Fatigue damage calculation of ULCS based on hydroelastic model for springing

Abstract

Ship transport is growing up rapidly, leading to ship's size increase, particularly for container ship. The last generation of container ship is now called Ultra Large Container Ship (ULCS). Due to their increasing sizes (LBP close to 400 m nowadays), they are more flexible and their structural natural frequencies may fall into the range of encounter frequencies. Therefore, waves may induce springing vibration of the whole hull girder, which will increase the fatigue damage. The purpose of the paper is to present a practical and reliable spectral fatigue damage methodology based on 3D linear hydroelastic model using 3DFEM and 3DBEM (‘Boundary Element Method') coupling procedure in frequency domain for fatigue design of ULCS. This paper presents the validation of the hydroelastic numerical model with springing tests. Moreover, it presents the validation of the spectral fatigue methodology used to calculate fatigue damage of ULCS due to springing by calibration with respect to Rainflow counting method. This methodology was applied for the fatigue study of 16,000 TEU ULCS typical structural details. The results show that springing response has a very significant impact on fatigue damage for this type of ULCS having L_BP length close to 400 m.