The basis of all balancing procedures relies on the linearity of the system. However, the fact is that many machines – particularly those using oil-journal bearings – do not behave in a linear manner. What’s more, knowledge of the rotor mode shapes is vital for modal balancing, which normally is obtained from an FE model or measurements. Often, the mode shapes are estimated by ignoring nonlinear effects. In order to develop a practical balancing approach for real nonlinear rotor-bearing systems, the capacity of the modal balancing method must be extended. In this paper, modal balancing of a nonlinear flexible rotor-bearing system based on nonlinear normal modes (NNM) is investigated. The proposed algorithm relies on two main steps. The first step is to compute NNMs using the shooting method and the sequential continuation method and to get the rotor mode shapes. In the second step, the linear mode shapes are replaced by NNMs to get the unbalance corrections of each mode of interest and to get the total unbalance correction. To demonstrate the accuracy and effectiveness of the proposed method, various simulation results are studied and the response at disks after balancing with NNMs are compared with the original method.

 

Nonlinear normal modes; Flexible rotor-bearing systems; Modal balancing; Rotor dynamics;