cylinders، helically، VIV، inclined، “inclined، vortex

اندازه‏گیری‏های تجربی انجام گرفته بر روی استوانه‏های ساده و دارای تیغه‌ی حلزونی منفرد پرداخته است. ارائه نمودارهای جابجایی- سرعت اصلاح‌شده، نسبت فرکانس- سرعت اصلاح‌شده و محاسبه نیروهای وارد بر استوانه‏‌ها و مقایسه و بحث و بررسی آن‌ها از موارد مورد بررسی در این فصل می‏‏باشد.
فصل ششم از این مجلد به ارائه نتایج اندازه‏گیری‏های تجربی انجام گرفته بر روی استوانه‏های قائم و مایل ساده پشت‌هم پرداخته است. ارائه نمودارهای جابجایی- سرعت اصلاح‌شده، نسبت فرکانس- سرعت اصلاح‌شده و محاسبه نیروهای وارد بر استوانه‏‌ها و مقایسه و بحث و بررسی آن‌ها از موارد مورد بررسی در این فصل می‏‏باشد.
در فصل هفتم و پایانی نتیجه‌گیری و پیشنهادهایی برای تحقیقات آینده اختصاص داده شده است.
Abstract
Vortices shed downstream of a bluff body that is placed in a fluid flow. When the frequency of vortex shedding gets close to the natural frequency of the structure, amplified oscillations are developed in the cylinder.
Effects of suppression devices on the VIV response of inclined cylinders appear not to have received previous due attentions. In the current paper the vortex induced cross-flow vibrations of bare and helically straked cylinders in vertical and inclined arrangements were investigated. Towing tank experiments were conducted in a uniform flow. Rigid cylinders were mounted on a single degree of freedom elastic support. The inclination angles examined were θ=0o, ±20o and ±45o. The Reynolds number ranged from 4,000 to 45,000 and the reduced velocity from 1 to 16. With all tests the mass parameters and the mass-damping parameters were kept constant.
Test results on “inclined bare” and “inclined helically straked” cylinders showed that the peak amplitude of the cross-flow oscillations decreased as the inclination angle increased. The suppression ratio remained almost the same in the vertical and inclined cylinders. The predictions obtained by the so called “Independence Principal” (IP) were also examined against the test data from the current study. With “inclined helically straked” cylinders the IP predictions were almost inconsistent with all test data. In addition, the up-and downstream effects on the VIV response of the inclined bare and helically straked cylinders were studies. Hilbert Transform of the VIV responses showed that it was able to efficiently discriminate signals belonging to the lock-in, initial and lower branches of the response
Keywords: Vortex-Induced Vibration (VIV), Inclined circular cylinder, Helical strakes, Experimental study and Hilbert transform

K. N. Toosi University of Technology
Faculty of Civil Engineering
Department of Marine Structure
Thesis Title:
[Performance of VIV Suppression Devices in Inclined Gas and Oil Pipeline and Risers under Steady Flow]
By:
[Aref Farhangmehr]
Supervisor:
[Dr. Mos– Zeinoddini]
Winter 2015



قیمت: 11200 تومان

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