低阻力自适应旋转尾流隔板的涡激振动抑制方法和机理研究

本项目将针对深水立管的涡激振动问题开展流动控制研究。在综合利用物理实验、数值模拟和非线性动力分析方法的基础上，对“旋转尾流隔板涡激振动抑制方法”开展深入研究。理解和认识该流动控制措施的基本力学原理，揭示其对流动条件和结构参数的依赖作用，全面把握其有效适用条件。重点研究该涡激振动抑制方法所具有的非线性动力分叉特性（旋转尾流隔板的稳定平衡振动位置偏离流向），以及非线性迟滞响应行为的发生机理和作用机制。在此基础上，针对非线性流固耦合系统的动力分叉现象可能诱发驰振运动的潜在危害，探索通过引入结构回转刚度来消除动力分叉，进而避免大幅驰振响应的可能途径。针对轴向分段旋转尾流隔板，探索通过二维流动数值模拟来近似三维水动力学系数的参数化近似计算方法，进一步建立准三维分层流固耦合数值分析模型，为分段旋转尾流隔板抑制措施的优化设计和工程应用提供有效的技术支持。

This project focuses on the flow control of Vortex-Induced Vibration (VIV) of deepwater risers. Based on model test, numerical simulation and nonlinear analysis, a novel VIV suppression strategy by using rotatable splitter plate attached will be closely examined. The investigations of this project will bring deep insight into the fundamental mechanism involved in the proposed VIV suppression method, and lead to comprehensive understandings of its dependence on the flow conditions and structural parameters. Special attention will be paid on the conditions for the application of the present VIV suppression strategy. The physical mechanism behind the occurrence of bifurcate solutions and the nonlinear hysteresis phenomenon associated with the rotary response of the splitter plate will be examined. It was know that the bifurcate/bi-stable rotary oscillation with its equilibrium position deflecting the free-stream direction may lead to undesirable galloping response. In order to avoid this disadvantage, a possible method by introducing additional torsional stiffness into the rotating system will be studied. This concept is inspired by our recent understanding based on fully coupled numerical simulations of fluid-structure interaction. It was confirmed that the bifurcation disappears at relatively low reduced velocity (with structural stiffness) for specific plate length and Reynolds number. The investigations of this project will also include the sectional rotatable splitter plates for practical deepwater risers with large aspect ratio. The three-dimensional effects aroused from the two lateral ends of the rotating splitter plate are concerned. A simplified empirical approach will be proposed for the fast prediction of hydrodynamic coefficients by using two-dimensional CFD simulation rather than the much time-consuming three-dimensional computations. With the available hydrodynamic coefficients, a quasi-three-dimensional numerical model will be further developed for the prediction of the dynamic response of deepwater rises with sectional rotatable splitter plates attached.