Research On 4000t Ship Coupling Oscillation Of Diesel Speed Control System And Propulsion Shafting Torsional Vibration

The main propulsion system of 4000 tons special-working ship is comprised of three branches including dynamo,water pump,and propeller driven by the gearbox,respectively.When the dynamo works together with propeller,unstable speed phenomenon of the shaft,gear teeth knock and axial movement of the shaft parts would occur.In this thesis,torsional vibration models of three branches of the propulsion system are established using lumped parameter method under the five different working conditions.The free and forced torsional vibration of shafting are calculated.The results show that strength of crank meet the ship specifications.According to the traditional diesel speed control system simulating method,the inertia of the shafting is treated as a rigid body in the model.The results show that initial setting of PID parameters in factory make the diesel stable during operation.Then the shaft is replaced by a true multi-inertia and elastic model.Transient speed is treated as a feedback signal to the control system.This time the system turned unstable which is consistent with the phenomenon of the real ship.After resetting PID control parameters,the system turned smooth again.The coupling oscillation phenomenons of diesel speed control system and shafting torsional vibration are reproduced by simulation in this paper.A method of improving PID parameters is proposed.By applying to real ship,the simpleness and effectiveness of the proposed method is checked.The coupling phenomenon is proved to be existing between diesel control system and shafting torsional vibration.If the PID control parameters are not chosen appropriately,system self-excited oscillation would occur.This thesis depicts a simple and effective method to optimize control parameters which is worth of popularizing.