深水管道弃置回收非线性受力分析及其形态控制

采用弹性地基板理论和非线性梁理论分别建立弃置回收作业中深水管道触底段和悬跨段几何大变形管道模型。以悬链线理论对管道进行初始构形,将DnV规范与土样调查数据相结合处理触底段管道和海床地基的边界条件,得到垂向、侧向、轴向3个方向的土壤反力公式。以某深水气田管道为研究对象,采用有限元软件ABAQUS进行初选管道提升角的有限元分析,得到管道的应力分布。结果表明:提升角增大,管线提升端的轴向拉力减小、最大应力位置从提升点向触地点转移。当提升角处于合理范围时,管道应力水平较低,提升端轴向力相对于AR绞车能力比较合理。顺流时轴向拉力最大,AR绞车负载较大;逆流时管道轴向拉力最小。管线等效应力主要取决于弯曲应力。来流方向对管道触地点等效应力的影响非常大,应避免逆流环境作业。

Nonlinear stress analysis and configuration control of deepwater pipeline in abandonment and recovery operation

Using the elastic foundation plate theory and the non-linear beam theory to set up models for touchdown segment and spanning section respectively, the mechanical behaviors of pipeline undergoing abandonment and recovery operation were analyzed. Taking spanning section as a space continuous curve, the initial configuration was obtained using catenary method. DnV and soil sample survey data were combined to deal with the boundary conditions, and the soil counterforces in vertical,lateral,and axial directions were achieved. In addition, for the pipelines used in a deepwater gas field, the reasonable ascending/recovery drag angle range, mechanical behavior in different angles were studied by F.E.M analysis software ABAQUS. The results show that with the increase of recovery drag angle, the pipeline axial tension on the top will decrease and the position of maximum stress will transfer from top to touchdown point. When the recovery drag angle is within its reasonable scope, the pipeline stress is relatively low, and the axial lifting load is located in the range of A&R winch capacity. The axial tension load for the parallel-stream orientation is the largest, and A&R winch load is large correspondingly. For the counter-current operation, the results are opposite. The pipeline equivalent stress mainly depends on its bending stress. The counter-current operation should be avoided since the flow direction affects the equivalent stress of pipeline in touchdown region greatly.