جستجوی مقالات مرتبط با کلیدواژه « پرتاب های جامی شکل » در نشریات گروه « آب و خاک »

One of the issues that researchers have always considered in the design of storage dams is reducing the kinetic energy of flow passing through the spillways to control the velocity, reduce the destructive energy, and scour depth downstream of spillways. Stepped chutes and flip buckets are the most common energy dissipator structures in emergency spillways at dams. Regarding the effect of scour depth at downstream of these structures on their stability and safety, in the present study, the effect of hydraulic and geometric parameters on variations of scour characteristics downstream of smooth and stepped chutes was investigated experimentally. Experiments were conducted at a hydraulic lab at the University of Guilan in 2020-2021 with a ratio of critical flow depth and step height (yc/h) of 0.53-0.97, bucket exit angles of 15° and 30°, the ratio of tailwater and critical flow depth (ht/yc) ranging from 1.5–2, the ratio of height falling and step height (HF/h) varied in the range of 2-4, and a spillway slope of 1:2 (V: H). The comparison of results demonstrated that implementing steps over a smooth chute profile reduced maximum downstream scour depth of the flip bucket by 15° and 30° exit angles in comparison with a smooth chute for the minimum relative critical flow depth by 22 and 41 percent, respectively, and for the maximum relative critical flow depth, by 14 and 20 percent, respectively. Also, with an increase in the exit angle from 15° to 30°, the maximum scour depth decreases for the minimum and maximum tailwater depths by an average of 18 and 11 percent, respectively, for a smooth chute and by an average of 19 and 17 percent, respectively, for a stepped chute. Furthermore, a regression relationship was derived for predicting the scour depth at downstream of stepped chutes with the flip bucket.

The use of free launch jets in flip bucket structures with associated submerged ponds, in the appropriate geological, and topographic and hydraulic conditions, could have significant economic and safety benefits. In this research, the downstream scour phenomenon of a flip bucket jet was investigated in free conditions, as well as in the presence of a trapezoidal and triangular slot in the coastal manner with different layout intervals at flow rate of 9, with a total of 45 experiments. The results of this study showed that the presence of the slot had significant effects on the depth and range of scour, so that the fit bucket jet with alternate triangular slots reduced the scour by about 12.7%, as compared to the no slot mode. Moreover, the maximum scour depth occurred in the bucket mode with the alternate trapezoidal slots in the more favorable interval than the rest of the models. Then, the results were compared with several empirical formulas and Veronese A relation showed closer results to the actual values.

Using flip buckets as a part of the flow dissipaters in vertical case in dams would lead to dissipation of the energy from the flood passage. This structure is used to reduce costs in comparison with other energy dissipaters. Water jet collision with the river bed leads to the creation of scouring hole which can reduce the stability of dams and relevant structures. In the present study, the scouring phenomenon of the downstream of a flip bucket in free conditions and also in the presence of slots with rectangular and triangular shapes in various intervals distances with 9 flow rates and a total of 45 tests have been investigated. The results of this study showed that the presence of a slot would have a lot of effects on the depth and extent of scouring, so that a flip bucket with alternate rectangular slot compared to a non-slotted case causes about 13 percent less scour. Also, the maximum scour depth in bucket mode with alternate rectangular slots occurred in a more favorable range than the rest of the models. Then, the obtained results were compared with a number of empirical formulas and it was determined that Martinez B relation provides closer results to real values.