VIBRATION ANALYSIS OF TIE-ROD/TIE-BOLT ROTORS USING FEM

摘要

Tie-rod and Tie-bolt rotors have different applications in industries. Vibration analysis of this type of rotors would be useful for condition monitoring and fault diagnosis purposes. Tie-rod rotors consist of several disks that are tightened by a rod crossed among them. Tie-bolt rotors also consist of several disks that are tightened by several bolts crossed among them. Modeling of these kinds of rotors is different from simple continuous rotors because of their multi-sectional configuration. In this paper, a novel finite element model has been developed for a typical tie-rod/tie-bolt rotor. In this model, the flanges of disks are assumed as an extra rotor which surrounds the main rod (or man bolts). In addition, the stiffness effects of webs are neglected and they are considered as inertial elements. The Timoshenko shaft element is used for modeling the tie-rod/tie-bolt rotor. Damping matrix including gyroscopic terms and internal damping of the shaft has been neglected. Considering the assembly mechanism of rotor (rod/bolts tensioned and disks pressed), the stiffness matrix is modified in order to take into account the axial force effect. As a result, the finite element model is applied for an industrial shaft. Using Campbell diagram, run up critical speeds and the corresponding mode shapes are extracted for different values of axial force. The results exhibit that the compressive axial force in rotor has decreasing effect on critical speeds. The results are compared with the experimental data available in the literature and good agreement has been achieved.