بررسی اثر تغییر نیم موج‌های محیطی بر فرکانس‌های طبیعی پوسته‌های استوانه‌ای در ارتعاشات زیر آب به‌صورت تجربی و عددی

نوع مقاله : مقاله پژوهشی

نویسندگان

1 گروه مهندسی مکانیک، دانشکده فنی و مهندسی، دانشگاه جامع امام حسین (ع)، تهران، ایران

2 گروه مهندسی مکانیک، دانشگاه جامع امام حسین (ع)

3 دانشکده فنی و مهندسی، دانشگاه جامع امام حسین(علیه السلام)، تهران، ایران،

4 دانشکده فنی و مهندسی، دانشگاه جامع امام حسین(علیه السلام)، تهران، ایران

چکیده

در پژوهش حاضر، اثر تغییر نیم موج‌های محیطی بر فرکانس‌های طبیعی پوسته‌های استوانه‌ای به‌صورت تجربی و عددی بررسی شده ‌است. سه پوسته استوانه‌ای با نسبت قطر به طول متفاوت مورد بررسی قرار گرفتند. حالت‌های مختلف تماس با آب هم با روش شبیه‌سازی عددی و هم آزمون‌های تجربی مورد مقایسه واقع شدند. اثرات عمق غوطه‌وری، نسبت قطر به طول، روند تغییرات فرکانس طبیعی در نیم موج‌های محیطی مختلف مورد ارزیابی قرار گرفت. بررسی‌ها نشان داد که کاهش فرکانس‌های طبیعی پوسته استوانه‌ای برای نیم موج‌های محیطی مربوط به فرکانس کمینه، اندک و برای قبل و بعد این نیم موج محیطی، بیشتر است و در آغاز غوطه‌وری و در غوطه‌وری کامل، کاهش فرکانسی به‌صورت ناگهانی است. همچنین با کاهش نسبت قطر به طول پوسته، فرکانس‌های مربوط به نیم موج‌های محیطی پایین کاهش یافته و کمترین مقدار فرکانس طبیعی به سمت نیم موج‌های محیطی کمتر متمایل می‌شود. در نیم موج‌های محیطی پایین، فرکانس‌های طبیعی، اختلاف قابلتوجهی دارند و با افزایش شماره n، این اختلاف کاهش یافته و به یکدیگر هم‌گرا می‌شوند.

کلیدواژه‌ها

موضوعات


عنوان مقاله [English]

Investigation effect of circumferential mode number on natural frequencies of under-water vibrations of cylindrical shells numerically and experimentally

نویسندگان [English]

  • Mohammad Reza Najafi 1
  • Saeed Mahjoub Moghadas 2
  • Seyyed Mohammad Mortazavi 3
  • Mahmoud Salari 4
1 Mechanical Engineering Department, Imam Hossein comprehensive University
2 Department of Mechanical Engineering, Imam Hosein comprehensive university, Tehran, Iran
3 Department of Mechanical Engineering, Imam Hosein comprehensive university, Tehran, Iran
4 Department of Mechanical Engineering, Imam Hosein comprehensive university, Tehran, Iran
چکیده [English]

In the present study, the effect of circumferential mode number on natural frequencies of cylindrical shells was investigated numerically and experimentally. Three cylindrical shells with different diameter to length ratios were examined. Different contact type with water were compared using both numerical simulation and experimental tests. The effects of immersion depth, diameter to length ratio, variations of natural frequency with different circumferential mode number were investigated. The reduction of the natural frequencies of the cylindrical shell for the minimum frequency of different circumferential mode number is low, but it increases for higher and lower frequencies, and at the beginning of immersion and at full immersion, the frequency decreases suddenly. Also, as the ratio of diameter to shell length decreases, the frequencies of the low circumferential mode number decrease and the lower value of the natural frequency tends to lower circumferential mode number. At low circumferential mode number, the natural frequencies differ considerably, and with increase of n number, the difference decreases and converges.

کلیدواژه‌ها [English]

  • Circumferential mode number
  • Fluid-solid interaction
  • Under-water vibrations
  • Natural frequency
  • Mode shape
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