جستجوی مقالات مرتبط با کلیدواژه « combined flow » در نشریات گروه « کشاورزی »

Weirs and gates are the common and important structures which are used for controlling and adjusting the flow in irrigation channel and rivers. In order to increase the efficiency of the weir and gate structure, the combined weir and gate structure can be used. In this case Weirs and gates can be combined together in order to pass the floating materials above weir and to move the sediments depositions in upstream of the gate simultaneously. This compound device create a new hydraulically condition in compression with weir or gate, each other alone. Before the year 1985, very little information about the use of these combined devices for flow measurements were available when Ahmed published his study on a combination of rectangular weir above a rectangular sluice without contraction. He tried to obtain a common discharge coefficient for the combined system, but his data were not enough to make generalization (15). After him Many researchers have tried to investigating of hydraulic characteristics of the combined structure such as El-saiad (1995), Alhamid et al (1996), Negm et al (1994) and Negm (1997) (6, 2, 14,16). They studied combined flow over V-notch weir and below contracted rectangular gate. The objective of this research was to determine the discharge coefficient of the combined weir-gate and provide the relation for estimation of discharge coefficient based on the hydraulic and geometry parameters. In this study, the effects of hydraulic flow and chanal geometry on the discharge coefficient of weir-gate system was studied by variation of parameters such as discharge, opening the gate and height combined structure in laboratory channels. Finally several relations was obtained with high accuracy for discharge coefficient by the genetic programming. For selecting the best relation, determination coefficient (R2), root mean square error (RMSE), average error (AE) and the average absolute deviation of the data (δ) were used. The results of the experiments were analyzed after checking and refining data and discharge coefficient was calculated by the above-mentioned relations. Then, by dimensional analysis and genetic programming, A relation was obtained for discharge coefficient of weir-gate system that determination coefficient is for teaching data 84.2 percent and for test data 88.1 percent. Geometric parameters of combined model have a fundamental role on discharge coefficient. Also the genetic programming can be used for presenting a relation for estimation of discharge coefficient with high accuracy.

In Combined weir - gate structures، interaction of flow over weir and through gate brings up intense mixing and change bed shear stresses distribution. Hence، simulation of flow pattern in downstream of these structures is very complex. The object of this research is numerical modeling of combined flow over weirs and through gates by Flow3D software. Flow3D is a high accurate model in computational fluid dynamics for simulation of problem with complex geometry on wide limits of fluid flows in open channel hydraulic. By applying VOF method and RNG K-ε turbulent models، a series of simulation combined flow in weir - gate structure on rigid bed were performed and results were compared by some experimental data that carry out in this research. Results for the equation of Qup/Qin (equation 13) calculation error statistics software based on RMSE and R2 was evaluated and these values obtained 0. 0994 and 0. 992. Results of this research show that Flow3D with RNG K-ε turbulent model is appropriate to simulation of combined flow in weir - gate structure and estimation of free surface profile and discharge ratio passed over weir to under the gate.

By combining weirs and gates the problems of sedimentation and floating materials upstream the weir and gate structure can be resolved. In combined structures a new hydraulic condition is created which is differing from hydraulic condition in weir and gate only structures. Due to jet flow passing through or under structure، the scour hole is formed downstream of structures that’s may endanger the stability of the structure. So determination of scour hole characteristics is attracted by researchers. The object of this study is numerical modeling of scour pattern downstream of combined flow over weir and under the gate by Flow3D software. For modeling the turbulence، RNG k-، k- and LES were used. Flow3D is a high accurate model in computational fluid dynamics for simulation of problem with complex geometry on wide limits of fluid flows in open channel hydraulic. By applying VOF method، a series of simulation scour pattern downstream of weir - gate structure were performed and results were compared by some experimental data. The results show that Flow3D with LES turbulent model can be used with high accuracy (with R2=0. 96، RMSE=0. 0117) to simulation of scour pattern and water surface profile in weir - gate structure.