Analysis of the direct calculation method of ship fatigue damage considering slamming load

Abstract

ObjectiveIn order to improve the calculation accuracy of the influence of slamming load on ship fatigue damage, and evaluate ship fatigue life more effectively, a direct calculation method of ship fatigue damage which accounts for slamming load is proposed. MethodsFirst, the time domain calculation of nonlinear load is combined with the spectral analysis method of linear frequency domain, and the stress time history of the ship in a short-term sea state is obtained based on beam theory. Second, the damage of the check points is calculated using the rain flow counting method and S-N curve, the contribution and influence coefficients of nonlinear slamming load on fatigue damage are calculated with reference to the CCS guidelines, and the corresponding stress response transfer function is corrected by combining the spectral analysis method. Finally, the stress spectrum is calculated and fatigue damage accounting for nonlinear slamming is obtained. ResultsThe results show that compared with traditional spectral analysis method, it is found that the ship fatigue damage obtained by the direct calculation method accounting for slamming load is about 10%–50%. ConclusionThe proposed method can improve the accuracy of load calculation when evaluating the fatigue strength of ships sailing in harsh sea states.

Keywords

• fatigue damage
• nonlinear slamming load
• spectral analysis
• direct calculation method