Normalization of complex modes from mass perturbations

Abstract

Operation modal analysis has become an alternative for structures in which input data is difficult to measure. The sensitivity-based operational mode shape normalization technique was originally introduced by Parloo et al. in 2002. The technique has been widely used and is still receiving a considerable amount of attention by modal analysis researchers. Up to this point attention has been focused on real mode shapes. There are instances, however, where complex modes may have to be used because the modal density or the damping distribution is such that the use of a normal modes model is not warranted. The essential problem in normalizing complex modes using eigenvalue sensitivity is the variability of the real part of the poles. This paper examine two options: 1) neglecting modal complexity and using standard real mode fit and 2) using the complex mode. Results from an experiment using these two alternatives are presented.