【作者】 彭程；

【导师】 杨树耕；

【作者基本信息】 天津大学 ， 船舶与海洋结构物设计制造， 2007， 硕士

【摘要】 自升式平台是海上石油开发的主要工程结构之一。其自身柔性较大,自振周期较长,易与波浪中低频部分发生共振,同时在波浪作用下会产生较大的动力放大效应。因此对平台进行动力分析就显得非常重要。平台在海洋环境中会受到波浪的循环作用,在平台结构上会产生循环变化的交变应力。虽然应力水平低于材料的屈服强度,但是在长期的交变应力的作用下,平台有可能产生突然性的疲劳破坏。因此对平台进行疲劳分析也有着重要的意义。本论文采用ANSYS有限元软件进行模拟分析。对不同状态下的平台进行模态分析,求出平台在不同状态下的固有频率,并与波浪频率进行比较,判断平台与波浪发生共振的可能性。在模态分析的基础上,采用模态叠加法对平台的较完善有限元模型进行瞬态动力分析,解决了大型模型难以应用动力分析的难题。本论文还应用“设计波”法和“谱分析”法对平台的部分关键构件进行了疲劳分析,并详细对比了两种方法的计算结果,分析计算结果产生差异的原因,对如何选择疲劳分析方法提出了建议。更多还原

【Abstract】 Jack-up is one of the major engineering structures in offshore oil development. Because of its large flexibleness and long natural cycles, it is easily resonant with low frequency wave. Meanwhile, waves will give a greater dynamic magnification effect on platform. So the dynamic analysis on jack-up is very important.Platforms in marine environment will be affected by the cycled waves, and alternating stresses will appear on the platform structure. Although the stress level is below the yield strength, long-term exposure to the alternating stresses may make the platform suffer the suddenly fatigue damage. So it has important significance to apply fatigue analysis to the jack-up platform.In this paper, we will use ANSYS for simulation analysis. We will do Modal Analysis on platform under different conditions, calculate the platform’s natural frequencies under different conditions, compare them with wave frequencies, and estimate the possibility of the platform to resonate with waves. After Modal Analysis, we will apply transient dynamic analysis using modal superposition method on better platform finite element model, and we have solved the problem to apply dynamic analysis on large finite element model.In this paper, we also use the“design-wave”method and“spectrum”method to apply fatigue analysis on key components of the platform. Then we compare the calculation results from the two methods, analyze the causes for the differences, and give an advice for how to choose fatigue analysis methods.更多还原