| Abstract: |
8.1 SUMMARY:The present study aims to minimize the local scour DS of multi-vent regulators for the free hydraulic jump created in a radial stilling basin. An extensive literature review of the previous studies related to the investigated phenomenon were carried out.In the theoretical approach, the dimensional analysis was carried out to determine the various dimensionless parameters affecting the scour depth and the protection length. An experimental study was carried out on a horizontal bed in glassed smooth rectangular channel. More than one thousand experimental runs were conducted. All the experimental results were analyzed and discussed. The relationships between the relative scour depth ds/y1 and protection length Lp./y1 are presented versus the initial Froude number.8.2 CONCLUSIONS:The main conclusions of the present study can be summarized in the following categories:1. Gate Operating System Effect on Scour Parameters:Case of Three-Operating Gates, (e = 1.41) The different relative scour parameters give an increasing trend as the initial Froude number F1 increases and vice versa, Case of operating the three-emergency gates gives the maximum scour parameters; ds/y1 and Lp./y1. Hence, it can be said that the emergency gates must be used temporary for a short time, The scour parameters resulted due to the mixing scenarios are of smaller values compared to operating the main or emergency gates only, and The maximum relative scour parameters decrease as the number of the submerged emergency gates increases. It means that, combination between the main and the emergency gates is the suitable solution for a safe operating scenario.Case of Two-Operating Gates (e = 2.12) Case of operating the two-side emergency gates gives the maximum scour parameters, ds/y1 and Lp./y1, Case of operating the two-separated main gates gives the minimum scour parameters, Mixing between the emergency and main gates give moderate scour parameters with values in between the previous two cases at the same flow condition, and The symmetric operating systems give small scour parameters compared to the asymmetric operating systems at the same flow conditions.Case of One-Operating Gate (e = 4.22) Case of operating the middle main gate gives the minimum scour parameters for the different flow conditions, and Case of operating the side emergency gate increases the scour activities DS of the multi-vent regulators for the different flow conditions.2. Expansion Ratio Effect on Scour Parameters: For symmetrical gate operation, it was found that the smallest expansion ratio, e = 1.41 gives the maximum scour parameters, ds/y1 and Lp/y1 at the same flow conditions, In addition, for asymmetrical gate operation the scour parameters have been maximized for the smallest expansion ratio, i.e. e = 2.12, at the same flow conditions, and The optimum cases, which result the minimum scour parameters are e = 2.12 and 4.22, for the symmetrical and asymmetrical gate operations, respectively.3. Sudden/Ordinary Gate Opening Effect on Scour Parameters: The sudden gate opening increases the relative scour parameters by more than 300% of that happened in the ordinary gate operation. Consequently, the sudden opening should be averted, In case of sudden gate opening, the symmetrical operating system of the maximum expansion ratio gives the minimum scour parameters compared to the other operating systems, and Case of operating the middle main gate is advised to be used as a tool to fill the channel reach DS of the regulator at the beginning of the operating. In the contrary, it should not be adopted for the continuous operating system.4. Hydraulic Design of the Current Deflector: The deflector located within the first quarter of the stilling basin acts with the best performance. Definitely, the deflector of Ld/L = 0.10 gives the minimum relative scour parameters for the different operating systems, The deflector of relative height hd/y1 = 1.0 successfully minified the different scour activities for the different operating systems of e > 1.41. On the other hand, the deflector of hd/y1 = 0.50 is the best tool to minimize the different scour parameters for operating system of e = 1.41. In general, the deflector of hd/y1 = 0.50 can be considered as an acceptable one for the different operating scenarios, The current deflector of deflection angle = 270o is an effective tool to minimize the scour parameters DS of multi-vent regulators for the different operating systems compared to the deflector of other deflection angles, For the different operating system, it can be said that, the deflector of relative width bd/bc = 0.60 gives the minimum relative scour parameters, and The overall reduction percent of the scour parameters at presence of the deflector of the best shape parameters are about 60%, 35% and 45% in case of the symmetrical operating systems of e = 4.22, 2.12 and 1.41, while it is reduced to be 40% and 55% for the asymmetrical operating systems of e = 4.22 and 2.12, respectively.5. Predicting Models of Scour Characteristics: Two statistical prediction models are proposed, calibrated, and verified to predict the different scour parameters, ds/y1 and Lp/y1, and In addition, Artificial Neural Network models (ANN) were developed for most of the experimental results to predict the main characteristics of the scour hole. The ANN models were compared to the statistical models and performed significantly better than the statistically developed equations. Finally, it can be said that the neural network models are promising in the field of the Hydraulic Engineering.8.3 RECOMMENDATIONS:The present study suggests that investigating of the following topics are necessary:1- Studying of the bed slopes effect on scour characteristics during operation,2- Velocity and pressure distribution measurements are needed along the length of the basin,3- Studying of the optimum length of the stilling basin and piers,4- Applying this study on regulators having a sudden expansion basin,5- Applying this study on regulators under a submerged hydraulic jump,6- Applying this study on another model of more than three vents,7- Studying of the end sill efficiency on the scour characteristics,8- Studying of the movable bed effect characteristics on scour parameters during operation,9- Investigating the effect of opening different vents with different gate opening, and10- If experimental facilities are available, the problem should be treated as three dimensional problem.
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