DYNAMIC COUPLING CHARACTERISTICS BETWEEN TORSIONAL VIBRATION AND SPEED CONTROL OF DIESEL ENGINE PROPULSION SYSTEM

摘要

The coupling problems between speed control system of diesel engine and shafting torsional vibration system are very common as a result of the increasing complex marine propulsion system. Neglecting the coupling interactions sometimes leads to serious oscillation and vibration. To investigate the coupling interactions between these two systems, a modified coupling model is developed. In such a model, the propulsion shafting and the crankcase are modelled as a lumped parameter model, in which the flexibility of the studied shafting is considered. The speed control system and the shafting torsional vibration are coupled together by instantaneous speed. Both the cylinder excitations and the propeller resistance moments are considered, such cylinder excitations include gas excitations (GEs) and reciprocating inertia torques (RITs). In the modified coupling model, the GEs are modified by the control signal of PID controller while the RITs are modified directly according to the instantaneous speed. The influences of some shafting parameters, viz., the stiffness of elastic coupling, the damping of propeller and the damping of torsional damper, on the dynamic characteristics of the coupling system are analysed. The results illustrate that the instantaneous speed of flywheel and the additional torque of elastic coupling are positively associated with the stiffness of elastic coupling and the damping of propeller, and are negatively associated with the damping of torsional damper.