基于环-梁三维理论模型的深水海底管道整体式止屈器穿越失效机理研究

In order to prevent the widespread destruction of deepwater pipelines from buckle propagation, the most effective engineering method is to place integral buckle arrestors along a pipeline at regular intervals. But it is still not clear about the crossover failure mechanism of integral buckle arrestors, the design of which can only depend on the empirical formulas in design standards..In this project, the crossover failure mechanism of integral buckle arrestors for deepwater pipelines is studied based on the improved three-dimensional theoretical model of ring-beam. Firstly, the length of transition zone and stress-strain status during the crossover of integral buckle arrestors are researched utilizing numerical simulation and model experiment; then the continuous ring model is used to represent buckling deformation of cross-sections of pipelines and buckle arrestors, and the improved beam model is used to simulate the longitudinal membrane stretching, bending and shearing effect between the cross-sections in the transition zone. Considering structural nonlinear deformation, elastic-plastic constitutive relationship of materials and the contact between inner walls of pipelines, the energy-balance equations of structural buckling deformation is established to solve the crossover pressure theoretically. Finally, by the verification of numerical results and experimental data, a more accurate method for prediction of the crossover pressure of integral buckle arrestors is established. And the effects of geometries and material properties of both pipelines and buckle arrestors on crossover mode and crossover pressure are quantitatively revealed. The expected achievements can provide theoretical reserves for the rational design of integral buckle arrestors for deepwater pipelines.

为防止屈曲传播造成深水海底管道大范围结构破坏，工程上主要采取间断布置整体式止屈器的方式。目前，整体式止屈器的设计主要依赖于规范中的经验公式，但对其真正的穿越失效机理尚不明确。.本课题通过建立环-梁三维改进理论模型，研究深水海底管道整体式止屈器的穿越失效机理。首先利用数值模拟和模型试验的手段，对止屈器的穿越过渡区长度和应力应变情况进行研究；然后以连续圆环模型模拟穿越过程中管道和止屈器截面的屈曲变形，并以改进梁模型模拟过渡区截面间的薄膜拉伸、弯曲和剪切作用；考虑结构非线性大变形、材料弹塑性本构关系和管壁间接触作用，建立结构屈曲变形能量平衡方程，对止屈器穿越压力进行理论求解；最后，通过与数值模拟和试验数据进行对比验证，建立较为准确的整体式止屈器穿越压力理论预测方法，定量揭示管道和止屈器几何尺寸、材料特性对穿越模式和穿越压力的影响机制。预期成果可为深水海底管道整体式止屈器的设计提供理论储备。

随着水深的增加，海底管道承受的外部水压对结构安全运行的影响越来越大。制造、搬运和安装过程引起的管道椭圆度缺陷会使管道的外压承载力降低，进而发生屈曲传播，给管道造成大范围的破坏，而整体式止屈器是目前解决深水海底管道屈曲传播问题最有效的方式之一。我国在此方面的研究刚刚起步，开展深水海底管道屈曲传播机理和整体式止屈器性能研究具有重要意义。.管道的屈曲传播属于后屈曲问题，本课题首先研究了管道的前屈曲问题，即管道的局部屈曲。通过二维圆环理论模型和三维有限元分析相结合的方式，对带初始椭圆度缺陷的管道局部屈曲压力进行了预测，随后又对影响局部屈曲压力的各种敏感性因素（如：径厚比、初始椭圆度、材料特性等）进行了较为全面的分析。在屈曲传播方面，本课题通过建立环-梁模型来对屈曲传播进行理论分析，并与有限元模拟分析、模型试验研究相结合，对管道的屈曲传播压力进行了预测，有限元方法还获得了从局部屈曲到屈曲传播的整条加载响应曲线，随后对屈曲传播压力进行了敏感性分析。在整体式止屈器性能分析方面，本课题利用三维有限元数值模拟和模型试验分别对止屈器的准静态止屈问题进行了研究，并预测了止屈器的穿越压力，之后又对穿越压力的影响因素进行了敏感性分析。预期成果可为深水海底管道整体式止屈器的设计提供理论储备。