【作者】 薛鸿祥；

【导师】 张圣坤； 唐文勇；

【作者基本信息】 上海交通大学 ， 船舶与海洋结构物设计制造， 2008， 博士

【摘要】 随着海上油气资源开发由浅海逐渐走向深海区域,为适应深海环境作业要求,很多不同于传统固定式采油平台的新型浮式结构物不断涌现。其中,Spar平台以运动稳定、安装拖航灵活等优点,受到了世界各大石油公司的广泛关注。由于我国南海海域的地理环境和气候条件与墨西哥湾较为相似,而Spar平台在墨西哥湾的成功应用,为该类型平台应用于我国南海深水油气资源开发创造了有益条件,发展潜力巨大。本文作为国家自然科学基金专项基金资助项目“深海平台的动力特性研究”、上海市科委重大基础研究课题资助项目“深海单柱式平台关键动力特性的理论与实验研究”以及国家863计划资助项目“深水油气开发工程试验技术”等研究课题的组成部分,旨在研究新型深海多柱桁架式平台(Cell-Truss Spar)在复杂海洋环境下关键节点的疲劳性能以及平台顶端张紧式立管在涡激振动下的疲劳寿命预报方法。本文将理论研究与工程应用紧密结合,在海洋工程结构物疲劳寿命预报方法的理论研究、Spar平台关键节点疲劳性能评估、深海立管涡激振动响应预报以及深海立管涡激振动疲劳寿命预测方法等多方面开展了深入研究,取得了积极的进展。本文开展的主要研究工作如下:1.全面回顾和总结了近年来深海Spar平台的发展、海洋结构物疲劳寿命研究方法以及深海立管涡激振动响应和涡激振动疲劳寿命研究等国内外研究成果和进展。对本文的研究对象——上海交通大学海洋工程国家重点实验室提出的新型深海多柱桁架式平台(Cell-Truss Spar)的概念和结构特点进行了介绍。2.基于疲劳累积损伤理论和谱分析方法,在南海海域海况条件下开展了Cell-Truss Spar平台各关键节点处的疲劳寿命评估及可靠性分析研究,同时开展了不同类型海域环境对Spar平台关键节点疲劳寿命影响的对比研究,总结了该Spar平台各关键节点疲劳损伤的特点和规律。3.通过对疲劳线性累积损伤理论充要条件的理论证明和对规范中推荐采用的裂纹扩展模型的分析评述,指出了传统疲劳谱分析方法存在的局限性。针对该局限性,本文基于谱分析法中的频域信息,采用小波分析技术对疲劳交变应力的随机过程进行时间历程仿真,并结合一定的随机裂纹扩展模型,探索出了一套适用于船舶与海洋工程结构物疲劳寿命评估的时-频混合分析模型,并将该混合分析模型应用于Cell-Truss Spar平台的疲劳寿命评估。该时-频混合分析模型较好地解决了全时域疲劳分析计算量巨大与传统谱分析无法考虑载荷先后顺序影响之间的矛盾。4.针对均质等截面深海顶端张紧式立管的特点,结合近年来两类涡激振动实验的现象和重要结论,从振型函数、锁定区域判定、附加质量模型、最大响应幅值以及流体阻尼等5个方面对以往的计算模型进行了改进,建立了深海顶端张紧式立管在非均匀来流下涡激多模态响应的简化分析模型。并应用若干个涡激振动实验结果对预报模型进行了验证,简化分析模型绕开了流体力的求解,可为深海立管及其它海洋工程挠性结构物的初步设计提供依据。5.针对变参数的细长立管涡激振动问题,本文基于de Wilde受迫振荡实验的流体力信息并采用能量平衡的思想建立了VIV有限元预报模型。通过与变参数立管模型的VIV实验对比显示,该预报模型能较合理地反映出低质量比系统的涡激响应特性,并克服了简化分析模型只适用于等截面匀质立管的局限性,可以对参数变化较复杂的立管结构开展更为细致的VIV分析工作,在工程应用中也更具通用性。6.根据本文建立的涡激振动简化分析模型,推导了横流方向单模态涡激振动疲劳损伤度的计算表达式,提出了立管在均匀流下涡激振动疲劳损伤度的经验公式。研究了环境条件和结构设计参数对立管在涡激振动下疲劳寿命的影响,总结了各因素对疲劳损伤度影响的一般规律。针对涡激横流振动诱发立管轴向共振的现象进行了探讨,给出了诱发立管轴向共振的临界条件和轴向共振对立管疲劳寿命影响的定量计算方法。7.根据本文建立的涡激振动有限元计算模型,通过将预报结果与大尺度立管现场观测实验结果的对比分析,推荐了一个适合工程应用的多模态涡激振动疲劳损伤度计算方法。8.针对国内外部分学者所提出的立管涡激振动疲劳载荷概率模型进行了分析评述,指出了其不合理性,根据海流长期分布的统计特征建立了涡激振动疲劳载荷长期分布的概率模型,提出了一种适用于深海立管涡激振动疲劳寿命分析的“设计流”方法,并基于该方法对Spar平台的顶端张紧式立管进行了涡激振动疲劳寿命的计算。本文的相关理论研究内容及所得到的一些具有参考价值的结论可为进一步开展深海Spar平台及立管结构疲劳寿命评估工作、保障深海工程装备安全提供有益的参考。更多还原

【Abstract】 With the rapid tendency of the oil and gas exploitations to deep-water areas, more and more new types of floating units have been used to adapt the operation conditions in severe deep sea environment. Among these floating structures, Spar platform has excellent stability, relatively benign motion performance and easy to disassemble, which makes many international oil companies put great efforts on it. Spar platforms have been used successful in Gulf of Mexico for more than one decade which provides instructive conditions for its application in South China Sea for the similar climate conditions in the future.The present research in this thesis is a part of the projects of“Research on Dynamic Response of Deep-water Platforms”supported by the National Natural Science Foundation of China,“Theory and Experiment Research on Critical Dynamic Performance of Deep-water Spar Platform”supported by the Key Program for Basic Research of Shanghai Committee of Science and Technology and“Experimental Technology for Deep-water Oil and Gas Exploitations”supported by National High Technology Research and Development Program of China. The purpose of this research is to improve more understanding of fatigue behavior of the novel Cell-Truss Spar platform and the fatigue life prediction method for deep-water top tensioned risers of Spars due to vortex-induced vibrations.The present research combined theoretical research and engineering application effectively. The contents cover some main hot issues, including the theoretical research on fatigue life prediction approaches of ocean engineering, fatigue damage assessment of critical joints for Spar platform, vortex-induced vibration (VIV) response prediction and VIV fatigue analysis of deep-water risers. The main contents and contributions of this thesis may be summarized as follows:1. An overview of recent research and progress concerning Spar platform and its key technologies, fatigue life prediction approaches of ocean engineering, VIV response of deep-water risers and the fatigue damage due to VIV is presented. The new concept and its structural characteristic of a novel Cell-Truss Spar platform proposed by State Key Laboratory of Ocean Engineering of Shanghai Jiao Tong University are introduced.2. Fatigue spectral analysis and reliability assessment of the critical joints of Cell-Truss Spar is carried out based on S-N curve method. Sensitivity analysis of fatigue life with different ocean environments is also studied. The characteristic and regular patterns of fatigue damage are summarized.3. The limitations of traditional fatigue spectral analysis is pointed out based on the mathematical proof of the necessary and sufficient condition of the fatigue linear accumulation rules and the commentary on the crack propagation model proposed by vessel and ocean engineering rules, while a new time-frequency domain hybrid model for fatigue analysis is put forward to overcome the limitations. In this hybrid model, frequency information is obtained by spectral analysis and the time series of fatigue cyclic stress is simulated by wavelet transform, while a random crack propagation model is employed. The time-frequency domain hybrid model can solve the contradiction of the huge amount of calculation in full time domain analysis and neglecting the effects of load sequence in traditional spectral analysis method preferably. In addition, the hybrid model is also used to predict the fatigue life of Cell-Truss Spar.4. According to the characteristics of deep-water top tensioned risers with homogeneous mass property and diameter, a simplified model is presented to predict the multi-modal response of VIV in non-uniform flow based on the experimental data from self-excited and forced oscillations of rigid cylinders. The predicted values show reasonable agreements with several VIV tests of riser models. The simplified model can obviate the solving of hydrodynamic force, which can be used as a practical method in preliminary design of marine slender structures.5. A VIV finite element prediction method is presented based on the experimental information of forced oscillations test by de Wilde to overcome the limitation of VIV simplified prediction model, the VIV finite element prediction model can take account of the intrinsic characteristics of low mass ratio VIV system, and it is more universal which can provide detail analysis in engineering practice for complicated risers in shape.6. Based on the VIV simplified prediction model, a cross-flow single-mode VIV-induced fatigue damage prediction model for Top Tensioned Risers (TTRs) is presented and an empirical formula of fatigue damage is obtained under conditions of uniform flow. The effects of environment conditions and design parameters of the structure on VIV fatigue are studied, and the regular patterns of influence factors are summarized. The phenomenon of riser’s axial resonant due to cross-flow VIV is also discussed.7. Compared with the large scale model test of deepwater risers, a reasonable prediction method for the multiple mode VIV-induced fatigue damage is recommended for engineering application based on the VIV finite element prediction model.8. The inappropriate of probabilistic model for VIV fatigue proposed by a few foreign scholars is pointed out, and a new Design Current Method for deepwater riser’s VIV fatigue analysis is put forward based on the long-term distribution of current. Finally, fatigue life prediction for a TTR of the Cell-Truss Spar platform is carried out based on the new method.In conclusion, the theoretical research contents and many valuable conclusions obtained in this thesis will be helpful for the future work on fatigue assessment of Spar platforms and other equipments used in deep-water oil and gas exploitations.更多还原