Identifying the modes of a vibratory system excited by narrow band random excitations

The random decrement technique is investigated in connection with the analysis of the modes of a vibratory system excited by a narrow-band random oscillation. A discrete version of the random decrement technique is applied in which the excitation has a bandlimited spectrum. The results obtained with this method are compared with the results obtained using the linear prediction method. The passband is within the bandlimited spectrum of the random excitation and includes the complete frequency response of one or more modes of the free vibration of the structure. Since these modes are excited by natural forces, they reflect the main characteristics of the structure. The signature obtained by the random decrement method is superior to that obtained by the linear prediction method. The resulting signature has been used to monitor the structural health of vibratory systems under test.<
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