Study On Additional Mass For Ship Hull’ Global Vibration

Outboard water of Ship hull has an important effect on ship hull’s global vibration. Global vibration is a distinctly important and special issue for ship in the process of operating. Vibration stress and the maximum amplitude due to global vibration are more than ten times as much the requirement of vibration regulation law. Under the effect of such harmful exciting force, global vibration will not only bring great harm to hull structure, but also have a bad effect on human body. Once the resonance of global vibration happened, the cost of reinforce and remedy is very high. The computing method of outboard water has a closely relationship with the inherent frequency of global vibration. Therefore, it is necessary to take account of the influence of outboard water when forecasting the global vibration.In this article, our ship model is one87000t container ship and one210000DWT bulk cargo ship. In the paper, the main contents include the following four aspects:(1) The calculation and analysis of the added mass of Lewis Theory.(2) The calculation and analysis of the added mass of fluid-structure interaction.(3) The calculation and analysis of the added mass of boundary element method.(4) The comparative analysis of three kinds of algorithm.Firstly, the paper introduces the Lewis calculating theory. The added mass of target ship is calculated based on the Lewis theory. Then the inherent frequency of global vibration is calculated based on the added mass of Lewis formula.Secondly, in this paper, based on the fluid structure interaction theory, the fluid structure interaction theory is carried on for the added mass. Through meshing the structure and the fluid respectively, the fluid-structure coupling model is built. Then the inherent frequency of vertical vibrationN horizontal vibration and torsion vibration is calculated.Additionally, the paper describes the boundary element method used to calculate the added mass, as well as use MSC/NASTRAN to calculate the inherent frequency in different loading conditions by BEM.Finally, the paper has carried on the comparative analysis of three methods of the above introduction, In addition, average ralative deviation and applicability of three methods are summed up.