大型薄膜型LNG船疲劳强度分析

Fatigue strength analysis of a large membrane LNG carrier

以某17.5×10^(4)m^(3)LNG船的结构设计为例,采用谱分析法对全船典型结构进行疲劳强度分析。针对LNG船的满载和压载2种常用航行载况,分别建立全船有限元模型和水动力模型。利用三维水动力软件计算在多个浪向、波浪频率的规则波上的波浪载荷,进一步求得结构的应力传递函数。根据Miner线性累计损伤理论,选用北大西洋波浪散布图和适当的S-N曲线,计算结构的疲劳损伤。除了计算波浪诱导的高周疲劳损伤,还通过简化算法计算装货/卸货诱导的低周疲劳损伤。评估结果表明,部分结构可以通过适当增加结构尺寸和优化结构型式以满足NA40年的设计要求,但也有少量位置需要打磨。基于实船的设计过程,通过和船东、船级社紧密沟通,对建造需求和规范条文有较深入的理解,对大型LNG船设计有较高的参考价值。

For the structural design of a 175 000 m^(3) LNG carrier,the fatigue strength of typical details is analyzed through spectral method.For two most frequently used seagoing loading conditions,the finite model of global ship and hydrodynamic model are built.The wave loads are calculated for a series of wave directions and frequencies,the Response Amplitude Operators(RAO) between the waves and the stresses,for each operating condition are obtained later.According to Miner's rule,calculated the fatigue damage with North Atlantic scatter diagram and suitable S-N curves.In addition to the high-cycle wave induced fatigue damage,the low-cycle fatigue damage due to loading/unloading sequences is also calculated.The results show that some structural details can meet the requirement of NA40 years by increasing the size and optimizing the type,thus little ones need to be grinded.Based on a project,has a good understanding of construction demands and rules by close communications with the owner and the class society,can provide valuable references for the design of large LNG carriers.