The large gas turbine rotor used for power generation has a structural characteristic comprising a shaft, disk, and blade assembled to the disk. Because the start/stop is repeated, the tightening force may be reduced in the process of repeating the tightening force between the tie rod and the disk. When the tightening force falls below the threshold, changing the critical speed, increasing the vibration, or in extreme cases, the rotor may loosen and cause a major accident. Also, it is imperative to continuously maintain the proper tightening force because the thread of the tie rod is damaged when the tightening force exceeds the yield stress condition of the tie rod. In this paper, the gas turbine rotor system is modeled and simplified to identify the control variable of the tightening force of the tie rod bolts of the rotor. For verification, a simplified model of the gas turbine rotor was designed, manufactured, and verification tests were conducted to confirm the adequacy of the calculation method. As a result, the tightening force decreased as the stiffness of the pressing disk decreased, so the stiffness of the pressing disk should have a stiffness range similar to that of the tie rod.

The vibration analysis of flexible rotor systems supported by angular contact ball bearings is presented. Vibration analysis of rotor-ball bearing systems has often been performed via simplification of supporting bearings as linear springs with constant stiffness. In this study, an improved model of rotor-ball bearing systems was proposed. It utilizes a general bearing model based on response and time-dependent bearing characteristics. The system equations of motion were established using the finite-element method and numerically solved using the Newmark-β method. The method was used to recalculate the bearing stiffness matrices at every interval of numerical integration as a function of the instantaneous bearing displacements using a separated five-degrees-of-freedom bearing model. The method was verified via comparison with experimental data available in the literature. The extended simulations were conducted to investigate the unbalanced responses of a rotor-ball bearing system using the proposed and conventional methods. Numerical results showed a meaningful discrepancy between the vibrational responses obtained by the proposed model using the response and timedependent bearing stiffness model and the traditional constant-stiffness model.

The role of dynamic behavior of operating rotor system in rotor design may or may not be evaluated under the impact of an external force such as earthquake. This article reports the result of an experimental study to resolve the dilemma. First, a sine weep test was performed to determine the first natural frequency of a Jeffcott rotor and compared with the ANSYS mode analysis demonstrating the reliability of experimental tests. The operating rotor vibrations were measured under the impact of sinusoidal forces at several frequencies, generated by the MTS vibration exciter. The experimental data suggest the need for a rotor design considering the dynamic behavior of the operating rotor under exciting external forces.