結構系統之模態參數，可藉由激勵訊號與響應訊號進行識別。而在真實的世界中，結構系統受環境振動影響下，卻僅能獲得其響應訊號。因此如何規避激勵信號的量測而直接由響應資料識別模態參數，為本文探討之重點。本文考慮當線性結構系統在環境振動下，假設激勵信號為非定常過程，其響應訊號經隨機遞減法處理後，隨機遞減訊號與脈衝響應或自由振動衰減響應有相同之數學形式，進而利用亞伯拉罕時域模態參數識別法計算出結構系統之自然頻率、阻尼比與模態振形。另外，結構系統受有色訊號激勵下，可利用模態正交性區別其結構模態與假想激勵訊號模態。最後經由數值模擬，驗證本文所探討的方法能有效地識別出結構的主要模態參數及振動反應。

　　Identification of system characteristics is usually accomplished using both input and output data from the structural system. In many cases, however, only output measurements are possible for structures under ambient conditions. It is shown that if the input signals can be modeled as non-stationary white noise the theoretical auto- and cross-random decrement vibration signature of the response of a linear structure are in the same mathematical form as free vibration of the structure. The objective of this thesis is to develop a modal parameter identification method by using time domain identification techniques with the response randomdec signatures treated as free vibration data. In this fashion, the problem of unknown inputs has been circumvented. The structure’s responses fixed time solely are then used to identify the structure system. In this thesis, the Ibrahim Time Domain method is employed as the modal identification schemes to extract modal parameters from vibration data. Through numerical simulation, the applicability of the modal parameter identification method proposed is confirmed.

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