半潜平台结构强度分析.doc

摘 要
随着陆地油气资源的不断枯竭，海洋成了未来能源的主战场。作为深海油气开发的主流装备，新型半潜式海洋钻井平台对我国而言，还有很大的空间有待探究。其一，就水动力性能而言，半潜平台的低垂荡运动有利于更高的时间比例进行钻探，较低横摇、纵摇幅值运动有助于平台操作和运输，以及其他水动力性能的研究有利于动力定位系统的开发，等等；其二，就结构强度分析而言，结构强度是平台良好运行的先决条件，其意义不言自明；其三，由于波浪载荷的循环作用，就必须考虑疲劳强度；其四，在结构设计阶段，往往只考虑强度，而工艺建造水平以及经济效益才是真正决定该领域的发展方向，故在结构设计时也要多考虑工艺和经济效益；等等。
本文依托ABS规范，用DNV.SESAM软件完成了平台结构强度分析、水动力性能分析和关键部位疲劳可靠性分析。其主要研究内容和结论如下：
1）统计了半潜式钻井平台的发展历史和现行状况，分析了平台结构和技术特点，总结了国内外波浪载荷和疲劳可靠性的研究现状。
2）阐述了水动力分析的基本理论，其中包括零航速的三维势流理论求解，任意位置任意点的morison杆上波浪力的求解，平台水动力参数的物理意义以及波浪载荷长期预报的理论推导。根据ABS《近海结构物疲劳评估》规范，从理论上推导了采用S-N曲线与Miner线性累积损伤理论为基础的疲劳谱分析法，总结了结构热点谱疲劳可靠性分析的完整过程。
3）完成了三种半潜平台的波浪载荷计算和水动力性能比较分析，得出斜撑平台的垂荡响应运动最优，以及撑杆结构的变化对平台一阶波浪激励力影响不大。
4）总结了目标半潜平台的结构强度分析方法和流程，并采用随机性设计波法，确定了三种半潜平台的设计波参数，得出中纵剖面的最大纵向剪切状态时波浪载荷最恶劣。同时，根据ABS规范对三种平台的关键部位进行了屈服强度校核，得到斜撑平台最好，但疲劳热点数较多，推荐改用空间交叉型的撑杆结构。此外，还分析了水平撑杆的焊接工艺技术和探讨了不同撑杆形式对建造的影响，可知斜撑结构工艺相对复杂。
5）采用疲劳谱分析法，预报了撑杆趾端疲劳寿命，结果显示符合ABS规范的设计寿命20年要求，并得到了97.13%以上的可靠度。

关键词：半潜平台；谱分析法；结构强度；水动力性能分析；疲劳可靠性






Abstract
As the hydrocarbon resources inland is unceasingly decreasing, the exploitation of those resources is transferring to the ocean, and the marine energy is becoming the major energy resources in the future. Nowadays, the semi-submersible drilling platforms have played key roles in the deep-sea exploitation, and still, with a lot of scope of development. Firstly, as to hydrodynamic performance, for instance, reducing the heave motion of the semi-submersible platform can bring more time for drilling; decreasing the amplitude of roll and pitch can contribute to platform operation and transportation; studying on further hydrodynamic performance will benefit to the development of the dynamic positioning, etc. Secondly, since structural strength analysis is treated as the priority of maintaining the platform in good condition, the further research on it is of great significance. Moreover, due to the effect of cyclic loading, we should take fatigue assessment into consideration when we get down to analysis. Additionally, in the stage of structure design, we should pay more attention to the construction level and economic returns instead of the mechanical properties.
The analysis of structural strength analysis, hydrodynamic analysis, and fatigue reliability analysis of a hotspot location for aimed semi submersible platform will be carried out by DNV.SESAM software, which are based on ABS specifications. So the following problems are emphatically investigated.
1) In this paper, the development history and current status for the deep-water semi-submersible drilling platform will be introduced as well as the analysis of structure and technical characteristics. Besides, the status quo of wave loads and fatigue reliability in China and abroad will be summarized.
2) The basic theory of hydrodynamic analysis is represented which includes solution for 3D potential theory at zero speed, solution for wave force in any location which be based on Morison theory, physical significance of hydrodynamic parameter for platform, and theoretical derivation of long-term forecast for wave load. With the requirements of ABS Guide for the Fatigue Assessment of Offshore Structures, the spectral-based fatigue analysis approach is derived theoretically by using S-N curve and Miner’s rule in accordance. The complete process of the spectral fatigue reliability analysis for hotspots is summarized.
3) With the calculation of wave load and comparative analysis of hydrodynamic performance for three semi submersible platforms, it was deduced that the third platform in diagonal brace has the minimum heave RAO swing motion response and the changes of brace structural make very little difference on 1st order wave exciting force.
4) The method and process of analysis for structural strength of semi submersible platform is summarized. The design wave parameters of three semi submersible platforms are determined by using random design wave method, thus the conclusion that the wave load in the state of longitudinal shear force between pontoons is the worst is put forward. Meanwhile, ..