The Torsional Vibration And Optimize Analysis For 76000DWT Bulk Carrier

Torsional vibration of shaft systems of ships is significant for the operational safety.To lower the bad effect of torsional vibration,increasing diameter of shafts,choosing alloy steel and couplings are the common strategies,in which much money should be spent.In this paper,the shaft system of 76000 DWT bulk carrier is analyzed to lower the expense of building the ship and keep the safety of the shaft at the same time.Lamped parameter system is established to study the free and forced torsional vibration.By considering the unbalance torque,including the fire force,inertia force and centrifugal force,the stress intensity of the bent axle,middle shaft and propeller-shaft was studied by frequency domain method.It is found that 5th order resonance force plays a more important part for the torsional vibration of this ship.The forbidden operational speed is given to keep the safety of the shaft.In order to lower the expense of the ship,some modification of the shaft is analyzed,such as,increasing the inertia of the flywheel and the propeller,adjusting the diameter of middle shaft,mounting spring dampers,and changing materials of shafts.From the comparisons,the strategy of mounting spring dampers is chosen which will decrease the stress intensity and forbidden operational speed is not necessary.At last,an experiment is taken to verify the theory which gives the theoretical fundaments for building economic ships.