Damping estimation from modal decay during normal mode testing

Abstract

The classical Phase Resonance Method is frequently applied for the experimental identification of modal parameters of large and complex aerospace structures. The identification of damping is usually realized under some limiting assumptions. This paper describes an alternate method for the estimation of the damping. The method is based on free decay vibrations occuring after the deactivation of a tuned excitation vector. The free decay vibrations are analyzed with the Ibrahim Time Domain method. Two variants are investigated. The first variant analyses the sensor signals directly whereas the second variant analyses modally transformed responses. The approach is demonstrated on a laboratory type structure and with measured data of a Ground Vibration Test on an Airbus. The results show that reliable values for eigenfrequency and damping can be obtained. The modal transformation with the previously tuned normal mode appears to be a quick and highly effective way to estimate the damping.