Complex Modes Arising from Linear dentification of Non-linear Systems

Date

1993-04

Author

Özgüven, Hasan Nevzat
M., İmregün

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When the modal analysis of a structure yields complex modes, it is customary to assume that the system is nonproportionally-damped. However, almost all analytical identification tools are geared toward the analysis of linear systems and it is not altogether certain if the identified complex modes indicate nonproportional damping or whether they are due to nonlinearities inherently present in the system, or to a combination of both. In this study, a set of nonlinear frequency response functions (FRFs) was generated theoretically for various forcing levels. A linear modal analysis of these FRFs showed highly complex modes that, clearly, indicated nonlinear behavior since the initial damping was proportional. Further studies showed a varying degree of sensitivity of the identified modal parameters to the amount of initial damping and to the forcing levels for which the FRFs were generated. It is concluded that complex modes are not necessarily an indication of nonproportional damping unless it can experimentally be verified that the structure under investigation is linear.

Subject Keywords

Dynamic Structural Analysis, Linear Equations, Nonlinear Equations, Vibration Damping, Vibration Mode, Modal Response, Stiffness Matrix, System Identification, Structural Mechanics

URI

https://ui.adsabs.harvard.edu/abs/1993IJAEM...8..151O/abstract
https://hdl.handle.net/11511/105147

Collections

Department of Mechanical Engineering, Article