تأثیر قطر و رقوم کارگذاری طوق نیم‌دایره‌ای بر میزان عمق آبشستگی و الگوی جریان پیرامون تکیه‌گاه پل

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری سازه های آبی، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران.

2 دانشجوی دکتری سازه های آبی، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد مشهد، ایران.

3 استاد تمام گروه علوم و مهندسی آب، گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه فردوسی مشهد، مشهد، ایران.

چکیده

کاهش آبشستگی برای جلوگیری از تخریب سازه­های هیدرولیکی که در مسیر جریان­های آبی قرار می­گیرند، امری اجتناب­ناپذیر است. در این تحقیق به بررسی اثربخشی طوق نیم­دایره­ای بر کاهش عمق آبشستگی در اطراف تکیه­گاه با هدف مشخص شدن تغییرات الگوی جریان در اطراف این سازه پرداخته شد. آزمایش­ها در شرایط آبشستگی آب­زلال و طوق­ها به شکل نیم­دایره­ای بر روی تکیه­گاه­های نیم­دایره­ای در دو اندازه L5/1و L2 (L طول تکیه­گاه در برابر جریان) و در سه تراز مختلف نسبت به بستر، هم‌تراز بستر و L2/0 زیر و بالای بستر مورد بررسی قرار گرفتند. نتایج نشان داد که وجود طوق علاوه بر کاهش میزان عمق نهایی آبشستگی موجب تأخیر در روند آبشستگی نیز شده است، که این اثر بخشی با افزایش اندازه طوق بیشتر مشاهده می­گردد. به­علاوه تراز قرارگیری طوق­های با اندازه برابر می­تواند موجب عملکرد بهتر طوق و در نتیجه کارآمدی آن در هزینه تمام شده طرح باشد. با توجه به نتایج آزمایش­ها طوق با اندازه L2 و قرارگیری در زیر بستر عملکرد بهتری از خود نشان داد و موجب کاهش 58 درصدی عمق نهایی آبشستگی نسبت به تکیه­گاه شاهد شد. همچنین با بررسی مشخصات جریان در اطراف تکیه­گاه در شرایط با و بدون طوق مشخص گردید که طوق باعث کاهش مقادیر سرعت در جهات مختلف بخصوص در بالادست تکیه­گاه می­شود و تأثیر آن بر روی جریان روبه­پایین، موجب کاهش قدرت گرداب­ها و تغییر رفتار رفت و برگشتی و جابجایی موقعیت گرداب­ها می­گردد. به طوری که وجود طوق مقدار ماکزیمم سرعت جریان روبه­پایین را در بالادست تکیه­گاه به میزان 39 درصد کاهش داده است.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Influence of Semicircular Collar Diameter and Its Alignment on Scour Depth and Flow Pattern around Bridge Abutment

نویسندگان [English]

  • hamed shahsavari 1
  • sobhan moradi 2
  • Saeedreza Khodashenas 3
1 Student of phd in the field of Hydraulic Structures, Agricultural College, Ferdowsi University of Mashhad , Mashhad, Iran .
2 Student of phd in the field of Hydraulic Structures, Agricultural College, Ferdowsi University of Mashhad , Mashhad, Iran .
3 Prof., Department of Water Engineering, Agricultural College, ferdowsi University of mashhad, mashhad, Iran.
چکیده [English]

Reducing scouring is inevitable to prevent the destruction of hydraulic structures on the water flows. In this research, the effect of semicircular collar on the reduction of scour depth around the abutment was investigated with the aim of identifying the flow pattern changes around this structure. Experiments were carried out under clear water conditions. Semicircular collars were examined on semicircular abutments in two sizes 1.5L and 2L (L is abutment length against the flow) and at three different levels relative to the bed; bed alignment, 0.2L below and 0.2 above the bed. The results showed that the existence of the collar, in addition to reducing the final scour depth, caused a delay in the scouring process. This effect has also been increased by increasing the size of the collar. In addition, the position of collars with the same size can improve collar performance and efficiency on the design cost. Based on the results of the experiments, the collar with 2L size and under the bed showed better performance and reduced the final scour depth by 58% compared to the control abutment. Also, according to the experiments, the position of the collar under the bed showed better performance. By investigating the flow pattern around the abutment in conditions with and without collar, it was found that the collar reduces the flow velocity in different directions, especially in the upstream of the abutment. Also, its effect on downflow reduces the strength of the vortices and changes the reciprocating behavior and displacement of the vortices. So that the presence of collar has reduced the maximum downflow velocity at the upstream abutment by 39%.

کلیدواژه‌ها [English]

  • Clearwater
  • Scouring
  • Flow pattern
  • Abutment
  • Collar
Afzalimehr, H., Bakhshi, S., Gallichand, J. and Sui, J. (2014), “Effect of Vegetaded-banks on Local Scour around a Wing-wall Abutment with Circular Edges”, Journal of Hydrodynamics, 26(3), pp 447-457.

Afzalimehr, H., Moradian, M., & Singh, V. P. (2017). Flow Field around Semielliptical Abutments. Journal of Hydrologic Engineering, 23(2), 04017057.‏

Ahmed, F., & Rajaratnam, N. (1998). Flow around bridge piers. Journal of Hydraulic Engineering, 124(3), 288-300.‏

Ardeshir, A., Cheraghi, R. and Karami, H., (2013) “Experimental Study of Effect of Collar on Local Scour Reduction around Vertical and 45˚ Wing wall Abutments”, Journal of Civil Engineering, 24(1), pp. 59-70. (In Farsi).

Barbhuiya, A.K. and Dey, S. (2003), “Vortex Flow Field in a Scour Hole around Abutments”, International Journal of Sediment Research, 18(4), pp 1-16.

Dargahi B. (1990). Controlling mechanism of local scouring. Journal of Hydraulic Engineering. 116(10): 1197-1214.

Ettema, R., Constantinescu, G. and Melville, B.W. (2017). Flow-field complexity and design estimation of pier-scour depth: Sixty years since Laursen and Toch (Doctoral dissertation, American Society of Civil Engineers).

Ettema, R., Nakato, T. and Muste, M., (2010). Estimation of scour depth at bridge abutments. NCHRP 20-24. Transportation Research Board, Washington, DC.

Foti, S. and Sabia, D. (2011). “Influence of scour of foundations on the dynamic response of an existing bridge.” Journal of Bridge Engineering, Vol. 16, No. 3, pp. 295-304.

Hong, S. H., Sturm, T. W., & Stoesser, T. (2015). Clear Water Abutment Scour in a Compound Channel for Extreme Hydrologic Events. Journal of Hydraulic Engineering, 141(6), 04015005.‏

Karami, H., Hosseinjanzadeh, H., Hosseini, K., & Ardeshir, A. (2018). Scour and three-dimensional flow field measurement around short vertical-wall abutment protected by collar. KSCE Journal of Civil Engineering, 22(1), 141-152.‏

Kayaturk, S.Y., Kokpinar, M.A. and Gogus, M (2004)."Effect of Collar on Temporal Development of Scour around Bridge Abutments", 2nd International Conference on scourand erosion, IAHR, Singapore, 14-17 November, pp. 180-186.

Khosravi Nia, P., Hosseinzadeh Dalir, A., Farsadizadeh, D., Fakheri - Fard, A. (2014). 'Effect of Collar on Scour Reduction Around Abutments', Water and Soil Science, 21(1), pp. 15-28. (In Farsi).

Khozeymehnezhad, H., Ghomeshi, M. (2016). 'Experimental Investigation of Collar Performance with Rough Surface on Local Scour Reduction around Bridge Abutment with Rectangular Section', Water and Soil Science, 26(1-1), pp. 213-223. (In Farsi).

Khozeymehnezhad, H., ghomeshi, M., hafaeeibajestan, M. (2014). 'Comparison of Symmetrical and Unsymmetrical Rectangular Collars on Reduction of Local Scour at Bridge Abutment', Irrigation Sciences and Engineering, 37(2), pp. 1-12. (In Farsi).

Koken, M., & Constantinescu, G. (2014). Flow and turbulence structure around abutments with sloped sidewalls. Journal of Hydraulic Engineering, 140(7), 04014031.‏

Kumar, V., Raju, K.G.R. and Vittal, N., (1999). Reduction of local scour around bridge piers using slots and collars. Journal of Hydraulic Engineering, 125(12), pp.1302-1305.

Lança, R. M. Fael, C. S. Maia, R. J. Pêgo, J. P. and Cardoso, A. H. (2013). Clear-water scour at comparatively large cylindrical piers. Journal of Hydraulic Engineering, 139(11), pp. 1117-1125.

Li, H.M.T., Kuhnle, R. and Barkdoll, B.M.T., (2005). Countermeasures against scour at abutments. Lab Publ, 49, p.150.

MacBroom, J. G. (2012). Bridge scour and sediment analysis for river restoration projects, Paper presented at the World Environmental and Water Resources Congress, Albuquerque, NM, DOI: 10.1061/ 9780784412312.252.

Mashair, M.B., Zarrati, A.R. and Rezayi, A.R (2004). "Time Development of Scouring around a Bridge Pier Protected by Collar", 2nd International Conference on Scour and Erosion, ICSE-2, Singapore, 8 p.

Melville, B. W (1992)."Local Scour at Bridge Abutments", Journal of Hydraulic Engineering, Vol. 118, pp 615-631.

Muzzammil, M .and T. Gangadhariah. (2003). The mean characteristics of horseshoe vortex at a cylindrical pier. J. Hydraul. Res. 41: 285-297.

Raudkivi, A. J. and Ettema, R. (1983). Clear-Water scour at cylindrical piers. Journal of Hydraulic Engineering. 109(3), pp. 338-350.

Shafai Bajestan, M. 1994. Hydraulics of Sediment. Ahvaz. univ. press. 327p. (In Farsi).

Sui, J., Hicks, F. and Menounos, B. (2006), “Observations of Riverbed Scour under a Developing Hanging Ice Dam”, Canadian Journal of Civil Engineering, 33(2), pp 214-218.

Wang, J., Sui, J. and Karney, B.W. (2008), “Incipient Motion of Non-cohesive Sediment under Ice Cover”, Journal of Hydrodynamics, 20(1), pp 117-124.