The Effect Of Partial Island Superstructure On The Hull Girder Vibration

In the traditional design of hull structure, the shipboard of transverse section is symmetric or approximately symmetrical layout, but now asymmetric structures often be designed due to the needs of ship types and general layouts. The asymmetric designs of hull structure will directly affect the section properties of hull girder, hence, this paper studies how the partial island superstructures (transverse section is left-right asymmetric form) influence the natural frequency of hull girder.So far, there are three common ways to calculate the free vibration of overall ship:the first is empirical formula; the second is regarding overall ship as a floating free-free variable section beam and scattering it into several parts (general 20 parts) by transfer matrix method and finite element method; the third is regarding overall ship as a spatial structure composed of plate beam structures and scattering it with three-dimensional finite element method. However, the traditional empirical formula were proposed earlier and many of them didn't take the impact on hull girder vibration caused by eccentric superstructure into consideration.This paper takes a ship as simplification, applies finite element software ANSYS to build three dimensional models.explores how partial island superstructures influence the vibration of hull girder by changing parameters of partial island superstructure, including height (number of floors), width, length and the distance to longitudinal section in center plane and corrects the empirical formula which calculates natural frequency of traditional ship with the calculating result of considering eccentric superstructures by contrasting three dimensional finite element results with the empirical formula results.Then building finite element model of one-dimensional beam to analyze above stated cases and contrasting the results with existing calculating results of three-dimensional finite element method, this paper explores the influence of changing the position of superstructure on vibration of one-dimensional beam and explains the influence of position of superstructure on the vibration of hull girder from the changing of moment of inertia after neutral axis deflection.