نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکترا، دانشگاه فردوسی مشهد، گروه مهندسی آب– سازه‎های آبی.

2 دانشیار دانشگاه فردوسی مشهد، دانشکده کشاورزی، گروه مهندسی آب

3 استاد دانشگاه فردوسی مشهد، دانشکده کشاورزی، گروه مهندسی آب.

چکیده

حفاظت از خطوط لوله انتقال َآب- فاضلاب و یا مواد سوختی، روی بستر فرسایشی دریا و رودخانهها در برابر عواملی چون خمش، لغزش و حتی شکستگی از مسائل مهم و پرهزینه در مهندسی دریا بحساب میآید. مشاهدات عینی نشان داد، خطوط لوله که بر بستر فرسایشی دریا و رودخانهها قرار گرفته، در اثر آبشستگی موضعی ایجاد شده، دچار دفن طبیعی(خوددفنی لوله) در بستر رسوبی میشود. اما در شرایط طبیعی فرآیند دفن با سرعت کمی اتفاق میافتد. از اینرو با نصب زائدهای روی خطوط لوله، سعی در افزایش سطح مقطع عمود بر جریان(ایجاد تغییرات الگوی جریان در اطراف خط لوله) و نهایتاً وقوع فرسایش در سرعتهای محیطی کمتر و با شدت بیشتر میباشد. مطالعات پیشین نشان میدهد که نصب باله در بالای خط لوله، سبب افزایش مقدار فرسایش در اطراف لوله میشود. کاربرد پیگیبکلاین(Piggyback line) نصب شده با شکل مقطع و زوایای متفاوت، روی خطوط لوله اصلی میتواند تفاوت عمدهای با تحقیقات انجام شده قبلی داشته باشد. در پژوهش حاضر، به روش پای-باکینگهام(Pi-Bukingham) تمامی متغیرهای تأثیرگذار بر ابعاد آبشستگی موضعی زیر خطوط لوله، تحلیل ابعادی شده است. و تأثیر پارامترهای بدون بعد بدست آمده مورد بررسی و تحلیل قرار گرفته است. نتایج آزمایشگاهی حاکی از آن است که، آبشستگی لوله به همراه پبگببکلاین تا 2 برابر نسبت به لوله ساده افزایش یافته است. پیگیبکلاین با شکل مقطع مثلثی، برای افزایش مقدار عمق حداکثر آبشستگی در زاویه نصب منفی 135 درجه، دارای بهترین عملکرد بوده است. و در بستر ریزدانه بطور میانگین تا 4 برابر و در بستر درشتدانه بطور میانگین تا 6 برابر عمق آبشستگی را نسبت به حالت لوله ساده افزایش میدهد.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Evaluation of the Time Development of Scour Around Pipelines With Optimization the Mounting Position of Piggyback-Line

نویسندگان [English]

  • Sobhan Moradi 1
  • Kazem Esmaili 2
  • Saeid Reza Khodashenas 3

1 Ph.D. Student, Ferdowsi University of Mashhad, Agriculture Collage, Water Structure Engineering Faculty.

2 Associate Professor,Ferdowsi University of Mashhad, Agriculture Collage, Water Engineering Faculty.

3 Professor, Ferdowsi University of Mashhad, Agriculture Collage, Water Engineering Faculty.

چکیده [English]

Protection of water pipelines - wastewater or fuel materials - on the bed of erosion of the sea and rivers against such factors as bending, slipping and even fracture are important and costly issues in ocean engineering. In order to protect the potential destruction and fracture of these pipelines due to hydrodynamic forces of flow-waves or human activities. It is necessary to be covered with a concrete-coat or buried at an appropriate depth of bed with trenching.Objective observations showed that the pipelines that are located on the erosion bed of the sea and the rivers have the potential to produce a natural burial (self-burial pipe) in a bed of sediment, due to localized scouring.But in natural conditions, the burial process takes place with little speed. Therefore, by installing the spoiler on the pipelines, it is attempting to increase the Perpendicular cross-section of the flow (making changes in the pattern of flow around the pipeline) and, finally, the occurrence of erosion and self-burial inlower environmental velocities, but more intense. Therefore, it is necessary to first investigate the factors affecting for erosion sediment bed and estimate the dimensions of scour hole under pipelines, to study the accelerating factors and its effects on ocean engineering.
Themost of researchers considered the local scouring around the pipelines relatede to be rapid, the depth of the flow, the pipe diameter and the particle size of the bed. Moncada-M and Aguirre-Pe (1999) describe that, the scour depth below the pipeline as a function of the flow loss number and the dimensionless distance between the pipe and the intact bed. Cheng and Chew (2003) and Zhao and Wang (2009), by simulating the flow area around the pipeline with the mounted fin on it, found that the lifting force and shear stress in the bed and the scour depth increased with the fin. (2012), by using laboratory results, showed that the flow loss number and the height of the fin had a significant effect on the depth of scouring under the horizontal pipelines. Shan et al. (2015) with numerical evaluation of self-burial of tube with the fin mounted on it, and in displacement mode, with Fluent software, found that increasing the flow loss number in near of the bed would help to increase the burial speed of the tube.
recently studies showed that the mounting of the fins on the pipeline lead to increasing the amount of erosion around the tube. The application of mounted Piggyback line with cross sectional and different angles on the main pipelines can be a major difference with previous research.

کلیدواژه‌ها [English]

  • Tunnel erosion
  • Scour
  • Piggyback-line
  • pipeline

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