非粘结柔性立管截面热力耦合响应及螺旋层失效特性研究

Unbonded flexible risers are multilayer composite structure, which are composed of metallic and polymeric layers, unique advantages enable them have a pivotal position in the deep-sea oil and gas resources development. However, in the cross-section properties and failure characteristics analysis of unbonded flexible riser, it involves strong nonlinear problems of material, geometric and contact, and internal and external temperatures of risers have an important impact on material properties and the structural constitutive equation. Therefore, nonlinear model is developed to study cross-section properties of unbonded flexible risers under coupled thermal-mechanical load, after that, failure characteristics of tensile armor wires with rectangular cross-section and helical layers with irregular cross-sections are deeply studied in this research, which provide some technical support for the key design technology of such riser.The main research contents are as follows: 1) Based on principle of virtual work, thermodynamic theory and three-dimensional numerical model, take material nonlinearity and the influence of local bending and torsion of helical strips into consideration, nonlinear analysis model of cross-section properties under coupled thermal-mechanical load is developed; 2) Based on the cumulative fatigue damage theory, strength theory, curved beam theory and combined with three-dimensional numerical model, fracture propagation, radial and lateral buckling of tensile armor wires are analyzed. 3) Collapse and crushing of helical layers with irregular cross-sections under uniform external pressure and crushing load are analyzed by model experiments, theory of elastic stability and three-dimensional numerical model.

非粘结柔性立管是由几何形式复杂的金属层和聚合物层共同构成的多层结构，独特优势使其在深海油气资源开发中具有举足轻重的地位。然而，在其截面响应和失效特性分析时涉及材料、几何及接触等强非线性因素的影响，且计入立管内外温度后将导致材料特性和结构本构方程发生重大改变。为此，本项目建立热力耦合载荷下非粘结柔性立管截面响应非线性分析模型，并对矩形截面抗拉铠装层以及不规则截面螺旋层失效特性进行研究，为此类立管关键设计技术提供参考。具体研究内容包括：1) 基于虚功原理、热力学理论和三维数值方法，计入材料弹塑性特征及螺旋带局部弯曲和扭转，建立热力耦合载荷下截面响应非线性计算模型；2)分别依据疲劳损伤累积理论、强度理论、曲梁理论并结合三维数值方法研究抗拉铠装层螺旋带断裂扩展、径向及侧向屈曲失效；3)采用模型实验、弹性稳定性理论及三维数值方法研究不规则截面螺旋层在均匀外压和径向压缩载荷下的压溃失效特性。

非粘结柔性立管由金属层和聚合物层共同构成，被广泛应用于深海油气资源开发中。目前，在非粘结柔性立管截面响应计算模型中引入了大量的简化和假设，对计算精度造成了一定影响；同时，对此类立管失效特性研究不足。针对上述问题，本项目建立了非粘结柔性立管截面非线性响应计算模型，并开展了金属螺旋层失效特性分析，可为此类立管结构设计提供理论及数值参考。项目取得的主要成果如下：计入材料非线性，建立了轴对称载荷下非粘结柔性立管截面非线性响应计算模型，同时，分析了理论和三维数值结果偏差较大的原因；基于三维数值模型研究了抗拉铠装层螺旋带断裂后载荷重新分配及截面响应特性，探讨了螺旋带断裂数目、边界条件、载荷方向的影响，并研究了层间摩擦力对断裂螺旋带承载力恢复的影响；引入形状因子，建立了不规则截面螺旋层等效厚度计算方法，并结合三维数值模型对形状因子进行了求解，同时，基于三维数值模型分析了不规则截面螺旋层在径向压缩载荷下的响应特性，结果表明应力奇点将不规则截面螺旋层分为两个压缩区和两个膨胀区，所提出的等效厚度模型可较好地模拟环向应力分布。