【作者】 张日曦；

【导师】 黄一； 张崎；

【作者基本信息】 大连理工大学 ， 船舶与海洋结构物设计制造， 2013， 博士

【摘要】 深水立管系统是深水油气开发装备中最为薄弱的构件之一,在风、浪、流以及顶部浮体运动的联合作用下,立管端部和触地段等局部位置会产生过度弯曲而导致立管发生强度破坏、屈曲破坏以及疲劳破坏等。深水立管系统中的弯曲抑制装置为过度弯曲问题提供了有效的解决途径。因此,本文依托国家高技术研究发展计划(863计划)资助项目“南海深水油气勘探开发关键技术及装备重大项目——深水立管工程设计关键研究课题”,重点研究了深水立管弯曲抑制装置的关键技术问题,主要内容包括：功能性接头设计、静水压溃分析、径向屈曲与屈曲扩展分析以及关键位置弯曲抑制结构设计等。深水立管主要呈现柔性结构的特征,当其与刚性结构固定连接时,就会在连接处的立管结构中形成弯曲应力的高度集中区。在这种情况下,通常采用应力接头结构作为过渡,以降低立管端部结构的弯曲应力集中程度。目前,有关应力接头的大部分研究工作都集中在新型材料的应用和对现有结构的分析上,而应力接头的设计工作主要还是凭借设计人员的实际工程经验来进行的。因此,如果立管系统服役的平台结构或海洋环境发生变化,就会给设计工作带来很大的难度。针对这一问题,本文提出了应力接头的设计原理和设计方法,并在综合考虑各方面影响因素的情况下,对重要参数的选择和控制方法进行了工程推荐。根据该设计方法可以快速准确地得到满足实际工程需求的应力接头结构,还能较为准确地对相关力学性能进行分析和计算。同时,本文在考虑百年一遇极端海况的条件下,应用数值模拟方法验证了设计结果的正确性及合理性,评估了应力接头结构的弯曲抑制能力。本文还基于实际工程项目,对带有应力接头的立管系统进行了动力响应分析和疲劳分析,进一步证明了该设计方法在实际工程应用中的可行性和有效性。然而,在深水立管系统的实际工程应用中除了设计相应结构来抑制过度弯曲以外,对由过度弯曲引发的相关工程问题的分析和评估也十分重要。特别是当这些过度弯曲位置含有结构缺陷时,立管就很可能产生局部径向屈曲甚至发生屈曲扩展破坏。而现有的立管径向屈曲及屈曲扩展评估工作大都是基于大径厚比海底管道进行的,由于结构特点和载荷环境的不同导致计算误差较大。因此,本文基于薄壁圆柱壳的径向屈曲理论深入研究了不同径厚比深水立管的压溃屈曲特点,并对大量具有不同径厚比和初始椭圆度的深水立管模型进行了压溃屈曲及后屈曲行为的分析计算,得到了适用于小径厚比深水立管压溃屈曲分析的临界压力公式。并在此基础上,对深水立管在联合载荷作用下的径向屈曲问题进行了深入研究,提出了立管径向屈曲的凹陷系数,建立了针对特定载荷环境和屈曲模态的径向屈曲分析方法以及局部径向屈曲条件下的屈曲扩展数值模拟方法,对发展深水立管的屈曲评估理论具有重要意义。同时,由于深水立管自身结构特点和环境载荷的影响,还会使其在除端部以外的立管触地段和悬浮段等局部位置产生过度弯曲。钢悬链线立管的触地段是典型的局部过度弯曲区域,常常由于过度弯曲而发生强度破坏和屈曲破坏,而且由于往复的弯曲运动还使得触地段成为疲劳破坏的高发区域。目前,在实际工程中对于这类可能发生过度弯曲的局部位置进行弯曲抑制设计时,主要还是简单地通过增加壁厚实现的,但随之而来的应力集中和疲劳等问题也十分突出。因此,本文以钢悬链线立管的触地段为例,基于应力接头的设计思想和设计原理,提出了对过度弯曲的局部位置进行弯曲抑制结构设计的一般方法。然后,根据建立的径向屈曲及屈曲扩展评估方法,对新型钢悬链线立管触地段进行了屈曲分析和评估,并通过有限元方法对其进行了动力响应分析和疲劳分析,为局部弯曲抑制结构设计方法的实际工程应用奠定了基础。综上,本文针对深水立管系统在设计阶段及服役期间所面临的过度弯曲问题,提出了应力接头和新型立管触地段等弯曲抑制结构的设计原理和方法,发展了深水立管的径向屈曲及屈曲扩展评估理论,为深水立管弯曲抑制装置的实际工程应用提供了理论和技术支撑。更多还原

【Abstract】 Deep-water riser system is one of the weakest components in deep-water oil and gas development system. The strength fracture, buckling failure and fatigue damage will be generated at riser ends and local bending position, especially under the combined loads of wind, wave, current and top floating body movement. This paper is funded by national high technology research and development program (863program), and focused on the key technical programs of deep-water riser bending restraint system. It includes functional joint design, hydrostatic collapse, buckling and buckling propagation and local bending restraint design.Deep-water riser mainly reflects the characteristics of flexible structures. When they are directly connected with rigid structures, high stress concentration will be generated at he connection structure. In this case, the Stress Joint (SJ) is developed to reduce the bending stress concentration at the ends of riser. At present, most research work of Stress Joint (SJ) is focused on new materials application and structural analysis, and the SJ design mainly depends on the actual engineering experience of designers. Hence, the design work is subject to loads enviroment. To resolve this problem, a SJ design method is proposed in the paper, and the parameters control methods are recommended for actual projects in consideration of various aspects of influencing factors. According to this new design method, the SJ design dimensions which satisfy practical engineering demands can be rapidly and accurately obtained, and the related mechanical performance can be assessed accurately. In the meantime, taking the100-year extreme sea state conditions into account, the accuracy and rationality of design results are verified based on the finite element analysis, and the bending stress reduction effects and bending control ability are evaluated for the designed SJ. Then based on the actual engineering project, the dynamic response analysis and fatigue analysis are carried out for a riser system with SJ, and the analysis results further validate the feasibility and effectiveness of this design method in practical engineering.In practice, in addition to design of SJ, the analysis and evaluation of engineering problems caused by excessive bending are also very important. The buckling and buckling propagation, especially in the defective structures, could occur in the large bending deformation area. The existing riser buckling assessments are based on submarine pipelines of large diameter-thickness ratio, which leads to enormous calculation error due to the different structural characteristics and load environments. So using the cylindrical shell buckling theory, the collapse buckling characteristics of deep water risers with different diameter-thickness ratio are investigated. The collapse buckling and buckling propagation analysis are implemented for riser models with various diameter-thickness ratio and ovality. A critical pressure formula for the collapse buckling analysis of small diameter-thickness risers is proposed for combined loads. And the riser depression coefficient of local buckling is proposed with the complicatd loading conditions and buckling modes. In addition, the numerical simulation method of buckling propagation is established under local buckling. The above researches have great significance to the development of deep-water riser buckling assessment theory.Furthermore, the local excessive bending, due to structural characteristics and loading conditons, could be generated beyond the end of riser. For example, at the near end of Steel Catenary Riser (SCR), the touch-down zone often has strength failure and buckling failure due to excessive bending. The near-end becomes a high risk area of fatigue failure because of the cyclic bending motions. At present, to deal with these problems is mainly achieved by increasing the wall thickness, which causes stress concentration and fatigue problems. Therefore, a structural optimization method is proposed for the excessive bending location based on SJ. Then, buckling and buckling propagation analysis and assessment are studied for a SCR touch-down zone according with the proposed methods in this thesis. The dynamic response analysis and fatigue analysis are carried out by finite element analysis. These analysis results useful for the SCR touch-down zone restraint design in the engineering application.To summarize, in order to resolve the excessive bending of deep-water riser system in design and service, a new design method for bending restraint structures is proposed. The radial buckling and buckling propagation theory is developed with recommendations for bending suppression system in the actual engineering application.更多还原