Uncertainty of Modal Parameters Estimated by ARMA Models

In this paper the uncertainties of identified modal parameters such as eigenfrequencies and damping ratios are assessed. From the measured response of dynamic excited structures the modal parameters may be identified and provide important structural knowledge. However the uncertainty of the parameters decides the value of the experimental obtained information.

The paper deals with the sources of uncertainty. The different sources of uncertainty have been categorized into physical errors, statistically errors and modal errors. The nature of the uncertainty due to those errors has been studied by a simulation study of a lightly damped single degree of freedom system. Identification by ARMA models has been chosen as system identification method. It is concluded that both the sampling interval and number of sampled points may play a significant role with respect to the statistical errors. Furthermore, it is shown that the model errors may also contribute significantly to the uncertainty.