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مطالعه آزمایشگاهی ضریب شزی در آبراهه های با شکل بستر | ||
| تحقیقات مهندسی سازه های آبیاری و زهکشی | ||
| دوره 22، شماره 84، آبان 1400، صفحه 89-104 اصل مقاله (1.05 M) | ||
| نوع مقاله: مقاله پژوهشی | ||
| شناسه دیجیتال (DOI): 10.22092/idser.2021.355441.1481 | ||
| نویسندگان | ||
| مصطفی حیدری1؛ محمد بهرامی یاراحمدی* 2؛ محمود شفاعی بجستان3 | ||
| 1کارشناس ارشد مهندسی عمران-آب و سازه های هیدرولیکی؛ گروه سازه های آبی دانشکده مهندسی آب و محیط زیست دانشگاه شهید چمران اهواز، اهواز، ایران | ||
| 2استادیار گروه سازه های آبی دانشکده مهندسی آب و محیط زیست دانشگاه شهید چمران اهواز، اهواز، ایران | ||
| 3استاد گروه سازه‌های آبی دانشکده مهندسی آب و محیط زیست دانشگاه شهید چمران اهواز، اهواز، ایران | ||
| چکیده | ||
| تعیین شرایط هیدرولیکی جریان در کانال‌های با بستر رسوبی مستلزم اطلاع دقیق از مقاومت جریان و ضریب شزی می‌باشد که برخلاف کانال‌های صلب علاوه بر اندازه زبری، به شکل بستر نیز بستگی دارد. به منظور بررسی میزان تاثیر اندازه ذرات بر مقاومت ناشی از شکل بستر، این مطالعه انجام گردید. شکل‌های بستر بصورت مصنوعی ساخته شدند و دو اندازه رسوبات (51/0 و 18/2 میلیمتر) بر سطح آنها چسبانده شد. آزمایش‌ها تحت تاثیر شیب‌های مختلف و شرایط هیدرولیکی متفاوتی در یک فلوم مستقیم آزمایشگاهی به طول 12 متر انجام شد. نتایج نشان داد که بطور کلی با افزایش شیب بستر و اندازه ذرات، مقاومت در مقابل جریان افزایش و یا ضریب شزی مربوط به ذره ذره ((C_b ) ́)، ضریب شزی مربوط به شکل بستر (C_b^'') و ضریب شزی کل (C_b) کاهش می‌یابند. نتایج نشان می‌دهد که ضریب شزی مربوط به ذره ((C_b ) ́) برای ذرات با اندازههای 51/0 و 18/2 میلیمتر بطور متوسط بهترتیب 98 و 93 درصد بیش از ضریب شزی کل (C_b) و 71 و 65 درصد بیش از ضریب شزی مربوط به شکل بستر (C_b^'') است. علاوه بر این ضریب شزی مربوط به شکل بستر (C_b^'') برای ذرات با اندازههای 51/0 و 18/2 میلیمتر بطور متوسط بهترتیب 16 و 17 درصد بیش از ضریب شزی کل (C_b) می‌باشد. | ||
| کلیدواژه‌ها | ||
| تلماسه؛ شکنج؛ ضریب شزی؛ شکل بستر؛ مقاومت جریان | ||
| عنوان مقاله [English] | ||
| Experimental Study of Chezy Coefficient in Open Channels with Bed Forms | ||
| نویسندگان [English] | ||
| Mostafa Heydari1؛ mohammad bahrami yarahmadi2؛ Mahmood Shafai Bejestan3 | ||
| 1M.Sc. in Civil Engineering (Water & Hydraulic Structures), Shahid Chamran University of Ahvaz, Ahvaz, Iran. | ||
| 2Assistant Professor, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. | ||
| 3Professor, Faculty of Water and Environmental Engineering, Shahid Chamran University of Ahvaz, Ahvaz, Iran. | ||
| چکیده [English] | ||
| Introduction Accurate estimation of flow resistance, such as Chezy coefficient, is important for calculating the hydraulic flow conditions and sediment transport in open channels. Chezy coefficient is affected by various factors: bed particles size, vegetation, irregularity of waterway cross-section, irregularity of waterway path, scour and sedimentation, presence of obstructions, suspended and bed load, and bed form (Bahrami Yarahmadi & Shafai Bejestan, 2010, 2011). Previous researches, Talebbeydokhti et al. (2006), Omid et al. (2010), Nasiri Dehsorkhi et al. (2011), Chegini & Pender (2012), Kabiri et al. (2014), and Kwoll et al. (2016), have shown that the bed forms can affect the hydraulic or sediment transport characteristics. However, there is a lack of study to investigate the effect of bed forms with different sediment sizes on the Chezy coefficient. Therefore, the present study aims to conduct experiments on a straight channel whose bed is covered with the artificial bed forms made from P.V.C sheet, and on its surface is glued sediment of different sizes in the range of 0.51 and 2.18 mm. Methodology The experiments were performed in a straight flume of 12 m in length and 0.30 m wide (Figure 1). In this study, different flow discharge of 10, 15, 20, 25, and 30 l/s and different bed slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 were tested. Two series of experiments were carried out: plane bed or bed without form and bed covered with form. Each form was made in a triangular shape with a P.V.C sheet. The form's length and height were equal to 20 and 4 cm, respectively, and the angles of its upstream and downstream to the horizon were selected as 16.4 and 32 degrees, respectively. After each form was built, the desired sediment size was glued to their surface. This study used two types of uniform granulation with average sizes (d50) of 0.51 and 2.18 mm. The total number of experiments in the present study was 100. Since in alluvial rivers with bed form, the resistance Chezy coefficient includes the grain Chezy coefficient and the form Chezy coefficient. A formless bed, covered with the same sediment size, was tested to determine the grain Chezy coefficient ((C_b ) ́). The bed with the form was used to determine the total Chezy coefficient (C_b) and the form Chezy coefficient (C_b^''). Ripple and dune form is formed in a lower flow regime, in which the Froude number of the flow is less than 1 (Shafai Bajestan, 2008). In this study, the Froude number values in all tests with bed form were 0.435 to 0.6, indicating a lower flow regime. Results and discussion Figure 3 shows the changes in the total Chezy coefficient (C_b) against Froude number for sediment-covered substrates of 0.51 and 2.18 mm. It can be seen that as the Froude number increased, the total Chezy coefficient (C_b) increased. In addition, increasing the longitudinal slope of the bed decreased C_b. Figures 4, 5 and 6 illustrate the effect of sediment particles size on (C_b ) ́, C_b^'', and C_b. These figures show that (C_b ) ́, C_b^'', and C_b decreased with increasing particles size. In addition, Figures 5 and 6 show that with increasing R/∆, the total Chezy coefficient (C_b) and the form Chezy coefficient (C_b^'') increased. Calculations showed that the value of C_b^'' in beds with a sediment size of 0.51 mm for slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 was, on average, 14, 12, 12, 15, and 16.4% more than 2.18 mm sedimentary beds, respectively. In addition, the value of C_b in beds with a sediment size of 0.51 mm for slopes of 0, 0.0001, 0.0005, 0.001, and 0.0015 was, on average, 15, 13, 13, 16, and 16.5% more than 2.18 mm sedimentary beds, respectively. The results of Table 1 shows that the grain Chezy coefficient ((C_b ) ́) for particles with sizes of 0.51 and 2.18 mm was, on average, 98 and 93% more than the total Chezy coefficient (C_b), respectively. In addition, The form Chezy coefficient (C_b^'') for particles with sizes of 0.51 and 2.18 mm was, on average, 16 and 17% more than the total Chezy coefficient (C_b), respectively. Conclusions The results of this study shows that generally with increasing the bed slope and the bed particle size of movable bed sediment channel, the flow resistance increases or the total Chezy coefficient , the form Chezy coefficient and the grain Chezy coefficient decreases. Increasing the bed particle size from 0.51 to 2.18 mm reduced the coefficients of Cb ́, Cb'', and Cb by 15.14, 12, and 12.9%, respectively. Moreover, the value of Cb ́, Cb'', and Cb in sedimentary beds with particles of 0.51 mm were, on average, 18, 14 and 15% more than sedimentary beds with particles of 2.18 mm, respectively. Keywords: Bed form, Chezy coefficient, Dune, Resistance to flow, Ripple. | ||
| کلیدواژه‌ها [English] | ||
| Bed form, Chezy coefficient, Dune, Resistance to flow, Ripple | ||
| مراجع | ||
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Bahrami Yarahmadi, M. & Shafai Bejestan, M. (2010). Effect of shape of sediment particles at the bed of open channel on friction coefficient. Journal of Irrigation Sciences and Engineering, 33(1), 1-13. (In Persian) Bahrami Yarahmadi, M. & Shafai Bejestan, M. (2011). Experimental study of the effect of sediment particles shape on Manning's coefficient. Journal of Water and Soil, 25(1), 51-60. (In Persian) Chegini, A.H.N. & Pender, G. (2012). Determination of small size bed load sediment transport and its related bed form under different uniform flow conditions. WSEAS Transactions on Environment and Development, 8(4), 158-167. Daghigh, H., karami Khaniki, A. & Ali Akbari Bidokhti, A. (2017). Evaluation of sandy bed ripples geometry using physical model and correcting existed practical relations factors. Iranian Journal of Marine Technology, 4(1), 64-74. (In Persian) Davarpanah-Jazi, S., Kabiri-Samani, A.R. & Afzalimehr, H. (2016). Effects of straight-crested gravel bed-forms and vegetated banks on turbulent flow characteristics. Modares Civil Engineering Journal, 16(2), 103-115.(In Persian) Dey, S. (2014). Fluvial Hydrodynamics: Hydrodynamic and Sediment Transport Phenomena. Springer-Verlag Berlin Heidelberg, 687P. Esmaili, K., Kashefipour, S.M. & Shafaie Bajestan, M. (2009). The effect of bed form on roughness coefficient in unsteady flows using a combined numerical and laboratory method. Journal of Water and Soil, 23(3), 136-144. (In Persian) Farhoudi, J., & Esmaeili Varaki, M. (2010). Erosion and Sedimentation. University of Tehran Press, 317P. (In Persian) Ghasemi, M., Heidarpour, M. & Tabatabaei S.H. (2016). Investigation of distribution of velocity and turbulence intensity in presence of dunes and vegetation in a rectangular open channel. Journal of Hydraulics, 10(3), 1-14. (In Persian) Julien, P.Y. (2010). Erosion and sedimentation. 2nd edition, Cambridge University Press, 390P. Kabiri, F., Afzalimehr, H., Smart, G. & Rousseau, A.N. (2014). Flow over gravel dunes. British Journal of Applied Science & Technology, 4(6), 905-911. Karbasi, M. (2005). Investigation of the effect of bed load movement on hydraulic resistance of flow in the presence of bed forms (M. Sc. Thesis), Faculty of Agriculture, University of Tehran. (In Persian) Kwoll, E., Venditti, J.G., Bradley, R.W. & Winter, C. (2016). Flow structure and resistance over subaquaeous high- and low-angle dunes. Journal of Geophysical Research: Earth Surface, 121, 545–564. Mahmoodian Shooshtari, M. (2006). Principles of flow in open Channel. First volume, Shahid Chamran University of Ahvaz Press, 513P. (In Persian) Nasiri Dehsorkhi, E., Afzalimehr, H. & Singh, V. P. (2011). Effect of bed forms and vegetated banks on velocity distributions and turbulent flow structure. Journal of Hydrologic Engineering, 16(6), 495-507. Omid, M.H., Karbasi, M. & Farhoudi, J. (2010). Effects of bed-load movement on flow resistance over bed forms. Sadhana, 35(6), 681-691. Ranga-Raju, K.G. & Soni, J.P. (1976). Geometry of ripples and dunes in alluvial channels. Journal of Hydraulic Research, 14(3), 241-249. Roshani, E., hossienzade dalir, A., farsadizade, D. & salmasi, F. (2017). Study of width reduced transition effects on ripple bed form height in various hydraulic conditions. Journal of Water and Soil, 31(1), 28-39. (In Persian) Simons, D.B. & Richardson, E.V. (1966). Resistance to flow in alluvial channels. Geological survey Professional paper, 422-J. Samadi-Boroujeni, H., Maleki, P., Fattahi-Nafchi, R. & Ketabdari, M.J. (2014). Experimental study on the effect of the parallel and flake ripple bed forms on the Manning roughness coefficient. Journal of Hydraulics, 8(4), 55-65. (In Persian) Shafai Bajestan, M. (2008). Basic theory and practice of hydraulics of sediment transport. Second edition, Shahid Chamran University of Ahvaz Press. 549P. (In Persian) Talebbeydokhti, N., Hekmatzadeh, A.A. & Rakhshandehroo, G.R. (2006). Experimental modeling of dune bed form in a sand-bed channel. Iranian Journal of Science and Technology, Transaction B, Engineering, 30(B4), 503-516. Yang, C.T. (1996). Sediment transport: Theory and practice. McGraw-Hill, 396P. | ||
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