深水半潜式平台疲劳损伤评估技术研究

发布时间：2018-09-07 21:02

【摘要】：经济的高速发展导致油气资源的消耗量急剧上升,进一步加快海洋油气资源的开发是缓解油气资源压力的重要途径之一。深水浮式平台是目前深水油气资源开发的主要设备,其长期处于海洋环境当中,在循环荷载的作用下不可避免的产生累积疲劳损伤,最终使得结构发生疲劳失效,引发灾难性事故。疲劳损伤是海洋结构物重要的损伤形式之一,因此有必要对结构的疲劳损伤进行深入研究。本文系统的总结了疲劳分析相关理论模型和常用的分析方法,对结构疲劳分析的研究现状进行了详细的论述,并在结构的疲劳评估技术方面开展了一些研究工作,本文主要研究内容如下：1、针对本文研究的半潜式平台建立了水动力模型、结构有限元模型和质量模型,对其频域水动力模型进行了分析研究,得到了结构的水动力参数。利用格林函数、源强函数和Morison公式对作用在半潜式平台结构上的波浪荷载进行了计算。利用设计波法得到了半潜式平台典型受力工况下的设计波要素,并对该设计波条件下的结构强度进行了计算校核。研究结果表明本文研究的半潜式平台水动力性能优良,结构强度满足要求。2、根据半潜式平台结构的受力特点和应力分布规律,筛选了容易产生疲劳损伤的六个关键点。对关键点部位的结构进行了网格加密处理,经结构强度分析得到了关键点处的热点应力传递函数。利用谱分析方法对不同方向波浪作用下关键点的疲劳损伤规律进行了对比研究。研究结果表明,波浪纵向作用时造成的关键点疲劳损伤最小,横向时次之,斜向时最大。波浪斜向作用时,立柱和纵向浮筒以及立柱与斜撑连接处的疲劳寿命偏小,其他点的疲劳寿命满足要求。3、针对半潜式平台结构系泊耦合运动进行了研究,得到了不同海况下结构的运动时程和系缆张力时程,对结构在极限环境条件下的运动和系缆张力进行了校核。利用时域方法对系缆的疲劳损伤问题进行了研究,探讨了波浪波高和波浪周期对系缆损伤度的影响规律。研究结果表明,若波浪波高恒定,随着波浪周期的增大系缆的疲劳损伤度呈现先增大后减小的变化趋势;若波浪周期恒定,随着波高的增大系缆的疲劳损伤度呈指数增长的变化趋势。三段式系泊的疲劳寿命可以分为三个区域：低寿命的上端系泊锚链区、高寿命的中段系泊钢缆区以及低寿命的拖地段系泊锚链区。在相同条件下系泊钢缆的抗疲劳性能要远优于系泊锚链的抗疲劳性能,R4级系泊锚链的抗疲劳性能要优于R3级系泊锚链的抗疲劳性能。4、针对提高疲劳评估时域方法的计算效率问题展开了研究,通过对多个短期海况组块进行等效,减少时域评估时计算的海况个数来达到提高时域方法的计算效率的目的。研究提出了四种波浪海况组块划分方式,设计了评估偏差参数和计算效率参数用于各种组块划分方式优劣的比较。研究结果表明,对海况组块进行等效的思想能够极大的提高时域评估方法的计算效率；与基准计算方法相比,等周期组块划分方法会高估结构系缆的疲劳寿命;等波高组块划分方法会低估结构系缆的疲劳寿命；六海况组块划分方式会高估结构系缆的疲劳寿命；四海况组块划分方式的计算结果与海况组块未进行简化处理的计算结果最为接近,能够满足要求。提出的高效组块划分方法是本文的主要创新点。
[Abstract]:With the rapid development of economy, the consumption of oil and gas resources has risen sharply. Further accelerating the development of offshore oil and gas resources is one of the important ways to relieve the pressure of oil and gas resources. Fatigue damage is one of the most important damage forms of offshore structures, so it is necessary to study the fatigue damage of structures deeply. This paper systematically summarizes the relevant theoretical models and common analysis methods of fatigue analysis, and points out the fatigue components of structures. The main contents of this paper are as follows: 1. The hydrodynamic model, the finite element model and the mass model of the semi-submersible platform studied in this paper are established, and the frequency domain hydrodynamic model is analyzed and studied. Hydrodynamic parameters of the structure are obtained. Wave loads acting on the semi-submersible platform structure are calculated by using Green's function, source strength function and Morison's formula. Design wave elements under typical loading conditions of semi-submersible platform are obtained by using design wave method. Structural strength under the condition of design wave is calculated and checked. The results show that the semi-submersible platform studied in this paper has excellent hydrodynamic performance and the structural strength meets the requirements. The results show that the fatigue damage caused by longitudinal wave action is the smallest, then the transverse wave action is the second, and the oblique wave action is the largest. The fatigue life of the connection with the diagonal brace is relatively small, and the fatigue life of the other points meets the requirements. 3. The mooring coupling motion of the semi-submersible platform structure is studied. The motion history and the mooring tension time history of the structure under different sea conditions are obtained. The motion and the mooring tension of the structure under the limit environment are checked. The fatigue damage of mooring cables is studied, and the influence of wave height and wave period on the damage degree of mooring cables is discussed. The results show that if the wave height is constant, the fatigue damage degree of mooring cables increases first and then decreases with the increase of wave period; if the wave period is constant, the damage degree of mooring cables increases with the increase of wave height. The fatigue life of three-stage mooring can be divided into three zones: the upper mooring chain zone with low life, the middle mooring cable zone with high life and the mooring chain zone with low life. The fatigue resistance of the R4 mooring chain is better than that of the R3 mooring chain. 4. To improve the calculation efficiency of the time-domain method for fatigue assessment, a study is carried out. The calculation efficiency of the time-domain method is improved by equivalence of several short-term sea conditions blocks and reduction of the number of sea conditions calculated in the time-domain method. Aim. Four kinds of block partitioning methods for wave and ocean conditions are proposed, and the evaluation deviation parameters and calculation efficiency parameters are designed to compare the advantages and disadvantages of different block partitioning methods. The fatigue life of structural mooring cables can be overestimated by the method of time block partition; the fatigue life of structural mooring cables can be underestimated by the method of equal wave height block partition; the fatigue life of structural mooring cables can be overestimated by the method of six sea conditions block partition; the results of four sea conditions block partition are the closest to those of non-simplified sea conditions block partition. The proposed efficient block partition method is the main innovation of this paper.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TE951

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