FPSO结构低周疲劳寿命计算方法研究

FPSO在海洋环境中频繁地进行装载与卸载操作,使FPSO船体结构产生较大的应力幅值,尤其是承受货油压力的内底纵骨。由于局部的应力集中,应力幅值超过材料的屈服强度,其装卸载次数小于104时,结构将产生低周疲劳。研究一种新的计算方法,根据Neuber假设进行塑性修正,通过应变范围得到伪热点应力范围,并确定热点应力与伪热点应力之间的关系。推导出一种新的S-N曲线作为低周疲劳的设计曲线,以伪热点应力作为计算量来预测低周疲劳寿命,降低了船体结构低周疲劳寿命计算的难度。

Study on computing method of low cycle fatigue life for FPSO structures

The frequent loading and unloading patterns of an FPSO in the marine environment make the FPSO hull structure produce larger stress amplitude, especially for the inner bottom longitudinal under cargo oil pressure. Because of the local stress concentration, the stress amplitude will exceed the material yield strength. While loading and offloading cycle number is less than 104, the structures will suffer low cycle fatigue. A new calculation method is studied, and a plasticity correction is performed according to the Neuber rules. Pseudo hot spot stress range is obtained by strain range. The relationship between the hot spot stress and pseudo hot spot stress is determined. A new S-N curve is deduced as low cycle fatigue design curves using pseudo hot spot stress as the value of calculation to predict the low cycle fatigue life, thus reducing the difficulty of low cycle fatigue life calculation of hull structure.