In this paper, the effects of underwater-chain-stopper (UCS) bearing friction at fairlead connection and time-varying interlink EI (bending stiffness) at the UCS exit on the OPB-fatigue-induced chain failure are investigated. To demonstrate their effects through numerical simulations, three different approaches, such as only considering time-varying EI, considering both time-varying EI and fairlead bearing friction, and neither considered, are modeled and the results are systematically compared. With fairlead bearing friction, the fairlead boundary condition is adjusted during the time-marching simulation according to the criterion between UCS angle and breakout angle. The numerical results show that the fairlead bearing friction plays much more important role than time-varying EI in significantly increasing OPB-induced fatigue damage, which is due to the significant increase of interlink angle and bending moment by the former especially at taut side. Furthermore, the present approach considering both time-varying EI and fairlead bearing friction is compared with widely adopted BV (Bureau Veritas) methodology. Also, since fairlead bearing friction effect is coupled with UCS bending stiffness, the bending moments and fatigue damages at UCS exit for various UCS bending stiffness are compared. Finally, the effects of residual stresses at hot-spots on OPB-induced fatigue damage are investigated.

本文研究了水下导链器（UCS）在导缆接头处的摩擦以及UCS出口处时变的互连EI（弯曲刚度）对OPB疲劳引起的链条破坏的影响。为了通过数值模拟证明其效果，对三种不同的方法进行了建模，例如仅考虑随时间变化的EI，同时考虑随时间变化的EI和导缆轴承的摩擦而未考虑的方法，并对结果进行了系统比较。在有导缆轴承摩擦的情况下，根据UCS角和突围角之间的准则，在时间行进模拟过程中调整了导缆边界条件。数值结果表明，导缆轴承摩擦在显着增加OPB引起的疲劳损伤方面比时变EI起重要作用，这是由于前者尤其是在拉紧侧时，互连角度和弯矩的显着增加。此外，将同时考虑到时变EI和导缆轴承摩擦的本方法与广泛采用的BV（Bureau Veritas）方法进行了比较。另外，由于导缆轴承的摩擦效果与UCS的弯曲刚度有关，因此，针对各种UCS的弯曲刚度，比较了UCS出口处的弯矩和疲劳损伤。最后，研究了热点处的残余应力对OPB引起的疲劳损伤的影响。由于导缆轴承的摩擦效果与UCS的弯曲刚度有关，因此比较了各种UCS的弯曲刚度时，UCS出口处的弯矩和疲劳损伤。最后，研究了热点处的残余应力对OPB引起的疲劳损伤的影响。由于导缆轴承的摩擦效果与UCS的弯曲刚度有关，因此比较了各种UCS的弯曲刚度时，UCS出口处的弯矩和疲劳损伤。最后，研究了热点处的残余应力对OPB引起的疲劳损伤的影响。