Comparison of various techniques for computing modal mass

In this paper, we compare modal mass estimates from a resonance frequency shift technique with those estimated using traditional drive point response matching and mode shape integration techniques. The data for the computations was derived from experimental modal analyses of a small homogenous, carbon fiber composite rectangular flat plate with free boundary conditions. We applied several point masses to the plate to obtain modal frequency shifts. For this problem, the modal masses computed using the frequency shifting technique are slightly higher than those estimated using traditional methods. The overestimates may be due to ignoring the effects of the added mass inertias. Also, the results show that the modes of the plate become distorted when the added masses are greater than approximately 0.6% of the structure's static mass, thus invalidating the frequency shift technique.