On the Wave Loads for Accurate Structural Design of Ships

对于目前的船舶结构设计，船级社的规范认可直接强度计算，并给出了计算所需的波浪载荷。然而，将这种波浪载荷应用于船舶疲劳强度的研究是值得怀疑的。在船舶疲劳分析中，准确地估计压力在时间和空间上的波动是最重要的。本文首先计算了波浪压力在时间和空间上的波动，然后计算了波浪压力在时间和空间上的波动。通过对沿着船体船体压力分布的测量，介绍了4种典型的压力脉动分布模式，用于船舶疲劳分析。利用该压力，可以利用船舶的子结构模型进行结构疲劳强度分析，但在利用子结构模型进行结构分析时，不容易施加足够的不平衡力和设置适当的边界条件。迄今为止，为克服这些困难，采用了几种经验技术。其次，研究了船体子结构模型中不平衡力和边界条件的几种处理方法，阐明了各种处理方法对应力的影响，并利用所介绍的压力分布模式，对适当不平衡力和边界条件的子结构模型进行了结构分析。分析了内底板和舱底底板的应力分布，并对疲劳分析所需的设计波浪载荷进行了分类。

As for the recent structural design of a ship, direct strength calculations are approved in classification society's rules, and wave loads for the calculation are given. However, it is questionable to apply such wave loads to the investigation of fatigue strength of a ship. In fatigue analysis of a ship, it is most important to estimate accurate pressure fluctuations in time and space. The stress fluctuation can be calculated with the use of the pressure fluctuations.In this research, the fluctuations of wave pressure in time and space were calculated firstly. Surveying the pressure distributions along ships' hull, 4 typical patterns of distribution of pressure fluctuation were introduced for fatigue analysis of ships. Using this pressure, structural analyzes for fatigue strength of a ship can be conducted with the use of a sub-structured model of the ship.In the structural analysis using the sub-structured model, however, it is not easy to apply the adequate unbalanced force and to set up the proper boundary conditions. Several empirical techniques were adopted to overcome such the difficulties so far. In this research, several methods to treat the unbalanced force and the boundary conditions in the sub-structured model of the ship were investigated secondly, and the effects of each treatment on the stress were clarified.With the use of the introduced pressure distribution patterns, structural analyzes were performed for a sub-structured model with proper unbalanced forces and boundary conditions surveyed herein. The stress distributions on the inner bottom plate and the bilge hopper tank plate were investigated, and the design wave loads for fatigue analysis of a ship are classified.