【作者】 冯国庆；

【导师】 任慧龙；

【作者基本信息】 哈尔滨工程大学 ， 船舶与海洋结构物设计制造， 2003， 硕士

【摘要】 疲劳破坏是船体结构主要的失效模式之一，因此，国内外的船舶结构研究人员和机构都十分重视船体结构的疲劳问题。目前，世界上各主要的船级社均发布了自己的结构疲劳评估规范，作为船舶疲劳评估的指导性文件。但是，由于影响结构疲劳性能的因素十分复杂，如波浪载荷和局部的货物压力，各种应力成分的组合，结构的局部细节应力集中，平均应力的影响，结构分身所处的腐蚀环境等等，所以各个船级社有关的规定也不一样，这样必然造成各个评估方法之间的差异。本文以DNV疲劳评估规范为指导，以12300吨滚装船为依托，探讨了DNV疲劳评估规范中不同方法之间的差异，其主要内容包括： 1、对DNV疲劳评估方法的要点做以说明，利用DNV疲劳评估文献提供的简化方法对感兴趣的节点进行疲劳评估。并计算和讨论了简化算法中计入平均应力和不计入平均应力对疲劳寿命的影响水平。 2、参考船体的结构图，对船体结构进行合理的模型化，建立整船的有限元模型。针对谱分析方法中需要求得响应幅值的特点，给出了一种简化分析过程的方法。 3、由于向有限元模型施加压力的时候，船体湿表面的压力不尽相同，并且没有规律可循，如果单元很多，那么手工加载的效率就很低，本文开发了基于PCL的自动加载程序，提高了工作效率。 4、按照谱分析方法，对线性波浪载荷下结构的疲劳寿命进行了计算。并讨论了计入平均应力影响和不计入平均应力影响的差别。由于在谱分析方法中考虑到了由波高、特征周期及浪向确定的不同海况，所以本文也分析了各海况对疲劳寿命的影响。更多还原

【Abstract】 Fatigue and fracture have been an important issue for ship and offshore structures for a long time. Growing attention has been paid to it from researchers and institutes in this field. Until now, the major classification societies have already released their fatigue assessments notes. But due to the complexity of factors influencing fatigue performance, such as wave load and pressure from cargo, the combination of different stress components, stress concentration of local structure details, mean stress and the corrosive environments, etc, there are different specifications with varying classification societies, so it will lead to the diversity of results from different fatigue assessment methods. The prime goal of this paper is to conduct the fatigue analysis for certain type of structural details of 12300T Ro/Ro vessel by means of three different approaches stated in DNV classification notes "the fatigue assessment for ship structures" and contrast the results from the three different methods.Firstly, the key points of DNV fatigue assessment are addressed, and then the fatigue strength of some nodes concerned is conducted using the simplified analysis provided by DNV fatigue assessment rules.. And the key the influence of mean stress for fatigue strength is computed and discussed when the mean stress is accounted for or not.Secondly, the molded lines and structural alignment should be referenced rationally in the process of the finite element modeling, but structural idealization should be based on the stiffness and anticipated response of the ship structure. And an approach is given to seek the response amplitude needed by spectral analysis method aiming at simplified the response amplitude seeking procedure.Thirdly, imposing pressure load on the wetted surface is a hard job because the pressure value is various and there is no regularity to fellow especially when the model is large. So it’s very important to find a feasible automated loading approach that can be used in the FEM analysis of ship structure. This paper proposes an automated loading approach based on Patran command language that will enhance the efficiency of loading.Finally, the spectral fatigue analysis has been conducted under linear wave load and ship motion. In this analysis procedure, the mean stress is accounted for by obtaining the equivalent stress derived from Goodman formula or not and the difference between the two cases are discussed. At the same time, the contribution of each sea state to the fatigue damage is dissertated.更多还原