There are generally two kinds of methods to evaluate the fatigue life for ship structures. One is based on the simplified fatigue analysis and the other based on direct fatigue analysis.
In the simplified fatigue analysis method, fatigue loads are estimated from formulas in the KR Rules and then the fatigue lives for longitudinal end connections and the hopper knuckle parts are calculated.
In the direct fatigue analysis method, fatigue loads made from the direct load analysis are applied to the whole ship FE model (or a hold FE model) with a very fine mesh element for evaluation of the hot spot stresses on the fatigue structures and then the fatigue lives for vessel's specific structures are calculated.
And the direct fatigue analysis method may be split into the spectral fatigue analysis method, stress influence coefficient method and design wave method.