Abstract: A perturbation method for analyzing the vibration frequencies, damping ratios and modes of damped vibration system, whose matrices have small changes, is presented in this paper. When the mass and stiffness matrices of the original syatem vary slightly, the eigensolutions can be obtained without solving a large generalized eigenvalue problem again. The vibration frequencies and modes of the updated system can be derived by matrix perturbation method based on the original vibraton mode coordinate transformation. The damping ratios of the updatea system can also be given by using the vibration frequencies of the updated system and proportional damping parameters. The results of the engineering computational examples show that the presented method having simple computational and high accuracy properties is an available perturbation method.

Key words: dynamic structural analysis, vibration charaeteristics, perturbation method