IJE TRANSACTIONS C: Aspects Vol. 28, No. 3 (March 2015) 368-377   

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M. J. Emamgholizadeh, A. R. Mostafa Gharabaghi, K. Abedi and M. H. Sedaaghi
( Received: November 27, 2013 – Accepted: November 13, 2014 )

Abstract    Submarine pipelines are appropriate method for transmission of oil and gas from sea bed. Free spans may occur due to the natural uneven seabed or by under-scouring. Vortex Induced Vibration (VIV) can happen in such free spans at high Reynolds number. Resonance occurs if the frequency of vortex shedding is close to the pipeline’s natural frequency leading to its fatigue that can break the pipeline causing economical and environmental losses. In literature, there are different methods for suppressing the vortex shedding and pipeline vibration and consequent scouring under the pipe such as the usage of splitter plates. In this paper, the effect of splitter plate’s angle on the scouring under the pipeline is studied experimentally. For this purpose, a new experimental setup is designed and constructed in order to allow for the cylinder to vibrate in both in-line and cross flow directions over an erodible bed. The reduced velocity for the experiments is in the range of 2.45-5.06 and gap ratio is zero. Experimental results indicate that the relative scour depth is reduced with increasing the ratio of gap to pipe diameter. By comparing between relative frequency and reduce velocity, we can conclude that the relative frequency gives a constant value for a large air gap ratio ( ) and also, the pipe has not more effect on the bed. Finally, the scouring depth below the mean location of vibration related to the pipes with a splitter plate and angles 0-30 degrees are less than those without a splitter plate. While, inversely, the scouring depth related to the pipes with a splitter plate and an angle between 60-90 is more than those without a splitter plate.


Keywords    Pipeline, Vortex induced vibration, Splitter plate, Two degree of freedom, free span.


چکیده    خطوط لوله از جمله سازه­های فراساحلی می­باشد که دارای کاربرد فراوانی می­باشد. وجود دهانه آزاد ممکن است به دلیل آبشستگی بستر و یا ناهمواری ابتدایی به­وجود آید. دهانه­های آزاد ممکن است در اعداد رینولدز بالا تحت نوسانات ناشی از تشکیل گردابه­ها قرار گیرند. اگر فرکانس گردابه­های به­وجود آمده با فرکانس لوله یکی شود، پدیده تشدید اتفاق می­افتد و مخاطرات را افزایش می­دهد. در ادبیات فنی روش­های مختلفی برای کنترل گردابه­ها و ارتعاش لوله وجود دارد که از جمله این روش­ها استفاده از صفحات شکافنده جریان می­باشد. در این مطالعه تاثیر زاویه­قرارگیری صفحات برروی پاسخ ارتعاشی و فرکانسی لوله به­صورت آزمایشگاهی مورد بررسی قرار گرفته شده است. چیدمان آزمایشگاهی جدید به منظور ایجاد ارتعاش لوله در دو بعد از صفحه و برروی بستر ماسه­ای، طراحی و ساخته شده است. سرعت کاهش یافته در محدوده­ی 5.06-2.45 می­باشد و از نسبت شکاف صفر استفاده شده است. همچنین از روش غیر تماسی پردازش تصویر به منظور ثبت پاسخ ارتعاشی لوله مورد استفاده قرار گرفت. نتایج حاصله نشانگر آن می­باشد که استفاده از صفحات شکافنده تحت زوایای مختلف، رفتار کاملاً متفاوت در پاسخ ارتعاشی لوله خواهد داشت. به­گونه­ای که استفاده از آن تحت زوایای خاصی باعث کاهش دامنه ارتعاش لوله شده و فرکانس ارتعاش را افزایش می­دهد، ولی در زوایای دیگر نتایج عکس خواهد داشت.



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