【作者】 远航；

【导师】 贾永刚；

【作者基本信息】 中国海洋大学 ， 环境工程， 2009， 博士

【摘要】 海底管线是海洋油气集输与储运系统的重要组成部分,被喻为海上油气田的“生命线”,在海洋油气资源的开发利用中发挥着重大作用。海底管线运行环境恶劣,失效概率高,在波浪、海流、潮汐的作用下,其稳定性状况一直是研究热点。位于现代黄河水下三角洲的胜利埕岛海上油田,海底管线稳定性成为重要的安全隐患。这与该海区海床沉积物独特性质及海洋动力条件密切相关。目前设计上采用的常规方法,由于缺少地区特色的针对性使其结果受到置疑。在中石化重点攻关课题“埕岛海管剩余寿命评价及海缆监测技术研究-海底管线安全防护对策”(JP05007)资助下,本论文针对埕岛油田海区特点,在搜集整理分析研究区水文与地质资料的基础上,利用数值模拟的方法,较为系统地研究了海底裸置管线、埋藏管线的稳定性,取得了一些突破性的研究成果,同时在研究方法上也取得一些进展。本文的主要研究工作与成果有:1.现场调查并收集研究区地质与水文资料,依据138个钻孔数据的统计分析,将埕岛海域研究区地层分为三个亚区,并对各亚区内的海床土性质及水动力特征进行了统计分析,为进一步管线稳定性分析提供必要的水文与地质资料。2.基于Biot固结理论,根据埕岛海域特定的水文、地质条件,建立了波流作用下裸置管线动力响应问题的数学模型。采用WakeⅡ模型计算了裸置管线所受的拖曳力和升力,改善了以往采用Morison方程计算管线受力时忽略尾流效应的不足,使计算结果更加符合实际情况。通过与相关研究的对比,验证了本文所采用方法的可靠性。根据所建模型对影响裸置管线横向稳定性的各项因素分析表明,忽略尾流的影响会严重高估裸置管线的在位稳定性,影响管线稳定性最主要的因素是单位长度管线重量。在此基础上建立了埕岛油田地区的裸置管线稳定性校核曲线,可为本地区管线设计提供指导。3.将非线性波浪理论和随机波浪理论引入有限元模型,建立了埕岛地区埋置管线复杂波浪荷载作用下瞬态响应的数学模型。讨论了波浪的随机性对管线及海床动力响应的影响及海床土体与埋置管线的接触效应。与前人研究结果相比,本文中所采用的数学模型更为接近实际情况,可以更好的反映波浪作用下埕岛油田地区海床土体与埋置管线之间的相互作用。并据此模型对复杂波浪荷载下埋置管线的动力响应进行分析,发现波浪的非线性和随机性以及管线-土体之间的接触效应对计算结果的影响十分显著,如果忽略这些因素,则会在分析埋置管线动力响应时造成较大误差。4.基于大变形理论,开发了基于ABAQUS的用户单元子程序,对波浪作用下埕岛地区海床土体内残余孔压的发展进行了计算,及海床液化判别分析。将液化后土体视为Bingham体,开发了大变形下的用户材料子程序,对管线在液化土体内的移动进行了研究。结果表明,埕岛海域不同工程地质分区土体液化行为差别较大,海床土液化深度随波浪作用时间的增加而增加,但是最终会趋于稳定;液化后土体的粘性系数影响到管线在液化土中的运动速度,但不影响其运动趋势。主要创新点:针对埕岛油田具体水文、地质条件,采用更为合理的水动力模型计算裸置管线所受荷载,在此基础上建立了埕岛油田地区裸置管线与土体相互作用的数学模型,提出了适合埕岛油田裸置稳定性分析的校核曲线。建立了复杂波浪荷载作用下埋置管线与周围土体相互作用的数学模型,并基于大变形理论,对管线在液化土体中的移动进行了模拟,并对影响土体液化和管线在液化土体中行为的因素进行了分析。更多还原

【Abstract】 Submarine pipeline is the important part of ocean oil and gas transportation and reposition system. It is the lifeline of ocean oil field. The stability of submarine pipeline is a key question for pipelines engineering. CoMPared with the pipeline on land, submarine pipeline run in a harder environment, the probability of destability is much higher than former. The pipeline in service is easy to lose destability under wave, current and tide load. At the present time, few investigation about the stability of submarine pipeline with given hydrologic and geologic file is reported. For pipeline laid on seabed, the induced wave force is calculated with Morison model, neglect the wake effect to the velocity of water around pipeline. And to the buried pipeline, the induced wave force is calculated mostly based on the linear wave theory, and the contact effect between pipeline and soil is neglected. The analysis about pipeline is mostly about the wave induced pore pressure stress and strain ect. in the soil around pipeline, few study about the behavior of pipeline in the liquefied soil is reported. Contraposing these shortages, a more reasonable numerical model of pipeline/soil is developed, and the stability of submarine pipeline in Chengdao oil field is analyzed based on the model. The work of this dissertation mainly includes:1.Collecting and analyzing file about 138 bores, classing Chengdao oil field 3 different zones, and hydrologic and geologic characteristic of each zone is dissertated. This work has an important tpracticality for oil reconnoitring and transporting in this area. Based on Biot theory and hydrologic、geologic file of Chengdao oil field.2.Based on Biot theory and hydrologic、geologic file of Chengdao oil field, a numerical model is developed for analyzing the stability of submarine pipeline. The ii WakeⅡmodel is imported into ABAQUS by developing a subroutine‐DLOAD, this make the numerical model more reasonable coMPared with previous models. The reliability is testified by coMParing with the relevant research. The main factors of affecting the stability of submarine pipeline are analyzed, and the result shows: effect of Wake has disadvantage for pipeline stability, weight of per length unit pipeline is a important factor affect the stability of pipeline. Based on the result of numerical model, a set of curve for checking the stability of pipeline in Chengdao oil field is discussed.3. A numerical model of pipeline/soil under the nonlinear wave and random wave loading is developed. In the dissertation, the wave loading is calculated based on nonlinear wave theory and random wave theory, and so, the nonlinear effect and randomicity of wave is considered. Besides, the contact effect between pipeline and soil is considered. Compared with previous models, the numerical model in this dissertation is more reasonable.Based on this model, the response of pipeline/soil under the wave loading is analyzed,and the result showes that the nonlinear effect of wave and contact effect between pipeline and soil are can not neglected.4. Based on the finite strain theory, a subroutine‐UEL for ABAQUS is developed , and the residual pore pressure under wave load is computed, and stability of soil around pipeline and seabed is analyzed. Regarding the liquefaction soil as model, a subroutine‐UMAT for ABAQUS is developed , and the behavior of pipeline in liquefaction soil analysis qualitatively. The stability of buried pipeline is analyzed with numerical model, and the numerical result shows that: the coefficient of permeability affect the cumulation ratio of pore pressure remarkablely; The coefficient of permeability is greater, the pore pressure cumulates more slowly, and vice versa. The depth of liquefaction increases with the wave load’s action time, and finally tend to a constant.To the 3 different geologic areas, the depth of liquefaction has the followed relation:Ⅰ<Ⅱ<Ⅲ.The viscidity coefficient of liquefaction soil affect the velocity of pipeline only, can not affect the movement trend. With the numerical models, a formula for checking the stability of pipeline is discussed. The main innovation points in this dissertation include:According to the hydrologic、geologic file of Chengdao oil field, the more reasonable hydrodynamic model is adopted to compute the load of pipeline laid on seabed.A numerical model of pipeline laid on seabed and soil interaction in Chengdao oil field is developed,a set of curve for checking the stability of pipeline in Chengdao oil field is discussed.Moreover,a numerical model of embeded pipeline/soil interaction under complex wave laod is developed, the behavior of pipeline in the liquefied soil is simulated base on finite distortion theory, finaly the influence factors are analysed and a set of conclusions are put forward.更多还原