Quasi-static and dynamic characteristics analysis of a marine gear system under coupling misalignment

Diaphragm couplings are critical in marine gear trains but inevitably suffer from both parallel and angular misalignment, which degrade tooth-mesh conditions and excite low-frequency vibrations. This paper presents a quasi-static contact analysis model for gear systems that accounts for coupling misalignment using a coupled iterative calculation framework that integrates the misalignment mechanics model, the sliced static model, and the loaded tooth contact analysis (LTCA) model. The study analyzes the impact of coupling misalignment on the contact characteristics of the gear pair under non-ideal mesh conditions and establishes the differential equation of motion for the marine gear system. Findings reveal that coupling misalignment significantly affects mesh stiffness, which fluctuates at the misalignment frequency (twice the shaft frequency). As the imposed misalignment increases, the differences in meshing misalignment and load distribution between the left- and right-hand teeth of the double-helical gear pair increase progressively. At light loads, the quasi-static contact characteristics are more susceptible to coupling misalignment, resulting in regions of contact loss on the tooth surfaces. Coupling-misalignment excitation also induces system resonance. As misalignment and load torque increase, system vibration intensifies, with load torque primarily influencing vibration responses to mesh frequency excitation. These insights deepen the understanding of marine transmission systems and inform strategies for addressing misalignment-induced vibrations, which can enhance the performance, reliability, and longevity of marine gear systems in practical applications.