Abstract: Springing occurs obviously for ultra-large ships due to their relatively low stiffness. The conventional quasi-static spectral analysis method cannot solve the problem of ship fatigue damage with consideration of springing, as it ignores the coupling effect of the elastic characteristics of the hull and the hydrodynamic load. To address the above problems, the stress-mode superposition method is used to solve the problem of the fatigue strength assessment for ship hull considering the springing effect. The fatigue of an ultra-large ore ship is calculated and compared with the results of the quasi-static spectral analysis method. The results show that considering the springing effect, the fatigue stress response has double peaks or even multi-peaks in the high frequency band when the encounter frequency is close to the natural frequency of the hull. The springing effect has a greater impact on fatigue when the ship sails in the bow quartering sea, and the springing greatly reduces the fatigue life of partial hull structures. This method can provide references for the ship fatigue assessment under the consideration of springing effect.

Key words: ultra-large ship, springing, stress modal superposition, spectral analysis method, fatigue damage

摘要： 超大型船舶由于相对刚度较低,导致波激振动现象明显。常规的准静态谱分析法未考虑船体的弹性特征及与水动力载荷的耦合效应,无法求解考虑波激振动下的船舶疲劳损伤问题。针对上述问题,以应力模态叠加法为基础,来解决考虑波激振动影响时的船体疲劳强度评估问题,并以某超大型矿砂船为例进行疲劳计算,将结果与准静态谱分析法的结果进行对比分析。结果表明：计及波激振动效应,疲劳应力响应在高频段出现双峰甚至多峰现象,峰值点出现在遭遇频率接近船体固有频率时。波激振动效应使船体结构疲劳寿命大大降低,对于北大西洋海况,船舶在压载工况下的波激振动效应相较满载工况更明显。此方法对解决考虑波激振动下的船舶疲劳评估问题具有一定的参考意义。

关键词: 超大型船舶, 波激振动, 应力模态叠加, 谱分析法, 疲劳损伤