression as one of the machine learning approaches, the flow roughness coefficient in alluvial channel with dune bedform is predicted for four experimental data series under three scenarios (modeling based on flow characteristics, flow and bedform characteristics and flow and sediment characteristics) and the rate of input parameters is investigated using different performance criteria. The obtained results show that the support vector regression approach has desired accuracy in predicting the roughness coefficient. Also, the flow Reynolds number parameter with the most impact was recognized as the most significant parameter in estimating the roughness coefficient in the erodible beds with dune bedforms.

An accurate prediction of the roughness coefficient in open channels with bedforms has a significant impact on the planning, design and operation of water resources projects, including water transport and river systems. Different bedforms such as dunes have obvious effects on flow resistance. However, due to the impact of various parameters on the roughness coefficient, accurate estimation of this parameter is difficult. In this paper, the efficiency of Gene Expression Programming (GEP) method in estimating manning roughness coefficient in open-channel channels with dune bedforms has been evaluated. In this regard, various models were defined based on flow, bedform, and sediment particles characteristics and were tested using four laboratory data series. The results proved capability of GEP in predicting Manning roughness coefficient and it was observed that the applied method is more accurate than semi-theoretical relationships. It was also found that the model with input parameters related to both flow and sediment particles characteristics is more successful in estimating Manning roughness coefficient. According to the results of the sensitivity analysis, the Reynolds number parameter has the most significant impact in predicting the roughness coefficient.

Sand dunes developed in 15 provinces with an area of 4.4 million hectares and 56 Citadel, are one of the most important geomorphological features in Iran. Sand and desert stabilization technical office studies, according to project results identify focal and present four regions including Ahvaz, Dasht-e-Azadegan, Susa and the Omidiyeh in Khuzestan province. The mentioned area includes 279505 hectares of land in Khuzestan. This study has used remote sensing technology, GIS techniques and analyzed effective recorded winds data. Toward were reviewed and analyzed the wind regime of the area for direction of source area using Windrose Diagrams. In this study, based on utilizing and composing of image processing techniques such as image enhancement, threshold, false color composition, filtering and analysis and results of wind data analysis, with other investigations is useful to find the source of sand dunes. The results from direction of source area confirm that source of sand dune located in NW to W, notice Windrose in Khuzestan. The source area are flood alluvial fan plain, alluvial fan, agriculture land, meandering rivers and sensitive formation to erosion including Aghajari formation and Bakhtiari formation that located in the in NW to W section.

Study in mixing processes for the management of water quality of rivers is important and one of the environmental concerns. The substrates, such as dunes, are effective in control of transport, production of turbulence and flow resistance in rivers, canals and wetlands It is therefore essential that study is done in this subject. The objective of this study is to investigate the transversal mixing coefficient of dunes. For this purpose, measurements carried out on the fifth to the ninth of dunes in a series of ten dune sand of the synthetic twodimensional. The experiments carried out in a laboratory channel with dimensions of length, width and depth, 20, 0.6 and 0.6 respectively. The dunes had a wave-length of one meter, height 0.8 meters, downstream side slopes 28 degrees and width equal to the channel width. The average diameter of sand dunes used was 14 mm. To evaluate the effect of the delicately ratio on lateral mixing coefficients, two different depths were used. The results showed that dune plays an important role in increasing the lateral mixing coefficient so that in this case this rate was 2.36 times the flat bed. Complete mixing length in the channel bed dunes was 11 meters to the amount indicated on the flat bed of a third. This parameter showed a decrease with increasing depth over the dunes. The tests indicate that the self-purification power of the river on the dunes, comparing to a flat bed, with increasing water depth above of the dunes, increases.

Fine-grained materials of Clayey Loess deposits of Gorgan region were mixed with sand dune in the lab with various rations and their shear behavior was measured and evaluated by direct shear test. The result of the study showed that the increase of fine-grained clay in sand dune was directly related to the adhesion force and inversely to the internal friction angle. The increase or reduction in shear strength was affected by the fine-grain percentage. Dry condition and saturation of the test and sand dune had a less influence on shear parameters but in the mixed samples in dry condition and saturation, shear parameters revealed a considerable difference. The results of this study can be used in sand stabilization, erosion prevention, slope stability, embankment construction, compaction increase, and environmental pollution, and dust and water channels avoidance.