Study On Structural Vibration Problem Of Very Large Crude Oil Carrier

The superstructure of VLCC is usually arranged in the stern, which is near the two main excitation source——the propeller and main engine, making the vibration problem of superstructure more severe. However,in recent years, the proposition of aft stepped structure changed the structural type a lot, making the inherent characteristics of stern many changes. Therefore, it is very necessary to study the vibration related problems of the steppedstern design on VLCC. Concretely, this paper had done some study on the following content:(1). Whole ship vibration evaluation: built a coarse mesh FEM model of a 318000 DWT VLCC which has aft stepped structure; researched the effect of the stepped stern design on the whole ship vibration characteristic; in addition, discussed the effect of the entrained water mass on the whole ship vibration characteristic.(2).Substructure vibration evaluation: chose the vibration force under the blade frequency of propeller and each order moment of main engine as the vibration force to calculate the substructure’s response; compared and analyzed the response results of different design plans; studied the differences among the inherent frequency calculation methods of superstructure; stated the methods that can reduce the vibration force of main engine and improve the bridge wing structure.(3). Local structure vibration evaluation: evaluated the local structure of the VLCC, including the fundamental frequency of panels, grillages and stiffeners; studied the laws of subcritical dynamic design criterion and the effect of the entrained water mass on the inherent mode of local structures.