ABSTRACT The operational stability of long‐shaft dual‐rotor systems, as key components in high‐speed rotating machinery, directly affects equipment performance, and service life. Vibration instability, accelerated fatigue damage, and even shaft fractures can be induced by the coupling effects of unbalance excitation and crack faults. Consequently, elucidating the dynamic characteristics and parametric influence mechanisms under such complex conditions is essential for ensuring operational safety. This study develops a finite element method‐based dynamic model, with accuracy confirmed through cross‐verification between theoretical derivations and software simulations. By introducing rotor unbalance excitation and solving the equations of motion via the Newmark‐HHT method, the unbalanced response characteristics are characterized using three‐dimensional waterfall plots and time‐frequency analysis. The influence of speed ratio, unbalance magnitude, and bearing stiffness on vibration characteristics is systematically investigated. Furthermore, a hollow outer shaft dynamic model incorporating a breathing transverse crack is developed to analyze the system response under coupled unbalance and crack faults, with focused investigations on crack depth, location, and multi‐crack coupling. The harmonic balance method is introduced for comparative validation, ensuring the reliability of the conclusions. Results demonstrate that increased speed ratio and unbalance elevate vibration amplitudes, while optimized matching between the external support bearing and intermediate bearing stiffness effectively suppresses vibrational responses. Deeper cracks and positional deviations intensify dual‐frequency resonance, whereas multi‐crack coexistence induces significant morphological distortions in axis trajectories. This study provides theoretical guidance for vibration control and fault diagnosis in long‐shaft dual‐rotor systems.
Jiang et al. (Wed,) studied this question.