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اثر بخشی بلوک های V شکل بر آبشستگی موضعی در پاییندست سرریز اوجی | ||
| تحقیقات مهندسی سازه های آبیاری و زهکشی | ||
| مقاله 8، دوره 21، شماره 80، آذر 1399، صفحه 115-132 اصل مقاله (1.25 M) | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.22092/idser.2020.128706.1417 | ||
| نویسندگان | ||
| حامد شهسواری1؛ سبحان مرادی2؛ علی پرموده2؛ کاظم اسماعیلی* 3 | ||
| 1دانشجوی دکترا گروه علوم مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران | ||
| 2دانشجوی کارشناس ارشد، گروه علوم مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران | ||
| 3دکتری تخصصی گروه علوم مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران. | ||
| چکیده | ||
| آﺑﺸﺴﺘﮕﯽ ﻣﻮﺿﻌﯽ ﭘﺎﯾﯿﻦدﺳﺖ ﺳﺎزهﻫﺎی ﻫﯿﺪروﻟﯿﮑﯽ ﻫﻤﻮاره از مسائل مهم در ﻃﺮاﺣﯽ آنها و نیز ارائۀ راه حلهایی برای کاهش میزان خسارات ناشی از این پدیده بوده است. در این مقاله، با استفاده از نتایج آزمایشگاهی روی یک مدل ساخته شده سرریز اوجی به بررسی تأثیر بلوکهای V شکل نصب شده در پایین دست سرریز بر میزان آبشستگی موضعی بستر پایین دست سازه پرداخته شده است. آزمایشها در سه نسبت بی بعد دبی ماکزیمم برابر با 71/0، 85/0 و 1 و در اعداد فرود مختلف اجرا و عمق و طول آبشستگی ثبت گردید. برای دستیابی به بهترین عملکرد بلوکها در جهت کاهش آبشستگی، موقعیت بلوکها و ارتفاع آنها بررسی شد. بدین ترتیب چهار موقعیت نصب بلوک، به صورت نسبتی از طول کل قسمت صاف Lb/Lf برابر (88/0 و 66/0، 44/0، 22/0) و همچنین چهار نسبت ارتفاع بلوک Hb/D ( 2 و 33/1 ،1 ، 66/0) برای آزمایشها در نظر گرفته شد. نتایج آزمایشهای حاضر در زمینۀ فاصلۀ قرارگیری بلوکها نشان داد که با کاهش فاصلۀ قرارگیری بلوکها نسبت به پنجۀ سرریز، آبشستگی در عمق و طول کاهش می یابد. علاوه براین، افزایش ارتفاع بلوکها نیز موجب اثر بخشی بیشتر بلوکها در کاهش آبشستگی شد. سرانجام اینکه برای شرایط جریان با اعداد فرود مختلف، بلوک با ارتفاع 2Hb/D= و در موقعیت قرارگیری 22/0Lb/Lf= نسبت به پنجۀ سرریز بهترین جانمایی را داشت که موجب کاهش عمق نهایی آبشستگی بین 30 تا 76 درصد شد. | ||
| کلیدواژهها | ||
| بافل؛ جانمایی موانع؛ سرریز اوجی؛ فرسایش موضعی | ||
| عنوان مقاله [English] | ||
| Effect of V-shaped Blocks on Local Scour Downstream of Ogee Spillway | ||
| نویسندگان [English] | ||
| Hamed Shahsavari1؛ Sobhan Moradi2؛ Ali Parmodeh2؛ kazem Esmaili3 | ||
| 1ferdowsi university of mashhad | ||
| 2ferdowsi university of mashhad | ||
| 3Associate Professor, Water Sciences and Engineering Department. Ferdowsi University of Mashhad, Mashhad, Iran. | ||
| چکیده [English] | ||
| Abstract Introduction Flow over spillways has a great amount of potential energy, which is converted into kinetic energy downstream control structures. This energy should be dissipated to prevent the possibility of excessive scouring of the downstream waterway bed, minimize erosion and undermining of structures, which endanger the structure safety. Local scour downstream is usually one of the most important issues in designing process of hydraulic structures, which is mainly some applications have been proposed to reduce this occurrence. Present study has been carried out on the effects of V-shaped baffle piers in order to reduce the local scour downstream of the ogee spillway. Methodology Experiments were carried out in a flume which is 6 m long, 0.5 m wide and 0.6 m deep with horizontal bed slope. A pump with a maximum discharge capacity of 14 lit/s circulated water from sump. A movable weir located at downstream of flume controlled water level. The hydraulic and geometric characteristics of these baffle piers were investigated with three different discharges (20, 24 and 28 Lit/s.m). The positions and height of these blokes were presented to decrease the amount of scour downstream. The position and height parameters were defined based on the length of stilling basins as follows respectively, Lb/Lf=(0.22, 0.44, 0.66, 0.88) and Hb/D=(0.66, 1, 1.33, 2). The test area in the channel was 2 m long and 12 cm in height, 2.5 m from the beginning of the channel. The experiments were carried out using non cohesive sediments with median diameter of 0.72 mm, specified gravity of 2.65 and geometric standard deviation of 1.12. Results and Discussion The presence of the block decreases the final depth of scour and the length of the scour which shows the role of the blocks and their role in this case. According to laboratory observations, the existence of the block distinguishes three types of flow around it. The first is a flow that jumps above the block. The second is the convergence flow between the blocks and the third the eddy flow that forms in front and inside the blocks. The presence of the block and the three types of flows resulted in greater turbulence and reduced jump energy, resulting in a shorter jump length and an earlier secondary depth. Taken together, these factors reduce the flow strength at the bottom of the plate and also cause less sediment transport downstream. The more the Froude number increases, the more stable the jump is due to the category of jump types. (Depending on the group of jumps created in this study) The amount of scour depth decreases due to the presence of blocks. Also, the result indicates that by decreasing the distance of baffle from weir toe, the length and the depth of scour have been remarkably diminished. Meanwhile the raise of baffle height decreases the scour depth across a longitudinal section. In addition, in different block positioning, as the height of the blocks increases, the length of the scour decreases. So that block with height (Hb/D=2) has a significant decrease during scouring compared to block with height (Hb/D=0.66). Conclusion Overall, the suitable geometrical condition proposed in order to reduce this sediment deposition which is propose based on length of stilling basins and Froude number as, Hb/D=2, Lb/Lf=0.22 It assumes that the scour depth is decreased between 30 to 76 percent and the scour length is decreased between 57 to 71 percent. The present study demonstrates the importance of positioning the blocks and their height at different Froude numbers. Therefore, pre-execution modeling is suggested for better conclusions to achieve the best position and height of the block. | ||
| کلیدواژهها [English] | ||
| Baffle, Local Scouring, Locating blocks, Ogee Spillway, V-shaped blocks | ||
| مراجع | ||
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Amin, A.M.A. (2015). Physical model study for mitigating local scour downstream of clear over-fall weirs. Ain Shams Engineering Journal, 6(4),1143-1150. Aydin, M.C. & Ulu, A.E. (2018). Effects of different shaped baffle blocks on the energy dissipation and the downstream scour of a regulator. Journal of Science and Technology. 8(2), 69–74. Beirami, M.K. (2013). Water Conveyance Structures. Isfahan: Isfahan University of Technology. Blaisdell, F. W. (1948). Development and hydraulic design, Saint Anthony Falls stilling basin. Transactions of the American Society of Civil Engineers, 113(1), 483-520. Chahardahcheriki gholi zadeh. P., & Shafai-Bajestan, M. (2016). Scour Dimensions of the Downstream Hydraulic Jump Stilling Basin with Bed Covered with Six-Legs Elements. Irrigation and Drainage Structures Engineering Research, 17(66), 105-118. (In Persian) Dargahi, B. (2003). Scour development downstream of a spillway. Journal of hydraulic Research, 41(4),417-426. Dey, S. and Sarkar, A. (2006). Response of velocity and turbulence in submerged wall jets to abrupt changes from smooth to rough beds and its application to scour downstream of an apron. Journal of Fluid Mechanics, 556, 387-419. El-Azab, E. E. D. Y. (2014). Minimizing scour downstream of hydraulic structures using single line of floor water jets. Ain Shams Engineering Journal, 5(1), 17-28. El-Masry, A.A. (2001). Minimization of scour downstream heading-up structures using double line of angle baffles. In Proc of 6th international water technology conference (IWTC). March 23–25. Alexandria, Egypt. El-Masry, A. A., & Sarhan, T. E. (2000). Minimization of scour downstream heading-up structure using a single line of angle baffles. Engineering Research Journal of Helwan University, 69. Farhoudi, J. & Smith, K.V.H. (1985). Local scour profiles downstream of hydraulic jump. Journal of Hydraulic Research, 23(4), 343-358. Hamidifar, H. Omid, M. H. Nasrabadi, M. (2011). Scour downstream of a rough rigid apron. World Applied Sciences Journal, 14(8), 1169-1178. Koochak, P., & Shafai-Bajestan. M. (2011). The effect of horizontal plate roughness and bed sedimentary materials on their downstream scour. Iranian Journal of Watershed Management Science and Engineering. 6(17), 23-30. (In Persian) Oliveto, G., & Comuniello, V. (2009). Local scour downstream of positive-step stilling basins. Journal of Hydraulic Engineering, 135(10), 846-851. Raudkivi, A. J. & R. Ettema (1983). Clear-water scour at cylindrical piers. Journal of Hydraulic Engineering, 109(3), 338-350. Rice, C. E., & Kadavy, K. C. (1993). Protection against scour at SAF stilling basins. Journal of Hydraulic Engineering, 119(1),133-139. Taebi, H,. Fathi-Moghadam M., & Shafai-Bajestan, M. (2011). Estimating riprap size to prevent scouring in downstream of stilling basins (Case study: Namrood Dam(. Iranian Water Researches Journal. 5(8), 23-32. (In Persian) Vischer DL, & Hager WH. (1995). Energy dissipators. Swiss Federal Institute of Technology, Zurich, Switzerland. Zolghadr. M. & Shafai Bejestan. M. (2018). Effect of Six-Leg Elements installation arrangement on bed topography around Wing-Wall Abutments. Journal of Water Resources Engineering, 11(36), 47-58. (In Persian) | ||
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