考虑管土相互作用的钢悬链式立管与浮式平台整体分析方法研究

The regions of high cyclic stress are generally located at the top hanging and bottom touchdown zone (TDZ) of Steel Catenary Riser (SCR). Fatigue damage occurs in these areas. At present the global response analysis of SCR is obtained by mainly using commercial software and uncoupled analysis method, which has some limitations in the mechanical model and the coupling analysis, and lacks the independent development software and the global analysis method. By means of numerical simulation and model test, based on the fundamental theory of mechanical analysis and local analysis of flexible joint and TDZ, the global analysis method and program are established and developed taking into account combination of pipe-soil interaction and coupling analysis with offshore platform. The SCR global response analysis is carried out to reveal the dynamic response and fatigue damage mechanism under the complex ocean condition. The main contents are as follows: According to the theory of curve beam and elastic foundation beam, a combined mechanical model is developed based on the structural feature of SCR, and the nonlinear dynamic responses are analyzed by numerical simulation; The 3D pipe-soil interaction model would be improved to consider normal stiffness degradation and lateral resistance, and then applied to the global analysis; The coupling analysis of SCR and floating platform is studied based on the simulation of the nonlinear rotational spring, and a couple model of SCR-floating platform is established. The effect of motion of floating platform on the dynamic response of SCR is studied; The global analysis test will be conducted through imposed 3D cyclic motion at the top-end of the riser model. The global response characteristic is explored through detail analysis of the float motion, the pipeline internal force, curvature variation and the pipe/soil interaction, and verified with the numerical simulation.

钢悬链式立管(Steel Catenary Riser, SCR)顶端和触地区因存在高循环应力，成为疲劳破坏的关键部位。目前立管全局响应分析以商业软件和解耦分析为主，在力学模型和耦合分析上有一定局限，缺少自主开发软件和整体分析方法。从SCR力学基础理论出发，结合顶端和触地区的局部分析，数值模拟和模型试验相结合，以建立SCR与浮式平台整体分析方法为目的，自主开发分析程序，开展复杂海况下SCR全局响应分析，揭示立管动态响应和疲劳损伤机理。首先基于大挠度柔性索和弹性基础梁理论，根据SCR结构特点建立组合式力学模型，进行三维非线性动力响应分析；改进管土作用模型，建立考虑刚度退化和侧向阻力的非线性海床模型，用于SCR整体分析；采用非线性旋转弹簧模拟柔性接头，建立SCR-浮体耦合分析模型，研究浮体运动对立管动态响应的影响；开展整体分析试验，从浮体运动、内力及曲率变化、管土作用等方面与数值模拟进行验证。

钢悬链式立管（Steel Catenary Riser, SCR）因具有结构简单、成本低和对浮式平台的良好适应性等优势，广泛应用于海洋油气开发中。考虑管土耦合作用下的SCR与浮式平台的整体分析方法展开深入研究，包括建立考虑海床土刚度退化和沟槽发展的管土作用模型、浮体运动对立管触地区动态响应的影响及缓波型立管优化设计等内容，探究SCR与复杂海床的相互作用机理，完善多介质耦合效应下立管动力分析程序，从而提高SCR响应预报精度。主要工作如下：.首先，基于P-y曲线建立考虑海床土刚度退化和沟槽发展的管土作用模型。运用土刚度退化因子和记录沟槽形成过程来改进管土作用模型，结合立管流线段的弹性地基梁模型，改进立管动力分析程序CABLE3D RSI，开展SCR触地区参数敏感性分析。.其次，基于改进的立管动力分析程序，建立浮体-SCR-海床的耦合分析模型，研究浮体二阶运动对SCR触地区动态响应的影响程度。浮体的二阶运动即慢漂运动会使立管在不同位置发生振荡运动，近端漂移时触地区产生更大的弯曲应力，远端漂移时则顶端产生更大的轴向应力。通过编写程序接口，将平台水动分析软件得到的实际运动响应导入立管分析程序，数值分析结果表明二阶运动会造成触地区更大的疲劳损伤。.然后，建立土吸力模型改进管土作用模型，研究管线拔出速度对吸力和触地区动力响应的影响。深海以软黏土海床为主，吸力是软黏土海床的重要特性，研究表明管线拔出速度影响吸力大小和持续时间。拔出速度越大，则吸力越大且作用距离增加，这和试验结论一致；运用改进程序分析立管直径、管线拔出速度等因素对触地区动态响应的影响。.最后，对传统钢悬链线立管进行结构优化设计，将触地区设置为缓波型，开展动力分析。通过建立浮体和立管的耦合模型，开展缓波型立管的参数敏感性分析，在同种工况下与传统简单式悬链线立管进行对比分析，结果表明缓波型立管能够有效抑制海底沟槽的发展，改善触地区的动力响应。