شناسایی فرکانس‌های طبیعی بر‌ پایه تبدیل ارتقا یافته هیلبرت- هوآنگ

نویسندگان
سهیل رمضانی
امید بهار
پژوهشگاه بین المللی زلزله شناسی
چکیده
چکیده- در مقاله حاضر، بر اساس تبدیل ارتقا یافته هیلبرت- هوآنگ که به تازگی به وسیله مؤلفان توسعه یافته، روشی خروجی-تنها برای شناسایی فرکانس های طبیعی سازه های چند درجه آزاد پیشنهاد شده است. در روش پیشنهادی، با تحلیل پاسخ سازه به وسیله تبدیل ارتقا یافته هیلبرت- هوآنگ، یک طیف دامنه- فرکانس موسوم به «طیف حاشیه ای میانگین» برای سازه فراهم می شود که به وسیله آن فرکانس های طبیعی سیستم سازه ای شناسایی می شوند. برای ارزیابی کارایی روش شناسایی پیشنهادی، شتاب نگاشت های حاصل از آزمایش ارتعاش محیطی انجام گرفته روی یک پل و یک ساختمان در قالب دو مطالعه موردی تحلیل شده اند که در آن ها شش فرکانس اول پل در جهت قائم و سه فرکانس اول ساختمان در سه جهت شرق- غرب، شمال- جنوب و پیچشی شناسایی شده اند. با توجه به سادگی روش پیشنهادی و تطابق نتایج حاصل از آن با دیگر روش های معتبر شناسایی سیستم، زمینه کابرد آن به عنوان ابزاری کارامد در شناسایی سیستم های سازه ای فراهم است.

کلیدواژه‌ها

عنوان مقاله English

Identification of Natural Frequencies Based on a New Enhanced Hilbert-Huang Transform

نویسندگان English

S. Ramezani
O. Bahar
چکیده English

Hilbert-Huang transform (HHT) consists of two main parts: (1) empirical mode decomposition (EMD) to extract intrinsic mode functions (IMFs) and (2) Hilbert spectral analysis to obtain time-frequency characteristics of the IMFs through the Hilbert transform. Recently, a new enhanced HHT is proposed by the authors in which, two mathematical limitations that restrict the application of the Hilbert transform are circumvented and also an additional smoothing parameter is applied to decrease noise effects on the results. In this paper based on the HHT approach, a simple method for output-only identification of natural frequencies of linear structures is proposed in which HHT or enhanced HHT can be employed. In the proposed method, ambient response data measured at all degrees of freedom of the structure are used to obtain an averaged marginal spectrum. The averaged marginal spectrum is used for identifying the natural frequencies of the structure. In order to validate the effectiveness of the proposed identification method, ambient response data of an arch bridge and a 15-story building are examined. In the first case, the first six natural frequencies of the bridge in vertical direction are extracted. And in the second case, the first three natural frequencies of the building in East-West, North-South and torsional directions are identified. From the results, first, it is found that the enhanced HHT by employing the smoothing parameter is more efficient than the HHT in increasing the readability of the time-frequency-amplitude spectrum and also is capable to provide more accurate amplitude-frequency distribution; second, by comparing results of the proposed method with those obtained from other valid methods, it is concluded that the proposed identification method by using the enhanced HHT is accurately able to estimate the natural frequencies of structures. Regarding to simplicity of the proposed method, it can be applied as an efficient tool for identification of structures or employed to extract changes in frequencies due to occurrences of damages during strong ground motions.

کلیدواژه‌ها English

Signal processing
Enhanced Hilbert-Huang transform
Structural system identification
Identification of natural frequencies
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مهندسی عمران مدرس
دوره 12، شماره 3
مهر و آبان 1391
صفحه 47-59