مجله مهندسی آبیاری و آب ایران
پیاپی 2 (زمستان 1389)

There are many conditions in open channel flows where the steady flow of water passes through a cluster of vertical cylinders. These vertical cylinders may represent piers of bridge، jetty or vegetation on the floodplain of rivers. Research on vortex shedding has been mainly focused on the acoustic resonant noise generated from heat exchangers when a gas flows through bank of tubes. In contrast، research on the vortex shedding and related phenomena for water as the transfer medium is very limited. Consider a free stream of velocity U that flows past a cylinder of diameter D، Periodic vortex shedding occurs downstream from the cylinder when the Reynolds Number، defined in terms of the cylinder diameter is greater than approximately 40. When each vortex is shed، the cylinder and the fluid experience equal and opposite forces. These forces have components perpendicular to the direction of the mean flow and are the exciting forces capable to create transverse surface waves. In this study attention is focused on the transverse waves generated in an open channel، where the flow passes through a cluster of rigid vertical cylinders. The experiments were conducted in a laboratory flume with 6m in length and 0. 72m in width and 0. 6m in height. The rigid rods were screwed into the bed of the flume at different distances and spacing (i. e. different T and P) and for pattern distributions (i. e. staggered and in-line). In this study، the height of the outlet control weir was changed from the highest to the lowest levels، with ten modes of oscillation occurring across the laboratory flume for each sequence and the discharge of flow was varied. A comprehensive set of experiments (3304 in total) were conducted in flume. In some of the experiments (398 Exp.) the flow was submerged on the obstructions and for some of these experiments the waves still were formed. The waves were produced from the periodic forces created by the vortex shedding from the cylinders. In specific conditions these forces may create transverse waves with maximum amplitude in the channel. The maximum relative amplitudes in each mode of the waves (in each type of the experiments) are selected and used for the further analysis. The results provided an explanation for different wave formations that might occur due to vortex shedding for free and submerged flow on the obstructions. Finally new formulations were obtained from dimensional analysis، to estimate the amplitude of the transverse wave generated by vortex shedding in open channels.

Deposition of sediment inside the conduit structures reduces the flow cross section area and increase the flow roughness which causes reduction of flow discharge passing through the conduit. Among the methods in which can be achieved such goals is to design the structure in such a way that the flow velocity to be greater than incipient motion velocity. A lot of work has been recently done to determine the conditions of incipient motion velocity in bed with usual and deep slope. All of these studies have been done on natural sediment with 2. 65 densities. This research studies conditions of incipient motion velocity in open channel flow with rectangular section by using physical modeling and dimensional analysis. In this study 12 non-sticky sediment specimens with different dimensions and density in. 5%، 1% and 1٫5% slope have been tested. One graph was drown that can be used for determining of incipient motion in open channel and rectangular section; the findings of this study were also compared with other experimental relation.

For investigation of effect of deficit irrigation on quantitative properties of winter wheat، a completely randomized design consisted of 36 plots (9 irrigation treatments and 4 replications) was conducted at farm research (with sandy loam texture) of Shahrekord university in 1384-1385. The irrigation treatments were applied since the first of Khordad، 1385، because before the date irrigation requirement was zero in Shahrekord climate. The irrigation time was determined base on which time 50% depletion of soil water content in full irrigation treatment occured. T1 and T2 treatments were over irrigation، T3 was full irrigiation and other treatments were under different levels of deficit irrigation. The results showed that the deficit irrigation effect on quantitative properties of winter wheat (consists total، grain and straw yield and wheight of thousand grain) significantly، so that depth of apply water which maximize grain yield per hectar was 314mm. Finally the depth of applied water for irrigation of winter wheat that maximizes net income was 106 mm. While according to crop production function the depth of applied water that maximizes grain yield was 314 mm. Thus in the water limiting situation the optimum depth of applied water is equal to 34% of full irrigation. Thus، using deficit irrigation، irrigated area can be increased 2. 9 time related to full irrigation.

In this paper، the discrete singular convolution is applied to non-darcian seepage equation in porous media which is non linear. Since the equation does not have analytical solution، results have been verified with finite volume method. According to the results، DSC method has high conformity with F. V method; moreover the convergence ratio of DSC is much higher.

In this research the methodology of underground dams’ monitoring was expressed in order to study the effect of underground dam construction on the subsurface flows as a quantity or quality study. therefore a suitable site selected in the margin of desert in distance of 10 km from the east of Ravar city and the required investigation were done in several steps. Before constructing the dam the hydrological studies were done for for determining the volume of subsurface flow which passed from the alluvium of the river in the place of dam construction. In first a borehole which dug well excavated and used for pumpage test to determining the hydrodynamic coefficient and subsurface flows calculating. Then four piezometric well were drilled by percussion and rotary method in which two of them were in the upstream (one of them with a distance of 800 meters and the other with a distance of 850 meters from the underground dam axis) and the other two piezometric well were in downstream (one of them with a distance of 100 meters and the other with a distance of 150 meters from the underground dam axis) and they were piped and equipped for the monitoring operation in future. After constructing the dam، the well was collecting and tansfring the water of dam reservoir was prepared and equipped. Immediately، after complementing the dam’s constructing operation، measuring of the underground water level was stared in 4 peizometric well and the dam’s water transferring well. this operatioin was continued during the periods of 1 to 4 months for 4 years. and also measuring underground dam’s discharge was carried out during the different periods. Then the data were analyzed the results shows that the construction of dam has been very sussessfuly and was shown the positive effect on the underground flows as the quantity or quality.

Application of 2-D hydrodynamic models for simulation of flow around dike fuse plug spillways is inevitable due to complexity of flow in the vicinity and beyond the breach. Because of popularity of MIKE21 in Iranian institutions، this research tries to assess the performance of MIKE21for this application. First، the performance of MIKE21 in dike breach simulation was assessed using experimental data. After verification of the model results in an experimental case، a case study which was Helleh River near Borazjan، was considered to show the performance of method in a real situations. To specify the initial and boundary conditions، the river reach was initially modeled by 1-D model، HEC-RAS. After comparison of 1-D and 2-D results in prediction of maximum water surface elevation، assuming no dike breach، flow due to fuse plug breaches in several places werestudied in different scenarios. Finally، some issues related to propagation of flow on initially dry bed and wetting and drying were discussed. The computational cost of the 2-D model was also much more than 1-D model.

Forecasting of hydrological variables are suitable tools for water resources management. On the other hand، using time series concepts in forecasting is very useful. Therefore in present research for this aim، measured monthly discharge in 21 hydrometric stations from 1984 1985 to 2004-2005 in Karkheh watershed used، Then different method in forecasting and modeling in time series analysis include Trend Analysis، Holt-Winters method and various Autoregressive Moving Average Models (ARMA) suggested by Box-Jenkins were fitted to data. Afterwards، condition and accuracy of fitted models in forecasting of future monthly discharges considered using Akaike Information Criterion (AIC) and Root Mean Squared Error (RMSE). The results showed that trend analysis have the best forecast and autoregressive moving average models with few differences are in next place. In addition، Akaike Information Criterion showed that ARMA models with higher orders have better accuracy in modeling، but in forecasting ARMA with lower orders have better efficiency. There are high error in Holt-Winters method and is not recommended in this area. Finally، forecasted values using expressed methods have an overestimation in comparison with observed data.