عملکرد فواصل عناصر‌ زبری در کاهش عمق آبشستگی و تأثیر آن‌ها روی پروفیل‌های سرعت قائم اطراف تکیه‌گاه پل

نویسندگان

1 کارشناسی ارشد سازه‌های آبی، دانشکده کشاورزی، دانشگاه صنعتی اصفهان

2 استاد گروه مهندسی آب دانشکده کشاورزی، دانشگاه صنعتی اصفهان

3 مربی گروه مهندسی آب دانشکده کشاورزی، دانشگاه صنعتی اصفهان

چکیده

      در ﻣﻮرد ﺗﺨﺮﯾﺐ پل‌ها، ﺳﯿﻠﯽ ﮐﻪ ﻣﻨﺘﺞ ﺑﻪ آبشستگی می‌شود اصلی‌ترین ﻋﺎﻣﻞ ﺷﮑﺴﺖ پل‌ها ﺷﻨﺎﺧﺘﻪ شده است. از این رو یافتن راه­کاری برای کاهش عمق آبشستگی حیاتی می­باشد. در این تحقیق اثرات زبری­های موضعی با فواصل متفاوت، برای تکیه­گاه نیم­دایره­ای تحت شرایط آبشستگی آب­زلال مورد بررسی قرار گرفت. نتایج نشان داد که وجود زبری باعث کاهش در روند آبشستگی و کاهش 47% درصدی عمق نهایی آبشستگی می­شود. ارتباط معناداری بین عملکرد زبری­ها و فاصله بین آن‌ها وجود داشت. به‌طوری که وجود یک مقدار بهینه برای فاصله بین زبری­ها، عملکرد زبری را افزایش و روند آبشستگی را کاهش داد. بعلاوه، بررسی پروفیل­های سرعت قائم نشان داد که، وجود سرعت­های قائم مثبت در درون حفره در بالا­دست تکیه­گاه و هم­چنین سرعت­های منفی در اعماق بالاتر نشان دهنده وجود جریان­های رو به پایین اﺳﺖ. در نتیجه، این جریان­های رو به پایین  منجر به ایجاد ورتکس­های قوی در درون حفره آبشستگی و در جلوی تکیه­گاه می­شوند. مقایسه پروفیل جریان در اطراف تکیه­گاه حاوی زبری با تکیه­گاه شاهد نشان داد که سرعت جریان رو به پایین برای تکیه­گاه زبری­دار به مقدار قابل توجهی کاهش می­یابد. علاوه بر این، به دلیل اثر زبری بر روی پروفیل­های سرعت قائم در پایین­دست تکیه­گاه، عمق گودال آبشستگی در پشت تکیه­گاه نیز کاهش یافت. به طوری که میزان کاهش سرعت جریان قائم در جلو و پشت تکیه­گاه زبری­دار به ترتیب U13/0 و U4/0(U سرعت جریان نزدیک شونده) بود.

کلیدواژه‌ها


عنوان مقاله [English]

Performance of the Roughness Elements Distances to Reduce Scour and Their Impact on Vertical Velocity Profiles around Bridge Abutment

نویسندگان [English]

  • H Shahsavari 1
  • M Heidarpour 2
  • E Landi 3
  • A Rahiminia 1
1 M.Sc. Department of Water Engineering, Agricultural College, Isfahan University of Technology, Isfahan, Iran
2 Prof. Department of Water Engineering, Agricultural College, Isfahan University of Technology, Isfahan, Iran
3 Instructor Water Engineering Department, Agricultural College, Isfahan University of Technology, Isfahan, Iran
چکیده [English]

Among the issues related to bridges distraction, a flood which causes scouring has been known as the main reason of bridges destruction. Therefore, finding an effective solution is vital for decreasing scouring depth. In this study, the effects of local roughness elements with different distance were investigated for a semicircular abutment under clear water scouring condition. Results showed that existence of roughness reduced the scouring process and reduced the final scour depth by 47%. There was a significant relationship between roughnesses function and the distance between them. So that the existence of an optimal value for the distance between the roughnesses increased the roughness function and decreased the scouring process. In addition, the study of vertical velocity profiles revealed that existence of positive vertical velocity in the hole located at upstream of the abutment and also negative velocities at higher depths were the indicator of downflows. As a result, these downflows lead to the formation of powerful vortexes inside the scouring hole and in front of the abutment. Comparison of the flow profile around the roughened abutment with the control abutment showed that velocity of downflow is significantly reduced for abutment with roughness. Moreover, the depth of scouring hole was reduced at behind of the abutment, due to the impact of roughness on vertical velocity profiles at downstream of abutment. So that, the velocity reduction of the vertical flow in the front and behind of the roughened abutment was to 0.13 U and 0.4 U (U approaching flow velocity), respectively.

کلیدواژه‌ها [English]

  • Abutment
  • Local scouring
  • Local Roughness
  • Vertical velocity profiles
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