Local Fatigue Analysis Research Of Special Ship Structures

The fatigue of ship structures is an important problem influencing the safety of ship structures for a long time. Every classification society has carried out lots of researches of the fatigue of hull structures, and formed interrelated criterions, which are mainly aimed at common hulls, such as oil tanker, bulk carrier and container ship. There are few researches for the fatigue of special hulls, such as Wave Piercing Catamaran (WPC) and submarine pressure hull.This dissertation mainly includes the following aspects:(1) The whole WPC finite element model is built, and the loads cases are added loads cases according to involved guide. Then the static analyses are carried out. The fatigue loads probability model of Weibull distribution and the fatigue loads spectrum are set up. The local fatigue analyses of 3 typical cross sections of main hull of the WPC are carried out based on Miner linear cumulative damage theory with an aluminum alloy's S-N curve. The rules of distribution of stress, fatigue life and damage can be found. The effects of mean stress and the shape factor of Weibull distribution on fatigue life are examined. The effects of every random variable on fatigue reliability are researched.(2) The typical submarine cone-cylinder shell model is built, and the appropriate loads cases are added for the static analysis. The external surface of salient of corn-cylinder shell exists high tension stress, and becomes hotspot of fatigue researches. The fatigue of deep-diving submarine's pressure hull structure belongs to low-cycle fatigue. So two types of fatigue life are calculated: crack initial life with local stress-strain method and crack growth life with fracture mechanics method. Then the effects of some factors on fatigue life are researched, including loads, material, geometry, residual stress, initial crack, and so on.In this dissertation, finite element modeling and static analyses are carried out with MSC.Patran/Nastran, and the fatigue calculation and analyses are achieved with MSC.Fatigue. The fatigue calculation in this dissertation includes 3 methods: S-N curve method, local stress-strain method, and fracture mechanics method. The reliability calculation is also involved, so this dissertation has some universality. This dissertation expounds the effects of variable factors on fatigue lives of WPC and submarine pressure hull in different aspects, and it has some referenced value for relational researches and anti-fatigue designs.