Research On Vibration Modal Of 686TEU Container Ship

With the growing of transportation demand of shipping market, ship built orients to a large-scale size and high-speed, at the same time, with the application of high strength steel, the weight of hull structure reduces, both of them result in ship hull vibration problem more and more obvious, especially for large opening ship. Excess vibration may induce extra fatigue problem of hull structure, influence the normal operation of shipping, and have an adverse effect on the crew’s work efficiency and the health of passengers. Therefore, the natural frequency of a ship and the effect principle of external factors must be accurately predicted in the design stage to avoid the resonance phenomenon. In order to improve the accuracy of ship vibration modal calculation prediction, this paper investigates the influences of factors including loading conditions, the welding residual stress, and additional water mass on the natural frequency of the ship hull vibration. The details are as follows.Finite element method is utilized to analyze the influence of factors, such as loading conditions and welding residual stress, on the ship vibration modal of a 686 TEU container ship. The three-dimensional finite element model of the container ship has been modeled in a routine of bottom to up direct process by ANSYS software. The loading conditions considering the ballast loads and fully loads difference have been analyzed and compared through the simulation of the quality of goods scattering on the corresponding nodes of lumped mass element. Considering the presence of welding residual stress or not, the vibration modals of container ship have been compared by designating welding residual stress in seam. The comparison results show that the vibration natural modal of container ship are shifted by loading conditions and welding residual stress level in a way of shifting the mass and stiffness, respectively.The numerical simulation method of fluid-structure coupling are used when analyzing the effect of the additional water mass on hull vibration mode. Taking advantage of the Modeling of MAXSURF and meshing of ICEM model in ANSYS, the modeling and meshing of fluid-structure coupling based method are carried out. After the loads calculated by FLUENT, the load data of fluent-structure coupling method from FLUENT are utilized in WORKBENCH software to solve wet vibration modal in the case of different load conditions and speeds. After that the results are compared to that in dry modal case.The comparison of the presented simulation results in this paper with published one shows that the consideration of loading condition, welding residual stress level and wetted included factors may improve the prediction accuracy of natural frequency of vibration modal for ship structure. It is an effective method for calculating ship structure wet vibration modal by adopting the combination of software of fluid-structure coupling.