Biased Modal Estimates from Random Decrement Signatures of Forced Acceleration Responses

The following study investigates a parameter identification problem of a linear dynamic system resulting from forced acceleration responses without any knowledge of input forces. When such a forced acceleration response is used by the random decrement technique, the formed random decrement signature of the acceleration response has an additional amount from the random decrement signature of the input force. The random decrement signatures obtained from a three degrees of freedom dynamic system excited by white noise forces are used to show the identification problem using the Ibrahim time domain algorithm. Results reveal that the random decrement signatures of the white noise forces corrupt the random decrement signatures of the acceleration responses, leading to the biased estimates of the modal parameters, especially for the damping estimates. To avoid the random decrement signatures of input forces in the random decrement signatures of the forced acceleration responses, a solution is provided for the use of the random decrement technique.