非线性波浪力对海洋平台疲劳寿命评估的影响研究

发布时间：2018-05-28 22:18

本文选题：疲劳分析 + S-N曲线法　；参考：《中国海洋大学》2014年硕士论文

【摘要】：随着我国经济的飞速发展，能源的需求量也越来越大，加速我国海上油气资源开发是当务之急。浅海导管架平台与深海浮式平台作为目前海上石油开发普遍采用的形式，在随机波浪载荷作用下会产生累积疲劳损伤，严重的会发生疲劳破坏，造成严重后果。随着平台服役年限的增长和平台老化问题的日益加剧，疲劳损伤已成为海洋平台构件损伤的重要原因。因此疲劳寿命分析和评估研究对海洋平台的安全至关重要。本文系统回顾了疲劳分析相关理论和常用的疲劳分析方法，，对疲劳分析的研究现状及非线性因素对疲劳分析影响进行了论述，重点针对非线性波浪力对海洋平台疲劳寿命评估的影响展开研究工作，主要研究内容和创新点如下： 1)本文系统研究了频域法、确定性法和时域法三种疲劳分析方法，开展了针对导管架平台的疲劳寿命评估工作，对比和分析了不同疲劳分析方法所得疲劳寿命。将时域法计算结果作为基准，则得出确定性法高估结构疲劳寿命和频域法低估疲劳寿命的结论。同时，在频域方法中考虑循环计数修正因子可以提高频域法分析结果的准确性。 2)本文在确定性方法中根据线性波与Stokes5阶波的适用条件引入非线性波浪理论，并针对导管架平台开展疲劳寿命分析工作，研究并分析了非线性波浪理论代替线性波浪理论后对疲劳寿命结果的影响。通过计算可以得出引入Stokes5阶波浪理论以后，结构的疲劳寿命有所增加，增加量在20%左右，影响较为明显。 3)针对小桩柱求解波浪力时普遍使用线性化波浪力谱计算的现状，本文在疲劳计算中引入了非线性拖曳力谱，推导了非线性波浪力谱表达式，并针对导管架平台结合非线性波浪力谱进行疲劳分析。计算结果表明，增加非线性拖曳力谱修正项的影响后，导管架平台的疲劳寿命减少10%左右，对疲劳结构有较大影响。 4)深海浮式平台系泊系统在受到波频波浪力作用的同时，还会受到二阶差频波浪力的影响，且在疲劳计算中经常被忽略。本文为研究二阶差频波浪力对深海平台系泊系统的影响，进行了深海平台系泊系统的时域耦合分析，分别计算波频张力时程、差频张力时程和总张力时程，利用波频张力时程、差频张力时程和总张力时程进行疲劳损伤与疲劳寿命的计算。研究结果表明，差频波浪力引起的疲劳损伤度在总损伤度占有一定比例。说明对于深海浮式平台的疲劳寿命评估必须考虑二阶差频的影响.
[Abstract]:With the rapid development of China's economy, the demand for energy is increasing. It is urgent to accelerate the development of offshore oil and gas resources in China. Shallow water jacket platform and deep-sea floating platform are widely used in offshore oil development at present. Under random wave loads, cumulative fatigue damage will occur, and fatigue damage will occur seriously, resulting in serious consequences. With the increase of the service life of the platform and the increasing aging of the platform, fatigue damage has become an important reason for the damage of offshore platform members. Therefore, fatigue life analysis and evaluation are very important to the safety of offshore platforms. In this paper, the related theory of fatigue analysis and the commonly used fatigue analysis methods are reviewed systematically, and the research status of fatigue analysis and the influence of nonlinear factors on fatigue analysis are discussed. Focusing on the influence of nonlinear wave forces on fatigue life assessment of offshore platforms, the main contents and innovations are as follows: 1) in this paper, three fatigue analysis methods, frequency domain method, deterministic method and time domain method, are systematically studied. The fatigue life evaluation for jacket platform is carried out, and the fatigue life obtained by different fatigue analysis methods is compared and analyzed. Based on the results of time-domain method, it is concluded that the deterministic method overestimates the fatigue life of structures and the frequency-domain method underestimates the fatigue life. At the same time, the accuracy of the analysis results can be improved by considering the cyclic counting correction factor in the frequency domain method. 2) in the deterministic method, the nonlinear wave theory is introduced according to the applicable conditions of linear wave and Stokes5 order wave, and fatigue life analysis of jacket platform is carried out. The influence of nonlinear wave theory instead of linear wave theory on fatigue life is studied and analyzed. It can be concluded by calculation that the fatigue life of the structure increases by about 20% after the introduction of Stokes5 wave theory, and the effect is obvious. 3) in view of the current situation that linearized wave force spectrum is widely used in solving wave force of small pile column, nonlinear drag force spectrum is introduced in fatigue calculation, and nonlinear wave force spectrum expression is derived. Fatigue analysis of jacket platform combined with nonlinear wave force spectrum is carried out. The results show that the fatigue life of jacket platform is reduced by about 10% with the addition of the correction term of nonlinear drag force spectrum, which has great influence on the fatigue structure. 4) the mooring system of deep-sea floating platform is affected by the wave force and the second-order differential wave force, which is often neglected in fatigue calculation. In order to study the influence of second-order differential wave force on the mooring system of deep-sea platform, the time-domain coupling analysis of deep-sea platform mooring system is carried out. The wave-frequency tension time history, differential frequency tension time history and total tension time history are calculated respectively, and the wave-frequency tension time history is used. The fatigue damage and fatigue life were calculated by the time history of differential tension and total tension. The results show that the fatigue damage caused by differential wave force accounts for a certain proportion of the total damage. It shows that the influence of second order difference frequency must be considered for fatigue life evaluation of deep sea floating platform.
【学位授予单位】：中国海洋大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：P731.22;P751

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