风暴潮作用下在役海洋导管架平台疲劳可靠度研究

发布时间：2018-04-30 22:12

本文选题：风暴潮 + 随机波浪力　；参考：《江苏科技大学》2014年硕士论文

【摘要】：随着全球气候的不断变化，海洋环境变得异常复杂。特别是近年来我国沿海地区台风频发，由此产生的台风风暴潮给近海采油平台的安全带来了严峻考验。在高幅值随机波浪力的长期作用下，容易引发结构的疲劳问题。结构疲劳寿命的影响因素大多是不确定的，必须从可靠度理论入手，对结构的疲劳寿命作出合理的预测。应力幅值和应力集中系数是影响结构疲劳寿命的两个重要因素。选取桩腿底部和每层横梁的部分管节点作为研究对象，考察平台结构在随机波浪力作用下的疲劳性能和可靠度。本文以某一导管架平台为例，对风暴潮作用下结构的疲劳可靠度进行了系统地研究。主要研究内容包括：（1）基于随机海浪的二维模型—Longuest-Higgins模型，以改进的JONSWAP谱作为理想海浪谱，，通过MATLAB编程实现风暴潮环境下随机海浪的数值仿真。根据Welch算法基本原理，利用MATLAB中的pwelch函数对仿真结果进行功率谱估计。通过与原有的JONSWAP谱进行对比，可以看出仿真效果良好。在此基础上，提出影响仿真结果和功率谱估计的几个主要参数及其取值标准。（2）根据不同波浪理论的适用范围，选用Stokes二阶波和线性波理论，结合线性化Morison方程，分别给出随机波浪力的时域表达式。在此基础上，利用MATLAB求解任意时刻作用在导管架平台杆件上的随机波浪力。运用有限元软件ANSYS建立结构有限元模型，通过施加随机波浪力，对其进行瞬态动力分析，得到平台各点的名义应力时程。（3）考虑到应力集中系数对结构疲劳损伤的影响，首先在ANSYS中利用SHELL63单元建立管节点的局部有限元模型，通过施加整体有限元模型中的位移边界条件，求出各管节点的热点应力，从而得到热点处的应力集中系数。接着，运用雨流计数法统计出各热点的应力时程所对应的等效应力循环。最后，根据S-N曲线和Miner线性疲劳累积损伤理论，估算出各热点的疲劳损伤度D和疲劳寿命N f。（4）介绍了随机疲劳载荷作用下考虑不确定因素的结构疲劳损伤计算方法，给出结构疲劳寿命的参数表达式。通过定义随机变量来描述影响结构疲劳寿命的几种不确定因素，给出不确定因素下结构的疲劳寿命可靠度计算公式。由此，可计算出该导管架平台各点的疲劳寿命可靠度Pr和失效概率Pf。
[Abstract]:As the global climate changes, the marine environment becomes extremely complex. Especially in recent years, typhoon occurred frequently in coastal areas of China, and the typhoon storm surge brought severe test to the safety of offshore oil production platform. Under the action of high amplitude random wave force for a long time, it is easy to cause the fatigue problem of the structure. The influencing factors of fatigue life of structures are mostly uncertain. It is necessary to make a reasonable prediction of the fatigue life of structures based on the reliability theory. Stress amplitude and stress concentration factor are two important factors affecting fatigue life of structure. The fatigue behavior and reliability of the platform structure under random wave force were investigated by selecting the pipe joints at the bottom of the pile leg and the cross beam of each layer as the research object. In this paper, the fatigue reliability of a jacket platform under the action of storm surge is systematically studied. The main research contents include: 1) based on the two-dimensional model of random wave, the improved JONSWAP spectrum is used as ideal wave spectrum, and the numerical simulation of random wave in storm surge environment is realized by MATLAB programming. According to the basic principle of Welch algorithm, the power spectrum of the simulation results is estimated by using the pwelch function in MATLAB. By comparing with the original JONSWAP spectrum, we can see that the simulation effect is good. On this basis, several main parameters affecting simulation results and power spectrum estimation and their values are proposed. 2) according to the applicable range of different wave theories, Stokes's second-order wave theory and linear wave theory are selected, and the time-domain expressions of random wave forces are given in combination with linearized Morison equation. On this basis, the random wave force acting on the jacket platform member at any time is solved by MATLAB. The finite element model of the structure is established by using the finite element software ANSYS. By applying random wave force, the transient dynamic analysis is carried out, and the nominal stress time history of each point of the platform is obtained. Considering the effect of stress concentration factor on fatigue damage of structure, the local finite element model of pipe joint is established by using SHELL63 element in ANSYS. By applying the displacement boundary condition in the integral finite element model, the hot stress of each pipe joint is obtained. The stress concentration factor at the hot spot is obtained. Then, the equivalent stress cycles corresponding to the stress history of each hot spot are calculated by the rain flow counting method. Finally, according to S-N curve and Miner linear fatigue cumulative damage theory, the fatigue damage degree D and fatigue life N f of each hot spot are estimated. In this paper, the fatigue damage calculation method considering uncertain factors under random fatigue load is introduced, and the parameter expression of structure fatigue life is given. Several uncertain factors affecting the fatigue life of structures are described by defining random variables, and the formulas for calculating the reliability of fatigue life of structures under uncertain factors are given. Therefore, the fatigue life reliability and failure probability of the jacket platform can be calculated.
【学位授予单位】：江苏科技大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P742;TE952

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