海底管道悬跨段在内输段塞流和外部海流共同作用下的动力行为研究

Gas-liquid two-phase slug flow can generate dynamic fluid forces which may induce structural vibration of subsea pipelines conveying oil and gas production fluids. Excessive vibration may cause component failures due to fatigue and fretting-wear. This phenomenon may generate more severe damage when considering the vortex-induced vibration of subsea pipeline free span subjected to external marine current. Such detrimental vibration can be avoided by comprehensive dynamic analysis of subsea pipeline free span, preferably at the design stage. This requires a fully understanding of vibration excitation mechanisms of subsea pipeline free span subjected to simultaneous internal slug flow and external marine current, however, the literature focused on this aspect is quite limited. Therefore, to perform a systematic study of vibration behavior of subsea pipeline free span subjected to such loadings, constructing the dynamic model for subsea pipeline free span conveying gas-liquid slug flow, is essential to form the theoretical framework. The proposed work will make an overview of the existing two-phase slug flow models, creating the governing equations for vibration behavior of horizontal tube subjected to internal two-phase slug flow and external current. Theoretical analysis, numerical simulation and experimental approach are utilized to investigate the dynamic characteristics of subsea pipeline free span subjected to internal two-phase slug flow and external current, where the theoretical analysis is mainly based on the generalized integral transform technique (GITT), the numerical simulation is based on the commercial code for fluid-structure interaction (FSI) problems ANSYS-CFX and ANSYS-Mechanical, and the experimental approach is based on a pulse-echo ultrasonic technique with a single fast transducer and a visualization technique with a high-speed digital camera for measuring the hydrodynamic parameters of slug flow. The effect of the statistical characterization of gas-liquid slug flow on the dynamic behavior of free span is analyzed. The effect of volumetric flux of gas and liquid phase, physical parameters, hydrodynamic parameters, slug frequency, external current speed, initial drapability of free-span, material parameters and boundary conditions on the dynamic characteristics of subsea pipeline free span (including natural frequency, mode shape, maximum amplitude, stability, resonance, bifurcation and chaos). The aim of this project is to reveal the excitation mechanism of subsea pipeline free span by internal gas-liquid slug flow, to create the failure criteria for free span vibration subjected to simultaneous internal slug flow and external marine current, and to form the systematic investigation methods for such FSI problem, which is supply the indispensible theoretical support for the pipeline vibration control and design.

油气输运海底管道中气液两相段塞流引起的压力波动会使管道悬跨段产生振动，而振动过大将导致管道关键部件因疲劳或微动磨损发生破坏。内输段塞流海底管道在外流引起的涡激振动作用下会产生更严重的疲劳损伤。避免管道失效的理论基础是对内输段塞流海洋管道振动特性的深刻理解，但目前对该问题的研究报道很少。因此，开展海底管道悬跨段在内输段塞流和外部海流共同作用下动力行为研究尤为重要。本项目通过理论分析、数值模拟及实验手段研究海底管道悬跨段在内输段塞流和外部海流共同作用下的非线性振动特性，揭示内输段塞流的统计特性对海洋管道动力学特性的影响，阐明气液各相流动参数及管道结构参数对海洋管道振动特性的作用。研究目标在于澄清内输气液两相段塞流对海底管道振动的激励机理，建立内输段塞流海底管道的失效判据，形成海底管道悬跨段在内输段塞流和外部海流共同作用下振动特性的系统研究方法，为深水管道设计及振动控制提供必要的理论支持。

本课题建立了考虑海床坡度的海底输流悬跨管道振动数学模型，总结了海床坡度对海底悬跨管道固有频率的影响规律，分析了海床坡度、内外流流速对海底悬跨管道系统动力行为及涡激振动锁定区域的影响。. 通过理论分析及数值模拟两种方法研究了内输多相流海洋管道的动力行为。利用多相流理论及相关试验数据建立多相流模型，分析不同流型下管道所受的压力及附加质量的分布情况，获得气体体积分数、平均流速对海洋管道的振动特性影响规律。同时，应用CFD与CSD计算相结合的方法，建立内输多相流管道的三维双向流固耦合计算模型，得出管道内流场域的分布特点及流动特性对管道振动的影响规律。. 研究了阻尼对内输多相流海洋管道振动的影响问题，建立了考虑结构阻尼及流体粘滞力阻尼的线性流动阻尼模型，并利用积分变换法求解内输多相流管道的阻尼振动控制方程，得到不同体积分数、平均速率条件下阻尼系数的变化规律。根据衰减周期及损耗能量结果，得到振动幅值在流型转换区域附近衰减最快的重要结论。.基于小变形原理及欧拉-伯努利梁模型对弯曲管道动力学问题进行建模，利用积分变换求解六阶偏微分振动方程组，得到弯曲管道振动响应的半解析解。分析弯管的弯曲角度、曲率半径及内输流体速度对振动频率的影响，获得不同弯曲角度及内流速度下的位移-速度相图轨迹。. 以上成果的取得能够完善内输多相流海洋管道振动特性的理论体系，解决了海洋管道非线性振动方程难以有效求解的问题，为海洋管道振动特性分析提供了有效分析方法，深化了关于气液两相流特性对內输流管道振动特性影响机制的认识，对海洋油气输运管道的疲劳寿命预测研究工作具有重要的参考价值。