Comparison Study on the Fatigue Damage of a Container Ship Applying Hydroelastic Fatigue Analysis Procedures of LR and BV Classification Societies

Abstract

Container ships, which have hatch openings, are subject to low natural frequencies and exhibit elastic behavior due to wave loads, a phenomenon referred to as the hydroelastic effect. Classification societies have established hydroelastic fatigue analysis procedures to address the increased fatigue damage caused by this effect. This study compares the fatigue damage increase ratios at the hatch coaming top corners according to the procedures provided by Lloyd's Register (LR) and Bureau Veritas (BV). The weight distribution was adjusted using mass and interpolation elements, and normal mode analysis was conducted to obtain the natural frequencies and mode shapes of the ship, which were then used in frequency-domain hydroelastic motion analysis. The fatigue analysis was performed based on LR and BV procedures, using mode response amplitude operators (RAOs) and hydrodynamic coefficients derived from the hydroelastic motion analysis. Despite the differing methodologies between LR and BV, similar stress RAOs were obtained, with the midship showing a higher fatigue damage increase ratio than the forward and aft ends. For the LR procedure, more modes are needed for greater accuracy at the aft end, and for the BV procedure, further investigation is required to address the unreasonable response of the dynamic stress RAO in the low-frequency region, which is distant from the resonance frequency.

Keywords

• hydroelastic fatigue analysis
• springing
• normal mode analysis
• cut-off frequency
• dynamic elastic modes response