改變結構物材料參數在HHT結構健康監測方法之應用;Application of Changing Structural Material Parameters in Hilbert-Huang Transform Structural Health Monitoring Method

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/83037

Title:	改變結構物材料參數在HHT結構健康監測方法之應用;Application of Changing Structural Material Parameters in Hilbert-Huang Transform Structural Health Monitoring Method
Authors:	謝晉瑋;Hsieh, Chin-Wei
Contributors:	土木工程學系
Keywords:	有限元素分析;ABAQUS;模態參數;時頻分析;希爾伯特-黃轉換;時頻域放大函數
Date:	2020-07-29
Issue Date:	2020-09-02 14:30:15 (UTC+8)
Publisher:	國立中央大學
Abstract:	過去在結構安全監測領域，大多採用傅立葉轉換(Fourier Transform, FT)作為分析方法，將地震外力激發出的結構反應訊號由時間域轉為頻率域觀察。但是傅立葉轉換使用不隨時變的諧和函數作為基底函數來展開訊號，只適合處理線性、穩態的訊號，無法獲得訊號瞬時變動的特性。在結構安全監測領域，用以處理地震力與結構振動反應等非線性、非穩態的訊號，則需更完善的方法進行分析。希爾伯特-黃轉換(Hilbert-Huang Transform，HHT)為一較新穎的時頻分析技術，其具有後定基底與局部隨適基底兩大特性，適合用於解析非線性、非穩態的訊號。此轉換方法可將原始訊號表示為在時間域與頻率域上的能量分布情形，以便進一步觀察結構物隨時間變化之動態特性。HHT SHM方法則是以希爾伯特-黃轉換為核心，整合了一些數值分析方法而成，透過時頻域放大函數(Time-Frequency Domain Amplification Function, T.F.AF)以及模態時間曲線(Modal Temporal Variation Curve, MTVC)，找出能代表結構動態資訊的模態參數。本研究使用雙線性材料，以改變彈性模數來模擬結構物之弱化情形，又將其分為「彈性段斜率E折減」、「降伏應力σ_y折減」以及「塑性段斜率Ep折減」三部分進行分析。透過有限元素軟體ABAQUS建立研究模型，並輸入地震外力進行分析，由結果提取出基底與樓頂之加速度歷時資料。接著將加速度訊號以HHT SHM方法轉為時頻譜，由時頻譜上擷取模態振動特質，計算出模態參數。最後探討彈性模數改變的各種情形對於模態參數的影響，並且歸納出改變趨勢，以便解讀日後於實際案例中測得之模態參數。 ;In the past, Fourier Transform (FT) was mostly used in the field of structural health monitoring as the analysis method to convert the structural response signals excited by seismic forces from the time domain to the frequency domain. However, Fourier Transform uses time-invariant bases to expand the signal which is only suitable for processing linear and stationary signals, and the characteristics of instantaneous signal fluctuations cannot be obtained. In order to deal with nonlinear and non-stationary signals such as seismic forces and structure responses, more sophisticated methods are needed for analysis. Hilbert-Huang Transform (HHT) is a relatively new time-frequency analysis technique featuring with two characteristics of posteriori base and adaptive base, which is suitable for the analysis of nonlinear and non-stationary signals. This conversion can express the original signal as an energy distribution in time-frequency domain, so as to further observe the dynamic characteristics of the structure over time. HHT SHM is a method based on Hilbert-Huang Transform and integrates some numerical analysis methods. Through the time-frequency domain amplification function (T.F.AF) and the modal temporal variation curve (MTVC), we can find out the modal parameters that can represent the dynamic information of the structure. In this study, bilinear materials are used to simulate the weakening of structures by changing the elastic modulus. The simulation can be divided into "elastic slope reduction", "yield stress reduction" and "plastic slope reduction ". Through the finite element software ABAQUS, a research model is established. We then apply seismic forces on the base for analysis and obtain the acceleration data of the base and the roof. To proceed, the acceleration signal is converted into a time-frequency spectrum by HHT SHM method, and the modal vibration characteristics can be extracted from the spectrum. Finally, we discuss the impact of altering elastic modulus on the modal parameters, and summarize the trend in order to interpret the modal parameters measured in actual cases in the future.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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