Abstract The flexible riser top connection to the floating unit is a critical region considering extreme loading and fatigue lifetime assessment and is generally protected by a bend stiffener to limit the curvature in this region. The top connection usually interface the floating unit with two main configurations: i) end-fitting and bend stiffener directly connected to a riser balcony or ii) riser connected to the floating unit in the end of an I-tube, which reduces the end-fitting bending loading, and bend stiffener assembled to a bellmouth with a given inclination in relation to the I-tube longitudinal axis. The traditional modeling approach considers the riser/bend stiffener system attached to the floating unit, representative of the first configuration. A more realistic modeling approach, capturing the complex interactions of flexible riser/bend stiffener with I-tube interface can be employed for preliminary assessment with less conservatism. In this work, a large deflection analytical beam model is developed for the riser top connection with I-tube considering the bellmouth transition region with a straight rigid surface followed by a curved section. The riser follows a nonlinear bending behavior described by a bilinear moment vs curvature function and the bend stiffener polyurethane material exhibits nonlinear elastic symmetric response represented by a power law function. It is assumed that there is no gap between the riser and the bend stiffener and the riser is fixed in the end-fitting position. The mathematical formulation of the statically indeterminate system results in three systems of coupled differential equations combined with the corresponding multipoint boundary conditions to be numerically solved by an iterative procedure. A case study is carried out with a 7” flexible riser protected by a bend stiffener connected to an inclined I-tube bellmouth. The system is subjected to extreme loading conditions and the influence of the sleeve shape and I-tube length on the riser curvature distribution, including the end-fitting position, and contact forces between the riser/sleeve and riser/bend stiffener sections are assessed.

中文翻译：

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带工字管的柔性立管弯曲加劲肋顶部连接分析模型

摘要 考虑到极端载荷和疲劳寿命评估，柔性立管顶部与浮动单元的连接是一个关键区域，通常由弯曲加强筋保护以限制该区域的曲率。顶部连接通常将浮动单元与两种主要配置连接起来：i) 端部配件和弯曲加强筋直接连接到立管阳台或 ii) 立管连接到 I 形管末端的浮动单元，这减少了端部-装配弯曲载荷，并将弯曲加强筋组装到喇叭口，相对于工字管纵轴具有给定的倾角。传统建模方法考虑连接到浮动单元的立管/弯曲加强筋系统，代表第一种配置。更真实的建模方法，捕获柔性立管/弯曲加强筋与 I 形管界面的复杂相互作用可用于初步评估，保守性较低。在这项工作中，考虑到带有直刚性表面和弯曲部分的喇叭口过渡区域，为与 I 型管的立管顶部连接开发了大挠度分析梁模型。立管遵循由双线性弯矩与曲率函数描述的非线性弯曲行为，弯曲加强筋聚氨酯材料表现出由幂律函数表示的非线性弹性对称响应。假定立管和弯曲加强筋之间没有间隙，并且立管固定在端部装配位置。静态不定系统的数学公式产生三个耦合微分方程系统，并结合相应的多点边界条件，通过迭代程序进行数值求解。使用连接到倾斜工字管喇叭口的弯曲加强筋保护的 7 英寸柔性立管进行了案例研究。系统承受极端负载条件，评估套管形状和工字管长度对立管曲率分布的影响，包括端部配件位置，以及立管/套管和立管/弯曲加强筋部分之间的接触力。使用连接到倾斜工字管喇叭口的弯曲加强筋保护的 7 英寸柔性立管进行了案例研究。系统承受极端载荷条件，评估套管形状和工字管长度对立管曲率分布的影响，包括端部配件位置，以及立管/套管和立管/弯曲加强筋部分之间的接触力。使用连接到倾斜工字管喇叭口的弯曲加强筋保护的 7 英寸柔性立管进行了案例研究。系统承受极端载荷条件，评估套管形状和工字管长度对立管曲率分布的影响，包括端部配件位置，以及立管/套管和立管/弯曲加强筋部分之间的接触力。