At what condition does torsional critical speed typically occur in a Marine Reduction Gear (MRG)?

Torsional critical speed in a Marine Reduction Gear (MRG) typically occurs at low speed because this is where the system's natural frequency can closely align with the frequency of the excitation forces acting on the gearbox. At lower RPMs, the inertia of the rotating system and the stiffness of the gear connections create conditions conducive for resonant vibration. As the speed increases beyond this point, the forces may become more dampened by the system's mass and stiffness properties, reducing the chances of reaching torsional critical speed.

At high speeds, the dynamics of the system change, often moving past the resonant frequencies associated with low-speed operation. Similarly, mid-range and cruising speeds are less likely to engage the system in the critical speed phenomenon due to different dynamic equilibria than those experienced at low speeds. Thus, the correct understanding of torsional critical speed highlights its occurrence under low-speed conditions in a Marine Reduction Gear setup.