شبیه‌سازی آبشستگی پایین دست کف‌بند افقی با استفاده از مدل عددی

یکی از مهمترین عوامل آسیب و تخریب سازه‌های هیدرولیکی، وقوع آبشستگی موضعی است. در بررسی و مطالعه سازه‌های هیدرولیکی درون رودخانه‌ای ، تعیین میزان فرسایش و رسوب گذاری امری ضروری است. تعیین مقدار فرسایش و یا رسوبگذاری در زمانی که یک سازه هیدرولیکی اجرا شده است، می‌تواند از تخریب سازه و تغییر ژئومرفولوژی رودخانه ممانعت بعمل آورد و باعث کاهش هزینه های اقتصادی شود. در این تحقیق کارایی مدل عددی flow 3d به منظور شبیه‌سازی آبشستگی پایین دست کف بند افقی مورد بررسی قرار گرفت. نتایج صحت سنجی این مدل عددی با مدل آزمایشگاهی ولی زاده و همکاران نشان‌دهنده قابلیت مدل مذکور در شبیه سازی پدیده مورد نظر بود. با توجه به ماهیت بستر و کارایی کف‌بند افقی، از سناریوهای مختلف شبیه سازی استفاده شد که این سناریوها شامل پنج عدد فرود، سه ضریب زبری مانینگ و یک قطر ذره به میزان 1.8 میلیمتر برای پایین دست کف بند افقی می باشد. نتایج حاصل از شبیه سازی نشان داد که با افزایش ضریب زبری، سرعت جریان گذرنده و آبشستگی پایین دست نیز کاهش یافته است. علاوه بر این، نتایج این پژوهش نشان داد که با افزایش ضریب زبری، رسوب گذاری و تنش برشی افزایش یافته است. با توجه به تاثیر پذیری پدیده آبشستگی و رسوبگذاری نسبت به عدد فرود، نتایج نشان داد که با افزایش عدد فرود نیز آبشستگی افزایش یافت.

numerical simulation of scouring downstream of horizontal apron

introduction scouring occurs when the shear stress of the flow in the river is greater than the critical shear stress of the materials forming the bed. one of the kinds of scouring is the scouring of the bottom of the horizontal apron. the horizontal apron is one of the in-river structures, which is used downstream of stilling basin and as a bed for in-river structures. one of the most important problems of using aprons is their downstream scouring. because the stream flows after passing through the aprons erodes the alluvial bed of the river and causes the erosion to intensify after that. therefore, before using this protective structure, an accurate estimate of the erosion rate should be obtained.methodology in this research, the numerical simulation downstream of the horizontal apron using the flow3d model, for three manning’s roughness coefficients of 0.025, 0.02 and 0.014, five froude numbers were 0.32, 0.3, 0.25, 0.2, and 0.15 and also for a particle diameter of 1.8 mm, a total of 15 currents tests were simulated. after comparing the data of this research with the laboratory data of valizadeh et al. (1401), the validation of the model done accepted according to numerous implementations, finally nelson's sediment transport model with the k-ε turbulence model had the most accuracy with the laboratory results.results and discussion according to the results of the numerical model, it was observed that in all the scenarios related to the roughness coefficients, with the increase of the roughness coefficient of the apron, the amount of the maximum amount of scouring decreases. the reason for this is the increase in resistance to the flow in the aprons area, which reduces the scouring rate in the downstream. also, with the increase of froude number, the starting point of the scour hole has become closer to the bottom of the apron, and with the decrease of the froude number, the scour hole has occurred in a place further away from the bottom of the apron. the reason for this is related to the strength of the flow in higher froude numbers. in addition, with the increase in velocity, the amount of shear stress has decreased. according to manning's equation, velocity decreases with increasing depth; as a result, it increases the shear stress in the scouring area. it was also demonstrated that the shear stress decreases with the increase of froude number and decrease of bed depth.conclusions the results showed that with the increase of the roughness factor of the horizontal apron, the amount of the maximum scour hole decreases. also, with the increase of froude number, the starting place of the scour pit has become closer to the bottom of the horizontal apron, and with the decrease of the froude number, the scour hole has occurred in a place further away from the bottom of the apron.also, the results show that the rate of erosion increases with the increase in velocity along the apron. according to manning's equation, velocity increases with decreasing depth; as a result, it increases the erosion along the horizontal apron. it was also observed that with the decrease of froude number and increase of bed depth, erosion decreases and subsequently sedimentation increases.