由前人研究得知，在頻率域探討當系統具有重根模態時，需利用多輸入多輸出的方法才能有效識別出模態參數。本文探討將頻率域理論推廣至時間域，對具有重根模態系統進行模態參數識別。本文應用特徵系統實現法，並考慮量測雜訊之問題，經由數值模擬顯示，在阻尼比的識別不盡理想，因此利用結合相關函數法來降低雜訊對識別結果的影響。吾人進一步利用相關矩陣直接進行模態參數識別，省略再次建構韓克矩陣的過程，相較特徵系統實現法與資料相關特徵系統實現法更具效率。

Previous studies show that when a system have an repeated modes in frequency domain, the method of using multiple-input and multiple-output method can effectively identify the modal parameters. In this research, the frequency-domain theory is extended to the time domain for identification of modal parameters for systems that have repeated eignvalues.With the application of eigensystem realization algorithm method and consideration of the measurement noise, numerical simulations show that the identification result in the damping ratio is usually poor. Therefore, with the combination of concept of the correlation function in modal parameter identification, the influence of noise on identification result is reduced. The correlation matrix is also used directly to identify modal parameters, omiting the process of constructing the generalized Hankel matrix, which provides a more efficient method of identififcation of modal parameter.

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