【作者】 刘羽霄；

【导师】 周晶； 李昕；

【作者基本信息】 大连理工大学 ， 防灾减灾工程及防护工程， 2010， 博士

【摘要】 随着海洋油气资源的开发,特别是深水和边际油田的开采,越来越多高温／高压海底管道应用于工程实际,海底管道在温度应力下的整体屈曲变形问题成为管道设计的关键性问题。因此研究海底热荷载作用下管道屈曲的发生机理及控制屈曲策略具有现实的工程意义和较高的理论价值。本文采用理论推导和数值仿真相结合的方法,系统的开展了高温/高压海底管道横向屈曲分析方法和新的高温管道控制措施研究。具体研究内容如下：基于能量法给出了理想情况下横向屈曲模式1、2对应的临界屈曲荷载,并与Hobbs的解析解进行了对比验证。基于经典热屈曲理论,推导了平坦海床上存在初始几何缺陷的裸铺管道横向屈曲的临界荷载解析解,给出了无限远处管道轴向力及临界温度的计算公式。并与有限元计算结果进行了对比,验证了本文解析公式的合理性。通过与Hobbs解析解的对比表明,初始几何缺陷将降低管道临界屈曲荷载和临界温差。建立了平坦海床上裸铺管道的非线性有限元模型,用于分析管道屈曲的临界荷载及后屈曲变形、弯矩、应变。总结了与工程实际相对应的两种初始几何缺陷的有限元模型引入方法,研究了管道因初始几何缺陷形成的残余应力对管道前屈曲及后屈曲的影响。结果表明残余应力提高了管道临界屈曲温差和后屈曲的最大轴向总应变。开展了初始几何缺陷、横向摩擦系数、轴向摩擦系数、土体屈服位移、径厚比、钢材强度等敏感参数对管道前屈曲及后屈曲的影响因素敏感性分析。探讨了温度呈非线性分布管道的轴向运动及与横向屈曲之间的相互作用,分析表明横向屈曲有利于降低管道的轴向运动。屈曲的间距决定了相邻屈曲能否均得到激发,若屈曲间距过小则将会导致屈曲局部化,基于含初始缺陷管道横向屈曲的理论研究提出了相邻屈曲最小间距的控制准则。提出了一种新的蛇形铺管形状-正弦曲线形状,并建立了相应的非线性有限元模型。新的蛇形铺管形状有效降低了管道屈曲的临界荷载,且可以更有效地控制管道后屈曲的弯矩及应变。基于非线性有限元模型,探讨了铺管半径、铺管段长度、铺管角度及铺管距离等敏感参数的影响。研究发现,铺管角度越大管道屈曲的临界荷载越低,后屈曲的弯矩和应变越小;在铺管角度一定的情况下,管道后屈曲的最大弯矩随铺管段长度呈先降低后增加的趋势。根据有限元分析结果,提出了最优铺管角度及铺管段长度范围的判断准则。针对蛇形铺管法控制管道横向屈曲中存在的问题,结合蛇铺法及枕木法各自的特点,提出了一种新的蛇形铺管—枕木组合控制法,并建立了相应的海床-枕木-管道的非线性有限元接触模型。基于此模型,分析了枕木高度对管道前屈曲及后屈曲的影响。组合控制法有效降低了管道临界屈曲荷载,管道后屈曲的弯矩亦有明显降低。根据有限元分析结果,提出了枕木高度的控制准则。在管道的铺设及运行过程中悬跨不可避免。建立了悬跨管道的非线性有限元接触模型,开展了单个悬跨管道的悬跨深度及悬跨长度对管道横向屈曲的影响分析。针对两个悬跨情况,研究了悬跨间距对管道横向屈曲的影响,并提出了管道的最不利悬跨间距范围的控制准则。通过对存在单个悬跨的蛇形铺设管道的研究提出了避免悬跨出现在蛇铺管道弯曲段的顶点位置的建议。更多还原

【Abstract】 With the development of the offshore oil and gas resources, especially for the exploitation of deep water and marginal oil fields, more and more high temperature and high pressure (HT/HP) pipelines are used in practice. Global buckling of pipeline under HT/HP is becoming key factor for pipeline design. Thus, it is of significance to study thermal buckling mechanism and controlling methods of submarine pipeline. Combined with theoretical deduction and numerical simulation, the study on global buckling of HT/HP submarine pipeline is carried out in the paper.Critical axial compressive forces of lateral buckling mode 1 and mode 2 of flexible pipeline without initial imperfection are derived on the base of energy theory. The comparison of the results from energy method and Hobbs’s method is conducted. Based on the theory of thermal buckling, and considering the effect of initially imperfect geometry on lateral buckling of pipeline installed on the flat seabed, analytical solutions to critical axial forces in buckling segment and out of buckling segment as well as critical temperature are proposed. The comparisons between analytical and numerical results validate analytical solutions suggested in the paper. Through the analysis, initial imperfections have great effect on critical buckling force and temperature.Nonlinear finite element (FE) model of subsea pipeline laid on even seabed is established to analyze critical buckling of pipeline, post-buckling deformation, bending moment and strain. Two methods are introduced to simulate initial imperfection corresponding to practical engineering. The effects of residual stress due to initial imperfection on pre-buckling and post-buckling are carried out. The results show that residual stress can increase critical temperature and axial strain of post-buckling pipeline. Considering the effects of initial geometry imperfection, lateral and axial frictional coefficient between soil and pipe, yielding soil deformation, ratio of diameter to wall thickness of pipe, steel strength on lateral buckling, sensitivily is completed. Interaction between pipe walking and lateral buckling is studied in this paper, it can be seen that lateral buckling can effectively decrease pipe walking. Buckling distance between two potential buckling positions is the key to initiate lateral buckling at the positons at the same time. Based on analytical studies in imperfect pipeline lateral buckling, control criterion of minimum distance between two adjacent buckles is presented. Sine shape as a new shape of snaked-lay pipeline is presented in this paper. FE analysis display the new snaked-lay shape can effectively reduce critical buckling force and control bending moment and strain of post-buckling pipeline. The effects of pipe-lay radius, length, angle and distance are discussed. Based on FE results, the optimum offset angle and pipe-lay length of sine shape are suggested.Considering the characteristics of snaked-lay method and sleeper method, a new lateral buckling controlling measurement combined with snaked-lay and sleeper (SS) is proposed. Using ANSYS, nonlinear FE model considering the interaction of seabed, sleeper and pipeline is established. SS method can overcome deficiencies of snaked-lay method and sleep method through FE analysis. Numerical results show that sleeper height has significant effect on pre-buckling and post-buckling of pipeline. The controlling criterion of sleeper height is proposed.Due to scour and erosion of wave and current or pipeline laied on uneven seabed, span is inevitable during operation. Nonlinear contact FE model is established to study the effect of spanning depth and length on global buckling of pipeline with single span. For the pipeline with double spans, spanning distance is studied, and the controlling criterion of spanning distance is presented to reduce the interaction risk of the double spans. For snaked-lay pipeline with single spanning, the crest of snaked-lay pipeline should avoid locating at spanning segment.更多还原