Investigating the vibration characteristics of vector thrusters under rolling condition.

The vector propulsion system with a universal coupling joint exhibits complex spatial positioning and dynamic interactions. Under challenging sea conditions, the installation foundation of autonomous underwater vehicles (AUVs) rolls with the hull motion, transmitting complex alternating loads to the steering mechanism through the support structure. This significantly impacts the vibrational response of the propulsion shafting. First, based on coordinate transformation methods, the stiffness matrix and the inclination and rolling angles of key parameters are analyzed. The absolute velocity of the propeller is derived using velocity synthesis principles and coordinate transformation matrices. Next, a unified dynamic model of the propulsion system under basic motion is established using the Lagrange equation, with centroid displacement as the generalized coordinate. Finally, the vibration characteristics of the propeller and its corresponding propulsion performance under AUV rolling motion are investigated through numerical simulation and experimental methods. The results demonstrate that rolling conditions not only transmit low-frequency vibrations but also excite high-frequency structural-roll coupled vibrations. Shorter rolling periods and larger inclination angles increase vibration amplitudes and cause significant thrust losses. This effect is a critical consideration for the process control of vector propulsion systems.