Estimation of Variance of the Frequency Response Function and its Application to the Curve Fit

Modal analysis is widespread and many curve-fit techniques which estimate modal parameters such as natural frequencies, modal damping ratios and natural modes have been developed. A new method based on the maximum likelihood principle which utilizes the frequency response function (FRF) as input data has been proposed by one of the authors. According to that method, it is necessary to estimate not only FRF itself, but also the variance of the FRF by a vibration test. Following the previous report, this paper presents a method of estimating FRF's variance for the "Hv" estimator in the case of multipoint excitation. Furthermore, an approximate estimation method of the Hv's variance is presented aiming at the convenience of calculation. Errors of modal parameters estimated by the maximum likelihood method are also evaluated in the form of standard deviation.