Precise Assessment of Load/Structural Response and Development of Practical Design Method in Fatigue Strength Design of a Ship

在船舶疲劳强度设计中，准确估算船舶某个结构构件在波浪中的应力波动是至关重要的。如果用累积疲劳损伤系数来评价结构构件的疲劳强度，则需要获得应力波动发生的长期概率，并结合S-N曲线。对于船舶在波浪中的横向强度而言，波浪动水压力是最重要的外载荷，尤其是对船舶的疲劳强度而言，波浪动水压力是最重要的外载荷。为了得到海压力引起的应力响应函数，原则上需要在每种波浪条件下进行有限元分析，因为海压力的分布规律以及大小，沿着船的长度， ...更多信息 的船体根据波浪条件而变化，并且由于自由表面高度沿着舷侧壳体的非线性起着重要作用。然而，在结构设计阶段进行这种结构分析可能是不可能的，因为它需要大量的计算时间和精力，在本研究中，应力响应函数和波压力引起的应力发生的长期概率计算使用目前最精确的方法。在这个过程中，将研究由于自由表面沿侧壳沿着升高而引起的非线性的处理。在此基础上，提出了预测应力响应函数和应力长期发生概率的简化方法，即最小-最大法和相似响应函数法。比较了精确法、近似法和常规法的计算结果，从船舶疲劳强度设计工具的角度讨论了预报方法的准确性。少

In the fatigue strength design of a ship, it is most important to estimate the accurate stress fluctuation of a certain structural member of the ship in waves. In case the fatigue strength of the structural member is evaluated by the cumulative fatigue damage factor, it is necessary to obtain the long-term probability of occurrence of the stress fluctuation, which is combined with S-N curves. For this purpose, a probabilistic approach is usually adopted, and it is essential to calculate the frequency response function of stress accurately in the probabilistic approach.As for the transverse strength of a ship in waves, hydrodynamic sea pressure in wave is the most important external load, particularly for fatigue strength of a ship. In order to obtain the stress response function caused by the sea pressure, a finite element analysis is necessary to be carried out in every wave condition in principle, because the distribution pattern of sea pressure, as well as the magnitude, along ship' … More s hull varies according to the wave conditions, and a non-linearity due to the free surface elevation along the side shell plays an important role. However, it may not be possible to conduct this kind of structural analysis in the structural design stage, because it requires enormous time and effort in computation.In the present research, the stress response function and the long-term probability of occurrence of stress caused by wave pressure are calculated with the use of the most exact method at present. The treatment of the non-linearity due to the free surface elevation along the side shell will be investigated in this process. Then, simplified methods to predict the stress response function and the long-term probability of occurrence of stress are proposed ; that is, Min-Max Method and Similar Response Function Method. Comparing these calculated results by the exact method, approximate method and conventional method, the accuracy of the prediction method is discussed from the viewpoint of the design tool for fatigue strength of a ship. Less