Paul Robert Gemin

Ship Propulsion Self-Excited Torsional Vibration

Self-excited vibration is demonstrated in many common day events, for example, wheel-castor shimmy or a traffic sign twisting in a steady strong wind [1]. Another example, blade flutter, is well known in the gas turbine community. The affected system will typically oscillate at its natural frequency. When applied to propulsion shafting, the phenomenon produces significant levels of alternating torque that negatively affects the reliability of the drivetrain hardware. Starting with basic principles, this paper examines the conditions that can lead to self-excited torsional vibration. A screening parameter is developed that can be used to evaluate the potential for system instability. System stability mapping results are presented showing the effect of basic input parameters such as inertia, stiffness, and damping. The potential for self-excited torsional vibration is discussed in the context of recent trends in marine gas turbine propulsion (e.g. lightweight propulsors). Finally, countermeasures using the engine control system are outlined.Copyright