脉动内流-立管-外流漩涡脱落流-固耦合系统的非线性动力学特性研究

Marine risers are the main connect equipments between floating platforms and the wells at the seabed, they simultaneously undergo multiple environmental loads, the dynamic response is very complicate. More recently, with the increasing interest in worldwide deep-water petroleum production,the application of large length risers and high-power pumps make the fluid transported inside the riser has a large pulse. Excited simultaneously by internal pulsating fluid and the vortex shedding due to external flow, the dynamic characteristics of marine risers become more and more intricate. Up to now, it is deficient in understanding this issue in engineering fields and the academic circles. The present research project will study the nonlinear dynamic characteristics of the Fluid-Structure Interaction (FSI) system consisting of internal pulsating fluid-marine riser-external vortex shedding mainly by experiment investigation, supplemented by theory analysis and numerical simulation. The special nonlinear vibration phenomena(such as jump, multiple equilibrium solutions, subharmonic resonance, superharmonic resonance, bifurcations and chaos etc) of marine riser conveying internal pulsating fluid will be explained, the significant influences of some key parameters(mean velocity of internal pulsating fluid, amplitude of the internal fluid velocity fluctuation, frequency of the internal fluid velocity, velocity of external flow, drag force and top tension etc) on theses nonlinear phenomena will be illustrated, the aim of present research project is to supply the theory knowledge and engineering methods for marine risers vibration control and design.

海洋立管是连接浮式平台和水下井口的关键设备，一般承受多种海洋环境载荷作用，其动力响应十分复杂。特别是近年来深海油气开发步伐的加快，大长度立管和大功率泵的应用，导致立管内部输运的流体在流动时产生较大的脉动。脉动内流与外流漩涡脱落共同激励下，海洋立管动力学特性变得更加丰富和复杂。目前，工程界和学术界对该问题的理解和研究还存在诸多不足。本项目拟以实验研究为主，理论分析和数值模拟为辅的研究手段，分析脉动内流-立管-外流漩涡脱落流-固耦合系统的非线性动力学特性，揭示海洋输流立管非线性振动所特有的现象(如跳跃、多解、亚谐共振、超谐共振、分岔、混沌等)，探寻多种参数(脉动内流平均流速、脉动幅值、脉动频率、外流流速、水动力阻尼、张紧力等)对其动力学特性的影响机理，为海洋输流立管的振动控制和工程设计提供科学的理论依据和工程实用方法。

海洋立管是连接浮式平台与水下井口的关键装备，它的主要作用是隔绝海水和输送内部流体介质。深海环境下海流的经过会诱发立管后缘发生涡激振动，导致结构的疲劳破坏。漩涡脱落激励下的输流管道是一个典型的非线性流-固耦合系统，属于涡激振动-自激振动-参激振动联合作用的振动问题，至今工程界和学术界对此仍无法完全理解和彻底掌握，围绕输流管道动力学特性的研究一直是海洋工程领域重要的前沿课题。本项目以张紧式海洋输流管道为研究对象，开展了输流管道纯顺流向涡激振动研究、探究了漩涡脱落激励下输流管道非线性动力学特性，并设计完成了倾斜圆柱结构涡激振动实验，取得了系列重要研究成果，包括：(1) 提出了刚性圆柱纯顺流向涡激振动预报模型，并发现在第一、第二不稳定区内，圆柱结构纯顺流向涡激振动存在临界质量比；(2) 构建了预报柔性圆柱结构纯顺流向涡激振动的预报模型，并分析了纯顺流向涡激振动特性；(3) 开展了倾斜柔性圆柱涡激振动实验，发现了较大的倾角条件时倾斜圆柱涡激振动的不相关原则不再适用。上述研究的开展及成果的获得可为海洋输流管道的工程设计和振动控制提供必要的理论和技术支持，具有重要的理论价值和工程意义。