【作者】 白兴兰；

【导师】 黄维平；

【作者基本信息】 中国海洋大学 ， 港口、海岸及近海工程， 2009， 博士

【摘要】 随着油气资源勘探和开发活动不断向深海发展,涌现出了多种新型浮式结构系统以适应深海恶劣的环境载荷并较大程度地降低成本。钢悬链线立管(Steel Catenary Riser, SCR)成为了深海浮式生产系统油气输送的首选立管形式,在一定程度上克服了传统的柔性立管和顶张力立管(Top Tension Riser, TTR)在更深海域应用的局限性,被认为是深水立管系统成本有效的解决方案。由于受浮式平台运动以及深海水动力载荷的共同作用,相比于海底管线,钢悬链线立管的动力响应更加复杂。因此,对钢悬链线立管进行动态响应分析及非线性分析方法研究具有重要的科学意义和广泛的应用价值。本文介绍了锚缆动力分析程序CABLE3D,是2002年由美国A&M大学的Chen等人开发的三维非线性有限元分析程序。该程序可以求解两类结构的静力和动力问题,一种是无抗弯刚度且允许有较大拉伸的杆结构,另一种是有抗弯刚度且允许有较小拉伸的梁结构。基于程序CABLE3D,本文运用大挠度柔性索理论,采用具有弯曲刚度的大挠度细长梁模拟钢悬链线立管,触地点随着SCR的运动而变化,并且考虑了触地点处立管曲率的影响,同时解决了采用直梁模型模拟时单元长度受限的问题。大挠度细长梁模型模拟钢悬链线立管,对研究立管与海床的相互作用以及疲劳分析有重要作用。基于锚链/立管系统分析程序CABLE3D,提出了基于惯性耦合的深水钢悬链线立管与Spar平台的整体分析法,并开发出整体分析程序V-CABLE3D,这是本文的重要创新点之一。该方法是将SCR与Spar看作一个整体系统,Spar作为刚体,顶端边界条件是系泊系统/TTR的弹性位移约束和Spar平台的激励力约束,SCR的底端法向约束采用弹簧系统或弹簧阻尼系统模拟。由于Spar平台的几何对称性,将其简化为3自由度浮动圆柱体,其波浪激励力仅考虑了一阶绕射作用,运用绕射理论求解纵荡力、垂荡力和纵摇力矩。分别运用CABLE3D和V-CABLE3D程序对SCR进行动力分析,结果表明,基于惯性耦合SCR与Spar平台整体系统分析法能够较好地反映结构之间的动力效应,特别是平台惯性力对SCR动态响应的影响很大,因此不能忽略。本文还详细介绍了立管与海床法向相互作用模型在钢悬链线立管分析中的应用现状,主要包括立管向着海床运动时海床刚度的影响和立管拔出海底时的吸力作用。根据STRIDE围绕SCR与海床相互作用的二维模型试验,2001年Willis数值模拟得到了准确的二维吸力模型。基于该吸力模型,在海床的法向分布力中考虑吸力,进一步改进CABLE3D和V-CABLE3D程序,并分别应用改进的程序对钢悬链线立管进行动力分析,给出动态响应的时程曲线和FFT幅值谱。计算结果表明,立管拔出海底时的吸力作用将会引起立管动态响应时程曲线的小幅度高频振荡,增大了立管的极限应力。本文通过对新型深水钢悬链线立管国内外研究方法的分析,提出了一些新的见解和方法,为深水立管的设计和非线性分析提供理论依据,同时对钢悬链线立管在我国深海领域的应用具有一定的指导意义和参考价值。更多还原

【Abstract】 When offshore oil and gas activities move to deeper and deeper oceans, various innovative floating structures are proposed and developed to comply with severe deep-water environments and to reduce the cost. Steel catenary risers (SCRs) for deepwater development have become a viable option for oil and gas export from floating production facilities to shore, shallow water platforms, or to subsea pipeline hubs. SCR is considered over both traditional flexible riser and TTRs in deepwater development and a cost effective solution to deepwater oil and gas production. The concept of SCR is inherently simple and is often thought of an extension of the flow line or pipeline. However, the dynamic movements experienced by the SCR from vessel motions and hydrodynamic loading result in a more complex behavior of the structure compared with flow lines and pipelines. So, dynamic response analysis and nonlinear investigation of SCR are of both great scientific significance and extensive application value.The cable dynamic analysis program CABLE3D, which is 3-D nonlinear analysis program developed by Chen (2002) is introduced in this paper. Cable static and dynamic problems of the two structures including BAR (with bending, large elongation) and BEAM (with bending, small elongation) elements can be solved using this program. Based on the theory of a slender rod with bending stiffness, SCR is modeled as a small extensible beam considering large curve at Touch Down Point (TDP) of SCR. The situation of TDP changes along with motion of SCR. Moreover, the length of element at TDZ is not limited. The slender beam model with large curve used in SCR analysis have an important role on the study of pipe/soil interaction and fatigue analysis of SCR.The thesis, with its marked innovation of this subject, gives the integrated model of SCR-Spar and its mooring lines/TTRs considering inertial coupling, and the original CABLE3D is improved. Based on previous works by Garrett (1982), Ma, Webster (1994) and Chen (2002), a dynamic equation for integrated model of SCR-Spar is derived and the integrated analysis program V-CABLE3D is obtained. In the program, Spar moored by a spread mooring system is modeled as a rigid body, and mooring lines/TTRs are modeled by springs which act on the top of SCR. Both response of Spar induced by wave loads and SCR/soil interaction model (a spring-damping system) are considered in code. In the integrated analysis, the Spar can be approximated by a rigid body of three degrees of freedom (surge, heave and pitch), known as a 3-DOF body. First-order is only considered in the calculation of wave loads by diffraction method. The wave forces are calculated using approximation of diffraction method. The results of dynamic analysis of SCR by CABLE3D and V-CABLE3D show that large inertial force induced by mass of Spar has a large effect on dynamic response and it is not ignored. The method of integrated analysis considering inertial coupling factually reflects dynamic effect between SCR and Spar platform.The state of the art of vertical pipe/soil interaction models developed for use in SCR analysis is also described in detail. These model pipe move vertically downwards (soil stiffness) and vertically upwards (soil suction). The soil suction curve presented in this paper was the upper bound curve based on the previous STRIDE 2D pipe/soil interaction work by Willis (2001). The case studies investigated the effect of soil suction on SCR dynamic response. CABLE3D and V-CABLE3D are modified by SCR/soil interaction model with soil suction. Dynamic response of SCR with soil suction in time domain is analyzed by the improved program. The time histories of dynamic response and its amplitude spectrums by FFT at key zone of SCR are plotted in figures. The results show that soil suction has a large effect on extreme stress and induces small-amplitude and high-frequency oscillation of time histories of SCR dynamic response when the riser is pulled away from the seabed.The new research idea and method of deepwater SCR are proposed in this thesis through analyzing research method at home and abroad. The conclusion of this paper supplies the design and nonlinear analysis of deepwater SCR with theoretical-based calculation as well as the applications of SCR in China with the guiding significance and the reference.更多还原