Fatigue Analysis of Structural Details of an Oceangoing LPG Ship

Abstract:

Structural details of ship structures are prone to fatigue damage mainly due to high-cycle wave load and low-cycle cargo loading/unloading. Full stochastic fatigue analysis of selected structural details on an oceangoing 6500 cbm LPG ship is presented. A critical Y-joint of longitudinal bulkhead and bilobe tank shell as well as double-bottom girder details are selected due to different reasons. The eccentricity of the Y-joint, leads to significant stress concentration. Saddle supports of gas tanks cause stress concentration in ship double bottom due to weight and dynamic loads. Wave load on ship structure is calculated using linear strip theory for ship in ballast condition and full ship. Wave load is transferred to ship finite element model and notch structural stresses are determined using finite element analysis. Stochastic fatigue analysis is then performed, taking into account sailing route and other ship operational parameters. Finally, fatigue damage summation is done and results are discussed.