Formulation and experimental validation of a frequency transfer function of a rotor system with both an open crack and anisotropic support stiffness

Abstract

This paper proposes a transfer function of rotating shaft system considering both an open crack and anisotropy in bearing support stiffness, which are both fundamental characteristics often observed in the rotating machinery. Due to the interaction of anisotropy in bearing support and rotor crack, vibration component is generated without limitation. In this paper, the order of generated component is evaluated and a transfer function focusing on five vibration components is derived. Each transfer function is analyzed and characteristics of all resonances are explained theoretically. Then, the validity of this derived transfer function is confirmed by comparing with numerical simulation result. Furthermore, the experimental system of the rotating shaft supported by the bearing with anisotropic support stiffness is developed, and the harmonic excitation was added to this system by the active magnetic bearing. Several harmonic excitation experiments were carried out, and the resonances due to anisotropy in bearing support, rotor crack, and the interaction of anisotropy in bearing support and rotor crack were examined. The vibration characteristics of observed resonances showed quantitatively almost agreed results to the expected theoretical results. These theoretical and experimental results clarified the usefulness of the derived transfer function.

Keywords

• rotor dynamics
• rotary machinery
• vibration of rotating body
• parametric excitation
• cracked rotor
• transfer function
• active magnetic bearing