计及砰击载荷的舰船疲劳损伤直接计算法分析

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

[目的]为了提高砰击载荷对舰船疲劳损伤影响计算的准确性,提出一种计及砰击载荷的疲劳损伤直接计算法。[方法]首先,将非线性载荷的时域计算与线性频域的谱分析方法相结合,基于梁理论得到舰船短期海况下的应力时历;然后,采用雨流计数法和S-N曲线计算出考核点的损伤;其后,参考中国船级社(CCS)指南计算计及非线性砰击载荷对疲劳损伤的贡献度及影响系数,再结合谱分析方法修正对应的应力响应传递函数;最后,对应力谱进行计算,得到计及非线性砰击载荷的疲劳损伤。[结果]结果显示,相比传统谱分析方法,采用计及砰击载荷的舰船疲劳损伤直接计算方法得到的损伤结果其损伤度约增加了10%~50%。[结论]研究表明,对航行于恶劣海况下的舰船进行疲劳强度评估时,使用所提方法可以提高载荷计算的准确性。

[Objective]In 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.[Methods]First,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.[Results]The 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%.[Conclusion]The proposed method can improve the accuracy of load calculation when evaluating the fatigue strength of ships sailing in harsh sea states.