مطالعه عددی خصوصیات جریان در آبراهه روباز مرکب با پوشش گیاهی لایه‌ای ناهمگون در سیلابدشت

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه علوم و مهندسی آب، دانشکده کشاورزی، دانشگاه بوعلی سینا، همدان، ایران

2 گروه مهندسی آبیاری و آبادانی، دانشکده کشاورزی و منابع طبیعی کرج، دانشگاه تهران، کرج، ایران

چکیده

پوشش گیاهی نقش اساسی در تغییر خصوصیات جریان آبراهه‌های طبیعی مانند رودخانه‌ها دارد. مدلسازی کارآمد هیدرولیک جریان در آبراهه مرکب با سیلابدشت‌های دارای پوشش گیاهی برای درک و تعیین فرآیندهای طبیعی جریان ضروری است. آبراهه‌های طبیعی و یا انسان‌ساخت اغلب دارای پوشش گیاهی گوناگون با تراکم و ارتفاع‌های متفاوت هستند. هدف اصلی این پژوهش بررسی تاثیر پوشش گیاهی لایه‌ای بر خصوصیات جریان در آبراهه‌ مرکب با استفاده از مدل FLOW-3D می‌باشد. نتایج مدل عددی با نتایج نظیر از مدل فیزیکی تحقیق  Takuya et al., (2014)واسنجی و تایید شده است. آزمایش‌ها در سال 2014 در آزمایشگاه هیدرولیک دانشگاه ملی فناوری آکاشی در ژاپن، و در یک کانال ذوزنقه‌ای مستقیم به طول 8/4 متر و عرض 8/0 متر انجام یافت. خطای برآورد مدل برای سرعت متوسط عمقی بترتیب در مرحله واسنجی در دامنه 4 تا 6 درصد بود، که در مرحله تائید مدل به حدود 5/1 درصد کاهش یافت. متوسط خطای برآورد عمق آب نیز در حدود 3 درصد بوده است. در شبیه-سازی الگوی جریان، تطابق خوبی بین نتایج مدل عددی با نتایج مدل فیزیکی وجود دارد. نتایج شبیه‌سازی مدل نشان داد که برای شرایط سیلاب‌های بزرگتر که پوشش گیاهی در سیلابدشت مستغرق می‌شود، پروفیل عمودی سرعت در سیلابدشت ‌بصورت S شکل است. در حالی‌که در شرایط سیلاب‌های کوچکتر یا زمانی که پوشش گیاهی کوتاه و بلند غیرمستغرق باشند، پروفیل سرعت عمودی دارای توزیع نسبتا یکنواخت یا لگاریتمی است. مقاومت ناشی از حضور پوشش گیاهی در سیلابدشت‌ها سبب کاهش سرعت جریان در ناحیه سیلابدشت رودخانه، و همچنین افزایش ظرفیت انتقال بده جریان در آبراهه اصلی می‌گردد.

کلیدواژه‌ها

عنوان مقاله [English]

Flow characteristics in a compound channel with double-layer vegetated floodplains: a numerical study

نویسندگان [English]

  • fariba ahmadi dehrashid 1
  • Mehdi Yasi 2
  • majid heidari 1
1 Department of Water Science and Engineering, Faculty of Agriculture, University of Bu Ali Sina, Hamedan, iran
2 Department of Irrigation and Reclamation Engineering, College of Agriculture and Natural Resources, University of Tehran, Karaj, Iran
چکیده [English]

Vegetation plays an essential role in modifying the flow characteristics of natural channels, such as rivers. Efficient hydraulic modeling of flow in compound channels with vegetated floodplains is necessary to understand and identify natural flow processes. In both natural and artificial channels, there are various types of vegetation with differing densities and heights. The main goal of this study is to investigate the effect of double-layered vegetation on flow characteristics in compound channels using the FLOW-3D model. The results of the numerical model have been calibrated and validated with the results of the physical model of the research of Takuya et al., 2014. Experiments were conducted in 2014 in the hydraulic laboratory of the Akashi National University of Technology in Japan, and in a straight trapezoidal channel with a length and width of 4.8 and 0.8 m respectively. During calibration, the model's estimation error for the depth-averaged velocity was within 4 to 6%, which was reduced to approximately 1.5% during validation. The average error in water depth estimation was around 3%. The numerical and physical models showed good agreement in simulating the flow pattern. The numerical model showed that, for larger floods when vegetation is submerged, the vertical profile of velocity in the floodplain is S-shaped. However, during smaller floods or when short and tall vegetation is emergent, the vertical velocity profile is relatively uniform or logarithmic. The resistance caused by the presence of vegetation in the floodplains leads to a decrease in the flow velocity in the floodplain area of the river and an increase in the capacity of flow transfer in the main channel.

کلیدواژه‌ها [English]

  • Double-layered vegetation
  • Mixing layer
  • Numerical modeling
  • Physical model
  • Velocity profile

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تحقیقات آب و خاک ایران
دوره 53، شماره 11
بهمن 1401
صفحه 2515-2531

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